Developments in Aquaculture and Fisheries Science - 33
DESIGN AND OPERATING GUIDE FOR AQUACULTURE SEAWATER SYSTEMSSECOND EDITION
DEVELOPMENTS IN AQUACULTURE AND FISHERIES SCIENCE The following volumes are still available:
9.
WATER QUALITY MANAGEMENT FOR POND FISH CULTURE By C.E. Boyd 1982 xii + 318 pages
17.
DISEASE DIAGNOSIS AND CONTROL IN NORTH AMERICAN MARINE AQUACULTURE Edited by C.J. Sindermann and D. V. Lightner 1988 xv + 412 pages
19.
CLAM MARICULTURE IN NORTH AMERICA Edited by J.J. Manzi and M. Castagna 1989 x + 462 pages
22.
FRONTIERS OF SHRIMP RESEARCH Edited by RE DeLoach, W.J. Dougherty and M.A. Davidson 1991 viii + 294 pages
23.
MARINE SHRIMP CULTURE: PRINCIPLES AND PRACTICES By A. W. Fast and L.J. Lester 1992 xvi + 862 pages
24.
THE MUSSEL MYTILUS: ECOLOGY, PHYSIOLOGY, GENETICS AND CULTURE By E. Cosling 1992 xiv + 589 pages
25.
MODERN METHODS OF AQUACULTURE IN JAPAN (2ND REVISED EDITION) Edited by H. Ikenoue and T. Kafuku 1992 xiv + 274 pages
26.
PROTOZOAN PARASITES OF FISHES By J. Lom and I. Dykova 1992 xii + 316 pages
27.
AQUACULTURE WATER REUSE SYSTEMS: ENGINEERING DESIGN AND MANAGEMENT Edited by M. B. Timmons and T. Losordo
28.
FRESHWATER FISH CULTURE IN CHINA: PRINCIPLES AND PRACTICE Edited by J. Mathias and S. Li 1994 xvi + 446 pages
29.
PRINCIPLES OF SALMONID CULTURE Edited by W. Pennell and B.A. Barton 1996 xxx + 1040 pages
30.
STRIPED BASS AND OTHER MORONE CULTURE Edited by R. M. Harrell 1997 xx + 366 pages
31.
BIOLOGY OF THE HARD CLAM Edited by J.N. Kraeuter and M. Castagna 2001 xix + 751 pages
32.
EDIBLE SEA URCHINS: BIOLOGY AND ECOLOGY Edited by J. M. Lawrence 2001 xv + 419 pages
33.
DESIGN AND OPERATING GUIDE FOR AQUACULTURE SEAWATER SYSTEMS (2nd EDITION) by J.E. Huguenin and J. Colt 2002 viii + 328 pages
D e v e l o p m e n t s in A q u a c u l t u r e and F i s h e r i e s S c i e n c e - 33
DESIGN AND OPERATING GUIDE FOR AQUACULTURE SEAWATER S Y S T E M S - S E C O N D EDITION
JOHN E. HUGUENIN Falmouth, Massachusetts U.S.A.
JOHN COLT
Northwest Fisheries Science Center National Marine Fisheries Service Seattle, Washington U.S.A.
2002
ELSEVIER
A m s t e r d a m - L o n d o n - New York - O x f o r d - Paris - S h a n n o n - T o k y o
ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 RO. Box 211, 1000 AE Amsterdam, The Netherlands
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Contents
Chapter 1.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 2.
Problem definition and establishing requirements . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.1
Design process ........................................................................
5
2.2
Defining objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.3
Quantifying requirements ..............................................................
7
2.4
Production cycle ......................................................................
2.5
Production modeling ..................................................................
12
2.5.1
Growth models ..............................................................
12
2.5.2
Mortality models ............................................................
13
2.5.3
Length-weight relationships
13
.................................................
9
2.6
Types of systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
2.7
System carrying capacity ..............................................................
20
...................................................................
22
2.7.1
Ammonia
2.7.2
Nitrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
2.7.3
Nitr ate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
2.7.4
Dissolved oxygen ............................................................
24
2.7.5
Carbon dioxide ..............................................................
25
2.7.6
H y d r o g e n sulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
2.7.7
Total gas p r e s s u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
2.7.8
pH ..........................................................................
27
2.7.9
Residual chlorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
2.7.10
Temperature .................................................................
28
2.7.11
Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
2.7.12
Heavy metals ................................................................
28
2.7.13
Biocides .....................................................................
28
2.8
Carrying capacity guidelines ...........................................................
2.9
Design requirements ...................................................................
39
2.9.1
W a t e r flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
2.9.2
Rearing volume/area
42
2.9.3
R e a r i n g c o n t a i n e r size a n d n u m b e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10
........................................................
Constraints ............................................................................
Chapter 3.
Site considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
43 43 47
3.1
Marine conditions .....................................................................
47
3.2
Terrestrial c o n d i t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
3.3
Permitting ............................................................................
54
3.4
Site s e l e c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
Chapter 4. 4.1
Seawater sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
Options and considerations ............................................................
59
VI 4.2
Artificial seawater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
4.3
S e a w a t e r wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
4.4
M a r i n e intakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
Chapter 5.
System planviews and elevations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
5.1
Generic s y s t e m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
5.2
Elevations and head tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
5.3
Intake and p u m p house considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
5.4
Discharge considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
79
Chapter 6. 6.1
Piping design and calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
81
M a j o r tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
81 82
6.2
Biofouling control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3
Water h a m m e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
6.4
Frictional losses in pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
87 93
6.5
Frictional losses in fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.6
O p e n channel flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
6.7
M o m e n t u m in pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
Chapter 7.
Pump Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
P u m p options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
7.2
Generic centrifugal p u m p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
104
7.3
N P S H and d y n a m i c head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
108
7.4
M a t c h i n g s y s t e m and p u m p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110
7.1
Chapter 8. Materials selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Biological constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
117
8.2
Seawater constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120
8.3
Piping materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
122
8.4
P u m p materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
124
8.5
M a r i n e concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
126
8.6
P r o b l e m areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
126
Chapter 9.
Seawater flow control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
117
129
9.1
Gravity flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
129
9.2
Water level control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
131
9.3
Control of flow rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
133
9.4
Flow measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
134
Chapter 10.
Suspended solids removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
10.1
Considerations, tradeoffs and options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
10.2
Cartridge filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
139
10.3
D i a t o m a c e o u s earth filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
140
10.4
Filter bags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5
Centrifuges and cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
141 141 141
10.6
Sand filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7
Microscreens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
144
10.8
Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
145
VII
Chapter 11.
Heating and cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
151 151
11.1
Setting requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2
Heat exchangers .......................................................................
154
11.3
P r o b l e m areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
157
Chapter 12.
A e r a t i o n and degassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.1
A b s o r p t i o n efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
163 163 163 165 168 168 168 171
12.3.2
Blower selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
173
12.3.3
Pumping and mixing .........................................................
175
12.1
Aeration system requirements ..........................................................
12.2
G r a v i t y aer ator s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2.1
12.3
Packed columns .............................................................
12.2.2
P e r f o r a t e d tray a e r a t o r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2.3
L a t t i c e aerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
S u b m e r g e d aer ators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.4
Gas supersaturation and degassing .....................................................
178
12.5
Removal of other gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
180
Chapter 13.
Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.1
Considerations and options ............................................................
13.2
Chemical compounds ..................................................................
13.3
Ozone ................................................................................
13.4
Ultraviolet (UV) radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 14.
Alarms, monitoring and automatic control systems . . . . . . . . . . . . . . . . . . . . . . . . .
14.1
Characteristics and options ............................................................
14.2
A l a r m points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3
Automatic control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 15.
183 183 184 187 190 193
193 195 197
15.1
Water recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Setting r e q u i r e m e n t s a n d o p t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2
Nitrification a n d biofilters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
202
15.3
Foam fractionation ....................................................................
206
15.4
A c t i v a t e d c a r b o n a n d ion e x c h a n g e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
207
15.5
Algae .................................................................................
210
Chapter 16.
201 201
16.1
Wet laboratory areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G e n e r a l c o n s i d e r a t i o n s a n d trade-offs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2
I n d o o r areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
212
16.3
O u t d o o r areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
215
Chapter 17. 17.1
Construction considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
211 211
217
Construction arrangements .............................................................
217
17.2
Construction cost estimating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
217
17.3
Design changes .......................................................................
219
17.4
I n s t a l l a t i o n o f s e a w a t e r lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
219
17.5
Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
220
VIII
Chapter 18. 18.1 18.2 18.3 18.4 18.5 18.6
Operational considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operating procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A s s i g n m e n t o f responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spares and redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preventive maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Monitoring and control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operational p r o b l e m areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
223 223 224 224 226 226 228
Chapter 19.
Putting it all together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
233
Chapter 20.
Summary commandments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
249
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
253
Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
263 264 264 265 269 272 276 281 284 287 291 295 298 306 309 314 320 322 322 323 323 324 324 324 325 325 325
A
B C D E F G H I J K L M N
Conversions, definitions and seawater properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A- 1 Conversion factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3 Seawater properties as a function o f temperature and salinity . . . . . . . . . . . . . . . . . . F l o w - t h r o u g h seawater system bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reuse seawater system bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water quality bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biofouling bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Materials bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suspended solids removal bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temperature control bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aeration and degassing bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disinfection bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Culture unit shape, size and flow pattern/hydraulics bibliography . . . . . . . . . . . . . . . . . . . . . . . Feeder bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indexes for equipment and supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C o m p u t e r data search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-1 Traditional fee-based searches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2 Internet sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2.1 Governmental sites (and sites with a lot o f free information) . . . . . . . . . . N-2.2 N o n - g o v e r n m e n t a l sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2.3 D o c u m e n t delivery services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2.4 E-mail alerting service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2.5 Society web sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-2.6 On-line journals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N-3 Aquaculture information lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
327
Chapter 1
Introduction
There is a strong and broad-based need from many educational, research and commercial organizations and individuals for information on the planning, design, construction and operations of seawater systems (salinities from freshwater to brines) with flow rates in the range of 10-1000 gallons per minute (40-4000 liters per minute). While the objectives of these systems vary widely, they all depend on a common technological and biological database. Since the seawater system is usually only a means to an end, most potential users have little prior practical experience or technical knowledge in this area. Practical information on seawater systems for culturing purposes tends to be fragmented and not readily available in usable form. Most conventional engineering experience is with marine systems which are orders of magnitude larger. This technology is often not readily scaled down, or directly useable and, more than likely, prohibitively expensive. Unfortunately, neither a good understanding of the biology nor the engineering alone is likely to result in a practical system. Biologists generally do not understand the mechanical and hydraulic aspects, engineers usually do not sufficiently appreciate the biological requirements, and usually neither appreciate the economic and regulatory constraints that can heavily influence decisions. In short, because success depends on a blend of expertise, avoidable mistakes with seawater systems are common. While many may claim expertise, there are, in fact, few experienced bioengineers available and they tend to be associated with small consulting companies specializing in these matters. Bioengineers generally spend much of their time 'educating' the user or client to the tradeoffs and consequences of major-system decisions. Not uncommonly, major-system decisions have already been made and fixed prior to seeking bioengineering assistance. This can be a serious problem. In addition, this bioengineering expertise may be either unavailable or unaffordable to many potential users. While considerable knowledge and experience has been gained with the design, construction, and operations of seawater culture systems, this accumulated experience has been very poorly documented and is therefore not readily available. In addition, much of this knowledge has been learned the hard way by trial and error. Since communications are poor, the same mistakes tend to be made over and over again. This book is intended to fill these gaps and hopefully reduce seawater systems problems. For simple systems and conditions, this book may be completely adequate. For more complex systems or conditions, this book may avoid the expensive mistakes often made by users early in a project and greatly reduce the 'user education' phase of system design. Even with this book as a guide, many projects will be sufficiently complex to require the user to seek outside technical expertise. There are usually a number of sources of 'free' technical help, such as universities, equipment manufacturers, or various governmental
extension services. This is all well and good if the needs are limited to advisory services. These sources will generally not provide any design services, such as systematic evaluations of alternatives, numerical sizing of systems or components, or providing drawings, construction specifications or cost estimations. At some project scope or stage of development, the user may have to seek professional aquacultural consulting services. There are a number of considerations, alternative approaches, tradeoffs, and potential problems in this complex matter (see Mayo, 1998). The seawater flow rate range of 10-1000 gallons per minute (gpm) or approximately 40-4000 liters per minute (lpm) has been chosen because it includes the vast majority of such systems currently in use. Many educational systems tend to the low side of the range while large research-oriented systems are towards the upper end. This also includes marine aquariums and most commercial and governmental molluscan, crustacean and marine fish hatcheries. The only major omission is large-scale commercial grow-out operations (as distinct from the hatchery phase). For economic reasons these systems tend to be much larger and often tidally pumped, either with ponds, pens or cages, and are outside the scope of this book. The stated flow rates of interest are very small by industrial water use standards. As an example, a single-unit 1000-megawatt nuclear power plant may pump 500,000 gpm (1,900,000 lpm) of water through its condensers. While the necessary equipment and techniques to handle the flows of interest to us are well within the mechanical and hydraulic state of the art, aquaculture imposes additional constraints on the design and operations which are not normally encountered in industrial applications. The primary additional constraints are due to the life support requirements of the culture organisms. This may include both maximum and minimum concentrations of dissolved gases, major ions, heavy metals, trace organic contaminates or particulate matter, to name just a few. Therefore, the available industrial water handling equipment and techniques must be used with caution when applied to seawater culturing systems. The primary objective of this book is to provide, in one place, basic information and considerations necessary to plan, build and operate seawater systems for culturing purposes. Due to the complexities of the subject and the fact that requirements of specific situations are highly variable, all the potentially important information cannot be fully developed or presented in a single book. Since a unit of aquatic animal or plant biomass, to a good first-order approximation, will react similarly under identical conditions, species differences have purposely been de-emphasized. This simplifies the presentation, broadens the usefulness of the text, and allows generalized conservative guidelines to be developed. Considerable thought and effort has been applied towards providing directions for more detailed efforts in the form of references and appendices in various technical areas. The book is not primarily intended for the experts or those already very experienced with seawater systems, although conditions vary widely and 'experts' may also find it to be of value. The primary value to 'experts' may be in the substantial accumulation of readily accessible data. The authors have found the first edition of their own book to be a valuable and frequently consulted reference. Of particular importance is Appendix A, which covers conversions of units, definitions, and seawater properties. The subject of this book crosses many different disciplines, interests, and backgrounds. This can cause considerable confusion with definitions and units of measure. Mixed systems of units are common and often unavoidable. Even within a system of measure,
there may be several different parameters and units commonly used for a particular purpose. Appendix A provides definitions, conversion factors between units and important constants to reduce this confusion. However, the problem is often more complicated than straightforward numerical conversion. As an example, a 1 in. pipe is not the same as a 2.54 cm pipe. A '1 in.' pipe is not a dimension, since neither the inside nor outside diameters are likely to be exactly this dimension, but rather a designation, which does not readily convert without knowing the type of pipe and the industrial standard involved. At least in the Western Hemisphere, industrial equipment and engineering practices are still predominantly in 'English' units while scientific matters are largely metric. The International System of Units (abbreviated SI in all languages) is intended as a basis for worldwide standardization of measurement units. Even in those countries using SI units, it is unlikely that all units will be SI (though they may be related to SI units). For example, the units of volumetric flow are cubic meters/second. A flow of 50 gpm is equal to 0.0032 m3/s, an inconveniently small number for practical use. The units of hour, day, month, liter, and hectare are not SI units. For practical applications, one must often cope with mixed units. For these reasons, this book has purposefully not standardized on either system. Numerical examples, provided to demonstrate methods, may be in either system or even have mixed units. In the United States, the conventional decimal marker is a dot ('.'). Outside of the United States, the comma (',') is sometimes used as a decimal marker. In the United States, the comma is also used to separate digits into groups of three (for example, 24,567), a practice that can cause confusion. The SI convention recommends separating digits into groups of three using a small space instead of the comma (for example, 24 567). This book will use the dot as a decimal marker and the comma as a separator. Another area of confusion arises in the use of parts per hundred (%) (or parts per thousand, %0). While this convention is convenient in many situations, it is important to understand that because the parameter is expressed as a percent, the actual number has not changed. A 2% growth rate is 2 parts per hundred or actually 0.02. A 1000 lb of fish growing at 2%/day, will grow 1000 x 0.02 = 20 lb, not 1000 x 2 -- 2000 lb. Computer spreadsheets can reduce the chance of errors as they allow numbers to be displayed as percentages, but retain the actual values for use in computations. The First Edition of this book was published in 1989. There have been a number of developments in this field since that time. Probably the most significant is the rapid growth in the industrial infrastructure specifically designed for aquatic life support activities. In the past, most of the equipment has had to be taken and adapted on an individual basis from other fields such as wastewater treatment, chemical process industries and various industrial and manufacturing applications. This change, while dramatic, has been more of an adaptation and modification process rather than the development of any radically new processes. In short, while there is now a considerably wider choice of parts and equipment and they are also easier to identify, the basic principles are unchanged. The changes that have occurred are reflected in the unit process chapters of this Second Edition. Computer use has accelerated rapidly in our society. This has had some impact in the form of greater computer usage in the monitoring and control of life support system and for data acquisition and dissemination. Chapter 14 has been renamed (Alarms, Monitoring and Control Systems) and expanded and Appendix N (Computer Data Search) added to include these changes. Since the first edition of this book was published, three important
changes have impacted the organization of this revised edition: the widespread availability of computer spreadsheets (EXCEL and 123), the consolidation of the software industry, and the ability to communicate rapidly over the Internet. For routine computations, the spreadsheet has largely replaced both the remote mainframe computer and to a significant degree, the use of hand-held calculators. (Newer hand-held calculators are much more user-friendly and many have the ability to plot results.) The combination of these two technologies allow the posting of useful spreadsheets on a website, the downloading (or e-mailing) of these programs to personal computers, and use of these programs. The common spreadsheet programs are available on a wide number of platforms (IBM, Macintosh, Sun, etc.) and commonly can read other spreadsheets (for example, EXCEL can read Lotus 123 spreadsheets). The regulatory and permitting environment has, in general, gotten a lot more severe since the First Edition. This is due to a lot of factors, such as reduced site availability, expanding populations, competition and conflicts in the near-shore environment, and increased legislation. The effects can differ considerably between regions and can be quite local in their specific characteristics. Increased constraints exist on both the supply side, for access to good water, and on the discharge side, relative to discharge permitting. Treatment prior to discharge is becoming much more common and more extensive. Water problems have increased interest and development in greater water reuse. While considerable progress has been made in high reuse system technology, these systems are not suitable for some applications and are still economically constrained for other applications. Biosecurity, in terms of reducing the transmission of pathogens between internal units as well as with the outside, has gained in importance in some applications. These include marine mammal rehabilitation facilities and for hatcheries of various kinds. This can have major design impacts. Physical security has also increased in importance due to possible treats of vandalism or terrorism as well as due to liability concerns in our increasingly more litigious society. The numerical problems contained in the First Edition have proven useful. The Second Edition includes even more examples in the various subject areas. However, practical problems rarely include only one subject area but more often require application and synthesis of a number of different technical and non-technical aspects. For this reason, Chapter 19 (Putting It All Together), dealing with integrating problems and examples, has been added in the Second Edition.
Chapter 2
Problem Definition and Establishing Requirements
2.1 Design process The design process is a complex and iterative operation. It has many characteristics that are common to all hardware systems, whether they are seawater systems or space shuttles. There exists many simplified schematics of the process. Fig. 2.1 has many of the common components of such models and has been chosen to be compatible with the format of this book. All human activities are motivated by subjective human needs. These are basic needs such as for food, shelter, clothing, security/defense, educating and rearing of the young and, by extension, making money. These needs have to be translated into specific objectives (see Section 2.2) which might be satisfied by hardware systems, in our case seawater systems. These statements of objectives generally need considerable greater refinement and quantification before any design calculations or dimensioning can be done (see Sections 2.3
Subjective Human Purpose
Define Objectives
C--'--
Quantify Requirements
Environment -Physical -Economic - Legal / Political/Social
_.
,~
System Synthesis and Evaluation
Implementation I and Construction J
...
~
Operations
Benefits
Fig. 2.1. Simplified design process.
and 2.4). Systems synthesis or, if preferred, systems design, is done in the next phase. However, it cannot be done in isolation. The total environment (physical, economic and legal/political/social) within which the system is expected to operate must be considered. The environmental factors impose limitations or constraints on system design. These constraints may be physical, economical, legal, time or other factors. It is not at all uncommon that the constraints are sufficiently severe to make the design of a workable system impossible or impractical. In this case, the only option is to reexamine the statements of objectives or requirements. This evaluation and feedback will often occur, even when it is not a matter of infeasibility. It is often done to improve performance or lower initial or operating costs. Many cycles of design, evaluation and redesign may occur before the decision to build is made. Feedback often occurs into the construction and operating phases, but is hopefully limited to matters of 'fine tuning'. Major reevaluations in the later phases can be serious matters that can be fatal to projects. The benefits that result from the operations of the system hopefully meet the needs that initiated the project in the beginning, assuming that these have not appreciably changed with time.
2.2 Defining objectives A critical first step in the design process is the clear definition of the objectives of the system. While this book is directed towards applications with educational, research or commercial objectives, what does this actually mean? Is the education to be of the 'show and tell' variety common to public aquariums, or of the participatory type more characteristic of field stations or in a more formal academic context and for what age group or audience. Is it for tropical or temperate species, how many species, both animals and plants, which species, how many, etc.? What specifically are the educational goals? How many people at a time and for how long? Similar questions can be developed for research and commercial systems. While the answers may vary widely, they will strongly influence the specification and design of the system. Wrong directions or assumptions at the beginning of a project can seldom be reversed later without high cost, extensive delays, or poor system performance. Such mistakes often prove fatal to the project. System objectives may be based on (1) a clear present need, (2) a potential need that must be addressed, (3) an anticipated future need, or (4) a combination of the first three. While it is very difficult to clearly define in quantitative terms, present and future objectives, it has to be done. Considerable time and effort should be devoted to checking all assumptions, identifying implicit assumptions and resolving differences in objectives between the participants. Many doomed projects have been launched based on a false premise, which no amount of engineering ingenuity or operator expertise can overcome. It is also not uncommon to have different participants in a project working towards different and sometimes conflicting objectives. In addition, there is often the problem of unstated or 'hidden' objectives. These might involve aspects of 'prestige', bureaucratic needs, or even individual egos. What can considerably complicate the matter is that it is very rare to have just a single well defined objective. The more common pattern is a series or a hierarchy of objectives in decreasing priority. Educational systems are often also used for research purposes, commercial systems usually have active research aimed at improving production, and research systems may have limited holding or production requirements. The problems are generated by the fact
that the requirements to support the different objectives may be in direct conflict or indirectly competing for scarce resources (time, money, water flow, etc.). The ordering and relative priorities of the various objectives can significantly influence design decisions. Since relative priorities of objectives is by necessity subjective, personnel changes can dramatically alter project objectives. Not uncommonly an important requirement or objective is not considered during design. The discovery of new requirements can prove to be seriously disrupting and expensive. An example is provisions for visitors, both formal and informal. While considerably removed from their basic objectives, research and commercial systems often entertain visitors for educational, promotional or 'public relations' reasons. These visitors can easily get in the way, pose a biosecurity hazard, threaten the work in progress or present a liability risk, if these potential problems have not been foreseen. Making a good impression and 'looking good' does have some value and might be considered during design, even for these types of systems. During the early stages of a project, the objectives are not fixed but dynamic. They change as new evaluations are made and design feedback is provided. They characteristically proceed from an initial general statement to greater and greater refinement and detail, which consider all of the objectives, priorities, and given conditions. A simple example for a commercial shellfish hatchery is given below:
Initial statement 9 Raise oysters for sale. Rising enthusiasm for project 9 Raise 25 million oyster larvae, 20 million clam and 5 million bay scallop larvae a month, and produce 1 million half-shell oysters per year. Consideration of seasonal demands and costs 9 Raise 100 million oyster larvae a month during June to September, 25 million oyster larvae during the rest of the year, and produce 1 million half-shell oysters per year. After first detailed cost estimate and discussion with banker 9 Raise 40 million oyster larvae a month during June to September, 10 million during the rest of the year and produce 1 million half-shell oysters a year. Mortgage house, postpone buying new car, and get spouse a secure job. After discussion with lawyers on permitting problems and additional inputs from engineers and banks 9 Restructure program to small-scale part-time 'Pilot Project' pending finding high rolling venture capitalist.
2.3 Quantifying requirements The problems of establishing requirements for a new culture system and defining them quantitatively is a very difficult task. It is the source of the biggest and costliest mistakes. The basic statements of needs, which launch the project, are often quite subjective and not quantified. These statements of need must go through many iterations of progressively greater detail, refinement, and evaluation before anything can be built and operated. The problems of translating basic objectives into quantitative terms necessary for construction are usually not given the attention and scrutiny they deserve.
TABLE 2.1 Major systems decisions 9 Species 9 Site 9 Capacity or scale (initial and future) 9 Seawater source 9 Freshwater source 9 Flow-throughor reuse options 9 Biomass loading (normal and maximum) 9 Operating schedule (seasonal or year-round) 9 Power sources 9 Monoculture or Polyculture 9 System Lifetime 9 Pumping schedule 9 Redundancy and reliability 9 Operator skill levels 9 Future options
One common and frequently encountered basic mistake is that the user at the very beginning of the project makes a number of major system's decisions without knowing the system consequences, without any sort of systematic evaluation and based solely on a priori judgment. These types of decisions are listed in Table 2.1. Such decisions may be irreversible, such as the site having already been purchased or otherwise secured. These decisions and the specifics of any given situation are so interactive that, if these decisions have to be accepted as 'givens', the project may be doomed before it starts. The tradeoffs involved with these decisions can be long and complex. Species selection may be fixed by research or educational needs. Criteria for selection of species for commercial culturing can be more involved (Webber and Riordan, 1976a) but the decision is often erroneously made on marketing considerations only. Site selection is equally complex with many important considerations (see Chapter 3). While there is no such thing as a perfect site, a bad site can easily doom a project. Bad choices with respect to the other decisions in Table 2.1 can, depending on circumstances, be equally serious. The probability of irreconcilable conflicts between the 'fixed' system's decisions and the project objectives and criteria is greatly increased if there exists strong economic constraints. It is common to have 'no acceptable solution' without fundamental changes in the project. If not recognized early, this can prove fatal to the project. The considerations and tradeoffs involving many of these decisions will be considered further. Another basic mistake is for the user to provide the general objective statements and then bow out of the process expecting someone else to 'engineer' the system. This can result from the users inability to answer detailed quantitative questions about both present and future needs. The user then assumes that the questioning engineer is better qualified to quantitatively define the requirements. The end result can be equipment and facilities which, in their approach, dimensions and capabilities, have implicit statements about not only present and future objectives and requirements but also on priorities, future growth, and management and operating philosophies. In addition, if the engineers do not have considerable prior experience with biological systems, 'sound engineering judgment' can produce systems that cannot adequately support the culture organisms and may hurt them directly. Sometimes such
mistakes can be remedied, but often can only be reversed at unacceptable cost. Working around such built-in problems often results in accepting reduced capacity, reduced efficiency, operating constraints, increased cost and increased risks. It often happens that even after considerable iteration between users and engineers, future requirements cannot be precisely defined. This is not surprising, since a fixed major seawater system and associated facilities may have a useful lifetime of 50 years or even more, and external conditions can dramatically change several times in this period of time. The problem is likely to be most acute for research oriented systems, due to the rapidity with which their requirements can change. Philosophically there are two extreme approaches to this problem. One is to purposely build the system for only the limited period of time for which the requirements can be clearly defined. This can be the best approach, especially for some seasonal or temporary systems, which may be entirely reconfigured and rebuilt from year to year, or if intended for some highly specialized purpose. This approach generally has the lowest initial cost. The dangers are that the requirements may change faster than anticipated or the system may not be abandoned or replaced when originally planned. The result may leave the user with an expensive to maintain system with low reliability and marginal usefulness. Under these conditions the overall cost could be very high. The alternate extreme approach is to hedge against all uncertainty by providing extra capabilities to match the range of uncertainties and by providing design features which will simplify future additions and modifications. Experience has shown that system requirements can change very rapidly with time and are not entirely predictable. However, the vast majority of changes in system requirement's are usually in directions that were at least considered during design, and often even anticipated. Changes in requirements are likely to occur late in the design phase or early in the operational phase and they can be very disruptive if they were not foreseen. The problems with this approach are that future requirements may develop in completely unanticipated directions and that, in the extreme, this approach inevitably becomes money limited. A flexible or adaptive system can cost much more than one whose requirements can be precisely stated with confidence.
2.4 Production cycle Based on the system objectives, the production cycle must be defined and may include the following items. (1) The total number of steps in the production cycle. For many species, a separate rearing or holding unit may be needed for each step. For short-term holding of a single adult species, there may be only one step. In contrast, a hatchery for even a single species might include broodstock holding, adult maturation, spawning, larval rearing and rearing of juveniles. Each of these steps or phases might have distinctly different requirements and facilities. (2) The total amount of time required for each step. This may be highly variable, depending on assumed environmental conditions, such as temperature, food sources and other factors. (3) The reproductive potential of the adults and the survival during each step. The reproductive potential in many species can be strongly influenced by conditions during the maturation process. Survival can also be highly variable depending on the system used, culturing conditions, and the skill and knowledge of the operators.
10
Example 2.1. Computation of required capacity per stage It is desired to produce 100,000 of the rare alpha fish, with an average weight of 1.5 pound each. The following data on alpha fish have been derived from previous operations. The tendency is to use for design the best of previous results, with the consequences that expectations are extremely over-optimistic relative to initial operations of a new system. Compute the number of individuals needed at the start and end of each rearing stage. Eggs/female Females/male Broodstock margin Survival data: juvenile fry eggs
10,000 4/1 300%
Number at end Number at start, end/survival, 100,000/0.80
100,000 harvested fish 125,000 juveniles
Number at end Number at start, end/survival, 125,000/0.70
125,000 juveniles 178,572 fry
Number at end Number at start, end/survival, 178,572/0.20
178,572 fry 892,858 eggs
Number females, 892,858/10,000 = 90 x 3 (margin) Number males, 270/4
270 females 68 males
80% 70% 20%
Starting with the production objective and survival data for the last step, the number of animals needed at the start of the last step can be computed. This process is repeated for each production step in reverse order and will result in the total number of animals or adult spawners needed at the front end (see Example 2.1). This information for each stage will also be used to compute the required water flows and tank volumes needed, as shown in a more detailed example for a shrimp hatchery (Example 2.2). However difficult, these parameters must be quantified. Since the inputs for these calculations are functions of assumed environmental conditions, operating procedures, and expertise of personnel, the numerical results usually have high uncertainty. The planning numbers often prove to be very optimistic relative to actual subsequent performance. If multiple species are being considered, the problems and uncertainties are increased. If the species are closely related, the differences may be important to the project but fortunately are often of minor importance in terms of impacts on equipment requirements and procedures. Since the parameters are interdependent, there are also a number of possible tradeoffs between production cycle values and water quality, environmental conditions, food sources, procedures, loading densities, economics and acceptable risks. One of the most common tradeoffs is the faster growth versus increased costs of more optimum temperature control. Other common tradeoffs are the increased cost of higher water quality or greater feed quantity versus the faster growth they may produce. In the absence of hard data directly relevant to the conditions of a given project, these tradeoffs can become highly subjective with a high premium on prior direct personal experience.
11
Example 2.2. Shrimp hatchery capacity and sizing A marine shrimp hatchery is designed to produce 1,000,000 post-larval (about P-20) shrimp per month. The total process takes about a month. The following data for a 'large tank' hatchery have been compiled from similar operations. Eggs/female Females/male Brood stock margin Stocking density: brood stock Naupli P-1 P-20 Survival data: Eggs-Naupli Naupli-P- 1 P-1 to P-20
= 400,000 = 1/1, average weight 90 g -- 700% (factor of 7) = = = =
2/m 2 60/1 = 60,000/m 3 20/1 = 20,000/m 3 15/1 = 15,000/m 3
= 50% -- 60% = 80%
(A) Compute the number of animals at the beginning and end of each stage. P-1 to P-20, at end at beginning Naupli to P-I, at end at beginning Eggs to Naupli, at end at beginning Brood stock: females 4,166,666/400,000 x 7 males
1,000,000 1,250,000 1,250,000 2,083,333 2,083,333 4,166,666 73 73
(B) The spawning females are temporarily moved to the spawning tanks and then quickly returned to the maturation facility. If the brood stock animals average 90 g each and the maturation tanks are shallow (typical water depth 12-18 in., use 12 in.), estimate the total maturation tank bottom area, water volume, and required seawater flow rate using research criteria. Tank bottom area (based on 2 animals/m 2) = 146/2 = 73 m 2 (2580 ft 2) For 1 ft water depth, volume = 22.25 m 3 (786 ft 3) Interpolating Fig. 2.7C for 100 g animals, 20~ = 0.1 kg/lpm Total biomass = 146 x 90 g = 13.1 kg of animals Required flow -- 13.1 kg/0.1 kg/lpm = 131 lpm (C) If the culturing from eggs through P-20 takes place in the same tank, estimate the total required tank volume at each stage and identify the limiting condition. Stage
Max. No.
Density
Volume
Naupli P- 1 P-20
2,083,333 1,250,000 1,000,000
60,000/m 3 20,000/m 3 15,000/m 3
34.7 m 3 62.7 m 3 66.7 m 3
The most limiting time from a loading standpoint is, not surprisingly, at the end of the culturing cycle. Note: While the numbers in this problem have been taken from several sources on 'large tank' hatcheries, the example presented in Fig. 5.2 is for a similar 1,000,000 PL/month penaeid shrimp hatchery.
12 2.5
Production
modeling
The space and water requirements of aquatic species depend strongly on size of the animals. Therefore, in cases where significant growth occurs, it is necessary to estimate total biomass, space, and water requirements on a weekly or monthly basis. Production modeling typically requires the following input components: - Time-step for the model; Estimated starting and ending dates; Initial and final weights (or lengths); - Growth model; - Mortality model; Water flow and animal density requirements; Metabolic production functions (if needed). The output of the production model is an estimate of the total biomass in the group as well as the water and space requirements. This information can be used to estimate the ending date of the production cycle or estimate what temperature changes would be necessary to achieve a needed ending date. For commercial operations, this type of analysis is used to adjust the starting dates of multi-batch production facilities to achieve maximum output or relative constant harvest rates (Watten, 1992). There are a vast number of different types of growth models for different life stages, or for different species. Three simple models will be discussed: A L method, degree day method, and the exponential method. Additional information on length-weight relationships, presented as conversions between lengths and weights, is commonly needed by species. 2.5.1 Growth Models The AL method is based on Haskell's work on trout (Haskell, 1959). He observed that at a constant temperature and adequate food supply, the increase in the length of a fish is a constant. This same relationship has been commonly observed for mollusks and crustaceans: Lt+l
--
Lt + AL
(2.1)
where Lt+l is equal to the length at time t 4- 1, L is equal to length at time t, and AL is the change in length/unit time. The AL is typically expressed in inches per day or inches per week. It is also possible to derive the following relationships for specific growth rate and specific feeding rate: Specific growth rate (%) -
[AW] 3xALxl00 -100 L
(2.2)
Specific feeding rate (%) -
IF ] 3 x AL x 100 x FCR ~ 100 L
(2.3)
where A W is change in weight, W is weight, F is wet weight of feed/time period, and FCR is feed conversion ratio (feed input/change in weight).
13 If the AL is expressed as inches per day, the specific growth and feeding rates will be in %/day. Once the A L is known, growth and feeding rates can be computed if the feed conversion ratio and length are know. The AL method can be applied to variable temperatures by the use of what is commonly called the temperature unit theory. This 'theory' is based on the assumption that over some temperature range, growth is directly proportional to temperature. The dependence of AL on temperature has the general form of AL = ( T U G R ) ( T - To)
(2.4)
where TUGR is equal to temperature unit growth rate (inches/day per ~ T is the water temperature (~ and To is the temperature (~ that results in no growth (AL = 0). For many cold-water species, To is generally assumed to be equal to 0~ (Westers, 1981). Eq. 2.4 can be used to modify Eqs. 2.2 and 2.3 for changes in temperatures. This discussion has been based on daily ~ temperature units; other forms of the temperature unit have been used (monthly temperature units and temperature units based on ~ An example of production planning with the AL method is presented in Example 2.3. When weight is plotted against time, the growth of many species can be described by an exponential curve of the form:
Wt = Woe Gt
(2.5)
where Wt is weight at time t (g), e is base e (2.71828183 .... ), W0 is weight at t -- 0 (g), G is specific growth rate (%/day), and t is time (days). In general, a single value of G may be valid for only part of the growth curve, although the growth over the whole period may be modeled by dividing the growth curve into successive exponential segments. Many aquatic species are only reared over short periods of their total life, and a single value of G may be entirely adequate. The value of G will depend on species, temperature, and the specific rearing conditions (see Example 2.4). If the weight is known at two times, Eq. 2.5 can be solved for the growth rate (G):
G -- [ln(W2) - ln(W1) tl I
(2.6)
where In is the natural logarithm, W1 = weight at tl, and W2 is the weight at t2. 2.5.2 Mortality Models Mortality data are typically quite site- and system-dependent. For modeling purposes, it is common to assume a fixed mortality in terms of %/day or %/week. 2.5.3 Length-Weight Relationships The relationship between length and weight for aquatic animals has the form of:
W = cL"
(2.7)
where W is wetweight in grams, L is length in mm, and c and n are species-specific constants. Typical values for c and n are presented in Table 2.2 for important culture species.
Example 2.3. Growth model using the A L method Compute the total biomass, specific feeding rate, and total feed requirement for 100,000 chinook salmon using the AL method (Eqs. 2.1-2.4). The temperature (~ is equal to 11.5 § (7.5) sin (0.985d + 238.4), where d is the Julian day (1-366). The initial length = 140 mm, c = 8.1910 -6 mm/g, n = 3, FCR = 1.3, mortality -- 0.25%/week, TUGR = 0.08 mm/day per ~ and To = 0~ The fish are ponded on 4/19/95 and the final target weight is 300 g. With the given conditions and equations, the following table of predictions can be developed. The final weight of 300 g is estimated to be reach on 9/13 after 21 weeks of rearing. Date
Temperature (~
Number #
Length (mm)
AL (mm/week)
4/19/95 4/26/95 5/ 3/95 5/10/95
9.66 10.54 11.44 12.34
100,000 99,750 99,501 99,252
140 146 152 159
n/a 5.90 6.41 6.91
Weight (g) 22 25 29 33
Continue computations on w e e n y time step until massis equalto 300 g 9/13/95 17.19 94,879 334 9.63 305
#/kg
Total biomass (kg)
Specific feeding rate (%/day)
Total feeding rate (kg/day)
44 39 35 30
2,247 2,537 2,879 3,281
n/a 2.25 2.34 2.42
n/a 57 67 79
3
28,904
0.36
210
Initial conditions (4/19/95):
Julian Day Number of fish Length Mass, 8.19 x 10 -6 (140) 3
109 100,000 fish 140 mm 22.47 g
End of week 1 (4/26/95):
Julian Day Temperature, 11.5 + (7.5) sin (0.985 • 116 + 238.4) Number of fish, 100,000 • (1.00 - 0.0025) A L, 0.08 x ( 1 0 . 5 4 - 0) x 7 Length, 140 mm + 5.9 mm Mass, 8.19 x 10-6 (145.90) 3 #/kg, 1000/25.44 Total biomass, 99,750 x (25.44/1000) Specific feeding rate, 3 x (5.90/7) x 100 • 1.3/145.90 Total feed, 2537.64 kg x 0.02253
116 10.54~ 99,750 fish 5.90 mm 145.90 mm 25.44 g 39.31 fish/kg 2537.64 kg 2.253%/day 57 kg/day
Repeat computations on weekly time step until mass is equal to 300 g (9/13/95)
15
The weight term in Eq. 2.7 is generally reported on a wet weight basis. For mollusks, wet body weight (excluding shell weight) may be reported. For crabs, the width of the carapace is used. For crayfish, shrimp, or lobster, length is measured in terms of carapace length or total length. Carapace length is typically measured from the back of the eye socket. The value of n for fish is near 3.0. The value of c for fish typically ranges from 5 x 10 -6 to 15 x 10 -6. Both n and c may vary with sex, especially for mature animals (see Example 2.5).
Example 2.4. Comparison of exponential growth curve with AL methods The following growth curve was observed over a 360-day trial (Actual weight column). Compute the exponential growth rate from Eq. 2.5 and compute the predicted weight for each time step. Compare results with AL method (c -- 11.22 x 10 -6 and n -- 3.00) using the mean AL for the whole production cycle. Days
Actual weight (g)
Actual lengths (mm)
Actual AL (mm/15 days)
0.0 15.0 30.0 45.0 60.0 75.0 90.0 105.0 120.0 135.0 150.0 165.0 180.0 195.0 210.0 225.0 240.0 255.0 270.0 285.0 300.0 315.0 330.0 345.0 360.0
5.0 8.4 13.0 19.3 27.4 37.7 50.4 65.8 84.2 105.9 131.4 160.8 194.5 232.9 276.4 325.2 379.7 440.3 507.5 581.4 662.6 751.4 848.3 953.5 1067.6
76.4 90.8 105.0 119.8 134.7 149.8 165.0 180.3 195.8 211.3 227.1 242.9 258.8 274.8 291.0 307.2 323.5 339.8 356.3 372.8 389.4 406.1 422.8 439.7 456.5
. 14.4 14.2 14.8 14.8 15.1 15.2 15.3 15.4 15.6 15.8 15.8 15.9 16.0 16.1 16.2 16.3 16.4 16.5 16.5 16.6 16.7 16.8 16.8 16.9
Mean AL =
.
Computed weight using G . 6.3 7.8 9.8 12.2 15.3 19.1 23.9 29.9 37.4 46.7 58.4 73.1 91.4 114.2 142.8 178.6 223.4 279.3 349.2 436.7 546.0 682.8 853.8 1067.6
Computed L using G
Computed L using mean AL
Computed weight using mean AL
82.3 88.7 98.5 102.9 110.9 119.4 128.7 138.6 149.3 160.9 173.3 186.7 201.2 216.7 233.5 251.6 271.0 292.0 314.6 338.9 365.1 393.3 423.8 456.5
92.2 108.1 123.9 139.7 155.6 171.4 187.3 203.1 218.9 234.8 250.6 266.5 282.3 298.1 314.0 329.8 345.7 361.5 377.3 393.2 409.0 424.9 440.7 456.5
8.8 14.2 21.3 30.6 42.3 56.5 73.7 94.0 117.7 145.2 176.6 212.3 252.4 297.3 347.3 402.5 463.4 530.0 602.8 681.9 767.7 860.4 960.3 1067.6
.
15.84
Note that it is always possible to fit an exponential growth curve between any initial and final weights of any growth curve. This does not mean that it is a good fit. For this example, the AL method (Eq. 2.1; column 7) gives a far better fit than the exponential method (Eq. 2.5; column 5). See the following plot of the actual weights versus the predicted weights from the exponential and AL methods.
16
Example 2.4. (continued) 1200
1000 -
[]
Actual Weight (g)
O
ComputedWeight (G)
4"
ComputedWeight (AL)
t3
~o
800 -
~ o ,~
600-
~
,~
o o
400o o o
200 -
04 0
o
~,.,no08~ooO~176176176 i
I
I
100
200
300
400
Days
Step 1.
Compute G using Eq. 2.6 G = 100[ln(1067.6) - ln(5)]/360 - 0
= 1.490%
Step 2.
Mean A L (from above spreadsheet) A L = 15.84 mm/15 days
Step 3.
Compute length at day 0 (solve Eq. 2.7 for L) Length = (5/11.22 • 10-6) 0.33333
= 76.38 mm
Step 4a.
Compute weight at day 15 (G method, use Eq. 2.5) Weight = 5e (0"0149)(15)
= 6.252 g
Compute length at day 15 (solve Eq. 2.7 for L) Length = (6.252/11.22 x 10-6) 0.33333
- 82.29 mm
Step 5a.
Compute length at day 15 (AL method, use Eq. 2.1) Length - 76.38 + 15.84
= 92.22 mm
Step 5b.
Compute weight at day 15 (use Eq. 2.7) Weight = 11.22 • 10 -6 • (92.22) 3
= 8.80 g
Step 4b.
Go back to Step 1" continue computations until day 360.
2.6 Types of systems
There are several possible types of seawater systems and these are classified at two extremes as open cycle and closed cycle systems. Open or flow-through systems depend on relatively large quantities of good quality incoming seawater to provide life support to
17 TABLE 2.2 Constants for length-weight relationships Common name
Species
c x 106
n
Length basis
Atlantic sturgeon Channel catfish Largemouth bass Chinook salmon Muskellunge Northern pike Rainbow trout Walleye European eel Milkfish Pacific bonita American lobster Blue crab
Acipenser oxyrhynchus Ictalurus punctatus Micropterus salmoides Oncorhynchus tshawytscha Esox masquinongy Esox lucius Oncorhynchus mykiss Stizostedion vitreum Anguilla anguilla Chanos chanos Sarda chiliensis Homarus americanus Callinectes sapidus, female Callinectes sapidus, male Procambarus acutus acutus Macrobrachium rosenbergii Procambarus clarkii Cancer irroratus Penaeus stylirostris Penaeus vannamei Artica islandia Loligo pealai Chelonia mydas
1.1402 5.160 12.748 8.190 4.429 5.012 11.224 8.303 0.04302 8.989 7.729 589 287.4 181.4 8.026 1.305 8.837 87.10 15.2 9.88 68.436 1809 1659.0
3.18 3.11 3.00 3.00 3.00 3.00 3.00 3.00 3.63 2.99 3.09 3.07 2.64 2.78 3.32 3.42 3.28 3.14 3.10 3.05 2.89 2.15 2.54
total length total length total length total length total length total length total length total length total length total length total length carapace length carapace width carapace width total length total length total length carapace width total length total length shell length dorsal mantle length carapace length
Crayfish Freshwater prawn Red swamp crayfish Rock crab Shrimp Shrimp Ocean quahog Squid Sea turtle
W - cL n, where length is in mm and weight in grams. Note that the actual value of c is the value of c in the table • 106. The value of n does not depend on the units of weight or length, but the value of c depends on the units of both. Much of the length-weight data reported in the literature are based on other units. The value of c in other units can be converted to c based on millimeters and grams by observing that if L = 1 mm then W = c. The value of c is equal to the weight in grams of a 1 mm animal. Therefore, in a system based on inches and pounds, convert 1 mm to inches and solve for weight. Convert weight in pounds to grams - - this is the value of c that should be used in Eq. 2.7.
the culture organisms. When the seawater's properties become unacceptable, the water is discharged. The advantages of open systems are proportional to the input water quality and quantity. If the input water parameters are consistently good and no discharge treatment is required, these systems are clearly the simplest, cheapest, most reliable and have the least risk (see Fig. 2.2A). Few, if any, completely open systems exist. The incoming seawater may require some treatment before use. This may include filtering to protect pumps or remove eggs, larvae or debris, heating/cooling, aeration/degassing or settling of solids. In addition, it is very rare that there would not be some internal water treatment in the system (see Fig. 2.2B). This might include adding oxygen, removing uneaten food and fecal matter or reducing the concentrations of pathogenic organisms. Flow-through systems can become quite complex. Depending on physical and regulatory conditions, it may be necessary to treat process water prior to discharge (see Fig. 2.2C) and such requirements are becoming much more common. Systems that are predominantly open or flow-through systems are by far the
18
Example 2.5. Computation of weight from length-weight relationship Compute the weight of a 250 mm largemouth bass, chinook salmon, and European eel in grams and #/kg. From Table 2.2 Species
c
n
Largemouth bass Chinook salmon European eel
12.748 x 10 -6 8.190 x 10 -6 0.04302 x 10 -6
3.00 3.00 3.63
From Eq. 2.7 W = 12.748 x 10 -6 (250) 3.00 W = 8.190 x 10 -6 (250) 3.oo W = 0.04302 x 10 -6 (250) 3.63
A
Seawater
B
Seawater~ Coarse I v[ Filtration I
= 199 g or 5.02/kg (largemouth bass) = 127 g or 7.87/kg (chinook salmon) = 21.8 g or 45.9/kg (European eel)
URearing Unit
Discharge ,~
U Rearing Unit
Discharge ,~
iv
iv
~-Aeration C
'
SeawaterJ Pre! "1 treatments I
J Rearing Unit 9
Posttreatment
Discharge ,~ v
....
~--Aeration Fig. 2.2. Open or flow-through systems. (A) Completely open system. (B) Limited pretreatment and internal aeration. (C) More extensive pretreatment, internal aeration and treatment of discharge water. Many other variations may also exist.
most common type, although this is not reflected in the available literature (see Appendix B). The available literature on flow-through systems is sparse, unbalanced in representation and biased towards research oriented systems. A completely closed cycle system, such as a well balanced aquarium, has no water inflow requirement, except to make up for evaporation, and no discharge (see Fig. 2.3A). The water is treated and reconditioned internal to the system by a series of complex biochemical and physical processes. If everything is working well, all the processes are in equilibrium and good water quality is maintained. Any changes, such as increased feeding, chemical additions, adding or removing animals, or even cleaning parts of the system, can destroy the delicate balances. For most practical uses, a completely closed system of any appreciable size is difficult to monitor and manage and is often uneconomic if any alternatives exist. There
19
Water Treatments A
Distilled Water
Rearing~Unit
"1 Water Treatments~, ~ B Seawater J Prey[ treatments
RearingUnit
I POst] Discharge treatment
Fig. 2.3. Closed or reuse systems. (A) Pure closed system, with water addition only to make up for evaporation. (B) More common reuse system with some flow-through.
can be depletion of necessary trace materials and build-ups of other persistent contaminants to troublesome levels. Periodic recharging with new seawater is often required. Thus, even closed systems need access to good quality seawater or use high cost artificial seawater. Therefore, some net flow through the system is usually present and a better label for most systems would be a water reuse system (see Fig. 2.3B). Generally a 90% water flow reuse (10% new water and 90% reconditioned water) can be achieved with reasonable processing. Technical and management difficulties progressively increase as one approaches 100% reuse (completely closed system). The difficulties and their severity are conditional on the specific circumstances. A reuse system being operated at a fraction of its carrying capacity is likely to be much less trouble than one being operated at its limits. In spite of the difficulties, complexities and costs of seawater reuse systems, there is considerable prior experience with such systems in the size range of interest (see Appendix C). Closed systems have primarily been used in marine aquariums, which are often far from the sea or in urban areas with highly polluted seawater. In marine aquariums small numbers of organisms are held in good water quality conditions. The operating costs of these systems may be in the range of US$10-1000 per year per pound of animals. Much of this expense is due to maintaining the appearance of the water (turbidity and color) required for public viewing, rather than for the life support requirements of the animals themselves. High reuse systems, under some conditions, may be economical for hatchery operations, short-term holding, or for very high value organisms, but have generally proven uneconomical for the growth of shrimp, lobsters and fish to marketable size for human food unless heavily subsidized. Thus, there is a spectrum of possibilities between completely open and completely closed systems. If sufficient quantities of good quality water are readily available, the decision will be towards the open systems due to their greater simplicity, reliability and lower costs. However, if sufficient water is not available or of poor quality, or if environmental considerations are paramount, there will be a tendency towards greater water reuse. While leaning towards one type or the other, most seawater systems have some net water flow through the system as well as some degree of water reconditioning internal to the system and increasingly some required post treatment of discharge water. It is, therefore, useful to consider the systems externally as
20 open or flow-through systems while considering various water reuse or reconditioning options internally. In short, internal reuse loops in a flow-through system (Fig. 2.3B) or in a more elaborate version as shown in Fig. 5.1.
2.7 System carrying capacity The carrying capacity of a flow-through system is dependent on many parameters and the specifics of any given application. Table 2.3 lists just some of the factors that might be critical. These factors cannot be considered independently, but must all be evaluated relative to the biology of the culture organisms. This complex evaluation of environmental parameters and organism biology is often termed 'water quality'. While much is known relative to economically important species, there are nevertheless a number of important data voids for culturing purposes (Huguenin and Colt, 1986). One of the most significant problems is that most of the data on water quality criteria are based on short-term experiments, and in many cases, lethal effects. Detailed criteria based on chronic effects and long-term experiments are unavailable for many species over their life spans. Low risk and fast growth require not stressing the organisms. The acceptable values for 'no stress' are often not precisely known. Determining the water quality requirements and inherent tradeoffs for specific culture organisms and life stages is critical and essential to the specification of the seawater system (see Appendix D). A very brief review of water quality parameters and water quality considerations is presented in this section. Water quality criteria for use with marine systems will be needed in the site selection process and loading computations. They may be quite different from published environmental protection criteria (for example, USEPA, 1976, 1986), as these criteria are formulated to protect a wide range of ages and species. In a specific marine system, (a) only a single species TABLE 2.3 Seawater properties affecting carrying capacity Physical parameters
Chemical parameters
Temperature range (daily and seasonal pH and alkalinity variability) Gases Salinity range (tidal and seasonal variability) total gas pressure oxygen Particulates (solids) composition (organic and inorganic) nitrogen size carbon dioxide hydrogen sulfide concentration Color Nutrients nitrogen compounds Light artificial or natural phosphorus compounds trace metals and speciation total annual incident energy Organic compounds intensity of radiant energy biodegradable quality of light photoperiod (daily cycles) non-biodegradable Toxic compounds heavy metals biocides
Biological parameters Bacteria (type and concentrations) Virus Fungi Others
21 TABLE 2.4 Preliminary water quality screening and production levels for marine applications Parameter
Screening level
Production level
Ammonia (except for plants)
< 1 Ixg/1 NH3-N
Nitrite Dissolved oxygen (except for plants) Total gas pressure Carbon dioxide (except for plants) Hydrogen sulfide Chlorine residual pH Temperature Salinity
0.05 mg/1 NO2-N 90% of saturation 76 mm Hg 5 mg/1 CO2 2 ~g/1 as H2S 10 ~g/1 7.9-8.2 Depends on life stage and species Depends on life stage and species
< 1 Ixg/1 NH3-N research <10 l~g/1 NH3-N production <40 Ixg/1 NH3-N holding, little or no feeding 0.10 mg/1 NO2-N 6 mg/1 20 mm Hg 10 mg/1 CO2 1 Ixg/1 as H2S 1 ~g/1 7.9-8.2 - 1 to 4 0 ~
1-40 g/kg
Metals (total)
Cadmium Chromium Copper Iron Mercury Manganese Nickel Lead Zinc
1 ~g/1 10 Ixg/1 1 Ixg/1 300 Ixg/1 0.05 ~g/1 50 ~g/1 2 Ixg/1 2 Ixg/1 10 Ixg/1
3 ~tg/1 25 ~tg/1 3 ~tg/1 100 Ixg/1 0.1 lxg/1 25 Ixg/1 5 Ixg/1 4 Ixg/1 25 Ixg/1
may be cultured and for a only a part of its life, (b) the animals may be held for only a short time (example, holding of lobsters or test animals), or (c) the condition of the animals may not be too important as long as they do not die too rapidly. For some key parameters such as ammonia, the formulation of a single fixed criterion based on a no-effects level may be inappropriate or at least costly for many applications. Water quality criteria for research applications may be more restrictive than for environmental protection. For the small volumes of seawater flow involved in most research projects, the cost of maintaining exceptionally high water quality is usually not significant compared to labor, equipment, and supplies. Two types of water quality criteria may be specified: screening criteria and production criteria. Preliminary screening and production criteria for fish and crustaceans are presented in Table 2.4. The screening criteria are used to screen potential sites or seawater sources. If measured water quality does not satisfy the screening criteria for all components, small-scale rearing experiments may be needed prior to construction or more extensive water treatment will be required prior to use. High concentrations of ammonia, nitrite, and metals may make a site unacceptable as they are expensive and difficult to remove. On the other hand, low dissolved oxygen, high concentrations of nitrogen gas or hydrogen sulfide, while not desirable, can sometimes be economically treated. Production criteria are the criteria used in the actual culture system. They may be significantly different for marine algae than for fish and crustaceans. In particular, carbon dioxide, ammonia, and phosphorus compounds may
22 have to be enriched m a n y times to support rapid growth of aquatic plants. The important water quality criteria p a r a m e t e r s are given in Table 2.3 and are discussed below. 2.7.1 A m m o n i a A m m o n i a is the m a j o r end-product of protein m e t a b o l i s m in most aquatic animals. The toxicity of a m m o n i a is due to the free or un-ionized form (NH3) while the ionized form (NH +) has little toxicity. U n - i o n i z e d a m m o n i a is typically reported as nitrogen and written as NH3-N. A m m o n i a concentration expressed as the NH3 c o m p o u n d can be converted to a nitrogen basis by m u l t i p l y i n g by 0.822. Wet chemical tests m e a s u r e the sum of the un-ionized and ionized a m m o n i a or the total a m m o n i a (called total a m m o n i a nitrogen or TAN when expressed on a nitrogen basis). The c o n c e n t r a t i o n of un-ionized a m m o n i a depends primarily on total a m m o n i a , pH, temperature, and salinity. The m o l e fraction of un-ionized a m m o n i a is equal to the percent un-ionized a m m o n i a / 1 0 0 . The concentration of un-ionized a m m o n i a is equal to: U n - i o n i z e d a m m o n i a (mg/1 as NH3-N) - otTAN
(2.8)
U n - i o n i z e d a m m o n i a (Ixg/1 as NH3-N) -
(2.9)
or 1000otTAN
TABLE 2.5 Mole fraction of un-ionized ammonia in flesh and brackish waters based on NBS pH scale Temperature
pH
(~
7.0
7.8
7.9
8.0
8.1
8.2
8.3
9.0
0.0012 0.0019 0.0027 0.0039 0.0056 0.0080 0.0111 0.0153
0.0078 0.0116 0.0169 0.0243 0.0346 0.0483 0.0663 0.0894
0.0098 0.0145 0.0212 0.0304 0.0431 0.0600 0.0820 0.1100
0.0123 0.0182 0.0266 0.0380 0.0537 0.0744 0.1011 0.1345
0.0154 0.0229 0.0332 0.0474 0.0667 0.0919 0.1240 0.1638
0.0193 0.0286 0.0415 0.0590 0.0825 0.1130 0.1513 0.1978
0.0242 0.0357 0.0516 0.0731 0.1017 0.1382 0.1833 0.2367
0.1107 0.1567 0.2144 0.2833 0.3621 0.4455 0.5293 0.6088
0.0009 0.0013 0.0019 0.0028 0.0040 0.0057
0.0055 0.0082 0.0121 0.0174 0.0247 0.0347
0.0070 0.0103 0.0151 0.0218 0.0310 0.0433
0.0087 0.0130 0.0190 0.0273 0.0387 0.0539
0.0110 0.0163 0.0238 0.0341 0.0482 0.0669
0.0138 0.0204 0.0297 0.0426 0.0599 0.0828
0.0173 0.0256 0.0371 0.0530 0.0743 0.1020
0.0810 0.1162 0.1620 0.2191 0.2868 0.3629
Salinity = 0 g / k g (freshwater)
5 10 15 20 25 30 35 40 Salinity = 5 g / k g
5 10 15 20 25 30
Notes: For normal applications, interpolation within and between Tables 2.5 and 2.6 may be adequate. Based on freshwater equilibrium constants developed by Emerson et al. (1975), seawater relationship found by Khoo et al. (1977), and the equation for the computation of ionic strength presented by Whitfield (1974). The NBS pH was converted to the pHT scale (Hansson, 1973) by subtracting 0.0007 x Salinity + 0.131 (Millero, 1986).
23 TABLE 2.6 Mole fraction of un-ionized ammonia in marine waters based on NBS pH scale Temperature
pH
(~
7.0
Salinity = 5 10 15 20 25 30
15
7.8
7.9
8.0
8.1
8.2
8.3
9.0
0.0051 0.0075 0.0111 0.0160 0.0228 0.0320
0.0064 0.0095 0.0139 0.0200 0.0285 0.0399
0.0080 0.0119 0.0174 0.0251 0.0356 0.0497
0.0101 0.0149 0.0218 0.0314 0.0444 0.0618
0.0126 0.0187 0.0273 0.0392 0.0553 0.0766
0.0159 0.0235 0.0342 0.0489 0.0686 0.0946
0.0747 0.1075 0.1506 0.2048 0.2697 0.3436
0.0042 0.0063 0.0093 0.0134 0.0192 0.0270
0.0053 0.0079 0.0117 0.0169 0.0240 0.0338
0.0067 0.0100 0.0146 0.0211 0.0301 0.0422
0.0084 0.0125 0.0183 0.0265 0.0376 0.0525
0.0106 0.0157 0.0230 0.0331 0.0469 0.0652
0.0133 0.0197 0.0288 0.0413 0.0583 0.0808
0.0631 0.0915 0.1293 0.1776 0.2367 0.3057
g/kg 0.0008 0.0012 0.0018 0.0026 0.0037 0.0052
Salinity = 35 g / k g
5 10 15 20 25 30
0.0007 0.0010 0.0015 0.0022 0.0031 0.0044
Sames notes as Table 2.5.
where ol is mole fraction of un-ionized ammonia (%/100), and TAN is total ammonia nitrogen (mg/1 as N). Values of the mole fraction of un-ammonia are presented in Table 2.5 for freshwater and brackish waters and in Table 2.6 for marine waters. At a given pH and temperature, the concentration of un-ionized ammonia is significantly less in seawater (see Example 2.6). For equal concentrations of total ammonia, the concentration of un-ionized ammonia is typically higher in seawater because of the generally higher pH compared to freshwater. Therefore, the carrying capacity in seawater is generally lower relative to freshwater (see Section 2.7). There are situations where one may wish to increase or adjust the un-ionized ammonia concentration (see Example 2.7). The concentration of un-ionized ammonia is strongly dependent on pH. In freshwater, pH meters are calibrated with low ionic strength buffers, commonly called 'NBS' or National Bureau of Standards buffers. Tables 2.5 and 2.6 are based on the use of these buffers. The National Bureau of Standards has been renamed as the National Institute of Standard and Technology (NIST), but commonly these buffers are still called 'NBS' buffers. In seawater, many chemists use a 'tris' seawater buffer (Hansson, 1973). While the use of this buffer has important thermodynamic advantages, it is not commercially available. Experimental work on the ammonia equilibrium in seawater (Khoo et al., 1977) is based on this pH scale. A number of researchers have published tabular listings or computer programs for the computation of percent un-ionized ammonia in seawater based on this work (Hampton, 1977; Bower and Bidwell, 1978; Spotte and Adams, 1983). The computation of un-ionized ammonia from these articles must be based on the use of the 'tris' seawater buffer. The error resulting from the use of 'NBS' type buffers with these data will be greater than the use of equilibrium constants for freshwater.
24
Example 2.6. Computation of un-ionized ammonia nitrogen Given a water temperature of 20~ pH of 7.9, salinity of 35 g/kg (ppt) and a measured total ammonia nitrogen (TAN) of 0.82 mg/1, what is the concentration of un-ionized ammonia nitrogen in Ixg/l? Is the concentration of un-ionized ammonia greater in freshwater or seawater at the same pH and temperature. (A) Using the pH and water temperature read the mole fraction (or) from Table 2.6 and Eq. 2.9. c~ = 0.0169 (dimensionless) NH3-N = 1000 (c~) (TAN) = 1000 (0.0169) (0.82) = 14 Ixg/1 (B) Comparison of un-ionized ammonia in seawater and freshwater Mole fraction (or) for freshwater - 0.0304 (Table 2.5) Mole fraction (or) for seawater = 0.0169 (above) From Eq. 2.8, the concentration of un-ionized ammonia is proportional to mole fraction and therefore the concentration in freshwater is greater by: { 0"0304 0.169- 0"0169 ] 100 = 79%
2.7.2 Nitrite Nitrite, an intermediate in the conversion of ammonia to nitrate, can oxidize the iron in hemoglobin such that it is unable to transport oxygen. The toxicity of nitrite, while still formidable, is significantly reduced in seawater due to the high concentration of chloride and calcium (Lewis and Morris, 1986). 2.7.3 Nitrate Nitrate is the final compound produced by the oxidation of ammonia. This compound is largely nontoxic, except at very high concentrations, which can occur in closed systems. 2.7.4 Dissolved Oxygen The equilibrium or saturation concentration of dissolved oxygen depends on temperature and salinity. Saturation concentrations of dissolved oxygen are presented in Table 2.7 for salinities in the range of 0 - 4 0 g / k g and water temperatures of 0-40~ Photosynthesis and solar heating can produce dissolved oxygen concentrations higher than saturation (supersaturation). Dissolved oxygen concentrations significantly less than saturation are commonly produced by pollution. Dissolved oxygen concentration must be measured immediately after sampling to avoid changes with time in the sampling container. For fish and crustaceans, growth will be reduced when the dissolved oxygen falls below 6 mg/1 and significant mortality will result below 2 - 3 mg/1. Bivalve shellfish may be able to tolerate lower dissolved oxygen concentrations for extended periods of time, especially if the temperature is low. Water
25
Example 2.7. Adjustment of un-ionized ammonia A bioassay tank contains 40 1 of water with a temperature of 5~ salinity of 35 g/kg and a pH = 8.0. How much NH4C1 must be added to produce an un-ionized ammonia concentration of 1000 Ixg/1 NH3-N? (A) Compute concentration of TAN From Table 2.6, From Eq. 2.9,
mole fraction (or) --- 0.0067 1000 Ixg/1 = (1000) (0.0067) TAN
TAN = 149.3 rag/1 (B) Compute concentration and weight of ammonia chloride. TAN or total nitrogen is based on nitrogen with a molecular weight of 14.0 g/mole, therefore, molecular concentration is equal to: 149.3 x 10-3/14.0 = 1.066 x 10 -2 moles/1 The molecular weight of NH4C1 is:
N H C1
(1 • 14.00) (4 • 1.01) (1 • 35.45)
--=
14.00 4.04 35.45 53.49 g/mole
NHaC1 = (1.066 x 10 -2) (53.49) = 0.570 g/1 Total amount of NHaC1 required = (0.570 g/l) (40 1) -- 22.8 g
temperature, even within seasonal variations, can significantly impact the oxygen saturation concentration (see Example 2.8). 2.7.5 Carbon Dioxide High carbon dioxide concentrations reduce the ability of animals to transfer oxygen. Carbon dioxide concentrations should be maintained below 10 mg/1 (Smart et al., 1979), although many animals can tolerate higher levels, especially if the dissolved oxygen is high. For marine plants, the more dissolved carbon dioxide the better, as it is often the growth limiting substance. In fact, in the mass culturing of phytoplankton, such as may be needed in bivalve or shrimp hatcheries, direct carbon dioxide injection into the water may be used to increase growth rate. Some care must be taken to control carbon dioxide concentrations even in aquatic plant culture as it is possible to reduce the pH to below 5 at extremely high concentrations. 2.7.6 Hydrogen Sulfide High concentrations of hydrogen sulfide may be present in well waters or the bottom water of some marine bays with restricted circulation. Samples used for total sulfides analysis must be specially treated to prevent loss of hydrogen sulfide gas during transport and analysis. A criterion of 1 t~g/1 of hydrogen sulfide gas is suggested as a maximum for fish and crustaceans.
TABLE 2.7 Air solubility of oxygen (Cx)in seawater (rng/l), 0 4 0 g/kg at 760 rnm Hg (1 atm pressurej Temperature
Salinity (g/kg)
("'4
0
5
10
15
20
25
30
35
40
0 I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
14.621 11.216 13.829 13.460 13.107 12.770 12.447 12.139 11.843 11.559 11.288 11.027 10.777 10.537 10.306 10.083 9.870 9.665 9.467 9.276 9.092 8.914 8.743 8.578 8.418 8.263 8.113 7.968 7.827 7.691 7.558 7.430 7.305 7.183 7.065 6.949 6.837 6.727 6.619 6.514 6.412
14.120 13.733 13.364 13.011 12.674 12.352 12.043 11.748 11.465 11.194 10.933 10.684 10.444 10.214 9.993 9.780 9.575 9.378 9.188 9.005 8.828 8.658 8.493 8.334 8.181 8.032 7.888 7.748 7.613 7.482 7.354 7.230 7.110 6.993 6.879 6.767 6.659 6.553 6.449 6.348 6.249
13.636 13.266 12.914 12.577 12.255 1 1.047 11.652 1 1.369 11.008 10.839 10.590 10.351 10.121 9.901 9.689 9.485 9.289 9.099 8.917 8.742 8.572 8.408 8.250 8.098 7.950 7.807 7.668 7.534 7.404 7.278 7.155 7.036 6.920 6.807 6.697 6.590 6.485 6.383 6.283 6.186 6.090
13.167 12.815 12.478 12.156 1 1.849 11.554 11.272 l 1.002 10.743 10.495 10.257 10.028 9.808 9.597 9.394 9.198 9.010 8.829 8.654 8.486 8.323 8.166 8.014 7.867 7.725 7.588 7.455 7.326 7.201 7.079 6.961 6.846 6.735 6.626 6.520 6.417 6.316 6.218 6.121 6.027 5.935
12.714 12.378 12.057 11.750 11.456 11.175 10.905 10.647 10.399 10.162 9.934 9.715 9.505 9.302 9.108 8.921 8.740 8.566 8.399 8.237 8.081 7.930 7.785 7.644 7.507 7.375 7.247 7.123 7.003 6.886 6.772 6.602 6.555 6.450 6.348 6.248 6.151 6.056 5.963 5.873 5.783
12.277 11.956 11.650 11.356 11.076 10.807 10.550 10.303 10.066 9.839 9.621 9.412 9.210 9.017 8.830 8.651 8.478 8.311 8.151 7.995 7.846 7.701 7.561 7.126 7.295 7.168 7.045 6.926 6.810 6.698 0.589 6.483 637rl 6.278 6.180 6.084 5.991 5.899 5.810 5.722 5.636
11.854 11.548 11.256 10.976 10.708 10.451 1O.ZOh 9.970 9.744 9.526 9.318 9.117 8.925 8.739 8.561 8.389 8.223 8.061 7.910 7.761 7.617 7.479 7.344 7.214 7.089 6.967 6.849 6.734 6.623 6.515 6.410 6.308 6.208 6.1 1 1 6.017 5.924 5.834 5.746 5.660 5.575 5.492
11.445 11.154 10.875 10.608 10.352 10.107 9.872 9.647 9.431 0 223 9.024 8.832 8.648 8.470 8.300 8.135 7.976 7.823 7.676 7.533 7.395 7.262 7.134 7.009 6.888 6.771 6.658 6.548 6.441 6.337 6.236 6.137 6.042 5.948 5.857 5.768 5.681 5.597 5.513 5.432 5.352
11.051 10.773 10.507 10.252 10.008 9.774 9.550 9.335 9.128 8.930 8.739 8.556 8.379 8.210 8.046 7.888 7.737 7.590 7.449 7.312 7.180 7.052 6.929 6.809 6.693 6.581 6.472 6.366 6.263 6.104 6.066 5.972 5.880 5.790 5.702 5.617 5.533 5.451 5.371 5.292 5.215
Based on Benson and Krause (1984).
27
Example 2.8. Air solubility of oxygen in seawater
It is important to understand the air solubility effects created by seawater temperature changes. Assume a salinity of 20 g/kg and atmospheric pressure. (A) Increasing the seawater temperature from 5~ to 20~ will increase or decreases the air solubility of oxygen and by what percentage? Table 2.7, for 5~ C* = 11.175 mg/1; for 30~ C* -- 6.772 mg/1 [6.772-11.17511.175] 100=-39% (decrease in solubility) (B) Assuming oxygen saturation at 5~ and none of the dissolved oxygen is allowed to escape during the heating to 30~ what is the percent saturation of oxygen at 30~ The final dissolved oxygen concentration is the same = 11.175 mg/1 11.1751 100 : 165% of saturation 6.772 J
2.7.7 Total Gas Pressure Gas supersaturation can be produced by a variety of natural and man-made conditions (see Section 12.4) and many surface waters and seawater wells are, at least at times, supersaturated with dissolved gases. Lethal gas pressure ranges from 100 to 200 m m Hg, but levels in the range of 4 0 - 5 0 m m Hg may increase the mortality of fish on a chronic basis (Colt, 1986). Gas supersaturation must be measured in situ. A maximum criterion of 20 m m Hg is suggested for fish and crustaceans. Dissolved oxygen is n o t a good measure of total gas supersaturation. 2.7.8 pH The normal pH of seawater ranges from 7.9 to 8.2. Values outside of this range may indicate pollution or excessive freshwater runoff. Animals that typically live in full-strength seawater can be very sensitive to changes in pH outside the normal range. Animals that live in tidal streams or estuaries may be much more tolerant to changes in pHs. A criterion of 7.9 to 8.2 is suggested. As discussed in the ammonia section, pH meters may be calibrated by use of two different types of buffers. The low ionic strength buffer ('NBS' type) is widely available for general use and most pH readings are based on this buffer. 2.7.9 Residual Chlorine Chlorine is widely used to disinfect drinking water, wastewater prior to discharge, and prevent fouling of heat-transfer systems in power plants. It is also used to control fecal coliform counts in marine m a m m a l pools and to disinfect water used in molluscan and shrimp hatcheries. A m a x i m u m criterion for chlorine residual of 1 Ixg/1 is suggested for fish and crustaceans. Marine mammals can tolerate considerably higher concentrations without ill
28 effects. Analysis of chlorine residual at this low level is difficult and expensive. Common wet chemical tests for chlorine residual are not reliable below 20-100 Ixg/1. 2.7. l0 Temperature The temperature of seawater may vary from - 1 to greater than 40~ No single criterion can be suggested, as some animals can survive over this full range, while most will be restricted to only a portion of this range. The water quality criteria for temperature will depend on the species and the life-stage. Rapid temperature changes are entirely another matter. Very few animals can tolerate even modest temperature changes if rapid and prolonged. For prolonged temperature changes, a change up or down of not more than I~ per day is recommended. 2.7.11 Salinity The salinity of seawater is expressed in terms of parts per thousand (g/kg). In older literature, the symbols %o or ppt (parts per thousand) are often used. The salinity of seawater may vary from 1 to greater than 40 g/kg. Salinity can be easily measured by use of conductivity or refractive methods. The water quality criteria for salinity will also depend on the species and life-stage. As with temperature, different organisms may have broad or narrow tolerances and rapid changes can be very stressful, even within the acceptable range. 2.7.12 Heavy Metals Heavy metals include cadmium, chromium, copper, iron, mercury, manganese, nickel, lead, and zinc. High levels of manganese and iron may occur in well water low in dissolved oxygen. Samples used for heavy metal analysis should be treated with acid to reduce loss of metals during travel and storage. The presented criteria (Table 2.4) are based on total metals (particulate § dissolved forms) as the toxic mode for iron and manganese may be physical blocking of the gills by particulate matter (Chen et al., 1985). If water is aerated and allowed to stand for days before analysis, the majority of the iron and manganese will precipitate out of solution. Therefore, high iron and manganese concentrations may not be reported if water samples are allowed to stand for sometime prior to analysis. The addition of 1-10 mg/1 of EDTA (ethylenediaminetetraacetate, a common chelating agent) can significantly reduce the toxicity of heavy metals and it is commonly used in some crustacean and molluscan hatchery facilities. Screening levels for metals may be several times higher than those listed in Table 2.4 if use of EDTA is anticipated. 2.7.13 Biocides A vast number of organic chemicals are introduced into the natural environment. These include herbicides, pesticides, and industrial chemicals. Rare storm events may introduce significant quantities of such chemicals from agricultural runoff or resuspend them from the bottom. Such storm drainage problems can be anticipated but are not obvious site selection considerations (see Chapter 3). Depending on the purpose of the seawater systems, it may be necessary to conduct detailed monitoring of water, sediment, animal tissue, or conduct a
29 pilot-scale operation to assess the potential problems from biocides and industrial chemicals. Acutely lethal concentrations of biocides can be introduced into streams and ponds from transport accidents (crop duster crashes, truck crashes, or railcar derailments). Extreme water levels may also result in destruction of agricultural and industrial distribution facilities and float containers of biocides and toxic chemicals for significant distances.
2.8 Carrying capacity guidelines While the carrying capacity of flow through systems are dependent on species biology and specific conditions, there are some generally valid 'rules of thumb' that can be used for planning purposes, assuming good quality input water. The intensity or carrying capacity of an aquaculture system can be described by a number of parameters. The most common parameters are: Volumetric density (lb/ft 3) -
Areal density (lb/ft 2) = Loading (lb/gpm) =
mass of animals (lb) volume of rearing unit (ft 3)
mass of animals (lb) area of rearing unit (ft 2) mass of animals (lb)
flow to rearing unit (gpm)
(2.10)
(2.11)
(2.12)
(60) (flow to unit, gpm) (2.13) volume of unit (gal) Loading, exchange rate and volumetric density are related by: 8.02 • density Loading (lb/gpm) = (2.14) exchange rate Another important measure of rearing intensity is cumulative oxygen consumption (COC). For a single rearing unit, COC is equal to D O i n - DOout. For n rearing units in series, the COC is equal to: i=1 COC (mg/1) - ~ (DOin DOout) (2.15) Exchange rate (exchanges/h) =
-
-
The COC depends strongly on animal size and temperature and therefore integrates both animal size and metabolic activity. If loading rates are maintained at low values (high exchange rate), densities in small-scale experimental systems have been as high as 34 lb/ft 3 (545 kg/m3). These numbers are well above any practical values. The maximum practical density will depend on water quality considerations, management skills and the ability of the particular species to tolerate crowding. Maximum loading rates in production systems typically range from 4 to 10 lb/gpm (0.5-1.2 kg/lpm). For research purposes maximum loading rates typically range around 1 lb/gpm (0.125 kg/lpm) or less. Carrying capacity may not be limited by water flow but by volumetric or area density. Surface area limitations often apply for plants due to their need for sunlight and to organisms that require a substrate, such as some shellfish. A substrate requirement may also be combined
30 with quantifiable territorial needs of the organisms. As an example, juvenile or adult lobsters and some crabs are cannibalistic bottom dwellers and generally must be individually isolated to prevent unacceptable mortality. In surface-limited systems, the capacity can sometimes be increased by stacking substrate layers or clever packaging. For organisms that tolerate communal crowding, volumetric density is an important economic parameter, having a direct impact on the required rearing volume and a major impact on capital costs. The maximum density depends on both the loading and behavior characteristics of the animals. Much of the available volumetric data are of questionable use because of the interactions between biomass, density and loading. As an example, if 1000 lb of fish is held in 1000 ft 3 of rearing volume with 1000 gpm of flow, this results in a loading of 1 lb/gpm and a density of 1 lb/ft 3. If the biomass of fish is doubled both the loading and the density are also doubled. If the flow is cut by half, the loading doubles but the density remains unchanged. If the loading is kept low (high exchange rate), the maximum density is only limited by the ability of the organisms to tolerate crowding. As a general rule, assuming good water quality and amenability to crowding, the following are suggested as maximum densities for organisms that are spread throughout the water column, such as most fish: Research: 0.01-0.1 lb/ft3; Production: 1-2 lb/ft3; Holding: 2-5 lb/ft 3. The consumption of oxygen by aquatic animals has been studied extensively by physiologists because it can be used to estimate energy expenditure. The respiration or oxygen consumption of aquatic animals is composed of three components T = Tstandard --[- Tactivity -3I- Tsd a
(2.16)
where T is total respiration (mg/h per individual), Tstandard is oxygen consumption of an unfed and resting animal (mg/h per individual), Tactivity is additional oxygen consumption due to swimming or movement (mg/h per individual), Tsda is additional oxygen consumption required for digestion, assimilation, and storage of material (mg/h per individual). The standard metabolic rate can be determined by extrapolation to zero activity from determination of oxygen consumption at various levels of forced activity. The sum of Tstandard + Tactivity is the routine metabolic rate and is a measure of the random activity of the animal. The routine metabolism of an individual animal may vary more widely than its standard metabolic rate. The active metabolic rate is the maximum sustained metabolic rate of an animal swimming or moving steadily. Most oxygen consumption studies are conducted on unfed animals and measure either the standard or routine metabolic rate. The effect of weight on oxygen consumption of aquatic animals has been studied extensively. At a given temperature and feeding level (typically a zero feeding rate), the oxygen consumption of a single animal is equal to: T ' = a' W b'
(2.17)
where T' is oxygen consumption in mg/h per individual, a' and b' are constants, W is weight of animal in grams.
31 The oxygen consumption may also be expressed in mg/h per kg biomass basis. Letting a = 1000a' and b = b' - 1, Eq. 2.17 can be rewritten as (2.18)
T = aW b
where T is the oxygen consumption in mg/h per kg. Typical values of a and b are presented in Table 2.8 for aquatic species. The value of b ranges typically from -0.100 to -0.300. For many species, the value of b is independent of temperature and feeding level. The value of a depends primarily on temperature, but feeding levels and activity can also have significant effects. The impact of temperature on the a value can be modeled as an exponential: a = ott ~ or T = o t t ~ W b
(2.19)
where ot and/3 are constants for a specific species and activity level, T is temperature (~ When available, values of ot and/3 are presented in Table 2.8. When oxygen consumption data were collected at a single temperature, only the a value has been listed. The impact of activity level and feeding is much more difficult to estimate. Commonly, the maximum oxygen consumption rate of fed fish is twice the standard rate. The average oxygen consumption rate of fed fish is about 1.4 the unfed routine rate. The impact of activity depends very strongly on species and culture system. For very active fish such as tuna or salmon, the active rate can be as high as 10 times the standard rate. The metabolic activity of animals depends strongly on size, temperature, and activity level. For example, the oxygen consumption of the American lobster (McLeese, 1964) is equal to: Oxygen consumption (mg/h per kg)
-- 5.52T~
-0"120
where T is temperature (~ and W is wet weight (g). At 12~ kg of 1, 50, and 1000 g lobsters is equal to: Size (g)
Oxygen consumption (mg/h per kg)
(2.20) the oxygen consumption of 10
Oxygen consumption (mg/h)
1
66
661
50
41
413
1000
19
192
Therefore, a given flow of water that would support the oxygen requirements of 10 kg of 50 g lobsters would also support 22 kg of 1000 g lobsters. An alternative approach to the computation of oxygen demand is based on the ingested ration. For trout, the average daily oxygen demand (Haskell, 1955; Willoughby, 1968) is proportional to the total ration: Average daily oxygen demand (lb/d) - OFR • R
(2.21)
where OFR is oxygen/feed ratio (lb/lb), R is total ration (lb/d). The oxygen requirement to process a given mass of feed depends on animal size, feeding rate, composition of the ration, digestibility of the feed components, and moisture content and can be described by the oxygen/feed ratio (OFR).
TABLE 2.8 Constants for the computation of oxygen consumption rates of aquatic animals Species
Form a
temp. (~ Freshwater fish Carp (Cyprinus carpio) Channel catfish (Ictalurus punctatus)
Mozambique tilapia (Sarotherodon
S R F R
Reference
Variable range
a
wt. (g)
2.157 2.685 1.540 2.078
-0.106 -0.200 -0.200 -0.348
10-35 24-30 24-30 16-37
30-400 2-1000 2-1000 10-150
Beamish, 1964 Andrews and Matsuda, 1975
0.866 0.903 0.944 1.514
-0.196 -0.142 -0.118 -0.250
4-10 12-22 5-20 8-24
12-900 12-900 2-2000 0.3-40
Muller-Feuga et al., 1978
[ 140 mg/h per kg] [57.6 mg/h per kg] 85.8 0.372 87.5 0.665 39.1 0.908 [288 mg/h per kg] [ 118 mg/h per kg] 1.14 1.759 1.87 2.15
-0.213 -0.180 -0.159 -0.207 -0.374 -0.376 -0.190 -0.145 -0.252
23 15-19 3-15 3-15 10-20 10 23-25 13-33 7-16
10-80 6000-13,000 90-3200 90-3200 4-50 1-320 400-6000 3-90 4-1000
Muir and Niimi, 1972 Graham and Laurs, 1982 Saunders, 1963
[114.2 mg/h per kg] [210.7 mg/h per kg] 5.52 0.999 10.9 0.785 17.4 1.11 [52.9 mg/h perkg] [275 mg/h per kg] 2.23 1.213
-0.390 -0.350 -0.120 -0.289 -0.194 -0.139 -0.293 -0.163
22 22 12-25 10-25 5-35 10 22-23 17-26
0.123 0.051 3.06 0.629
Caulton, 1978
mossambicus) Rainbow trout (Oncorhynchus mykiss) Sockeye salmon (Oncorhynchus nerka) Striped bass (Morone saxatilis) Marine fish Aholehole (Kuhlia sandvicensis) Albacore tuna (Thunnus alalunga) Cod (Gadus morhua)
Plaice (Pleuronectes platessa) Skipjack tuna (Katsuwonus pelamis) Striped mullet (Mugil cephalus) Turbot (Scophthalmus maximus) Crustaceans American lobster (Homarus americanus)
Blue crab (Callinectes sapidus) Brine shrimp (Artemia salina) Norway lobster (Nephrops norvegicus) Shrimp (Penaeusjaponicus) Spiny lobster (Panulirusjaponicus)
F F S S
36.9 50.4 11.7 1.87
0.004-0.05 0.004-0.05 0.6-12,300 20-200 0.0077 40-210 3-18 26-350
Brett and Glass, 1973 Klyashtorin and Yarzhombek, 1975 Kruger and Brocksen, 1978
Jobling, 1982 Graham and Laurs, 1982 Marais, 1978 Brown et al., 1984 Logan and Epifanio, 1978 Logan and Epifanio, 1978 McLeese, 1964 Laird and Haefner, 1976 Decleir et al., 1980 Bridges and Brand, 1980 Egusa, 1961 Nimura and Inoue, 1969
TABLE 2.8 (continued) Species
Form a
Variable range temp. (~
Molluscs American oyster b (Crassostrea salinity -- 32 g/kg salinity -- 14 g/kg salinity = 7 g/kg Clam b (Arctica islandica)
Reference wt. (g)
virginica)
Cuttlefish (Sepia officinalis) Dogwhelk b (Thais lapillus) Mussel b (Mytilus californianus) Pacific oyster b (Crassostrea gigas) a R = routine; S = standard; F = fed. b Based on dry weight excluding shell.
Shumway and Koehn, 1982 15.3 2.77 11.9 [374 mg/h [317 mg/h [196 mg/h 19.6 69.1 [922 mg/h
0.908 1.781 1.291 per kg] per kg] per kg] 0.596 0.583 per kg]
-0.490 -0.553 -0.615 -0.399 -0.578 -0.090 -0.400 -0.352 -0.230
10-30 10-30 10-30 10 10 17 5-20 13-26 20
0.03-0.7 0.03-0.7 0.03-0.7 0.03-1.0 2.9-16 0.1-1500 0.5-5.0 0.0-1.7
Taylor and Brand, 1975 Johansen et al., 1982 Stickle and Bayne, 1982 Bayne et al., 1976 Gerdes, 1983
34 In salmon and trout production systems, OFRs ranging from 0.20 to 0.22 kg oxygen/kg wet feed have been reported (Willoughby, 1968; Westers, 1981). In commercial high density warm-water fish culture, a value of OFR = 1.00 lb oxygen/lb wet feed is commonly used. Limited data are available for OFRs in recycle systems. The oxygen demand from bacterial oxidation of organic compounds, ammonia, and solids strongly depends on the unit processes and their operation. The upper bound for OFR equals the ultimate biochemical oxygen demand (BOD) of the feed, which for channel catfish feed is equal to 1.1 lb O2/lb dry feed (Harris, 1971). Careful feeding and rapid removal of solids from the system can significantly reduce the OFR. The feeding rate is commonly reported in terms the amount of actual feed fed (wet feed or on a 'as fed' basis). The feeding rate can also be reported in terms of amount of dry feed. Many commercial dry diets contain only 5-8% moisture, so the difference between the wet and dry values are small. This is not the case for 'semi-moist' diets (i.e., Oregon moist pellets) or diets that are made from unprocessed fish products. In these cases, the moisture content can vary from 30 to 90%. It is likely that the feeding rate used in Eq. 2.21 should be based on a dry fed basis for semi-moist and moist diets, although specific data are lacking. On a daily basis, the maximum oxygen consumption occurs 4 to 6 h following feeding in a flow-through system. The peaking factor can be reduced by increasing the number of feedings per day. Westers (1981) suggested a peaking factor of 1.44 to account for the maximum daily oxygen consumption rate: Maximum daily oxygen demand (kg/day) = 1.44 x OFR x R
(2.22)
Working with freshwater fish, Piper et al. (1982) popularized an approach to estimating stocking density as a function of animal size. This approach is based on a density index (DI) which is equal to: DI --
Biomass (lb) Rearing volume (ft 3) • Total length (inch)
(2.23)
The units of the DI are lb/(ft 3 • inch). Eq. 2.23 can be rearranged to: DI =
Density (lb/ft 3) Total length (inch)
(2.24)
or
Density = DI • Total length
(2.25)
For domestic rainbow trout, a DI = 0.50 is commonly used; for anadromous salmon, DI values in the range of 0.08 to 0.15 are used. For a DI = 0.50, 2-inch fish could be held at 1 lb/cf while 8-inch fish could be held at 4 lb/cf. For many hatchery fish, the behavioral impacts of density are not a significant problem. The density computed from Eq. 2.25 accounts for the impact of size on metabolic activities that would occur when the water flow over the production cycle is relatively constant. The intrinsic impact of density is much more important for crustaceans and many marine fish, especially for small juveniles. Regardless, of these impacts, Eq. 2.25 offers a simple way to evaluate the impact of animal size on metabolic carrying capacity. Water reconditioning and reuse internal to a flow-through system will raise the carrying capacity. This assumes
35
Fig. 2.4. Mass balance relationship for flow-through systems.
that the water parameters are the limiting factor, which is often but not always the case. It is also critical to know the specific limiting water quality parameter, because improving a nonlimiting parameter will not have much effect. Predicting the carrying capacity of a system with considerable water reuse approaching a closed system is complex and beyond the scope of this book (see Appendix C). In a flow-through system, flow is needed to supply oxygen and remove ammonia, carbon dioxide, soluble organic compounds, uneaten feed, and fecal matter. Typically, the most limiting water quality parameters are dissolved oxygen, un-ionized ammonia, and carbon dioxide. The flow needed to maintain a given water quality criterion can be developed from mass-balance considerations. For a given control volume (Fig. 2.4), the mass-balance on a single parameter under steady-state conditions (concentration is not changing) is simply: in § generation - decay -- out
(2.26)
The mass of compound 'x' leaving the control volume is equal to the mass entering, plus any generation within the control volume, minus any decay within the control volume. The ability to estimate mass (or concentrations) using the mass balance approach depends strongly on the complexity of the system and how well the biological and chemical processes are understood. Fig. 2.4 has generation of ammonia within the control volume but no decay. This is appropriate for a flow-through system where detention times are in the range of 20 to 60 min, but would be totally invalid in pond systems. The following equations are based on typical flow-through systems where gas transfer across the air-water or water-bottom surfaces is commonly small and may be neglected and the only metabolic loads are from the culture animals. These equations are not valid for pond systems because a significant part of the pond's metabolic activity may be from algae or bacteria and the gas transfer across the air-water and water-soil interface can not be neglected. Modeling of these types of systems is much more complex.
36 Application of the mass-balance equation to the system presented in Fig. 2.4 and neglecting mass transfer across the air-water and water-substrate interfaces results in the following two equations: Koxygen • R Qoxygen - - DO(in) - DO(out)
Qammonia - -
- o t Kammoni a x R
NH3-N(in) - NH3-N(out)
(2.27)
(2.28)
where Q is flow required to maintain a given oxygen (Qoxygen) and un-ionized ammonia criterion (Qammonia), K is production rate per unit of feed for oxygen (Koxygen) and un-ionized ammonia (Kammonia), R is total ration, DO is influent (DO(in)) and effluent dissolved oxygen concentrations (DO(out)), NH3-N is influent (NH3-N(in)) and effluent un-ionized ammonia concentrations (NH3-N(out)), el is mole fraction of un-ionized ammonia. The values of DO(out) and NH3-N(out) are set to the water quality criteria for the specific species under consideration. Values of Koxygen and Kammoni a are typically in the range of 200 and 30 g/kg of feed, respectively. Typically, the influent concentrations of ammonia in nearshore waters are small and can be neglected. Based on the above assumptions and unit selections of lpm for Q, kg/day for R, and rag/1 for all concentrations, Eqs. 2.27 and 2.28 can be written as: Qoxyge. =
Qammonia =
0.694 x SFoxygen • Koxygen • R DO(in) - DO(out) 0.694 x SFammonia • o/K~mmo,i~ x R NH3-N(out)
(2.29)
(2.30)
A safety factor (SF) term has been added to each equation. The K values are based on daily averages. This safety factor is used to adjust the flow requirement for periods of higher than average metabolic activity. The instantaneous K values can range from 0.5 to 3.0 (or larger) depending on feeding or other activities. The maximum K values for active fish such as tuna or striped bass may range as high as 10 times the average value. For typical fish, a SF of 2 is probably adequate. For less active crustaceans or mollusks, a value of 1.25 is suggested. For large systems, this safety factor can represent a significant cost and pilot-scale determination may be prudent. A similar equation could be written for carbon dioxide. When oxygen is not limiting, the consumption of 1 mole of oxygen produces approximately 1 mole of carbon dioxide (1.375 mg carbon dioxide per mg oxygen). Under normal surface water carbon dioxide concentrations (< 1 mg/1) and common loadings, carbon dioxide is rarely limiting. This may not be true if deep ground waters and/or pure oxygen aeration are used. Carbon dioxide does have a significant impact on flow requirements due to its impact on pH and un-ionized ammonia concentrations. Eqs. 2.29 and 2.30 can be used to estimate water requirements to maintain oxygen and un-ionized ammonia concentrations for a specific species under conditions typical of common flow-through marine culture systems. The water flow estimates will depend strongly on the water criteria values selected. The actual design requirement will be the largest of the two flows.
37
O
pH
=
7.9
.llnl
I n I I
8.0
I | l I l
8.1
,
1I l |
8.2 RR=0 ~
[
I
I
I
I
I
I
!
0
5
10
15
20
25
30
Temperature
I I
35
(C)
Fig. 2.5. Reuse ratio (RRoxygen/ammonia) as function of pH and temperature. Based on Koxygen = 200 g/kg, Kammonia = 30 g/kg, NH3-Nout -- 10 Ixg/1, DOin -- saturation, DOout -- 6 mg/1 and salinity of 35 g/kg. Note that between 32 ~ and 33~ the reuse ratio is equal to zero because DOin < 6.00 mg/1.
For general design considerations, it is also useful to consider the reuse ratio: Qoxygen RRammonia/oxygen - - Oammonia
(2.31)
If the reuse ratio is below one (Eq. 2.31), the maximum allowable ammonia concentration has already been reached and aeration will not help. The reuse ratio for typically marine conditions (salinity of 35 g/kg) is presented in Fig. 2.5 as a function of pH and temperature. The reuse ratio decreases as the pH increases due to the increase in the mole fraction of un-ionized ammonia. At a given pH, the reuse ratio first decreases as temperature is increased, then increases as the temperature increases above 20~ Over typical pHs and temperatures, the reuse ratio varies from 2 to 3, so aeration can often increase the carrying capacity. Above 25~ the reuse ratio rapidly increases, but the actual carrying capacity is decreasing because the available DO is rapidly decreasing. Above 32~ the reuse ratio is zero because influent DO is less than the DO criteria. In general, Eq. 2.30 will over-estimate the flows needed to maintain the required un-ionized ammonia concentration. This is due to chemical reactions of metabolic carbon dioxide in
38 water and the impacts of metabolic carbon dioxide on pH and un-ionized ammonia. The mole fraction of ammonia (c~ in Eq. 2.30) depends strongly on pH. If the metabolic carbon dioxide excreted by the animal reduces the pH, Eq. 2.30 will significantly over-estimate the value of Qammonia.The impact of these two factors on the required flows depends strongly on the amount of carbon dioxide retained in the water (under normal pHs, negligible ammonia (NH3) is lost to the atmosphere). Compared to oxygen, carbon dioxide is a very soluble gas and is much more difficult to remove by aeration. To accurately predict the impact of metabolic carbon dioxide on water requirements, it is necessary to estimate carbon dioxide losses to the atmosphere across the water surface (due to aeration or other processes). Limited information is available on the transfer of carbon dioxide to the atmosphere under marine culturing conditions. As a result, this book will neglect all reactions of carbon dioxide in water. This is equivalent to assuming that pH is constant and carbon dioxide gas is an inert gas. For more information on the impact of metabolic carbon on water chemistry and water flow, see Colt and Orwicz (1991 a). While the reuse ratio increases at high temperatures, the actual carrying capacity decreases. This is better demonstrated by looking at the total amount of dissolved oxygen that can be used before the un-ionized ammonia criterion is exceeded. Assuming that the influent water is saturated and the effluent DO concentration is a minimum of 6.00 mg/1, the maximum available oxygen to the animals ranges from 4.107 mg//1 at 5~ to 0.236 mg/1 at 30~ (Fig. 2.6). Even though the reuse ratio is higher at 30~ than at 5~ the potential available dissolved oxygen is less. If the oxygen consumption rate of the culture animal is known, the loading rate can be computed. The loading rate will depend on dissolved oxygen and un-ionized ammonia criteria, temperature, and size of animals. Guidelines for maximum loadings are presented for holding (Fig. 2.7A), production (Fig. 2.7B), and research (Fig. 2.7C) conditions. For holding conditions, aeration can increase the loading rate. For production conditions, it has been assumed that aeration will be used. The maximum loading for unaerated production conditions is typically 50 to 60% of the aerated values but falls off significantly above about 25~ For research conditions, maximum loading is controlled by the ammonia criteria and aeration will have no effect on loading. Note that the recommended maximum loading is higher for large animals and at low temperature. In the absence of more specific loading criteria, this information can be used in system design. While these recommended loadings should, in most circumstances, be conservative, they should still be used with caution. The loading rates in Fig. 2.7 are significantly less than under freshwater conditions, primarily due to the high pH of seawater increasing the toxicity of un-ionized ammonia. Depending on the pH, temperature, and water quality criteria, un-ionized ammonia is often the most limiting parameter and when this limit is reached aeration cannot be used to increase carrying capacity. In fact, above 20~ only 1-2 mg/1 of dissolved oxygen can be used before the un-ionized ammonia criterion is exceeded (Fig. 2.6). Increasing the loading above these somewhat arbitrary numbers results in rapidly increasing risk. The given values assume good conditions but no internal water reconditioning and may represent the carrying capacity of even a reuse system, whose water reconditioning has either mechanically or biologically failed. Earlier life stages are usually much more demanding on water quality and quantity then juveniles and adults and this must be considered when using data such as Fig. 2.7 in hatchery applications (see Example 2.9 for production and Example 2.10 for holding). Except as an
39 Available DO = 0
l I I I I I l i i I l l l I I I I I i g | I I I
o~
Influent pH
<
m |
Maximum available D O / for single pass system
I
I
I
I
I
I
I
0
5
10
15
20
25
30
35
Temperature (C) Fig. 2.6. Potential available dissolved oxygen. Based on same conditions and assumptions as in Fig. 2.5.
emergency measure, it would also be unwise to initially plan to use a seawater system at its maximum capacity until experience is acquired with the system. A great deal remains to be learned about water quality and water reconditioning. Success with heavily loaded systems is in many ways an art. The best policy for high water reuse or recycling systems is not to exceed very conservative limits, unless one is very experienced, is researching such questions or enjoys high risk. In those cases where little is known about the effects of ammonia on growth or mortality, chronic bioassays may be needed to develop design loading information (Meade, 1988). These tests are expensive but will allow optimum design and should be cost effective in the long-run, especially for large commercially oriented culture systems.
2.9 Design requirements Design is based on the loading criteria, density criteria, and production objectives. The most important design parameters to be computed in the design phase are the water flow rate, rearing volume (or area) for each step, and the size and number of individual rearing units.
40
Temperature (F) 35
40
100
45 I
50
55
60
I
65
I
70
I
75
I
80
I
85
I
90
I
I
~5 :700
70
A) HoldingConditions
50
"500 300
30 "200 20 -100 10
"" ",,
70 "50
..... :, ...... : ~ ....... ! ' %
30
~
"20
E
,, ] -
,:,..
",~.
"',,, i "',... " ~
~
looog
10
E m~
7 =
0.7 ~ 9
0.5
5
%%%
"- 9
"',,
9 9
10g
o
O
0.3
%
0.2
9
%%
",
= or
9
9
9 1 4 9 1 4 ~9
0.1 g 1
0.1 "
0.1 g
"
9149g 9
0.07
td000 g
~~ 9
t
0.7 0.5
0.05
9
.......
~t 9
Unaerated
0.03
I| 1
99
I
0.3
|1 It !
0.2
| | It I
0.1
'
Aerated
0.02
t t
0.01
I
0
5
10
i
I
15
20
;,
3'0
35
Temperature (C) Fig. 2.7. Maximum loading rate guidelines for a pH of 8.2 and a salinity of 35 g/kg. The loading rates are significantly less than for freshwater due primarily to the high pH and toxicity of un-ionized ammonia. These loadings will be even more conservative at lower salinities except at high elevations. Guidelines for maximum loadings for holding (A), production (B) and research (C) conditions, as a function of temperature and animal size. Dissolved oxygen for inflow assumed at saturation and discharge at 6.0 mg/1. Oxygen consumption is assumed equal to that for a fed rainbow trout for production and research and an unfed trout for holding. Ammonia criterion for holding is 40 Ixg/1, for production 10 Ixg/1, and for research 2 Ixg/1. The dashed lines are used in Examples 2.9 and 2.10. These guidelines should be used with caution and only in the absence of data more relevant to the species or conditions.
41
Temperature (F) 35
40
45
50
55
60
65
70
75
80
85
90
95
100
700
70
500
B) Production Conditions
50
300 30 200 20 100 10
70
7
50
5 30 3 20 2
gl. 10
l'
7
0.7
,I~ ~0
5
oJ,~
3
,..]
0.5 0.3 1000 g
0.2
1
0.1
10g
0.7
0.07
0.5
0.05 0.1g
Aerated
0.03
0.3 0.2
0.02 0.1 0.01 0
5
10
1
Temperature
20
25
35
(C)
Fig. 7 (continued).
2.9.1 Water Flow Given the loading requirements and number of animals at the start of each culture step, the water flow rates for each culture step can be computed. If some of the tanks are to be filled, it is important to compute the maximum water requirement that may occur when everything is 'on' and cleaning and tank filling is also in progress.
42
Temperature 35
40
I
100
45
I
50
I
55
I
60
I
I
70
(F)
65
70
I
75
I
80
I
85
I
90
I
I
700 500
C) Research Conditions
50
300 30 200 20 100
10
I
70
7
50
5 I
I
I
~
30
3 20 gl,
2
%9
I I
]
% %9
9 9149
Q~
@
10 7
9
0.7 ~
0.5
9 99
%% % %%
9
0.3
,.~
%
I
9
%%
%% 9%
%%
%%
0.2 9% 9
%
0.1-
9
3
@
%
1 %%
9 9
0.07
oil
%% %%
%~%
5
%%
%
0.7
%%
%%
0.5
0.05
,, 9
9 9 9 % 9 % 9
0.03
% 9
0.3
9 9%
Unaerated
0.02
1000 g
9
" 9.
% 9
9" , 9 0.01
I
I
0.2
lO'g"
0.1
g
I"
35
0
Temperature
(C)
Fig. 7 ( c o n t i n u e d ) .
2.9.2 Rearing Volume/Area Based on the density criteria and the total number of animals at the start of each culture step, the total volume (or total area) is computed for that culture step. If the animals spawn only once a year or fry are available only during a limited period, it may be prudent to size equipment and capacity based on the needs of this surge period.
43
Example 2.9. Carrying capacity m production One thousand pounds of fish are kept in a flow-through system at 12~ pH of 8.2, salinity of 35 g/kg (ppt) and a maximum ammonia criterion of 10 Ixg/1NH3-N. Compute the required water flow needed for 10 and 1000 g animals. How much more water is needed if the temperature increases to 25~ (A) Compute the water flow requirement at 12~ From Fig. 2.7B, loading = 1.0 kg/lpm for 10 g fish and 2.7 kg/lpm for 1000 g fish. Q =
454 kg
= 454 lpm for 10 g fish
1.0 kg/lpm
454 kg Q = 2.7 kg/lpm = 168 lpm for 1000 g fish (B) Compute the water flow requirement at 25~ From Fig. 2.7B, loading = 0.20 kg/lpm for 10 g fish and 0.51 kg/lpm for 1000 g fish. Q = 2270 lpm for 10 g fish Q -- 890 lpm for 1000 g fish
10 g fish Increase in flow =
2270 lpm 454 lpm
= 5.0 times or 500%
1000 g fish Increase in flow --
890 lpm
168 lpm
= 5.3 times or 530%
2.9.3 Rearing Container Size and Number While the volume or area needed can be directly computed, the size of the individual rearing unit can vary widely. A small number of large units are often cheaper to purchase than a large number of small units of the same total capacity. On the other hand, smaller units are easier to monitor and manage. In many systems, the number of individual units will be determined by the intended use or application. Often individual unit size will be determined by the optimum batch size as determined by production objectives and timing. 2.10 Constraints
While the bioengineer's solution to providing a successful low risk system is excellent input water quality and quantity coupled with very conservative density and loading of the system, there are many realistic constraints to this approach. The influent water quality parameters may not always be within the desired limits and the water may have to be treated before use. This creates costs which are proportional to the flow rate, degree of treatment specified, and risk of equipment failures. The limiting environmental parameters that can be controlled to increase system performance or reduce risk may vary depending on season and culture conditions. The
44
Example 2.10. Minimum required flow m holding
It is desired to hold 2560 one-pound lobsters at 10~ without aeration for several weeks. What is the minimum required flow rate in gpm? This is a holding situation. Therefore, Fig. 2.7A applies. From the figure, one pound (454 g) animals held without aeration at the stated temperature have a maximum recommended loading of 3.0 kg/lpm. Biomass of animals = (2560 animals)(0.454 kg/lb) = 1162 kg Flow rate x Loading rate -- Biomass of animals -- 1162 kg Flow rate =
1162 = 387 lpm, 3.0
387 lpm = 102 gpm 3.78 1/gal
The conversion factor is from Appendix Table A-1. This is the minimum flow rate and should be used with caution as there are many inherent assumptions in Fig. 2.7 and in the problem statement. Using flow rates in excess of the minimum will often reduce risks.
problem is most acute where there are economic limits on initial cost or profitability. The problem then becomes a tradeoff between treatment level, with associated cost and equipment reliability, and reduced growth and increased stress (risk) to the culture organisms without treatment. While retaining conservative loading is rarely a problem in educational or research systems, loading is often a critical factor in commercial systems. Overly conservative values may make the system economically unattractive. There are strong economic incentives in commercial systems to minimizing the water treatment quantity and quality (front end capital) and maximizing the loading of the system. In the inevitable absence of sufficient directly relevant hard data, the resulting evaluation and tradeoff of anticipated system performance versus risks is difficult and usually highly subjective. What is often forgotten, or at least minimized, is that most system parameters are interrelated and that pushing the limits on more than one variable at a time generally produces unfavorable interactions resulting in multiple sources of increased stress on the organisms. Unfortunately, quantitative cost factors usually dominate over subjective consideration of risk. If the decisions reached are overly optimistic, the resulting high risk operations often exhibit reduced growth rate, susceptibility to disease, increased cannibalism and frequent mass mortalities. Under most situations, input water parameters are very unlikely to be at optimum values at all times. A major problem is in determining the costs versus benefits of regulating these parameters and compensating for these naturally occurring deficiencies. Seawater processing equipment can be expensive to buy and maintain and quantitative requirements in these areas need careful evaluation. While the same types of equipment might also be useful for internal water reconditioning, the two functions should, at least initially, be considered separately. Additional information, including considerations and more specific tradeoffs are presented later. Since seawater processing equipment is expensive, a c o m m o n approach is to initially install only the m i n i m u m necessary to meet specific short-term needs. However, the initial design can be made sufficiently flexible to enable the easy retrofit of new types, higher performance, or larger-scale equipment to meet future needs or changing priorities. Without this early foresight, later retrofit may be very expensive or even prohibitive. This added
45 flexibility is not necessarily very expensive and in most cases requires only the crudest idea of future requirements. However, providing flexibility and preserving future options does involve costs and can be over done. The major considerations are easy access to seawater lines in appropriate places, spare floor space, floor drains and access to power. Additional flexibility can be acquired by not burying pipes, and by using threaded or flanged connections in piping, facilitating future reconfiguration of the piping system. In summary, considerable care should be exercised in the quantitative statement of 'requirements' for seawater systems involving living organisms. In particular, careful evaluations are needed of cost/benefit/risk tradeoffs for each specific application. Special care should be taken in differentiating between short-term and long-term requirements. In many applications, short-term requirements are readily quantifiable but are usually subject to frequent change and are often of peripheral importance. Long-term requirements are often more difficult to define but are usually of a more fundamental nature.
This Page Intentionally Left Blank
47
Chapter 3
Site Considerations
3.1 Marine conditions Ideally, the site should be selected by means of a thorough site reconnaissance and selection process (Webber, 1971; New, 1975). Some of the important selection parameters are listed in Table 3.1. In many private and public projects the site selection process is very abbreviated because the site options are either few or the site is already determined at the start. In public sector projects, it may be necessary to complete a formal selection process to justify the site picked, but in reality, the site has already been selected. This site may already be owned by the project owners (or good old Uncle Fred), or may be dictated by legal, political or economic reasons. Trying to design a system for a site chosen for reasons independent of seawater system requirements may prove to be very expensive or even impossible. While there is never an ideal site, a bad site can easily doom a project. Prior to the start of the design phase, basic information is needed on the marine conditions at the site. Seawater systems design requires detailed information on the tidal variations, including both high and low tidal information. The astronomical tides are due to the rotation of the earth, moon, and sun. These tides can be accurately predicted and detailed tidal predictions are available for major ports. Tides for other sites close to the reference station can be estimated by published tidal differences in elevation and time. The tables are only good for the published times. Typically, there are two high tides and two low tides per day. The height of the two daily tides may be equal or unequal. Some areas only have a single tidal cycle per day (one high and one low tide per day). The average interval between two successive high tides or between two successive low tides is 12 h and 25 min. In working with tides, it is important to clearly define the datum with which all tidal elevations are referenced. At least three datums are commonly used in tidal information: mean sea level (MSL), National Geodetic Vertical Datum (NGVD) and the chart datum (see Fig. 3.1). In general, computation of mean sea level, chart datum, and other tidal parameters requires long-term tidal data, commonly 19 years. Some of the most important tidal datums and parameters are defined below.
Mean sea level (MSL). This is the average hourly tidal heights over a 19-year period. On a global basis, sea level is rising approximately 0.50 ft/century. National Geodetic Vertical Datum (NGVD). This is a fixed surface whose elevation does not vary with time. Due to elevation changes in sea level and land surface, differences between MSL and NGVD in the U.S. range from - 1 . 9 0 to +2.33 ft (Harris, 1981a). Elevations on land are usually based on NGVD. Chart datum. Predicted tidal heights and chart soundings are referred to the chart datum. The chart datum is selected so that most tidal elevations are positive. In the U.S., either MLW
48 TABLE 3.1 Important site factors
Meteorological factors Winds - - prevailing directions, velocities, seasonal variations, storm intensity and frequency. L i g h t - total annual solar energy impingement, intensity, quality, photoperiod, diurnal cycle. Air temperature and variations. Relative humidity or dew point and variations. Precipitation - - amount, annual distribution, storm maximums and frequency.
Locational factors Watershed characteristics - - area gradients (elevations and distances), ground cover, runoff, up-gradient activities. Ground water supply - - aquifers, water table depth, quality. Tides w ranges, rates, seasonal and storm variations, oscillations. Waves - - amplitude, wave length, direction, seasonal and storm variations, storm frequency. Coastal currents - - magnitude, direction and seasonal variations. Existing facilities and characteristics. Accessibility of site. History of site - - prior uses and experiences. Soil factors Soil type, profile, subsoil characteristics. Percolation rate m coefficient of hydraulic permeability. Topography and distribution of soil types. Particle size and shape. Angle of repose - - wet, dry. Fertility. Microbiological population. Leachable toxins - - pesticides, heavy metals, other chemicals.
Biological environment Primary productivity - - photosynthetic activity. Local ecology - - number of trophic levels, dominant species. Wild populations of desired species - - adults, sources of seed stocks. Presence and concentrations of predators - - land, water, airborne. Endemic diseases and parasites. This listing includes only those factors most important to the technical aspects of the system. It does not include the many social, political, legal, and economic aspects that can be equally important or even critical in the selection of a site. (Modified from Webber, 1971.)
or MLLW (see below) are commonly used as chart datum, although different datums may be used for the Gulf Coast and Great Lakes (Harris, 198 l a). The difference in elevation between the chart datum and mean sea level is usually given in the tide tables and charts. Mean low water (MLW). Average height of the tide at low water over a 19-year period. Mean lower low water (MLLW). Average height of the tide at the lowest tide of the day over a 19-year period. Extreme lowest water recorded. Compiled as the lowest low water for each month. Mean high water (MHW). Average height of the tide at high water over a 19-year period. Mean higher high water (MHHW). Average height of the tide at the highest high tide of the day over a 19-year period. Extreme highest water recorded. Compiled as the highest high water for each month.
49 I~~Ext
S
rem~-'e'Highest Water Recorded
I~'--'~M HHW / (MeanHigher High Water) ~/MHW (Mean High Water)
~
I~--~/~xtreme
~
/ I~/M
SL (Mean Sea Level) ( NGVD) National Geodetic Vertical Datum
, ~ d
'~ ,
eon.o. Wo,erl
.Wor
MLLW often used MLLW ( Mean Lower Low Water )__.,Jas Chart Data
LowestWater Recorded
Fig. 3.1. Diagram of tidal datums.
In the U.S., tidal data are collected and tabulated by the National Ocean Survey (NOS). This agency maintains a running summary of the monthly mean and extreme high and low water of the month, and many other tidal statistics for approximately 50 reference stations (Harris, 1981 a) (see Table 3.2). This information is available at a nominal charge. A wide variety of tidal information may be needed in the design process. Depending on the type of intake and pumping cycle, detailed information may be needed on both the high and low tides at the site. The design of the intake, pumping system, and vertical location of the pumps will be strongly influenced by the tidal conditions. Ideally, the detailed information on the distribution of the high and low tides should be used to define the tide in a probabilistic manner. Detailed probability density distribution tables have been developed for seven tidal parameters for 50 sites in the U.S. (Harris, 1981 a) and include the following parameters: (1) (2) (3) (4) (5) (6) (7)
extreme monthly high water; extreme monthly low water; highest high water; high water; hourly water levels; low water; lower low water.
The tidal height corresponding to a desired probability can be simply interpolated from the appropriate table. Once the design tidal height is determined at the reference station, the design tidal height at the closest secondary station (listed in the tide tables) can be adjusted by use of the published tidal height difference for the station. The accuracy of this adjusted value to the actual site under consideration may depend strongly on the water depth and configuration of the coastline. For design of the pumping and intake system, a 1% probability level might be used. If the system was designed to be operable down to the 1% low tide, in an area with two
50 TABLE 3.2
Tidal data for selected stations Station
Standard
MHHW
MHW
MLW
MLLW
deviation Eastport, ME Portland, ME Boston, MA Newport, RI New London, CT Sandy Hook, NJ Atlantic City, NJ Hampton Roads, VA Wilmington, NC Charleston, SC Savannah River Entr., GA Mayport, FL
Miami Harbor Entr., FL Key West, FL St. Petersburg, FL
Pensacola, FL Mobile, AL Galveston Ship Chan., TX San Juan, PR San Diego, CA Los Angles Outer Harb., CA San Francisco Gold.Gate, CA Humboldt, CA Astoria, OR Aberdeen, WA Seattle, WA Ketchikan, AK Juneau, AK
Anchorage, AK Dutch Harbor, AK Honolulu, HI
6.32 3.24 3.40 1.33 0.94 1.70 1.52 0.92 1.51 1.88 2.52 1.66 0.95 0.58 0.71 0.54 0.58 0.53 0.54 1.81 1.66 1.75 1.93 2.53 2.99 3.50 4.91 5.31 9.01 1.24 0.60
9.32 4.87 5.16 2.18 1.48 2.66 2.41 1.41 2.26 2.87 3.77 2.49 1.33 0.92 1.04 0.67 0.73 0.57 0.87 2.90 2.63 2.59 2.97 3.98 4.54 4.83 7.36 7.82 12.73 1.52 1.08
8.88 4.45 4.72 1.93 1.22 2.33 2.01 1.22 2.02 2.50 3.38 2.20 1.26 0.63 0.72 0.61 0.65 0.47 0.57 2.11 1.91 2.04 2.26 3.28 3.74 3.94 6.46 6.93 11.99 1.21 0.58
-9.01 -4.46 -4.86 -1.69 - 1.34 -2.34 -2.07 - 1.22 -2.24 -2.67 -3.56 -2.27 -1.26 -0.64 -0.70 -0.57 -0.62 -0.44 -0.58 -2.09 -1.87 -1.93 -2.24 -3.19 -4.03 -3.75 -6.47 -7.10 -13.90 -1.07 -0.65
-9.41 -4.80 -5.19 -1.75 - 1.45 -2.47 -2.18 - 1.26 -2.33 -2.81 -3.70 -2.38 -1.40 -0.88 -1.14 -0.63 -0.70 -0.85 -0.79 -3.06 -2.82 -3.14 -3.44 -4.38 -5.35 -6.48 -8.02 -8.72 -16.18 -2.17 -0.81
Extreme values high
low
13.8 9.4 9.0 11.9 9.3 8.0 7.4 7.2 6.3 8.0 7.5 5.1 5.1 3.2 4.1 8.3 8.2 10.6 1.8 5.3 5.0 5.6 6.1 7.8 9.4 8.2 13.0 14.6 18.7 4.4 2.7
-13.6 -8.2 -8.7 -4.5 -4.8 -6.7 -6.0 -4.4 -3.6 -6.0 -8.0 -5.5 -2.9 -2.2 -3.7 -2.8 -3.8 -6.1 -1.7 -5.8 -5.4 -5.5 -6.4 -7.1 -8.4 - 11.3 - 13.2 - 13.8 -23.3 -4.9 -2.5
Computed datums, extremes, and standard deviations referenced to mean sea level. Extreme values are highest and lowest ever recorded. U.S. data from Harris (1981 a). All values are in feet.
daily tides this would correspond to approximately 7 tidal cycles/year when the system would not be operable. In choosing the design probability level, decreasing these periods of inoperability may, depending on conditions, result in significantly increased construction costs. For example, costs of providing storage or curtailing operations for the 7 tides/year when the intake system will not operate may be cheaper than designing the system to operate for the extra 7 tidal cycles/year. Under other conditions, it may be just as easy to design the pump station to withstand the 0.01% tidal level (one down time every 27 years). These considerations will tend to be more critical for areas with high tidal ranges. In most locations, detailed probability information on tides will not be available. Tidal data do not form a normal distribution and interpolations of data can be difficult and misleading.
51 It is still n e c e s s a r y for design and operations to develop m a x i m u m and m i n i m u m tidal elevations. In the absence of g o o d tidal data, the following p r o c e d u r e is r e c o m m e n d e d : D e s i g n low tide = M L L W -
( m e a n tidal r a n g e ) / C
D e s i g n high tide = M H H W + ( m e a n tidal r a n g e ) / C
(3.1) (3.2)
A value of C = 4 is r e c o m m e n d e d for intakes and a C = 2 for m o r e critical elevations such as for p u m p stations, electrical c o m p o n e n t s and rearing units. For m o s t conditions, this procedure will yield conservative results. However, it does not a c c o u n t for rare e x t r e m e events such as typhoons, hurricanes, and t s u n a m i s (see E x a m p l e 3.1 for a n u m e r i c a l example). W h e r e very expensive or critical facilities are involved, m o r e detailed site specific analysis m a y be prudent. T h e effects of b a r o m e t r i c pressure and w i n d are m u c h m o r e difficult to precisely predict. T h e s e two c o m p o n e n t s m u s t be added to the a s t r o n o m i c a l p r o d u c e d tides. T h e b a r o m e t r i c c o m p o n e n t m a y exhibit a seasonal pattern w h i c h is i n c l u d e d in tidal data, but these two factors are m u c h m o r e significant in relationship to m a j o r storms. Tides c a u s e d by m a j o r infrequent storms can be critical. E x t r e m e high water levels c o m m o n l y result w h e n (1) high a s t r o n o m i c a l tides and strong inshore winds occur simultaneously, or (2) m a j o r tropical w e a t h e r events occur. T h e s e events occur r a n d o m l y and the fact that a severe tidal event has not o c c u r r e d in the last 20, 30, or 40 years does not p r e c l u d e two serious floods occurring in the next year.
Example 3.1. Determination of design tide It is desired to build a culturing facility on the seashore near Atlantic City, NJ. What are the design tide elevations for normal operations for the intakes and facility components nearest to the water edge? Atlantic City tidal data can be acquired from Table 3.2 and design tide values calculated from Eqs. 3.1 and 3.2. MHHW = +2.41 ft (from Table 3.2) MLLW = -2.18 ft (from Table 3.2) Mean tidal range -- 2.41 + 2.18 = 4.59 ft (A) Using Eqs. 3.1 and 3.2 for the intakes: Design low tide = -2.18 - 4.59/4 -- -3.33 ft Design high tide = +2.41 + 4.59/4 = +3.56 ft (B) Using Eqs. 3.1 and 3.2 for the facility: Design low tide = -2.18 - 4.59/2 = -4.48 ft Design high tide -- +2.41 + 4.59/2 = +4.71 ft These values are all relative to mean sea level and tend to be conservative. A more detailed analysis using the probability functions of 1% and 99% yields -3.25 and +3.31 ft for the intakes and -4.12 ft and +3.45 ft for the facility. Note that the extremes of record at the site are -6.0 ft and 7.4 ft. This analysis accounts for seasonal weather factors but n o t rare extreme events, such as hurricanes, which must also be considered in placing components.
52
.;-.:9 ::.: ..-:-: ...i.:..! :::.:.:::...:....
...:!. _ .. :,.,, ...... !:. 'i:iii-
WinterFetch N W-'I'-- E S
~176 i.~
Fig. 3.2. Ocean exposure example. This example is of a relatively well sheltered site. Waves generated by prevailing winds in summer and winter will be relatively modest in size due to the short distances (fetch) the winds have available for generating waves. However, major storms coming up from the south may generate impressive waves coming in from the exposed south and southeast. These waves and their effects will be maximized if the site is actually hit by the northeast (for example on the east coast of the U.S.) quadrant of the storm due to its forward wind speed combined with the storm speed and general counter-clockwise rotation.
For extreme storm events, it is necessary to be able to predict both the peak surges and the wave run-up (how far up the beach the waves will climb). Wave run-up can result in physical damage to buildings or more commonly erosion of the foundation and total building collapse. The surge and run-up can be computed from the storm track, intensity, size, and forward speed (U.S. Army Corps of Engineers, 1975; Taylor, 1980). In many coastal areas, 100-year flood maps have been prepared by the National Flood Insurance Program (Fry and Rhodes, 1985). The prevailing seasonal wind directions and speeds should be obtained from local weather stations or published data and plotted on a hydrographic chart of the area. The greatest length of unobstructed length of sea over which the wind can blow is called the fetch (Fig. 3.2). The hydrological and meteorological conditions will determine the height and frequency of normal seasonal wind generated waves. Storm directions and associated wind velocities can be very different from prevailing seasonal wind directions and velocities. Since wave forces and wave effects associated with rare storms are usually the biggest threat to intakes, pump stations and other shore-side facilities, it is important to quantify these waves and their effects (see Section 5.3). Information on the beach profile is needed for specifying the burial depths for piping and locating the intakes (see Section 5.3). Beach profiles should be collected at least four times
53 Berm
~fCrest of Berm
~" ~' ~ ' - ~ -,, '--'~ \ ~ "--..~. "Winter" Profile-~ ~ ~
" Summer" Profile ~
~,,fPlunge Point ~,.~-Low Tide Terrace
0
I
0
High Tide
Low Tide
50m I
lOOft
lOOm I
20Oft
I
I
:50Oft
Fig. 3.3. Typical beach profile characteristics. Beach profiles can vary considerably. This figure shows some of the common features that may exist and possible seasonal changes for a typical 6 ft (2 m) tide. Additional features might include a scarp (sharp drop) in the beach above the normal high tide, an alongshore trough below low tide or an alongshore bar further out. Single events, such as major storms, can substantially alter beach profiles.
over a year, to get seasonal variations caused by changes in weather patterns and seasonal storms (Fig. 3.3). A longer period of observation would be even better. Beach profiles can be variable and depend on soil characteristics and oceanographic conditions and are dynamic in nature (Shepard, 1963). The profile should be extended to at least 10 ft or 3 m below the extreme low tide elevation, preferably deeper. The average slope of the off-shore bottom should be estimated from published charts. The salinity and temperature of the ocean water should be determined at least four times over the year. Other parameters that may also be required are presented in Chapter 2. For sites on coastal rivers or estuaries, it may be necessary to sample over the full tidal cycle as both temperature and salinity may vary widely. If the facility is near any rivers, special care must be directed towards determination of the salinity during the rainy season or during periods of maximum run-off. River effects may vary considerably from year to year, so long-term data are very desirable. Rainy season salinities may be so low or uncertain as to make the site unacceptable. If the site is located close to present or prior industrial and agricultural activities, detailed chemical analysis of soil and groundwater may be required. If a site has previously been used in agriculture, possible residues from past use of herbicides, insecticides and other chemicals could be important, especially if there are to be earthen ponds. In cases of questionable water quality, it may be necessary to test the water by bioassaying with target species or determine residues in native animals or plants. During site survey, information on quality and quantities of freshwater available near the site must also be collected. This can become critical if freshwater is required to control salinity. Evaporation during dry seasons or larval culture needs may require continual freshwater input to reduce salinity to acceptable levels. Some freshwater will also be needed for washing, laboratory use, or drinking. Hauling of freshwater or production by reverse osmosis is both expensive and troublesome. Freshwater requirements of 'marine' systems have often resulted in the elimination of otherwise attractive sites.
54
3.2 Terrestrial conditions Prior to the start of any serious design work, the property should be surveyed and all corners and sidelines clearly marked. It may also be prudent to establish permanent comer markers with concrete and steel. Unless the site is clearly within the property boundaries, it may be necessary to use registered surveyors so that there is a legal basis for any property disputes. It is also desirable to bring a vertical datum from the nearest benchmark. In sites where it is prohibitively expensive to survey in a vertical datum, comparison of observed and predicted tides may allow a rough estimate of mean sea level. A permanent vertical benchmark should be established nearby. A topographic survey of the potential site must also be completed as part of the property survey. In areas with low bearing strength soils, detailed soil testing may be required. Having to provide extensive filling and compaction can significantly increase the cost of site development. Soil permeabilities can be important factors for seawater or freshwater wells and if natural soils are to be used to seal ponds or raceways.
3.3 Permitting Major commitment of time and money may be required to obtain all the necessary permits for a marine or estuarine project. Permitting problems have increased substantially in the past decade. The actual cost of the permits themselves is typically low. The major costs are associated with the man hours that must be directed towards obtaining the permits, and possible delays to the project as a result of permitting complications. Permitting can easily be a long lead time item, requiting submissions very early in the design process. It is possible to spend years and thousand of dollars on permits, only to have the last agency refuse to grant approval. The number of permits required will depend on (1) the country, state, and county where the project is located, (2) the type of agency proposing the project (government, company, private individual), (3) the year the process was started, (4) the ownership of the site, (5) the organism to be maintained or cultured, and (6) the project characteristics. The construction and operation of a seawater system must be consistent with local county or city zoning. A specific seawater system may be classed as agriculture, fisheries, education, or some other industrial operation. An unfavorable ruling on zoning can eliminate many potential sites. Very often, the acquisition and use of land for a seawater facility is a new use not contemplated by zoning authorities and not designated under the guidelines of a local master plan (Wypyszinski, 1984). Therefore, it may be necessary to obtain a variance or an amendment to the zoning code, which can be difficult and time consuming. In many coastal areas of the U.S., Flood Insurance Rate Maps (FIRMs) have been developed by the National Flood Insurance Program (Fry and Rhodes, 1985). Areas covered by FIRMs are classified from high to minimal flood hazard. Construction in high hazard areas will be restricted or limited to structures built above the flood line of the 100-year storm. In the United States, the Federal Government passed the Coastal Zone Management Act (CZMA) in 1972 and established a system of federal grants as incentives for individual states to develop enforceable programs for land and water use planning in the coastal zone. The coastal zone includes just about all possible sites that may need a seawater system. Installation
55 of new facilities or construction in the coastal zone will require a water development permit and require detailed engineering drawings. Permit applications may require a formal environmental impact statement. An archeological survey may also be required. Evidence of old buildings or native American activities may seriously constrain facility layout on a site. In developed countries, other than the U.S., the details will vary but the nature of the problems is very similar. Even in third world countries, considerable attention will be focused on possible environmental impacts. The days when large coastal areas could be bulldozed into ponds and mangrove swamps destroyed without any questions are over. Generally, anyone seeking to raise or hold freshwater, marine, or anadromous animals must apply for an aquaculture permit from a state fish and game agency for a nominal fee. The species to be cultured must be listed on the permit. As long as commonly reared indigenous species are cultured, this type of permit is sometimes simple and straightforward to obtain. Exceptions can exist when the culture species is a 'game' animal and possession of under-sized specimens or holding 'out of season' is illegal. If game and conservation laws are interpreted to apply to culturists, this can doom projects. Problems are also aggravated when dealing with exotic species, which have to be brought in from somewhere else. Acquiring permits to import, even between adjacent counties and states, can be difficult. Possible ecological impacts, escapes, and disease and parasite transmission to indigenous species may become significant issues. The discharge of waters from aquaculture projects are regulated by the Environmental Protection Agency through the National Pollutant Discharge Elimination System (NPDES) and generally administrated by the states. An application for a discharge permit must be filed before the pollutants are discharged. Certain types of aquaculture facilities may be exempted, but most agencies will make a case-by-case ruling. Exemptions are much less likely today than they were in the past. The following factors may be considered in the designation of an exempted facility. (!) (2) (3) (4)
The location and quality of the receiving waters. The holding, feeding, and production capacities of the facility. The quantity and nature of the pollutants from the facility. Other factors relating to the significance of the pollution problems in the area.
NPDES permit applications may require a definition of a proposed facilities effluent waste stream. Common parameters that may need to be specified include BOD, solids (settleable and suspended), nitrogen and phosphorus loading, and residual chlorine (if applicable). Necessary input data include design biomass, anticipated feed type and feeding schedule (% body weight per day) and species-specific waste generation numbers. Unfortunately, waste generation data on many aquatic species are not presently available. Numbers can be extrapolated from trout/salmon (Liao, 1970; Clark et al., 1985; Seymour and Bergheim, 1991) or catfish data (Chen, 1998). Trout and salmon could be considered representative of high animal protein users, while catfish would be more typical of low protein users. Additional data exist for seed clams (Pfeiffer et al., 1999) and adult clams (Zhu et al., 1999). Another possibility is the use of 'rules of thumb', such as one pound of feed generates 0.03 pounds of ammonia, 0.5 pounds of fecal matter, and 0.4 pounds of BOD. For some applications waste generation data from terrestrial animals may be useable. There are a lot of data on farm animals. However, it
56 may be surprising that there is information on the waste generation of Bengal tigers but none currently available for seals. In aquaculture facilities, simple removal of settleable solids may be the only type of treatment required to achieve discharge standards (Federal Register, 1978; Harris, 1981b). This is equivalent to the 'primary treatment' process in municipal wastewater treatment. Information on the types and quantities of drugs and chemicals to be used in the facility may also be requested. The U.S. Environmental Protection Agency is currently reviewing NPDES regulations for aquaculture facilities. While the final regulations have not been drafted, possible changes to the regulations may include use of best available technology for treatment of discharges and regulation of pathogens in discharges. Construction in navigable water requires a permit from the U.S. Corps of Engineers. The definition of 'navigable waters' includes the ocean, tidal rivers, and just about any water connected to or within 20 miles of the ocean. Regulated activities include construction of intake and discharge lines, pilings, piers or dikes. A permit submitted to the Corps of Engineers may be reviewed by the U.S. Fish and Wildlife Service, state fish and game agency, National Park Service, National Marine Fisheries Service, Coast Guard, coastal zone management agency, and the EPA. If one of these agencies objects, the Corps will seek project modification from the applicant. The Corps requires that all other permits must be obtained before the Corps will process an application (Bowden, 1981). This makes the Corps of Engineers the last step in the permitting process in marine or estuarine areas. When permits are finally issued, they may contain specific restrictions that may have major impacts on design, construction, and/or operation of aquaculture facilities. These restrictions could be on effluent parameters, pipe intake/discharge placement or the timing of activities. In some areas, in-water construction is only allowed when it is difficult to impossible to carry out such work, such as during the winter. This restriction may be due to a possible negative impact on migration or spawning of aquatic or terrestrial species that occur during specific time periods. Many of the permit fees and monitoring requirements are based at least in part on effluent flow. A relatively small laboratory or commercial operation can have a flow similar to a small town. An effluent flow of 500 gpm (1900 lpm) corresponds to the wastewater from a town of about 7000 people. Municipalities, however, have a considerably greater ability to pay for permits, monitoring, and reporting activities than aquaculture and research projects. The costs of water quality monitoring can be very significant, especially if nutrient analysis is required. The mandated administrative aspects of keeping record and reporting can also become burdensome. These problems are increasing with time. 3.4 Site selection
Many considerations have been mentioned as being important in evaluating sites. However, all factors are not of the same relative importance. No site is ever perfect in all regards. So how does one select one site among a selection of useable sites. It has to be assumed that all the choices are 'possible' and without any major 'red flags' (problems of sufficient severity that, if not resolved, can doom a project). Picking a site with 'red flag' items is a very fast, and unfortunately not uncommon, fatal mistake. Schedule or funding considerations or wild optimism can sometimes force such a serious premature decision. A common variation on
57 this problem is that there is only one site being considered and it has serious 'red flag' items. Going ahead, while assuming that these problems will be resolved in time or go away, is often fatal to the project. Site selection is a critical decision and, unfortunately, often has a high subjective content. One approach that can be useful in clarifying choices and in decision making is shown in E x a m p l e 3.2. In this example, important factors are listed. S o m e are positive factors (i.e., good water quality) and some are good in the negative (i.e., lack of archaeological sites). Relative subjective weighing factors can be assumed based on the project's objectives, proposed scale of application and technical approach. This evaluation method, and a n u m b e r of similar variations, is helpful in eliminating obviously less desirable sites but should be used with considerable caution if the numbers are close. As in this example, water quality and quantity tend to be the key considerations. This is not u n c o m m o n , especially in predominately flow-through systems. If, as sometimes happens, there are no suitable sites, this requires a basic rethinking about project objectives, assumptions and approaches. With basic changes, there may be a suitable site. Site problems involving suitable water quantity and quality and sometimes coupled with area limitations, have been a big factor in the increasing interest in reuse systems.
Example 3.2. Site evaluation and selection Four sites (numbered 1 to 4) are to be evaluated for shrimp culturing using pond grow-out. Each site is graded on a 1-5 scale (5 is best) for 13 considerations. The importance of each consideration is adjusted by the use of a weighing factor (1-10). The overall score for each factor is equal to the weighing factor times the 1-5 grade. The total score is equal to the sum of the overall scores of the 13 factors for each site. The site with the highest total score is the most desirable and the relative values an indication of site differences. (A) Determine the relative importance of the 13 considerations by choosing weighing factors (1 to 10) for each of the factors in column 2 of the table below. On-site evaluation of each of the sites has resulted in the given 1-5 grades indicated in the table. Considerations
Water supply Water quality Terrain/topography/soils Physical access Purchase availability Proximity to seed stocks Future land use/expansion Human comfort/amenities Past agric, spray/chem. Flooding and storm potential Archaeological sites Availability of utilities Permitting Total
Weighting factor
Sites
1
2
3
4
4 2 3 4 5 4 3 3 4 3 4 4 4
3 3 4 5 4 4 4 4 2 3 5 5 4
3 3 4 5 5 5 4 4 3 2 5 4 3
5 5 5 5 3 2 3 2 5 5 2 4 3
47
50
50
49
58
E x a m p l e 3.2. (continued) (B) With the data above and the assumed weighing factors given below, complete the numerical evaluation and determine the 'best' site. The presented weighing factors are subjective and are presented as only one possible set of values. Values in columns 4 through 7 below are intermediate 'solutions' to be calculated by the reader. Considerations
Water supply Water quality Terrain/topography/soils Physical access Purchase availability Proximity to seed stocks Future land use/expansion Human comfort/amenities Past agric, spray/chem. Flooding and storm potential Archaeological sites Availability of utilities Permitting Total
Weighting factor 10 10 9 5 6 4 6 4 9 9 5 7 7
Maximum score
Sites 2
1
3
4
50 50 45 25 30 20 30 20 45 45 25 35 35
40 20 27 20 30 16 18 12 36 27 20 28 28
30 30 36 25 24 16 24 16 18 27 25 35 28
30 30 36 25 30 20 24 16 27 18 25 28 21
50 50 45 25 18 8 18 8 45 45 10 28 21
455
322
334
330
371
Using this methodology, site 4 is the superior site. By changing the weighting factors, it is generally possible to 'select' a given site.
59
Chapter 4
Seawater Sources
4.1 Options and considerations If a seawater supply is needed for the system, there are only three possible sources. The three sources are artificial seawater, a seawater well, and an ocean or estuarine intake. This supply may be needed continuously, for just a part of each day, only during certain seasons, or in batches at intervals. Artificial seawater is used mostly for small aquariums, research projects that need a highly repeatable and predictable seawater source, or inland systems where there is little choice. If large quantities of seawater are required at an inland site, a closed system will be needed. The advantages of artificial seawater are a defined composition with a reduced risk of chemical and biological contamination, but this risk is not zero. Artificial seawater systems often work quite well, especially if operated very conservatively. However, for some specialized applications, such as the hatchery phases of delicate organisms, there may be some problems due to the complex interactions of seawater and marine organisms which are not presently completely understood. Seawater wells are another option (Clark and Eisler, 1964; Cransdale, 1981). Their advantage is that the water is already filtered, reducing or eliminating the introduction of disease microorganisms, parasites and predators. In addition, diurnal and seasonal water temperature variations are damped out resulting in much greater temperature stability and predictability (Cransdale, 1981). In-ground temperatures down to 50 ft below the surface are usually fairly constant and very close to the yearly mean average air temperature for the site. If seawater is withdrawn from this zone, it will be at ground temperature. Depending on the biological requirements, this may greatly reduce system complexity and cost by reducing needed water processing equipment, such as filters, disinfection and heating equipment. The big problem with seawater wells is that the site conditions and geology are usually unfavorable. In addition, high flow requirements can prove difficult and expensive, even where the geology is favorable. By far the most common source of seawater is from shore side or offshore intakes. The water may be drawn from a sump constructed on a very protected shore or canal, or from behind a dike or berm with a large-diameter pipe connecting it to the sea. Intakes can be suspended from a dock or pier with the pumps immediately above on the pier. Where there is a suitable dock and conditions permit, this is a very desirable approach. The seawater lines can be run to shore along the side or even under the dock. The seaward section of the seawater system tends to be relatively inexpensive and everything including the intakes are easily accessible for maintenance. However, the intake pipes hanging down from the pier may be subject to ice and wave damage and the presence of treated wooden pilings and boats may create potential water quality problems. A variation is intakes suspended from a floating
60 platform which also holds the pumps. The platform is often moored to a pier providing both access and power. This approach may be particularly attractive for seasonal systems or if there is a large tidal range, which otherwise might seriously complicate pump placement, selection and operations due to excessive suction lift. Like the pumps on the pier, this approach tends to have easy access for maintenance and to be relatively inexpensive. However, such floating platforms can be very susceptible to ice damage, boat collisions, and waves and currents from major storms. Alternatively the water may be drawn from a pipe leading to an offshore submerged intake. Submerged intakes, while the most common type, are often very expensive to install and maintain, and are still somewhat vulnerable to damage by major storms, boat traffic and fishing gear. While there are many complex considerations (see Section 4.4), there is also considerable prior experience with such intakes in culturing systems. In all cases, the input water quality will be subject to all the diurnal and seasonal variations of the natural environment. Drawing seawater in batches and trucking it to a distant seawater system is sometimes used as a cheaper substitute for artificial seawater. The intake, in this case, may be simply dropping an intake hose from a tank truck over the side of a dock. This approach can work but if, as commonly occurs, the water quantity requirements prove greater than originally planned, it can be expensive, annoying and time consuming. Some variation of this approach is often used for systems that bioassay industrial waste effluents, drugs or chemicals on indicator marine organisms. Due to potential and often unknown toxicity, these systems are required to be completely disconnected from any seawater system. Post-use seawater processing, handling and disposal can get complicated. 4.2 Artificial seawater
There are a large number of published recipes for the preparation of artificial seawater (Bidwell and Spotte, 1985). This comprehensive citation lists 169 seawater and enrichment formulations for culturing everything from marine yeasts, fungus, and up to vertebrates. Enrichment formulations contain trace elements and compounds that may not be present in artificial seawater formulations or may be depleted in culture systems, but are incapable of supporting marine organisms by themselves. Many artificial seawater formulations have been developed and used in specialized applications involving single species and for only parts of the life cycle. In addition, there exist commercial mixtures that have broader uses. An artificial seawater should have some specific characteristics (see Table 4.1). Many of the published mixtures do not meet these requirements. Some have compositions far removed
TABLE 4.1 Characteristics of good artificial seawater mixtures (derived from Spotte, 1979) (A) (B) (C) (D)
It is simple but contains in reasonable concentrations elements known to be essential to animals and plants. It is relatively easy to measure and mix. Major ions are present in concentrations and ratios approximating natural seawater. Components consist of salts that do not easily precipitate out of solution.
61 TABLE 4.2 Some applications of different synthetic seawater formulations in the holding or cultivation of marine animals Name of mixture
Purpose
Reference
Many different species and culture purposes
Bidwell and Spotte, 1985
Culture of oyster larvae, Ostrea edulis Bioassays with mussel embryos, Mytilus edulis Culture of Pacific oyster larvae Culture of colonial hydroid, Bouganvillia sp.
Helm et al., 1973 Courtright et al., 1971 Zaroogian et al., 1969 Tusov and Davis in Kinne, 1976
Instant Ocean Instant Ocean Instant Ocean
Nurse sharks, Ginglymostoma cirratum Culture of lobster juveniles Culture of prawn larvae, Macrobrachium
Honn and Chavin, 1976 Gallagher and Brown, 1976 Maddox and Manzi, 1976
Instant Ocean and Utility Seven Seas Marine Mix
Culture of crab larvae, Rhithropanopeus harrisii
Sulkin and Minasian, 1973
Holding lobsters and depuration of oysters/clams
Wood and Ayers, 1977
Review articles
Summary of 169 mixes Custom formulations
Summary of 169 mixes Summary of 169 mixes Summary of 169 mixes Tusov and Davis Commercial formulations
rosenbergii
Simplified recipes
Instant Ocean and Utility Seven Seas Marine Mix
Modified from Wickins and Helm (1981). Complete citations in Reference Chapter.
in content and concentrations from natural seawater. Others have very elaborate preparation processes involving up to four steps. Very few can simply be dumped into the right amount of freshwater and used soon thereafter, except in small quantities. Preparation of large quantities of artificial seawater requires use of specialized dissolving equipment (see Spotte, 1979). Some formulations require considerable time for components to dissolve and reach chemical equilibrium. Artificial seawater mixtures that are useable with animals (see summary Table 4.2) may not be suitable for plants. Even for only marine animals, a given mixture may not be suitable for a particular species or life stage. Using a mixture for a new application will involve some risk. Unless there is specific information that a mixture is suitable for a given application, the risk can be minimized by using a commercial preparation that has been demonstrated to have broad applications. One such commercial mixture, trade-marked 'Instant Ocean', was developed based on earlier research (Segedi and Kelly, 1964) and is listed in Table 4.2. For routine use, commercial mixtures may be a better choice than custom mixing of components because of better quality control of individual components and the mixing process. Trace contamination of specific components can be a serious problem in critical applications. For critical applications, enough chemicals (or commercial mixture) should be purchased for the entire experiment and preliminary bioassay should be conducted to ensure that the resulting seawater is acceptable. Commercial seawater mixtures, however, neglect the needs of marine plants (Spotte, 1979). Mixtures suitable for marine plants have been reviewed by Droop (1969), McLachlan (1973) and Kinne (1976).
62 One of the major problems with artificial seawater in closed systems is that if something goes wrong, it may be impossible to determine the precise cause. It could be the original mixture or a whole host of other problems involved with closed systems, such as build-up or depletion of critical substances. The precise requirements of many species are not well documented, especially in the area of trace components. Since all mixtures are a simplification of natural seawater, the small missing components may prove critical in a given situation. 4.3 Seawater wells The relationships between seawater and freshwater ground waters near the shoreline can be quite complex and variable depending on specific site conditions. Fig. 4.1 shows two simple possibilities. Even in the case of a narrow sand spit surrounded by seawater, there can be significant freshwater present. The higher elevation of the freshwater is due to the lower density of freshwater and static equilibrium conditions. The second case is also typical, with alternating permeable and impermeable layers. It demonstrates how it is possible to get freshwater offshore and just below the bottom. Since the layering can be complex, discontinuous, folded and spotty in distribution, the number of variations is immense. Therefore, it is very important to have a clear understanding of the local geology of the site before one can seriously discuss the possibility of developing seawater wells. For any type of seawater well the soil permeability will be critical. Permeability is measured by hydraulic conductivity, in older texts also called the coefficient of permeability, which may have a number of units (ft/day, cm/s). Gravel and clean sand, preferable coarse and large grained, might be suitable for a seawater well. Clays and soils with high organic
~
/1 Mean
~a itwaii~\ \ Freshwate~~ ~'~S~'\~iw~ el
B --- FreshwaterMReUan noff Freshwater_i.~---..."c~... SeaLevel Freshwater rnn..... . .... FOlW __~T~.__~b~ . Freshwaatslta,wPari2g
Fig. 4.1. Simplifiedexamples of near-shore geology.(A) Sand spit or peninsula. (B) More commoncoastal geology with alternating permeable and impermeable layers.
63
Example 4.1. Determination of hydraulic conductivity A l0 cm diameter cylinder of undisturbed soil (as close to in situ condition as possible) is tested for hydraulic conductivity with a constant head permeameter. The difference in the water elevations in the two standpipes connected to the soil sample at a vertical separation of 20 cm is 127 cm. The flow rate through the column is found, with a graduate tube and stop watch at the bottom, to correspond to 1 1 in 2.88 m. What is the value of the hydraulic conductivity for this sample and is there any possibility of developing seawater wells in this soil material? Cross-sectional area of cylinder -- 0.00785 m 2
Overflow
Area (A)
Soil Column
Q = 1/2.88 = 0.347 1/min = 500 1/day = 0.5 m 3/day L =0.2m h = 1.27 m (0.5)(0.2) 0 = 10.0 m / d a y (1.27)(0.00785) This is an attractive value characteristic of coarse sand, and seawater well possibilities should be further examined. K = QL/hA
--
content, unfortunately very common in estuarine and sheltered waters, are clearly unsuitable. While soils vary widely and generalities without knowing the specific requirements of a given situation are hazardous, some 'rules of thumb' can be presented. Soils with hydraulic conductivities less than about 10 ft/day or 3.0 m/day are poor prospects. The higher the value the better. Hydraulic conductivity of coarse-grained soils is usually determined by a constant head permeability test (Lowe, 1969). In this test, water is supplied from an elevated constant head tank (see Section 9.2) to an undisturbed vertical column of soil. There are two standpipes connected to the column with a fixed difference in elevation on the column, one near the top of the sample and one near the bottom. The differences in elevation of the tops of the two static water columns in the two standpipes is measured as is the flow rate through the column. The hydraulic conductivity is then calculated from the equation below, while being careful with dimensions (see Example 4.1). K --
QL hA
(4.1)
where K is hydraulic conductivity, Q is flow rate through sample, L is sample length in flow direction (vertical separation between standpipe taps), h is difference in head (elevation) across sample as measured by water levels in standpipes (hydraulic gradient), A is cross-sectional area perpendicular to flow. Many times it is impossible to obtain a truly representative and undisturbed soil sample and it may be necessary to drill a test well to determine hydraulic conductivity and well yield. This approach has the additional advantage that the water quality can be tested. There are several approaches to seawater wells. One is to lay a gravel-packed crib just below the bottom (see Fig. 4.2A). This in effect uses the overlying coarse sand as a sand filter (see Section 10.6). The cap is needed to prevent short-circuiting directly above the crib
64 Seawater
Cove.-u nClean ~ d ba or~Gravei Bottom , ~
. . . . . . . . . . . . . . . . . .
SolidCap
"~
,/
~ ['I'~'s r,~_-I FilteredSeawater__~
Highly Perforated Box or Cylinder
Gravel Pack
Seawater
. . . . . Side
B
View Top View
\ () / I~ I I~
Clean Sand
or~f~,-~
\()/ \ Q) / Filtered Seawater---~ ~ 12x4./Perforated I~t l j~ ~--~176 'Laterals{ [=~ / l Filtered Seawater ---I~
Seawater
~
Clean Sand or Gravel Bottom
c
/
~ I "~--_~
~
Packing Well
Pain! . . . . .
Slots Typically 1.5-2.5mm
Fig. 4.2. Basic approaches to seawater wells. (A) Offshore gravel-filled crib with internal header pipe. (B) Offshore header system, side and top views, length and diameter of laterals to suit. (C) Conventional well point, penetration may be shallow or deep, for shallow penetration may be packed with gravel or coarse sand, system may have more than one such well point.
and in the event of backflushing. There are a number of variations of this approach and in a variety of sizes. Placement can be intertidal, which lowers the pumping opportunities but makes installation easier, or preferably for operational flexibility, sub-tidally. Large flows are produced by thin layers of highly permeable sands. Even in geographic areas composed primarily of coarse sand, the bottom's surface layers just offshore are likely to be more impermeable and to have quantities of organic and inorganic fines to clog the system. In addition, too thin a cover could be removed by currents, wave action or backflushing of the filter. If there is little likelihood of strong currents or waves even during storms, the cover could be as small as about a half foot (15 cm). Since breaking waves, even small ones, can cut terraces in near-shore bottoms, a much safer value for most sheltered sites would be about 1.5 ft (0.5 m). If large ocean waves can be encountered during major storms, considerably more may be needed. The flow possible from such a crib will be highly variable but a 'rule of thumb', assuming favorable conditions, is 1 m 3/h per 3 m 2 of perforated crib surface area (0.14 gpm/ft 2) (Cransdale, 1981). Generally, several smaller cribs can produce more water
65
than a large one. If more than one is to be used, they should be separated by at least 20 (6 m) and preferably about 30 ft (9 m). Another way is to lay an offshore leaching field of perforated piping a few feet below the bottom and just below or above the low tide line (see Fig. 4.2B). One can specify the size of the trench, the quantity of coarse material packing around the well and the depth of uniform cover based on the same considerations as for a crib or sand filter (see Example 4.2). However, properly installing such a system sub-tidally, in an area with any currents or wave action, range from difficult to impossible. Intertidal placement reduces pumping opportunities and the
Example 4.2. In situ sand filter A 1-ft-diameter slotted or screened pipe (or a smaller pipe with a packing) is buried with its center-line 2 ft below the surface of a submerged sand bottom. The sand is the same as in Example 4.1 (K = 10 m/day) and the sand is barely covered by seawater at low tide. (A) If the maximum acceptable head loss across the sand filter is 3 ft of water, roughly estimate the seawater flow rate in gpm per linear foot of filter pipe. Using Eq. 4.1 with K = 10 m / d a y = 32.8 ft/day, L = 2 ft (average), h = 3 ft Pipe surface area/unit length = red = 3.1 = 3.14 ft2/ft K -
Q• h x A
Qx2
-
= 32.8
3 x 3.14
Q = 155 ft3/day per ft of pipe = 0.81 gpm/ft of pipe (B) What is the minimum length of sand filter pipe to be buried underwater to provide a 100 gpm system? Qtotal --- QL or 100 = 0.81L L -- 123 ft, to allow some safety margin specify minimum of 150 ft (C) At 100 gpm, what is the equivalent loss coefficient for this sand filter? Eq. 6.6 h -- KvZ/2g, h -- 3 ft Q = 100 gpm = 0.222 ft 3/s
V = Q/A = 0.222/(3.14 x 150) = 0.000471 ft/s (water moves very slowly through soils) 3=
K x 0.0004712 2 • 32.2
K = 8.7 x 108 (a huge number compared to loss coefficients for pipe fittings given in Table 6.4) (D) If the pump (just before it fails due to NPSH limitations, see Section 7.3) can create a maximum partial vacuum in the well equivalent to an extra 10 ft of head (which is a lot), what is the maximum possible flow rate Q'? You can assume that the K in part C is constant (see Section 6.5). 8.7 x 108 x V '2 13=
V' = 0.00098 fl/s
2 x 32.2
Q,
Q
!
0.00098 ft/s = - - = A 471
Q ' = 0.45 ft3/s (208 gpm)
66 hydrostatic head available for filtering. Even under the best of conditions and using the same 'rule of thumb' provided for the crib, the size of the required leaching field may be impressive. The laterals must be sufficiently separated, at least 10 ft (3 m), preferably more. There is always the possibility of storm waves carving a terrace fight through the system, burying it much deeper than intended or exposing parts, thereby short-circuiting the filtering action of the bottom. If the design is overly optimistic or the flow requirements increase, the pumps will pull an increased partial vacuum in the well system. There is a high probability that this deterioration in pump suction side conditions will lead to major pump problems (see Chapter 7). The crib system also shares some of these problems. The leaching field approach will often prove to be both expensive and risky. The crib system is usually easier and cheaper to install and is somewhat less vulnerable to storm damage. If working properly and conditions are good, neither should have any fouling problems nor loss in performance with time. If shortcircuiting and resulting biofouling occur, or fines clog the intake, backflushing may be helpful. The third approach uses more conventional well technologies (Driscoll, 1986) with the hope of finding seawater which has percolated in from the nearby ocean (see Fig. 4.2C). These well points may be shallow, in the order of 15 ft (5 m) or much deeper. If shallow, they can be 'jetted' in and the oversized hole packed with gravel or very course sand. What one may find instead of seawater is freshwater, even at the shoreline, or fossilized seawater. Coastal areas, even sand barrier beaches, often have sub-layers of impermeable clay or organic materials, such as peat or old mangrove swamps. Even if seawater is found, it may be of poor quality. It may be low in dissolved oxygen, even anaerobic, and may contain dissolved hydrogen sulfide. With the exception of iron and manganese, the concentrations of heavy metals from seawater wells is generally lower than that in the open ocean (Scholes, 1980; Chen et al., 1985). In addition, the salinity and pH of well water also are usually lower than the sea. On aeration of anaerobic waters, iron and manganese may precipitate out. These solids can clog the gills of larval forms resulting in high mortalities. A quick test is to place a few young specimens of the culture organisms in the well water. If they quickly die, the water quality is clearly inadequate; on the other hand, their survival for more than a few hours would mean that the water should be thoroughly analyzed for more subtle factors. When the seawater quality is marginal, treatment may increase water quality. However, this negates most of the advantage of such systems relative to intakes and increases complexity, cost and risk. Even though the quality is good, it may be difficult to get the needed quantity, requiting a number of separated wells, increasing costs. If the conditions are favorable and the system is designed and constructed properly, a well point system will have the highest reliability and the most consistent water quality (see Example 4.3). 4.4 Marine intakes
Submerged marine intakes are the most common type of intake. There are a number of important interactions between the location of the intakes and the rest of the system. These are discussed in Section 5.3. This section will concentrate on the engineering considerations dealing with the intakes themselves. Marine intakes by necessity must protrude above the bottom. They are, therefore, subject to currents and wave forces. Wave effects associated with rare storms are usually the biggest threat to intakes, pump stations and other shore-side facilities. It is important to quantify
67
Example 4.3. Seawater well A four inch seawater well is to be placed on a sand spit. The static level of the seawater in the ground is at about mean sea level (MSL) and there is no freshwater present. The sand layer is believed to extend at least 50 m below M S L . A m a x i m u m draw down of 5 m, a radius of influence of 25 m and a tested soil hydraulic conductivity of 10 m / d a y (see Example 4.1) are believed to be reasonable for this site. Based on the equation given below for an unconfined aquifer, what is the m a x i m u m sustainable flow rate from this seawater well? Q = l ' 3 6 6 K ( H 2 - h2) (flow in m3/day)
K R r H h
= hydraulic conductivity (m 3 / m 2 per day) = 10 m / d a y -- radius of cone of depression = 25 m - radius of well - 2 inches - 0.0508 m --- static head from base of aquifer to static water level -- 50 m = static head from base of aquifer to depth of water in well = H - draw down = 50 - 5 = 45 m
Q =
1.366K(10)(502 - 452) log {
= 2410 m 3 / d a y = 0.279 m 3 / s
25 0.0508 }
Q = 0.0279 m 3/s = 0.985 ft 3/s = 443 gpm
these waves. Wave characteristics can be predicted from meteorological conditions such as wind speed, wind duration, direction, distance over which the wind blows, and depth of water relative to the waves (Pierson et al., 1955; U.S. Army Corps of Engineers, 1975). These methods are based on empirical data. Since our interests are centered on rare extreme storms, the accuracy of these methods is low. This is due to the rarity of data-taking opportunities and problems of taking accurate data under extreme conditions. Based on a cost-risk evaluation, a 'design' storm is chosen. For large permanent systems, this may be the 25, 50 or 100 year storm (the worst storm that on the average occurs with this frequency). For short-term systems it could be a lot lower, say the 5 to 20 year storm depending on the desired system lifetime and season of use. Since the winds create a whole series of different waves, the predictions are for the 'significant wave height'. The significant wave height is the average of the highest one-third of the waves present. Although it is not a normal distribution, the wave height is inversely proportional to the probability of occurrence. At very low probabilities, a very impressive wave might be seen during a not very rare seasonal storm. For design purposes a maximum wave height of twice the significant wave height of the design storm is conservative. There are no unique values for wave length or period for a given wave height. However, most probable values can be used. The characterization of the worst or 'design' wave includes the wave height and the most probable associated wave length and period. Wave forces at any depth can now be calculated on different shapes (U.S. Army Corps of Engineers, 1975). Wave forces decay hyperbolically with depth, at a depth of one-half wave length wave forces can be neglected. As waves approach shore, their heights will increase and their wave lengths decrease. Given the near-shore bottom topography, wave characteristics and possible changes
68
4
Potential Surf Zone
~f'Seaward Extremity of Potential [ Surf Zone under Design Low Tide ..[ and Storm Conditions Design Wave
/
[ / ~ e a .c h
Slope
"X~. ,%,.
"~~1~
" ~
~-2-~----..-.. Low Tide Wave Allowance 4 ~ v~
All~
,__.J L._, Ingestion Allowance I Intake I / , / /IStucJ u/re,,/ / / //~ ~, , / / / / , , , / / , / / ,-
Fig. 4.3. Intake elevations and placement. Near-shore topography, wave characteristics and required vertical
dimensions will dictate intake placement and lengths of intake lines. Efforts to reduce required intake water depths and resulting intake pipe lengths with their high associated construction costs may introduce substantial risks and losses in operational flexibility.
in direction due to refraction can be calculated as a function of position. At some point, the wave will break. Using the maximum and minimum tidal elevations that could be associated with the selected design storm and the offshore beach slope, it is important to determine the maximum and minimum distance from the shore that the storm waves will break (U.S. Army Corps of Engineers, 1975). The reason is that wave forces due to breaking waves can have peak values as much as 100 times higher than the already impressive numbers from a non-breaking wave with the same parameters. Intakes or other structures caught in the surf zone of a major storm have a high probability of being destroyed. Waves can be destructive even above the highest water elevation due to wave runup (U.S. Army Corps of Engineers, 1975). Storm waves and storm flooding are a serious threat to many coastal facilities. The intakes should be sufficiently seaward and deep enough to be outside of the area of breaking storm waves at an extreme low tide (see Fig. 4.3). There is also a minimum water depth which is required above vertically oriented open pipe intakes to prevent them from drawing air. At high levels of air ingestion the pumps may cavitate and self destruct. At lower levels of air entrainment, high levels of gas supersaturation may be produced (see Section 12.4), with possible resulting mass mortalities. The minimum water cover is a function of the average velocity in the intake pipe (see Fig. 4.4). This submergence is also helpful in avoiding collisions with small craft, which can be a serious hazard to intakes too close to the surface at low tide. The intake lines should be sufficiently buried to avoid exposure by storm induced beach profile changes (see Section 5.3). The intakes may be screened or unscreened. In areas with floating and drifting debris of natural or man-made origin, or ample marine life, there is no choice. In the vast majority of cases, the intakes have to be screened to prevent the possible ingestion and resulting damage from these causes. If there is little or no seaweed, debris or fish, even associated with storms, then the risk of not using a screen may be acceptable. The advantages of unscreened intakes are greater simplicity, reduced cost and lower suction-side frictional losses (see Chapter 6). Intake screens can be a complex subject whose basic characteristics and tradeoffs are often not understood even by longtime users (Huguenin and Huguenin, 1984).
69 (m/s) |( ~ r
I i
10
2 i
3 I
,3
i,.
E =~E E ._c .
5-
E
_
0
0 5 t0 Average Fluid Velocity in Pipe
(ft/s)
Fig. 4.4. Minimum intake submergence to preclude air ingestion. Vortexing of a submerged intake is a very complicated subject without any easy answers. It can sometimes occur even with considerable submergence, especially at high pipe flow velocities. The presented guidelines are believed to be conservative under most conditions and assume a vertically oriented straight pipe intake (the worst case situation). A velocity cap or horizontal plate above the intake may dramatically reduce the minimum required submergence.
There are a number of important points with screens. The mesh openings should be as large as possible and still protect the pumps. The pump manufacturer will usually state the size of the largest solid object that a given pump can accommodate without damage. Some pumps, such as 'trash' pumps, allow ready access to the pump impeller without disconnecting the piping, resulting in easy removal of any pump-clogging debris. Small screen holes foul much faster than big ones. The usual range would be with hole dimensions of about 0.5 to 1.5 in. (13-38 cm), preferably on the large side. Fish with lengths as much as five times the hole size can get through, sometimes unhurt although most will get hashed by the pumps. The screen area should be as large as possible so that the through screen velocity (flow rate/screen open area) is very low, in the order of 0.1 ft/s (3 cm/s) (see Example 4.4). A low velocity reduces both the capture effect of the screen on nearby drifting marine life and debris and the frictional head loss across the screen. A properly designed screen in clean condition will have a negligible head loss. However, blockage from drifting objects and biofouling can dramatically increase the head loss, if the screens are not periodically cleaned and maintained. A vacuum gage on the suction side of the pump should be used to monitor the fouling of the screens and intake line. Intake screens have to be regularly inspected and kept clean of any significant biofouling. Rapid biofouling of screens can be a serious problem (Huguenin and Ansuini, 1981) and a maintenance nightmare. With proper care, biofouling-resistant copper-nickel metal screens have been successfully used for marine laboratory seawater intakes. The screens, if made from thin mesh, should be internally reinforced to structurally withstand the pressure differential caused by even modest fouling. At high fouling levels, the pressure differential could approach one atmosphere, at which point pump system problems are certain. Most screens will collapse under these conditions, sometimes restoring flow but without providing any protection for the pumps. Another consideration is that the screen should be shaped to best shed drifting debris. A spherical shape is best but impractical. An uptight cylinder or cone is the next best. The intakes should not be placed where debris is likely to accumulate due to local flow patterns.
70
Example 4.4. Intake screen You have to design an intake screen to flow a maximum of 100 gpm. (A) You wish to keep the average through screen velocity to under 0.1 ft/s, what is the minimum open area on the screen? 100 gpm = 0.222 ft3/s Flow = area x velocity = 0.222 = area x 0.1 Area -- 2.22
ft 2
(this is the minimum required open area of the screen)
(B) You are considering an intake made of large-diameter plastic or fiberglass pipe drilled with 1-inch holes. What is the minimum required number of 1-inch holes? Area of 1 inch in diameter hole = 0.00545
ft 2
Number of holes = required area/area per hole = 2.22/0.00545 = 408 holes (C) 1-inch holes on 2-inch centers with staggered rows gives an effective open area of only 20% of the screen area (prove this to be true). If you use only the sides of the cylinder and a 1-ft-diameter pipe, what is the minimum height of the intake screen? Screen face area = 2.22/0.2 = 11.1 ft 2
=
7r(d)(height) = (3.14)(L)(height)
Minimum screen height = 3.5 ft (D) If you use strong expanded metal formed into a 1-ft-diameter cylinder with an effective open area of 60% instead of the pipe above, what is the minimum height of the screen? Screen face area = 2.22/0.6 = 3.7 ft 2 = 7r(d)(height) = (3.14)(L)(height) Minimum screen height -- 1.2 ft
A v e l o c i t y cap is a h o r i z o n t a l plate a b o v e an intake pipe w h i c h c h a n g e s the intake flow f r o m the vertical d i r e c t i o n in the pipe to h o r i z o n t a l l y at the point of intake. T h e cap s h o u l d be p o s i t i o n e d a b o u t a h a l f d i a m e t e r or m o r e a b o v e the intake pipe and should have a s o m e w h a t larger d i a m e t e r than the pipe, in the order of one and a h a l f diameters. Studies have s h o w n that s m a l l s w i m m i n g m a r i n e o r g a n i s m s are m o r e resistant to capture by the intake if flow is h o r i z o n t a l rather than vertical. A cap can also greatly r e d u c e the r e q u i r e d intake s u b m e r g e n c e d e p t h s h o w n in Fig. 4.4, e s p e c i a l l y at the h i g h e r fluid velocities, but adds surface area for b i o f o u l i n g and for s t o r m w a v e s to act upon. A v e l o c i t y cap can be used alone or built into a screen structure as a solid h o r i z o n t a l top surface (see Fig. 4.5). T h e screen top m a y be h i n g e d to allow access to the interior w i t h o u t h a v i n g to r e m o v e the entire screen. This can be helpful in r e c o v e r i n g pipe c l e a n i n g 'pigs' f r o m inside the intake. M a n y different types of intake structures have b e e n u s e d but m o s t have b e e n s o m e variation of the t w o a p p r o a c h e s s h o w n in Fig. 4.5. B o t h have flanges, a l l o w i n g t h e m to be d i s c o n n e c t e d f r o m the intake piping, facilitating initial a s s e m b l y and s u b s e q u e n t r e p l a c e m e n t in the e v e n t of d a m a g e by storms or fishing gear. A p p r o a c h 'A' uses a s m a l l light block, w h i c h is buried, and it can be u s e d w i t h or w i t h o u t a screen. A p p r o a c h ' B ' uses a m o r e m a s s i v e block, w h i c h is o n l y partially buried. It is u s u a l l y u s e d with a screen w h i c h is attached directly to the
71 Approach A Small Light Block
Approach B Large Heavy Block Upward Extension of Pilings Can Protect Intake from Fishing char r
Fig. 4.5. Two conceptual approaches to intake design. Both approaches should use as dense a concrete as possible. Approach 'A' can be used with or without a screen. If the block in approach 'B' is heavy and dense enough and the area is not subject to strong currents or major storm effects, it may not need further anchoring. block. A variation of Type B is to have a truncated pyramid with a solid top and mesh on its four sides. The advantage is that the shape more readily sheds fishing gear and boat anchors. The disadvantage is that the base is larger and heavier, increasing handling and placement problems. All types are often secured to the bottom with pilings, screw augers or other means, especially if placed on the surface. The pilings can be steel pipes or concrete-filled plastic pipes with or without steel reinforcement bars. Any appreciable penetration of the intake structure into the bottom will substantially reduce the need for piling to resist lateral forces. In benign areas with no appreciable currents or waves, even during storms, mass of concrete alone may suffice for anchorage. On a flat surface, a general guide for clump mass anchors is that they can withstand a horizontal force of about one-half their in-water weight (Myers et al., 1968). There is an advantage in using denser concrete. Obviously the dimensions and specifications of these systems will depend on individual conditions and site characteristics. Another variation is building the intakes on a sled (Bouck, 1981), which can be towed into position and secured. Storm forces being what they are, even a good intake design may not compensate for a poor intake location. Another type of submerged intake sometimes encountered in sheltered areas involves an above-bottom variation of the crib shown as A in Fig. 4.2. In this case, no fine filtering with its attendant advantages occurs. However, the gravel can provide coarse filtering, acting in the manner of a screen. However, with this type it is harder to remove biofouling than from a screen, since much of it will be on the gravel internally. Frictional head losses through the gravel are likely to be much higher, especially once biofouled. It is usually much bigger and heavier, but possibly cheaper if made of available materials, than comparable screen intakes of the types shown in Fig. 4.5. Since larger, it will also experience greater current and wave forces and will have to be better secured to prevent movement. Due to its mass, it may provide considerably greater protection to the intake from boat and fishing gear collisions.
This Page Intentionally Left Blank
73
Chapter 5
System Planviews and Elevations
5.1 Generic system Assuming that the general site and desired system flow rate are known, it is necessary to consider piping layout options and considerations. The physical dimensions, soil types, elevations, and orientations of the site should be precisely determined. It is particularly important that the elevations of the seawater source be precisely known under all possible conditions relative to the site. This includes normal as well as unusually high and low tides associated with extremely rare storms (see Section 3.1). Errors of only a few feet in elevation could have serious consequences to the operation of the seawater system. From a strictly seawater system perspective, the best location is to have all the components close together and as close to the seawater source as topographical constraints and storm-tide elevations and wave run-up will allow. Unfortunately, the specific locations are often fixed by previous facilities, practical considerations not directly related to the seawater system and site-specific factors. In short, economic, political and regulatory factors, rather than technical considerations, often dominate. A simplified diagram of a generic seawater system is given in Fig. 5.1. It does not show any redundancy, parallel operations, or cross-connections that may be required. The water processing equipment may be at positions noted as #1, #2, both, or neither locations. If all the water to be used in the system is to receive the same level of treatment, the water processing equipment will usually be at location #1. The advantage is that the pumping equipment can then be selected to compensate for whatever frictional head losses are created by the equipment. If only part of the water needs treatment or some part of it needs more extensive treatment than the rest, treatment equipment is likely to be located at position #2 Short Circuit to Drain
Intake(s)
Pump(s)
Pro_ cessmg 1
Tank(s)
g2
Unit A Culture Unit B
Water Culture Pro- .. F - - ~
cessing~'l [-~ NaterUni Ct :~econ:litioning
Fig. 5.1. Generic seawater system.
74
.,__Two Screened 8" Intake Pipes
I Pumps J
[~-----8" Pipe
[Sand Filterl i -,----8" Pipe I Head Box] Seawater in ~ ~ PipeTransition 8"~6"
Max Flow Rate 872~pm (23tgpm) ~
4" Pipe Maturation 198,000~pd Max 1384~pm
~-.--6"Pipe
1.5" Pipe Spawning 6,020 J~pd Max 50.2~pm
Hatching 2,400 ~pd Max 20~pm
Artemia 6,0 O0 ,Ppd 1 l ,, Max 502pm 1.5"Pipe ~ 2 Pipe
Larval 240,0002pd Max 480J)pm
Intensive Mass Algal Algal 3,0002pd tO,O00Ppd Max 50 ~pm Max8:3.3 2 pm
Fig. 5.2. Crustacean hatchery seawater distribution example (Colt and Huguenin, 1992).
and only on those parallel lines where specifically required. For multiple small-scale culture units with diverse requirements, such as is typical in a marine laboratory context, location #2 is often at the point of use immediately adjacent to the culture unit. The nature of the processing equipment at any position #2 will vary according to the requirements of that culture unit. While location at position #2 allows use of smaller-sized equipment, it can also have undesirable effects on flow stability and regulation downstream. This problem is most serious if any of the treatment units has significant head losses (see Sections 5.3 and 9.1). To correctly place, size, and specify the processing equipment, it is very important to know the specific seawater quality and quantity requirements for the different parts of the system. All the uses may have the same requirements or they may be quite different. Furthermore, experience has shown that off-line operational needs, such as tank filling, rinsing and cleaning, can increase the maximum flow requirement by as much as 20%. It is necessary to determine both the total daily water requirement as well as the maximum flow rate. Fig. 5.2, as an example, shows the internal water distribution in a crustacean hatchery and placement of processing equipment (Colt and Huguenin, 1992). In this case, algal culture needed finer filtration than the other functions. A diatomaceous earth filter with an integral booster pump was used. Determining the scale for each activity is not as straightforward as it may appear, if the activities are interrelated. There are inherent assumptions both present and future as
75 to loading, growth, survival ratios, and efficiency in each activity and these are linked to the activity-specific water treatment specifications. Under-capacity in one part of the system can limit the entire system, while over-capacity is irrelevant and expensive (unless it can be translated into extra production at some intermediate stage, such as post-larvae, that can be sold to other culturists). 5.2 Elevations and head tanks
Head tanks, head boxes, or head ponds are needed to minimize the pumping steps in the system by providing the elevation required for gravity flow. The importance of water elevations in head tanks has already been stated. Even so, it can get complicated. Fig. 5.3 shows the elevations and relationships of components in one marine research facility. In this case, elevations were very precisely determined because there are many steps in the gravity flow sequence for different process waters. A head tank is a common component of most seawater systems and can serve a number of other functions (Table 5.1). It provides a buffer to smooth-out transients between supply and demand caused by irregularities in demand and variations in supply. Irregular demand can be created by batch processes and the cleaning or refilling of tanks. Variations in supply can be caused by tidal effects, switching of pumps or changes in water processing. By necessity the average supply must be greater than the demand. If the supply is adequate to maintain the head box elevation at overflow and the piping between the head box to points of usage are large enough to have negligible frictional losses, the head box can be used to provide a constant flow rate at any desired point. This control through the use of fixed orifices (see Section 9.1) or valves can be quite accurate and stable, sometimes eliminating the need for expensive flow control devices. A major function of head boxes is to provide water for a period of time after a seawater supply failure. This provides time to troubleshoot the failure
NUTRIENT _.~OOVERFLOW RETURN HEAD BOX
! SEAWATER .
. P MP
.
-- v ; ~9. ~ _ . ~ , z ~
.
r STANDI
~TOeAG~
/
~JP,PE I' t
~
;~;E ~
~No
I..~ ~,-,~,.,~
~
IND
R
STAND | PUMPS"'" ,~.M - - , , . P - , . ~ v , , , . ~ v n l PIPES t ~
i
.
.....
9
I
S E . w A , ER SuPPL,r
HEADCHANNEL
INTAKES
Fig. 5.3. Woods Hole Oceanographic Institution's Environmental Systems Laboratory seawater system elevations. From the head boxes the fluids flow by gravity from one level to another. The nutrient distribution system shown is actually a double system, since two different fluids can be fed simultaneously to the ponds and raceways from the three large storage tanks. The seawater inflow is about 600 gpm with one pump on (Huguenin, 1974).
76 TABLE 5.1 Headtank functions 9Buffer transients between supply and demand 9Storage for aging, treatment or part time pumping 9Provide time after supply failure 9Flow control (constant head) 9Sedimentation tank 9Distribution system (large header)
and/or make repairs without loss of seawater supply to the culture units. The time available is a function of system design and can vary from minutes to days. The time period available for critical uses can usually be increased by stopping or cutting back the flow to lower priority uses. The size of the head box is usually determined by the time estimated to be needed after failures under the range of likely present and future operating conditions. Cost is also a factor, but in the range of flows being considered the head boxes are still usually rather modest in dimensions, and the costs are a small part of the total system cost and can be further reduced by clever design. Another service performed by head boxes is to act as sedimentation chambers (see Section 10.8). This may be especially valuable during storms, due to the large increases in suspended materials often encountered in shallow coastal areas. Performance in this capacity is dependent on several factors, including the size and specific gravity of the suspended particles. Generally, residence times in the head box of greater than 1 h can significantly reduce turbidity. During severe storms that produce high concentrations of suspended solids, even a few minutes of settling may produce dramatic improvements. On the other hand, suspended colloidal-clay particles may never have sufficient time to settle. Provisions must be made to periodically remove the settled solids. The quantity and weight involved, even for just one short storm, can be impressive. It is worth remembering that sediments not removed in the head box may be deposited in other places downstream within the system wherever the flow velocities are reduced. Head boxes can affect water parameters other than turbidity. They often develop surprising amounts of resident life forms, which can affect water properties. Surprisingly, while water temperatures may be much different from ambient temperatures around the head box, water temperatures do not change significantly from that in the incoming water. This is due to the high specific heat capacity of the water, the limited residence time in the head box, and the insulative properties of the tank materials. However, indoor head boxes can under humid conditions condense impressive amounts of freshwater out of the air on their cold sides. Over-head seawater pipes can also 'sweat'. This sweating can be reduced by insulation. Electrical and corrosion hazards from the condensed water can be reduced by careful layout.
5.3 Intake and pump house considerations While water quality should have been one of the primary considerations in site selection, there are often intake location options on a given site which will maximize the available water quality. The intake should be placed far away and upstream from any possible source of
77 water contamination. In addition to other discharges, these include inlets, streams or brooks, boat anchorages, industrial or municipal outfalls and storm drainage. Some of these possible contaminant sources are readily visible, others may be less obvious. Sources of drainage may only be obvious at certain seasons or after major storms. Sewage or industrial outfalls may not be shown on hydrographic charts, even when completely legal. Illegal or quasi-legal outfalls can sometimes be spotted, especially from the air, at extremely low tides or by chemical, physical, or biological differences at slack water, when the discharge water may rise to the surface. For examples, seagulls may congregate over sewage outfalls to feed or the water color may be significantly different. Another way of maximizing water quality is to draw water from an area where its properties show the highest consistency and least variation. This usually means as deep and as far from shore as possible. This will also minimize wave damage and possible boat damage to the intake structure but increases the installation cost and probability of damage from fishing gear. If they exist, there is a strong temptation to use sheltered shallow water areas for the intake. This minimizes the probability of storm damage, simplifies the system and decreases costs. On the other hand, shallow areas often have reduced circulation, higher probability of pollution incidents from other users or boat traffic, variable water temperatures and may be subject to rapid salinity drops after heavy rains. The probability of short-circuiting the drain may also be increased. The best intake location is strongly a function of the specific site conditions, evaluation of risks, and the available budget. Tidal water elevations and their variations are very critical to the design of the seawater system. There are three tide components: astronomical, barometric and wind (storm) tide. The astronomical tide, being due to the rotation of the earth, moon and sun, is the only completely predictable component. The barometric component may exhibit seasonal patterns, which can be factored in on a probabilistic basis. On top of these values it is important to get an appreciation of the extreme highs and lows that could be associated with really rare events, such as the 25, 50 or 100 year storms (see Section 3.1). Once the water elevations can be quantified in a probabilistic manner, there are a series of decisions to be made relative to the intake system and pumps. If the range of elevation values from maximum high to minimum low are not great, there is no problem with continuous operations throughout the tidal range. If the tidal range is high, say greater than 18 ft or 6 m, then continuous operations may add cost to the system. Pump selection and elevation becomes critical (see Chapter 7) and pumps can provide serious design problems at both high and low tides. At this point it is worth considering pumping only during some portion of the tide, usually the high side. For a given daily flow, this will require bigger and more expensive pumps and place some restrictions on the operators, but will reduce the excavation depth of the pump house with possible major cost savings. Obviously, this is an area of complex tradeoffs. Placing the pumps on a floating platform will solve the high tidal range pump problem but may create a number of others. The criterion with respect to major storms is usually one of survival and damage minimization. One of the important decisions is defining the storm which the system is designed to survive. This is a cost and risk assessment tradeoff. The more extreme the storm, the higher the system's cost. Luck also helps, as one could get hit with the 100 year storm the very first year. Assuming survival, some parts of the seawater system, but not necessarily the intakes and main pumps, may have to remain functional during the storm, such as for providing life
78 '" Ill Note-C ~.~~EL:+t7
EL =
550' (Pipe is Longer) 500' (Pipe is Longer)
Note-A ~-- ' - ' ~ . . ~ . [-,-,EL=+6' A ~ . ~ ~ ~,. Prefabricated ~ Fiberglass Pumping Station
L~
"J,,~
EL=+IO' High-High W a t e r ~ All ~
Elevations Relative to
Mean Low Water
A "~
Two Polyethylene Pipes L a y e d - ~ . _ _ ~ Side by'Side in s Trench ~ , ~
~
EL:-2L-~Low-Low Water,-----. e - D
, Two Intakes w'th Screens
-"
EL=-6'
Fig. 5.4. Seawater intake profile example. There are several potential trouble points in a marine intake. This example is typical of benign or sheltered sites, where the probabilities of large waves and major storms effects are small but not zero. Note A. Pipes in this area near the pump station should be straight and especially well supported from below before backfilling. All turns should be as gradual as possible to prevent flat spots and stress concentrations on the pipe, which might lead to pipe collapse under partial vacuum. Note B. The points where the beach changes its slope is where the cover over the pipes is likely to be at a minimum. One such point generally occurs at or just below the normal low-tide elevation. Care must be taken during installation to assure the minimum cover over the pipes at this vulnerable point. Note C. If direct wave action is a possibility during rare storms, some measures to protect the investment in the pump house are likely. The hatch on the access trunk would be elevated above grade and water tight. The area around the hatch should have a sloped concrete collar to protect the access trunk. The base of the collar should extend below grade to counter scouring. To prevent the lateral movement of the collar and subsequent shearing of the access trunk, there should be at least four steel pilings or concrete-filled plastic pipe, say about 6 ft or 2 m long, acting as pilings and rigidly cast into the collar. The pump house should have a strong steel snorkel of adequate height to provide ventilation, an automatic sump pump and an external means of turning off power. Note D. The cast concrete intake structures should be buried with the tops as close to grade as possible. The actual opening of the intake pipe should be at least 1 ft above grade to prevent the ingestion of bottom-drifting sediments and debris. The intake structures must be well secured to the bottom with small pilings or screw-auger anchors, as forces from breaking waves under some conditions could be substantial. Under extreme conditions, destruction of screens and riser pipe are highly probable and spares should be available for replacement.
suppo rt to b r o o d stocks or critical life-stages. H o w e v e r , for the duration of the storm, w a t e r quality r e q u i r e m e n t s can u s u a l l y be greatly r e d u c e d with little or no l o n g - t e r m c o n s e q u e n c e s . E m e r g e n c y survival r e q u i r e m e n t s h a v e to be c o n s i d e r e d during the d e s i g n phase. B e a c h profiles are also i m p o r t a n t in s y s t e m s layout. D a t a on b e a c h profiles s h o u l d be a c q u i r e d at least four t i m e s over a year, to get s e a s o n a l variations (see Fig. 3.3). A l o n g e r p e r i o d of o b s e r v a t i o n o v e r several years w o u l d be e v e n better. T h e profile s h o u l d be e x t e n d e d to at least 10 ft or 3 m b e l o w the e x t r e m e l o w - t i d e elevation, p r e f e r a b l y deeper. B e a c h profile i n f o r m a t i o n is n e c e s s a r y for s p e c i f y i n g burial depths for p i p i n g and p o s i t i o n i n g intakes. T h e intake lines h a v e o t h e r potential h o u s e s h o u l d be as c l o s e to the m i n i m i z e suction side frictional e x c a v a t i o n r e q u i r e d to install the
p r o b l e m s , s o m e of w h i c h are s h o w n in Fig. 5.4. T h e p u m p intakes as tides, w a v e s and flood z o n e r e g u l a t i o n s allow to losses (see C h a p t e r 6). This also g e n e r a l l y m i n i m i z e s the p u m p h o u s e (see C h a p t e r 7). H o w e v e r , p u m p h o u s e s p l a c e d
very c l o s e to the w a t e r m a y i n c r e a s e the p r o b a b i l i t y of s t o r m d a m a g e and p l a c e m e n t on the flood plain (flood z o n e defined by 100 y e a r flood in coast al z o n e regulations) can t ri gger a n u m b e r of r e g u l a t o r y issues. T h e worst case is an e x p o s e d shore w h e r e a piping t r e n c h c a n n o t be e x c a v a t e d or r e a d i l y blasted. Blasting, in any case, is very u n p o p u l a r with r e g u l a t o r y
79 agencies and in some area may not be allowed. Fortunately for rocky shores, it is often possible to find at least a partially sheltered intake location for protecting and securing the pipes and intakes. For unfavorable site conditions, even the best engineering and construction may result in a system with very high risk of damage to intakes and piping during storms. The best answer may be to have backup equipment that can be quickly deployed after damage from a major storm. A major new and rapidly expanding problem with intakes, pump houses and discharges concerns regulatory restrictions. Coastal Zone Management regulations in the USA make it very difficult to place pump houses in the 'flood plain'; in short, on a spot with a ground elevation below the 100 year storm surge for that area. This results in longer suction side pipe lengths and deeper pump house placements, with increased costs. The deeply buried pump houses activate 'confined space access' regulations, which make routine access legally very difficult without elaborate and costly procedures. The increased costs and operational restrictions often result in serious compromises in the design with subsequent increased risks of system failure. Another area of regulatory restriction is on when and how to construct and emplace intakes and discharges. In some areas, in-water construction is only permitted in the winter, due to possible construction impacts on 'migration' and 'spawning' of fish and birds. Winter weather can make actual construction very difficult or even impossible. The costs in winter are very much higher and also impossible to predict with any confidence ahead of time due to uncertainties about the weather. In addition, use of sediment fences along in-water pipe excavations may be required, even in winter. In-place casting of concrete may not be allowed due to restrictions permitting only fully cured concrete. Due to serious weather and time constraints, the resulting construction may have important and serious deviations from specifications and design criteria. It is imperative for the user to inspect all in-water construction as soon as possible after emplacement and certainly before any legal 'sign-off'. If serious deviations are found, what can realistically be done to 'fix' the situation may be very limited. All this impacts available design options and may result in serious compromises with good design practices. Regulatory construction restrictions are highly site-specific. Construction in some areas is getting much harder to accomplish. It may not be long before otherwise excellent sites are, for practical purposes, no longer useable due to regulatory restrictions. It is unfortunate that many of the restrictions appear illogical and based more on ideology than scientific facts.
5.4 Discharge considerations The discharge is an often neglected aspect of seawater systems. Since metabolic wastes, chemicals, disease organisms, and decay products will be in the drain water, it is essential that the drain be situated so as to prevent discharge water from reentering the intake (short-circuiting). This is easy to state but sometimes hard to do. There are several basic possibilities, which will be determined by the site configuration and conditions (see Fig. 5.5). The best situation is to have intakes on one side of a sand spit and the discharge on the other with no nearby inlet (Fig. 5.5A). If the site has a consistent alongshore current, the discharge can be placed downstream and as far from the intakes as practical (Fig. 5.5B). An alongshore current under some conditions can switch direction and develop countercurrents or large
80
// Barrier 1 Beach or / Peninsula
A
/
1--I Inflow----I~
I I Discharge j v
/
Intake
/
Facility
/
/S~horeli ne f
... Disc arge
B Inflow Intake ~Consistant jl AlongshoreI
Facility
JJCurrent
C
i;orelin e
Inflow L "J Inshore"~. Intake I Discharge 0
r---] l !
Facility
Alternating ~"j Alongshore r~. Currents I.,/ Fig. 5.5. Discharge configurations.
eddies, resulting in short-circuiting of water flow. If the alongshore currents are unpredictable or switch direction with the tide, which is a common situation, the intake can be taken from as far out as practical while the discharge is dropped along the same line but as close to shore as possible (Fig. 5.5C). The discharge could even be on the beach or buried in a rock jetty. Factors of aesthetics and environmental regulations must also be considered. Short-circuiting under various environmental conditions can be checked with fluorescent dyes. Another major consideration is that drain lines should be greatly oversized. They cannot be sized for the normal flow but must be capable of handling much larger transients. These high transient flows can occur when someone pulls the plug on a tank for cleaning, recycling or repair. If the drains cannot handle the flow, it will be quickly apparent. The consequences run from annoying to serious, depending on the circumstances. Subsequent tank draining procedures will then require much more time and attention to avoid overflow. In addition, drains have a great tendency to fill with sediments, wastes, debris, and assorted garbage, further reducing flow capacity. Any sumps or other chambers in the drain system will be particularly susceptible to clogging or fouling due to biological growth. Most gravity-flow drain lines do not have sufficient flow velocity to be self-cleaning. Drains must be frequently inspected and maintained and can require considerable time and effort. The extra costs of oversizing drain lines can usually be easily recovered in reduced problems and reduced servicing.
81
Chapter 6
Piping Design and Calculations
6.1 Major tradeoffs There are basically two ways to transport water: open channels and pipes. Open channels require strict control of elevations over their entire length but usually have very low frictional losses compared to pipes. At flow rates one or more orders of magnitude above our area of interest, open channels can be cheaper than pipes if the soil types, required length, and topography are favorable. For our flow rates and typical conditions, channels are clearly not competitive, with one possible exception. This is for drain lines. Even in this case, a prepared channel will most likely be more expensive than pipes. However, the cost difference may be compensated for by the improved access to channels for inspection and cleaning (see Section 6.6). Given a desired flow rate, one apparent choice is between a small pipe with high frictional losses or a large pipe with low frictional losses. Frictional losses in pipes or equipment can be measured in pressure units or elevation (head) units. These are interchangeable by knowing the specific weight of the fluid, i.e., seawater (see Table A-3). Considerations include the extra cost of large diameter pipe balanced by the increased pumping costs of small pipes due to higher frictional losses resulting in more powerful pumps and increased energy costs. Smaller pipes have higher velocities, which make them more susceptible to water hammer (see Section 6.3). As will be seen, predicting frictional losses is difficult, imprecise, and may vary with time and conditions. Frictional losses are a function of the fluid properties, pipe velocity, pipe material, pipe condition, and pipe diameter. Additional frictional loses also occur wherever piping changes direction, such as at an elbow, a T, or where the pipes change diameter, such as at a reducing fitting or the inlet/outlet of a tank. If flow is controlled by gravity rather than pumps, the acceptable frictional losses for the desired flow rate may be severely constrained by the available elevation differences and the piping system will have to be carefully designed to minimize frictional losses. For preliminary design purposes, pipes can be sized by using a velocity criterion, such as 1.5 m/s (5 ft/s). This is a suitable compromise for many conditions, although gravity flow situations and long pipe runs may require even lower values. In calculating average pipe velocities it should be noted that the nominal pipe sizes are not exactly the same as the inside diameter dimensions. However, for rough calculations the errors will usually be small. An exception is polyethylene pipe on the suction side of a pump, where concern for possible pipe collapse under partial vacuum requires thick walls. As an example, 16 inch nominal polyethylene SDR 11 pipe can have an inside diameter of only 12.9 inches (an error of about 35%). Since pipes come in discrete sizes and not all sizes are readily available or provide the same selection of fittings, the velocity criteria will not necessarily provide a clear decision on the best pipe size.
82 A fact not fully appreciated by many, is that the specifics of the piping, processing system and the pumps are highly interdependent in seawater systems. If you alter the specifications or operating conditions of the piping or other system components, you will alter the operation and performance of the pumps, and vice versa. How a seawater system will perform is dependent not only on the installed equipment but also on the precise operating conditions at any given time, especially in areas with high tidal variations. If the conditions exceed the operating envelope of the system, problems and possible failure will follow. For this reason determining system head losses and pump selection are very complex and receive considerable attention.
6.2 Biofouling control One of the most important factors which can affect the performance of a seawater system over a period of time is due to marine biofouling. Its control is also one of the most troublesome factors associated with the operation and maintenance of seawater systems. The extent of the problems is highly dependent on season and location. Different sites can have high variations in biofouling rates, even over relatively short distances. Biofouling roughens the surfaces of pipes and equipment, thereby increasing frictional losses. If allowed to continue, it will effectively reduce the flow areas, dramatically increasing pipe velocity and frictional losses while reducing flow capacity. Over a period of 12-16 months, a heavy growth of mussels can turn an 8 inch pipe into a 3 inch pipe. High frictional losses can lead not only to greatly reduced system performance but also to total system failures. As a consequence, considerable efforts are often devoted to biofouling control. Biofouling control will be much easier if the various control options are considered during the design phase, rather than only after problems become evident during operations, as is common. If biofouling is allowed to proceed until flow rates are significantly reduced, it may be necessary to turn the system off for a prolonged time period, days, weeks, or even months, to fix the problem. The methods needed to clean heavily fouled lines may seriously damage plastic or fiberglass pipes and fittings, especially in turns. In some cases, it may be quicker and cheaper to completely replace heavily fouled pipes and fittings. Many methods have been used to control biofouling in seawater systems and all have their advantages and disadvantages (Table 6.1). In a complex system, many of them may be used in different parts of the system. It is general practice to have at least two options for every part of the system. There can be major cost and reliability considerations involved with these decisions and they will affect system design. A common approach in many research oriented seawater systems is to have two complete parallel piping systems, suitably cross-connected for maximum flexibility. This allows the water in the non-operating system to go anaerobic, thus killing all the fouling organisms, while the other system is in use. These two systems are alternated in use on a fixed schedule, usually about every 2 weeks. This approach is very reliable and works well but has the increased cost associated with a double system. In the special case of a short term or seasonal system in a low biofouling area, the same control method might be used with a single system. Another approach is to design the system such that the water velocities in the pipes are sufficiently high to preclude biofouling. Minimum water velocities in the range of 8-10 ft/s (about 3 m/s) are required. These values are valid only under conditions which preclude
83 Small flow of high pressure water needed to move pig into the pipe being cleaned
,/
Blind flange or threaded cap
Valve section one size larger ~ --'- Pipe diameter than pipe being cleaned
(3
Expansion fitting Pig Types:
II
I Y Fitting
Fig. 6.1. Pig launcher schematic and pig configurations. photosynthesis, such as opaque pipe, since some attached algae can tolerate much higher velocities. This approach can be reliable, works well and is best suited to long straight pipe runs, especially for supply lines. If operational conditions change and the velocities drop below the minimum, the lines may foul. Intakes, discharge areas, and lateral branches, where velocities could be lower, may be particularly susceptible to biofouling. If the velocities are in the region of 15 ft/s (4 m/s) or above and there are entrained abrasive particles, such as sand, the life time of plastic pipe may be seriously reduced by erosion, especially in turns. In areas of substantial tide, the flow velocities in the main supply lines may vary by 1.5- to 3-fold over a tidal cycle. Therefore, if the minimum flow velocity is high enough to prevent biofouling, excessive velocities may be produced at other times. In addition, high water velocity coupled with long pipe runs increase the hazard from water hammer (see Section 6.3). In spite of its potential problems, this approach is sometimes attractive because it is simple and tends to minimize front end capital expenses. For long pipe runs, it is often combined with a 'pigging' option (see below). Mechanical methods are very reliable and can be practical, if provisions for their use have been anticipated by allowing for easy access. Often these methods are the method of last resort because all others have failed to restore system capacity. Few of the other methods actually remove attached biofouling, sediments or debris. If biofouling is allowed to get out of hand, these other methods may kill the organisms without restoring adequate flow capacity. 'Snakes' are the most effective for short runs while polyurethane or plastic 'pigs' work well on long runs. These 'pigs' are bullet- or spherically shaped, flexible and contractible (see Fig. 6.1). They are of somewhat greater diameter than the inside diameter of the pipe to be cleaned. They are pushed through the piping under pressure, cleaning the pipes by friction as they proceed. They are available for various types of biofouling, from just surface films to major encrustation. They can make 90 degree turns and get through partially closed gate valves. The increased pressure normally does not exceed 100 psi and is often considerably
4~
TABLE 6.1 Biofouling control methods used in seawater systems Method
Advantages
Disadvantages
Comments
Double system, half anaerobic at a time
Very effective Built in flow growth potential No need for prior water processing
Very expensive
Commonly used for main lines at research labs
Desiccation
Cheap Must assure complete drainage
Long downtime Does not remove dead organisms
Effective, especially for larger systems
High flow velocity
Cheap and with care effective Can be backed up by mechanical methods No need for prior water processing
If velocity too low, get biofouling If velocity too high, can get excessive pipe erosion Very susceptible to water hammer No flow rate growth potential Problems at slow spots and laterals High energy losses due to friction
Most likely in large systems with long pipe runs where cost is a major factor
Hot water pulse
Eliminates need for redundant system May exploit existing capabilities
Plastic pipes susceptible to high water temperatures Does not remove dead organisms Downtime during treatment
Most likely in closed temperature-controlled loops
Chlorination
With care, usually effective
Problems with chlorine residuals Possible environmental objections Possibly high operating costs
Mostly limited to discharges and batch processes
Freshwater pulse
Periodic use, usually effective Usually cheap
At large scales, freshwater supply may be limiting Does not remove dead organisms Downtime during treatment
Most applicable at small scales
Mechanical devices
'Snakes' effective for short lengths 'Pigs' effective in long straight lines Removes fouling, restoring flow capacity 'Pigs' have little downtime and are cheap
Need discipline to carry out periodic maintenance before problems arise 'Pigs' need access to both ends
Usually last resort; more effective if considered during design
TABLE 6.1 (continued) Method
Advantages
Disadvantages
Comments
Toxic surfaces
Effective for small surfaces where fouling consequences most severe Environmentally acceptable if used within limitations
Limited applicability Must be conscious of surface area, leaching rate, flow rate relationships to avoid problems
Used in limited high value applications
Filtration
Can greatly reduce fouling problems if equipment needed for other reasons
Can be expensive at high flow rates Failures or short circuits can nullify effectiveness with no warning
For best effect need fine filtration
UV treatment
Can greatly reduce fouling problems if equipment needed for other reasons
Can be expensive at high flow rates Performance must be monitored
Commonly used in lab and hatchery systems
Ozone treatment
Can greatly reduce fouling problems if equipment needed for other reasons
Potential toxicity problems from residue oxidation products, especially with seawater
Very effective in reuse systems
86 less and suitable for plastic pipes. They take only a few minutes of system downtime for use but require piping access for the launch and recovery of the 'pigs'. 'Pigs' can be launched from a pressurized cleanout in the line or a specialized 'pig' launcher. A 'pig' launcher for 'bullet-shaped' pigs can be made with a 'Y' fitting (see Fig. 6.1), with the branch having an expansion fitting connected to a section of pipe one size larger in diameter and with a length about twice that of the pipe to be cleaned. The end of the branch should be closed with a removable cap to allow insertion of the 'pig'. The end of the branch requires a means of adding a launching pressure to the back of the 'pig'. This can be a small auxiliary pump or small diameter line from the discharge side of a pump. 'Pigs' can be recovered from cleanouts, rock traps, wetwells, intake screens or tank water surfaces (most types float). This method is cheap, quick, efficient and reliable but does require the discipline to carry out the scheduled cleaning. The time interval is dependent on conditions, but cleaning intervals of about 2 weeks during the fouling season should be adequate under most conditions. Many of the other biofouling control methods depend on the availability of specialized processing equipment already there for other purposes. These include filters, sterilizers, and heat exchangers. They can all be very effective in reducing biofouling problems. Other options, such as chlorination and biofouling resistant surfaces, may be acceptable and attractive under some conditions. Chlorination is most likely to be used in a flowing system for treating the drain lines. An application of 1-1.5 mg/1 chlorine for 24-48 h every 2-4 weeks, if allowed by environmental regulations, should suffice to keep drain lines free of biofouling. However, this will have no effect on clogging problems. 6.3 Water hammer
Water hammer is a transient pressure phenomenon caused by the rapid stopping of flow. The rapid deceleration causes a pressure wave to propagate upstream, where it is reflected and returned creating an increased pressure pulse at the slowing point. This pressure pulse causes a loud 'bang' to be heard followed by others at regular intervals. The intervals are determined by the sound velocity in seawater (5000 ft/s or 1500 m/s) and twice the upstream distance to the point of reflection. The pressure pulse can have a value several orders of magnitude above the normal operating pressures. Due to the widespread use of relatively low pressure rated synthetic pipe materials in seawater systems, the transient pressures produced by water hammer can easily rupture pipes or blow fittings apart. The magnitude of the pressure pulse depends on the average velocity in the pipe, pipe length and rate of valve closure. High velocities and long pipe runs are the worst combination. Pipe diameter or flow rate, by themselves, are not important. The most common situations producing water hammer are the rapid opening of a line resulting in a high velocity flow proceeding down an open pipe and suddenly encountering an elbow or almost closed valve, or the closing of a valve in a flowing line too rapidly. The quarter turn full-open to full-close ball or butterfly valves commonly found in seawater system are particularly dangerous in this regard, since they can be fully cycled with a flick of the wrist. If these types of valves cannot be avoided, such valves in critical places should be red flagged, have their handles removed, or be locked. Fig. 6.2 is a nomograph for calculating water hammer with an example to demonstrate the use of the figure. In order to further illustrate the danger, if a typical main supply line from a pump house had a velocity of 10 ft/s, a length of 700 ft from the pumps to the valve and
87 D 2,000
4~ t 30
B
- t,000
=~opoo ==5poo
2o
-
_;.00
i
-
=100
- .6 .8
6
---
5-
50
800
600
500 400
Ol o
_o >
-
o
-
(D
-
(1)
-2
r
3 V-
"o 2 -
0
L
--
-5 -6 -
~_ o m
=5
a
1-
-40
., _~
-i-.
-1
J:
_-0.5 _
~
-0.1
>
-50
I
Ol
LL
60
=10
~
200
- 100 - 80
4-
e~
<
-
3OO --.4
8 _---.5j
~
-
~.
- -
10
C
J
,.i,,,0
>
a.
-i.E~ r" a) _J (I) (3. o~ n
-
30
-
20
-10
Fig. 6.2. Water hammer nomograph. The pressure pulse due to water hammer can be found by knowing the average velocity of the fluid in the pipe, the pipe length, and the valve closing time. The fluid velocity is found on the left side of scale (A) and the pipe length on scale (D). These two points should then be connected by a straight line. The intersection of this line with scale (C) is noted and connected with a second line to the appropriate value for the closure time on the right side of scale (A). The pressure pulse in psi is then read from the intersection of the second line with scale (B). The pressure pulse must be added to the existing line pressure to find the m a x i m u m pressure needed for selecting pipe type and wall thickness. The example shown is for a pipe length of 200 ft, fluid velocity of 20 ft/s and a valve closure time of 1 s. The resulting transient pressure pulse has a value of 270 psi.
the same closure time of 1.0 s, it would produce a pressure pulse of about 500 psi above normal pressure. Most synthetic pipes have pressure ratings of only a few 100 psi at best. It may require a closure time in the order of 15-20 s to avoid unacceptable pressures. While this is a potential problem with a straightforward solution, operating personnel may not have the patience to close valves this slowly. Example 6.1 is an example of a real water hammer problem with a real system. Its pipe velocity with one pump operating was just sufficient to preclude biofouling for decades until pump wear significantly reduced the flow velocity. This site has a negligible tide. 6.4 Frictional losses in pipes Frictional losses are usually measured in elevation or head units, which have the dimensions of length (ft or m). Sometimes frictional losses are given in pressure losses between two points.
88
Example 6.1. Main seawater line water hammer The system shown in Table 5.3 was designed with a single 1000 ft long 6 inch (actual ID = 5.72") polyethylene main intake line between the pump house and the facility. This was done to save the cost of a double line and the pipe was sized to provide sufficient flow velocity to prevent biofouling in the line (see Section 6.2). The system was designed to provide 600 gpm with one pump and 1000 gpm with both main pumps on. The pressure rating for normal usage of the main pipe is 100 psi. (A) What is the minimum closure time for a valve at the end of this 1000 ft supply line to not exceed the pressure rating of the pipe due to water hammer for the two design flow rates? Since the transient pressure must be added to the normal operating pressure in the line, there is in fact less than a 100 psi margin. In the context of this example, the normal operating pressure is unknown but is usually half or less of the rating. The rating is usually determined by the shut-off head of the pump (or the other way around). The ratings are also usually conservative, especially for very short duration transients. Realizing that it may be a bit optimistic, we will assume that the full 100 psi is available. 600 gpm = 1.33 fi3/s,
V = Q/A
=
1000 gpm = 2.22 ft3/s,
V = Q/A
= 2.22/0.1785 = 12.4 ft/s
1.33/0.1785 = 7.5 ft/s
Using Fig. 6.2 with L = 1000 ft and pressure increase = 100 psi For V = 7.5 fl/s (600 gpm),
Tminimum :
4.5 S
For V = 12.4 fl/s (1000 gpm),
Tminimum :
7.0 S
(B) What are the minimum closure times if the normal operating pressure at the valve is around 50 psi? Using Fig. 6.2 with the same length and velocities but with an allowable pressure increase of 50 psi instead of 100 psi With 600 gpm, Tminimum-- 8.5 s With 1000 gpm,
Tminimu m :
11.0 s
(C) The main seawater valve at the end of the line in this system is in fact a quarter turn full-open to full-close valve. What is the transient pressure pulse if the valve is inadvertently closed in one second? Using Fig. 6.2, closure time = 1 s, length = 1000 It, and stated velocities At 600 gpm get 500 psi pressure increase At 1000 gpm get 800 psi pressure increase (D) Is there a significant threat of system's damage? Given the existing system, discuss your options. Yes, serious threat Options in increasing order of intensity: 9 Place red streamer on valve with written warning 9 Remove the valve handle 9 Lock valve 9 All of the above
The conversions from one unit to another are from the equation below. h =
Pl - P2
(6.1) V where pl - p2 is pressure drop, lb/fl 2 (Pa), h is head loss, fl (m), and ~, is specific weight of fluid, lb/fl 3 ( N / m 3)
89 The value of specific weight varies slightly with temperature and salinity (Table A-3). At 35 g/kg salinity and 25~ 1 atm (14.7 psi) is equal to 10.10 m or 33.12 ft of head. In the English system of units, it is important to note the units of pressure are expressed as lb/ft 2 rather than the common units of lb/in. 2. There are many factors which effect the frictional head loss in pipes. All of the following discussion relates only to pipes running full. Pipes with a free surface are open channels (see Section 6.6). While the frictional losses will depend on both fluid temperature and salinity, over the range of 1-35 g/kg salinity and 0-40~ temperature, these effects are relatively small due to the small changes in the physical properties of water (see Table A-3). Other major factors affecting frictional head losses are the specific characteristics of the pipe. This includes not only the pipe material but also the existing and future condition of the pipe. The condition of the pipe depends on age, velocity and sand load, formation of scale, deposition of sediment, and biofouling. There are a number of analytical methods for estimating frictional losses in pipes (Davis and Sorensen, 1969). They all use a 'flow coefficient', which has various definitions depending on the method. All these coefficients are estimated for 'average' or 'normal' conditions, primarily based on freshwater applications where biofouling is not generally as severe a problem as in seawater. Therefore, the choice of a coefficient value is at best an educated guess as to the current or projected situation and is time dependent. Usually, one will carry out the calculations for a 'used' pipe with minor biofouling. The head losses for a new pipe will be much lower than for a 'used' pipe, but once in operation a new pipe will very soon become a used pipe. The inherent assumption is that the lines will be maintained and that biofouling will be controlled. If the lines are not maintained, the biofouling will reduce the pipe diameter, increase the pipe velocity and dramatically increase the frictional losses, and reduce the flow rate. Many pipe manufacturers and engineering texts will present frictional head losses in pipes in tabular form (see Table 6.2). The input variables are nominal pipe diameter (which may be quite different from the actual inside diameter) and the flow rate. The outputs are the average pipe velocity and the frictional head loss per unit length. The total frictional head loss is then calculated by multiplying the table value by the number of unit lengths in that pipe run. These tables are fine if the assumptions and conditions of the table and the resulting errors are acceptable. Most of the available tables are for freshwater (Table 6.2 is for seawater), a fixed temperature and assumed pipe type and conditions. Since most tables do not consider biofouling, such values should be used conservatively. Depending on conditions, errors from use of such tables may or may not be significant. They are useful for preliminary calculations but should be checked by more rigorous methods during the detail design phase. Because of potential biofouling problems, these tables should be used very conservatively. There are a number of methods to calculate estimated frictional losses in pipes. Probably the most common method in fluid mechanics texts (Granet, 1989; Roberson and Crowe, 1990; Munson et al., 1994) is based on the Darcy-Weisbach equation (6.2). A major advantage is that it is readily useable in both metric and English units. h =
flV 2 2gd
(6.2)
where h is frictional head loss in ft (m), f is resistance coefficient or flow coefficient (non-dimensional), I is length of pipe run in ft (m), d is pipe inside diameter in ft (m), V is
TABLE 6.2 Frictional losses in plastic Schedule 80 pipes Flow GPM
Flow LPM
Nominal pipe sizes (inches) 1
10 20 30 50 70 100 150 200 250 300 350 400 500 600 700 800 900 1000 1200
0.63 1.26 1.89 3.15 4.42 6.31 9.46 12.62 15.77 18.93 22.08 25.24 31.55 37.85 44.16 50.47 56.78 63.09 75.71
1.5
2
3
4
vel.
loss
vel.
loss
vel.
loss
vel.
loss
4.4 8.9 13.3
8.8 32.0 72.1
1.8 3.6 5.5 9.1 12.7 18.2
1.1 3.7 7.9 20.0 37.1 71.7
1.1 2.2 3.2 5.4 7.6 10.8 16.2
0.31 1.1 2.3 5.6 10.7 20.2 42.8
0.5 1.0 1.5 2.4 3.4 4.8 7.3 9.7 12.1 14.5 17.0 19.4
0.04 0.16 0.32 0.81 1.5 2.9 5.9 10.2 15.5 21.7 29.5 37.4
6
vel.
loss
0.6 0.8 1.4 2.0 2.8 4.2 5.6 7.0 8.4 9.8 11.2 13.9 16.7 19.5
0.04 0.09 0.21 0.39 0.74 1.5 2.6 4.0 5.5 7.4 9.7 14.5 21.5 26.9
8
12
vel.
loss
vel.
loss
vel.
loss
0.6 0.9 1.2 1.9 2.5 3.1 3.7 4.3 4.9 6.2 7.4 8.6 9.9 11.1 12.3 14.8
0.03 0.05 0.10 0.21 0.36 0.54 0.74 0.98 1.25 1.9 2.7 3.6 4.6 5.7 6.9 9.7
0.7 1.1 1.4 1.8 2.1 2.5 2.8 3.5 4.2 4.9 5.6 6.3 7.0 8.4
0.03 0.06 0.09 0.14 0.19 0.26 0.32 0.49 0.68 0.90 1.16 1.4 1.8 2.4
0.5 0.6 0.8 1.0 1.1 1.3 1.6 1.9 2.2 2.5 2.8 3.2 3.8
0.008 0.014 0.020 0.028 0.036 0.047 0.070 0.097 0.127 0.166 0.202 0.242 0.336
These values should be typical of clean used plastic pipe and seawater. Note assumptions inherent in calculations. They do not include allowance for any significant biofouling, which can create much higher losses. Since Schedule 80 pipe has relatively small inside diameters, these values should be conservative for Schedule 40 or other thinner-walled pipes. Velocities in ft/s and losses in ft of head per 100 ft of pipe. Assumptions: seawater, 70~ (21~ kinematic viscosity 1.1 x 10 -5 ftZ/s; equivalent sand roughness 4.2 x 10 -5 ft; PVC Schedule 80 pipe inside diameters, Darcy-Weisbach equation.
91 TABLE 6.3 Equivalent sand roughness for internal pipe surfaces Pipe material
Feet
Glass, plastics, fiberglass, copper, brass, drawn tubing Steel, wrought iron Asphalted cast iron Cast iron Riveted steel Concrete
4.2 1.5 4 x 8.5 3 x 1 x
Meters x 10 -5 x 10 -4 10 -4 z 10 -4 10 -3 t o 3 x 10 -2 10 -3 to 1 x 10 -2
1.3 4.6 1.2 2.6 9 x 3 x
x 10 -5 x 10 -5 x 10 -4 x 10 -4 10 -4 t o 9 • 10 -3 10 -4 to 3 • 10 -3
Approximate values under 'normal' conditions for used pipe. Pipe materials are those that might be used for supply or drainage in a seawater system. Values do n o t have allowance for significant biofouling.
average pipe velocity, isvolumetric flow/pipe cross-sectional flow area, in ft/s (m/s), and g is gravitational constant, is 32.2 ft/s 2 (9.81 m/s2). While the equation is straightforward, this is not true for getting the proper values for f . A parameter called equivalent sand roughness (Ks) must be developed. This is an estimate of the roughness of the pipe's interior surface due to basic material, service use and cleanliness. Table 6.3 presents values for average conditions. These values are not specifically for seawater uses and do not allow for any significant biofouling. If a plastic line has ever been heavily biofouled, its values are likely to be in the range of steel to concrete pipe values even after rigorous cleaning due to unremovable calcareous deposits. Pipes with significant biofouling in effect have reduced diameters. Losses for biofouled pipes can be calculated using the estimated effective or available unfouled pipe diameter and high Ks values in the order of 0.01 ft or 0.003 m. The actual value of equivalent sand roughness to be used in design calculations is a function of where the specific length of pipe is situated in the system, the natural biofouling characteristics of the water expected to go through the line and the degree and quality of the expected maintenance on this section. In short, no simple answer and it is best to be conservative. Another needed parameter must be derived from the equivalent sand roughness, and this is the relative roughness. Relative roughness is defined as Ks/d and is dimensionless. Another non-dimensional factor to be defined is called Reynold's number (Re). Reynold's number is used to characterize and compare fluid flow. Vd Re = (6.3) 13 where Re is Reynold's number (non-dimensional), V is average pipe velocity in ft/s (m/s), d is pipe inside diameter in ft (m), and v is kinematic viscosity, Table A-3, ft2/s (m2/s). The relative roughness and Reynold's number are used to estimate the resistance coefficient ( f ) by use of the Moody diagram (see Fig. 6.3). The relative roughness value is found at the fight-hand margin and followed to the left and slightly upward until it intersects a vertical coming from the calculated Reynold's number on the bottom margin. The output is the resistance coefficient (f), also non-dimensional, which is read by going directly to the left-hand margin from this intersection. Most practical applications will fall in the fight half and, especially if biofouled, towards the top of the Moody diagram. The read value of f can now be inserted into the Darcy-Weisbach equation (6.2) to determine the line's frictional head loss.
92 .oi .09 .08 .07
.05
.06 N,,.-
~-
- 0, (.)
.05 -
.04
"01
0 . ~( j .~
o
-.,7_.. "E
LL
8 (I.) 0
0
.025
~ .02 n,- .015
.01 .009 .008
E
.005
DO ~
i"II
I 10 3
z 34
.001 .0005 .0001 .000,05
.ooo,o~ 681
10 4
105
106
1Or
-.000,001
Reynold's Number, Re = V..~D V
Fig. 6.3. Moody diagram: resistance coefficient vs Re. Modified from Moody (1944) courtesy ASME.
If the flow goes through several different pipe diameters or if the pipe materials or conditions change along the line, each section must be calculated separately with the procedures above and the results added to get the total pipe losses. Another method for estimating frictional losses in pipes involves the Hazen-Williams coefficient (C) and equation. There is a metric (6.4) and an English (6.5) form for this equation listed below. h -
10.7Q]-85/ C1.85d4.87
(6.4)
where Q is flow rate in m3/s, l is pipe length in m, C is the Hazen-Williams coefficient (dimensionless), d is pipe diameter in m. 4.72Q1.85/ h -
C1.85d4.87
(6.5)
where Q is flow rate in ft3/s, l is pipe length in ft, C is the Hazen-Williams coefficient (dimensionless), and d is pipe diameter in ft. One advantage of the Hazen-Williams equations is that the coefficients are independent of flow rate and velocity. Useable values for 'used' plastic pipe is C -- 100 and for new conditions C - 130. 'Used' concrete pipe is about C -- 60 and new around C -- 100. As with the Moody approach, these values do n o t allow for significant biofouling, assuming that the pipes will be well maintained.
93
6.5 Frictional losses in fittings If a section of pipe has any fittings, equipment or transitions (changes in diameter), these items will have additional frictional losses themselves. It must be remembered that both a pipe exiting a tank and a pipe flowing into a tank are pipe diameter transitions with associated frictional losses. These losses must be calculated separately and added to the pipe losses to get the total losses between any two points. The frictional loss will depend on the type of fitting or transition, the abruptness of the flow change, the material and the present condition of the internal surfaces. Usually only the type of fitting and the abruptness are considered. For some fittings, such as valves, there can be considerable variation in losses from one manufacturer to another due to internal dimensional differences. Even for more standardized fittings, the variations can be as much as 50%. The frictional head loss for any given fitting or transition is calculated from the equation below. KV 2
h =
2g
(6.6)
where h is head loss in ft (m), K is loss coefficient (non-dimensional), V is average velocity in adjoining pipe in ft/s (m/s), and g is gravitational constant, 32.2 ft/s 2 (9.81 m/s2). The loss coefficient (K) is a function of the type of fitting and conditions (see Table 6.4). Note that losses are keyed to the velocity in the adjoining pipe and that for transitions it is either the upstream or downstream velocities depending on conditions. Head losses for some inline components, such as heat exchangers and UV systems, may be given by the manufacturer for only the rated flow rate. If the diameters of the inlet and outlet pipe are known, a loss coefficient value can be computed. This will allow calculation of head losses at other flow rates (see Example 6.2). The engineering assumption is that the K value is constant and independent of the flow rate or velocity (if the internal configuration is not altered). Head losses and K values will be very manufacturer- and model-specific. A length of pipe may contain a large number of fittings and pieces of equipment. Many of these fittings may be identical. If the pipe diameter is constant over this length and there is no flow branching, the velocity will also be constant. In this case, it is not necessary to calculate the head loss for each fitting individually but to take the sum of the K values. With the sum of all the contained K values, the head loss from all the fittings can be acquired with one calculation and combined with the pipe loss (see Example 6.3). If there is more than one pipe diameter or pipe material, the sum of the K values have to be taken separately for the fittings associated with each type pipe. Another method that might be encountered for finding head losses in pipe fittings involves the concept of equivalent length. In this method, the head losses for the fitting are expressed in terms of the length of straight pipe with the same head losses. Tabulated data on fittings are presented as a factor which is multiplied by the associated pipe diameter to produce an equivalent length of straight pipe.
6.6 Open channel flow Seawater flow in open conduits or channels is more common at flow rates much higher than those of interest to us. However, it may still occasionally be encountered, especially in
94 TABLE 6.4 Loss coefficients for welded or flanged fittings K as a function of fitting size:
Fittings
Couplings and unions 45 ~ elbows 90 ~ elbows 180 ~ return bend T (line flow) T (branch flow - - tee used as elbow) Ball valve, open Gate valve, open Globe valve, open Butterfly valve, open Basket strainer Foot valve Swing type check valve (fully open) Disk type check valve (fully open) Ball type check valve (fully open)
2 inches
6 inches
20 inches
0.08 0.20 0.38 0.35 0.20 0.8 0.15 0.4 9 0.57 1.5 0.8 2 10 70
0.06 0.17 0.28 0.26 0.12 0.6 0.04 0.1 6 0.15 0.9 0.8 2 10 70
0.04 0.14 0.21 0.20 0.07 0.4 0.02 0.03 5 0.05 0.45 0.8 2 10 70
Transition
Loss coefficient (K) Contraction
"~ , 71 " - - - " / ~ D1
,
D2 ,
I
{
~
72
v for Computations = V2 Expansion
D1
v I ---~')
,
i
D2
I
/
._.~ V2
! v for Computations = V 1
D2/D1 0 (from large tank) 0.2 0.4 0.6
0.50 0.49 0.42 0.32
0.8
O. 18
D1/D2 0 (into large tank)
1.0
o2
o92
0.8
O. 16
0.4 0.6
0.72 0.42
These are approximate loss coefficients for standard fittings and transitions (adapted from Hydraulic Institute, 1979 and other sources). There is no allowance for biofouling. Threaded fittings will have higher values than flanged fittings or solvent welded fittings. Check valves that are not flowing sufficiently to fully open will have much higher losses. The loss coefficients are dimensionless. Actual values depend strongly on type of material, specific brand, and installation; the typical range of variation may be as large as 4-25 to 50%.
drains. The advantage of drains is easy access for cleaning and amenability to very much higher transient flows, which drains must be able to handle. The channels can be of any shape but are often roughly rectangular or semi-circular in cross-section. Open channels used for drain lines must be over-sized as the maximum flow will occur during draining of tanks or during cleaning. Drains should be designed for at least 10 times the average flow rate for the system. If possible, they should be covered to preclude photosynthetic biofouling in the channels. If the channel fouls, the frictional head losses go up. If the frictional head losses exceed the available elevation in the channel, it will no longer
95
Example 6.2. Head losses in processing equipment A heat exchanger is installed in a 2 inch inside diameter line to heat seawater. The manufacturer gives the frictional loss to be 10 psi at the rated flow of 100 gpm. However, this system is designed to flow at 80 gpm. What is the expected head loss of the process water through the heat exchanger at a flow of 80 gpm? It is first necessary to translate the frictional pressure loss into frictional head loss by using Eq. 6.1. However, the fluid properties used by the manufacturer are rarely stated but can be assumed to be freshwater at room temperature. p~ - p2 :
10 psi = 1440 lb/ft a
y = 62.3 lb/fi 3 for freshwater of (0 g/kg salinity), temperature of 20~ h = (pl -
(Table A-3C)
Pz)/V = 1440/62.3 = 23.1 ft
100 gpm = 0.223 fi3/s, conversion from Table A-1 2 inch diameter gives a pipe flow area of 0.0218 ft 2 Fluid velocity : flow/pipe area :
0.223/0.0218 : 10.2 fi/s
Using Eq. 6.6 h -- 23.1 --
KV2/2g : K(10.2)2/2(32.2)
K -- 14.3 can now be used to solve for h at other flow rates. As done above, 80 gpm correspond to a flow of 0.178 ft3/s and a resulting average fluid velocity of 8.17 ft/s. At 80 gpm the frictional heat loss through the heat exchanger is:
h--kV2/2g = 14.3(8.17)2/2(32.2)-- 14.8 ft Note that a 20% reduction in flow rate results in a 36% reduction in frictional losses. Assuming that frictional losses are a linear function of flow can lead to large and important errors.
be able to flow at the required rate and water will back-up and overflow. There are a number of ways to calculate flow velocities and flow capacities but one of the most common is based on the Manning equation. The equations in English form are given in Eqs. 6.7 and 6.9, and for metric units in Eqs. 6.8 and 6.10 below (see Example 6.4) 1.486R0.667 S0.5
V =
(for English units)
(6.7)
n R0.667 80.5
V =
(for metric units) (6.8) n where V is average velocity (ft/s, m/s), n is the Manning coefficient, about 0.015 for concrete lined and 0.0225 for earth lined, this assumes n o significant fouling, R is hydraulic radius (ft, m; see Fig. 6.4), and S is channel slope (see Fig. 6.4). 1.486A R 0"667 S 0"5 Q (for English units) (6.9) n A R 0"667 S 0"5
Q -
n
(for metric units)
where Q is flow rate (ft 3/s or m 3/s), and A is channel cross-sectional area (ft 2 or m2).
(6.10)
96
Example 6.3. Frictional losses in pipes and fittings A 500 ft horizontal length of 2 inch Schedule 40 PVC pipe (actual inside diameter of 2.067 inch) flows seawater at 68~ and 35 ppt (g/kg) salinity at a rate of 50 gpm. The pipe includes one open gate valve, four 90 ~ elbows and ten couplings. What is the average pipe velocity and the total frictional losses for pipe and fittings in both head and pressure units? Q = 50 gpm = 50/448.83 = 0.111 ft 3/s conversion from Table A-3 d = 2.067 inch -- 0.172 ft Pipe area = 0.0233 ft 2 Velocity = flow/pipe area = 0.111/0.0233= 4.78 ft/s Kinematic viscosity of seawater at stated properties from Table A-3 v = 1.0459 x 106 ftZ/s Eq. 6.3 Re = V d / v -- 4.78(0.172)/1.0459 x 106 - 7.9 x l05
Equivalent sand roughness (Ks) = 4.2 x 10 -5 ft from Table 6.3 Relative roughness -- K s / d -- 0.00024 Into the Moody diagram (Fig. 6.3) with Re and Ks~d, read f = 0.020 Using Eq. 6.2 and pipe length of 100 ft h -- f l v Z / 2 g d
= 0.02(100)(4.78)2/2(32.2)(0.172) = 4.13 ft/100 ft
The calculation above was done for 100 ft pipe length rather than the total of 500 to enable a comparison to losses for a 2 inch Schedule 80 pipe as shown in Table 6.2. Schedule 80, due to its thicker walls and smaller inside diameter, has a somewhat higher average pipe velocity of 5.4 ft/s and frictional loss of 5.6 ft/100 ft of pipe. Using Table 6.2 directly would have produced quicker and more conservative values. Using the calculated value to get total frictional loss for the pipe Pipe frictional loss = 5(4.13) = 20.6 ft Now for fittings losses using Eq. 6.6 Fittings losses = (Kvalve q-4Kelbow -k- 10Kcoupling)V2/2g = (0.19 + 4(0.85) + 10(0.08))(4.78)2/2(32.2) -- 1.56 ft Total head losses -- pipe losses + fittings losses -- 20.6 + 1.56 = 22.2 ft Using Eq. 6.1 to convert to pressure units Fluid specific weight y = 63.975 lb/ft 3 from Table A-3d h = (pl - p z ) / y = 22.2 = (pl - p2)/63.975
Frictional pressure loss = Pl - P2 = 1420 lb/ft 2 = 9.9 psi
To ensure water drainage the slope must be 0.0013 or greater and to ensure self-cleaning the slopes of open channels should be in the range of 0.005 to 0.010 (0.5 to 1 unit of elevation for each horizontal length of 100 units). If there are appreciable solids or debris in the flow, the minimum slope can go up to 5-fold. Since these slopes required for self-cleaning with appreciable solids content are often not possible, drains usually require constant maintenance to remove deposited solids.
97
Example 6.4. Open channel flow A central rectangular open channel drain has been cast into the concrete floor of a wet lab. This wet lab has a number of large tanks, which need to be periodically drained and refilled. If the channel has a width of 6 inches (15.24 cm) and a m i n i m u m depth of 4 inches (10.16 cm) and a slope of 3 / 8 inches per foot of drain length, what is the m a x i m u m rate at which the tanks can be emptied without overwhelming the drain? What is the average velocity in the drain under the m a x i m u m flow conditions? Calculate these values in both English and metric units. S = 3 / ( 1 2 • 8) - - 0 . 0 3 1 2 5 dimensionless n -- 0.015 for concrete, dimensionless A -- 4 x 6 = 24 inch 2 -- 0.1667 ft 2 A -- 10.16 x 15.24 = 154.84 cm 2 = 0.01548 m 2 R = 0 . 1 6 6 7 / ( 2 0 / 1 2 ) = 0.1 ft R -- 0 . 0 1 5 4 8 / 0 . 5 0 8 = 0.0305 m
Q =
1.486A R0.667 S 0 . 5
=
1.486(0.1667)(0.1) 0.667 (0.03125) 0.5
n 1"486AR~176 O
__
n
= 0.628 ft3/s = 282 gpm
0.015 (0"01548)(0"0305)~176 0.015
- 0.01779 m 3 / s __
0.628 ft3/s (check) ___
V = Q / A = 0 . 6 2 8 / 0 . 1 6 6 7 = 3.77 ft/s
V = 0 . 0 1 7 7 9 / 0 . 0 1 5 4 8 = 1.149 m/s = 3.77 ft/s (check)
The design of open channels requires some trial and error. The following procedure is recommended. (1) (2) (3) (4) (5)
Estimate design flow based on 10 times average system flow. Select likely slope based on site conditions and guess trial channel dimensions. Compute flow. Compare estimated flow to required flow rate in step (1). If necessary, recycle to step (2) with new channel trial dimensions.
6.7 Momentum in pipes When a fluid flowing at constant speed changes direction there is a change in velocity. This is due to the vector property of velocity (magnitude and direction) as distinct from the scalar property of speed (magnitude only). A change in velocity of flowing mass requires an acceleration of that mass to rotate the velocity vector to the new direction. This requires outside forces at the bend to maintain static equilibrium. If these forces are not provided, the pipe will move until it either breaks or something provides the required forces. These forces are usually provided by thrust blocks placed at the bends, which are in turn secured to the ground or some other rigid structure. They are generally not provided for very small pipes with low fluid velocities, say below about 2 inches (4 cm) in diameter, as the pipe
98
o•
Channel Cross Section
/
Hydraulic radius (ft or m) = R=
flow cross-sectional area wetted perimeter
Slope (dimensionless) = S=
elevation A - elevation B horizontal channel length A to B
Fig. 6.4. Diagram for open channel flow. Method assumes constant channel cross-section and uniform slope. Flow area (ft2 or m 2) is function of flow area shape, for rectangle is channel width times flow depth. Wetted perimeter (ft or m) is function of channel shape (does not include free surface), for rectangle is twice the flow depth plus the channel width.
itself and the pipe hangers placed next to the bend can usually provide these balancing forces. We will consider only steady state flow (constant speed) in pipes of constant cross-section and laying in the horizontal plane. The horizontal assumption lets us assume that the pressure inside the pipe is the same on both sides of the bend. The only pressure loss would be due to frictional effects (pipe and bend fitting) and under most conditions, for the short distances involved from one side of the bend to the other, would be negligible. If one leg of the bend is in the vertical plane, there might, or might not, be an appreciable pressure change due to hydrostatic effects. We will also ignore the dead weight of the pipe and contained fluid, which can be very appreciable, which are in the vertical direction and must be supported at regular intervals by mountings or hangers. We will concentrate on the momentum effects, which, for our conditions, places all forces to be considered in the horizontal plane. We have to resolve all forces into x and y components. Static equilibrium requires that all forces in the x direction sum to zero and that all forces in the y direction also sum to zero. We will cut off a section of the pipe near the bend to determine the forces involved. The forces include the pressures times the areas of the two pipe cuts, the momentum effects and the reaction forces (Rx, Ry) required at the bend to sum to zero. The governing equations in the x and y directions are given below. In the x direction:
pO(Vxout-
Vxin) -~- Rx +
~__PAx --0
(6.11)
99 In the y direction;
,oQ(Vyout- Vyin) -~- Ry + Z P A y
-0
(6.12)
w h e r e p is m a s s d e n s i t y of fluid ( k g / m 3, slugs/ft3); Q is v o l u m e t r i c fluid flow rate ( m 3 / s , ft3/s); pQ is m a s s flow rate ( k g / s , s l u g s / s ) ; Rx, Ry is e x t e r n a l r e q u i r e d thrust forces in the x and y directions at b e n d s due to m o m e n t u m ; ~ P A x , ~-~PAy is s u m of p r e s s u r e times area (force) in the x and y directions. T h e m o s t likely a p p l i c a t i o n s of this section are for d e t e r m i n i n g thrust b l o c k r e q u i r e m e n t s at 90 d e g r e e and 45 d e g r e e e l b o w s . E x a m p l e 6.5 p r o v i d e s a n u m e r i c a l e x a m p l e of e a c h of these cases. N o t e the explicit definition of the cut-out e l b o w sections (control v o l u m e ) and the specified sign c o n v e n t i o n . Table 6.5 p r o v i d e s ' s t a n d a r d ' thrust b l o c k details for use with flowing water.
Example 6.5. Thrust block requirements at elbows due to momentum You have a 4 inch inside diameter pipe flowing seawater (p - 2.0 slugs/ft 3) at a speed of 5 ft/s in the horizontal plane. The pressure in the pipe around the elbow is measured to be 7 psig. Given the control volumes and sign conventions specified for each of the elbows below, solve for the required thrust block forces (Rx, Ry) for each elbow. These forces are shown on the sketches but without magnitudes or plus or minus directions, which remain to be determined. We must first solve for some more dimensionally useable numbers from the given data.
rcd2/4 - :r(4/12)2/4 = 0.0873 Q -- VA = 5(0.873) = 0.436 ft3/s
Cross-sectional area of pipe =
ft 2
P = 7 psig = 7(144) = 1008 lb/ft 2 (A) 90~ elbow
in PAin = PAx ~
I Ry
+y
5 fi/s~ I!
Rx +x
PAy 5 ft/s
l
x direction, Eq. 6.11
pO(Vxout- Vxin)+ Rx + EPAx --0 2(0.436)(0- 5 ) + Rx + 1008(0.0873) = 0 Rx = -83.6 lb minus sign means going to the left by the sign convention y direction, Eq. 6.12 pQ(Vyout - Vyin) § Ry + ~ , P a y : 0
2(0.436)(-5 - 0) § Ry -- -83.6 lb
Ry § 1008(0.0873) : 0
minus sign means going downward by the sign convention
100
Example 6.5. (continued) (B) 45 ~ elbow
i RY in
PAin= PAx --~ 5 f t / s ~
+y
~,
l-I!
, Rx
--X \ ~ 4 5 PAout
~
PAyout
PAxout
out~ s X
5 ft/s x direction, Eq. 6.11 pQ(Vxout- g x i n ) + Rx + EPAx - 0 in this case there are two components of E PAx, PAin and -PAout(COS 45) 2(0.436)(5 cos45 ~ 5) + Rx + 1008(0.0873) - 1008(0.0873 cos45 ~ = 0
Rx -- - 2 4 . 5 lb
sign says to the left
y direction, Eq. 6.12
pQ(Vyout- Vyin)-[-- Ry + }]PAy--0 2 ( 0 . 4 3 6 ) ( - 5 sin 45 ~ - 0) + Ry + 1008(0.0873) sin 45 ~ = 0 Ry -- - 5 9 . 1 lb
sign says downward
TABLE 6.5 Guideline for horizontal thrust block dimensions for average soil conditions up to 150 psi working pressure (based on Louis Berger and Associates, Consulting Engineers)
Plan
Pipe size
Tee H
4" 6" 8/I 10" 12" 16"
1' 1' 1' 1' 2' 2'
L 0" 0" 4" 8" 0I' 0"
2' 2' 2' 3' 4' 6'
0" 0" 8" 4" 0" 0"
Plan
90 ~ Elbow
45 ~ Elbow
H
H
1' 1' 1' 1' 2' 3'
L 0" 0" 4" 8" 0" 0"
2' 2' 2' 3' 4' 6'
0" 0" 8" 4" 0" 0"
1' 1' 1' 1' 2' 2'
L 0" 0" 4" 8" 0" 0"
1' 1' 1' 2' 2' 4'
undisturbed 4" 4" 6" 0" 2" 0"
Section A-A or B-B
Notes: (1) For pipes smaller than 4", use values for 4". (2) Tables are based on an allowable soil pressure of 3000 psi on undisturbed earth behind the anchor block; where soil has been disturbed by excavation or where soil cannot
101
Chapter 7
Pump Selection
7.1 Pump options There are many types of pumps (see Table 7.1), although very few of them are likely to be used as main supply pumps in culturing applications. Axial and mixed-flow pumps are widely used in aquaculture, but in low-head high-flow situations. These usually involve grow-out operations with ponds or raceways and open-channel flow distribution. Archimedes' screw pumps are much rarer but fulfill the same requirements. The highest flow rates of interest to us are at the lower extremity for all three of these type pumps. The vast majority of applications will use radial (sometimes called centrifugal) pumps. Determining the best type of pump for any given application depends on a non-dimensional parameter called specific speed (see Fig. 7.1). This parameter, as shown, is a function of the desired flow rate and head conditions. Some of the other pump types shown in Table 7.1, such as the reciprocating positive displacement pumps, while capable of pumping water, are not very likely to be encountered as main seawater supply pumps. Rotary cam and vane type pumps are often used for low pressure air blowers in culturing applications. Peristaltic pumps are commonly used as metering pumps at very low flow rates. Screw pumps are often used to transport and meter dry chemicals or feeds. Air-lift pumps are widely used to circulate seawater in tanks. Any project will have quantitative values for average, m a x i m u m and minimum flow requirements. The m a x i m u m and minimum values may be determined by daily or seasonal
TABLE 7.1 Classification of pumps for main seawater supply Radial
Also called centrifugal pumps, well suited for low-flow, high-head applications. Most common type used in seawater applications.
Axial
Also called turbine pumps, well suited to high-flow, low-head applications. Commonly used in large pond and raceway applications.
Mixed flow
Combination of axial and radial, with applications in between.
Reciprocating
These are positive displacement pumps and include piston and diaphragm pumps; can be used for very high head applications, not normally encountered in seawater systems. Also commonly used as metering pumps.
Rotary
These include screw, cam, vane, peristaltic and squeegee pumps. Archimedes's screw pumps are suited for high-flow low-head applications, others are encountered in auxiliary functions.
Miscellaneous
Air lift, jet, hydraulic ram pumps, none of which are likely to be used for main seawater supply; air lifts are used for circulation in tanks.
102 Axial Flow
o~
v
C)
OW
._o '4.--
LLJ E
o.oi
I
I
I
I
I
I
I
I
I
0.1
I
I
I
I
I
I
I
I
I
1.o
Specific Speed (Non Dirnensionol) Fig. 7.1. Specific speed and selection of optimum pump type: Specific speed - n Q ~ 075 H 0"75, nondimensional" n = pump speed in revolutions per second; Q = flow rate, ft3/s or m3/s; g -- gravitational constant, 32.2 ft/s 2 or 9.81 m / s 2" H - head across pump, ft or m.
requirements. They must include all auxiliary water requirements, and not just the flows required for life support. Auxiliary flow requirements such as for backflushing, cleaning tanks or refilling tanks can be significant. In addition to present values, there should be an idea of possible future requirements. The most severe problems will be encountered if the maximum and minimum values are widely different or if the pumping conditions are highly variable, such as in areas with high tidal variations. When the water requirements vary significantly with time of day, seasonally, or over the production cycle, variable speed motors for the pumps may be considered. However, these are expensive, may have reduced reliability, and complicate the operation and maintenance of the system. A far better method, the dominant one in practice, is to provide sufficient water flow to a head box, using it as a buffering device. High transient flow requirements can then be satisfied by temporarily drawing down the water level in the head box. Excess water during periods of low demand can be short circuited to drain or the input to the headbox reduced by a valve on the discharge side of the main pump. Wasting a little water is often a very acceptable price for gains in system simplicity and reliability. On centrifugal pumps, throttling the pump's discharge will actually reduce the power requirement. The problem is that the valve will have to be reopened if the demand increases. If the demands are highly variable and prolonged, multiple pumps can be installed. When demand is high, additional pumps in parallel can be turned on (see end of Section 7.4). However, turning on two pumps instead of one does not double the supply, since the frictional losses are proportional to the square of the water velocity. Pumps placed in parallel are often identical, but this is not a requirement. Mixing pumps of different capacities can increase flow-rate options and flexibility. However, there are restrictions on the selection of parallel pumps (see Section 7.4) and mixing types can complicate operations and maintenance. There are two separate reasons to install multiple pumps in parallel and it is very important to clearly differentiate these functions. One is to provide greater flow rate during periods of peak demand, which has already been discussed. The other is to provide redundancy in the form of a backup system in the event of failure of the primary pump. The backup equipment should never be used for flow peaking, except under the greatest emergency. If
103 one gets in the habit of depending on the backup for normal operations, it is no longer a backup but a primary. One has, in effect, increased the probability of failure by using multiple units, eliminated any backup capability, and increased the consequences of an uncompensated for failure by increasing the scale of operations. If greater flow is required, additional capacity should be installed. If during the design phase the consequences of failure were considered unacceptable without backup, increased scale is unlikely to alter this judgment. The temptation to use backup equipment in normal operations should be vigorously resisted as false economy. The number of pumps needed depends on several factors. If the flow demand is considered to be relatively constant, only one pump is needed. If the consequences of failure are severe, a second identical pump is needed as a backup. The two pumps are then alternated in service as primary and backup. This is a very common situation. If flow demand is quite variable, several pumps may be required to meet requirements under different operating conditions. If backup is needed, the backup pump should have the same capacity as the largest primary. The two largest pumps can then be alternated in service. In this case, the backup can compensate for the failure of any given pump. Lastly, there is the question of possibly future increased flow requirements. Due to the high cost of pumping equipment, there is reluctance to install capacity in the form of larger pipes and pumps for which there is no firm current requirement. What can be done is to design the piping system conservatively and provide floor space and access to piping for additional pumps without actually installing them. This has two additional benefits. It provides more working room around the equipment and enables replacement equipment to be installed without requiting prior removal of the older pump. This also avoids the high risks that may be associated with operating without a backup during the replacement process. If this additional floor space and access to piping have not been provided and the flow requirements increase in the future, the practical options to meeting the increased demand may be very limited. Adding floor space in a pump house or increasing the main line pipe sizes, can easily prove cost prohibitive and require that the whole system be shut down for an extended period of time. The practicality and flexibility of a pump system is dependent on more than just the selection of the pumps. It depends to a great extent on the accessibility to the pumps and internal critical parts (such as the impellers), capability to monitor pump performance, and flexibility of use inherent in the piping and cross-connections in the immediate area of the pumps. The diameter of the suction and discharge lines are often larger than the suction and discharge fittings on the pumps. The transitions from the larger pipes to the smaller fitting diameters should be as close to the pump as possible, especially on the suction side. This will minimize suction-side frictional losses (see next section). Provisions for maintaining, cleaning and back-flushing are usually provided in the piping around the pumps. Fig. 7.2 shows a typical pump installation. This example has two pumps in parallel, only one of which is intended to be 'on' at any given time. However, additional pumps could easily be added in parallel. This configuration also shows two intake lines and has the capability to back-flush either intake line using the other line with either pump or to back-flush the intake lines using water from the head or storage tanks. The capability to back-flush the intakes is helpful in removing sand and other debris that may collect in the lines and on the intake screens and to prevent water that has been standing in unused pipes from contaminating the system on start-up.
104
Suction Side ~ Pump House Wall Intake I Line 11 i i I Q,. Flong
......
.~-.-/-" ~
5
Reducer o n c l /"Union/Flange k,4 ~,,m,,
Discharge Side 2 and Expander
~
5
I
Vacuum
....
/C~'
,
aooe
^ ;<"
/ 9
I '
( \,
^ I-iT.
"L ~
.-'-
Union/Flange
9 ')Turn V~l ! 90d'i'urn . V " Small Valve ( Pump Exit I
Pump House Wall E,bow I tFlancjes I kl i -I 4
I/"4
3
-
~/I//
._.
I Hor,zonto, Run
Pum
Fig. 7.2. Generic pumphouse piping example. (1) Suction-side fittings should be the same size as the intake lines. This is more costly but reduces critical suction-side frictional losses and increases NPSH margins. Suction-side piping is in the horizontal plan and at a specified elevation. Considerable care is required to avoid any air leaks on this side, as they can cause mass mortalities due to supersaturation and, at higher levels, pump problems. (2) Discharge side is in the vertical plane followed by 90 degree elbow and horizontal run to point of use. (3) These valves must be ball or gate valves to allow use of pigs. With quarter turn full open to full close valves, water hammer is a serious threat. Operators must be cautioned to open and close valves slowly when the system is operating. (4) Pig launchers with arrows in launching directions. Provisions must be made to recover the pigs at the ends of the intake and discharge lines. (5) Crossing headers should have X and T fittings with threaded or flanged caps on unused faces for accessibility and cleaning. (6) Reducers and expanders are to transition the main pipe diameters to the inlet and outlet diameters of the pumps. There is a choice of unions or flanges. These will allow the disconnection and/or removal of the pumps without having to damage the piping system. The union/flanges may not be necessary if the adjacent valves have union ends.
There are some additional critical data that are required before anything definitive can be stated about the pumps. For the pumps, the most critical values are the water elevations, and distances of the pumps from the seawater supply, and from the points of application. Hopefully, the elevations and placement of the intakes, pumps, processing equipment, and headbox(es) as well as pipe diameters will be design variables that can be changed if problems develop during the design process. Matching pump selection to the conditions, which might be highly variable, is a very interactive and complex process (see Section 7.4, Walker, 1972). It is very easy to get into situations for which there are no acceptable alternatives.
7.2 Generic centrifugal pump Since the vast majority of applications of interest will use radial (centrifugal) pumps, it is necessary to consider the characteristics of such pumps. A centrifugal pump is a kinetic energy device, which accelerates water from a low to a high velocity and converts the velocity into increased pressure or head at the discharge. A centrifugal pump has no capability to lift water from a lower level, unless it has been primed and all air has been removed from the suction piping and pump body. While 'self priming' centrifugals exist, this capability is limited (specified by the manufacturer as a maximum vertical lift) and cannot always be relied upon, especially on the first start of a new pump. When starting or restarting centrifugal pumps with suction lift, one must assure that the pump is adequately primed or the pump may, after a period of time, self-destruct. It is usually very obvious when the pump 'catches'.
105 ~Shut Off Head
>,!
- Max. - ' E~'ciency ~ , ~ Po'mt ~ -
c-
._(2
.X
.-....--r--....Efficiency :
- Headat Max.E;,~c~ency Efficiency. . . . . . . . . . . -Head
\, \ .
- ~
LtJ
O
i
/9
O
Ix.
"
-Power
T"
at"M/ax.Efficiency. . . .
i
\ ~
~
" " "
-~.-=.--'~ ~ " ~ ' ~ -
~~-Power
:
\
izFIow at Max.Efficiency
..... 0
\
Flow Rate
Fig. 7.3. Generalized centrifugal pump curves. The pump may be primed by allowing water from a headbox to flow backward through the pump, connecting a vacuum pump to the pump suction or discharge, using a hand pump to backflow water through the pump, or by using an available freshwater source (the temporary salinity dilution in the head box will generally be insignificant). Backflowing water through a pump just before starting it may make the impeller rotate in reverse. Most, but not all, pumps can tolerate reverse rotation, so check with the pump manufacturer before attempting this procedure. Due to high head losses and biofouling problems associated with seawater, check or foot valves on intake lines are n o t recommended. Reciprocating pumps and other positive displacement pumps, are truly capable of self priming if the plunger and valves are tight. Centrifugal pump data are specific to each pump. For a given pump body, data are presented for a number of different impeller sizes and pump speeds (rotational rate, usually in rpm). A generalized pump curve is presented in Fig. 7.3. Usually a given pump and impeller are offered with various speed controllers, resulting in a series of essentially parallel curves for related equipment packages. Fig. 7.3 shows only one speed option to simplify presentation. Information on developed head, efficiency, and power is presented as a function of flow rate. The head across the pump (ft, or m) can be converted to a pressure across the pump using Eq. 6.1. Due to the wide number of pump body, impeller, and speed combinations available, the data catalogue from a single pump manufacturer may be 6 to 12 inches thick. The actual shape of the head capacity curve is critical to the pump selection process. In general, the head capacity curve decreases uniformly from high head/low flow to low head/high flow conditions as shown in Fig. 7.3. If the head capacity curve has a flat spot or decreases at low flows, the pump may not operate smoothly in this region either by itself or in parallel with other pumps. Another characteristic of centrifugal pumps is that as the head is reduced, both the flow rate and horsepower increases. Therefore, the maximum current requirement to the pump's electric motors will occur at exceptionally high tides and, unless the motors are sized for this increased load, they may trip out or burn up. If electrically
106 powered pumps have a tendency to trip breakers during unusually high tides, a remedy is to very slightly close a valve on the discharge, never the suction, side of a pump. This will reduce the electric power requirements to the pump motors. The minimum power requirements will occur under high head conditions, such as at low tide or operations against a partially closed valve. If a discharge side valve is completely closed, the flow is zero and the head will usually be at a maximum. This head is called the 'shut-off head'. The pressure (head) rating of all piping and components on the discharge side of the pump must be higher than this number or catastrophic system failure may occur. This mistake is often made when using plastic pipe and hose clamps. A centrifugal pump can be operated for short periods of time against a closed valve. If this operation is prolonged, the pump may burn up, as the frictional heat generated by the pump is no longer removed by the flowing fluid. When the discharge valve is opened, the initial slug of water might have an elevated temperature and pose a thermal shock threat to culture organisms if not sufficiently diluted before use or rerouted. Generally, centrifugal pumps function best around their region of maximum efficiency. Continuous operations far from this region and at the extremities of their performance envelope, is not recommended. It may be difficult to find a pump that will stay within its operating boundaries under all conditions likely to be encountered, especially if the site has a high tidal range. Centrifugal pumps require either stuffing boxes or mechanical seals to prevent excessive leakage around the pump's shaft. Stuffing boxes use soft plastic-like materials cut in rings and tightly fitted around the shaft or shaft sleeve. Stuffing boxes must be lubricated either by allowing some water leakage through the packing or by providing a separate cooling flow. The stuffing box must never be tightened to the point that cooling flow is stopped; otherwise the packing will overheat, shrink and fail. Stuffing boxes require continuous attention and small defects can prevent satisfactory operation of the pump. However, they are cheap and rarely fail completely without warning. Mechanical seals are much more varied in their designs and features. Seals are a technical specialty and the best course of action is to consult the pump manufacturer. The right choice of a mechanical seal is an excellent investment and can give many years of trouble-free service. Their reliability is very high but when mechanical seals fail, it is usually due to excessive vibration or misalignment, rather than any inherent seal defect. They can fail spectacularly, emitting high pressure streams of water. This can pose an electrical hazard. Spare seals for critical pumps are a good spare-parts item to have on-hand, especially if the equipment is remotely located. Mechanical seals can be lubricated with water or oil. If freshwater is not available, seawater has been taken from the discharge side of a pump filtered through a small cartridge filter and used successfully. Oil leaking into the seawater, even in minute quantity, might pose a hazard to delicate culture organisms. More acceptable mineral oil can usually be substituted. All such seal questions should be referred to the pump manufacturer before implementation. Centrifugal pumps are generally well behaved but can develop a number of problems, especially when operating conditions change. Table 7.2 is a useful trouble shooting chart for such equipment.
107 TABLE 7.2 Troubleshooting chart for centrifugal pumps (from Karassik, 1981, courtesy Marcel Dekker, Inc.) Ten pump symptoms
Possible problems (numbers defined below)
Does not deliver water Insufficient capacity Insufficient pressure Loses prime after starting Requires excessive power Stuffing box leaks too much Packing has short life Vibrates or is noisy
1 , 2 , 3 , 4 , 6, 11, 14, 16, 17,22,23 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 17, 20, 22, 23, 29, 30, 31 5, 14, 16, 17, 20, 22, 29, 30, 31 2 , 3 , 5 , 6 , 7 , 8 , 11, 12, 13 15, 16, 17, 18, 19, 20, 23, 24, 26, 27, 29, 33, 34, 37 13, 24, 26, 32, 33, 34, 35, 36, 38, 39, 40 12, 13, 24, 26, 28, 32, 33, 34, 35, 36, 37, 38, 39, 40 2, 3, 4, 9, 10, 11, 21, 23, 24, 25, 26, 27, 28, 30, 35, 36, 41, 42, 43, 44, 45, 46, 47 24, 26, 27, 28, 35, 36, 41, 42, 43, 44, 45, 46, 47 1, 4, 21, 22, 24, 27, 28, 35, 36, 41
Bearings have short life Overheats and seizes Forty-seven possible causes of problems
Suction problems 1. Pump not primed 2. Pump or suction not filled with liquid 3. Excessive suction lift 4. Insufficient margin between suction and vapor pressures 5. Excessive air or gas in liquid 6. Air pocket in suction line 7. Air leaks into suction line 8. Air leaks through stuffing box 9. Foot valve to small 10. Foot valve partially clogged 11. Suction inlet insufficiently submerged 12. Water seal pipe plugged 13. Seal cage improperly placed in stuffing box, not forming seal System problems 14. Speed too slow 15. Speed too high 16. Wrong direction of rotation 17. Total system head higher than pump operating range 18. Total system head lower than pump operating range 19. Specific gravity of fluid different from pump design 20. Viscosity of liquid different from pump design 21. Operating at very low capacity 22. Parallel pumps unsuited for operating conditions
Mechanical 23. Foreign matter in impeller 24. Misalignment 25. Foundation not rigid 26. Shaft bent 27. Rotating part rubbing on stationary part 28. Bearings worn 29. Wearing rings worn 30. Impeller damaged 31. Casing gasket defective, permitting internal leakage 32. Shaft or shaft sleeves worn or scored at packing 33. Packing improperly installed 34. Wrong type of packing for operating conditions 35. Shaft off-center due to worn bearings or misalignment 36. Impeller out of balance 37. Gland too tight, no flow of liquid to lubricate packing 38. No water provided to water cooled stuffing boxes 39. Packing being forced into pump interior, excessive clearance between shaft and casing at bottom of stuffing box 40. Dirt or grit in sealing fluid, scoring of shaft/shaft sleeve 41. Excessive pump thrust, likely due to mechanical failure 42. Excessive grease/oil in anti-friction bearing housing or lack of cooling causing high bearing temperatures 43. Lack of lubrication 44. Damaged, mis-matched or badly installed bearings 45. Dirt getting into bearings 46. Rusting of bearings due to water getting into housing 47. Excessive cooling of water cooled bearings, condensing atmospheric water in housing
108
7.3 NPSH and dynamic head For a centrifugal pump to operate, seawater must enter the eye of the impeller under pressure. This pressure is called the available net positive suction head (NPSH) and deals only with the suction side of the pump. The design of the intake suction side piping (see Dornaus, 1976) is particularly important in maximizing the available NPSH. This available NPSH is shown in Fig. 7.4. The frictional losses are the sum of the losses from the pipe, fittings and screen on the suction side and are calculated as discussed in Chapter 6. The vapor pressure of water increases with temperature, further reducing the available pressure at the pump. At a water temperature of 32~ (0~ it is 0.2 ft and at 100~ (38~ it is 2.2 ft. The atmospheric head at sea level is normally 33.9 ft (10.6 m). Storms can cause the atmospheric head to drop, and values of as low as 29.5 ft (9.2 m) are not uncommon during major storms. This is a loss of 4.4 ft (1.4 m). Seawater systems with small operating margins are most likely to fail due to suction side limitations when it is least convenient, which is during major storm events. Storm-related clogging of screens from seaweed and debris adds to the risk of system failure. The available NPSH is shown in equation form below. All components have dimension of length (ft or m). NPSHavailable -- H a -
(7.1)
M s - H f - Hvapor
where Ha is atmospheric head, Hs is static lift (elevation of centerline of pump minus elevation of water source) (can be negative if the water levels is above the pump), Hf is sum of all Vapor Pressure (ft) Friction Losses in Suction (ft) T Available NPSH (ft)
\
Useful Pressure at Surface (ft of Head)
l
Atmospheric Pressure at Surface
1 Water Surface
\ \ \ \ \ \ \ \
Fig. 7.4. Centrifugal pump with suction lift.
109 frictional losses on suction side of pump, Hvapor is vapor pressure (absolute) of fluid at given temperature. There are in fact two NPSH values. One is the available NPSH as defined by Eq. 7.1 and the other is the minimum required NPSH as specified by the pump manufacturer. The required NPSH is usually given with the pump curves as a function of flow rate (see example in Section 7.4). It is generally given for the highest speed available for a given pump. The required NPSH is a slight function of speed, but using the manufacturer's data will be conservative for the same pump and impeller operated at a slower speed. For proper operation of a pump, the available NPSH must be greater than the required NPSH. If it is not, the pump will not only produce little or no flow but will cavitate and may quickly self-destruct. If a cavitating pump operates for prolonged period of time, such as over low tide, it will tend to 'eat' pump impellers over the long-term (weeks to months). The appearance is like a rapid corrosion of the impeller requiting frequent replacement (weeks to months). Cavitation is often audible, in the form of a high pitched screeching. NPSHavailable must be greater than NPSHrequired
(7.2)
The problem is that the available NPSH is not a fixed or constant value. The frictional losses in the suction piping is dependent on both flow rate and time. This term is highly dependent on the degree of fouling on the screens and intake lines, which can vary with time. In addition, the static lift can vary with the tide and the atmospheric head with weather conditions. In short, available NPSH must be determined for a range of possible conditions. It must be greater than the required value under all possible combinations. Since many of the analytical methods lack precision, suitable minimum margins of available NPSH are strongly recommended. The margin should be no less than a few feet under the most severe set of operating conditions. Not meeting suction side requirements is the single biggest source of
pumping system problems. The major impact on NPSH limitations is determined by the choice of suction-side pipe diameters and the design elevation of the pumps. Continuous operation of an intake system in areas of high tidal range may require that the pumps be located below the high water or even mean water elevation. Construction may be very expensive and difficult, due to the volume of earth to be removed and site-dewatering problems. If the minimum elevation of the pump is raised, due to cost or construction considerations, the system may not be operable over the complete tidal cycle. The total dynamic head (TDH) of a seawater system is sometimes called the system head and is equal to the head across the pump. It is defined below in Equation 7.3. TDH-
Z 2 -
Z 1
-+- hps + hfs + hpd + hfd -+- vZ/2g
(7.3)
where Z 2 is elevation of discharge at head tank (fl, m), Z1 is elevation of ocean surface (ft, m), hps is frictional losses in suction piping (ft, m), hfs is frictional losses in suction fittings (ft, m), hpd is frictional losses in discharge piping (ft, m), hfa is frictional losses in discharge fittings (ft, m), V is average pipe velocity at discharge to headtank (ft/s, m/s), and g is gravitational constant (32.2 ft/s 2, 9.81 m/s2). TDH is the sum of the static lift from water source to line discharge (often an elevation slightly above the water level of the headbox) and all frictional losses from intake to line discharge. The velocity term is often negligible. These frictional losses include piping, fittings
110 and processing equipment on both the suction and discharge sides of the pump (see Chapter 6). The pump itself is ignored in these calculations. Since the frictional losses will be a strong function of flow rate, these calculations have to be done for a range of flows. This will produce a locus of values as a function of flow rate for a given set of operating conditions. Both biofouling and tidal elevations can introduce major variations into these calculations, requiring the calculation of completely new curves. It is of course impossible to do these calculations at all, unless the piping system has been completely defined as to lengths, diameters, fittings, elevations, etc. The iterative nature of the problem is due to the fact that you need a feel for the outcome from these calculations before you can specify the inputs. If any operating conditions change or if the specifications of any components in the lines are changed or altered, the calculations have to be redone. If frictional losses increase by fouling, someone partially closes a valve, or smaller diameter components or greater pipe length are introduced, then the new curve will swing to the upper left side. Decreased tidal elevations will have the same effect. If the tide rises or frictional losses are less than expected, it will swing towards the bottom right. Even for a completely specified system, there are many different piping configurations and operating conditions. A single valve in the system represents a continuous range of possibilities. Each of the possible combinations will produce different systems curves. Needless to say, this can require a great deal of 'number crunching'. No amount of computer help can make up for wrong assumptions or incorrect input values.
7.4 Matching system and pump The operating point for a piping system and pump in combination is where the pump head curve intersects the system's head curve. At this point the total dynamic head is equal to the head across the pump. The operating point is specific to a fixed piping system configuration, operating conditions and pump impeller and speed. With the specified system, the operating point is the only possible set of operating conditions, IF the pumping system is pumping at all. In short, if it is pumping, it will do so only at the specific flow rate and TDH. If the pump impeller or speed is changed or there are any changes in the system or conditions, the operating point will move. Given a spectrum of possible system curves, the task is to find a pump that will meet the flow requirements and remain within its operating constraints under all conditions. There are regions of TDH and flow rate where it is difficult to find pumps. Even in the more usual regions, the choices may not represent a continuum. In order to find a match, the system specifications may have to be modified. Reduction of suction-side frictional losses or lowering the elevation of the pumps are two of the most common changes. Sometimes, due to cost constraints, there will be evaluations of possible changes towards smaller or cheaper components and elevations with reduced construction requirements. These cost-reducing exercises may require changes in operating approaches. A common option in areas of high tidal variation is only pumping over a portion of the tidal cycle. While this may reduce construction costs, larger pumps and piping as well as greater storage capacity will be required to maintain the same average flow rate. In short, the system and pump are an iterative design problem with many considerations. The pump and system matching process can best be illustrated with an example. The site and system information is presented in Example 7.1. This site had a high tidal variation and
111
E x a m p l e 7.1. Developing the systems curve m low tide The system is completely specified including pump and water elevations. The total dynamic head (TDH) for the specified system and conditions is tabulated below. These TDH values as a function of flow rate are then graphically plotted on the selected pump curve (Fig. 7.5) to determine the interactive operating point of about 125 gpm between the pump and system at a very low tide.
System specifications Tidal elevation = MLW - 2 ft Height of pump datum above MLW = 15.0 ft Height of water level discharge above MLW = 40.0 ft Suction lift = 17.0 ft Pump discharge lift -- 25.0 ft Total lift -- 42.0 ft Hazen-Williams coefficient for pipes = C -- 100 Length of 6 inch intake pipe = 575 ft Length of 6 inch pump discharge pipe = 70 ft Sum of K values for fittings/transitions - - 6 inch intake = 1.2 Sum of K values for fittings/transitions - - 6 inch discharge = 20.4 Assumed water temperature of 82~ Flow (gpm)
0 50 100 150 200 250 300 350 400 450 500 550
Velocity (ft/s)
Suction head losses (ft)
Discharge head losses (ft)
suct.
disc.
pipe
fit
pipe
fit
0.0 0.6 1.1 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.5 6.1
0.0 0.6 1.1 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.5 6.1
0.00 0.26 0.93 1.98 3.37 5.09 7.13 9.49 12.15 15.11 18.36 21.90
0.00 0.01 0.02 0.05 0.09 0.14 0.21 0.28 0.37 0.46 0.57 0.69
0.00 0.03 0.11 0.24 0.41 0.62 0.87 1.16 1.48 1.84 2.23 2.67
0.00 0.10 0.39 0.88 1.56 2.44 3.51 4.78 6.24 7.90 9.75 11.80
NPSH avail. (ft)
TDH (ft)
16.0 15.7 14.9 13.7 12.1 10.1 7.7 5.0 1.9 - 1.6 -5.4 -9.6
42.0 42.4 43.5 45.1 47.4 50.3 53.7 57.7 62.2 67.3 72.9 79.1
an average flow requirement of about 150 gpm (9.5 l/s). The normal extreme tide over a year ranged from - 2 to 18 ft relative to mean low water (20 ft or 6.3 m tide). This is a relatively severe requirement for continuous operations. Fortunately, it was on a very benign coast, with very low probability of additional storm effects. It was necessary to design for both the extreme low-tide (Example 7.1) and high-tide (Example 7.2) operating conditions. Note that both the suction and discharge sides are completely specified as to lengths, pipe roughness and loss coefficients of fittings and transitions. At high tide the pump is below the water level with a suction head. The TDH data from the tables for low and high tide are plotted over the pump curve for a specific pump in Fig. 7.5. Note that the pump is specified not only as to model but also as to impeller and speed. All the data irrelevant to this specific set of conditions have been
112
Example 7.2. Developing the systems curve - - high tide This physical system is the same as specified in Example 7.1, except that it is operating during a very high tide. This alters only three specifications as given below. The high tide TDH values are graphically superimposed on the selected pump curve (Fig. 7.5) and yield a high tide operating point of about 290 gpm.
Altered System Specifications (all others as given in Example 7.1) Tidal elevation = MLW + 18.0 ft Suction lift = - 3 ft (suction head) Total lift --- 22.0 ft Flow (gpm)
Velocity (ft/s)
0 50 100 150 200 250 300 350 400 450 500 550
Suction head losses (ft)
Discharge head losses (ft)
suct.
disc.
pipe
fit
pipe
fit
0.0 0.6 1.1 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.5 6.1
0.0 0.6 1.1 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.5 6.1
0.00 0.26 0.93 1.98 3.37 5.09 7.13 9.49 12.15 15.11 18.36 21.90
0.00 0.01 0.02 0.05 0.09 0.14 0.21 0.28 0.37 0.46 0.57 0.69
0.00 0.03 0.11 0.24 0.41 0.62 0.87 1.16 1.48 1.84 2.23 2.67
0.00 0.10 0.39 0.88 1.56 2.44 3.51 4.78 6.24 7.90 9.75 11.80
60 ~--~//~)C,~r 50 - ~ ~ r v e / l ~
.s~e~~
1=)
o I
TDH (ft)
36.0 35.7 34.9 33.7 32.1 30.1 27.7 25.0 21.9 18.4 14.6 10.4
22.0 22.4 23.5 25.1 27.4 30.3 33.7 37.7 42.2 47.3 52.9 59.1
M
~
g ;~)5;Pr;mm'ng9'ff[
o,,o. . . .
40 -4--
NPSH avail. (ft)
_
Operoting Point~ ~ . .
~
30
2O
NPSH 21.6' Margin
(Avai lable NPSH 125gpm,mlw-2'
0
I
50
I
100
I
t50
I
200
I
250
Flow Rate g pm
I
300
I
350
I
400
I
450
Fig. 7.5. System operating points. Gorman-Rupp T3A-B pumps with 8~3 inch impellers and speed of 1350 rpm.
113
-8
~
o
h, n
-6
SystemCurve (SpecifiedSystem
~
PumpCurve \ for OnePump \ Operating_.~ " ~'\~ ~~llIA
~andConditions) ~
~
D.... r- .... "I x'/ror%o~u~p s i
~
ating
FlowA FlowB Flow Rate Fig. 7.6. Two identical pumps in parallel. The curve for a single pump is supplied by the manufacturer but the curve for two in parallel must be developed from the supplied information. At every value of pump head, such as hi shown, the value of the flow rate for two pumps can be found by doubling the value X for a single pump to develop the two pump curve. The system curve is the same as developed for finding the operating point with one pump operating (A). The operating point for two pumps operating is seen to be the intersection of the systems curve and the two pump curve at point B.
removed from the figure. The limits of the pump's operating range and the required NPSH have also been specified by the manufacturer and are also shown in Fig. 7.5. The operating point at low tide produces a flow of about 125 gpm (7.9 l/s) and 290 gpm (18.3 l/s) at high tide. Intermediate tidal elevations will fall between these extremes. Computation of total or average flows over a day will require the estimation of tidal elevations and resulting flow rates at periodic intervals, such as hourly, over one or two tidal cycles, depending on if there are equal or unequal daily tides. The N P S H margin between the available and required N P S H is 10.1 ft (3.2 m) at low tide and 21.6 ft (6.8 m) at high tide. These are very ample margins and allow for biofouling and other contingencies. At low tide the suction lift is 17 ft, which is below the m a x i m u m repriming lift of 19 ft specified by the manufacturer for the stated pump speed. Irrespective of the margin, the operator should always assure the pump's 'catching' before going on to other things. Another c o m m o n situation is where more than one pump in parallel is 'on' at any given time. If pumps are identical or have identical head curves, there usually will be no problems. The important point is that the second pump must have a shut-off head higher than the existing head in the pump discharge manifold or it will not be capable of starting. If we assume two identical pumps in parallel, each with a head curve as shown in Fig. 7.6, and a single pump operating point given as point A, what will be the capacity if both are turned on simultaneously? This is a c o m m o n question. The pump curve for both pumps operating together must be constructed. This is done by adding their capacities at every value of head. The systems curve, assuming no changes in the system or external operating conditions, will now form a new operating point at intersection B. This may or may not be close to a doubling
114
of flow depending on conditions. If the systems curve intersects the single pump operating curve near its shut-off head the gain from the second pump will be small and very possibly outside of the operating requirements. If point A is at a small fraction of the shut-off head, the gain may be large. This is important to consider, if adding pumps in the future is a serious possibility. A little extra initial expense, in the form of larger pipes and fittings, especially on the suction side, producing lower system frictional losses, will buy options for the future as well as reducing energy costs in operations. If in the future, more flow is desired, one possible way to get it is to install a larger pump motor with a higher rotational speed. This approach is usually relatively cheap compared to adding an additional pump in parallel. If the original design was conservative, especially on the suction side, it will often work. This is one reason that suction side piping is often of
Example 7.3. Changing pump speeds You are given a system to p u m p seawater (35 g/kg, 40~ as shown. The given pump curves indicate a choice of two speed controllers for the selected pump. All the piping is 12 inch ID with a resistance coefficient f -- 0.01, suction side length of 300 ft and a discharge of 500 ft. The intake/screen has a K -- 5.0 and the discharge above the reservoir has a K = 0. The systems curve (Eq. 7.3) has already been calculated and is shown superimposed on the p u m p curves. 50'
EL = 30" ...... ,,v-~/x_/-,/'xA ....... EL = 15'
-.~mf"
(a)
\\\\\~x\\\\\\\
100 Pump Model XYZ Impeller Diameter = 6 in
80
:trevm
60
40 10 20 NPSHRequired
(b) 0
I
I
I
I
I
2
4
6
8
10
Flow (ft3/s)
0 12
Z
115
Example 7.3. (continued) (A) If the 1134 rpm speed controller is chosen and the pressure differential across the pump is measured in operation to be 19.1 psi, what is the seawater flow rate, the required net positive suction head at the pump intake and the average velocity in the pipe? / Head across pump = pressure/specific weight -- (19.1)(144)/64.1 -- 42.9 ft. Specific weight from Table A-3. Note that this head corresponds to that at the 1134 operating point confirming the validity of the systems curve. Intersection of system curve and pump curve for 1134 rpm, read Q = 4 ft3/s. By reading down from the operating point to the NPSH required curve and then to the scale at right, the required NPSH = 4 ft. V = Q/ar ea = 4(4/rr D 2) -- 5.09 ft/s (B) At the 1134 rpm speed, what is the NPSH available for this system. Assume an atmospheric pressure for a stormy day at 14.0 psi and a vapor head at 40~ -- 0.28 ft. Atmospheric head = (14.0)(144)/64.1 -- 31.5 ft Suction side frictional losses -- pipe (Eq. 6.2) + fittings (Eq. 6.6) h -- (5.09)2(0.01)(300)/(2)(32.2)(1) + (5.09)2(5.0 + 3(0.9))/(2)(32.2) h = 1.21 + 3.10 = 4.31 ft suction side frictional losses Eq. 7.1, available NPSH = 31.5 - 15 - 4.31 - 0.28 -- 11.91 ft (C) Does the system above meet its suction side requirements? What is the value of the NPSH margin or deficit? Required NPSH -- 4 ft Available NPSH = 11.91 ft Eq. 7.2, the available NPSH must be greater than the required NPSH Yes, suction side operating requirements are met, margin of 11.91 - 4 = 7.9 ft (D) More flow is required and you change the speed controller to 1332 rpm. Nothing in the system or pump has changed except the pump's spin rate. Graphically determine the new flow rate, the required NPSH and head across the pump. The new flow and pump head could also be calculated by assuming the pump's discharge and head coefficients to be constant. Intersection of system curve and pump curve for 1332 rpm, read Q -- 7 ft3/s Required NPSH -- 5 ft and TDH or head across the pump = 59 ft (E) Is the predicted performance above actually attainable? V = Q / A -- 7/0.785 = 8.91 ft/s New suction side losses = ((8.91)2/(2)(32.2))(3.0 + 7.7) -- 13.2 ft Eq. 7.1, available NPSH = 31.5 - 15 - 13.2 - 0.28 -- 3.02 ft Required NPSH - 5 ft Eq. 7.2 not met Available NPSH less than required NPSH by deficit of 5 - 3.2 - 2.3 ft deficit
System as specified will not work at 1332 rpm Note that manufacturers of NPSH required numbers are usually quite conservative and this pump under these conditions might in fact pump water with the specified flow and head but one should not count on it.
larger diameter than the discharge piping. Note that in Example 7.3, both the suction and discharge piping is of the same diameter. In this example, the system does not meet its NPSH requirements at higher pump speeds. Unfortunately, major concerns with initial cost result in
116 systems that are NPSH limited both at faster speeds and with added pumps in parallel. This type of system has limited expansion potential without major costs. The savings in the initial costs are often relatively small.
117
Chapter 8
Materials Selection
8.1 Biological constraints Selecting materials for use in marine culturing systems involves several major sources of problems. One set of constraints is due to the potential toxicity of many common construction materials. Materials may leach out or release specific ions, chemicals, or corrosion by-products from their surfaces. These released substances, in most cases, may not be clearly identified. The rates of release depend strongly on natural conditions (temperature, water velocity, dissolved oxygen level, pH, etc.). The rates may also be time-dependent, being generally highest with 'new' materials. Whether these released materials are toxic to a marine organism is an important subject, but one for which hard answers are often lacking. Toxicity is not only species-specific, but also a function of the total environmental conditions and the specifics of the age, genetic strain, history, and present health of the target organisms. At high levels, the effects are obvious m mortality. Considerable data are available on lethal levels of many substances, although these chemical forms might be somewhat different from those released from construction materials and the interpretation of the data to real situations is often very debatable. At lower levels, toxicity may result in reduced growth, susceptibility to disease or cannibalism and decreased survival rates. These symptoms may not even be obvious and it may be difficult to separate potential materials-related problems from other chronic stresses producing the same effects. There are very little direct data on toxicity of potential seawater system materials on delicate organisms, and what data exist sometimes seems contradictory (see Appendix F). Most of these data have been generated from short-term tests for lethal effects on marine phytoplankton. The assumption is that marine phytoplankton are very sensitive and can be used as a limiting case or 'representative' organism. Whether delicate larval forms of many marine animals are less sensitive than phytoplankton under any given set of circumstances, is certainly debatable. In the absence of more specific data, the algal data as summarized by Blankey (1973) can be used as a preliminary material selection guide for biological acceptability (see Table 8.1). There are no construction materials that are acceptable for all purposes, especially for culturing of larval forms and for research applications. This even includes plastics and glass, which may be toxic to some degree. Toxicity can be primarily temporary or it can be more permanent. Even such common seawater system materials such as polyethylene and polyvinyl chloride, are usually initially toxic and should be conditioned in running seawater for at least 2 weeks before use with marine organisms. The reduction in toxicity can be due to the removal of surface coatings (sometimes applied to prevent the sticking of hot plastics to other surfaces during manufacturing), the leaching out of solvents from the near surface, or by the formation
118
T A B L E 8.1 Effects of materials on algal cultures (from Blankey, 1973) Material
Safe
Inhibitory
Toxic
Acrylic (Lucite, Perspex, Plexiglas) A l u m i n u m alloy Charcoal, activated Copper alloy Cotton Epoxy resin Iron M e m b r a n e filter (Millipore, Membranfilter) Nylon Paraffin Plywood Polycarbonate Polyethylene, black Polyethylene, white, clear Polypropylene Polystyrene Polytetrafluoroethylene (Teflon, etc.) Polyurethane foam Polyvinyl chloride Polyvinyl chloride (Tygon, clear) Polyvinyl chloride (Tygon, black) R u b b e r - white, black, green, Buna N, neoprene, etc. Silicone (stoppers, tubing, stopcock grease) Silicone (cement, sealant) Solder, silver Solder, soft Stainless steel Titanium
abdde eeeeeee ee b ee ab be d f e ab abe b abe aa abcee e abeee e ee e eeeeee e
bg e e a d a aa e aab d abd b a -
eee a ab e aaaabee b aaaaaaaaabcee e -
Each letter represents the result of one test of a specific formulation or product, as reported by the indicated author (see references below). Where more than one species was tested by an author, the most adverse result is tabulated. All tests were marine except those of references c and e. This table should only be used as a general guide, as specific manufacturer and product formulation, prior treatment of materials, and conditions of use can dramatically alter the acceptability of materials.
References: a. Bernhard, M., A. Zattera and E Filesi, 1966. Suitability of various substances for use in the culture of marine organisms. Pubbl. Sta. Zool. Napoli, 35: 89-104. b. Blankey, W.E, Unpublished observations. c. Davis, E.A., J. Dedrick, C.S. French, H.W. Milner, J. Myers, J.H.C. Smith and H.A. Spoehr, 1953. Laboratory experiments on Chlorella culture at the Carnegie Institution of Washington, Department of Plant Biology. In: J.S. Burlew (Ed.), Algal Culture From Laboratory to Pilot Plant. Carnegie Inst. Washington Publ. #600, pp. 105-153. d. Doty, M.S. and M. Oguri, 1959. The carbon-fourteen technique for determining primary plankton productivity. Pubbl. Sta. Zool. Napoli, 3 l(Suppl.): 70-94. e. Dyer, D.L. and D.E. Richardson, 1962. Materials of construction in algal culture. Appl. Microbiol., 10: 129-132. f. Lewin, J., 1966. Physiological studies of the boron requirement of the diatom, Cylindrotheca fusiformis Reimann and Lewis. J. Exp. Bot., 17: 473-479. g. Ryther, J.H. and R.R. Guillard, 1962. Studies of marine planktonic diatoms. II. Use Cyclotella nana Hustedt for assays of vitamin B-12 in seawater. Can. J. Microbiol., 8: 437-445.
119 of protective coatings, which separate the seawater from contact with the toxic material. In the past, lead pipes were often used in marine laboratories because they were readily acceptable after such aging due to the impermeability of the surface oxide. However, if the mechanism is a protective coating, a 'good' cleaning could renew the toxicity. Machining-off or removing the surface layer of a seawater-aged plastic pipe may rejuvenate the toxicity. When there is any doubt (there always will be doubt, if one is dealing with sensitive organisms), a sample of the material from the same batch as is to be used, after pre-leaching in running seawater, should be tested for toxicity with the culture organism. If the test organisms die, the materials are not acceptable. All adhesives, paints, and coatings that are to be used should be similarly tested. The 'same batch' requirement is due to the fact that manufacturers, especially of plastics and adhesives, often change their formulations or manufacturing processes without notification. In the U.S., the Environmental Protection Agency is requiting all sealants, paints, and coatings to be reformulated to reduce Volatile Organic Carbon (VOC) releases. This may be far worse as instead of high initial toxicity followed by acceptable toxicity, there may now be long-term chronic effects from the new formulations. One batch may be good and another bad. Some synthetic materials exhibit persistent toxicity and should be avoided. For example, Hyperion tank liners in seawater have been found to be toxic to marine phytoplankton for more than 2 years. The possibility of long-term subtle effects, even from 'acceptable' materials may still exist. While it is generally considered good practice to eliminate all metals from contact with culture water, this is often not done. It is difficult, if not impossible, to acquire high-precision, high-temperature, and high-strength parts made of more biologically acceptable materials, especially at reasonable costs. These materials are often not basically suited for these types of uses, although composite technology is advancing rapidly. Some metals, such as titanium, appear to be biologically inert and therefore biologically acceptable. Titanium heat exchangers, while expensive, are found in a number of seawater culture systems. Other metals, particularly steel and cast iron, are commonly used, because they are cheap and available, compared to more preferred materials. While rust may be unsightly, steel and cast iron have little or no direct toxicity and in modest amounts rust may often be biologically acceptable. In particular, it may be possible to get relatively cheap and reliable pumps made from these materials. Stainless steel components are also commonly used, particularly 316 stainless steel, because a considerable amount of industrial equipment is available in this material. Stainless steel will corrode in seawater under some conditions (see Section 8.2) and its corrosion products are toxic. Stainless steel components should only be used with considerable caution. Even potentially objectionable materials, such as copper alloys, can be safely used in small quantities if the seawater flow is high and the contact time with the water is short (Huguenin and Ansuini, 1975). An individual brass or bronze fitting or valve under conditions of high flow rate might be used, due to its availability, without any apparent ill effect. However, it is important to remember that if flow rates decrease, toxicity problems may result. As a general rule, the amounts of potentially toxic materials in the system should be reduced to an absolute minimum. Flow-through systems can often take small amounts of objectionable material without ill effects, but this is not true in reuse loops. Metallic ions, organic solvents, and other leachates can quickly build up to dangerous levels. While the clinical signs might be obvious, identifying it as a material problem and then identifying the specific source may be very difficult. As has been discussed, all materials can be potentially toxic or objectionable under
120 some conditions and great caution must be exercised. Material toxicity problems produce clinical signs that are similar to many other sources of culture stress.
8.2 Seawater constraints One set of constraints involved with the selection of materials for use in marine culturing systems is due to the engineering properties and life time of materials immersed in seawater. Unfortunately, most materials dissolve or corrode to some degree in seawater, some faster than others. In addition, seawater often contains organisms, both large and microscopic, that like to eat, burrow into or otherwise destroy materials, including wood, concrete and synthetic materials. In addition, there are natural processes associated with seawater that physically and chemically destroy materials. These include abrasive particles in high current flows, wave forces, biofouling effects and a number of possible problems from ice. Thus, it is often difficult to find biologically acceptable materials that will meet the engineering requirements and last for long periods of time in seawater. Selecting marine materials is an engineering specialty (Tuthill and Schillmoller, 1965; Dexter, 1979) and may require special assistance, especially for large projects. On exposure to air or oxygenated water metals will form oxides. Most of these oxides are protective, in the sense that their formation slows or inhibits further corrosion. The notable exception is carbon or structural steel, where rust does not preclude deeper oxidation. For many metals, corrosion tends to be uniformly distributed over the material, such as with copper alloys, and for others, such as stainless steels, all the corrosion tends to occur at specific places in the form of deep pitting. Most of these oxides are relatively soft and can be removed by water flow, especially if the flow contains abrasive particles. Therefore, corrosion rates for most metals increase with increasing fluid flow. The exceptions are the chromium (including 316 and 304) and nickel (400 series) stainless steels, which have very hard oxides and much higher corrosion rates at very low velocities and under stagnant conditions. For the stainless steels, lack of flow inhibits the removal of the acidic corrosion products from the bottom of the pits and reduces the transport of oxygen into the pits needed to form the protective oxides. These low oxygenated areas that promote rapid local corrosion can also occur in corners, cracks and under washers, nuts or biofouling. This mechanism is called an oxygen concentration cell or crevice corrosion. In stagnant water, stainless steels can corrode very quickly. This can be important when pumps with stainless steel components are turned off. All corrosion mechanisms are also temperature-dependent and higher temperatures increase corrosion rates. If two conductive materials are immersed in seawater and electrically connected, a battery or galvanic cell is formed. These conductive materials include not only the metals, but also carbon, which is a common material for heat exchangers and pump linings. In such a cell, the more electronegative material will be the anode and will corrode. The more electropositive material will be the cathode and will be protected from corrosion. Fig. 8.1 shows the relative potentials of common marine materials. While the precise values of electropotential are dependent on velocity and temperature, the relative positions of the materials will not be substantially altered for different conditions. Table 8.1 is therefore useful even at conditions other than those specified. Note that the potentials are not points but ranges of values. These values cover the variability of cleanliness, surface oxides and composition from different
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122 sources for the given material. In any combination of two materials, the one on the fight will corrode and the one on the left will not. If their ranges overlap, you cannot be sure which one will in fact be the anode. The stainless steels have two ranges of values. The one on the fight is called the active state, and is often associated with stagnant water conditions, low dissolved oxygen, and rapid corrosion. The one on the left is the passive state. Another factor affecting the corrosion rate on the anode in a galvanic cell is the relative exposed surface areas of the anode and cathode. This is called the area ratio. If the corrosion rate (in thousands of an inch/year or mg/cm 2 per year) is X with both materials having the same area, and the cathode area is then increased to 10 times the anode area, the corrosion rate will now be about 10X. The converse linear proportionality also holds. If the cathode area is reduced to 1/10 of that of the anode, the corrosion rate on the anode drops to about 1/10X. Small dimensionally critical components (shafts, beatings, seals, impellers, etc.) should be designed to be the cathode and the large dimensionally non-critical parts to be the anode. Also the cathodes should be painted and anodes should generally not be painted or covered. Small 'holidays' in the coating of the anode may see a very large and unfavorable area ratio and experience a phenomenal corrosion rate. The bi-modal behavior of the stainless steels coupled with an unfavorable area ratio as they switch from cathode to anode explains why these materials may be satisfactory for a long period of time and then suddenly will corrode rapidly. This is most common with stainless impellers in pumps that have been 'off'. There are a number of other marine corrosion mechanisms but they would rarely be encountered in seawater culturing systems. For these less common forms of corrosion see Tuthill and Schillmoller (1965).
8.3 Piping materials Table 8.2 presents the most common piping materials used in seawater culturing systems. While they all have been successfully used, the labels can represent a wide variety of different chemical compositions, mechanical properties and physical characteristics or forms (see Dexter, 1979). The caveats in Section 8.1, about the biological acceptability of any components made from these materials, must be assured on an individual basis. These materials are used because they are available from other types of applications. Occasionally more exotic piping materials (glass, Teflon, etc.) are used in culturing systems but are generally very expensive and available components are limited. Rigid PVC is probably the most common piping material. It is widely used in wet lab areas for seawater distribution and drainage. It is available with thick walls for threaded applications (Schedule 80) and thinner walls (Schedule 40) for joining by solvent welding or flanging. Because of its rigidity, it is not particularly suitable for in-ground or offshore placement. Uneven bedding support will cause stress concentrations and distortions in the pipe and it is not flexible enough to adjust to the existing profile without failing. It is also prone to cracking, especially when cold. An additional hazard on the suction side of pumps is minute leaks in the many couplings required to join PVC pipe. Any air leakage could lead to mass mortalities due to gas supersaturation. Water leakage into the system could also be detrimental. PVC piping is readily available, easy to work with and is usually affordable. However, when comparing costs on piping materials it is necessary to include the many required couplings, which can significantly increase the cost.
123 TABLE 8.2 Common seawater system piping materials Name
Properties
Uses
Polyvinyl chloride (PVC)
Extremely versatile, wide range of properties
Rigid forms used in wet lab and pump house
Polyethylene
Usually flexible, range of density, toughness at low temperature, large diameters
Main supply and discharge, wet lab, outdoors
Acrilonitrile butadiene styrene (ABS)
Impact resistance, toughness, dimensional stability under load
Small to medium pipe and fittings, discharge
Polypropylene
Low density, fatigue resistance
Small pipe and fittings
Fiberglass
Higher strength and temperature capability than plastics
Where plastics inadequate
Concrete
Versatile, variable properties, to large diameters
Discharge piping
Lined steel
Mechanical properties of steel without direct contact with seawater
Around pumps and equipment
Steel
High strength, good impact resistance, rigid and cheap
Main intake lines, around pumps and equipment
Polyethylene is probably the most common piping material for main seawater and drain lines and is available in different densities, of which the higher densities are more commonly used in marine applications. It is also available in different wall thicknesses with different pressure ratings and in a wide range of pipe sizes. Since it is widely used for industrial and municipal water distribution, it is readily available and relatively cheap. It can be very quickly welded together by thermal fusion, but requires special equipment. Fusion-butt joints are usually neat and stronger than the basic pipe. Long sections can be quickly joined into a homogeneous flexible pipe. It is available in individual lengths or it can be shipped prefabricated to the correct length with flanged ends and coiled with a radius of about 15 pipe diameters. Its flexibility makes handling and deployment easier and allows it to adapt to gradual changes in the bedding of a prepared trench. Solid joints make it attractive for suction-side applications, greatly reducing the possibility of air ingestion and gas supersaturation. It is likely to be the preferred pipe material for offshore intake and discharge piping for both practical and economic reasons. One potential problem with all the plastics, high density polyethylene in particular, is the possibility of collapse under partial vacuum on the suction side of a pump. The problem is not the pressure rating of the pipe but the care with which these sections are emplaced. If the pipe is bent or has a flat spot or out of roundness (ellipticity) due to local stresses, it will be much more prone to collapse. All bends should be very gradual. The solution is thicker walls on the sections near the pumps and careful installation (see Fig. 5.4). Fiberglass piping is generally used when the strength or pressure ratings of the plastics prove to be inadequate. It is also useful for higher temperatures than most plastics. Generally,
124 temperatures above the practical range for plastic pipe are not common in culturing systems. Exceptions are at the seawater discharge of heat exchangers or in low pressure air distribution system fight near the compressor. High temperatures will tend to weaken and melt the plastics and will also tend to leach out any volatile components in the plastic, with possible resulting toxicity. Fiberglass is more expensive than any of the plastics and is not as readily available. Concrete pipe is widely used industrially, readily available and usually rather cheap to purchase. It is variable in its properties and may be reinforced or not reinforced, and comes in large diameters. When its cost is compared to other large diameter pipes, it usually is at least initially attractive. However, transportation and installation costs of concrete pipe are significantly higher than for plastic or fiberglass pipe. Concrete pipe is heavy and hard to handle. For large diameter pipe, installation may require specialized equipment and experienced contractors. In addition, because of sealing problems between sections and the high probability of air or water leakage, it should not be used on the suction side of pumps. Steel pipe with an inside liner of plastic is an attempt to get the biological and chemical advantages of the plastic lining material and the mechanical and cost advantages of steel. It is most likely to be used in piping and fittings around pumps. Unfortunately, the bonding between the pipe and liner tends to fail and when they suddenly separate the liner material may clog the pipe or pump. After removal of the lining, you have some rusting steel pipe, which may or may not be acceptable. Steel pipe, if biologically acceptable, has a strong advantage in applications requiting high strength and impact resistance. Such an application could be for main lines on a rocky coast with high exposure to the sea and the possibility of frequent impacts by rocks and other debris.
8.4 Pump materials Seawater pumps are available in a wide variety of materials (INCO, 1976), including many metals, carbon, fiberglass and plastics. Pumps may have homogeneous parts made from different materials or may only be coated or lined with these materials. It is unlikely that any of the available pumps were designed specifically for marine culturing applications. Therefore, some care must be exercised in the selection of pump materials (see Example 8.1). The materials that might be most biologically desirable, carbon, fiberglass, and plastics, do not generally have the mechanical or physical properties best suited for pump use. Again, biological acceptability must be determined on an individual basis and not assumed. Carbon readily cracks, and does not have the strength or abrasion resistance often required. Pumps made with these materials are primarily used in specialized applications in chemical process industries. They are not generally designed to pump abrasive particles, safely pass large solid objects or operate over a wide range of conditions. In culturing applications, they can readily cause operating, maintenance and spare parts problems. Since they are specialized, they tend to be very expensive, often custom items, and the selection may be very limited. However, in recent years a number of equipment suppliers specializing in aquaculture have emerged. They carry a limited amount of fiberglass and plastic pumps with (presumably) a good track record in culturing applications. Chapter 7 discusses in detail the problems of matching the system to the pumps. Limited selection of pumps can considerably complicate the design process and may result in major compromises in overall system performance or flexibility.
125
Example 8.1. Suitability of pump materials for use in seawater You have a need to pump 10,000 gpm of seawater (70~ 30 g/kg salinity) into an elevated channel. The total head across the pump, including both frictional losses and static lift, is expected to be 10 ft or less. You have found a locally manufactured vertical turbine or axial pump with a very good service record in irrigating cranberry bogs with freshwater. These pumps can be driven with a wide variety of engines (you have a few readily available) or the power takeoff of a tractor across many speeds and operating conditions. Assume an operating speed of 1000 rpm. Since these pumps are very simple in design and locally used in agriculture, they are very inexpensive relative to more widely known brands. You have considerable economic incentives to use these pumps, if they are judged to be suitable for the given application and for use with seawater. (A) Is this type of pump suitable for the given application? Specific speed equation accompanying Fig. 7.1, with n = 1000 rpm = 16.7 rps, H = 10 ft Q = 10,000 gpm = 22.2 ft3/s n Q o.5
Specific speed - g0.75H0.75 -
16.7(22.2) ~ (32.2)0.75 (10) ~
= 1.04
From Fig. 7.1 and specific speed = 1.04, turbine pump clearly suitable (B) The pump's lower body and propeller are cast iron, the shaft is low-alloy steel and the bearings are a hard rubber type material in an unspecified bronze sleeve. The pump's vertical tube is either fiberglass or a wooden box structure, in either case a nonconductive material. Is this material combination suitable for pumping seawater? Conductive materials in contact with seawater, cast iron, low-alloy steel and bronze. From Fig. 8.1, the most reactive to most noble, cast iron-low-alloy steel-bronze. Cast iron and low-alloy steel overlap. The biggest pieces (lower body and large propeller) are likely to be the anode, are likely to corrode uniformly and are not dimensionally critical. Good prospects for satisfactory seawater service. Note: A number of these inexpensive pumps in several sizes up to 20,000 gpm gave excellent long-term
service with seawater at a Central American shrimp farm.
Pumps made of cast iron and steel are readily available with a wide selection, are cheap, and often very reliable. These materials under many conditions are biologically acceptable, especially in limited applications such as pumps. The cheapest pump impellers are carbon steel. Abrasive particles such as sand and cavitation due to inadequate suction-side conditions can seriously reduce the lifetime of steel impellers. Under these conditions harder but more expensive impeller materials should be considered. These include specialized steel alloys and stainless steels. If available, titanium would also be an excellent choice. In all this, it is important to remember the significance of Fig. 8.1. The electropotentials of all the materials exposed to seawater and electrically connected must be considered. The small high precision parts (shaft, beatings, impeller, etc.) must be the cathode and the large non-critical parts the anode (usually the pump body). Sacrificial anodes, such as zincs, are usually not realistic in culture systems because of the toxicity of their corrosion products.
126 8.5 M a r i n e concrete
Concrete is often used around seawater for items such as tanks, channels, bases for intakes and piping. It is an excellent and very adaptable marine material and methods for handling it, even underwater, are available (Gerwick, 1969). By using various aggregates, additives or techniques it can be made with densities of as low as 30 lb/ft 3 (which if sealed will easily float) to as much as 220 lb/ft 3. Normally, it is about 150 lb/ft 3. It can be dense and highly impermeable to seawater or completely porous. Its properties appear to get better with time in seawater. Under extreme conditions, it is subject to erosion by abrasive materials carried by strong currents and waves and poor quality concrete can be bored into by tropical marine mollusks. Unless foreseen during design, freeze-thaw cycles on exposed concrete can be very destructive. Concrete is often reinforced with steel to improve its structural properties. When steel is included, great care has to be taken to assure that seawater or any form of salt does not get to the steel. Common mistakes include inadvertently allowing salt into the mixture. Salt can get in from poor choices of sand, aggregates, chemical additives, and use of brackish or seawater in the mix. Salt corrodes the steel, which expands and cracks the concrete, letting in more seawater. If such a mistake is made it will be obvious within a few years. Properly prepared reinforced concrete (Table 8.3) may last forever in seawater. Cover is the minimum distance from the outside of the concrete to the shallowest steel reinforcement. Covers of as low as 3/16 to 1 in. are adequate with dense impermeable concrete. Irrespective of what the construction specifications say, it is important to assure the placement and minimum cover of the steel before the concrete is poured. Using a sealer, such as epoxy, waxes or paints, is usually not necessary with top quality concrete but can be beneficial with more common types of concrete. Another sealing method is using a thin layer of superior concrete over a lower quality core. 8.6 P r o b l e m areas
In practice, preferences of materials have to be balanced against cost considerations. It is interesting to note that similar materials can have greatly varying costs depending on how they are specified and where they are purchased. Recent years have seen ever increasing industrial and non-culturing uses of synthetic pipes and components. Substantial savings can be achieved by considering such mass produced and readily available equipment. The less exclusive the market of the supplier, the lower the prices are likely to be. Large catalogue
TABLE 8.3 Guidelines for protecting steel reinforcements in marine concrete 9Use only good quality concrete of low permeability. 9Carefully select sand, aggregates, water and additives to assure that they are salt-free. 9Assure adequate cover (minimum distance from the steel rebar to exterior surface). 9Seal exterior surface. 9Require high pH in mix. 9Select rebar with non-conductive coating.
127 stores, especially for smaller sizes of equipment, can be good sources of materials and components. The specialized aquaculture equipment suppliers should also be checked. Since a big part of the cost of components such as plastics is due to the basic materials costs, thinner gauges, such as those used in drainage applications, can also lead to savings if the mechanical properties and pressure ratings are acceptable. While potential toxicity problems from seawater-system components is obvious, there are many less obvious potential sources of toxicity. These include paints, insulative materials, and wood preservatives in the building. Toxicity can be introduced into the water directly from the air, especially if the building gets hot, or with small particles that might fall into culture water, possibly from above with condensation or carried by air currents. As an example, a 'no pest strip' hung in a hatchery to control flies, can completely preclude larval culturing. The occasional dripping of condensation or the dropping of insulative material from overhead piping may result in toxicity problems. All building materials and supplies used in building maintenance should also be checked for toxicity, especially if one plans to work with delicate organisms. Creosoted pilings and organotin antifouling boat paints (no longer legally available), if situated near intakes, can also produce toxicity problems. Paints, bug sprays, cleaners and solvents should be used around culturing systems only with great care, if at all. Another source of problems can be the low pressure air often used in culture operations. The air could at times be contaminated. This could occur from the ingestion of automobile or diesel generator exhausts under some conditions or oil from the compressor. Oil lubricated compressors should not be used without the use of oil traps. Regenerative or carbon-vaned blowers are more desirable. Carbon-vaned units throw carbon particulates that may clog the gills of delicate organisms or merely be unsightly. If high pressure building air is to be used, it must be filtered to remove any oil, water or particulates before use. Air, which has been rapidly compressed, can get quite hot. If the air is very hot, it can leach volatile materials from synthetic pipes. As an example, an air system with one compressor 'on' may produce only warm temperature in downstream piping. Infrequently, multiple compressors may be 'on' simultaneously, producing elevated temperatures downstream. The first few times this is done, it may produce mortalities, reduced growth or other biological problems. In complex systems, such correlations are not always noted.
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129
Chapter 9
Seawater Flow Control
9.1 Gravity flow Flow control means knowing what the distribution of seawater flow is to the various parts of the system and having sufficient control to adjust it to whatever flow is desired. It also means that these flows will be stable over time and reliable. This requires control over the fluid head or pressure within the system. In a gravity flow situation, this means control over either the water elevation in the head tank or the discharge elevations. Controlling the frictional head loss between the head-tank water elevation and the discharge is also critical in gravity systems. Fig. 9.1 shows a typical gravity flow situation from a head tank, which also serves as an emergency supply (see Section 5.15). The various priorities of use in emergencies can be reflected by the elevation of the taps into the head tank. Taps for large-flow low-priority or noncritical uses would be highest and taps for critical high-priority uses would be near the bottom. If the distribution system between the head tank and the point of application has low frictional losses (see Sections 6.4 and 6.5) relative to the driving head (H) and the water elevation in the head tank is constant, the flow rate can be well controlled, stable with time Inflow
,~ --Constant Elevation--
Over Flow
Head Tank
q---~
Driving Head H
Manifold/Header
]
/ TVariati~
Discharge..LL_31Lh in Discharge
Fig. 9.1. Gravity flow from head tank.
130 and reliable. I f the l o s s e s are an a p p r e c i a b l e f r a c t i o n o f H , the flow rates will c h a n g e e v e r y t i m e c o n d i t i o n s on any o f the b r a n c h e s o f that distribution s y s t e m are altered. T h e m a i n l i n e s should, t h e r e f o r e , be v e r y g e n e r o u s l y sized to v i r t u a l l y e l i m i n a t e frictional l o s s e s and in-line p r o c e s s i n g e q u i p m e n t r e m o v e d or m i n i m i z e d (see E x a m p l e 9.1). Since the l e n g t h s i n v o l v e d are o f t e n short, this is u s u a l l y not a hardship. E x a m p l e 9.1 s h o w s the interactive p r o p e r t i e s o f pipe v e l o c i t y and r e s i s t a n c e coefficient at l o w R e y n o l d s n u m b e r s . A g e n e r a l g u i d e is that if the v a l v e s are s i z e d to k e e p the pipe v e l o c i t y at 1 f t / s (0.3 m / s ) or less, that all the v a l v e s c a n be o p e r a t e d i n d e p e n d e n t l y . H o w e v e r , the r e d u c e d v e l o c i t y will i n c r e a s e the s e d i m e n t a t i o n and b i o f o u l i n g in t h e s e lines, r e q u i r i n g m o r e f r e q u e n t s e r v i c i n g to m a i n t a i n the l o w friction. H o w e v e r , a n o t h e r a d v a n t a g e o f l o w pipe v e l o c i t y is that the thrust b l o c k s at p i p e ends c a n u s u a l l y be o m i t t e d . T h r u s t b l o c k s are often r e q u i r e d to h o l d pipes in b e n d s due to m o m e n t u m effects o f c h a n g i n g flow directions (see S e c t i o n 6.7). T h e d i s c h a r g e e l e v a t i o n is often v e r y e a s y to c o n t r o l at the point o f application, since it
Example 9.1. Flow control with constant head tank and discharge elevations You have a laboratory distribution system similar to Fig. 9.1 with a large constantly overflowing head tank and a distribution system made with 'large' diameter piping and terminating immediately below a header pipe with distributed 'small' ball valves at a fixed elevation. The valve discharge is to the air and presumably over a tank. You wish to limit the amount of water that can be used at any specific point of application to 0.0005 m 3/s (about 8 gpm) for each user. The elevation difference between the water level in the head tank and the valve discharge is 4 m. (A) What size small valve should you use? If the piping is 'large', it can be assumed that the only frictional lose in the line is at the small valve. This also means that no matter what each user does with his valve he cannot substantially impact anyone else's flow rates. Using Bernoulli's equation, which is a more general form of Eq. 7.3 without a pump (TDH -- 0), with Point 1 on the water surface of the head tank and Point 2 being in the discharge plane of the valve, y~ hf is the sum of the piping losses between Points 1 and 2 as defined in Eq. 6.2 and y~ hi the sum of the fitting losses as defined in Eq. 6.6. The Zs are the elevations at the respective points.
vZ/2g + P1/Y -k- Z 1
-"
vZ/2g + P2/Y -k- Z 2 -'[-Y~ he + ~_, hi
The pressure at Points 1 and 2 are both atmospheric or zero gage pressure. Assuming a 'large' head tank, the velocity at the head-tank water surface is also zero. The seawater velocity at Point 2 depends on the 'size' of the valve. Putting in the zeros and replacing ~ hi with Eq. 6.6 produces the following: Z1 -
Z2 --
4 m = vZ/Zg + KvVZ/Zg = (1 + Kv)VZ/Zg = (1 + 0.2)V2/2(9.81)
We get the 'small' ball valve loss coefficient (Kv) from Table 6.4. We now have one equation and one unknown. Solving for V2 = 8.09 m/s. Now solving for the cross-sectional diameter that will produce the maximum stated flow at this velocity: Velocity = flow rate/cross • area = 8.09 m/s = O.O005/(rcd2/4) Solving for the diameter d: d = 0.0089 m = 0.89 cm (about 1/2 inch valve) Now valves come only in discrete sizes and the nominal size may not correspond to the actual flow diameter, so some adjustments have to be made in valve selection.
131
Example 9.1. (continued) (B) What is the minimum size of the 'large' pipe that will make the pipe losses 2% of the previous total frictional losses with the valve fully open? Let us assume an 'equivalent pipe' length of 25 m. We will neglect losses from fittings and transitions or include them in the specified 'equivalent' length (see Section 6.5 for discussion). We will also estimate from experience a fairly clean plastic 'smooth' pipe with a resistance coefficient = 0.03. Total losses before = elevation head - velocity head -- 4 - v2/2g = 4 - (8.09)2/2(9.81) = 0.66 m 2% of 0.66 = 0.0132 m, so pipe losses = f l V 2 / 2 g d
(Eq. 6.2) = O.03(25)V2/2(9.81)d = 0.0132 m
In this equation the velocity is that in the pipe. This appears to be one equation with two unknowns, but V and d are not independent, substituting in: V -- flow rate/(rcd2/4) and solving for d = 0.065 m = 6.5 cm (about 2.5 inches) We now can solve for the pipe velocity (0.15 m/s) and the Reynolds number (1 x 104) and can check the assumed resistance coefficient using Fig. 6.3. The estimate was good. (C) If there are 10 users, what is the minimum pipe diameter for the main distribution lines to still to be 'large'? We have to tenfold the flow rate, estimate a new resistance coefficient (which will be checked later) for a smooth pipe equal to 0.02 and keep the pipe frictional losses at the same 2% (0.0132 m). Recalculating the equations above: d' = 0.0899 m -- 8.99 cm (about 3.5 inches) v' -- 0.79 m/s, Reynolds number = 7
x 10 4
Check Fig. 6.3 for resistance coefficient, 0.02 was a good estimate Main seawater distribution pipes of about this size should assure the independence of each system user's flow rate from the actions of the other users.
u s u a l l y i n v o l v e s m u c h s m a l l e r flow rates than t h o s e at h e a d tanks. T h i s can be d o n e w i t h flexible t u b i n g on the d i s c h a r g e spigot and a vertical s u p p o r t stand. T h e a m o u n t o f c o n t r o l this will p r o v i d e o v e r the flow rate is p r o p o r t i o n a l to the m a g n i t u d e o f the p o s s i b l e e l e v a t i o n v a r i a t i o n at the p o i n t o f a p p l i c a t i o n relative to the total driving h e a d at that point. I f h is a substantial f r a c t i o n o f H (see Fig. 9.1), t h e r e will be a c o n s i d e r a b l e r a n g e for flow rate control.
9.2 Water level control T h e r e are a n u m b e r o f w a y s to c o n t r o l w a t e r levels in h e a d tanks, or any o t h e r t y p e o f tank. T h e s e are s h o w n in Fig. 9.2. T h e y w i l l all e f f e c t i v e l y c o n t r o l the w a t e r elevation, p r o v i d i n g that the flow into the tank is g r e a t e r than any flow d e m a n d s on the t a n k (not s h o w n ) . T h e first is the s i m p l e overflow. S i n c e this is built into the tank, it has the least c a p a b i l i t y to alter the w a t e r elevation. T h e o n l y p o s s i b i l i t y is to c h a n g e the e l e v a t i o n o f the entire tank, w h i c h for s m a l l h e a d tanks m a y not be too difficult. T h e r e m o v a b l e s t a n d p i p e can be s w i t c h e d for
132
Overflow
Removable Stand Pipe with "0" Ring Socketor Threaded Joints ~
I
"11
Removable Stand Pipe
Stand Pipe
Special Drain
(;
Internal , Stand Pipe V~
"0" Ring Socket or Threaded Joint
~ ormal Drain Drain
Auxiliary M~ Box I
Syphon
l
Fig. 9.2. Water level control approaches. Least flexible to most flexible.
a longer or shorter one (within limits) to change water elevations. A related alternative is an external standpipe. This allows unrestricted access to the tank and easier drainage. As with the internal standpipe, water elevation in the tank can be controlled by selecting the length of the standpipe and both provide easier tank cleaning than the other options due to the inherent bottom drain capability. The siphon is the most flexible as the small auxiliary box can be readily moved up or down. It does not require any modifications to the main tank. The only constraints are that the siphon must be sufficiently large so as to have negligible frictional losses and must be secured at both ends. The small tank should contain at least 15 seconds of flow to keep the velocity effects negligible. It is helpful if the siphon is flexible and transparent. There are a number of other possible variations on the use of siphons in level and flow control and more detailed design information is presented by Garrett (1991). Under normal operating conditions all four approaches can accurately control the water level. During periods of water stoppage, critical flow needs supplied from the tank or even small leaks in the tank or standpipe may allow complete or partial tank drainage. This may be more important for siphon systems, as the siphon effect is broken when the water level drops below the siphon intake hose and it will not restart by itself when the water is restored. Also, all four approaches can fail by flooding, if overflow pipes or screens become clogged with debris.
133 If water levels become too high or to low, it is important to find out about it as soon as possible. Changes in water level are often the first noticeable sign of a failure. For these reasons, water levels are often instrumented to set off alarms or trigger other actions at predetermined high or low water elevations. As an example, if a pump is drawing from a tank that loses water and the pump is not automatically shut off, it will run dry and self destruct. There is a wide variety of programmable water level switches available, many made with synthetic materials. In addition, one can easily be made with a small float, a vertical rod, two brackets, two rod guides and two contact switches. The rod is connected to the float and is allowed, by the two guides, to go up and down with the water level. The brackets are fastened to the rod at the correct elevations and activate the contact switches as the rod moves up and down with the float.
9.3 Control of flow rate The desired flow can be controlled with a valve at the point of application. This is commonly done and in many cases is a satisfactory solution, if the rest of the distribution system has negligible frictional losses. More precise control of flow rate may be required under some conditions. Fig. 9.3 shows the discharge of an orifice to air. This can provide flow rates that are consistent for long periods of time to within a few percent, even for wide seasonal water-property variations and with raw seawater. However, the hole diameter (D) must be larger than the biggest particles to be encountered to avoid clogging. H can be the driving head directly from the head tank, if the distribution system to the point of use has negligible losses, or it can be the head of a small auxiliary head box at the point of application. For accuracy it is important that the flow velocity just upstream of the orifice be negligible. A large pipe is adequate if the flow velocity in the pipe is very low. It is also important that the edges of
n
Constant Water Elevation
Fig. 9.3. Discharge of circular orifice to air. O = C(rcD2/4)(2gn) ~
where Q = discharge flow (ft3/s or m3/s); C -- nondimensional coefficient -- 0.6-0.7; D = orifice diameter (ft or m); g --- gravitational constant (32.2 ft/s 2 or 9.81 m/s2).
134
Example 9.2. Submerged orifice flow control A submerged orifice discharging to air with a diameter of 1 cm is connected to an overflow head box in a manner similar to that shown in Fig. 9.3. This head box has an adjustable overflow pipe. At what elevation H above the center line of the orifice should the overflow pipe be set to get a desired flow rate of 0.1 l/s?
Q : C(:rDZ/4)(2gH) ~ Q -- 0.1 1/s : 0.0001 m3/s C = 0.65 D=
lcm--0.01m
g -- 9.81 m / s 2 Jr = 3.14 0.0001 = 0.65(3.14 x 0.012/4)(2 x 9.81 • H ) ~ H--0.196m
=20cm
This H value should get you close to the required flow rate. Fine adjustments should be made by checking the flow with a graduate tube and stopwatch.
the orifice be sharp, to prevent variations in flow separation and resulting changes in flow rate. This approach has been used successfully with orifices cut into threaded PVC caps on 4 and 6 in. lines with flows over 50 gpm (3.1 l/s) and down to flows as low as 0.25 gpm (0.0016 l/s) with raw seawater and auxiliary head boxes (see Example 9.2). A similar water flow control device for use inside tanks, but with its discharge underwater, has been demonstrated to be precise, inexpensive and reliable (Kinghorn, 1982a). Discharging to air above the water surface has the distinct advantage that the proper operation of the device can be easily checked visually and by sound. With a little experience, even small changes in flow due to partial clogging or loss of head are readily observed. The amount of servicing required depends on prior processing of the water (filtering, sterilization, sedimentation, etc.). With a little care, even under the worst conditions, such devices can often be left unattended for long periods. Another variation for very low flow rates in the order of 0.08 gpm (0.005 l/s) involves the use of nonwetting micropipette tips. These can be cut with a razor blade and fine flow adjustments accomplished by varying the discharge elevation above the water surface (see Fig. 16.1). With filtered water the tips will not clog, but with water containing high concentrations of phytoplankton daily attention is required. This approach provides very precise flow control and is an alternative to very expensive metering pumps. 9.4 Flow measurement
It is sometimes necessary to monitor flow rates in pipes and there are several approaches to this requirement. There are a number of industrially available induction or ultrasonic flow meters that can precisely monitor most flows from outside the pipe. Other types of flow meters have rotors or other appendages exposed to the flow but are generally undesirable for extended marine uses due to biofouling and seawater corrosion problems. However, remote reading propeller flow meters have been successfully used in freshwater hatcheries. Orifices or venturi
135
Example 9.3. A venturi flow measurement A 1-cm-diameter venturi is in a 2-cm-diameter pipe with an air-seawater manometer attached as shown in Fig. 9.4. The manometer deflection is 50 cm, what is the flow rate and average velocity of seawater in the pipe?
Q - - K(rrdZ/4)(2gh) o.5 d D
=lcm =2cm
-0.01m =0.02m
d/D = 0.5 h
--50cm
g
-- 9.81 m / s 2
=0.5m
K
= 1.0 (to be confirmed)
Q --- (3.14)(1.0)(0.01)2/4[(2)(9.81)(0.5)] 0.5 -- 0.000246 m3/s = 0.25 1/s V = Q / p i p e area = 0.78 m / s At this point, it is not known if the assumed K value is reasonable and within the specified conditions.
Re = V d / v v
= 1.0459 x 10 -6 mZ/s, from Table A-3 for 20~
and 35 g / k g salinity
Re = (0.78)(0.01)/1.0459 x 10 -6 = 7.5 x 103 which is greater than minimum of 5 x 103 Reynolds number is within the specified range and flow rate estimate should be close. Actual calibration of flow rates versus manometer deflections would be more accurate than such calculations.
combined with a simple manometer or differential pressure gauge provide a cheap and reliable alternative to expensive industrial equipment (see Fig. 9.4). The manometer is an air-seawater type and may require a vertical height of around 6 ft (2 m). It has a captive air bubble and the measurement is the difference in the elevation of the two sides (see Example 9.3). It is helpful if the tubing from the devices to the manometer's glass or clear plastic tubing is flexible and transparent. If any bubbles are in the lines, other than the big one at the top of the manometer, the accuracy of the measurement can be greatly degraded. The venturi has much lower frictional losses than the orifice and this may be an important consideration for some applications. The manometer deflection, h, happens to be the actual frictional head loss for the orifice, but this is not true for the venturi. The orifice ports should be a few pipe diameters on either side of the orifice. The orifice edge should be sharp to get consistent flow separation. The loss coefficient K is dependent on the diameter ratio d/D (higher ratios higher values) and somewhat on the Reynolds number (Re), especially with Re below 5 x 103. More precise values for K can be found in fluid mechanics texts (Roberson and Crowe, 1990). More recent fluid mechanics texts tend to eliminate coverage of manometers. If a differential pressure gauge is to be used in place of a manometer in Fig. 9.4 or Example 9.3, the manometer deflection (head of manometer fluid) can be converted to a pressure reading. The maximum and minimum manometer deflections can likewise be converted to maximum and minimum pressure readings needed to specify the pressure gauge.
136
s
Closed ,~ve
~6~__~d ~; I
/ ~
Clear'"'"-~Flexible
Tubn ig
Water
IIhManometer Deflection I
Venturi
|
To ...... Manometer
Orifice \
J
Air-Water Manometer Fig. 9.4. Flow rate measurement in pipes using venturi and orifices. Re = Reynolds number = Vd/v
Q = K(rcd2/4)(2gh) ~
where V -- average pipe velocity (ft/s or m/s); d = throat diameter of venturi or orifice (ft or m); v -- kinematic viscosity of fluid, see Table A-3 (ft2/s or mZ/s); D = pipe inside diameter (ft or m)" Q -- flow rate (ft3/s or m3); h - manometer deflection (ft or m); g -- gravitational constant (32.2 ft/s 2 or 9.81 m/s2); K = nondimensional flow coefficient; K = for venturi -- 0.95-1.05 for Re greater than 5 x 103 and d/D of 0.4-0.6 - - the higher the d/D the higher the K" K = for orifice --- 0.60-0.75 for Re greater than 5 x 103 and d/D of 0 . 1 - 0 . 6 - - the higher the d/D the higher the K, much higher values are possible at lower Re and higher d/D.
Occasionally, flow might have to be measured in open channels. Some of the available open channel flow measurement devices can be used down to relatively low flow rates of about 0.5 gpm (0.028 l/s), even though such equipment is usually associated with very high rates. Open-channel flow measurement devices include V-notch, rectangular, and trapezoidal weirs and Parshall flumes. They all involve the prediction of flow rate based on the backing up of water upstream of the device. For more information see Davis and Sorensen (1969) and Leupold and Stevens (1975). All the flow measurement and control devices mentioned have to be checked and calibrated with various versions of 'graduate tube (bucket) and stopwatch'. Calibrating with actual measurements can result in excellent subsequent flow measurement and control.
137
Chapter 10
Suspended Solids Removal
10.1 Considerations, tradeoffs and options Filtering is a term that generally means more than simply straining. Depending on the type of filter and conditions, the operating mechanisms can include: straining, sedimentation, adsorption, diffusion and chemical bonding. Filtering options are usually classified by the size of the smallest particle removed. Note that the older unit of micron is equal to the SI unit of micrometer (txm). Because of the complexity of some of the processes that might be involved and the dependence on conditions, many of which vary with time, predicting the performance of at least some of the filter types at any given point is often, at best, an estimate with low precision. There are some recent data comparing the solids removal of several alternative approaches (Piedrahita et al., 1998). Quantifying the filtering requirements is also often an approximation based on anticipated conditions. Generally, when additional filtering is required at all, these requirements tend to fall into three categories. Some coarse filtering is likely to have been already done by intake screens and places in the system with high residence time (headboxes, storage tanks, etc.), where sedimentation would have occurred (see Section 10.8). The next coarsest type requirement is to remove zooplankton, larvae of larger animals and eggs of various kinds. This requires filtration down to the 75-100 Ixm (0.075-0.10 mm) region. The next is to remove all phytoplankton, which generally requires filtering down to 2-10 txm (0.002-0.010 mm). The most severe requirement is to remove very fine suspended colloidal particles, usually clays, that occur in some areas and can greatly reduce the clarity of water, giving it a cloudy or smoky appearance. They will usually not settle by themselves, no matter how much time is allowed. These very fine particles, often in the 1-2 Ixm range, have generally little biological impact and their removal is usually required only where viewing conditions are important, such as in aquariums and some educational systems. This requires filtering down to about 1 Ixm (0.001 mm) or less. It is important to not overstate filtering requirements. Filters can be a source of system failure, high initial and operating costs, and high labor demand. They have the capability to be a continuous source of problems and irritation to operating personnel. These types of problems usually increase proportionally to the requirement for finer filtration. Fine filters must not be exposed directly to raw seawater. During storms or periods of heavy waves, impressive amounts of coarse solids can be suspended in coastal waters and pumped into the system. Exposing fine filters directly to such waters will produce virtually instantaneous filter clogging. It is imperative that the fast settleable solids be removed by sedimentation (see Section 10.8). Even a few minutes of the fluid at rest can accomplish much, but the longer the better. A minimum of an hour of residence time is preferred but 15 min
138 might be adequate, especially if followed by coarse filtering. Normal design of a system often results in useful, but often inadvertent, sedimentation of the coarsest and heaviest particles in headtanks or supply channels. Since a single storm may deposit many inches of sediments in these areas, provisions for removal must be provided. In order to reduce the load on fine filters, it is common to have a two-step filtering process with two different types of filters, the first being a coarser filter. Another major reason for this two-step sequence is that only a part of the flow may require the finer filtration, with most of the uses being satisfied by the coarser filtering alone. Most filter operations are batch processes and time dependent. The filters start out clean and gradually or rapidly, depending on the solids content of the water, accumulate solids within the filter system. Most filters have appreciable head losses even when clean. As the filter becomes dirty, the head losses increase rapidly and the flow rate through the filter decreases. For a very dirty filter, the through flow will approach zero. Because of the variable and often high frictional head losses across filters, they are usually placed downstream of a pump to provide the required pressures (typically 10 to 60 psi). The head losses across the filter must be included in the matching of the pump and the system (see Chapter 7). Since the filter losses are usually a substantial part of the total piping system's losses, putting in or taking out a filter from a system not designed for it is very likely to lead to incompatibilities within the pump-piping system (see Chapter 7). In gravity flow situations adequate heads for operating many types of filters are generally not available and the variability in the head losses will degrade the flow-control capabilities inherent in gravity systems. Placing a filter in the gravity flow portion of a system often requires use of a dedicated booster pump. When batch type filters get sufficiently dirty to reduce the flow rate below some minimum value, they must be cleaned in place or changed. If this cleaning is carried out in place with a reversal of flow it is called backflushing or backwashing. During backwashing the filter system is generally out of operation. The time out of operation can range from 2 to 15 min. The time interval between replacements or backflushings is called the filter run. It is highly variable and depends on conditions. Servicing requirements may, therefore, also be highly variable. Exceptions to these problems of variable head loss and flow rate are filters which are classed as continuously backflushing. Because of their much more constant head losses, flow rate and continuous operation, they are very desirable from a systems' design and control stand point. Unfortunately, most of these filter types are towards the coarse end of the particle spectrum. The backflushing water for one unit may be the filtered output of one or more identical parallel units or a prefiltered supply, such as from a headtank. For continuously backflushing units, the backwash flow is usually a small fraction of its own filtered output (in the order of 5-10%). It is important that the backflushing flow be sufficient to completely clean the filter, or subsequent filter runs will be gradually shortened to unacceptable levels. Since backflushing flows are discharged, the seawater supply to the system must be designed with consideration for this and other auxiliary flow requirements. It is important to not filter more water than is required. To do so is a waste of energy and filter servicing time. Such a situation is very common, especially when the filters are located between the main pumps and the headtank. Headtanks are usually of the overflow type, with excess filtered water being discharged to the drain. One possibility is to throttle the discharge side of the pump to reduce the flow rate so that the headtank is barely overflowing. If tidal
139 TABLE 10.1 Filtration equipment for use with seawater systems Maximum filtration
Flowrate 1 gpm or less
1-10 gpm
10-100 gpm
100-1000 gpm
1 Ixm or l e s s
Cartridgefilter, diatomaceous earth
Cartridgefilter, diatomaceousearth
Diatomaceous earth
Diatomaceous earth
1-10 Ixm
Cartridge filter, centrifuges and cyclones
Cartridgefilter, centrifugesand cyclones
Centrifuges and cyclones,sand filters
Sand filters
10-75 p~m
Filter bags, centrifuges and cyclones
Sand filters
Filter bags, centrifuges and cyclones, sand filters
Filter bags, sand filters
75-150 Ixm
Filter bags, microscreens
Filter bags, microscreens, sand filters
Filter bags, s a n d filters, microscreens
Microscreens
150-1000 Ixm
Screen bags, microscreens
Screen bags, microscreens, sedimentation
Screen b a g s , sedimentation, microscreens
Microscreens
The generic identifications used in this table encompass a wide variety of equipment with many different specifications. The table is only intended as a general guide to the major areas of applicability and most probable use.
or other pump system conditions are continuously changing, this would require continuous adjustments. In this case, it would not be worthwhile trying to get the minimum at all times but only using this approach for coarse-flow adjustments. An option is to place the filter on a gravity line between the headtank and the point of application. This has the advantage of only filtering the water required but may have other problems in this location (see above). Another option for small scale use is to loop the filtered overflow back to the suction side of the pump (see Fig. 16.1). If this is done, great care must be taken to assure that no air gets ingested into the suction side of the pump to prevent mass mortalities from gas supersaturation. There are many different types of filters available. Some types are adequately covered in the available literature on filters in seawater-culturing systems (see Appendix G), while others are not. Manufacturers can be found through equipment supplier indexes (Appendix M). Filters can be categorized by filtration performance and flow rate. The types commonly used in seawater systems are listed in Table 10.1. Since much of this equipment has been developed for use in quite different applications and is available in many variations of materials and material combinations, considerable care is required to assure biological acceptability and compatibility with seawater (see Chapter 8).
10.2 Cartridge filters Cartridge filters can be used directly in a seawater line under pressure. The disposable cartridge is usually in a transparent canister for the smaller sizes, which is easily unscrewed
140 to get access to the cartridge. Replacement does require turning off the system. The cartridges are available in a wide variety of sizes, materials and filtration performances (Nickolaus, 1975), not all of which would be acceptable for use in seawater systems. Multiple filter units can be placed in parallel to increase flow capacity. There are a number of manufacturers specializing in these components. Since cartridges are interchangeable, this provides considerable operational flexibility to meet changing requirements. Head losses for the finer filters when clean can be as low as about 16 ft (5 m), increasing as the cartridge gets dirty. It is important to continuously monitor the flow rate through the cartridge, usually visually at a discharge over a tank. Visual estimations from observation of filter coloration through the transparent cases are not a reliable indication of either flow rate or cartridge filtering status. Careful specification of the filtering equipment and its loading can assure filter runs sufficiently long to go through unattended periods. Replacement will often be required about once a day. If the seawater to the filter can be highly variable in its particulate content, such as due to storms or blooms, the filter runs could be greatly shortened. If the dirty cartridge is not replaced, the filter will stop flowing and the pump may overheat and burn up. An example of a practical use of such equipment for fine filtering is shown in Fig. 16.1. In this case, the raw seawater was coarsely filtered and exposed to a large tank (residence time well over 1 h), where sedimentation could take place before being fine filtered. It was operated unattended at night but did require daily cartridge replacement and servicing, including weekends.
10.3 Diatomaceous earth filters Diatomaceous earth (DE) filtering and related equipment are an alternative to cartridges and are available to handle higher flow rates. In fact, disposable cartridges already coated with DE are offered by some suppliers. DE is a granular material composed of the skeletal remains of diatoms. Before it can be used as a filter medium, it must be deposited in a dense layer on a porous substrate forming a filter cake. If the filter cake is not uniform, there can be partial short-circuiting of the filter. The substrate is a cloth-like material, often polypropylene, in the shape of a long tube or two-sided flat plate (leaf). This material, usually called the sleeve, is removable because it may be periodically cleaned or replaced. This cloth has no structural strength and must be supported by a core structure. There are basically two types of DE units. One is called a gravity unit with the supply side at atmospheric pressure. This type is powered by a partial vacuum on the discharge side. The other type is a pressure DE unit driven by a pump on the supply side. Both types require a preparation cycle to establish the DE layer on the porous substrate by addition of DE to the supply side in a closed loop. Once in the operating mode, the filter run can often be greatly lengthened by the continuous addition of small amounts of DE to the unfiltered water. Filter runs are highly variable and dependent on conditions, but are often designed to be normally about 24 h. Once dirty, the DE filter is backflushed and a new filter cake established to complete the cleaning cycle. Very little pressure is required to backlash, since the filter cake is only held to the substrate by operating pressure or partial vacuum. The performance of the DE filter is determined by the specifics of the DE material used, the equipment, operating conditions and the servicing procedures (Spotte, 1979). DE equipment can be expensive to own and operate, sometimes requiting considerable servicing and labor.
141
10.4 Filter bags Filter bags are cloth materials (usually nylon or polypropylene) in the shape of a bag and attached to a semiflexible ring at the open top. They are placed at the end of a pipe by a diskshaped pipe fitting, over which the slightly deformed ring is placed edgewise and rotated into position. They usually discharge over or within an open tank and several can be used in parallel. When clean, their head loss is very small. When they are dirty, they balloon. This shape change is easily visible. It takes only a few seconds of downtime to replace a filter. A dirty filter can be surprisingly heavy, due to trapped water. They are usually cleaned by hand. This cleaning is not 100% and the bags ultimately have to be replaced. A typical application is shown in Fig. 16.1. A wide variety of equipment variations are available. The basic approach is quite flexible. For coarser filtering applications, synthetic microscreening meshes have been formed into bags or socks and used to screen the inflow to tanks and ponds. If large, the socks have to either be supported or be placed in the water, since their weights when dirty can be impressive. The only penalty for in-water use is that their status is not as easily visually checked. These microscreen bags are typically custom-made from bulk screening material, although some ready made units are available.
10.5 Centrifuges and cyclones Centrifuges and cyclones do not filter by size but rather on differences in specific gravity between the fluid and particulate matter. Since many organic particles have densities close to that of seawater, high rotational speeds are required. Continuous centrifuges have been used in commercial bivalve hatcheries. Since this equipment was developed for other applications, more care than usual in selection is required. Due to the high energy contained in the spin rates (order of 30,000 rpm), corrosion leading to imbalance or breakage, could result in a catastrophic explosion-like failure. In addition, due to engineering requirements, they are unlikely to be available in the most biologically acceptable materials. This equipment is complicated and expensive but the alternatives also have problems and limitations.
10.6 Sand filters Sand filters of various kinds are very common in seawater systems. Their performance is dependent not only on the type of filter and operating procedures, but heavily on the sand characteristics. There may be only one type of sand in a filter (single medium) or several (multi-media). The lower limit for a single-sand medium is about 20 ~m. Each sand is characterized by its grain size, uniformity of grain size, grain shape and specific gravity, all of which are important to filtering performance. The physical differences between sands can be critical. Choosing the sand for a given application and predicting its performance is a very difficult matter (Rich, 1961; Spotte, 1979) that still contains considerable subjective judgment. Even the 'experts' make mistakes in this area. If not done properly, sand filters can easily prove to be a continuous source of operational problems. Most of the filtering action in a sand filter occurs in the first few inches. Since many of the organic particulates are compressible, they can easily cake. Proper sand parameters can considerably reduce the resulting head losses.
142 Water to be _ . ~ Filtered ~ J ~ u . ~
,
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11 Rapid Sand Filter
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Continuously Backflushing Sand Fi Iter
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Fig. 10.1. Types of sand filters. Most of the problems with sand filters are a result of improper backflushing. The backflushing must be sufficient to fluidize the bed without blowing the media out the discharge. This means that the backflushing velocity must reach but not exceed the terminal velocity of the sand particles and must do so uniformly over the filter area; obviously, this is a delicate process. If more than one sand is included, they must be matched so that they will segregate properly on backflushing. If they mix appreciably, head losses may be substantially increased. If the sand changes shape over time due to friction on backwashing (becoming more spherical), or the fluid temperature or salinity changes, the particles' terminal velocities will also change. This will affect the required backflushing flow. Uniformity over the filter area is a big problem. Dead spots not adequately fluidized or cleaned will become even 'deader'. High velocity spots may locally blow out the finer media causing a short-circuit across the filter. Sand filters can be classified a number of ways. Fig. 10.1 presents three general categories of sand filters. The rapid and slow filters in fact represent a continuum of loading (flow/area)
143 possibilities rather than two distinctive types. They both often use a foundation of coarse gravel with high specific weight (about 2.5) and manifolds with slotted laterals. There are other alternate under-drain systems. Filter loading values have to be used with caution, as performance is heavily dependent on input water parameters and specific filter conditions. The key to minimizing the very considerable potential problems from sand filters is to lightly load them and service them properly. Rapid sand filters are pressurized units often used in multiple parallel units. They are available from a number of manufacturers in varying sizes and capabilities. They require relatively small floor area. The pressure case may be steel, often epoxy-coated inside, in the larger sizes. The smaller varieties are often fiberglass. Both of these types are used in many industrial applications. In rapid sand filters the loadings typically run as high as 20 gpm/ft 2 (1.4 lps/m2), although one would be very unwise to use such values with raw seawater. More reasonable maximum values would be about a quarter of this number. Their head losses when clean can be in the order of 30-90 ft (9.1-27.4 m). The head or pressure across the filter must be monitored to determine when backflushing is needed (see Example 10.1). Backflushing is often automated, but this adds substantially to the cost. The advantage of automation is that it reduces the problem of erratic servicing requirements due to variation in filter runs, especially if raw seawater is the input. When the filter clogs and if the shut-off head of the pump is higher than the pressure rating of the filter, then the filter will literally blowup; furthermore, this may occur rapidly if the input seawater suddenly becomes turbid due to storm or wave action. This is a common source of failure when 'swimming pool' filters of this type are used in culturing systems, due to relatively low cost and availability. Because they are definitely high head-loss devices, putting them in or taking them out of a seawater system will usually require a major system redesign. Slow sand filters usually have loadings of 1 gpm/ft 2 (0.68 lps/m 2) or less. As a consequence they require more floor space. Unlike the rapid sand filters, these are usually provided on a custom design and manufacturing basis (see Example 10.2). They are usually unpressurized, although a positive displacement pump applying a partial vacuum to the discharge will increase their flow. They are also low head devices (a few inches of head loss) and as such can sometimes be used in gravity flow situations. When they clog, the top sand layers can be scraped off and replaced, or they can be configured for backwashing as shown in Fig. 10.1. The problems of sand characteristics and uniformity of rapid sand filters will also apply to the backflushing of slow filters. Since their operation is usually visible, they are easier to monitor. If they clog heavily, they will simply overflow to drain, cutting off the seawater supply. The continuously backflushing sand filter (see bottom drawing in Fig. 10.1) is a relatively new approach and has been successfully used in seawater-culturing systems. Its maximum loading is about 8 gpm/ft 2 (5.4 lps/m2). It has a constant head loss of only about 2 ft (0.6 m) and is available in a range of sizes. It has no downtime for backflushing and appears to solve all the backflushing problems of more conventional sand filters. Its low head makes it attractive from a system design standpoint, as it can be placed or removed from any place in a system with little in the way of repercussions. In most applications, it only requires a small flow of low pressure compressed air and does not require electronic controls or automatic valves.
144
Example 10.1. Rapid sand filter A fine filtering requirement has resulted in the selection of a fine but angular sand with a K -- 10 m / d a y being placed in a rapid sand filter similar to that shown in Fig. 10.1. The filter bed has an effective thickness of 6 inches and is circular in cross-section with a diameter of 5 ft. Upstream of the filter there is a centrifugal pump drawing seawater (30 g/kg, 68~ off of a wet well and after going through the filter, the flow discharges to a head tank as shown in Fig. 5.3. The pump is the same model as specified by the pump curve in Fig. 7.5. You can assume that all the other frictional losses on both sides of this pump are negligible compared to the losses across the filter (usually a good first-order assumption). (A) What is the maximum flow rate through the filter when it is completely clean? K = 10 m / d a y = 0.0228 ft/min L = 0.5 ft A -- red2~4 -- (3.14)(5)2/4 = 19.63 ft 2 Using Eq. 4.1, Q = K h A / L = 0.895h (Q in ft3/min). To convert to gpm, the previous equation should be multiplied by 7.48 gallons/ft 3, so Q -- 6.70h (Q in gpm). h is the filter loss plus the elevation change from the wet well water surface to the discharge elevation above the head tank (ft). Since the filter is the only appreciable loss in the system, the above is the effective system curve. Plotting h vs gpm in Fig. 7.5, results in a straight line and an operating point (intersection) of about 250 gpm. This is the maximum possible flow through the filter with this pump. (B) Based on the guidelines of Section 10.6, what is the estimated nominal flow of this unit? Conservative value given as 5 gpm/ft 2 gives 5 x 19.63 = 98.2 gpm or about 100 gpm. (C) If it is decided to backflush the filter when the flow drops to 75 gpm, what will be the pressure difference measured across the filter bed in psi? From Fig. 7.5, at 75 gpm the total head loss is 47 ft, which is assumed to be entirely due to the filter loss and the static lift. In the case of the system in Fig. 5.3, the static lift was about 12 ft. The specific gravity (V) comes from Table A-3 for seawater at 68~ and 30 ppt. Eq. 6.1, Pl - P2 - (h)(v) -- (47 - 12) x 63.74 = 2231 lb/ft 2 -- 15.5 psi
10.7 Microscreens Microscreens are industrially available in a wide variety of materials, configurations, and sizes. There are versions for pressurized and unpressurized applications. The unpressurized applications are usually rotating-meshed barrels 75% submerged across a flow channel. Filtering usually takes place from inside to outside of the barrel. The filtered flow leaves in a channel 90 ~ to the input flow. A small horsepower motor rotates the barrel and a strip of the mesh across the top is continuously backwashed by a small pump to a drainage tray inside the barrel. Unlike sand filters, there is no problem with a little overkill on the backflushing. The head loss across the screen is negligible, a few inches at most. The pressurized units also involve a rotating cylinder. The filtered water is removed from the center and backwashing occurs to a slipper-type discharge on the outside of a small section of the cylinder. The head losses are usually within 12 ft (3.8 m) and constant. With careful choices of mesh, materials,
145
Example 10.2. Slow sand filter Slow sand filters are generally not commercially available and you have decided to build your own down-flow system with backflushing capability as shown in Fig. 10.1. The filter bed is to be 6 inches of coarse sand (K = 100 m/day) and the bed dimensions are for practical construction reasons to be 4 • 8 ft. The minimum pressure below the sand layer at the filter exit can be assumed to be atmospheric. The overflow and backflushing drain is 12 inches above the sand layer. (A) What is the maximum flow rate through the filter in gpm when it is clean and with the maximum amount of water over it? K = 100 m/day = 0.228 ft/min A=4• 2 L = 0 . 5 ft h=lft Eq. 4.1,
Q-
kHA
L
-
(0.228)(1)(32) = 14.6 ft3/min (109 gpm) 0.5
(B) While performance and length of filter run are quite variable, from the guidelines of Section 10.6, what would you specify as the nominal flow rate of this filter? Conservative loading of slow sand filters is 1 gpm/ft 2 32 • 1 = about 32 gpm (C) By dropping a number of individual sand grains in a long graduated cylinder of still water, you find that the average settling velocity is 0.5 ft/min. What is the approximate backflushing flow rate needed to fluidize the filter bed during backflushing? Q = V A = (0.5)(32)= 16 ft3/min = 120 gpm
and coatings, these units can give long periods of relatively low maintenance and trouble-free
service, especially if the filtering requirement is not too fine. Problems can develop if they receive large amounts of debris or seaweeds. However, this will be true for any kind of filter. Microscreens have also been used to remove solids from culture effluent (Bergheim et al., 1993). They are much more compact than a sedimentation chamber and have faster processing time. Microscreens also reduce the amount of water associated with the sludge, simplifying sludge handling and disposal. 10.8 Sedimentation Sedimentation depends on the particle density relative to the fluid, particle shape and particle size. The larger the particle size and density, the faster the particle will settle. Very small particles such as clay may not settle at all, as the random movement of water molecules is larger than the settling velocity. Sedimentation in marine culture systems may be required to remove sand from the influent or waste solids from the discharge. The ideal sedimentation tank is commonly rectangular with a uniform horizontal fluid velocity (Vh). The solids that collect on the bottom of the basin must be removed either
146
periodically on shutting down of the unit or automatically during normal operations. Ideally the performance of the settling basin is independent of basin depth but practical considerations associated with sludge accumulation limits the use of shallow basins. Typical depths are in the range of 1.2-1.8 m . For a single sized particle with a settling velocity of Vc, complete removal of the particles will occur when: Vc:
OVh L
(10.1)
where D is depth of basin (ft, m), L is length of basin in horizontal flow direction (ft, m), Vc is vertical settling velocity (ft/s, m/s), Vh is horizontal velocity, is Q~ cross-sectional area, is Q/D W (ft/s, m/s), Q is flow rate (ft3/s, m3/s), and W is width of basin (ft, m). Combining Eq. 10.1 and the definition of the horizontal velocity results in:
Q
Q
Vc -- L W : horizontal area of basin (10.2) The velocity Vc is also called the overflow rate or surface loading rate and is expressed in m/day or m3/m 2 per day. In practice, design must allow for inlet and outlet turbulence, short-circuiting, and sludge storage (see Example 10.3). Available data on settling rates of aquaculture solids and protocols for the measurement of settling rates are presented by Wong and Piedrahita (2000).
E x a m p l e 10.3. Sedimentation - - removal of uneaten feed and fecal solids It is desired to remove all particles with settling velocities greater than 0.5 i n c h / m i n from a 100 g p m flow. This is typical of a post-treatment process involving the removal of uneaten solid food and fecal matter. Compute the m i n i m u m length of the sedimentation basin. Assume a water depth of 1.8 m and a width of 3.0m. 0.5 i n c h e s / m i n = 18.29 m / d a y 100 g p m = 545 m 3/day Eq. 10.2, Ve = Q / ( L x W) or 18.29 -- 5 4 5 / ( L x W) (L)(3.0) = 29.8 m 2 L =9.9m If 1000 mg/1 of solids drop out in the sedimentation basin, how long will it take to deposit a 6 inches layer? Assume that the average density of the deposited solids is 1500 k g / m 3 and the solids are uniformly distributed. 6 inches -- 0.152 m Volume of solids = (0.152)(3.0)(9.9) = 4.51 m 3 Mass of solids --- volume x density -- 4.51 m 3 x 1500 k g / m 3 -- 6772 kg Deposition rate --- flow rate x concentration = (100 gpm x 3.78 1/gal x 60 m i n / h x 1000 mg/1)/106 m g / k g -- 22.8 k g / h Mass of solids -- deposition rate x time Time = 6772/22.8 = 297 h -- 12.4 days
147 In real systems, there is a wide range of particle sizes present. All particles having settling velocities greater than Vc, will be completely removed. If the particle sizes are uniformly distributed at the inlet zone, particles having velocities less than Vc will be removed in the proportion of V~ Vc, where V is the settling velocity. Decreasing the overflow rate will remove smaller or lighter particles at the expense of increasing the size of the sedimentation basin. The determination of the overflow rate required to meet a given removal efficiency can be based on batch settling testing or pilot-scale experiments. The designs of sedimentation basins for aquatic culture sygte-riis are quite different from those used in wastewater treatment. Freshwater hatchery wastes are denser, settle faster, and tend to form a heavy viscous sludge (Mudrak, 1981). The solids loading to the sedimentation basin tend to be lower than wastewater applications so that continuous sludge removal is not generally required. However, if the sludge is allowed to remain for much longer than six weeks, it may become very viscous and difficult to remove (Mudrak, 1981). To reduce the amount of water that must be treated, a variety of dual drain systems have been used in production applications. Solids that accumulate on the bottom are removed by a separate drain while the majority of the clean water is discharged from an upper drain (Timmons et al., 1998). The solids concentration in the bottom waste stream can be a factor of 10 times or higher than the concentration of solids in the upper drain. Because the bottom flow ranges from only 1% to 20% of the total flow, the capacity of the solids processing equipment can be reduced by a factor of 5-100. In addition, the higher solids concentration in the bottom water discharge results in improved sedimentation efficiency more typical of primary sedimentation. Typical overflow rates range from 40 to 60 m/day for cold water fish and 160 to 175 m/day for warm water fish. The overflow rate should be based on the peak hourly flow. Mudrak (1981) has recommended that an earthen stabilization pond follow the sedimentation basin. The pond should be designed with a 4 h detention time and an average depth of 1.2 to 1.5 m. This pond will serve as a 'buffer zone' should any operational problems occur with the sedimentation basin. Based on freshwater fish precedents, a properly designed sedimentation system should be able to remove approximately 85% of solid wastes (Mudrak, 1981) and produce effluent solids concentrations near 6 mg/1 (Henderson and Bromage, 1988). Detailed information for most marine animal wastes is lacking at this time (see Section 3.3). An ongoing dramatic change is in the sophistication and availability of prepackaged (modular and prebuilt) wastewater treatment plants and systems for modest flow rates well within our area of interest. Much of this equipment may be readily useable to meet culturing wastewater treatment needs, especially if using double drains on culturing units to drastically reduce water entrainment with waste solids. With the nature of culturing solid wastes, one can expect this equipment to work even better than it does with municipal wastewater. Most of this equipment is already made with materials suitable for exposure to seawater (plastics, fiberglass, etc.). Another change is greatly increased restrictions on sludge handling and disposal. Simple sludge drying beds may no longer be acceptable due to concerns about smell, public health and possibilities of ground water contamination. Since even 'good quality' sludge may have more than 90% water content, removing this water (dewatering) can considerable simplify sludge handling and disposal. Again, equipment from the wastewater treatment field may be directly useable.
148 W h i l e s e d i m e n t a t i o n is often u s e d to r e m o v e s u s p e n d e d solids f r o m effluents b e f o r e discharge, there is a n o t h e r s e d i m e n t a t i o n situation c o m m o n in coastal a q u a c u l t u r e facilities, w h i c h is i n a d v e rt e n t . T h e s u s p e n d e d solids c o n c e n t r a t i o n s in coastal water is h i g h l y variable. It d e p e n d s on s e d i m e n t sources and e n v i r o n m e n t a l c o n d i t i o n s in a specific coast al area at a g i v e n time. M a j o r factors are b o t t o m agitation c a u s e d by waves, tidal currents and their inte r ac t i o n s with the coastal bathymetry. T h e c o n c e n t r a t i o n s are k n o w n to be often h e a v i l y d e p e n d e n t on p r e c i s e e l e v a t i o n a b o v e the b o t t o m . T h e r e is a lot k n o w n about this turbid l a y e r a b o v e the b o t t o m in e s t u a r i n e areas u n d e r n o r m a l c o n d i t i o n s (general l y with t h i c k n e s s e s of inches to feet), but u n d e r the effects of m a j o r s t o r m s it is entirely a different matter. S e a w a t e r intakes (see S e c t i o n 4.4) are g e n e r a l l y a foot or two a b o v e the b o t t o m and c l o s e to shore, w h e r e the s u s p e n d e d m a t e r i a l s are likely to h a v e the h i g h e s t c o n c e n t r a t i o n s d u r i n g storms. S u s p e n d e d m a t e r i a l s b r o u g h t in to the facility will tend to settle at the first low v e l o c i t y parts of the s y s t e m . T h e s e can be h e a d tanks, s u p p l y c h a n n e l s , w e t wells or st orage tanks. U n d e r n o r m a l c o n d i t i o n s the a c c u m u l a t i o n rate of s e d i m e n t s in these areas can be e x p e c t e d to be m o d e s t but can a c c u m u l a t e to a p p r e c i a b l e depths o v e r a p r o l o n g e d p e r i o d of time. A n e x a m p l e of this slow a c c u m u l a t i o n is p r o v i d e d in E x a m p l e 19.6. H o w e v e r , w h e n m a j o r s t o r m s hit coastal areas the s u s p e n d e d solids c o n c e n t r a t i o n s in s h a l l o w coastal waters can i n c r e a s e m a n y f o l d . A lot of this m a t e r i a l can be c o a r s e and very fast settling given a chance. It is also p o s s i b l e that certain c o m b i n a t i o n s of wind, waves, tide, and fiver flow c o u l d p r o d u c e the s a m e effects w i t h o u t the p r e s e n c e of an actual s t o r m event. A few feet of solids a c c u m u l a t i o n f r o m a single event, e v e n in tanks or c h a n n e l s with m o d e s t d e t e n t i o n times, are not u n c o m m o n .
Example 10.4. Estimating storm sedimentation in a storage tank A tidal pumping system draws water from the mouth of a river from a salt wedge, which is present at high tide. Seawater is pumped for a minimum of 3 h per tidal cycle to a large storage tank. The average flow rate to the facility is 500 gpm (1900 lpm). Due to the mix and interactions of waves, river currents and tidal currents, a lot of sediment can be suspended from the bottom in this area. A really rare and nasty storm can have effects which last a maximum of 48 h and can produce in the estuary an average suspended solids concentration of 50 ml/1. Since the storage tank has considerable volume margins that are seldom used, the detention time in the tank is at least 6+ hours. With this very long detention time, a suspended solids capture efficiency of at least 70% (and very possibly higher) can be anticipated. (A) If the tidal pumping storage tank is 20 m in diameter, how thick a solids blanket can be deposited by this single storm? Flow over 48 h -- 1900 x 2 • 1440 = 5.47 x 106 1 Solids deposited = (0.7)(50)(5.47 x 106) - 1.92 x 108 ml = 192 m 3 Bottom area = 314 m 2 Depth of solids blanket = 192/314 = 0.61 m = 2.0 ft (B) If the settled material contains a lot of sand and has a specific gravity of 1.3, what is the approximate weight of solids that must be handled from this single event? Solids volume = 192 m 3 Sludge weight = 10,000 x 1.3 x 192 = 2.5 x 106 N -- 561,151 lb = 281 tons
149 If the detention time in the first 'slow spot' is less than 1 h, appreciable quantities of the finer and lighter solids may not settle there but proceed through the system accumulating or causing complications down stream. Solids accumulation must be anticipated during design and means provided for accessibility, removal and handling. Unfortunately, there does not seem to be any published data on suspended solids concentrations or compositions at seawater intakes in shallow coastal waters during major storms. In the absence of real data, some estimates must still be made. An example (see Example 10.4) is provided with an average of 50 ml/1 suspended solids in the influent for 48 h. The concentration could equally be much higher for a shorter interval and get the same result. If there is a lot of 'lighter' and 'fluffier' materials present, the accumulation depth could be considerably greater. Suspended solids concentrations in shallow coastal areas due to major storms are believed to be higher than those encountered in wastewater treatment processes. In waste water treatment the typical ranges for settleable solids is 5-20 ml/1 and suspended solids 100-350 mg/1, with the settleable solids typically being 60-65% of the suspended solids on a weight basis (Tchobanoglous and Burton, 1991). Converting between volume and weight is complicated by the fact that weight is on a dry basis and volume measurements are wet loosely packed solids with highly variable properties in water. Solids accumulation due to storm effects can prove to be a serious operational problem in coastal facilities.
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151
Chapter 11
Heating and Cooling
11.1 Setting requirements The heating or cooling of culture water is a frequent systems requirement (see Appendix H). This may be to eliminate natural temperature variations and achieve longer periods of time at optimum growth temperature or to provide a number of precisely controlled temperatures for research purposes. If species exotic to the region are involved, heating or cooling may be essential for survival. Rapid changes in temperature, even for temperatures within the natural range of an organism, can easily prove fatal. Such fatal temperature changes could occur by turning something 'on' or 'off', or by the failure of a seawater heating or cooling system. The reliability and modes of failure of such systems can assume considerable importance. While the tolerance of marine organisms to temperature changes varies considerably, a rule of thumb is to limit temperature changes to a maximum of about 2~ (l~ Tolerances to momentary temperature changes are higher, although any rapid change will, at the least, be a source of stress. Fortunately, most culture organisms of interest are estuarine, with relatively high tolerances to temperature changes. Deep sea organisms and those from isothermal environments may prove much more sensitive to both water temperature values and fluctuations. Most of the requirements are for seawater heating rather than cooling. The two requirements are very similar. The principles, concepts, and some of the equipment would be common. The major difference would be in the need for a heat source for heating rather than a heat sink for cooling. It is often not appreciated that heating or cooling seawater involves moving considerable energy. The energy units most commonly used are the British Thermal Unit (BTU) and the gram-calorie. A BTU is defined as the energy necessary to raise the temperature of one pound of water one degree Fahrenheit at a water temperature of I~ The gram-calorie is the energy necessary to raise one gram of water one degree centigrade at 4~ In place of the gram-calorie, the kilogram-calorie or large calorie (1000 gram-calories) is often encountered in the literature. These heat-energy values for water can be assumed to be constant with temperature and salinity over the conditions encountered in aquatic systems. The efficiencies of the processes are defined as the energy moved divided by the energy input. For heating, this value must be less than one or 100%. For cooling, if a refrigeration cycle is used, the value is called the coefficient of performance and usually has a value greater than one. Energy flows (power), into or out of the seawater, can become substantial. See Appendix A for conversion factors between the various energy and power units. Thus to raise or lower 1 gpm I~ requires 8.5 BTU/min or 0.2 hp (149 W), assuming 100% efficiency. One lps raised or lowered I~ requires 1026 calories/s or 4300 W (5.8 hp). As an example, a winter
152 Seawater Temperature Increase (~ 10 20 1200
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Fig. ll.1. Seawater heating requirements. Based on a unit flow of one gallon per minute of seawater, fuel oil at 19,000 BTU/lb and specific gravity of 0.9, and several different overall thermal efficiencies. Lower efficiencies are due to heat losses at furnace, piping, and heat exchanger. Value will be determined primarily by degree of insulation provided to components. Also shown is the numerical example from Example 11.2.
heating requirement could be to raise 100 gpm 40~ This requires 800 hp to be transferred into the fluid. Typical fuel oil has a heat content of 19,000 BTU/lb, and this need would require about a gallon of fuel every 4.25 min or 339 gallons/day, assuming 100% efficiency. Fig. 11.1 provides information for a wider range of conditions. For higher flows, multiply the fight side results by the flow rate in gpm to get the required power or fuel oil inputs. The transfer efficiency will be determined primarily by the type of system and amount of thermal insulation provided. For high flow rates and large temperature increases, the energy costs can easily get out of hand, even at 100% efficiency. Seawater heating systems have been installed in test facilities and laboratories that could not be used to anywhere near their capabilities due to the impacts of high fuel costs on limited operating budgets. There are a few direct heating methods. One is the use of thermostatically controlled electric quartz or Teflon immersion units. While small ones are common in home aquariums, larger industrial units are available to very substantial power levels. Powers up to 1 kW are available in 120 volts and some as high as 3 kW may be available (see Example 11.1). Higher power units require higher voltages, which can substantially increase the risks around seawater to both culture organisms and operating personnel if not properly handled. These units typically have very high transfer efficiencies and can control the temperature to about a degree F (half degree C). However, they sometimes fail full 'on', resulting in an unintentional
153
Example 11.1. Electric immersion heat transfer Readily available electric power is limited to 120 V AC power. The highest readily available rating for a thermostatically controlled quartz immersion heater in 120 V AC is about 1 kW. How many gpm of seawater (30 ppt, 50~ can you heat to 80~ with a single immersion unit? Assume such electric resistance heating is 100% efficient. From Table A-3, average specific weight seawater (65~ is 63.8 lb/ft 3 Seawater is 63.8 lb/ft 3 or 7.48 gal/ft3 is 8.5 lb/gal Temperature change is 80~ - 50~ is 30~ Heat transfer in BTU/min is (flow in gpm)(8.5)(30) is 255(flow) Conversion factor, 1 BTU/min is 17.58 W 1000 W available is 56.88 BTU/min is heat transfer 255(flow) is 56.88 Seawater flow rate is 0.223 gpm per immersion heater Or directly from Fig. 11.1, 30~ 100%, read about 4.2 kW/gpm 1 kW/4.2 kW/gpm = 0.23 gpm
cooking of the culture organisms. Another possibility is direct steam injection. Some care would have to be taken as to its location in the system and, to our knowledge, it has never been used in culturing applications. Most heating or cooling processes need a heat source or heat sink. This is often also a fluid, which may or may not be seawater. If this fluid is in a closed loop and simply a carrier of heat from some other heat source or sink, it is called a working fluid. C o m m o n working fluids include steam, freshwater and a number of chemical refrigerants. Natural heat sinks and sources can be many and varied, and may be seasonal. They include lakes, the atmosphere, ocean, ground water, earth and rock. Any large mass with temperature above or below the culture water temperature can be utilized. The higher the heat capacity of the mass material the better. It may be possible to add heat to the mass in the summer and withdraw it in the winter. If these masses have temperatures that are higher (heating) or lower (cooling) than the desired culture temperatures, the processes can be simplified to simple heat transfer. If the heat sink is a pumpable fluid, it can be directly used through a heat exchanger. If the heat sink is a solid, a loop with a separate working fluid will be needed. If the heat source does not have quite high enough temperature, it can still be used with the addition of a heat pump. A heat pump is a refrigeration cycle run in reverse so that heat is removed from a 'cold' source and transferred to a 'warm' area. Depending on the temperatures of the heat sink and desired temperature, heat pumps can be designed to both heat and cool. Some care would have to be taken to prevent unintentional leakage of the working fluid into the culture system. Depending on the thermal fluid's properties and toxicity, this could be critical. The greater the temperature differences, the more attractive is the prospect of using natural heat sources or sinks. While such use is highly dependent on specific circumstances, when conditions permit, they often provide simple, reliable and inexpensive temperature control capabilities. If their temperatures are in the fight direction but not sufficient, they may still be used but powered assistance will be required.
154 For heating applications, the most common source of heat is an oil- or gas-fired boiler. These units are commercially available in a wide range of sizes and have excellent reliability. However, they generally have electrically powered controllers and thus will automatically shutdown on loss of electricity, even though they are run from an independent power source. This is an important factor in evaluations of overall system reliability and of need for backup electric power. Other sources of heat include waste heat from engines, power plants or solar collectors. Many of these heat sources may not be under the control of the culturist. Sudden loss or change in the heat supply could be catastrophic. Reliability and assurance of supply issues have precluded use of what might otherwise be a valuable resource. For cooling a refrigeration or chiller unit is generally used to cool a working fluid (usually a chemical in a sealed loop) to below the desired seawater temperature. These units usually include an evaporator, compressor, condenser, expansion valve, and control circuitry. They tend to be more complex and difficult to operate than heating units. A very common mistake is to enclose the refrigeration system in a small space without adequate ventilation. Since the heat removed from the working fluid must be discarded by the condenser, if ventilation is inadequate the space will quickly heat up and system performance will rapidly drop.
11.2 Heat exchangers Most heating and cooling processes will require the use of one or more heat exchangers. The heat exchanger separates the working fluid from the process water, while efficiently transferring heat between the two fluids. This prevents the corrosion of the heating or cooling equipment by seawater and contamination of the process water by potentially toxic working fluids. Due to the corrosive properties of seawater, considerable engineering efforts have been devoted to the design of marine heat exchangers. However, their use in aquatic culturing systems involves biological constraints not typically of other industrial seawater heat exchangers (see Sections 8.1 and 8.2). Heat exchanger types that have been successfully used in marine culturing applications are shown in Table 11.1. Some are for use with pressure on both the seawater and working fluid sides. Others can be used directly in open tanks, with only the working fluid being pressurized. In this case, the circulation in the tank has to be controlled to assure uniform heat transfer (see Fig. 16.1). Carbon and titanium units are particularly well suited to most marine culturing applications. Stainless steel (type 316) heat exchangers are readily available and common in marine applications, but should be used with caution in culturing systems (see Section 8.2). The symbol U shown in Table 11.1 is the overall heat transfer coefficient generally associated with the respective heat exchanger types and materials. It is an important parameter in sizing heat exchangers and is generally stated in equipment specifications. Heat transfer is a complex subject and is dependent on flow configuration, heat exchanger internal design, materials and fluid properties. Flow configurations include parallel, counter and cross flows. Counter flow is the most efficient in that it results in the smallest heat exchanger. It is also the type most likely to be encountered. In counter flow the seawater to be heated or cooled flows in the opposite direction to the working fluid. Total heat transfer must be integrated over the entire heat exchanger. Assuming steady flows, no phase changes,
155 TABLE 11.1 Industrial heat transfer devices for heating and cooling seawater (modified from Huguenin, 1976a) Material
Types available
Comments
Impervious carbon
Bayonet and plate immersion, crossbore and shell/tube, cascade coolers, etc.
Heat transfer areas of 0.5-12,000 ft 2, in order of increasing size-bayonet, plate, crossbore and shell/tube. Carbon has high thermal conductivity. For shell/tube water-water U = 150-250 BTU h -1 ft -2 ~
Glass
Coil, bayonet, cascade coolers, and shell/tube
Low thermal conductivity of glass compensated for by higher film coefficients and reduced fouling. Coils with 2-120 ft2 of heat transfer area are available. Shell/tube areas in multiples of 13.5 or 60 ft2. For shell/tube water-water U = 125-195 BTU h-1 ft-2 OF-1
Glass (electric heating only)
Bayonet-type quartz immersion heaters
Units of 300-1000 W with built-in thermostats will hold within 0.5~ Units of up to 36,000 W available in several configurations. Maximum of 3000 W possible with 120 volt power.
Teflon
Immersion coils and shell/tube
Low thermal conductivity but relatively high film coefficients and reduced fouling. High frictional loses across tubes. Heat transfer areas of 2-900 ft 2 and in small volumes. Shell/tube water-water U = 25-40 BTU h -1 ft -2 ~
Titanium
Heat transfer panels, plates and shell/tube
Variety of standard panel configurations with areas of 2-42 ft 2. Panel water-water U = 100-175 BTU h -1 ft -2 ~ value depends heavily on seawater circulation. Plate water-water U = 550-800 BTU h -1 ft -2 ~ -1 but high frictional loses. Titanium offered as optional material by some manufacturers of large industrial shell/tube heat exchangers. Shell/tube water-water U = 225-280 BTU h -1 ft -2 ~ -1
Stainless steel (Type 316)
Heat transfer panels, plates, shell/tube, etc.
Most manufacturers offer their units in 316 stainless. Very wide selection of sizes and types. Under some conditions 316 stainless steel can be incompatible with seawater and culturing applications. Panel water-water U = 100-175 BTU h -1 ft -2 ~ Shell/tube water-water U -- 225-280 BTU h -l ft -2 ~
c o n s t a n t specific heats, and n e g l i g i b l e h e a t losses, p r o v i d e s the e q u a t i o n s below. Q-
UA(LMTD)
L M T D --
(11.1)
DTA - DTB
(11.2)
ln(DTA/DTB) w h e r e Q is h e a t t r a n s f e r ( B T U / h ) , U is o v e r a l l coefficient o f h e a t t r a n s f e r ( B T U h -1 ft -2 ~
A is e f f e c t i v e a r e a o f h e a t e x c h a n g e r (ft2), L M T D is log m e a n t e m p e r a t u r e d i f f e r e n c e
o f b o t h fluids (~
DTA is t e m p e r a t u r e d i f f e r e n c e s b e t w e e n inputs (~
d i f f e r e n c e s b e t w e e n outputs (~
DTB is t e m p e r a t u r e
F o r c o u n t e r - f l o w w i t h b o t h fluids w a t e r and about equal flow
rates, DTA -- DTB and L M T D - DTA. Eq. 11.1 is a g o o d a p p r o x i m a t i o n for all t y p e s o f h e a t e x c h a n g e r s , a l t h o u g h a c o r r e c t i o n factor m u l t i p l i e r (less than 1) is n e e d e d for c o m p l e x m u l t i - p a s s units. T h u s for the c o m m o n
156
Example 11.2. Shell and tube heat exchanger sizing We have a winter heating requirement and wish to heat a maximum of l0 gpm of incoming seawater from 40~ to 70~ We wish to use a single pass carbon shell and tube heat exchanger. The heat exchanger will be connected in a counter-flow arrangement with its own circulator pump to a hot water system and it is expected to provide 20 gpm at 200~ (see Fig. 11.2). We need to size the heat exchanger, and for estimating operating costs, we need to estimate heat inputs and fuel oil requirements. From Table 11.1 for carbon shell and tube heat exchangers find a U-value of 150-250, so we will use U = 200 BTU h -l ft -2 ~ Heat input into the seawater can be obtained from Fig. 11.1 by using 100% efficiency. This results in a requirement of about 255 BTU/min per gpm. For 10 gpm, this means that 2550 BTU/min or 153,000 BTU/h must to transferred into the seawater. While the seawater in (40~ and out (70~ temperatures and the heating system in (200~ temperature are known, the hot water exit temperature may not be known. In this case the circulator flow rate is given and from knowing that the heat gained by the seawater must have come from the heating water, assuming no heat losses in the heat exchanger, the exit temperature must be about 185~ If the heating system has a high circulating flow, the temperature drop will be small. Even if one assumes no temperature drop of the hot input water, this will often not substantially change the required heat exchanger area. DTA = 2 0 0 - - 4 0 = 160~ DTB= 1 8 5 - 7 0 = l15~ LMTD = (160 - l15)/ln (160/115) = 136.3~ Q = 153,000 = (U)(A)(LMTD) = (200)(A)(136.3) A = 5.6 ft 2 of heat exchanger area From available options supplied by manufacturers, choose the next size above 5.6 ft 2. There will be some heat losses in the heating plant, heat exchanger, and piping runs. These losses will depend on the provided insulation. If we assume a 70% overall efficiency (30% thermal losses), going into Fig. 11.1 with a 30 degree temperature increase we find an estimated fuel oil requirement of about 3.8 gal/day per gpm or about 38 gal/day.
case of a s i m p l e counter-flow heat e x c h a n g e r , a s t r a i g h t f o r w a r d a p p r o x i m a t i o n is avai l abl e for e x c h a n g e r sizing (see E x a m p l e 11.2). A n e x a m p l e for h e a t i n g in an o p e n tank is given in E x a m p l e 11.3. T h e s e a w a t e r input and d e s i r e d output t e m p e r a t u r e s are usual l y k n o w n , as is the input t e m p e r a t u r e of the w o r k i n g fluid. Q can be c a l c u l a t e d f r o m the s e a w a t e r flow rate and r e q u i r e d t e m p e r a t u r e c h a n g e , l e a v i n g only the u n k n o w n h e a t - e x c h a n g e r h e a t - t r a n s f e r area. If n e e d e d , the w o r k i n g fluid output t e m p e r a t u r e can be c a l c u l a t e d f r o m fluid properties, a s s u m i n g that there are no heat losses out of the heat exchanger. C o r r e c t i o n factors for m u l t i - p a s s shell and tube units can be o b t a i n e d f r o m e n g i n e e r i n g texts such as M a r k ' s H a n d b o o k ( B a u m e i s t e r et al., 1978) or e q u i p m e n t m a n u f a c t u r e r s . A m o r e c o m p l e x shell and tube e x a m p l e , w i t h o u t s o m e of the s i m p l i f y i n g a s s u m p t i o n s p r e v i o u s l y m a d e , is p r e s e n t e d in E x a m p l e 11.4. W h i l e heat e x c h a n g e r s are not u s u a l l y cheap, they are not n o r m a l l y the d o m i n a n t cost c o m p o n e n t in a h e a t i n g or c o o l i n g system. B e c a u s e of m a n y uncertainties in r e q u i r e d c a p a c i t y or transfer coefficients, it is g o o d practice to c o n s e r v a t i v e l y size the heat exchanger. In this
157 way, the system's performance will be limited by the capacity of the heat source or sink, rather than by the heat exchanger. When money is limited, a number of inexpensive heat exchangers can be built, especially for temporary or small-scale applications. If a little rust is acceptable, epoxy painted cast iron radiators can be successfully used. Interestingly, a thin epoxy coat is better than a thicker one, because it is less likely to develop small cracks in the coating due to thermal stresses and will have higher heat-transfer rates. Even materials with poor thermal conductivity can be used, if the area is sufficiently large. Large coils of polyethylene pipe have been used as a heat exchanger in outdoor algae tanks. In this case, the heat source was brackish ground water at about 55~ (13~ It was sufficient to keep the algae ponds from freezing and in dramatically improving winter algal production for a commercial shellfish hatchery. 11.3 P r o b l e m areas
Cross-contamination between the working fluid and the process water can cause serious damage to both systems. Probably the biggest single risk is leakage through the heat exchanger or some of its associated fittings. Glass and carbon heat exchangers in particular are brittle and can crack due to miss handling during shipment or installation. Leakage of seawater into the working fluid can cause corrosion problems in the heating or chilling unit and dramatically alter the performance of the system. Since the working fluid is likely to be at a higher pressure than the process water, leakage into the culture system is more likely than the other way around. Such leakage of working fluid into the culture system can be serious, since many of the possible working fluids have significant toxicity to culture organisms. Even if the working fluid is fresh water, it may contain significant quantities of undesirable contaminates (rust inhibitors, metals, hydrocarbons, etc.). The heat source or sink may be the heating or cooling system of a building or industrial plant. This can work, but there are some potential problems in addition to cross-contamination. The building systems were probably not designed with culturing uses in mind. The loads on these systems from the culturing requirements and their consequences, as well as the mechanics of 'tapping-in', have to be investigated. From the culturing standpoint, it may be critical to understand the workings and timings of other demands and functions upon the system. The heat source/sink may be sufficiently variable in its temperature and flow as to make control of the culture unit's heating/cooling system very difficult. Resulting temperature variations could be lethal. The probability of total or partial failure also has to be considered. In addition, the plant being relied upon may have inconveniently planned and unplanned shutdowns over which the culturist has little control or influence. Some of these shutdowns may be for a number of possible reasons, such as maintenance, overhaul, or during holidays. Powering down during periods of school holidays is common at some universities. It may be cheaper and less risky to have a completely dedicated system to support culturing operations. There are a number of ways in which heating and cooling systems can fail. The heat source or sink can be cut off. Even momentary events may shutdown the system. Even when the power source is an on-site fuel, electric power losses to the controls can shutdown the system. On return of electric power, the system will often have to be manually restarted. Pressure losses, flame losses, insufficient fluid levels, etc. can also cause shutdown. If culture water continues to flow, the culture organisms may see a sudden and dramatic temperature change and the consequences could be lethal. It is usually better to immediately stop the flow, even though
158
Example 11.3. Open tank seawater heating A thin-walled titanium heat transfer panel is required to heat 5 gpm of 30 g/kg seawater from 30~ 70~ in a large open tank (8 ft long, 4 ft wide and 1 ft water depth) as shown in Fig. 16.1. This is the most demanding heating requirement that the system will experience. Hot water (200~ in large quantities is supplied from the building's hot water heating system. (A) Calculate the minimum panel heat transfer area required (being optimistic) and state the actual size that you would specify for this application. Table 11.1 gives a U-value of 100-175 BTU h -1 ft -2 ~ for this type of heat exchanger and states that the value is highly dependent on circulation. From Fig. 16.1 it is clear that circulation in the tank is artificially aided by a pump, greatly increasing convective heat transfer. The desired temperature increase is 70 ~ - 30 ~ = 40~ From Fig. 11.1, this requires an input of 345 BTU/min per gpm and 26 gal of fuel oil/gpm per day at 100% efficiency. If there is little opportunity for heat loss except between the two fluids across the heat exchanger, the efficiency will be high. At 100% and a flow of 5 gpm, the total requirement is for 1725 BTU/min or 130 gal of fuel oil per day or equivalent at the exchanger. Remember that this is a small research system and that the heating requirement is continuous seven days a week. The total fuel requirement would have to be adjusted for boiler inefficiencies and heat losses in the building's distribution system. Even though the panel is not completely a counter flow situation, the forced convection makes it a fair assumption and Eq. 11.1 can be used. The flow rate from the building's hot water system is not known but is stated to be high. The temperature drop of the hot water across the heat exchanger can therefore be assumed to be negligible. DTA = 2 0 0 - - 3 0 = 170~ DTB = 2 0 0 - 7 0 - - 130~ LMTD--(DTA--DTB)/ln(DTA/DTB) = (170 ~ 130~176 ~ = 150 U -- 175 BTU h-l ft-2 OF-1 (good circulation and being optimistic) Q = 1735 BTU/min = 103,500 BTU/h Q - - ( U ) ( A ) ( L M T D ) = 103,500 = 175 • a • 150 A -- 4
ft 2
(minimum panel heat transfer area, no losses, optimistic U)
A safety and contingency factor of 2 would not be inappropriate, making the area requirement 8 ft 2. The same operating conditions but using the lowest U (100), calculates out to 7 ft 2. The tank's water depth is 1 ft. If the panel is oriented in the preferred vertical plane (why would a horizontal orientation be less efficient?), this makes its maximum width to be 1 ft. For a required heat transfer area of 8 f t 2 and considering that the panel has two sides, results in a 1 x 4 ft heat transfer panel as shown in Fig. 16.1. (B) What are the potential problems inherent with this type of system? Discuss and quantify these problems and your approaches to reduce the risks and potential adverse consequences. 9 If the cold incoming seawater is saturated with dissolved gases, heating it will result in substantial levels of supersaturation. From Table 2.7, it can be seen that the saturation concentration of oxygen at 0~ is 11.9 mg/1 but only 7.5 mg/1 at 21~ producing a 158% supersaturation of oxygen. Similarly for the other dissolved gasses, especially for the more critical inert gases such as nitrogen. Fortunately this supersaturation takes place in a large open tank. The flow of 5 gpm (0.67 ft 3/min) and the tank's water volume of 32 ft 2, results in a residence time of 48 rain. The amount of gas removed in the tank will be limited, and some type of degassing system may be needed. For sensitive larval stages, degassing will be needed if hot and cold water are mixed even if both waters are saturated with dissolved gases. This is a result of the non-linearity of gas solubility with temperature.
159
E x a m p l e 11.3. (continued) 9 Another potential problem is loss of heat input, possibly due to heating plant shutdown or failure. It is vital to not expose the culture organisms to a rapid 40~ temperature drop. Even if the thermal shock is tempered by the water mass in the tank, it is almost certain to still be fatal. Prompt action is essential. Note in Fig. 16.1 that an alarm system is provided. If prompt restart of heating can not be accomplished, the cold water inflow must be stopped and water conservation measures (priority allocations and aeration) implemented. Auxiliary heating, such as immersion heaters, might be used to allow some cold water inflow. Electric heaters may not help much if the original failure is a loss of electric power to the building heating system's controls. In this case, a backup power source, even if limited, might prove critical. If the tank runs dry, the headbox pump must be turned off to prevent pump damage. 9 Another potential disaster is loss of seawater inflow. Since this heat exchanger is manually controlled, the water in the tank would be heated to levels well beyond those desired before being depleted. This type of failure would expose the culture organisms to a high temperature thermal shock followed by loss of flow. Prompt action is also required in this case. If water inflow can not be quickly restored or otherwise acquired, the heating must be turned off and the same water conservation measures previously mentioned imposed.
loss o f w a t e r m a y r e s u l t in d e c r e a s i n g d i s s o l v e d o x y g e n c o n c e n t r a t i o n or b u i l d u p o f a m m o n i a a n d o t h e r m e t a b o l i c s . T h e loss o f w a t e r c a n b e p a r t i a l l y c o m p e n s a t e d b y i n c r e a s i n g a e r a t i o n . H o w e v e r , this c a n b e d o n e o n l y if the f a i l u r e is i m m e d i a t e l y d e t e c t e d a n d a c t i o n taken. A s a c o n s e q u e n c e , h e a t - e x c h a n g e r c u l t u r e - w a t e r o u t p u t t e m p e r a t u r e s are a c o m m o n m o n i t o r i n g
Compressed Air Supply Hot W a t e r from Boiler Returnto ~,, Boiler ~~--7 ~
~'t"~~
~\~e
~ "
vNO~veRetu rn [
~
C o n t r ~
Signal.L,---~"T'~ I Temperature
& Aut~
I [~
Valve ~
1173 Con,ro,,er ~
) I
Warm ~ ) ~ , . . ~ ~ ' Seawater Out
J
Sensor
re
Heat Exchanger sC~
-
I ~
~ Drain
Fig. 11.2. Typical temperature control configuration using hot water heat source. Expanding and reducing fittings, circulator pump and line valves are not shown.
160
Example 11.4. Performance of given shell and tube heat exchanger You acquire use of a single pass counter-flow shell and tube titanium heat exchanger with 10 ft 2 of heat transfer area in a hot water loop as shown in Fig. 11.2. The dedicated hot water circulator provides 10 gpm at a temperature of 200~ at the heat exchanger. You have to maintain marine animals at 70~ during the winter. The coldest winter seawater temperature is 30~ the salinity is 30 ppt and you can assume negligible heat losses in and around the heat exchanger. (A) What is the maximum seawater flow rate you can count upon during the coldest part of the winter? The heat gained by the seawater must equal the heat lost by the hot water. The seawater inlet and outlet temperatures and hot water inlet temperature and flow are known. The seawater flow rate, hot water outlet temperature and the heat transfer (Q in BTU/h) are not known. The specific heat of seawater and freshwater are both about 1. The average specific weight of the seawater is estimated at 63.8 lb/fl 3 and 61.0 for the hot freshwater. F is the unknown seawater flow rate, T the hot water exit outlet temperature and 0.1337 the conversion factor (Table A-l) for gal to ft 3. The most pessimistic U of 225 from Table 11.1 for this type of heat exchanger is used in Eq. 11.1. Heat gained by seawater (BTU/h) = heat loss by hot water (BTU/h) A TswgswFsw = A THW)/I-IWFHW Q -- (60)(0.1337)(40)(61)F -- (60)(0.1337)(200 ~ - T)(63.8)(10) = 225(10)LMTD Q = 19,574F = 1,023,607-5,118T = 2,250(LMTD) Three equations and three unknowns, assuming a seawater flow rate, solving for T and LMTD and comparing to Q from Eq. 11.1, see below: Seawater flow, F (gpm)
Hot water outlet temperature, T
DTB, T - 7 0 (~
(~ 12 13 14 15
154.1 150.3 146.5 142.6
LMTD, 1 7 0 - DTB
Water balance, Q (BTU/h)
Eq. 11.1, Q (BTU/h)
234,888 254,462 274,036 293,610
274,651 269,090 263,475 257,625
In ( 170 \ 84.1 80.3 76.5 72.6
122.1 119.6 117.1 114.5
From inspection of the above and interpolation, the maximum seawater flow rate is about 13.6 gpm. (B) Assume that the boiler is relatively inefficient and the hot water distribution system is poorly insulated so that only half of the fuel oil's energy reaches the heat exchanger. If your seawater flow rate is the maximum, what is your worst case daily fuel consumption? From Fig. 11.1, temperature change is 40~ 50%, read 6.8 gal/day per gpm 6.8(13.6) = 92.5 gal/day
p o i n t o n a l a r m s y s t e m s . A f t e r the p r o b l e m c a u s i n g the s h u t d o w n is r e s o l v e d , the s y s t e m m u s t be c a r e f u l l y r e s t a r t e d to p r e v e n t t h e r m a l t r a n s i e n t s that m a y stress or kill the c u l t u r e o r g a n i s m s . Another major source of problems with heating and cooling systems involves problems w i t h the c o n t r o l s y s t e m . M u c h o f the a v a i l a b l e l i t e r a t u r e d e a l s w i t h t e m p e r a t u r e - c o n t r o l p r o b l e m s , e s p e c i a l l y for r e s e a r c h a p p l i c a t i o n s ( A p p e n d i x H). A t y p i c a l h e a t i n g a r r a n g e m e n t u s i n g h o t w a t e r f r o m a b o i l e r is s h o w n in Fig. 11.2. I f the p r o c e s s ( c u l t u r e ) w a t e r flow rate a n d
161 the ambient seawater temperature stay constant or change only slowly over a long period of time, this control system may be unnecessary (see Fig. 16.1). In this case the control system in the boiler, which maintained the hot water output from the boiler at a constant set temperature, and a heat-exchanger hot-water supply valve could be relied upon to accurately control the heat-exchanger culture-water output temperature. If there are tidal or daily ambient-seawater flow rate or temperature variations, a more active control system as shown in Fig. 11.2 will be required. This system monitors the process-water output temperature from the heat exchanger and controls a three way valve to bypass or use hot water from the boiler. If the 'dead band' on the heat-exchanger controller is set too wide, the resulting temperature fluctuations may stress the animals. This effect can be greatly reduced with higher water residence time in the culture units to dilute the temperature-controlled influent. If the band is too tight, the control system will be continuously operating, may overshoot and may become unstable, producing temperature pulses. If the power or air to the controller fails, the heating system will usually fail closed, which is the same as a heat loss. If it is configured to fail open, the culture organisms may be unintentionally cooked.
This Page Intentionally Left Blank
163
Chapter 12
Aeration and Degassing
12.1 Aeration system requirements Aeration or the addition of oxygen is one of the most common processes needed in culture systems. This may be required due to use of seawaters low in dissolved oxygen or to increase carrying capacity. Seawater may be supersaturated with oxygen and nitrogen gas due to heating, photosynthesis or breaking waves. Operational problems with piping, pumps, and water processing equipment, heating of process water, or aeration can also result in high levels of gas supersaturation (Colt, 1986). In addition, seawater from wells may contain high levels of hydrogen sulfide and carbon dioxide gases. All of these later conditions may require degassing. The design of aeration equipment is based on (1) the amount of oxygen needed, (2) the minimum dissolved oxygen concentration, and (3) the concentration of other gases such as nitrogen, hydrogen sulfide, and carbon dioxide. For juvenile fish and crustaceans, a minimum criterion of 6 mg/1 dissolved oxygen is generally used. It may be desirable to maintain dissolved oxygen higher than 6 mg/1, especially for eggs and very small fry. The average daily oxygen demand of aquatic species can be computed from Eq. 2.20 as a function of temperature and weight or from Eq. 2.21 as a function of ration. For salmon and trout, maximum daily oxygen demand is commonly assumed to be 1.44 times the average rate (Eq. 2.22). This assumption may under-estimate oxygen demand for active fish and over-estimate the oxygen consumption for mollusks. Aeration and reuse of water can increase the carrying capacity, if all the other water quality parameters are acceptable. Due to the high pH of seawater, un-ionized ammonia may be more limiting than dissolved oxygen under many situations (Section 2.7). Aeration and reuse of water under these conditions will result in increased disease and mortality problems. Commonly, aerators are designed to produce oxygen concentrations equal to 90-95% of local saturation values. As will be discussed in a following section, it is generally not economical to achieve saturation. For applications that have very high oxygen demands or requirements for oxygen concentrations greater than 95% of saturation, pure oxygen aeration systems should be considered (Colt and Watten, 1988; Colt and Orwicz, 1991b).
12.2 Gravity aerators Gravity aerators operate by allowing the water to run down over a physical substrate, thereby increasing the available air-water surface area. Gas transfer takes place at this interface. Since the process occurs at atmospheric pressure, there is no chance of producing gas supersaturation as there is with submerged aerators. Based on mass-balance considerations,
164 Header or Distributional r Plate I ! ! ,
Inflow i
I
l
Column Open at Top and Bottom to Allow for Air Circulation
hb b:6 0
o,,oq II O0
i - High Surface Area Low Flow Resistance Packing Media
9o_OV~ o,
'---Grating to Support --t~
Header or Distribution./ v h Plate ,, . . . .
=,~ lit
o,t
i
B
~-
''l
lilt
;,, ;,
I ~ - I
Column Open Top and Bottom to Allow for Air Circulation
'i I #ii |
II II I
Zl
~l--Inflow
.,
~
'~
Perforated or Slotted Plates
', /
,
Media
Outflow
, r'~"
:, , /ii a ..//',, .'/:, ;'fi ,i,
*
-~,
~
Outflow
~I--Inflow
.b, e ,
i ,.T,,
C
%, I :"~ ~r v,ll
L__ ,'"i,i,j I
"
Outflow
Fig. 12.1. Types of gravity aerators: (A) packed column aerator, (B) perforated-plate aerator, and (C) lattice aerator.
the amount of total and available dissolved oxygen in the effluent from a gravity aerator is equal to: Total dissolved oxygen (lb/h) = 5.00 • 10-4(Q)(DOout)
(12.1)
Avail. dissolved oxygen (lb/h) = 5.00 • 10-4(Q)(DOout- DOmin)
(12.2)
where Q is flow (gpm), DOout is effluent dissolved oxygen (mg/1), and DOmin is minimum dissolved oxygen (rag/l) Three common types of gravity aerators are shown in Fig. 12.1. The packed column aerator (Fig. 12.1A) consists of a column filled with a large surface area of a plastic medium. These mediums are available in a variety of sizes and shapes, such as barrel-shaped, curved or round. An ideal medium would have a high specific surface area (medium's surface area/medium's volume) and low resistance to air and water flow. While small mediums tend to have higher specific volume, biofouling may limit the use of a medium with a dimension of one-half inch or smaller. Many of the available types of mediums are also commonly used in biofilters (see
165
8 -25mt"~ j/85//,//:~,,~0
~ 0 9 Saturation
t/ / "-
T
"
2 .5
9
54_1.5 /
~
0
4 0-
3
2
~-1
I ~
~
50 5
0
0~'-
I0
~
9
--" o . v
k'DOout(mgl#)
60 15
70 20
80
(~
25 30 Temperature (~
Fig. 12.2. Packed aerator column height with DOin = 0 mg/1. Calculations assume 1.5 inch pall rings and a salinity of 35 g/kg. Calculated from Hackney and Colt, 1982.
Section 15.2). Water runs downward over the medium in a thin film, allowing absorption of oxygen from the air. The perforated tray aerator (Fig. 12.1B) consists of a series of vertically stacked perforated trays. Oxygen is absorbed as the water drips from one tray to the next. The lattice aerator (Fig. 12.1C) consists of a number of straight steps. The water runs down the steps in a thin film; thus, oxygen is transferred into the water. Important design considerations for gravity aerators include hydraulic loading rate (gpm/ft2), total available height (elevation), and operational limitations. Since the performance of the units will vary with temperature and influent water quality, design should be based on the specific project conditions. In the absence of specific site conditions, the most conservative values must be used. This will generally result in a workable system, but at increased costs. While gravity aerators are simple and have no moving parts, they only function when water is flowing; therefore, they may not be suitable for some applications. 12.2.1 Packed Columns The design of packed columns is based on influent DO concentrations, effluent DO concentrations, temperature, and salinity. Based on the work presented by Hackney and Colt (1982), column heights are presented for an influent DO = 0.0 mg/1 (Fig. 12.2) and an
166 7ft
6
O
5
9
,"
~/ 8
o ff-0.9
of Saturation Value
..C
._~
,/o
ESS
7.O
~o
~
0.5
0
6.5
9
~o--
o
6.o1~
o
1 ___~__o_.___~..o__5. 5 - - - o ~ ~DOout (mg/.~) 0
s
......
50 I,,.
60 i
70 ,
80 i
I
(~
2's so Temperature (~
Fig. 12.3. Packed aerator column height with DOin - 5 mg/1. Calculations assume 1.5 inch pall rings and a salinity of 35 g/kg. Calculated from Hackney and Colt, 1982.
influent DO -- 5.0 mg/1 (Fig. 12.3). These column heights include 0.25 ft for the influent line and 0.25 ft for the outlet collection system. It is also assumed that no distribution plate is used, reducing the efficiency of the column by 25%. Figs. 12.2 and 12.3 are based on a medium of 1.5 inch pall tings, a readily available size with good overall characteristics. The performance of packed columns based on mediums with other sizes and shapes can be calculated with the design equations presented by Hackney and Colt (1982). The required column height to achieve 90% saturation, decreases as the temperature increases; however, the required height to achieve a given DOout, in mg/1, significantly increases with increasing temperature. In the absence of influent dissolved oxygen information, Fig. 12.2 should be used for seawater wells and Fig. 12.3 for surface waters and reaeration of process waters (see Example 12.1A). If designing to achieve 90% of saturation, the design column height must be based on the minimum yearly temperature. If designing to achieve a dissolved oxygen concentration in mg/1, the design column must be based on the maximum yearly temperature. The required column heights increase significantly as the desired effluent DO concentration approaches saturation. Theoretically, an infinitely high column is required to produce a saturated effluent concentration. Based on a conservative hydraulic-loading rate of 25 gpm/ft 2, the capacity of standard large-diameter plastic pipe suitable for packed column aerators is presented in Table 12.1.
167
Example 12.1. Evaluation of aerator options A flow-through system with a flow of 250 gpm is used to rear cod to a weight of 1.25 lb each. Assume a maximum feeding rate of 1.5%/day, an influent DO of 5 rag/l, a minimum DO of 6 mg/1, water temperature of 10~ and salinity of 30 g/kg. (A) Compute the required height for a packed column to support 1,300 animals. Ration = (1300 animals)(1.25 lb/animal)(0.015) = 24.4 lb feed/day Eq. 2.22, using an OFR : 0.20 lb/lb feed (0.20 kg/kg feed) Maximum oxygen demand -- 1.44 x 0.20 x 24.4.45 = 7.03 lb/day = 7.03/24 -- 0.293 lb oxygen/h Eq. 12.2, 0.293 = (5 x 10-4)(250)(DOout - 6), DOout = 8.34 mg/1 Using Fig. 12.3, read column height = 5.2 ft (B) If a 3 ft lattice aerator is to be used, how many cod can be supported? From Table 2.7, C* = 9.32 mg/1 Percent saturation influent --- (5.0/9.32) 100 = 54% Use the 50% saturation curve in Fig. 12.4, effluent DO is 74% of saturation Effluent DO = 9.32 x 0.74 -- 6.9 mg/1 Eq. 12.2, available DO -- (5 x 10-4)(250)(6.9 - 6) = 0.113 lb oxygen/h From (A)" 0.293
0.113
1300 animals
X animals
X = 501 animals (C) Compute the blower horsepower required by a fine bubble aerator placed directly in the rearing tanks to support 1300 fish. Assume that No is 2.0 lb oxygen/kW per hour, c~ -- 0.80, # --- 1.00 and an aerator depth of 4 ft. Since aerators are rated in freshwater, use the freshwater value for Cstd in Eq. 12.3. Table 2.7, C* = 9.32 mg oxygen/1 Eq. 12.6, Ceff = 9.32(l + O.O16(4)) = 9.92 mg/1 Eq. 12.3: N - - - 2 . 0 / l( 1
x 9 " 3 2 --6 ) ( 1 " 0 2 4 ' ~ 1 7 6 9.02 Eq. 12.8, Blower hp -- 1.5 x 0.293/0.46 -- 0.96 hp I_
- = 0.46 lb oxygen/hp per hour 1
TABLE 12.1 Flow capacity of column aerators using large diameter pipes Column diameter (inches)
Flow gpm
lpm
12 16 18 24 30 36 48
20 35 44 79 123 177 314
74 132 167 297 464 668 1188
Calculations based on standard thin-walled plastic pipes and a loading of 25 gpm/ft 2.
168 Since there is little pressure on the column walls, the columns can be constructed from thin PVC pipe or fiberglass. Depending on the configuration of the system, it may be more desirable to use a number of smaller columns rather than one large column. This is especially true if the packed column is used prior to filtration. Under these conditions, fouling of the medium by barnacles, mussels or debris may be serious and it may be necessary to clean the column periodically. If a fully redundant system is designed (two columns), potential fouling organisms can be killed by alternating between the two columns every 2-3 weeks. For small columns, it may be practical to simply replace the fouled column with a clean unit. The biofouling organisms can be killed by allowing the column to dry. 12.2.2 Perforated Tray Aerator Detailed design information is not available for the perforated-plate aerators. Strasburg (1964) presents plans for a 100 gpm unit for aeration of anaerobic water from a seawater well for use with skipjack (Fig. 12.1B). The final design consisted of 16 perforated trays at 2 inch vertical intervals. The tray having 1/8 inch holes at 1/2 inch intervals. The overall dimensions of the aerator were 7 x 7 x 4 ft high. The trays could be withdrawn for cleaning, although this was not required due to the lack of biofouling with well water. This type of system may be ideal for small-scale applications, although the hydraulic loading (2.0 gpm/ft 2) is about 1/12 of that for a packed column, resulting in a much larger unit for a given flow. 12.2.3 Lattice Aerator A lattice type of aerator (Fig. 12.1C) is used in the La Jolla laboratory of the National Marine Fisheries Service (Lasker and Vlymen, 1969). The performance of a lattice aerator is presented in Fig. 12.4 as a function of influent DO and total height. These data are based on 2 inch steps, 36 degree slope, and 7.39 gpm/ft of width. This aerator is probably useful for aerating normal seawater with oxygen concentrations not too far from saturation, but would require excessive heights for water with low dissolved oxygen concentrations. For a flow of 100 gpm and a loading of 7.39 gpm/ft, the width of the system would be 13.5 ft. Increasing the hydraulic loading rate will decrease the performance. The surface area contained in a lattice aerator, 10 x 10 x 5 ft high, is equal to the surface area of only 5 ft 3 of 1.5 inch pall tings. One significant advantage of this type of system is that it is relatively resistant to the growth of fouling organisms such as barnacles and mussels (see Example 12.1B).
12.3 Submerged aerators Submerged aerators can be placed directly in the rearing or holding system and generally use a central source of low pressure air. Therefore, a number of individual units can be operated from one blower and individual units can easily be turned off and on. Gas supersaturation, corrosion and biofouling problems will limit the use of many of the more efficient submerged aerators. Only two types of submerged aerators are commonly used in seawater systems: diffused aerators and airlift pumps. The diffused aerator consists of a porous diffuser connected to a source of low pressure air, or in some systems, low pressure oxygen. Diffusers can be made
169 80-
o'/o "/o
70-
~- 6 0 -
.~o
/
o
/
0 7 ~ D O i n = 5 0 % Saturation /
/ /o
~0 5 0 o
v 0
a
40 -
/
y
o
w 50-
jo / O'
DOin = 0 % Saturation
o 2O 0.5 I
1
I
1.5 (rn)
1 I
2
/
5
I
I
4
I
Height (ft)
Fig. 12.4. Performance of lattice aerators. Based on 2 inch steps, 36 ~ slope and 7.39 g p m per foot of width. From Tebbutt, 1972.
of porous bonded silica, carbon, or polyethylene, and can be found in a range of shapes and sizes. The diffusers produce small bubbles. As the bubbles pass through the water, oxygen is transferred from the bubbles into the water. An airlift pump consists of a vertical tube with a diffused aerator placed inside the tube at, or near, its bottom. If the airlift pump is used for pumping (raising the water above the water surface), the vertical pipe will extend above the water surface (Fig. 12.5A). In many cases the airlift pump is used for mixing, and oxygen transfer, and therefore does not extend above the surface (Fig. 12.5B). The transfer efficiency of submerged aerators is usually stated at standard conditions of barometric pressure of 760 mm Hg (1 atm), temperature of 20~ and clean water conditions. The standard transfer efficiency is expressed in lb oxygen/hp per hour, or kg oxygen/kW per hour. The transfer efficiency under other conditions (Colt and Tchobanoglous, 1981) can be computed from the following equations: N -- No
( f l C e f f -- C )
1.024T-20Ot
Csto
(12.3)
N is transfer efficiency under field conditions (lb oxygen/hp per hour), No is transfer efficiency under standard conditions (lb oxygen/hp per hour), Ceff is mean effective dissolved oxygen saturation concentration (mg/1), Cstd is saturation dissolved oxygen concentration (mg/1) at 20~ barometric pressure 760 mm Hg, and salinity of interest, C]eld is saturated dissolved oxygen concentration (mg/1) at barometric pressure of 760 mm Hg, temperature and salinity of interest, C is bulk dissolved oxygen concentration in transfer system (mg/l),
170
o
o
9Q
--rLift
9,
~
A
I
0 o
Submergence
T~
1
OD
Air in
,0 0
~
0 '
oo o e
B
~0
oo
bo ~
o
Curr~'nt
T
o o
Submergence o 0 u
or 0 2 in Air
,~ v
0
J
Fig. 12.5. Airlift parameters: (A) pumping application, and (B) mixing or aeration application.
T -- temperature (~ fl --
-
C~eld
C~]d transfer rate - field conditions transfer rate - standard conditions
(12.4)
(12.5)
The mean effective saturation concentration of dissolved oxygen (Cen) is greater than the saturated values at the surface (Fig. 12.6) due to the effect of hydrostatic pressure. The actual increase in concentration will depend on the type of diffuser, bubble size, contact time, and turbulence. In the absence of specific data, the following relationships may be used: Ceff - C~eld (1.00 + K Z)
(12.6)
where Ceff is effective saturation value under field conditions (mg/1), Cfield* is saturation value under field conditions (mg/1), K is 0.008 for coarse and 0.016 for fine bubble diffusers, and Z is depth of diffuser (ft). In freshwater catfish ponds, values of fi are approximately equal to 1.0 and the value ot ranges from 0.66 to 1.07 (Shelton and Boyd, 1983). Under intensive culture conditions, values of fl may be lower than found in ponds. It is important to note that the fi value can
171 1.15 -
Lethal Gas Bubble Trauma Problems
~- 1.10-
0
I I
P_ Chronic Gas Bubble Disease P r o O f s
._
Q.
. . . . . . . . . . .
1.05
t .0
0
25
1 I
5
2 I
5 I
7.5
1.0
(m) I
12.5 Depth (ft)
Fig. 12.6. Increase in effective saturation due to hydrostatic pressure. This factor should be multiplied by the tabulated (standard pressure) saturation concentration at the specified temperature and salinity to find the maximum effective values.
not be measured with an oxygen probe because this instrument measures partial pressure (or fugacity) rather than concentration. Temperature will be the dominant factor in determining transfer efficiencies. For diffused aeration, the following values of the standard transfer rate (N) in lb oxygen/hp per hour may be used for preliminary design calculations Fine bubble diffusers Medium bubble diffusers Coarse bubble diffusers
2.0 1.6 1.0
The transfer efficiency under field condition depends strongly on the dissolved oxygen concentration (C) that is needed or desired. For a fine bubble diffuser, salinity of 35 g/kg, ot = 0.9,/~ = 1.0, diffuser depth 3 ft, the transfer efficiency under field condition is presented as a function of temperature and dissolved oxygen concentration in Fig. 12.7. The standard transfer rates of airlift pumps may be only 1/5 to 1/2 of the value for diffused aeration systems (Loyless and Malone, 1998). This appears to be due to the coalescence of air bubbles as they rise up the airlift riser. 12.3.1 Absorption Efficiency Absorption efficiency is the percent of oxygen transferred from the air to the water. The absorption efficiency depends on temperature, water depth, air flow, type of diffuser, and dissolved oxygen concentration (Mavinic and Bewtra, 1976). Air flow rate is measured in terms of standard cubic feet per minute and represents the flow rate at a temperature of 68~
172
5O
1.0[
~
Temperature(~ 60 70 I
80 i
I
09t~
y
ut
9
' c ~D
/-P)
x
o .IQ ~ z
9
o. 1
5
,
,
10
15
20
So,u?ion 25
,
:50
Temperature (~ Fig. 12.7. Field transfer rate (N) as a function of DO and temperature. Based on a No of 2.0 lb oxygen/hp per hour, salinity of 35 g/kg,/3 = 1.0, ot = 0.90, and diffuser depth of 3.0 ft. (20~ pressure of 14.7 psi (1 atm or 760 mm Hg), and 36% relative humidity. One standard cubic foot of air contains 0.0521 lb of air and 0.0173 lb of oxygen. The variation of absorption efficiency with depth and dissolved oxygen concentration is presented in Fig. 12.8. This is derived from freshwater data and a flow of 2.0 standard cubic feet of air per minute per square foot (Mavinic and Bewtra, 1976). The absorption efficiency is reduced at low water depths and high dissolved oxygen concentration. At typical aquaculture conditions, less than 1% of the oxygen is absorbed by the water. The actual mass of oxygen absorbed into the water is equal to: Oxygen absorbed (lb/h) = (1.038)(AE)(Qair)
(12.7)
where AE - absorption efficiency (decimal fraction, value in Fig. 12.8 divided by 100), and Qair is air flow (standard cubic feet per minute - scfm). The design of submerged aeration systems (diffused and airlift pumps) includes the design and specification of the diffusers, number of diffusers, piping, and blower. Design will
173
DO (% Saturation)
5
//
g4 -
g3
-
2
1
0
95%
0
I
2
I
I
4
I
l
6
I
I
I
3 (m) I
I
8 10 Diffuser Depth (ft)
Fig. 12.8. Absorption percentage as function of depth and DO. Based on o~ = 1.0, /3 = 1.0, temperature of 20~ salinity of 35 g/kg and a barometric pressure of 760 mm Hg (1 atm).
strongly depend on temperature, salinity, dissolved oxygen concentration, and diffuser depth. Once the oxygen demand is computed, the aeration system can be sized by two methods. The first method involves the estimation of the field transfer efficiency (Fig. 12.7) as a function of the temperature and required dissolved oxygen concentration and the computation of the total blower power from: 1.50 • OD Blower power (hp) = (12.8) N where OD -- oxygen demand (lb/h), and N is transfer efficiency (lb oxygen/hp per hour). The factor 1.50 is equivalent to assuming that the overall efficiency of the motor and blower is 67%. This method can be used to estimate the power requirement for a complete system (see Example 12.1C). The second method involves computing the required air flow rather than the blower power. Once the absorption efficiency is determined from Fig. 12.8, the oxygen absorbed can be computed. This method may be more convenient when the amount of air is fixed or the air flow per unit is known from other considerations. 12.3.2 Blower Selection Air used for aeration must be oil-free and typically in the 3-5 psi range. Three common types of low pressure compressors are the rotary vane compressors, rotary lobe compressors, and regenerative blowers. When the rotary vanes are constructed from carbon, a small amount of fine carbon dust may be present in process air. This material can be filtered, but is inert and
174 should have no effect on most aquatic animals. High pressure building air (60 to 100 psi) can be used, but must be filtered to remove oil and water. Many high pressure compressors are not rated for continuous duty and the high volume demand from an aeration system may result in early compressor failure as well as high power costs. The output of low pressure blowers depends on their discharge pressure and varies from high flow at low pressure, to low flow at high pressure. As the pressure of a blower is increased beyond the normal operating range, a phenomenon called surging may occur. This results in the rapid fluctuation in output between maximum and zero pressure. Surging can result in serious damage to bearings and rotating components. Most blowers are protected from surging by the installation of a high pressure relief valve. The relief valve will prevent the pressure from exceeding a safe level. The selection of a blower will depend on the air flow rate and system head (or pressure) requirements. The total pressure that a blower has to produce depends on the depth of submergence of the diffuser, the pressure losses through the diffuser, and the pressure losses in the distribution systems. Similar to Chapter 6, it is usually more convenient to express pressures in units of head or elevation (see Section 6.4 for definition). Some care has to be taken with clearly identifying the fluid column being considered. A unit head of water and one of air are quite different. Typically a blower is connected to a distribution system and a diffuser at a given submergence or depth below the surface. The head at the blower will be equal to: Total head (ft) = submergence + ULpipe § HLdiffuser
(12.9)
where submergence is submergence depth of diffuser (ft), HLpipe is head losses in the pipes (ft), and HLdiffuser is head losses in the diffuser (ft). The submergence term is equal simply to the submergence depth of the diffuser. The HLpipe term depends on air flow, pipe size, pipe roughness, and pipe length. Head losses in plastic pipe as a function of flow and pipe size are calculated the same way as was done with water in Section 6.4. In this case the fluid is air and the equivalent sand roughness values for clean pipe (Table 6.3) can be used, because there is no risk of biofouling with air. Typical piping frictional losses are presented in Table 12.2. Since blower manufacturers usually present their compressor data in psi, and to avoid possible confusion between heads of water and air, the frictional losses in the table are presented in psi per 100 ft of pipe. At the low pressures being considered, gas compressibility is not a major factor. However, the gas temperature will vary in the piping and choosing a representative temperature value is difficult. The compression of air in the compressor results in a significant rise in the temperature of the air. These high temperatures will be seen by the compressor's discharge piping. If this piping is made from synthetic materials such as plastics, the temperature may be high enough to substantially reduce the strength of the pipe and to release from the piping potentially toxic compounds to the compressed air. Such problems are most likely to occur when two parallel compressors are turned on at the same time. Considerable care should be taken with the piping in the immediate area of the compressor and a section of steel pipe may be needed. The HLdiffuser term depends strongly on the type of diffuser (the smaller the bubbles the higher the head losses) and air flow rate. Commonly only the frictional loss at the rated flow capacity (either in head or pressure units) is published by diffuser manufacturers. To determine the head losses at other flow rates, it is necessary to calculate the loss coefficient (K) for the diffuser the same as one would do for any other piping component (see Section 6.5).
175 TABLE 12.2 Frictional losses for air as a function of flow and pipe size Flow rate
Nominal pipe sizes (inches)
SCFM
1/2
5 10 15 20 30 50 75 100 125 150 200 250
3/4
1~1
1
2
vel.
loss
vel.
loss
vel.
loss
vel.
loss
vel.
loss
35.0 70.0 105 140
0.68 2.43 5.17 8.66
19.9 39.8 60.0 79.6 120 199
0.18 0.61 1.18 2.07 4.51 11.6
12.3 24.6 37.0 49.2 73.8 123 184 246
0.06 0.19 0.40 0.67 1.40 3.56 7.42 12.9
5.2 10.4 15.7 20.9 31.3 52.2 78.3 104 121 157 209
0.01 0.02 0.05 0.08 0.17 0.43 0.90 1.54 1.99 3.26 5.63
3.2 6.3 9.5 12.7 19.0 31.7 47.5 63.3 79.1 95.0 127 158
0.00 0.00 0.02 0.03 0.05 0.13 0.27 0.46 0.68 0.93 1.62 2.44
Calculations based on Schedule 40 PVC pipe internal diameters, pipe equivalent sand roughness of 4.2 • 10-5 ft, average pressure of 3 psi, average air temperature of 90~ and an air kinematic viscosity of 1.7 • 10-4 ft2/s. Velocities are in ft/s and frictional losses in psi per 100 ft of pipe. Under this temperature and pressure, the SCFM volume is 13% greater than actual and the conversion for frictional head losses in feet of air to psi is loss (psi) -head (ft)/1661.
Once the total head losses of the system at different flow rates are computed, a compressor (air pump) must be selected to supply the desired flow. This is exactly the same match-up problem between system and pump presented in Section 7.4. At the operating point, the head (or pressure) produced by the blower must be equal to the losses in the system (Fig. 12.9). Blower manufacturers and distributors are very helpful in this process. It should be noted that if rearing or holding units are operated with different water depths, the system must be designed to provide air to the deepest unit. Valves must be installed on the distribution lines to the shallower units to increase the head losses. If this is not done, all the air will flow to the shallower units. If the total system head losses increase, the blower output will decrease. The greatest source of increasing system head losses is diffuser clogging from either pipe scale or bacterial growth on the exterior of the diffuser. Some diffusers can be cleaned by soaking in acid or chlorine solutions. Removal of scale lodged deeply in the diffuser may be difficult or impossible. External clogging occurs more rapidly if the diffuser is submerged but not in use (i.e., no air flow). Therefore, diffusers should be removed from the water when not in use.
12.3.3 Pumping and Mixing In many situations, mixing rather than aeration is needed. Larval culture must be continuously mixed to (1) prevent the animals from settling out, (2) prevent the feed from settling out, or (3) distribute both the feed and animals evenly over the rearing volume. Phytoplankton and
176 If System Losses Are Changed, System Curve Will Shift Resulting in New Operating Point Compressor Curve / Provided by Manufacturer
Q) -~
o"
'~"
Increased Losses
\/"
o/
o Decreased ~ ~/~/ Losses Individual Calculation for ~"O~Operating Point Assumed Flow / System "~.~.'_i ~"~ L;urve
,
-'-4/ Loss / from Diffuser
es
\
from Pipes and Fittings
\
\
Submergence Air Flow Rate (SCFM) Fig. 12.9. Matching of aeration piping system with compressor. The operating point is where the system curve intersects the manufacturer's compressor curve. If there are any changes in the system, such as turning individual aerators 'on' or 'off' or adjusting any valves, the system's curve will move resulting in a new operating point.
seaweed cultures may be mixed to give the individual organisms exposure to the light, prevent settling, and to steepen gas concentration gradients on plant surfaces. Both diffused aeration and airlift pumps may be used for mixing. The mixing characteristics of diffused aerators is not well documented, but they have been used extensively in culture systems. Coarse bubble diffusers and high airflow rates may be more useful for mixing than medium or fine bubble diffusers. The design of a mixing systems is based on the criterion for pumping or a turnover rate (pumping flow rate/rearing volume). The number of units and their size are to be specified to achieve the required turnover rate. A number of smaller units may provide a more uniform mixing condition than a few large units. The distance between the water surface and the point to which the water is pumped is the lift. The submergence is the distance between the water surface and the level where the air is introduced. The percent submergence (Fig. 12.5A) is equal to: submergence (ft) Submergence ratio - X = (12.10) submergence + lift (ft) The maximum pumping rate of an air-lift pump depends on the submergence, lift, and pipe diameter (Spotte, 1979): Q - [ ( 0 . 7 5 8 x 3 / z ) ( L 1 / 3 ) + 0.11961]d 22
(12.11)
where Q is water flow rate (1/min), X is submergence ratio, L is submergence + lift (cm), and d is inner pipe diameter (cm).
177
Example 12.2. Air lift pump
A 4 inch (10 cm) diameter airlift pump picks up water 30 inches below the surface and drops it 1.5 inches above the surface. Calculate the submergence ratio and estimate the water flow rate in lpm and gpm for air flows of 1, 5, and 10 ft3/min. Eq. 12.10, submergence ratio is 30/(30 + 1.5) -- 0.95 Fig. 12.10, using D = 10 cm, X = 0.95, air injection at 30 inches -- 76 cm, approximately equal to 75 cm (line D) 1 ft3/min air --- 90 lpm (24 gpm) 5 ft3/min air --- 190 lpm (53 gpm) 10 ft3/min air = 260 lpm (68 gpm)
At high submergence ratios, the efficiency of the airlift pump is comparable to a centrifugal pump. Below a submergence ratio of 0.50, the efficiency of the airlift decrease rapidly (see Example 12.2). For applications requiting lifts of 0.1 to 3 ft, airlift pumps may be more efficient that centrifugal pumps, especially for flows less than 50 gpm. The selection of low-flow, low-head pumps is limited, especially for marine applications. The primary applications for low-head pumps are for irrigation or flood control and flow rates of 10,000 to 100,000 gpm are not uncommon. When centrifugal pumps are used for low-head applications, it is likely that they are medium- or high-head pumps operated far to the left of their best efficiency point (bep) and at a low efficiency. No general expression is available for the computation of the gas-to-liquid (G/L) ratio at the maximum water flow rate. The G / L ratios typically ranges from 3 to 35. Smaller G / L ratios can be used at high submergence ratios and for small diameter pipes. Generally, the air is introduced into the airlift at a single point without a diffuser. Parker and Suttle (1987) present water flow rate versus air flow rate for submergence ratios in the range of 0.90 to 1.00 for a number of pipe sizes. These types of airlift pumps are used for mixing. The maximum water flow rate occurred when the air was introduced at the lowest depth (Fig. 12.10). The water flow rate depended on the logarithm of the airflow rate. Therefore, a linear increase in water flow rate requires a proportionally larger increase in the airflow rate. The pumping characteristics of airlift pumps depend strongly on the construction of the units, especially the entrance and exit conditions (Loyless and Malone, 1998). Since their construction is simple and inexpensive, there is little standardization among designs. Care must be taken when applying published performance information. Under some operating conditions, the pumping performance of airlifts does not depend on the type of injector or diffuser used (Loyless and Malone, 1998). For a given system and airflow rate, the water flow rate was the same, but the power requirement for the diffuser option was significantly higher because of the higher head losses in the diffuser. However, the oxygen transfer and carbon dioxide stripping characteristics of the diffuser option was superior under most airflow rates. Therefore, there may be design trade-offs between the pumping and gas transfer requirements of a single unit.
178 Air FI0w (cfm) 600 500 E 400 0.
==t
~= 300 _o I.I.
.1.-
200
1 "1
5 I
I
10 I
/ B
-
I
III
f ~
//.c/.
-
-
50
I IIIIII
0 O/ ~ i o o ~o%o/ _ ~ , , / G
~ao 1oo
o
1 I00
140
~ o
:>5
oo
I,,,,,I
60
o IT ~.
40 , ,I,,,
t00 250 1000 Flow (@pro)
20
0
Air
Fig. 12.10. Water flow rates in an airlift. Airlift with an inside diameter of 10 cm with air injected at different depths below the surface: (A) 120 cm, (B) 105 cm, (C) 90 cm, (D) 75 cm, (E) 60 cm, (F) 45 cm and (G) 30 cm. From Parker and Suttle, 1987.
12.4 Gas supersaturation and degassing The use of submerged aeration equipment can result in lethal dissolved gas concentrations (Colt and Westers, 1982). For sensitive larval fish, this can occur at diffuser submergences as small as 1.0 m (Cornacchia and Colt, 1984). Higher levels of gas supersaturation result from the use of a fine bubble diffuser and other highly efficient submerged aerators. Approximate limits for diffuser submergence are presented in Fig. 12.6. Gas supersaturation problems will be relatively more serious in marine larval systems due to their increased sensitivity and required high concentrations of dissolved oxygen. In production systems, higher submergence can be tolerated because the ambient dissolved-oxygen concentration is likely to be significantly below saturation. Natural seawater may be supersaturated with dissolved gas from photosynthesis, solar heating, or air injection. Air entrainment on the suction side of pumps is a very serious problem in seawater systems due to rapid absorption of air (Kils, 1976). Air may be entrained due to leaks in the suction piping or through the pump seals (Colt, 1986). If saturated seawater is heated more than about 10~ (5.6~ it must be degassed prior to use. Lethal levels of gas supersaturation can be produced by submerged aeration systems and improper operation of water quality processes. In critical applications, the in-line installation of gas monitoring equipment is prudent (Bouck, 1982). The packed column, perforated tray, lattice aerator, and diffused aerators have all been used to degas water. The packed column is probably the most efficient degassing system (Bouck et al., 1984), but some of the other types may be used under special conditions. Also, more design information is available for the packed column compared to the alternative degassing systems. Perforated trays and lattice can be used for both aeration and degassing applications. These two systems are best suited for the degassing of natural seawater and probably should not be used for the degassing of highly supersaturated seawater.
179 5 -
4
-
-
~
tt
1.5
a)
10oC 50~
1
-g
v
r cD t
cE=2-
0 0
/
/ 4 f
/68
20~ ~F
rE
o.58
3ooc ~ B6~
/ 0
I
0
1
~/ I 2 :5 Influent DO (mg/.P)
~
4
0
5
Fig. 12.11. Degassing column heights for surface waters. Figure presents values that might be typical of supersaturated surface waters. Calculations based on 1.5 inch pall rings, influent supersaturation of 200 mm Hg, effluent supersaturation criteria of 20 mm Hg, and effluent DO criteria of 90% of oxygen saturation.
The design of packed columns for degassing will depend on the gas supersaturation level, gas supersaturation criteria, temperature, salinity, and medium's size (Colt and Bouck, 1984). The gas supersaturation criteria will depend on the species, life-stage and specific gases involved, but a maximum criterion of 20 mm Hg of total gas supersaturation can be used for many organisms. Naturally occurring gas supersaturation levels will strongly depend on rare or infrequent events such as storms, extreme low tides, or periods of high solar heating and low winds. Gas supersaturation levels in subsurface waters will be relatively more constant. The required column height for degassing will depend primarily on influent DO and A P (pressure above saturation, mm Hg) values. The column height information is presented in Fig. 12.11 for typical surface water (AP is 100 mm Hg) and in Fig. 12.12 for a groundwater (AP is 200 mm Hg). These figures are based on a packing medium of 1.5 inch pall tings, an effluent dissolved oxygen criteria of 90% saturation, an effluent gas supersaturation A P criteria of 20 mm Hg, 0.25 ft elevation allowed for inlet distribution and 0.25 ft for the outlet collection system. For different dissolved gas criteria or influent gas levels, column heights can be computed from Colt and Bouck (1984). The physical design of the degassing columns is identical to the aeration column presented previously. The cross-sectional area of the column can be based on a loading rate of 25 gpm/ft 2 or Table 12.1. As with the packed columns used for aeration, fouling by barnacles and mussels may be a problem and columns should be designed to allow easy replacement of mediums or with complete redundancy (i.e., at least two separate columns). The use of submerged systems, such as diffused aeration or airlift pumps, can result in some level of gas supersaturation (see Fig. 12.6). These systems will not reduce dissolved gas concentrations to equilibrium, regardless of the duration of aeration, and are unsuited for critical degassing applications. Diffused aeration or airlift pumps may have application in maintenance of dissolved oxygen and carbon dioxide concentrations in phytoplankton or
180
10o0 50~
/
_
1.5
/
"2
v
~.4
/
Y r-
20~ ~ 68~
/
Y
E 2
E z 5 o
o 0
86~
y I
2
4
_0.5 I
I
6 8 Influent DO (mg/~)
I
10
Fig. 12.12. Degassing column heights for groundwaters. Figure presents values that might be typical of supersaturated groundwaters. Calculations based on 1.5 inch pall rings, influent supersaturation of 100 mm Hg, effluent supersaturation criteria of 20 mm Hg, and effluent DO criteria of 90% of oxygen saturation.
greenhouse systems, or in other situations where slightly supersaturated concentrations of specific gases are desirable. 12.5 Removal of other gases
A number of other gases may need to be stripped out of process water. These include methane, carbon dioxide, and hydrogen sulfide. The removal of carbon dioxide and hydrogen sulfide present special problems because of their high solubility and liquid-phase chemical reactions. Methane is an insoluble gas that may be found in groundwaters and some ponds with high organic inputs. The bubbles observed rising from seawater ponds contain a significant amount of methane. Conventional packed column aerators are effective in removing this gas. In applications where a large amount of methane is present, the columns should be vented to the outside to avoid the potential for accumulation of explosive concentrations of methane gas. The carbon dioxide gas concentrations in marine groundwaters is highly variable and can typically range from below saturation (less than 0.5 mg/1) to 30-40 mg/1. While the concentration of carbon dioxide in surface waters is variable (and important to marine chemists), these variations are not important under most conditions. Carbon dioxide gas is difficult to remove because of its high solubility. Gas-to-liquid ratios in the range of 5-10 are needed to remove a significant amount of carbon dioxide (Piedrahita and Grace, 1994). When carbon dioxide gas is added to water, a portion is converted to bicarbonate and carbonate ions. Only the portion of carbon dioxide that is a gas can be removed in a gas transfer system. The kinetics of the carbonate system are slow compared to hydraulic transit time through a packed column. Therefore, only 40-50% of the added carbon dioxide gas can be removed by a well-designed packed column. For critical applications, packed columns are
181 not the best choice for carbon dioxide removal. The perforated tray or lattice aerator operated at very low hydraulic loading may have higher removal efficiency for carbon dioxide. Pure oxygen aeration systems remove a negligible amount of carbon dioxide because of very low gas flows. Diffused aeration or airlift pumps can also be used to remove carbon dioxide gas from culture units (Loyless and Malone, 1998). It is also important to note that the build-up of carbon dioxide gas in the gas phase will significantly reduce the effectiveness of carbon dioxide removal. High gas-phase concentrations of carbon dioxide have occurred in laboratory facilities built under strict energy conservation codes (restricted air flow rate). Hydrogen sulfide is similar to carbon dioxide, with high solubility and liquid-phase reactions with water. A forced-draft packed column is needed to strip significant amounts of hydrogen sulfide (Howe and Lawler, 1989). Because of the liquid-phase reactions, the amount of hydrogen sulfide removed depends very strongly on pH.
This Page Intentionally Left Blank
183
Chapter 13
Disinfection
13.1 Considerations and options
Disinfection is the reduction in the number of bacteria, viruses, or fungi to a desired concentration. Sterilization, or the complete elimination of all microorganisms, is generally not needed or in most cases not possible. The actual concentration of microorganisms required to cause a disease (or some other criteria) is not well-defined under most conditions, and disinfection procedures have developed primarily from an empirical basis. Disinfection may be needed for two distinctly different situations: (1) disinfection of nets, holding facilities, and piping prior to use; and (2) disinfection of process water prior to use or before reuse. In general, the first situation is much simpler as toxicity to culture organisms is not usually a problem. In the second case, the toxicity of the disinfection agent and its residues or derivatives to non-target organisms (i.e., culture organisms) is critical and will control the disinfection process. The effectiveness of a given disinfectant depends on the concentration of disinfectant, contact time, temperature, turbidity, particulate concentration, and specific microorganisms. Because the concentration of microorganisms varies widely, microorganism concentrations are typically expressed in what are called log units. If concentrations are expressed in #/ml, then the log concentration is equal to the base 10 logarithm of the actual concentration (see Table 13.1). The effect of disinfectant concentration and contact time on the mortality of typical microorganisms is presented in Fig. 13.1. For many microorganisms, the rate of kill is a straight line on a semi-log plot. Therefore, it takes the same time to reduce the concentration of microorganisms from 1,000,000 to 100,000/ml as from 100 to 10/ml. TABLE 13.1 Log units as used to define microorganism concentrations Log units concentration
(#/ml)
6 5 4 3 2 1 0 -1 -2 -3
1,000,000 100,000 10,000 1,000 100 10 1 0.1 0.01 0.001
184 _ A
E .~ 4
Initial Value
r" ~D 0
~ 3" E
2 0
"6~ 0 "
0ncentrati0ns of
" X-~-
"K~isinfectant
~ g-1-
x3
r-o
-P
0
I t
I
2
I 3
Time (min)
I 4
I 5
~ 6
Fig. 13.1. Effect of disinfectant concentration and contact time on mortality of typical microorganisms.
Note that a reduction in 1 log units is equal to a 90% reduction in concentration and a reduction in 2 log units is equal to a 99.0% reduction in concentration. Generally, as the concentration of disinfectant is increased, the rate of kill is increased. Therefore, to achieve a given final concentration of microorganisms, a high disinfectant concentration at a short contact time or a low concentration at a long contact time may be used. The options in disinfecting equipment are various chemicals, chlorine being the most common, and steam cleaning. Small steam generators are commonly used to disinfect culture equipment after a disease incident and work well on concrete, fiberglass, and epoxy tank surfaces but are unsuitable for most plastics or inaccessible areas, such as pipes. Chemicals can also be used to disinfect process water but only on a batch basis. Ultraviolet (UV) light is the most common method used in-line to treat process water. With some care, ozone treatment may also be useable in-line.
13.2 Chemical compounds There are many chemical disinfectants including chlorine, quaternary ammonium compounds, formalin, and iodine compounds. A good review of chemical options can be found in Flick (1998). An ideal disinfectant should quickly destroy bacteria, viruses, and fungi, but should have low toxicity to humans. The most commonly used disinfectants for netting and rearing containers are iodophors (organic iodine complexes) and common chlorine. Concentrations of iodophor in the range of 50-100 mg/1 for 10-30 min can be used to disinfect culturing equipment. One advantage of iodophors is the amber color which indicates the disinfectant is effective (Amend and Conte, 1982). Once the color turns yellow or colorless, it is no longer effective. While an ideal disinfectant, costs may limit the use of iodophor for large-scale applications.
185 TABLE 13.2 Recommended chlorine dosages for disinfection Item
Nets, buckets, boots Transport equipment Rearing containers
Time (min)
5 30 60
Requirement bleach (ml/1)
calcium hypochlorite (mg/1)
0.70 2.64 3.51
40 150 285
Values derived from recommendations of Amend and Conte (1982) and Hnath (1983). Assumes 3.70% available chlorine from bleach and 65% from calcium hypochlorite.
The most widely used disinfectant is chlorine. This may be applied as sodium hypochlorite (common liquid bleach), dry calcium hypochlorite or electrically generated in place from seawater. Chlorine is often used to disinfect in the batch mode (i.e., no flow-through) at relatively high concentrations and in the absence of any culture organisms. Concentrations recommended by Amend and Conte (1982) and Hnath (1983) for disinfection are presented in Table 13.2. These concentrations are based on 65% available chlorine for calcium hypochlorite and 3.70% available chlorine for sodium hypochlorite (bleach). Sodium hypochlorite solutions up to 15% are readily available from industrial sources. Household bleach typically is in the range of 3.70-5.25% available chlorine. The amount of chlorine compound added will have to be adjusted if the available chlorine percentages are different from the values in Table 13.2. Calcium hypochlorite (a solid, usually in granulated form) is more stable than sodium hypochlorite (a liquid) and occupies less space, but sodium hypochlorite is more available and easier to use (see Example 13.1). The disinfection power of chlorine depends strongly on pH. The presented time/concentration recommendations in Table 13.2 are based on addition of glacial acetic acid or sulfuric acid to produce a pH = 6.0. If it is not possible or desirable to drop the pH to 6.0, an immersion time of 24 h is recommended. The following procedure (Amend and Conte, 1982) must be used when acid addition is used. (1) Fill the tank or other container with the desired amount of water. (2) Add the amount of acid to the water. NEVER ADD WATER TO ACID. (3) After the water and acid are mixed, add the required amount of chlorine compound to the acidified water. Do NOT ADD THE ACID TO THE CHLORINE COMPOUND. Following disinfection, all equipment and holding tanks must be carefully rinsed to removed any remaining chlorine residual. First the chlorine containing water should be drained and then the water flow resumed. At least 6-10 container volumes should be passed through a rearing or holding tank before new animals are added. The surfaces above the water level should be washed down several times during this period. Inadequate rinsing of holding tanks or nets is a major source of mortality in hatcheries and holding facilities. Chlorine is commonly used to disinfect marine mammal pools (Spotte, 1991; Coakley and Crawford, 1998). Most marine mammals are relatively tolerant of chlorine residues as are people (swimming pools are commonly in the 1-2 mg/1 range and sometimes much higher). An exception is the otter, because chlorine and other disinfectants de-grease the fur, which
186
Example 13.1. Tank disinfection A hatchery rearing tank 3 • 3 • 3 ft is to be disinfected and scrubbed with bleach. The tank presently contains 1 ft of standing water. (A) If the water in the tank is to be used to clean and disinfect the tank, how many gallons of bleach should be added at a minimum before scrubbing the sides and bottom of the tank? Volume of water = 1 • 3 • 3 = 9 ft3 = 9(0.02832) -- 0.25488 m3 = 254.9 1 Conversion factor from Table A-3 Table 13.2, bleach dosage = 3.51 ml/1, 3.51(254.9) = 894.7 ml = 0.895 1 Conversion factor Table A-3, 0.895/3.785 = 0.24 gallons of bleach (B) Approximately how long should the disinfection process take? From Table 13.2, about 1 h (c) What other important factors should be considered? 9 Care should be exercised not to expose skin to bleach or disinfecting water; one would be wise to wear goggles to avoid possibility of splashing into eyes. 9 All rims, covers, plugs, equipment (samplers, nets, tools) or other items used in or around the tank should be disinfected at the same time to avoid recontamination. 9 After cleaning, tank and associated equipment they must be well rinsed with clean water and allowed to dry before restocking tank to avoid potential toxicity effects to culture organisms.
the animal counts on for thermoregulation. In reuse systems for dolphins and seals, a chlorine residual of 0.4 to 0.7 has been used for the disinfection of seal pool waters (Spotte and Adams, 1979). To maintain this residual, a p p r o x i m a t e l y 2.6 mg/1 of available chlorine had to be added daily. Residual concentrations of 1.0 mg/1 and higher are used but are not r e c o m m e n d e d for p r o l o n g e d exposure. Experience has shown that a chlorine residual of around 0.4 mg/1 is sufficient to produce nil fecal coliform readings in seal pools and has no detrimental effects on the animals (New E n g l a n d Aquarium). See E x a m p l e 13.2. Interestingly, biofilters in reuse loops can function with chlorine residuals up to 1.0 mg/1, but are seriously degraded. At the lower concentrations around 0.4 mg/1, biofilters can function relatively well after a period of conditioning. For fish and crustaceans, a chlorine residual of these magnitudes would be lethal within a short time. Chlorine is also used to disinfect process water for shrimp and oyster hatcheries. Chlorine in the range of 1 - 5 mg/1 is added to filtered seawater and allowed to stand for several days prior to use. The chemistry of chlorine c o m p o u n d s in seawater is very c o m p l e x and c o m m o n l y available tests for chlorine residual are not sensitive enough to detect chronic chlorine concentrations. Therefore, the lack of a positive residual m a y not indicate the absence of chlorine toxicity. The decay rate of chlorine c o m p o u n d s depends strongly on light levels and the trace c o m p o s i t i o n of the specific seawater. In freshwater, effective dechlorination requires c h e m i c a l addition or activated carbon filtration plus chemical addition (Seegert and Brooks, 1978). Activated carbon filtration by itself is not adequate to r e m o v e chronic chlorine residuals. S o d i u m thiosulfate and sodium sulfite have c o m m o n l y been used for dechlorination
187
Example 13.2. Disinfection of seal pools by use of chlorine You wish to control the coliform concentrations in a large seal pool to a concentration below 1,000 MPN (most probable number) per 100 ml as required by US Federal regulations. You know from experience that a chlorine residual of 0.4 mg/1 in the pool will produce a nil fecal coliform reading (tested weekly) and is well below any level that can in any way be harmful to the seals. The pool receives 200 gpm in a flow-through system and the detention time of the pool is 2.5 h. You estimate from experience, that with your conditions and maximum biomass loading of about 1,200 lb. of seals, you need a dosage of 8.0 rag/1 of chlorine into the pool influent flow to maintain the 0.4 mg/1 pool residual. You wish to use a sodium hyperchlorite 15% chlorine solution as your chlorine source. You decide to dilute the 15% dilution with water 10 to 1 to get a more dilute and safer solution. (A) How many pounds per day of chlorine do you require? 200 gpm = 200 x 3.8 = 760 1/min 60 1/min x 8 rag/1 = 6080 mg/min = 8.755 x 106 mg/day = 8.755 kg/day = 19.3 lb/day (B) How much of the 15% solution do you need per day? lb/day = 19.3/0.15 = 128.7 lb/day of 15% solution which is mostly freshwater at 8.34 lb/gal 128.7/8.34 = 15.4 gal/day of 15% solution (C) What is your actual dosage requirement for the more diluted solution? A dilution of 10 to 1 with a 15% solution, new concentration = 15/11 -- 1.36% solution 0.0136D = 8 mg/1, D = 588 mg/1 is required dosage of 1.36% solution (D) You wish the capability to leave the chlorine system unattended for the weekend, size your day tank of prepared diluted solution to carry you for three days. Chlorine flow for 3 days = 588 rag/1 x 7601 x 4320 rain = 1.93 x 109 mg solution = 1.93 x 103 kg = 4250 lb 4250 lb per 62.4 lb/ft 3 (assumed freshwater) -- 68.1 ft 3, multiplied by 7.48 gal/ft 3 = 509 gal You should allow some freeboard in the tank and an allowance for ullage (liquid that is not useable in the very bottom of the tank and in the pipes). The tank should be sized around 600 gal (80 ft3).
at 1 to 5 mg/1 concentrations. While these chemicals are non-toxic under freshwater conditions, 1 mg/1 of sodium thiosulfate proved toxic to larval penaeid shrimp (Johnson and Cichra, 1985). Therefore, these chemicals must be used with care for dechlorination; furthermore, toxicity of chlorine-treated water should be tested by bioassays with the culture organisms. 13.3 Ozone Ozone (03) is a strong oxidizing agent that has been widely used for disinfection of drinking water. There are also some data on inactivation of bacterial and viral pathogens by ozone in freshwater and seawater (Liltved et al., 1995). Ozone is unstable and must be generated on-site using ultraviolet irradiation (Lohr and Gratzek, 1986) or corona electrical discharge (Honn et al., 1976). Ozone can be formed from either air or pure oxygen. If air is used it must be very dry, as ozone production efficiency is very sensitive to minute amount
188 of water in the air. Moisture can result in (a) the formation of nitrous oxides that lead to corrosion and reduced output and (b) production of hot spots that reduce ozone output and result in cracking of the dielectric. Air treatment for ozone production commonly uses a heat-regenerated desiccant dryer with two independent units. When the desiccant in the operating unit is exhausted, the drier switches to the other unit and regenerates the desiccant in the unit by heating. Ozone production is sensitive to hydrocarbon fouling and oil-free compressors are needed. For important applications, monitoring of the ozone concentration in the process gas is highly recommended. For a given power input, the use of pure oxygen results in a greater ozone production rate. The use of pure oxygen will also reduce the potential for gas supersaturation and gas bubble disease. When ozone is added to water, chemical reactions may produce an immediate reduction in ozone concentration or 'ozone demand'. The ozone concentration remaining in the water after sometime, is called the 'ozone residual'. The oxidizing power of ozone is higher at elevated pH as found in seawater. Ozone oxidation of nitrite is much more rapid than the oxidation of ammonia (Colberg and Lingg, 1978; Lohr and Gratzek, 1986). In aquariums, the use of ozone decreased turbidity, color, COD (chemical oxygen demand), BOD (biochemical oxygen demand) and total protein (Lohr and Gratzek, 1986). The use of ozone for ammonia or nitrite oxidation is probably not economical except for research applications. Most of the work done with ozone disinfection has been done in freshwater (Colberg and Lingg, 1978; Brown and Russo, 1979; Oakes et al., 1979). Typically, ozone residuals in the range of 0.1 to 1.0 mg/1 and a contact time of 1-2 min are needed to produce a 99% reduction in bacterial concentrations (see Example 13.3). Spores appear to be much more resistant to ozone than bacteria. Ozone is highly toxic to fish and crustaceans, but it is also highly unstable and will decay to non-toxic concentrations in 10-20 min, even if no organics are present. Therefore, ozone cannot be stored for any appreciable period of time and must be used as it is generated. Depending on ozone demand, contact time before exposure to culture organisms can be a very much shorter time interval. In reuse loops with high ozone demand, due to high organic content in easily oxidized form, contact tanks with detention times of five minutes or less are common. In fact, some systems do not even have contact tanks per se but count on flow time in the recirculation loop to consume the ozone residuals. The addition of ozone to seawater may produce long-lived by-products such as hypobromous acid, bromates, trihalomethanes (THM), haloacetic acid (HAA), haloacetonitriles (HAN) and cyanogen bromides (Grosvenor, 1999). These compounds may make the use of ozone for the culture of fish, crustaceans and other sensitive organisms risky, because the toxicities of these compounds are not precisely known. Even very low concentrations of these ozone by-products may be fatal to some organisms. Ozone has been commonly used in marine mammal systems (Spotte, 1991: Coakley and Crawford, 1998: LaBonne, 1998). As discussed in the chlorine section, marine mammals are relatively very tolerant to oxidizing agents. In addition, chlorine or ozone addition in marine mammal systems can remove 'yellow substances' that are unsightly to human viewers. Ozone is widely used in aquaculture, particularly as part of reuse loops (Brazil et al., 1998; Singh and Wheaton, 1999). Singh and Wheaton (1999) in particular also point out the many unknowns relative to possible toxic effects of ozone by-products. Ozone has also been used for the disinfection and oxidation of ammonia with sharks (Honn and Chavin, 1976), but the biological impacts on the sharks was not well
189
Example 13.3. Ozone disinfection The disinfection rate of ozone for a specific bacterial pathogen can be described by the following equation: = - aC ~ t
In where N
No C a and n t
-= --=
concentration of bacteria at time -- t concentration of bacteria at time = 0 concentration of ozone in mg/1 constants for a given bacterium, temperature, salinity, pH, etc. contact time in minutes.
(A) Compute the contact time required to decrease the bacterial concentration from 1,000,000 to 10,000 bacteria/ml (a 99.0% reduction) with an initial ozone concentration of 0.1 mg/1. Assume a = 11 and n = 0.92. ( In
10'000 ) = - 1 1 ( 0 . 1 ) 0 - 9 2 t 1,000,000
t --- 3.48 min (B) Compute the contact time as above but for an initial ozone concentration of 0.5 mg/1. In
10,000 ~ __ 5)0.92 1,000~0 ] -11(0. t
t = 0.79 min (C) Compute the contact time required to decrease the bacterial concentration from 1,000,000 to 100 bacteria/ml (a 99.99% reduction) with an initial ozone concentration of 0.5 mg/1 and the same values of a and n. In
100 ~ = 1,000,, 000 ] - 11(0.5)~
t -- 1.58 min
defined. Ozone can be used to inactivate red tide metabolites (Blogoslawski et al., 1973) and in the depuration of shellfish (Rosenthal, 1981). Ozone can also substantially improve subsequent suspended solids removal (Reuter and Johnson, 1995). Until further information on the toxicity of ozone by-products becomes available, it should be used with caution in the culturing of sensitive species or life stages, especially in seawater with high organic content. Ozone also has some materials compatibility and human safety issues. Some commonly used aquacultural and building materials will degrade rapidly if exposed to ozone. There have been some interesting maintenance and repair projects around ozone units and their exhausts. There is some information available on materials compatibility (Singh and Wheaton, 1999, table 1) but it is limited. Ozone is also dangerous to people at very low concentrations. Some jurisdictions require ozone to be used only in isolated rooms with gas-phase ozone monitors, an alarm capability and an ozone 'destruct' unit on the contactor exhaust.
190
Fig. 13.2. Photograph of two horizontal multi-tube UV systems. The UV lamps are enclosed in quartz tubes to allow removal and replacement without having to stop water flow. The water flows (a) from the large tanks into the back of the units, (b) horizontally through the units and (c) vertically out of the bottom at the other end of the units. These units can be equipped with an automatic quartz wiper system to clean the quartz tubes and UV intensity monitors with output alarms (Engineered Products, used with permission).
13.4 Ultraviolet (UV) radiation Ultraviolet radiation is probably the most commonly used disinfection process with seawater. In many hatchery or research systems, UV systems are added for 'safety', without any specific need or end-result. These systems are modular and can be equipped with UV sensors to ensure effective operation. Newer models pass the water through the system in Teflon piping, which is transparent to UV radiation, with the UV bulbs placed outside of the piping (Fig. 13.2). This avoids the problems with leaks around the liquid-air seals and fouling on the exterior of the bulbs when in direct contact with process water. The units have no moving parts, but require replacement of bulbs on at least a yearly basis, as the UV output of the bulbs decreases with time. As a number of equipment and operating conditions can greatly reduce the effectiveness of UV systems, it is important to periodically check performance. The output of a UV system is measured in microwatts per second per square centimeter (IxW/s per cm2). Commercially available units are typically designed to provide 30,000 to 35,000 txW/s per cm 2 at the rated flow. This 'dose' is based on normal design of UV systems for human drinking water and has nothing to due with the use of UV for aquatic culture. The UV 'dose' can be increased by reducing the water flow through the units. Standard units are available up to 600 gpm (37.8 lps).
191 The UV 'dose' needed to prevent a given disease will depend on the specific pathogen, initial microorganism concentration, turbidity, particulate concentration of the water, and UV dose. Based on empirical studies, the adequate 'dose' for a variety of pathogens ranged from 35,000 to 156,000 txW/s per cm 2 (Hoffman, 1974; Fischer et al., 1976; Brown and Russo, 1979; Liltved et al., 1995). In marine mammal systems, yeasts appear to be more resistant to UV radiation than bacteria (Spotte and Buck, 1981). Viral fish pathogen have been shown to require several orders of magnitude higher dosages for the same 5 log deactivation as pathogenic bacteria (Liltved et al., 1995). For production conditions, where UV systems are added for general protection against microorganisms, a 'dose' of 30,000 to 35,000 txW/s per cm 2 is commonly used. If the UV system is to be used against specific pathogens, it would be advisable to acquire more specific data. Unfortunately, specific data of this type are not readily available. UV radiation is ideal for the disinfection of process water because nothing is added to the water that may prove toxic to the culture organisms. UV radiation is commonly used in oyster and crustacean hatcheries (Fischer et al., 1976; Brown and Russo, 1979). One disadvantage of UV radiation is that the presence of turbidity, particulate matter, or color will significantly reduce its effectiveness. This occurs either due to shielding of the microorganisms by the solids or reduction of the 'dose' due to absorption or attenuation of radiation by the water. Typically, filtration to 10 txm may be needed prior to treatment by UV radiation. While the lack of a residual (i.e., no remaining chemical concentration after the water leaves the unit) allows immediate use, it also means that when the power fails, the culture system will receive untreated water within seconds. In recycle systems or systems with long residence or detention times, the lack of a residual may result in little effect on the overall microorganism concentration in the rearing unit (Spotte and Adams, 1981). For example, in a simple flow-through system with a short residence time (Fig. 13.3A), an effective UV system
Seawater ,.. ' U ~ Inflow ~"
Rearing Un<~31I Discharge
..v
A
Seawater
m,.
Rearing U n i l ~ D i s c h a r g e ,~
Inflow
B Fig. 13.3. Placement of UV systems: (A) flow-through application, typical of hatchery uses; (B) water reuse application. Effective UV treatment in both cases may require filtration to remove solids that may shield pathogens from the UV radiation.
192 may result in a significant reduction in microorganisms. On the other hand, in recycle systems (Fig. 13.3B), growth of microorganisms either in the water or on walls and pipes may be rapid enough to maintain an unacceptable concentration of microorganisms. In short, even if the UV works, under these conditions it may have little or no effect on the concentrations of microorganisms in the culture tanks. The concentration of microorganism can be decreased by increasing the flow rate through the UV processing loop or by increasing the flow-through flow rate. While use of a disinfection agent, such as chlorine, that form a persistent residual is one solution (Spotte and Adams, 1981), this solution is probably only acceptable for marine mammals due to their reduced sensitivity to disinfection agents.
193
Chapter 14
Alarms, Monitoring and Automatic Control Systems
14.1 Characteristics and options The ultimate alarm system is an attentive human. A person can often observe and correct many problems before an automatic sensor or alarm system could detect an abnormal condition. In many cases, abnormal operation of machinery or alterations in water flow can be detected by a change in sound level or tone. When entering an operating area or building with seawater processing equipment, an experienced person may know instantly that something is amiss but may not be able to immediately identify the specific problem. There are three situations where an automatic alarm system can be useful. One is when the system is complex enough or sufficiently spread out that failures are not immediately obvious to operating personnel. The second situation is when the system is not continuously manned, such as at night, weekends and holidays. The third is when the time from failure to serious consequences is only a few minutes, which is common in heavily loaded reuse systems. Even if continuously manned, an alarm system can be very worthwhile. If long intervals between failures and their detection are acceptable, then the consequences of not having an alarm system may not justify the additional complexity and expense. If an alarm system is installed, it is likely to have several operating modes. Fig. 14.1 shows a typical alarm system for a seawater facility. There is a choice of alarm modes and these can be easily changed at will. One or more can be picked at anytime. These may include audible or visual alarms when the facility is manned and an outside alarm on an automatic telephone dialer when unmanned. Other types of remote alarms are also possible, such as having bells ring some distance from the seawater system. The best arrangement is having the dialer call a manned switchboard or security people. The person can then go down a list until someone is reached. Automatically leaving a 'message' may have unacceptable consequences if does not get through in a timely manner. The alternative is to continuously change the dialer telephone number or pager to that of the person 'on call' at any given time. The dialer may have more than one prerecorded message. However, on receiving an alarm, there is usually little information content as to the nature of the problem. If there are two channels on the dialer, one may have them divided into fire/intruder on one channel and seawater system problems on the other. This would be a logical split, since the responses might be quite different. There are two basic ways to wire an alarm system: normally open or normally closed. For normally open, the circuits are open until an alarm condition closes the circuit. In the normally closed approach, the circuit is closed until an alarm condition breaks the circuit. Since it has several advantages, the normally closed system is more common. Several sensors can be wired in series, any one of them breaking the circuit will activate the alarm. An example would be a high and low water level alarm on a wet well, head tank, or sump, which could be wired
194
Choices of Alarm Modes
L.~
I
ff
Large SYnSte Light "
Bellor ~ Light Horn ~k off on
0
~
off
~
on
Telephone Dialer Alarm Mode off on /Selector Switches oi' 16 Sensor Circuits
Individual Alorm Circuit ["Label Power Source 110v AC
I off
on
On-Off Switch~_._~ Small Status Light "On"----I-~o
Charger
~ I ,. I ! 1B2a~Dr, I
Alarm Console--16 Points Shown
Fig. 14.1. Typical alarm system.
together rather than requiring two separate circuits. Another advantage is that the normally closed system has a great deal more self-monitoring capability. Its circuits are powered at all times and any system failures producing breaks in the alarm circuits or loss of power will be immediately detected. The alarm system itself, or parts of it, are unlikely to fail without clear notification. If a normally open system has a faulty circuit, is short-circuited or has lost power, it will not alarm and will appear to be functional. The only disadvantage to normally closed is the continual requirement for power, although this is usually a minuscule amount. The loss of electric power is one of the most likely and serious failures, so the alarm system must have an independent power source. Since the power requirements are small and high AC voltages around seawater are undesirable, alarm systems often use 12 volt DC. A trickle charger is often connected across the backup batteries. When the electrical power is on, the alarm system is powered by the trickle charger. It is important that the backup battery be either manually or automatically checked at frequent intervals. An alarm system with dead batteries will fail when the external power is interrupted. The battery for the alarm system must not be the same as that used for starting the backup power generator. If the alarm system (or vice versa) was to short-circuit, it would also drain the starter battery and both emergency systems would have failed. Depending on an unreliable alarm system could encourage a false sense of confidence that might be a lot riskier than having no alarm system at all. The control console must have a master switch, very visible main system 'on' light, switches for choices of alarm mode and status of individual alarm points. It is very important that individual alarm points have separate on-off switches and status lights. If operating personnel get repeated 3 AM calls for false alarms or unimportant failures from specific alarm
195 points and cannot take them off the system, the entire system may be turned off. During unmanned operations, unimportant alarm points on the system should be turned off. The small status lights on the panel should tell at a glance what points are currently on the system.
14.2 Alarm points Table 14.1 lists some of the operating functions in seawater systems that are likely to be placed on an alarm system. The number of points required is dependent on the specifics of the seawater system and the operating conditions. However, a console with 24 points, especially if of the normally closed variety, should be more than adequate for the majority of applications, including rather complex seawater systems. For simple systems only a few may be needed. Not all the possibilities listed will be used in any given application, although several of any given type are probable. The more elaborate the alarm system the more expensive it will be. Water levels are very commonly monitored. Supply sumps (wet well) and head boxes can be monitored for both low level and high. The triggering values should be set generously so that normal operating transients do not activate an alarm. High means the overflow has backed up or some of the normal water demands have stopped, although the overflow pipe should be of adequate size to handle the total flow. A low level means loss of water supply. A low level alarm is also likely to be used to automatically shutdown any pumps drawing from the sump or head box to prevent pump damage. Drain sumps are only likely to be monitored for high elevations, indicating clogging problems. Any liquid storage tanks that are important to
TABLE 14.1 Typical alarm system monitoring points Water levels
- supply sumps (high/low: may also turn pumps on/off) sumps (high) - head tanks (high/low: may also turn pumps on/off) liquid storage tanks(water, nutrients, chemicals, etc.) - d r a i n
-
Water temperature
heating (heat - X output, high/low, especially low) - c o o l i n g (heat - X output, high/low, especially high)
Electric power
- electricity to main pumps, mechanical area and wet labs
Pressures
-
-
air pressure in aeration system - pressure in receiver for valve controller air pressures on suction and discharge sides of pump
-
Water flow
- main seawater supply lines
Specialized uses
-
alarm circuits of processing equipment - d i s s o l v e d oxygen sensors automated sampling equipment - residual chlorine or other discharge parameters wet lab experiments - o t h e r
-
Physical plant
- high temperature or smoke sensors (fire)
Security
- intruder sensors
196 the proper operation of the facility, might be alarmed for low level. This would give some warning of depletion and could also prevent damage to any pumps that might be connected to the tank. Whenever the temperature of culture water is altered, these temperatures are likely to be monitored. They may be monitored for excessive low or high, but the two extremes may not be equally important. As many temperature controllers are cyclic (i.e., either on or off), temperature limits should not be too tightly set. Alternatives are to build in a delay of a few seconds, so that a momentary temperature spike does not trigger an alarm, or install the sensor in a constant head tank or mixing tank where momentary changes in temperature will be dampened out. For heating, heat exchanger outputs are likely to be low-temperature alarmed, indicating loss of heat addition. This might also be used to shut off the flow of unheated water to prevent thermal shock to the culture organisms. Loss of heat source is the most probable source of failure and heating system control valves are usually configured to fail 'closed'. Failures resulting in excessively high temperatures are not as probable but have happened. In one case, a batch of fish were cooked because the temperature control sensor was mis-located and could not see the increasing water temperature. With cooling systems the reverse is true. Monitoring for excessively high temperatures, indicating loss of cooling, would be relatively more important than monitoring for too cold. Electric power is often monitored directly, even though it is somewhat redundant. Loss of power is likely to trigger many of the other alarm points, as electric pumps will turn off and the controls for most processing equipment, being electrical, will also shutdown. The advantage is that monitoring electric power directly gives an earlier indication of impending problems. If time is important, it will be worth doing. If a pump house is at some distance, it may be on a different transformer or distribution system from the rest of the facility. In this case, it is quite possible to lose electric power to one part of the facility but not the others. More importantly, main pumps are likely to require three-phase electric power. The electrical control system should have the capability to shutdown the pump when one phase is lost. The operation of a three-phase motor with only two phases will result in over-heating and rapid failure. Single-phase equipment connected to one leg of a three-phase supply may operate normally with the loss of one phase as long as the equipment is connected to one of the operating legs. If from different external power sources, the main pumps, mechanical area and the wet lab power supplies should be monitored separately. Pressures can also be monitored. The most important usually involves air pressures, such as that in the low pressure aeration system. Another important air pressure is that in the receivers for the compressed air that might power automatic valves, such as used with heat exchangers. Pressure sensors might also be used to monitor water levels, and the suction and discharge sides of pumps. Monitoring the suction side pressure (vacuum) of pumps is particularly important. Sometimes flows are monitored directly, although this might be redundant with other monitoring points such as elevations in head tanks. Flow measurement is more likely if the alarm function is tied into a monitoring and data logging system. There are many sensors available and some of them could be used with seawater, but these are likely to be expensive. The alarm could be triggered by high or low flow values. Simpler 'on-off' flow monitoring devices can be made with spring loaded plates with mercury switches, which are held down by the flow. A similar device has been published (Ross and Muir, 1987).
197 There is a whole host of monitoring points and parameters that might be important in a given applications. Seawater processing equipment, especially the more elaborate and expensive models, may have integral alarm circuitry that could be connected to the alarm system. These might include automatic filters, 'sterilizers' and heat exchanger systems. In some facilities the monitoring of dissolved oxygen is of considerable importance and this can be automated even for a large number of individual culture units (Kinghorn, 1982b). The ability to automatically monitor the various forms of nitrogen in seawater systems has been available for decades, but has been hampered by various practical problems such as excessive costs, complexity, and support requirements. However, more recent technology may be more practical for seawater system management (Moschou et al., 2000). There has been considerable interest and effort directed at counting and measuring large numbers of fish without having to handle them. There are a number of different sensor approaches to this difficult problem (Huguenin, 1993). If chlorine is added to drains, residual chlorine may be monitored and alarmed at the discharge. In research applications, individual experiments may be alarmed so that they can be left unattended for extended periods of time (see Example 14.1). Because of valuable culture organisms or equipment contained with the system, physical security against fire, and threat of theft or vandalism may be of considerable importance. Intrusion, smoke, and high-temperature (fire) sensors are widely used in seawater culturing facilities. They are essentially identical to those used for the same purposes in a variety of residential and industrial applications and can be integrated into the overall alarm system. The system may also include video cameras coveting facility entry points, video recording of camera outputs, and coded access requirements (especially during non-working hours). 14.3 Automatic control
Complex seawater facilities and some commercial operations are moving toward the use of dedicated computer based monitoring, data logging and control systems. These systems can be adapted, especially if planned for from the start, to monitor, control and alarm many complex processes. High/low alarm trip levels can be built into the software and can be changed as experience is accumulated or operating conditions evolve. If many people have access to the basic computer (many people may need access to the logged environmental and systems data), the alarm levels and control functions on the system should require passwords to prevent intentional or unintentional interference by unauthorized personnel. The use of computers for monitoring, controlling and alarming will require a backup power supply to retain functionality during loss of external power. Since computers generally use AC power, much more complex and expensive trickle chargers, battery and inverter systems may be needed. However, uninterrupted power is also of some importance for the monitoring and data logging functions. Acquiring data during emergencies may be particularly important. Alarm values on specific points may also be used to automatically activate some preplanned actions in addition to the alarm notification. Examples are turning pumps on-off, openingclosing automatic valves or starting a backup generator. In most cases, these actions would be initiated in parallel but separate from the alarm system. It has been common in the past to have individual sensors tied into the electric circuits of pumps or used to activate other individual units. Trip values were often mechanically determined at the sensor. If a dedicated
198
Example 14.1. Alarm points Using the system defined by Fig. 5.2, consider the desirability of providing an alarm capability. Discuss possible options and alarm locations/parameters. Group the possible alarm points into two categories of 'highly desirable' and 'useful'. Since many details about the system, its operating conditions and its operating procedures, are not given there is no 'correct' solution and answers may vary. An alarm system for a commercial hatchery as shown in Fig. 5.2 is highly desirable. Disasters can happen quickly and the economic consequences can be very high compared to the cost of alarm equipment and the benefits of early warning of serious problems. Such a system is inevitably spread out in different rooms or locations. Even when well manned, not all parts are under continuous supervision. Highly desirable alarm points 9 Alarm of main electric power supply to main pump motors. This would be the first indication of a pump shutdown. Particularly important, as the pumps may be at some distance and not continuously supervised. 9 Alarm of high and low temperature output from the heat exchanger. Without automated shutdown, quick response to this alarm is particularly important to avoid possible mass mortality. 9 Alarm of high/low (particularly low) water level in the head box. Useful alarm points 9 Alarm of excessively high pressure differential across the sand filter. This would be indicative of clogged filters, the end of the filter run and the need for servicing before more serious seawater supply problems developed. Many filter systems have alarm capability and can be directly connected to an alarm system. The DE filter could similarly be monitored, especially if operated continuously and unattended (it in fact proved to be a maintenance headache). 9 Alarm of excessive vacuum on the suction side of pumps. This would be indicative of clogged intake screens during storms or the accumulation of long-term biofouling of pipes and/or screens. In either case, a warning of more serious seawater supply problems if not serviced. 9 Some UV systems have a self-monitoring capability, which could be connected to an alarm system.
computer is used, these control actions can be done centrally by the computer and we are now talking about integrated systems. Using computers to actually control aquaculture systems has increased considerably in recent years. This is part of the general computerization of aquaculture functions (see Ernst and Nath, 2000). The major impetuous has been from highly loaded large reuse systems, where operational problems, if not immediately corrected, can quickly lead to disasters in minutes. The large monetary value of the biomass can justify the high complexity and cost of automatic monitoring and control systems. As a consequence, there have been dedicated conferences (Balchen, 1987; Libey and Timmons, 1998a) and book chapters (Ebeling, 1994) on the topic of automatic control. Additional good reviews include Plaia (1987), Ebeling (1998a,b) and Lee (1995, 2000). Automatic control is not the 'silver bullet' solution to the management of seawater culture systems. While they promise to reduce the risks of catastrophic events and reduce manning requirements, they can get very complicated and expensive. Sensors, automatic valves and
199 software can be very costly upfront and systems maintenance and calibration can consume considerable resources and effort. If sets of circumstances develop that have not been foreseen, the system may very well take the wrong action and actually make the situation much worse. Aquaculture is not a well defined, constant, steady-state and predictable process, like many of the manufacturing and processing industries from which these techniques and equipment are derived. If the control system is not flexible and adaptable to changing needs and requirements, it may become unusable. The control system should be able to operate in several modes, including automatic, semi-automatic (meaning that individual functions can be activated or inactivated without having to take the total system out of operation) and completely manually. A fully manual capability is the ultimate backup.
This Page Intentionally Left Blank
201
Chapter 15
Water Recycling
15.1 Setting requirements and options As the animal biomass loading per unit flow rate increases, life support limits are reached (see Section 2.7). Often the first limit is dissolved oxygen, which may be increased by aeration. The next is usually due to the accumulation of metabolic wastes from animal biomass in the system. The metabolic wastes of marine animals include ammonia, suspended solids, dissolved solids, and organic compounds which may be readily converted to ammonia. In addition, the concentrations of bacteria and other potentially pathogenic microorganisms can increase substantially above ambient levels. Removing or decreasing the toxicity of these wastes can be rather complicated and hard to accomplish. If, and this is a big if, this is done properly, the water can be recycled back to the culture system. Water reconditioning can be built fight into the culture tank or contained in a separate processing loop. The advantages of recycling are in reducing demand on external water supply and on heating/cooling requirements. On the other hand, proper operations usually require considerable analytical capabilities, formidable technical knowledge/experience, and a little luck. The higher the biomass loading, the more critical these problems. Some water treatment may be required to meet discharge standards imposed by regulatory agencies, since large marine biomasses represent a substantial potential source of pollution. In many cases, only simple sedimentation for effluent may be required (see Section 10.8). The following section pertains mostly to animal systems, as reuse systems with significant photosynthetic activity can be a different situation (Brune and Wang, 1998). The generation of metabolic waste is largely determined by the total biomass, the feeding rate, feed characteristics, and the feed assimilation efficiency (feed conversion) of the animals. Inefficient or suboptimum feeding practices can greatly increase the generation of metabolic wastes and recycling system requirement. In holding systems with no feeding, the metabolic load will depend primarily on water temperature, total biomass, and the quantity of dead animals and other organic debris. To reduce the metabolic load, solid wastes (settleable solids) should be removed as soon as possible by filtration or sedimentation to prevent solubilization or leaching of the solids. The removal of settleable solids leaves fine suspended solids, ammonia, nitrite, nitrate and dissolved organics (see Section 2.7), which can have varying degrees of toxicity depending on species, life stage, and environmental conditions (Colt and Armstrong, 1979). Ammonia toxicity is usually the most important. The toxicity of ammonia is due to the un-ionized form (NH3) and depends on pH, temperature, and salinity. Criteria for un-ionized ammonia and procedures for its computation are presented in Sections 2.7 and 2.8. Systems can be operated at higher levels but only with higher stress on the culture organisms and with the associated increased risk of greater disease and mortality.
202 TABLE 15.1 Water recycling approaches (in approximate order of frequency of use) 9Nitrification (biofilter)
Trickling filters (highly variable substrates) Bead filters Rotating biological contactors (RBC) Sand filters 9Foam fractionation (protein skimmer, air stripping) 9Ozonation (direct chemical oxidation of organics, disinfection) 9Carbon adsorption (at least partially an ion exchange process) 9Ion exchange 9Algal systems (nutrient uptake by aquatic plants)
A number of physical, chemical and biological processes have been used in seawater reconditioning (Table 15.1). Reconditioning or reuse in this section means the oxidation or removal of animal metabolic wastes. Many of these processes have several different functions that can be accomplished with various degrees of efficiency. As an example, ozone can both directly oxidize organics and can also act as a disinfectant. Many can both act as a biofilter and also filter out suspended solids. By far the most common reuse process is nitrification, with a number of options within this category, and others that are listed in approximate order of occurrence in seawater culture systems. Since use of at least one, and sometimes several, of these processes is essential for water reconditioning, substantial scientific literature on these processes in water reuse systems is available (see Appendix C). This literature provides an indication of the time, effort and resources that can be required to build, monitor and control water reconditioning processes. Much remains to be discovered about some of the processes. This is especially true for systems that are heavily loaded, have high water reuse and/or are operated for long periods of time. Considerable technical progress has been made on reuse technology since the first edition of this book. There have been dedicated conferences (Libey and Timmons, 1996, 1998b), specialized books (Timmons and Losordo, 1994) and special journal issues (Piedrahita and Verreth, 2000) as well as chapters in engineering books (Lawson, 1995). Reuse systems have established themselves for certain uses, particularly for small-scale applications where biosecurity is very important or for high value organisms. Their practicality for many other applications is still very much in doubt.
15.2 Nitrification and biofilters Nitrification, or biological oxidation of ammonia, is a two-step process carried out by aerobic bacteria. Recent research on the phylogenetics of ammonia- and nitrite-oxidizing bacteria has demonstrated that the dominant nitrifiers in aquaculture systems are not Nitrosomonas and Nitrobacter or close relatives as commonly believed. Rather, the nitrifying assemblage is composed of members of the Nitrosospira and Nitrospira groups of bacteria (Hovanec and DeLong, 1996). Ammonia is first oxidized to nitrite by Nitrosospira and then oxidized again to nitrate by Nitrospira. These bacteria generally use carbon dioxide or bicarbonate as their carbon
203
L No Significant NitrosomonasBacteria BalancedNitrifying ! Nitrifying Activity ..., Predominate ...Bacteria Pop. ,,J (Steady State) / / .o'- /
Critical Period Where N0?_Toxicity May Occur
13 .4-E O E: O O
Time from Start --~ Fig. 15.1. Nitrite accumulation during system start-up (Mayo, 1976). See Sections 15. and 15.2 for discussion of recent work on the groups of bacteria thought to be responsible for oxidation of ammonia and nitrite.
source. The complete oxidation of ammonia to nitrate requires 4.57 mg of oxygen per mg of total ammonia nitrogen. As a result of the high oxygen demand, oxygen is often limiting (Manthe et al., 1988). The oxidation of ammonia and nitrite supplies energy to the two groups of bacteria that can be used for metabolism and growth. Under high ammonia loadings and resulting high growth rates, it may be necessary to remove some portion of the biomass of these bacteria. The nitrifying bacteria are relatively slow growing and a change in ammonia loading, salinity, temperature, and dissolved oxygen can result in fluctuations in ammonia and nitrite concentrations. Especially critical is the start-up of a new filter (Fig. 15.1). Typically 1 to 3 months may be needed to achieve steady-state operations on a brand new system. The start-up process is characterized by the accumulation of ammonia until the Nitrosospira population has sufficiently increased. As the Nitrosospira start to oxidize ammonia, nitrite will accumulate until the Nitrospira population has time to increase to oxidize the nitrite to nitrate. The culture animals can be heavily stressed or even killed by the ammonia or nitrite peak concentrations during this adjustment process. There are available data (Rijn and Rivera, 1990) on nitrite concentrations within several different processes. Changes in biomass and feeding practices have to be approached with caution when using nitrification to avoid dangerous transients. Good reviews of nitrification principles include Wheaton et al. (1994a) and Watten et al. (1998). Nitrate is much less toxic, with concentrations below 200 mg/1 often being acceptable. However, prolonged exposure to high nitrate concentrations can lead to serious problems (Hrubec et al., 1996). Unless there is some flow-through of seawater, the nitrate concentration will continuously increase and the pH will tend to drop even in seawater. A flow-through of 5-10% will usually keep the nitrate concentration at acceptable levels. Bacterial denitrification can be used to convert nitrate to nitrogen gas, but it is an anaerobic process which will create considerable complexity, cost, equipment and operating problems, pH control has proven to
204 be a problem in some seawater recycling systems, even with some flow-through. Calcareous materials in the system, such as oyster shells and corals, may start to dissolve. In fact, these materials are sometimes intentionally added to adjust pH and alkalinity but tend to become coated with inorganic and organic materials and cannot be relied upon over the long run for this purpose. Addition of calcium bicarbonate, Ca(HCO3)2 or sodium carbonate (NazCO3), are usually better methods of adjusting pH. The long-term buildup of non-biodegradable organics (commonly resulting in a yellow color) may be of concern in the rearing of some sensitive organisms in recycling systems. There are also risks of depleting necessary trace materials if sufficient new water is not provided. Typically, the process of nitrification occurs in a separate container called a biofilter. The bacteria are grown on a physical medium and the biofilter may be submerged (filled with seawater), or exposed to air while water is allowed to trickle over the medium. In culturing applications, the submerged biofilter is the more common. In submerged biofilters, the water flow may be either upward (up-flow) or downward (down-flow). The down-flow mode has the advantage of being able to visibly observe the more heavily loaded top part of the filter. There are several other variations on biofilters, including rotating biological contactors (RBC), bead filters and a different function for coarse sand filters (see later in this section). Good reviews of biofilter design options are Turnbull and Timmons (1993) and Wheaton et al. (1994a). In cross-section, some biofilters are similar to slow sand filters (see Fig. 10.1). Instead of sand, they may use either a well graded calcareous gravel (oyster shell, dolomite, calcite or coral) of 2-5 mm in a bed with a minimum thickness of 3 in. (7.6 cm) (Spotte, 1979), or plastic media of various shapes and sizes such as used in column aerators (see Fig. 12.1A) and wastewater trickling filters, with filter depths in the range of about 2-4 ft (0.60-1.3 m). The calcareous substrates are low cost, buffer the seawater, and add trace materials needed by the bacteria; however, they have higher frictional head losses and are more prone to clogging with solids and short-circuiting than plastic media. Hydraulic loading rates will be in the order of 1 gpm/ft 2 (0.68 lps/m 2) for the calcareous gravel and 1.5-2.5 gpm/ft 2 (1.02-1.70 lps/m 2) for the plastic media. These values often produce a filter with a footprint (floor) area about equal to that of the total bottom area of the culture tanks. Biofilter performance can be monitored by measuring the dissolved oxygen consumption across the filter (Manthe et al., 1988). The choice of trickling filter medium can significantly affect the nitrification process (Lekang and Kleppe, 2000) as can directly manipulating the microorganisms (Horowitz and Horowitz, 1998). Rotating biological contactors (RBC) are drum- or cylinder-shaped with large internal surfaces for attachment of biofilms. An RBC is deployed with the cylinder axis horizontally, with about 40% of its diameter submerged and is slowly rotated about its axis. Water is trapped and rotated to the top and then splashed down through all the internal surfaces of the RBC. This flow also provides a self-cleaning aspect. RBCs used in aquaculture are greatly downsized variations of a common municipal wastewater secondary treatment process. The use of RBCs in aquaculture is covered in Wheaton et al. (1994b) and Hocheimer and Wheaton (1998). Bead filters and sand filters are classified as granular filters and can both provide substrate area for nitrification and can also remove suspended particulate matter. Both, with operating time and depending on conditions, will clog with solids and must be back-flushed similar to many other solids separation filters (see Chapter 10). Both functions cannot be optimized at
205 TABLE 15.2 Factors affecting biofilter performance Water properties
9 Water nutrient composition and concentrations 9 Recent changes in biomass or feeding practices 9 Water temperature 9 Salinity 9 pH 9 Suspended solids content (past and present)
Filter hydraulic loading
9 Biofilter characteristics 9 Total surface area of filter media 9 Voids ratio in media 9 Filter depth 9 Residence time in filter
the same time, forcing a decision on the systems designer as to priority. Bead filters are most often optimized as biofilters and used in reuse loops, while sand filters are commonly used primarily for suspended solids removal. Bead filters use roughly spherical pellets (3-5 mm diameter) of unexpanded polyethylene, polystyrene or polypropylene, which are slightly positive buoyant. Specific substrate area is in the region of 1150 mZ/m 3 (350 ftz/ft 3) (Malone et al., 1998). Water flows upward in a column, which commonly has an hourglass shape. The backwashing can be with air, water circulation or mechanically (paddles or propellers). The mechanical backwashing tends to be more aggressive and may be disruptive to the biofilms on the beads. Bead filters tend to be comparable to other biofilter options on floor space requirements and superior on a volume basis. However, comparative tests of bead filters against plastic media trickling filters indicates better performance from the trickling filter (Singh et al., 1999). Other similar comparative tests showed much higher specific nitrification for trickling filters, although the volumetric nitrification rate was better for the bead filters (Greiner and Timmons, 1998). Excellent reviews of bead filters and their design are Malone et al. (1998) and Malone and Beecher (2OOO). A review of sand filters, when used as biofilters in aquaculture, is in Timmons and Summerfelt (1998). Variations in sand biofilter performance as a function of sand size and location within the biofilter are given in Nam et al. (2000). The performance of biofilters can be influenced by many factors (see Table 15.2). Some are related to the water properties and some to the design of the biofilter. The influent to the biofilter should be pretreated by filtering or sedimentation to remove the settleable solids, which can very quickly negatively influence the performance of the biofilter. The finer suspended material and the increasing microorganisms biomass will in time start to clog the biofilter, which then must be back-flushing with water or air or both. While this may restore the hydraulic flow through the biofilter, if too vigorous, the bacterial populations may be seriously disrupted resulting in reduced biofilter performance. An alternative cleaning method for down-flow submerged biofilters is to siphon off the surface debris and then to gently stir the top layer and again siphon. Biofilters should be shaded from direct sunlight to prevent the growth of algae on the top of the filter. The nitrifying bacteria in the biofilters are also very
206 sensitive to many chemicals, possibly much more sensitive than the culture organism. These could be drugs used on the animals for control of diseases or parasites, airborne chemicals or leachates from construction materials (see Section 8.1). In water reuse loops using biofilters, there is considerable interdependence between systems parameters. See Example 15.1 for relating parameters of water quality, operating conditions, and system loading. This example is based on principles of this section and equations and data from Chapter 2. 15.3 Foam fractionation
Foam fractionation, also called protein skimming, air stripping and froth flotation, removes surface active (surfactants) dissolved organics and suspended solids, which may be produced in the culture system. If aeration is vigorous, the process can also drive ammonia and volatile components directly to the atmosphere. Additional benefits include the removal of fine particulates and excellent aeration. The process can be very efficient but in some applications has been disappointing. It can be very sensitive to small design details and choices in values of operating variables. The process is believed to be most effective in marine applications, especially in lightly loaded systems. Most seawater applications have been aquarium reuse systems. If it is to be combined with ozonation, some users have strongly recommended, for system control reasons, to separate the two processes by not using ozone in the foam fractionator's gas supply but applying it separately. The equipment, unlike biofilters, does not require much space and maintenance is usually minimal. It is sometimes used in combination with biofilters instead of as a substitute. Foam fractionation involves agitating aerated seawater to produce a foam rich in dissolved organics and suspended solids. The resulting foam must be collected and discharged to the drain. The performance of this process depends on the organic load and composition, surface tension, temperature, viscosity, pH, salinity, bubble size, air-water ratio, and contact time. Not all these parameters are independent. The ideal bubble size is about a diameter of 0.8 mm (0.03 in.) (Spotte, 1979). High air-water ratios and long bubble contact times increase removal efficiency (Wheaton et al., 1979). There are a number of configurations for foam fractionators. Some look like airlift pumps and others have a counter-flow arrangement between air and water to increase the contact time (Spotte, 1979; Wheaton et al., 1979). The process water may enter and leave submerged from the bottom or the process water may enter above the surface and counter-flows through the rising foam. In fact, any vigorous diffuser type aerator with an airlift pipe can be used in this manner, if the resulting foam is removed. Probably the most common configuration is the injection of air with a venturi and discharge of the resulting high velocity air-water mixture tangentially near the bottom of a column. This imposes a vigorous circulation, which delays the rise of the small bubbles, increasing contact time. Dimensional design information on the column and venturi (Hagen, 1970) and equations for guidance in optimization are available (Lawson and Wheaton, 1980; Weeks and Timmons, 1992; Timmons et al., 1995). A good review of its use in aquaculture is presented in Timmons (1994). There are indications that small dimensional changes and differences in operating parameters can have large impacts on performance. There is also evidence that prolonged use can lead to depletion of trace materials, especially some metals.
207 15.4 Activated carbon and ion exchange
Activated carbon (charcoal) in powdered or granular form can adsorb dissolved organics directly from seawater. These include not only organic wastes but therapeutic drugs (Marking and Piper, 1976) and chlorine residuals (Sharp, 1951; Seegert and Brooks, 1978; Giles and Danell, 1983). The exact mechanisms and conditions involved and their relative importance is not clear. This is thought to include mechanical filtration, chemical adsorption and bacterial action (Spotte, 1979). Carbon works well at very low organic concentrations and is often used in addition to a biofilter as a polishing stage to remove persistent non-biodegradable organics. There is evidence that carbon can also remove needed trace materials, especially copper. The adsorption capability of active carbon is highly variable, since it can be manufactured with a number of methods and materials. Furthermore, its removal capacity depends strongly on the specific organics to be removed. The larger molecules and those with branches or longer chains are believed to be removed at a slower rate (Spotte, 1979). Predicting the adsorptive capacity of activated carbon under any given set of conditions cannot be done without experimentation (Spotte, 1979). The performance of an activated carbon unit is influenced by a number of factors. These include the adsorption rate of the carbon for the organics in question, contact time, the concentration of the organics, biological films on the carbon, carbon particle size, pore surface area, and selectivity. Fluid properties can also be important, such as temperature and pH. Suspended solids can greatly reduce the performance of the carbon and the flow capacity of the unit and should be removed (see Chapter 10) before treatment. Powdered carbon, because of its greater surface area, results in faster adsorption, but costs more, has increases head losses and is more difficult to handle relative to the granular form. Therefore, the granular form is more common. For small systems, plastic pipe with threaded caps and a screen to retain the granules may be used. For larger systems, rapid sand filter or related swimming pool equipment is often used. At some point the carbon must be regenerated or replaced due to saturation of its adsorption capacity. This point may not be obvious, since the unit may continue to perform reasonably well as a biofilter. Since monitoring specific organic compounds can be difficult, a more practical policy is often to replace the carbon on a regular basis. Removal of the carbon for regeneration or replacement will be much more frequent than if the same equipment was being used for different purposes with gravel or sand. As a consequences, access and handling difficulties associated with the equipment can be substantially more important when using carbon. Saturated carbon can be regenerated with high temperature and steam but its adsorptive capacity does not return to the original clean value. After a few cycles, the carbon will have to be replaced. For small quantities, regeneration is not worth the effort or risk and used carbon is usually discarded. More complicated chemical regeneration methods have been tried but do not appear to have any advantages for the culturist. Zeolites, such as clinoptilolite, are naturally occurring minerals that selectively adsorb ammonia from solution (Dryden and Weatherly, 1989). Clinoptilolite is found in large quantities in the U.S., although its purity, strength and adsorption capacity differs considerably from deposit to deposit. It has been tested in a number of freshwater culture systems (Liao and Lin, 1981), but has yet to be used in any large-scale culturing application. The material is available in different grain sizes and can be used as one would use gravel or activated carbon.
208
Example 15.1. Water recycling Due to the fact that a developer got a deal on the property (from an old Army buddy), seawater must be trucked from the ocean and therefore is limited. The following recycle system was selected:
Biofilter Qr
d
V
c A ,w
a
y
b
The system must be able to hold 5000 lb of fish at a feeding rate of 2%/day. The environmental conditions and waste production rates are: Temperature = 15~ Salinity = 35 g/kg pH = 8.3 Ammonia concentration in influent water = 0.0 mg/1 Un-ionized ammonia criteria - 10 Ixg/1 Ammonia production rate = 0.02 lb TAN/lb feed Efficiency of the filter -- 78% (A) Compute the maximum total ammonia nitrogen (TAN) concentration in the discharge from the rearing unit (point b). oe = 0.0288 (Table 2.6) From Eq. 2.9, NH3-N -- 1000c~ TAN -- 10 TAN -- 10/(1000)(0.0288) -- 0.347 mg/1 (B) Compute the ammonia production rate. Feeding rate = (5000 lb)(0.02) = 100 lb feed/day Ammonia production rate = (100 lb feed/day)(0.02 lb/lb f e e d ) = 2.00 lb/day (2 lb)(453.6 g/lb)(1000 rag/g) = 907,000 mg/day (C) Assuming a 99% recycle flow (99% recycle water, 1% makeup water), compute the required makeup water flow (Q~) needed. Assume no change in ammonia concentration in the pipes. From conservation of mass considerations, the following relationships can be written in terms of M, the mass flux of TAN in mg/day: note that the mass flux is equal to the product of the flow x concentration. Between points a and b, Ma + 907,000 = Mb At point c, the mass flux is only 0.99Mb, because 0.01Mb is lost in the discharge from the system. Mc = 0.99Mb At point d, the mass flux is reduced to only 0.12Mc due to the biofilter.
209
E x a m p l e 15.1. (continued) Md -- (1.00 -- 0.78)(0.99Mb) At point a, the mass flux can be written in terms of the flows and concentrations )Via = Q~ C~ nt- OrCd Since, it has been assumed that C~ -- 0.0, then Ma = Ma
Ma = (0.12)(0.99Mb) Substituting this equation into the first equation results in: Mb = 1,029, 000 mg/day and Ma -- 122, 000 m g / d a y Since the concentration at point b is equal to Mb/Qtotal, 0.347 mg/1 = 1,029,000 mg/day per Ototal; Ototal = 2,965,418 lpd (542 gpm) Make up flow = 0.01Qtotal -- 5.42 gpm (D) Compute the flow required for a recycle system with a 100% efficient filter. This system is equivalent to a flow-through system with zero ammonia in the influent. Mb -- 907,000 mg/1; 0.347 mg/1 = 907,000 mg/day per Q Q = 2,613,833 lpd = 478 gpm While the use of the recycle system reduced the make-up water flow from 478 gpm to 5.42 gpm, the total water flow (Qtotal) increased from 478 gpm to 542 gpm. (E) Compute the total flow needed (Qtotal) if the filter efficiency drops to 43%. Ma + Ma = Mb = 0.347
907,000 = Mb (0.57)(0.99Mb) = 0.564Mb 2,082,000 mg/day mg/1 = 2,082,000 mg/day per Qtotal
Qtotal -- 6,000,000 lpd = 1096 gpm Decreasing the efficiency of the biofilter from 78% to 43% increased the total water flow from 542 gpm to 1096 gpm. (F) A series of deep seawater wells are drilled and develop a supply of seawater at pH = 7.0, salinity = 35 g/kg, and temperature = 15~ Compute the flow needed for a flow-through system (filter efficiency = 100%). c~ = 0.0015 (Table 2.6) From Eq. 2.9, TAN = 10/(1000)(0.0015) = 6.67 mg/1 6.67 mg/1 = 907,000 mg/day per Qtotal Qtotal "- 25.0 gpm
Once saturated, the material is regenerated with a back-flush solution having a high sodium or hydrogen ion concentration. It is, therefore, not too surprising that clinoptilolite is not very effective in seawater. However, there has been promising research done with a selective
210 ammonia passing membrane exchanger, with freshwater around the ion exchange material. This technique has been used in the short-term transport of marine tropicals but has not yet been proven practical in seawater culturing applications and must be considered experimental.
15.5 Algae Another interesting process for nutrient removal involves polyculture with marine algae. This includes both phytoplankton and macrophytes or seaweeds. Although there exist considerable data about the nutrient uptake properties of mass phytoplankton cultures, their microscopic characteristics make them difficult, in most cases clearly impractical, to separate from process water. Seaweeds are much easier to handle and very effective in removing nutrients from seawater. Since many seaweeds have high value for industrial, pharmaceutical and food additives, there are considerable data available on seaweed physiology but a great deal less on seaweed culture systems. Maintaining and operating algae cultures can require considerable time and effort. Unless the seaweeds are of direct interest, such as for educational or research purposes, they are not likely to be worth the trouble. Seaweeds need light, although too much can be inhibiting, a carbon source, substrate for attachment (sometimes), nutrients, trace materials and some water current. Algae cultures by themselves tend to drive the pH of the system to basic, while the animal wastes are acidic. With care a good pH balance is possible. One problem is that biological activity in recycling systems and some of the processing equipment tend to deplete essential trace materials that might be needed by the seaweeds. It is quite possible that there are a number of trace materials whose importance is not yet recognized. The addition of a seawater makeup flow will substantially reduce these risks. Sizing of the seaweed unit will depend on the animal biomass and their waste products. However, seaweeds are tolerant to wide variations in nutrient concentrations. Sizing data, design considerations and a bibliography can be found in Huguenin (1976b). While seaweeds can be effective in water treatment and can also be cultured for their extracts, optimizing for the two objectives produces different systems and modes of operation. Under many conditions, the seaweed unit may require an area comparable to that for the animal culture and may result in large heat gains or losses to the system. These can be major disadvantages.
211
Chapter 16
Wet Laboratory Areas
16.1 General considerations and trade-offs From an evaluation of present and future needs, one presumably can quantify seawater quantity and quality to be used in wet-lab areas. This also includes decisions on central seawater processing requirements and those that will be handled individually at the points of use. Water processing at the point of application has the advantage of minimizing the amount of water that needs to be treated and avoids the overspecification of required performance. From a management perspective, it also tends to shift the acquisition and operating expenses to the specific users' education or research funding rather than coming out of the facility's capital or operating accounts. In exchange, the user gets considerable more control and operational flexibility than from the central processing option. This still leaves many decisions involving wet-lab area sizing, configuration and distribution of services. The answers to these questions may dramatically change with time as the nature of the work or conditions change. This will be true for all applications to varying degrees. Research uses are likely to see the fastest and most dramatic changes and commercial operations possibly the slowest. In any case, flexibility in operations of wet-lab areas is highly desirable. Configurational uncertainties with time, make it difficult to size wet-lab areas, even if one knows the total flow rates. If primarily deep tanks with high turnover rates are used, relatively little floor area is needed, while with shallow tanks requiting little flow the converse will be true. The range of values based on maximum flow rate is from 30 to over 200 square feet per gpm of flow (44-295 m 2/lps). The smaller area is for deep high turnover tanks and the higher number for shallow low turnover configurations. The sizing, once decided, may be difficult to alter in the future. Oversizing to cover the range of uncertainty may not be a problem, such as would be typical for outdoor wet-lab areas. However, indoor wet-lab areas are relatively expensive. Both types of wet-lab areas have their merits, and if future requirements are either highly variable or very uncertain, a mix might be attractive. No matter what the purpose is of the seawater system, some types of tanks or trays will be required in the wet-lab areas. The specifics of these units will be very dependent on the purposes. Appendix K includes samples of the published literature on the best tank designs for various uses. In addition, a wide variety of other tank types, made with synthetic materials and in a variety of shapes and sizes, are commonly used. These tanks are often used industrially for holding various types of contaminated water or chemicals (see Appendix M for a list of suppliers). For some applications, children's wading pools from catalog stores, either the solid type or the frames with plastic liners, are a cheap and effective solution. Again, all tank materials must be carefully evaluated for biological acceptability on an individual basis (see
212 Section 8.1). Those that are acceptable should be leached in running seawater for at least two weeks before use. Large tanks in wet labs can mask serious potential problems with influent gas supersaturation (see Section 12.4). If the tank is large, the residence time long (i.e., low flow-through rate) and the circulation and aeration in the tank are good, the incoming seawater may be highly supersaturated without producing any ill effects. This is due to rapid dilution, large air-water surface area and aeration. However, if the operating conditions are changed, serious problems could suddenly develop. Wet-lab areas are the locations where there is likely to be a requirement to distribute dry solids materials at frequent intervals. These materials might be chemicals or fertilizers but most likely are feeds of various kinds. While doing this by hand does give excellent control and, for feeds, provides feedback information on utilization, it can require considerable labor. Automatic feeders can reliably dispense dry materials. Liquid materials can be handled similar to other liquids. Moist feeds, which are neither wet nor dry, are very hard to dispense automatically. Appendix L provides a bibliography of published data on feeders. As can be seen, most are for scales of operation just about perfect for wet-lab use. Much larger feeders exist, but are not well reflected in the available literature. 16.2 I n d o o r areas
Indoor wet-lab areas have some strong advantages. They are protected from the weather and are in an environment that is relatively stable and controlled. Workers find it much easier to monitor and service the equipment. Expensive and possibly sensitive auxiliary equipment, such as metering pumps, laboratory equipment and sensors, may be better protected from the elements than they might be outdoors. Some parameters, such as light cycles, may be easier to control inside. Other conditions, such as noise and vibrations, from nearby mechanical equipment and the activities of people, and humidity may be worse inside. Since the configurational requirements of wet-lab areas are expected to change with time, the total available floor area should be as unrestricted as possible. This means no internal structural walls (temporary walls and partitions are common) and no vertical support columns, if they can be avoided. In high grade research facilities, it may be necessary to provide a mix of different sized wet-lab areas (see Lasker and Vlymen, 1969). Class educational activities and general holding of animals can be conducted in the larger spaces, while specialized research can be conducted in individual lab areas. If test parameters (such as temperature, photoperiod, light level, acoustics or use of toxic chemicals) must be rigidly controlled, then self-contained environmental chambers may be required. Segregating the various research projects also reduces friction between different researchers carrying out delicate research, who otherwise would all be interacting in a large room. These unwanted interactions include inadvertent altering of water or air supplies, 'borrowing' of equipment or disruption of experimental protocols. The social intricacies of shared wet-labs, especially in an academic research environment, are beyond the scope of this book. Wet-lab areas are often rectangularly shaped rather than the preferred square, because of structural limitations and costs of large spans. The area should also be well lit and ventilated. This will avoid the 'moist cave' atmosphere of some wet labs and will reduce humidity, corrosion and electrical problems, as well as improving working conditions. If the floor
213 is concrete a good sealer should be applied. This will reduce concrete dust, reduce water retention and humidity, and facilitate the flow of water across the floor. Those services common to all uses will generally be processed centrally and uniformly distributed over the wet-lab area. These may include raw, filtered or temperature-controlled seawater, low pressure air, freshwater, electricity and auxiliary inputs. These auxiliary inputs could include centrally distributed feeds, nutrients, or test pollutants. Yet another possibility is transportation from some other part of the seawater system, such as phytoplankton or larvae. In short, there could be a number of distribution systems for the various inputs. In order to keep the wet-lab area unrestricted, the placement of these systems is itself restricted. The usual answer is overhead placement with the valves about 7 ft (2.2 m) above the floor and the actual lines somewhat higher. Temperature-controlled water supplies will generally require continuous circulation of the water through the system (i.e., a loop) to prevent temperature change before use. An alternative to overhead distribution are main distribution points either in the middle or at one or more corners of the wet lab. In this case, temporary distribution lines can be laid where ever needed. This solution is only practical for small areas, if few inputs are required or if there is ample space for the equipment required. It tends to get messy and cluttered but does not require a permanent distribution system within the wet lab area. There can be a tripping hazard and electric lines on the floor of a wet lab are a definite risk to be avoided. Whether the distribution system is permanent or temporary, the maximum practical span or radius of supply to individual tanks is about 10 ft (3 m) from a distribution point. Provision for drainage must also be provided throughout the wet-lab area. The supply radius of 10 ft (3 m) previously mentioned is already on the long side for the distance from individual tanks to the drain. Drains must be sized for the maximum transient flows that can occur, such as when a tank is drained. Another requirement is adequate pitch of the floor to accommodate the flow. The standard pitch or slope for floors, drain channels and pipes to assure drainage of clear water is a vertical drop of 1 to 96 of horizontal length (1/8 inches per foot) and should be higher for water that may contain solid residues. A slope of 5 to 96 (5/8 inches per foot) is needed to remove wet solids such as fecal matter, uneaten feed or sludge. Most wet-lab applications should be somewhere in between. Inadequate slope (floor or drain) or inadequate drain size will result in flooding or excessive labor to drain tanks. The resulting flooding could be a hazard as well as a mess to clean up. Drains can never be too large. They have to be protected from being clogged by various objects that could fall or be carried into them. The best way to do this is to use coarse screening, typically with a maximum hole dimension of one half of the drain pipe diameter. Open channels for drains are even better than large pipes, because they are easier to monitor and clean. What is sometimes done is to provide a large central drain channel with pipe drain laterals to more isolated areas of the wet lab. Even the largest drain and/or its screen can clog with time, if not maintained. If they clog, the drains will backup with subsequent flooding. The drain residues associated with many wet-lab operations can be impressive in quantity and smell. If drainage provisions have not been built into the floors, the bottoms of all tanks will have to be elevated to provide the elevation required to gravity flow the drainage from the bottoms of the tanks. The alternative is pumping them out when they have to be drained, an actuality that will require considerable manpower and should be avoided if possible. The required distribution of water within the wet lab may be highly uneven and vary with time. If one wants the flexibility to use the total supply at any given point, this will
214 have consequences in the selection of pipe and valve sizes and in operations. If one designs for uniform distribution and conditions unexpectedly change, requiring the concentration of services, serious problems may occur. For flow control reasons (see Chapter 9) one would like pipes as large as possible in the wet-lab distribution systems. These supply lines will often be connected at the ends in a loop to further reduce frictional head losses under varying flow distribution conditions. This automatically provides considerable flexibility in how to distribute the flow. The low flow velocities required for flow control, unfortunately, also make these lines susceptible to accumulating sediments and biofouling, requiring servicing. If the lines are small and the flow distribution changes (anyone opening or closing valves in the system), then flow control capability will be reduced. 'Small' and 'large' diameters can be determined by calculating frictional head losses from the head tank by using the procedures of Sections 6.4 and 6.5 (see Example 9.1). If the head losses are an appreciable fraction of the static head from the water level in the head box to the point of application, flow control will be very sensitive to all wet-lab flow changes. If large diameter distribution valves are used, they will add both flow flexibility and cost. While they are less prone to clogging and require less servicing, users are very likely to use more water than they really need. A compromise, if one cannot completely control the distribution, is to have a threaded reducer and relatively small threaded valves. These valves can then be exchanged for larger ones if needed. In research facilities with limited water supplies, it may be necessary to lock or secure individual supply valves in the system to prevent adverse flow changes to other experiments. Removing valve handles will eliminate casual alterations but will not deter a determined effort, often resulting in damage to the valve stems due to use of vise grips. If services to the general wet lab are required beyond what is already provided, such as specialized water treatment equipment, it can be added at the point of use. In research facilities, due to the variability and unpredictability of future requirements, it is generally more practical and economic to provide only minimal treatment to the water supply at the central point and require users to provide the additional processing to meet their own specialized requirements. Much of the needed processing information is included in Chapters 9 through 15. As an example, Fig. 16.1 shows a small but rather elaborate wet-lab system built to do HOT WATER
from
BUILDING HEATING ~ SYSTEM, RETURN TO U t T BUILDING ~ i ~I HEATING SYSTEM II I n CARTRIDGFJI I CONTROL VALVE
c
RAW
( VALVE ~'~
TANK
g FILTER
I
/
/'
m
I ~
,il
"~'~,"~~ If'II
'-,il~ II
'~
[ II
I I~
,
~
i~
[4')( I' TITANIUM HEAT ~TRANSFER PANEL
I
l'~~
I I v
'Jr iov~.,~ow I,I STANDPIPE
~,
M
~
III I f "
"'
-
PUMP
,
2k
I1_ :,,:;~,; I1"~ .... I I I
II
II %ECO~O,"R
I ISWITCHI
i ~n,
~CA-,'- II
IIII /I
I/
~ALARM SYSTEM
]
OVERFLOW
V,~
TEMPERATURE)
IL-.--....=. TO DRAIN
Fig. 16.1. Seawater heating and filtering system (Tenore and Huguenin, 1973).
ICROPIPETTE CONES
215 some very high precision research. The only services supplied centrally were raw seawater and hot water from the building's heating system. It was necessary to filter, temperature-control, and flow-control the seawater and to provide an auxiliary continuous supply of phytoplankton (not shown). Flow control was provided with a constant head tank and micropipettes (in place of expensive metering pumps, see Section 9.3). The same type of overflow constant head tank system was provided to control the flow of phytoplankton. 16.3 O u t d o o r areas
Outdoor wet lab areas also have some distinct advantages. Much larger areas are usually available, facilitating access for improved working conditions and possibilities for large or more numerous tanks. Contrary to what some may believe, outdoor culturing conditions for marine organisms can be as good as indoors. Tanks can be covered and auxiliary equipment protected. The heat capacity of water, with any reasonable flow-through, and the insulative properties of many types of tanks, assures thermal stability. Outdoor wet areas, even under conditions of ice and snow, can produce good culturing conditions and excellent data or performance. With a little care and ingenuity, whatever could be done indoors probably can be done equally well outdoors. The hardships under such conditions are not usually felt by the culture organisms but by the servicing personnel. If the weather is benign, there is no hardship at all. These areas make excellent facilities for seasonal overload use. These periods of high demand, such as summer programs, tend to coincide with good weather seasons. Needless to say, outdoor wet labs are relatively inexpensive for the areas and capabilities provided. How are these outdoor wet areas configured? They often have a prepared, sloped asphalt surface with built in drains, either pipes or channels. A gravel surface is not as good as concrete or asphalt but is usually acceptable. Bare dirt or grass is usually not acceptable, since it will generally become a mud hole. While most are open and unrestricted areas, some have been built with permanent concrete tanks. Services must be available. These might be few and simple or just as numerous and varied as indoors. Except for the drains, no fixed distribution systems are usually provided. Distribution systems are often temporary or quasi-permanent installations, usually on the ground and as neatly placed as possible. This is not as bad as indoors, because more space is usually available. If there are no drains below grade, tanks will have to be elevated to provide the needed drainage heads. Electrical service may be provided at only one or two points. Some parts of the outdoor wet-lab areas may have light roofing to provide limited sun and rain protection. Pre-fabricated buildings without side walls are simple and economic and might be attractive if an increased level of protection is required. Another common and often useful addition is a small shed or mobile trailer in which to store equipment, carry out simple laboratory tests or serve as an office.
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Chapter 17
Construction Considerations
17.1 Construction arrangements Arrangements for construction can be even more varied than arrangements for design. These can range from complete 'turn-key' contracts to complete 'do it yourself' approaches, with everything in between. Complete 'turn-key' situations are unlikely except for governmental facilities or for large companies with no previous experience in the field. Most of the smaller seawater systems to date have been predominately towards the 'do it yourself' side with varying degrees of outside contracted support. In many cases the user acts as his own general contractor. This has both advantages and disadvantages. The big advantage is that as problems surface they can be addressed and resolved with a minimum of contractual conflicts. In short, this option allows much more flexibility in handling the unexpected. On the other hand, the often stated major time and cost savings associated with being your own general contractor, in many cases, may not be that substantial. The big disadvantages are that the seawater user rarely has any directly relevant prior construction experience, does not have the required supportive infrastructure both in physical equipment or management systems, and generally grossly underestimates the problems encountered in the construction of aquaculture facilities. For a project of any size, a lot of time and effort goes into developing the required infrastructure, often by trial and error. Construction and deployment schedules, based on inexperience, rarely can anticipate errors or circumstances that lose time. Schedule slippage create a self-destructive panic mentality. This results in the adoption of short-term stop gap solutions rather than viable long-term answers. For owners with limited seawater construction experience, it may be prudent to retain an aquacultural engineer for some level of construction management (see Mayo, 1998) for a discussion of roles and responsibilities of the aquacultural engineering consultant). The level of involvement can range from periodic site visits to a full-time construction inspector. In large projects, the design engineer may also review shop drawings from the general contractor or subcontractors or review change orders (see Section 17.3). In the absence of a significant role in construction management it is difficult to hold the design engineer responsible for field changes made by the owner or contractor.
17.2 Construction cost estimating For many projects, being able to accurately estimate costs may be critical. Costs may well be the dominant factor in major design decisions. Large estimating errors that become apparent late in a project can prove fatal to the project. It is, therefore, important to look at the estimating process.
218 Costing numbers can come from many sources. Some of the better general sources are commercially available construction costing guide annuals (Dodge, 2000; Means, 2000). These guides have not only unit prices but also installation and service costs with adjustment factors for different parts of the U.S. Such convenient cost estimating guides may not be available for some parts of the world. Initial cost estimating for projects in some of these countries has used the available guides, for lack of a better alternative, with adjustment factors for transportation, importation and local service costs. Since much of the specialized equipment is commonly imported for projects in these countries, these estimates are usually adequate for preliminary design, evaluation of alternatives, and decision making. When operating in unfamiliar parts of the world, it is very advisable, at some point in the design process, to develop an arrangement with a local engineering and design firm that has specific knowledge about conditions in the area, even though they may not have any aquacultural experience. Additional general sources for pricing data are catalogues from major mail-order firms such as Granger, McMaster and Sears. With these equipment cost numbers, it is important to adjust the values for the passage of time from the present to the estimated ordering date. It is also important to include related services, such as engineering services, transportation, import duties, broker fees, storage and assembly or preparation for installation. Neglecting these considerations can lead to major cost underestimations. There are other major sources of error. These include uncosted essential components or services. These missed items are often necessary but secondary components. Examples include a chain link fence around the facility, a concrete base for machinery, or a storage area. Another major source of errors results from the inclusion of new or upgraded requirements. These might include the requirement for water filtering halfway through design, where it had previously been judged to be unnecessary. Increased flow rate or additional temperature control are also examples. Surprisingly, the overall error on correctly identified items is usually small, even though the uncertainty about the cost of individual items is often high. While some items may prove to have been estimated high, others will be estimated low, and they tend to cancel. An exception is estimating the cost of in-water construction of intakes and discharges. Even engineers and architects with some experience in this area, will generally estimate far too low, and the cost discrepancies can be large. Rapidly increasing regulatory construction constraints are dramatically increasing in-water costs. In addition to in-water work, any changes in direction or requirements, project stoppages, and overlooked items or services are the major sources of underestimated costs. Cost estimates will usually be generated early in the project and continually modified as design progresses. These estimates are usually as detailed as design definition will allow and are often a source of feedback information that strongly influences the design efforts. Cost estimates almost inevitably creep or sometimes leap upward as the design definition progresses. Without dramatic downward scope changes, a general guide is that the final cost after everything is included will be about a factor of 7r greater than the first estimate. Why Jr ? The humorous answer is because it is an irrational number, but considerable experience indicates that a cost increase of about 300% is correct. Downward cost changes are usually the result of specific management decisions to reduce the project's size or scope. The budgeted cost contingency factor over the current cost estimate is a function of the design status and specific circumstances. However, with a completely specified design ready for construction bidding and a complete cost estimate, the cost contingency should not be less than 25%. This
219 is a somewhat higher value than sometimes used for general contracting but it is not a large number, since the major cost estimating errors already discussed can easily increase costs by a factor of two or more.
17.3 Design changes The end purpose of the design and construction phase is an operational system. The design is based on a multitude of facts and assumptions about the site, species, operating procedures and operator skills. A specific project is likely to have some unique characteristics or unique combination of parameters that have never been tried before. Some of the possible inherent design problems and mistakes may show up during construction. Others will not be obvious until full-scale operations. The 'facts and assumptions' and value judgments on which the design is based may well change before construction is completed. This can occur as new information is received, from direct experience (if the site and species preparatory work has been properly done there should not be any site or species surprises, yet they do often occur), or from 'improvements' that are perceived during construction. Even more likely are important management decisions which result in a major change in the scale of the project, usually downward for cost and schedule reasons. Some design changes may be applied directly during construction, while the more disruptive changes may be held for retrofitting after the primary construction phase. Some changes may not fit either pattern. These are the critical changes that cannot be deferred or readily accommodated. These can halt construction completely while the problems are sorted out. These changes can easily kill a project, because a construction halt is very expensive, very disruptive, and certain to trigger a top management reassessment of the entire project.
17.4 Installation of seawater lines If an intake system is to be placed offshore, its installation may be the single most difficult aspect of the project. Under the unlikely conditions that a site has no waves or water currents under any conditions or that the deployment is for a very short time period, the intake lines can be left exposed on the bottom. Even in this case, they will have to be secured with heavy collars, screw auger anchors, tiebacks, pilings or bent over rods driven into the bottom. For most conditions, the lines and intakes will have to be both excavated and secured. This excavation, placement and backfilling of lines and intakes may only be possible at certain seasons, tidal conditions and environmental conditions. This may impose severe scheduling constraints or delays into the entire project. Environment regulatory constraints on construction may dramatically increase these problems (see Section 3.3). Deployment opportunities may be very limited and not completely predictable. Environmental changes that occur during deployment can severely threaten the operation. It is therefore important to carry out the deployment cleanly and quickly. Due to these problems, intake and discharges may actually be built at considerable variance with the design specifications. Excavation methods will depend on soil types and environmental conditions. For common sand, clay, and mud bottoms with no appreciable waves or current, the trenches for the lines can be excavated with a backhoe or dragline from the beach at low tide, and from a barge at high tide. The trench will usually not backfill itself before the lines can be installed. Jetting
220 and blasting, if allowed, are two other options. Sediment curtains surrounding the excavation may be required. In the presence of significant current or waves, the tasks become much more difficult and should not be attempted by the inexperienced. At best, the jobs are difficult and can be almost impossible. There are at least two ways to lay the lines in the excavated trench. Since most intake lines are likely to be continuous synthetic pipes, these pipes will readily float, especially if full of air. These lines need weight to hold them on the bottom, even when full of water. This can be done with concrete collars. The entire line with concrete collars can be pulled off the beach, floated and held in position, then sunk in place by opening a temporary valve at the offshore end (Sclairpipe Marine Pipeline Installation Construction, 1969; Janson, 1975). After removal of the end plug and valve, the intake structure can be lowered and secured to the end of the line. The intake structure and line can then be secured to the bottom and backfilled. Under some conditions, the pipe may tend to rise in the trench on being backfilled (Janson, 1975). The second method is to assemble the line and intake together on shore. If the intake is formed into a sled type arrangement, the intake and line can be dragged directly down the trench along the bottom (Bouck, 1981). In this case, weight was added after positioning, by filling some of the pipes with concrete. It would probably be possible to add some jetting capability directly to an 'intake' sled, so that it could excavate its own trench in some soil types. There is trenching equipment used in the offshore oil industry to bury pipe lines, which might also be useable but it is very expensive. If the trench shows a tendency to backfill itself, it may be possible to let nature carry out this task. In sheltered areas, nature may be too slow and the trench may have to be backfilled.
17.5 Start-up It is virtually inevitable, especially in the 'do it yourself' projects, that initial start-up and operations will commence before construction is fully completed. Even if both construction and operating crews work for the same company, it is imperative that there be a clear chain of command and coordinated activities between the groups to avoid mutual interference. Initial start-up of various systems has to be done with some care, whether by construction or operating personnel. The system to be started must be carefully and personally checked by the person in charge immediately prior to initial start-up. Things to be checked include that the system to be tested is complete (an incomplete system may not perform as intended), all components and parts are firmly secured (not just in position), there are no tools, rocks or debris in lines or sumps, the system is in start-up configuration (switches, valves and hatches in correct position, guards, interlocks and safeties 'on') and lastly that all personnel are clear of hazards and aware of what is about to happen. The previous sentences appear to be obvious and logical, but not doing these things has resulted in much serious damage. Examples of problems include a foreman taking the word of a worker that rocks have been removed from a sump, a switch in the full-on position instead of full-off, an open unvalved pipe in a large tank and a worker unaware of impending operation of a piece of equipment. Even if all these things are well done, the initial start-up is still a relatively high risk operation. If anything has been designed, fabricated, or installed improperly it may quickly become apparent. Start-up procedures have to be well thought out before hand, and implemented as planned. This is not the time for hasty or snap judgments. When starting equipment, alertness and prompt
221 shutdown can avert otherwise serious damage if something is wrong. This may require stationing people in various critical places and providing them means for communicating. Signs of problems include unusual noise or vibration, burning smells or smoke; water where it is not supposed to be; lack of water where it is supposed to be; and equipment getting hotter than it should. It is not uncommon to have several cycles of start-stop-reevaluate-restart, even for a perfectly good system. Common problems can be: a virgin 'self-priming' pump not priming itself the first time; some squeaking rotating machinery that was not lubricated; air locks in the pipes; vibrating parts that need to be better secured; and a system that is erroneously configured. The first few minutes of operations, as the equipment proceeds to steady state or equilibrium conditions, and testing over the first few operating cycles (such as tidal) are the most dangerous. Weak components usually will fail after some relatively short period of actual use, generally a few days up to a few weeks. After this 'burn in' period the probability of the equipment failing is relatively low. However, there is the possibility of operational problems due to seasonal factors, which may take some time to develop. In addition, there is a high potential for serious problems during the first few major storm events experienced by a new system. During initial start-up the experience level of all personnel with the specific equipment involved is usually at a minimum. The operators are not familiar with the equipment capabilities, limitations and specific constraints. Problems that have occurred include: toxicity due to 'new' materials; destruction of piping by water hammer due to closing valves too quickly; the overheating and death of brood stocks due to uncalibrated or poorly set heating controls; drain lines clogged with construction residues; or inadvertently contaminating or cross-feeding with different water types.
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Chapter 18
Operational Considerations
18.1 Operating procedures The design of the seawater system is partially based on the operating procedures that are expected to be followed. These include batch versus continuous operations in various parts of the system, expected seasonality in operations, scale and duration of culturing phases, need for water conditioning services, ranges of system operating values, training and experience of personnel, etc. The capabilities of the system will be dependent on these expected operating procedures. If they change, the seawater system may be found to be less than adequate to support the new procedures. This may require system modifications or putting up with marginal and inefficient operating methods. Operating procedures can change in many ways. If the need for some additional service becomes apparent after design or construction, serious problems may result if sufficient flexibility was not built into the system. Examples are addition of chlorination/dechlorination of culture water, need for better filtration, greater quantities of water, more aeration, or greater water temperature control capabilities. Often these needs had been considered during the design phase but dropped for cost reasons and because their need at that time had not been compelling. A designer with foresight will have left floor space and easy access to piping for possible later retrofit. Operating procedures also tend to be specific to individuals, especially in the details and in the organization of tasks. This is inevitable, as many culturing operations today are still more an art than an exact science. This does not make one set fight and the other wrong, they are just different. Design decisions are often based on the preferences and value judgments of key individuals. If key operating personnel are changed, incompatibilities and inefficiencies between the physical plant and the 'new' operating procedures can develop. The skill levels of personnel using seawater systems depends a great deal on the system's objectives. Research systems usually have a number of highly educated users, although this does not necessarily mean that they are all familiar with start-up and operation of complex mechanical equipment. The majority are usually from the biological sciences and they may have little background or interest outside of their areas of specialization. Manning of commercial systems usually follows the '6-3-1' Rule. For every ten people, six are intelligent and responsible but need no specialized knowledge or education; three have specialized knowledge through education or experience, or preferably both; and only one needs comprehensive knowledge and experience, including management experience. For commercial systems, a leader with only a Ph.D. and little practical experience usually proves inadequate. Commercial systems are hazardous enough, so that 'on the job training' for key individuals can be an expensive proposition.
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18.2 Assignment of responsibilities While the chain of command for use of the system or component parts is usually clear, this is often not the case for the servicing, maintenance and repair activities. Problems in these areas are at least as critical as any of the biological functions. There may not be a clearly identifiable individual in charge of these services and, if he exists, he is unlikely to have the same status as the other system users or as clear a chain of command. If the service personnel are considered to work for all the various user groups, problems can develop. Key system users and team leaders are continually trying to improve their areas of activity whether production, research or education and will assign the service people accordingly. In effect, having too many bosses may be suboptimizing the overall process by expending time and resources on noncritical nonlimiting activities which could be used much more productively elsewhere. Some of the modifications and maintenance tasks might even be in conflict and self defeating in terms of the overall system. It is essential that the service function be accountable only to the top operational person, the same as any other key individual, group, team or department. This will enable the correct priorities to be assigned and long-term, but critical aspects, such as preventive maintenance, scheduled overhauls, and adequate spare-parts inventory will not be overlooked. With all the problems that routinely occur with seawater systems, these important activities are often ignored until they become critical, usually by unfortunate but not completely unexpected equipment failure. If the service function does not have an identifiable leader, these responsibilities are generally fragmented or assumed by someone as a secondary function. However, these individuals may often have their own problems and may not be able to give the service area the full attention that it often requires.
18.3 Spares and redundancy During the design phase considerable thought is usually given to system reliability and the need for redundant equipment, which is ready to be used in the event of equipment failure. Decisions and trade-offs of cost for backup equipment versus system dependability must be carefully made. Areas for such redundancy often include spare pumps, compressors, motors, intakes, and backup power sources. Redundant equipment gives time for repairs of failed equipment without loss of services. Prolonged loss of services usually means disaster. What often happens in operations is that the backup equipment is brought on-line to increase the service. It then is no longer redundant but primary. If the consequences of failure without backup were considered unacceptable during design, are they likely to be less so with everything on-line? If the backup equipment is needed for a short-term emergency in a critical area, it will obviously be used. Once so used, like virginity, the redundant equipment may now be considered available for routine service. This must not be allowed to occur. If there is no alternative, additional equipment must be immediately purchased and installed. If it cannot be actually installed due to space or access limitations, it should be acquired and prepared so it can replace a failed unit in a minimum of time. Unfortunately, convincing management to purchase expensive equipment when there is no immediate problem with the current equipment and in the presence of other more immediate crises is very difficult. The same problem occurs with the purchase of spare parts. The inevitability of serious problems and the subsequent assignment of blame to the innocent is completely predictable.
225 TABLE 18.1 Critical spare parts and supplies Spare parts are expensive. What parts should be on-hand depends on ordering delays, assurance of supply, and consequences of not having them in-hand during an emergency. The items below are often justified spare parts and supplies. 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
Pump impellers Pump seals Pipe fittings (Couplings, L's, T's, etc.) Valves Lengthsof pipe Pipe thread cutting equipment Plasticpipe adhesives, thread sealer Pipe patching components Amplehand tools Electricalbreakers, fuses, GFI, etc. Skin and SCUBA diving equipment, small boat Spareintake screen Filtermedia, cartridges, bags, etc. Gasolinepowered pump unit with hoses Portable gasoline powered generator
The spare-parts problem has several other aspects. One is the availability of spare parts. If spare parts are readily and quickly available, then a minimum of on-hand parts are needed. If spare parts are difficult and time consuming to get, a large inventory is required. While the specifics of which spare parts to inventory dependent on the conditions, some items and supplies are often included (Table 18.1). Some spare parts are often ordered with the basic equipment and this is usually no problem. Those spare parts from the original purchase that are actually used should be immediately replaced, as these are the ones most likely to be needed again. This can easily be put off in the presence of more immediate problems, which surely would be a serious mistake. Management must be convinced of the importance of adequate on-hand spare parts. At remote sites, absence of parts can literally close down the system for prolonged periods of time. A loss of services and resultant mass mortality will automatically result in a minimum loss of one production cycle, even if the parts are quickly available, and possibly much longer if they are not. If larval forms are involved, only a few weeks may be lost, while for brood stocks decades of work maybe eradicated. When a piece of equipment fails and a backup is brought on-line, the system is now operating in a high-risk mode without a backup. It is essential to assign top priority to restoring a backup capability in the minimum time. Sometimes the equipment failure is not complete, in that the equipment still functions, but does not perform to the minimum requirements. In this case, the backup may be brought on-line and the defective unit becomes the backup, while repair plans are implemented. Until repairs are accomplished, it may be possible to reduce or reassign internal services to minimize the consequences of additional partial failures. When there is an equipment failure, it is very important to determine the cause. If the failure was due to conditions external to the equipment, then the backup equipment may soon
226 suffer the same fate. If a piece of equipment has been performing well and suddenly fails, the operating conditions may have changed and the equipment may have been forced to operate outside its specifications or some servicing requirements may not have been met. Failures due to age or normal wear rarely occur without a great deal of warning. While normal wear may be characterized by long-term decreasing performance, the same symptoms may indicate changing operating conditions and resulting accelerated wear. Typical examples include pumping water with a lot of sand and effects of biofouling. Biofouling can dramatically increase suction-side frictional losses and pumps can then no longer meet their suction-side NPSH requirements. The net result is cavitation, accelerated impeller deterioration and reduced flow. When some expensive parts, such as impellers, have to be frequently replaced, the tendency is to blame it on poor design rather than on poor servicing or use under improper conditions.
18.4 Preventive maintenance Much of the philosophy relating to spares and redundancy also applies to preventive maintenance. Equipment failures that cannot be quickly compensated for can lead to unacceptable consequences. Equipment that is not properly maintained will sooner or later fail. Since most maintenance tasks can be postponed without immediate or obvious consequences, it is very easy to get careless. Carrying out required maintenance demands discipline. Even if properly maintained, the equipment, or at least some parts of it, may be expected to wear out with extended service. In this case we are discussing normal wear, not that due to improper use, and the time interval may be many years. Whether wear is normal can be determined by experience with similar equipment or by consulting the manufacturer. Highly wear-prone parts are often readily accessible; however, other parts may have to be replaced in an overhaul activity which is more extensive than routine maintenance, or the entire unit replaced. These overhauls or replacements should occur when the probability of failure becomes sufficiently increased due to wear, or when the performance approaches a minimum acceptable value. Both routine maintenance and equipment overhaul and replacement should occur while the equipment is operating normally without immediate problems. This provides planning and scheduling flexibility and will tend to minimize impacts on other activities. All these servicing functions require personnel time, resources and sometimes appreciable money. Many seawater systems are operated in a 'crisis management' mode, that is, nothing is done or resources expended until a problem reaches crisis proportions. By this time the options are few and the costs and consequences are high. In the presence of immediate crises and tight budgets, maintenance activities are usually put off and the potential disastrous consequences of failures, for which one is unprepared, are forgotten. In actual operations it is very difficult to give maintenance activities the priority dictated by long-term economics.
18.5 Monitoring and control Monitoring and control is a critical activity, although this engineering phrase is rarely used. It is one's capability to know at any given time what is going on in the system and one's capability, by conscious actions, to alter or influence what is taking place. If something is going wrong and you do not know it, you obviously cannot do anything about it. If you know
227 something is going wrong, but do not have the capability to change it in a timely manner, you are no better off. With experience, monitoring and control functions are usually accomplished, but often without the realization of what they are. Greatly increased capabilities can result from more conscious attention. This does not necessarily mean more monitoring/alarm systems and automated equipment, although these can be very helpful (see Chapter 14). The most valuable inputs on the operational status of a system are often visual confirmation of water flow or water levels, and sounds or rather changes in sounds. These sounds may be associated with flowing water or mechanical equipment. An experienced person will react to even minor sound changes and promptly investigate. An inexperienced person may feel uneasy without knowing why, especially if the sound change is not dramatic. Timely action can often prevent serious damage. This does not mean that a lot of noise is good. However, it should be noted that excessive sound levels in mechanical areas can be a serious health problem and are not desirable for monitoring and control as they can mask the presence or absence of more important sounds. Having all personnel check equipment performance visually and listen during their normal daily activities and report anything unusual, buys a lot of monitoring capability. The problems arise when equipment is remote, rarely visited, or during periods of greatly reduced personnel activity, such as at night. Under these conditions, if something starts going wrong it may not be discovered for a long time or until it produces serious effects elsewhere. It is under these conditions that automatic monitoring and alarm systems are most valuable. It is important not only to know something is wrong, but also that this information gets to someone who can act quickly. In an emergency, actions may require sacrificing some activities to save others. Obviously, the overall priorities should rule rather than that of individual activities. While the normal chain of command for such decision making is usually clear, problems can develop in the absence of the key individual or at odd hours (like 3 AM). Time and circumstances in emergencies may force relatively junior personnel to make critical decisions. Under these conditions, a 'do nothing' or deferred decision may be worse than a wrong action. If there are critical operations in progress, there must be an identifiable individual and a backup person available at all times, who are responsible for reacting to emergencies. These people must be provided with decision making guidelines to forestall later recriminations, given access to system technical information, communications and keys or codes that they may require. Needless to say that they also have to be familiar with the equipment and its operation. Restarting a complex seawater system after a shutdown may be a very elaborate process. Rarely does it involve simply restoring power. There may be many flow, temperature, pressure, and water-level interlocks and automatic shut-offs, that restrict the restart sequence. For safety reasons, most equipment must be manually reset and restarted. Electric motors require three times their normal electric current during start-up. This can be an important consideration in the start-up sequencing with limited power reserves. Pumps in particular may have priming requirements or other eccentricities. Small pumps, which may automatically restart on resumption of power, or larger pumps, which are started without assuring prime, may self destruct if allowed to operate without priming or without water. Means of pump priming, possibly several options, should be readily available. All these problems can be compounded if the system has to be reconfigured to bypass or circumvent a failure. In some cases, the potential for doing additional damage during system restart may be high. These types of problems must all be anticipated before they occur. The ability to easily
228 restart after various failures may be as important as the operating characteristics under normal conditions.
18.6 Operational problem areas Operational problem areas tend to arise from two sources. One is due to internal process problems, that may be the result of design errors or inadequate operating procedures. Some of these include problems arising from materials, use of chlorine, gas supersaturation, and monitoring and control limitations. Many of these have already been discussed in previous sections. The other source involves failures of the system. The most common types and causes of such failures in coastal aquaculture facilities are listed on Table 18.2. A good review of types of failures and emergency procedures can be found in Shepherd and Morris (1987). Note that electrical power loss is high on the list of problems in Table 18.2. Backup power is very common in seawater system, and ranges from small gasoline powered units to large automatic starting diesel generators. Backup electrical power has a number of considerations (Wilton and Morey, 2000). Again, the best preventive measures against failure are care during the design phase and adoption of good operating procedures, including system maintenance. An important problem area, which has not yet been discussed, involves security. Few systems are manned 24 hours a day. Large complex reuse system, because problems can develop very quickly, are often the exception. Seawater systems and what they may contain can have a great deal of curiosity appeal and even monetary value. To limit inadvertent damage and for liability reasons, access to the system may have to be restricted. This may be easy or difficult depending on the circumstances. It may be as simple as doors, locks, and fences. In some cases theft and vandalism are also serious possibilities, which may require more extensive counter measures. For enclosed areas, the use of big dogs has in some cases proven useful. If an alarm system is already required, it should be relatively straightforward to connect up intruder and fire sensors to the system. Security and security related problems can become major operational concerns. One more topic must be considered. That is safety of personnel, especially electrical safety.
TABLE 18.2 Common sources of seawater systems damage and failures While the relative probability of various problems will depend on the conditions, the following list is in order of frequency for one large and complex seawater system over a prolonged period of time. (1) Loss of electric power (2) Screens or filters clogged (3) Human error (erroneous operations, foreign object blockages, misunderstandings) (4) Marine biofouling (5) Vandalism or unexplained damage (6) Corrosion (7) Storms and related effects (high water, heavy rains, water-borne trash, high turbidity, wave damage) (8) Boiler or heating plant failure (9) Boat anchor or fishing trawler damage to intakes (10) Failure to service suction side screens and piping leading to pump problems
229 TABLE 18.3 Tips for improving electrical safety around seawater systems 9 Provide all electrical circuits, both indoors and outside, with ground fault interrupters (GFI). In many areas, GFI protection is required by building code. 9 Have all electrical equipment properly checked before use in or around seawater systems. This is especially true for outdoor use. 9 Avoid splashing around drains. This will keep the floor dry, reduce humidity and avoid salt cake buildup. 9 Adequately pitch all floors towards drains to promote fast drainage and avoid puddles. 9 Adequately ventilate rooms to reduce humidity. 9 If salt builds up on floors, flush with fresh water. 9 Size drains for maximum transient flow, such as when draining a large tank. Place mesh screen (not too fine) on drain to avoid foreign object clogging. Clean drain screens regularly. 9 Do not place any electrical equipment under water pipes or tanks. Even if no leakage or accidents occur, components containing water can sometimes produce dripping water through condensation. 9 Do not place any electrical outlets on or near the floor. Overhead distribution of electric power is much preferred.
Considering what is often done, it is surprising that there are not more serious accidents involving seawater systems. Electric power and seawater do not mix very well. This is due to the extreme corrosiveness and high electrical conductivity of seawater. A current leak that would give only a 'tingle' in a freshwater system might be deadly with seawater. Table 18.3 is a list of good practical tips to minimize electrical hazards around seawater systems and in wet-lab areas. Electrical safety around seawater systems should be viewed as a personal problem, the life you save might be your own. A summary of much of the content of this chapter is included on Table 18.4. It specifically provides guidance for the management and operations of large marine science research and
TABLE 18.4 Suggestions for management of marine science facilities 9 A Lab Director should be appointed early in the Design Process. Programs must be planned, operational procedures developed, sources of operating funds secured, and staffing organized in parallel with facility design and construction. These activities can impact decisions during the detail design phase and greatly help the initial start-up and transition to operations. 9 The Lab Director should be an established marine scientist with management and people skills. Marine science tends to be a feudal system with each Principal Investigator (PI) or Faculty being a sovereign entity. The Lab Director's management of lab activities can be considered akin to trying to herd cats. The Lab Director has to have control over ALL activities taking place in the facility or chaos will result. 9 If the facility is of any size, the Lab Director should secure, as early as possible, a full time administrative assistant. The amount of paper work required can be impressive and includes both writing proposals and reviewing proposals of prospective PIs and Faculty. The Lab Director has to assure that all programs and projects using the facility comply with legal requirements from outside, those of the overall institution and the policies and operating procedures of the lab. The lab's fees or overhead rate, if distinct from that of the institution, also have to be included in all proposals.
230 TABLE 18.4 (continued) A major facility will require at least one, and very possibly several, full time facilities and plant people to keep the seawater system and physical plant operating efficiently. They should be paid through lab overhead funds. This staff will require regular assistance from the institution's Facility and Plant Department. This is distinct from animal husbandry or research assistant type activities, which are usually staffed and funded by project or departmental funds. The lab's Facilities and Plant Manager should report to the Lab Director rather than the institution's Facilities and Plant Director. The F&P Director has institution-wide responsibilities and priorities and may not be familiar with lab scheduling or with aquatic life support constraints and requirements. The F&P Manager's interest should be centered on supporting lab objectives. The F&P Manager will have to work on a close and probably daily basis with the institution's F&P Director. The institution's F&P Director still retains overall responsibility for the institution's physical plant. This arrangement can and has worked well in the past. 9 The lab's F&P Manager should be mechanically clever and resourceful, with a broad technical background, management skills, and seawater system experience. Past experience is much more important than a lot of degrees. Seawater systems are not static but in a continuous state of modification and change to meet new or expanding requirements. A good F&P Manager is critical to this process. 9 The lab F&P Manager should have sufficient status so that he does NOT have to respond to the wishes of individual PIs or Faculty, since they tend to suboptimize. The F&P Manager should be guided and protected by the Lab Director in his many day-to-day operating decisions. Adjudicating and allotting resources among the 'feudal lords' is the Lab Director's cross to bear. Guidelines for the F&P Manager and his staff to be used in emergencies have to be established before these situations arise (and they will). This involves relative priorities and who gets hurt first if critical decisions have to be made quickly and at times inconvenient for consultations (3 AM during a storm is a popular time for such emergencies). People on call have to have such guidelines and have to be protected from possible recriminations after the fact. 9 A difficult aspect for the lab's F&P Manager is maintaining an adequate inventory of critical spare parts. If something goes wrong, they have to be on hand to minimize any possible seawater system downtime. Seawater system downtime, even if short, can result in mass mortalities. The problem is that money for parts has to compete for funds with other lab activities and they do not seem important when operations are going well. The parts that get used first are likely to be those that will again be needed in the future and they should be replaced immediately. The problem of securing needed priority also holds for preventive maintenance, including replacing expensive equipment BEFORE it fails. 9 It is critical for the F&P manager to maintain an adequate inventory of plastic pipe and fittings. However, every PI and Faculty may see this supply as a source of parts for THEIR projects. Again, the F&P Manager must have sufficient status relative to individual PIs and Faculty to control this problem. The Lab Director should establish policy to this area. 9 An aquatic life support system is a complex system with many component parts. Policy is needed as to who is authorized to turn things on or off. PIs and Faculty should be authorized to turn things on or off only at THEIR point of use. They should not be allowed to tamper with other peoples setups, open valves upstream, increase the size of the valves at the point of distribution or turn on backup equipment to increase the resources available to them. Clear physical separation between system users and removing or securing valve handles helps. 9 The Lab Director has to resist pressure to turn on backup equipment under normal conditions to increase the available resources. Backup equipment is for use in an emergency. If the needs are that pressing, turning on backups increases the probability of a critical failure with unacceptably high consequences.
231 educational seawater systems. While the technical and operational aspects of marine science seawater systems is similar to all others, the social structure of marine science labs can considerably complicate their proper management. The Lab Director may be 'outranked' by the seawater systems users in terms of seniority, prestige/reputation, high positions elsewhere in the institution or in the 'outside' world, or just by the size of their egos. In contrast, commercial systems usually have a clear and universally accepted chain of command and a straightforward social structure. The table is based on considerable experience.
This Page Intentionally Left Blank
233
Chapter 19
Putting It All Together
As can be seen from this book, seawater systems have many interactive components. One can not randomly select parts and put them together with much chance of it 'working'. The specific objectives, site characteristics, system components (pipes, pumps and processing equipment) as well as water quality and material considerations are all highly interactive. The number of technical considerations that must be considered in system design are very large. Many of the important considerations have been discussed separately in the various chapters. It is now important to combine the factors and discuss the interactive effects. If one were doing one of the Examples in this chapter for actual implementation, it would be good practice to have the output reviewed by a colleague. It is very easy, even for the experienced, to forget or overlook an important factor in making the many design decisions that must be made. Due to the technical complexity, it is fortunate that many seawater projects are rather small scale, low key or remotely located. Many are additions to existing facilities and thus can be either 'grandfathered' or slide through without much notice. However, the opportunities for this are narrowing rapidly and do not exist for entirely new systems and systems of any size. While this chapter will focus on the technical aspects, the economic, political, legal and regulatory aspects often dominate decision making. There are many different participants with quite different objectives and interests (architects, lawyers, regulators, fund raisers, accountants, and hosts of managers). Few of these have any comprehension of the technical aspects. 'Image', public relations and visual aesthetics can sometimes take on extraordinary importance. Technical people and actual users (as distinct from their management) rarely are in the position of making any major decisions. There can be so much push and pull that it is like trying to herd cats. 'Managers' and architects like to move seawater system parts around and make them bigger or smaller with no comprehension of the consequences and tipple effects on the total system. More expensive mistakes have been made by managers trying to save small amounts of money in the short term than any other reason. Technical people are often in a continual 'management education' mode, while trying not be insulting or lose patience. Some core truths have to be continually iterated, such as water runs downhill, animals have life support needs, area is proportional to the square and volume of the cube, and many interactions are fixed by physical and biological laws and not by management, budgets or human schedules. Many of these core truths and useful principles are listed in Chapter 20, Summary Commandments. Site considerations have been discussed in Chapters 3, 4 and 5, but the interactions are even more extensive. A specific site will ALWAYS place technical constraints on system design. These constraints can be minor or serious enough to preclude use of the site. Unfortunately, a whole host of non-technical constraints can also be imposed. When these are added to the technical constraints it can seriously impact the feasibility of the project. Redesigning components slightly or rearranging them on a specific site can have major system consequences. Moving seawater components around on a site can be caused by such
234 considerations as parking needs or aesthetics. In short, considerations far removed from seawater technical requirements. Example 19.1 considers a large number of factors involved with the selection of seawater intake and discharge locations. While most are technical considerations, it tries to cover some of the more likely, legal, political, and regulatory considerations that might be present in a given situation. However, each situation can be very different in their specifics and this is not a comprehensive treatment of the subject. Many of these non-technical aspects can be critical. Once a seawater intake location is selected it is necessary to determine exactly how far offshore to place the intake. The cost of marine construction is so high that there is a strong inclination to minimize the in-water pipe lengths. This often becomes an important exercise in balancing risks and costs. Site factors (Chapter 3), intake depth considerations (Chapter 4) and suction side piping frictional losses (Chapter 6) can combine with factors not directly involved with seawater system requirements to establish these critical in-water pipe lengths. See Example 19.2. High tidal ranges complicate many aspects of seawater system design, including intake placement. High tidal range can greatly extend the in-water pipe lengths, aggravating both suction side frictional losses and construction cost concerns. When the lengths required to get water at a very low tide become excessive, a pump storage system might be considered. See Example 19.3. Pumps are generally selected after the seawater system is dimensionally laid out. Since the system and pumps are highly interactive, it can happen that pump selection options may be very limited. Design iterations between system design and pump selection are not uncommon. Example 19.4 further explores the dynamics of pump and system interactions and shows how important changes can occur with time due to biofouling or external conditions, such as major storms. A system that 'works' may not work under all conditions or over time if not properly maintained. Pump system failures can occur quickly due to the loss of available NPSH (see Chapter 7). This can be due to lowered atmospheric pressure or rapid accumulation of storm-generated seaweed and other debris on the intake screen. Many seawater systems are used for limited periods of time, such as over a summer or for a specific project. These are commonly set up on a pier or along the shore and, due to their short-term nature, can be greatly simplified in construction and operations. Example 19.5 shows the planning and design of such a system. Elements from just about every chapter of this book are included in this basic simple example. It is important to remember that there is no single 'correct' solution but a complete spectrum of options. However, some options may be much better than others. Many unstated factors or details about the specific requirements, environment or legal/political situation could easily have altered this design. It is important in system design to anticipate operations and maintenance problems that might occur and to plan for them. An example (see Example 19.6) is solids accumulation at the first 'slow spot' in the system. This example is for the slow accumulation of sediments in channels, large tanks and ponds that can occur from using seawater from more turbulent coastal waters. It is exactly the kind of problem that can take time to develop into a serious situation. Many things in the servicing, maintenance, overhaul and equipment replacement areas can act this way. You tend to put them off until they reach crisis proportions or cause a major failure. This example demonstrates that it may take major resources to address these types of operational problems and they must be confronted early in the project. They can add substantially to both initial costs for plant and equipment and to subsequent operating costs.
235
Example 19.1. Seawater system intake and discharge location In a real situation a very large number of factors may have to be considered and weighed in selecting the locations for seawater intakes and discharges, any one of them may be potentially critical. The hypothetical example illustrated by the provided sketch is intended to form a basis for qualitative discussion of possible options and considerations. However, such a simplified exercise tends to ignore, or understate, the many important but often highly specific legal, political, and economic circumstances that might be present in a given situation.
Open Water
Harbor Entrance
|
Steep Rocky Shore r
Sheltered Harbor
Q Winds & / " Waves/
(~5
Research, Fishing & " Groin
~ 1
'
Supply LengthsBoats to 250 ft
Sandy _...--__~} Beach ~ Public
Recreation
Area
l|
I! \\
0' , ,
,
,
,
500' , ,
,
,
1000' , i
(A) List and discuss the advantages and disadvantages of the sites numbered 1 to 5 as seawater intakes or discharge locations. #1
9 Easy land access due to road, probable cheap pipe run. 9 Easy access to deep water under pier, cheap seaward pipe run on or under pier for either intake or discharge. 9 Reasons A to E below indicate probable water quality problems. Water quality may eliminate otherwise attractive intake location. (A) Wooden pier pilings probably treated, additional likelihood of periodic dock repairs with introduction of new treated pilings. (B) Normal and accidental boat waste and fuel discharges. (C) Boat-induced turbidity.
236
E x a m p l e 19.1. (continued) (D) Other possible sources of harbor pollution (industrial, sewage or other ship discharges). (E) Possibly significant rapid changes in water salinity or temperature due to storms, shallow harbor, freshwater inflows or harbor circulations. 9 Good place for discharge, but discharge may not be allowed in harbor, little likelihood of recycling discharge if intake is on seaward side of peninsula. #2
9 Short pipe run distance on land. 9 Sheltered area for intake or discharge. 9 Offshore pipe run distance for intake unknown but likely long to get adequate depth in harbor. 9 Intake would have at least some of the water quality concerns of location #1. 9 Good possible discharge area, if allowed. 9 Little likelihood of recycling discharge if intake on seaward side of peninsula.
#3
9 Relatively long land-side pipe run, although most can be alongside of road 9 Steep contours near shoreline and probability of high tidal currents may create engineering problems. 9 Engineering of required but unknown length of in-water intake line may be especially difficult due to currents, ship traffic and partially exposed location. 9 Likely to have different water quality on incoming and outgoing tides (open water vs harbor water), possibly negating site as intake location. 9 Better as discharge location, with small probability of short-circuiting of discharge if intake at location #4 or #5 due to assumed prevailing currents. For harbor intake, somewhat higher probability of recycling but probably still small due to physical separation.
#4
9 Shortest land pipe run but complicated by steep contours and rocky shore. 9 Rocky shore and exposed location may lead to construction difficulties for offshore piping but contours indicate probable short intake length to get adequate depth. 9 Probability of consistent good 'open water type water quality.
#5
9 Longer land-side pipe length than most other locations but less severe contours. 9 Probability of consistent good 'open water' type water quality. 9 Likelihood of vehicular access to shoreline may be significant construction and servicing advantage, especially relative to locations #2, #3 and #4. 9 Backside of groin is somewhat sheltered but may have an eddy, which collects floating and drifting debris. 9 If a major storm comes in from the 'other' open water quadrant, the backside of the groin may be completely filled with sediment during a single event. 9 If intake is placed here, it should extend well past the end of the groin. 9 Best as intake location, for discharge would probably provide some short-circuiting to other locations (especially #3 and #4), which may be acceptable based on more detailed circulation data and specific location.
(B) Based on probable engineering, complexity, cost and water quality considerations, list the most promising intake and discharge locations as pairs in descending order. Since many possibly important factors are undefined and relative weighing of factors can vary, this listing is not definitive but only a guide. Desirability
Intake location
Discharge location
Most promising
4 4 4 5 5 5 5
2 1 3 2 1 4 3
Least promisin~
237
Example 19.2. Seawater intake placement depths A seawater system (4 in. intake pipe, 150 gpm flow) intake is to be installed in a well sheltered area near Pensacola Florida. The nearshore bottom has a slope of 1:40 and it is estimated that even waves from extreme events will not break in water depths greater than 5 ft. Waves under normal conditions are negligible. (A) Estimate the minimum water depth and distance from shore (relative to MSL) for the seawater intake under normal conditions. From Table 3.2 at Pensacola MHHW = 0.67 ft, MLLW = - 0 . 6 3 ft (mean tidal range 1.3 ft) Record high = 8.3 ft, Record low -- - 2 . 8 ft Using Eqs. 3.1 and 3.2 for intakes (C = 4) Design low tide (DLT) = - 0 . 6 3 - (1.3)/4 = - 0 . 9 5 5 ft Design high tide (DHT) = 0.67 + (1.3)/4 = 0.995 ft Design tidal range = 1.95 ft From Fig. 4.3, need allowances for elevation above the bottom and for vortexing. In this case, a wave allowance is not necessary. Flow velocity in intake pipe from Table 6.2 is about 4.2 ft/s and from Fig. 4.4, need about 2 ft minimum above the intake for a vortexing allowance. Assuming that the intake pipe is oriented upwards, a minimum elevation above the bottom of 1 ft is required to avoid ingestion of bottom debris (if intake is horizontal at least 3 ft is needed). This results in a minimum water depth below DLT of 3.0 ft. If small boat traffic is a potential problem, may need more clearance above the pipe than required for vortexing to clear propellers. A 3.0 ft minimum clearance above the intake pipe or screen should in most cases be adequate. This translates to a minimum water depth below DLT of 4 ft. With a 40:1 beach slope the horizontal distance is as shown on the sketch below and is 198 ft.
Intake Details 1' high, 3' of freeboard to DLT +10' .....
Record High
O' MSL'-
Slope of Bottom 1:40 No Scale Elevation Relative to MSL
~ .~ !~
198'
.5' _
312'-
-10' ,!
(B) Discuss the trade-offs in intake location and water depth to cover extreme events. If the record low tide was to be repeated and the system could be shut down for a short time interval without major consequences, no changes would be needed. For the intake in Part A (small craft clearance), operation at the record low would still leave about 1.2 ft of water above the intake. It would probably operate under these conditions but might vortex and ingest air, with possibilities of mass mortalities due to gas supersaturation. An additional 72 ft of pipe (extra 1.8 ft of depth) would substantially reduce the risks. However, it is important to remember that vortexing is a complicated phenomenon and not completely predictable.
238
E x a m p l e 19.2. (continued) If breaking waves hit the intake structure, destruction is highly likely. Going to deeper water to avoid breaking waves may save the intake, but does not guarantee that the waves will not uncover and destroy the more inshore parts of the intake line. The worst case situation (not very likely) is a record low tide combined with extreme waves. This would require a minimum of 5 ft of water relative to the recorded low (see sketch) and about 114 ft more intake line than in Part A. This is likely to have major cost impacts. If extreme waves were to hit at any tide of MSL + 1 or greater, an intake 198 ft seaward of MSL would already be safe from breaking waves. If probabilities and consequences of extreme waves are of serious concern, additional intake length and depth should be considered. Another trade-off is frictional losses in suction (intake) lines. From Table 6.2, this intake line has about 1.5 ft of head loss per 100 ft of pipe if clean, if biofouled it could be considerably greater. The pipe lengths seaward of MSL that have been discussed range from 198 to 312 ft. When the probable pipe lengths from MSL to the pump intakes are added, frictional losses may be of serious concern (see Section 6.4). For the longer distances, a larger pipe diameter may have to be considered, at obviously increased costs. The offshore lines and intakes are likely to be a very expensive part of the system and there are usually strong economic incentives to keep the lengths to an absolute minimum.
239
Example 19.3. Intake placement depth in region of high tidal range A seawater system (described in Examples 7.1, 7.2 and Fig. 7.5) has 575 ft of 6 in. intake pipe. The beach has a plunge point at about the M L W waterline as shown in Fig. 3.3. The M L W waterline is about 200 ft (pipe length) from the pumphouse and the beach slope is about 1 : 5 and the slope of the bottom seaward of M L W is 1:50. Assume a design high tide = MLW + 18' and a design low tide = M L W - 2'. Except for very improbable extreme events, wave action at this site is negligible, with a maximum wave height of 1 ft. (A) What is the minimum water depth at the intake during the design low tide? Offshore length from M L W - 575 - 200 -- 3 7 5 , 3 7 5 / 5 0 - - 7 . 5 ft elevation per MLW Design low tide = M L W - 2, water depth = 7.5 - 2 = 5.5 ft minimum (B) Does your value above seem reasonable? Explain! See Fig. 4.3 for required components Operating point at design low tide (Fig. 7.5) -- 125 gpm Pipe average velocity (Table 6.2) = 1.5 ft/s (interpolation between 1.1 and 1.9 for 125 gpm) From Fig. 4.4, vortexing allowance -- 1.0 ft (extreme end of curve and approximate) From problem statement, wave allowance -- 1.0 ft If the intake is 1.5 ft above the bottom and it is screened with the top of the screen extending 1 ft above the intake, this leaves a minimum of 3 ft above the screen for passage of small boat traffic. Since all components seem reasonable based on available information, the answer is YES. (C) If the cost associated with installing this length of intake pipe (especially the underwater parts) is considered prohibitive but that pumping only half the time (MSL and above, MSL = MLW + 8) is considered acceptable due to availability of water storage, where should the intake be placed and what would be the minimum pipe length from the pumphouse? Since the intake length has changed, for accuracy all the calculations should be redone. However, it is possible to estimate the operating point at MSL from Fig. 7.5 of about 215 gpm resulting in an average velocity of 2.5 ft/s (Table 6.2). From Examples 7.1 and 7.2, at this flow rate, the suction side losses are well under 10% of the total head. With shorter pipes, these losses would be even smaller. It is therefore possible to use the available computations for estimating purposes. With a higher velocity, the vortexing allowance (Fig. 4.4) = 1.5 ft, the wave allowance is still -- 1.0 ft, the bottom ingestion allowance still -- 1.5 ft and the small boat factor is meaningless (collision at lower tide becoming an accepted risk). In fact the intake is completely out of water for part of the tidal cycle, making cleaning and servicing very easy. Minimum water depth for pumping= (1.5 + 1.0 + 1.5) -- 4 ft Intake elevation -- M S L -
4 ft
Pipe length seaward of M S L = 4 x 5 = 20 ft (remembering that MSL is inshore of M L W and at a slope of 1:5) Pipe length M S L to pumphouse about 200 - 40 = 160 ft Pipe length pumphouse to intake= 160 + 20 -- 180 ft, down considerably from 575 ft Total length of intake piping saved 575 - 180 -- 395 ft (375 ft of it below MLW), a 65% reduction, and all of it in the relatively expensive low tidal and subtidal areas.
240
Example 19.4. Pump-system interactions and biofouling effects A system as shown is to pump seawater (35 ppt, 40~ Assume loss coefficients for intake screen K -- 5.0, undefined processing equipment K = 10.0 and discharge over tank K = 0. All piping is 6 in. ID plastic with 500 ft suction length and 300 ft discharge. Assume a normal atmospheric pressure of 14.7 psi and a seawater vapor head = 0.28 ft. The system curves for both low and high tide have been calculated and superimposed over the pump curve for the selected pump and speed (1500 rpm) controller as given. Remember that the ONLY possible operating points are at the intersections of the pump and systems curves. F"--"-3 Pressure Gauge
. .,.,.,.7. .MLW+6' ~
MLW+ 12
A.AZ.za,~,.,~,~ MLW -1'
100
Open Gate Valve __
MLW = +30 . . . . .
l--I~
Treatment I ~ W a t e r k_) v "" I Equipment I Pump
"r"
/
1500 rpm
j ~
lO~
50 MLW- 1' MLW+ 6' NPSH
0
0
0.5 Flow
2;
1.0 (ft3/s)
(A) At low low-water (MLW - 1), what is the flow rate and head across the pump? At high high-water (MLW + 6), what is the flow rate and head across the pump? Reading low water curve, Q = 1.0 ft3/s, head = 50 ft Reading high water curve, Q = 1.05 ft 3/s, head -- 45 ft (B) At low tide, what is the available NPSH? Atmospheric head = pressure/specific wt. seawater = (14.7)(144)/64.2 = 33 ft
V = Q/A -- 1.0/0.196 = 5.1 ft/s Suction side frictional pipe losses, Eq. 6.2, but need to acquire input values Pipe equivalent sand roughness (Ks) from Table 6.3 = 4.2 x 10 -5 (for plastic pipe, relatively clean) Relative roughness= Ks/d = 0.00008 ('smooth') From Table A-3F, v = 1.7 • 10 -5 Reynolds number= Re = Vd/v = (5.1)(0.5)/1.7 x 10 -5 = 1.5 x 10 -5 Using Re and Ks~d, read f = 0.016 from Fig. 6.2 Eq. 6.2, h = (0.016)(500)(5.1)2/(2)(32.2)(0.5) = 6.46 ft of suction side pipe losses
241
Example 19.4.
(continued)
Suction side frictional fittings losses, Eq. 6.6 (screen k = 5, given) and one 90 ~ elbow (Table 6.4) h = (5.0 + 0.28)((5.1)2/(2)(32.2)) -- 2.13 ft Total suction side losses= 6.46 § 2.13 -- 8.59 ft Eq. 7.1, available NPSH-- 33 - 13 - 8.59 - 0.28 -- 11.13 ft (C) If the pressure gauge on the suction side of the pump is a direct measure of available NPSH, what is its reading in psig? Eq. 6.1, absolute head -- 11.1 ft = absolute pressure/specific wt. Seawater = pressure/64.2 Absolute pressure -- 714.5 lb/sq ft --- 4.96 psi Gauge pressure = 4.96 - 14.7 -- - 9 . 7 psig; this is a partial vacuum (below atmospheric pressure) (D) For the low tide condition, does the system meet its suction side requirement and by what margin or deficit? At low tide operating point, read, required NPSH = 5.0 ft Available NPSH -- 11.1 ft, conditions of Eq. 7.2 are met by margin of 11.1 - 5.0 -- 6.1 ft margin (E) In specifying the system it is important to know the maximum pressure that can be seen in this system with the given pump and controller. What is this maximum pressure in psig? Maximum head = shut off head (Q = 0) -- 90 ft Eq. 6.1, 90 = pressure/64.2, pressure = 5778 lb/sq ft = 40.1 psig (F) After several months of use the flow at low tide has degraded to 0.65 ft 3/s due to biofouling. The suction side pressure gauge now reads - 1 2 psig. All the loss coefficients and pipe roughness values previously used are no longer relevant and the low tide systems curve has shifted dramatically up and to the left. What is the biofouled head across the pump and the available NPSH at low tide? The 'new' systems curve is stated to intersect the pump curve at a Q = 0.65 ft 3/s, finding this point and reading the head -- 74 ft Available NPSH-- (14.7 - 12)(144)/64.2 -- 6.1 ft (G) Since the system is stated to be operable in the biofouled condition at low tide, it must meet its suction side NPSH requirements (Eq. 7.1), but what is the margin? At 'new' operating point, read required NPSH = 3.0 ft Margin -- 6.1 - 3 = 3.1 ft, kind of a slim margin (H) A major storm is approaching and it is expected to hit at low tide and have an atmospheric pressure of 13.0 psig. Do you expect your biofouled system to be operable during the storm? Atmospheric head = pressure/specific wt. = (13.0)(144)/64.2 = 29.2 ft Available NPSH loss relative to normal pressure -- 33 - 29.2 -- 3.8 ft Margin of Part G is now deficit of 3.1 - 3.8 -- - 0 . 7 ft SYSTEM NOT OPERABLE ~ due to the conservative nature of the process, this system might in fact still operate but you cannot count on it
242
Example 19.4. (continued) (I) It is necessary in defining the system to specify the minimum power rating of the pump motor. This is normally done for the high tide condition as this is usually the greater requirement for centrifugal pumps. The power going into the water is called the water power. Assume that the system has been cleaned of biofouling and the original flow conditions restored and the pump has an efficiency of 60%. What is the required horsepower into the pump (pump brake power)? Operating point for high tide from Part A h = 45 ft, Q = 1.05 ft3/s Water power = (specific weight)(flow rate)(head across pump) = (64.2)(1.05)(45) = 3033 ft-lb/s Converting ft-lb/s to horsepower =3033/550 = 5.5 horsepower Pump brake power = water power/pump efficiency - 5.5/0.6 - 9.2 horsepower (J) Assuming that the pump efficiency does not change appreciably, will the required brake power be more or less for the biofouled conditions of Part F and what is the value? What minimum motor rating would you recommend for this system? Operating points from Part F, Q = 0.65 ft 3/s, h = 74 ft Water power--(64.2)(0.65)(74) = 3088 ft-lb/s 3088/550 = 5.6 horsepower Brake power = 5.6/0.6 = 9.4 horsepower, 1/5 horsepower more when biofouled Specify minimum installed horsepower -- 10 hp
Example 19.5. Outdoor wet lab design You want to design a summer outdoor wet lab for research and/or educational purposes at the corner of a pier or dock. The allocated area is 65 ft long on the seaward end of the pier by 30 ft on the side for a total of about 2000 ft 2. The hard asphalt surface is 5 ft above mean water and the maximum normal tidal elevations are mean water +2 ft. The water depths off the edges of the pier are both 7 ft at low tide. The average water temperature during the planned 3-months test period is about 70~ (34 g/kg salinity) and the water quality at this site is expected to be adequate and acceptable for the duration of project. Since there are no special system-wide water processing requirements, the seawater system is to be a straightforward supply, distribution and drain system. Any special needs will be met at the points of application and electric power is needed for these purposes. The program is expected to include four separate but related projects, each with about four students. The total system biomass is expected to be a maximum of about 40 lb of small marine animals (species and sizes not known). (A) Define the required seawater system flow rate. Using Fig. 2.7C (research criteria), 70~ constraining)
5 g animals (worst case, larger animals would be less
Conservatively estimate loading --- 0.4 lb/gpm For 40 lb biomass means design flow rate of 100 gpm
243
E x a m p l e 19.5. (continued) (B) Define and layout the system components, including intake and discharge locations and on-site seawater distribution pattern. Size and specify pipes and other seawater system components. Estimate required parts and develop parts list. After a number of design iterations, the following system has resulted.
I
I
1,__,1.~__6, ~ 3 , ,~2 ,13'J , , , - [!- ~ i
x
x
~i,--"~, 0.0 (Arbitary VerticalDatum)
Ls = 13', Ld - 15' Static Lift: +14' to +18' V(2" ID) = 10.2 ft/s
' \
2" ] ]3''pipeape
..............
Low Tide: Coarse Screen:
+11'
--+1o'
x
x
x
x
x
Discharge
_f9
o
4"2rain
12' Test #Ar~a
ne
12' Test Area #2
- -~
e
~ ( O p e n Top T
12' Test #Ar~
12'
Trailer/Lab
2' ,
24'
'
4"
_ _ Electrical [~ Panel
2'
2"
4"
adbox
2"
3~ i
l
l
l
l
l
l
l
l
l
/
l
l
l
l
l
l
l
i
i
i
l
l
l
l
i
l
i
i
l
l
l
l
Seaward Edge of Pier
l
l
l
l
l
l
l
l
l
l
l
l
i
l
l
i i i
~ Screen
Pump
Prevaling Tidal Currents (C) Estimate required parts and develop a parts purchase list. Pipe 2 in. 100 psi polyethylene pipe, need 112 ft, order 3 in. 100 psi polyethylene pipe, need 67 ft, order 4 in. PVC drain pipe, need 88 ft, order
120 ft 80 ft 100 ft
Fittings 2 in. hose L (hose fittings can be of any available plastic) 2 in. valves with hose adapters each side (3 included in each test area but not shown) 2 in. hose caps
7 14 sets 3
244
E x a m p l e 19.5. (continued) Fittings (continued) 2-3 in. hose T (run 3, branch 2) 2-3 in. hose L (or equivalent) 3 in. hose L 3 in. valve with hose adapter each side 4 in. PVC Sch 40 socket T 4 in. PVC Sch 40 socket L 4 in. PVC Sch 40 socket caps PVC cleaner and glue, lots of hose clamps
3 1
5 1 set 11 2 2
(An exercise for the reader is to find the inadvertent omissions from this list.)
Other system components 9 Head tank, any available synthetic material, 3 min minimum residence time = 40 ft 3, three threaded taps with thread to hose adapters (2 in. drain at bottom, 3 in. overflow at top, 3 in. supply, mid-depth on tank). 9 Centrifugal pump to deliver 100 gpm at estimated TDH of about 30 ft. Pump's shutoff head must be well below 225 ft (100 psi rating of piping system), conservatively about 1.5 hp required. 9 Screen with 0.1 ft/s through screen velocity, at 100 gpm (0.22 ft3/s) need 2.2 ft 2 of open area on screen, with expanded metal of 60% open area will need about 3.7 ft 2 of screen face. 9 Power distribution panel, pump may require voltage above 120 VAC, increasing on site risks. Distribution of 120 VAC will probably be required for individual projects, moveable outdoor boxes with GFI can be used if care is taken. Do not underestimate the electrical hazard. A central or several smaller moveable electrical compressors for aeration may provide a valuable backup capability. 9 If available, a small portable shelter or trailer provides many practical benefits. (D) Discuss the major factors leading to your choices of layout and system specification. 9 Intake and discharge were as widely separated as possible. The intake was placed on the seaward side, with the best circulation. The discharge was placed on the side of the pier, which on some part of the tide is likely to have eddies and collect floating debris. This is not a perfect arrangement as short-circuiting may occur under some conditions. A factor would be if the pier is solid or supported by pilings. 9 Three supply pipes versus three for drainage and selection of 4 in. for drain is due to more critical gravity flow situation for drains. Selection of fragile thin-walled PVC drain pipe is due to considerations of cost and availability. Thin PVC can crack, especially at low temperatures but not likely in this application. The drain piping should be protected from physical damage by placing wood on each side of the pipe connected by strapping across the top. 9 As shown, the wet lab area is divided into four equal working areas. If more information was available about individual requirements, the area allocations could be somewhat altered without to many problems. 9 Many of the components have been specified as made of any available plastic. This is due to an expected lack of relevant toxicity data specific to the culture organisms, high flow rates to dilute toxic materials and practical aspects of cost and availability. All materials should be adequately leached in seawater before use and materials choices (when they exist) should consider risks of toxicity (see Section 8.1).
245
Example 19.6. Seawater supply channel for shrimp farm Evaluate the following shrimp farm water influent seawater supply system. The discharge channels are not shown. The farm draws seawater from a shallow protected estuary, where currents and waves produce a considerable amount of suspended solids. The sediment concentration does vary over the tidal cycle. The sediment concentration used in this example can be assumed to be a long-term average. The sediment concentrations during a storm event could be 10-20 times higher, but it is likely that the pumps would be shut down under these conditions. The first part of the supply channel acts as a sedimentation channel. With the systems information provided, compute the water requirement, installed pump capacity, sediment production, and water elevation in the supply channel. A Mud Cat is an amphibious unit developed for working in the bayous of the U.S. Gulf Coast. It is commonly fitted with a suction dredge. SedimentationChannel
Water LevelControlWeir
~ ~ Slope = 2.5:1
Clear WaterZone Sediment CollectionZone
~
2.5 mI
J ' ~ ,
J
I2 m
100m
Crosssection of Sediment Collection Channel
lJ
Slope -- 2.5:1
L f
100 m
r
2.5 m
i
!
/
Crosssection of Supply Channel
System information Water quality Settleable solids Total suspended solids
2.1 ml/1 50.1 mg/1 (not including settleable solids)
Pump station Pump availability factor
70% (20 h/day + service time)
Ponds Number of ponds Size Water depth Water turnover
32 15 ha (300 m • 500 m) 1.2 m
6%/day
246
E x a m p l e 19.6. (continued) Sedimentation channel Capture efficiency Length Dimensions
100% of settleable solids + 50% of suspended solids 600 m see diagram
Settled solids Density of solids (wet) Solids content Capacity of Mud Cat Cost of Mud Cat
1200 kg/m 3 (1.2 times freshwater) 60% 6000 tonnes/week (dry) $250,000 US
Supply channel Capture efficiency Bottom elevation (after weir) n (Manning) Slope Dimensions
0% of suspended solids -+-2.1 m above an arbitrary vertical datum 0.03 0.00001 see diagram
(A) Compute the water requirement. 32 ponds x 15 ha/pond x 10,000 m2/ha x 1.2 m x 0.06/day Q =
86,400 s/day
Q = 4.00 m 3/s or 63,500 gpm (average) (B) Compute the required pumping capacity. Installed capacity=
4.00 m 3/s 0.7O
- 5.71 m3/s
(C) Compute the volume of settled and suspended solids. Volume of settleable solids = 4.00 m3/s x 86,400 s/day x 7 day/week x 0.0021 m 3 solids/m 3 = 5100 m 3/week Volume of suspended solids 0.50(4.00 m3/s x 86,400 s/day x 7 days/week x 50.1 mg/1 x 1000 1/m 3) 106 mg/kg x 1200 kg/m 3 = 51 m 3/week (D) How many Mud Cats would be needed (working 20 h/day)? Mud Cat capacity (dry solids) = 6000 tonnes/week ?a 20 h/day Mud Cat capacity (wet solids) = 6000 tonnes/week/0.60 = 10,000 tonnes/week Volume capacity =
10,000 tonnes/week x 1000 kg/tonne 1200 kg/m 3
= 8333 m 3/week Number needed = 5151 m3/8333 m 3 = 1 unit (E) How many days would it take to fill up the 2 m sedimentation zone assuming uniform deposition? Average width of channel = 102.5 m V o l u m e - 102.5 m x 2 m x 600 m = 123,000 m 3 123,000 m 3 Time to fill---- 167 days 736 m 3/day
247
E x a m p l e 19.6. (continued) (F) Compute the water depth after the weir. Note that this trapezoidal channel can be considered a rectangular channel with negligible error. Use Fig. 6.3 and Eq. 6.10 Area (m 2) = 100d 100d
Hydraulic radius R ( m ) = ( 100d
100 + 2d
100d ) ~ 100 + 2d
4.00 m 3/s =
(0.00001)~
0.03
By trial and error using Eq. 6.4, d - 0.562 m (G) Compute the water surface elevation at the first and last supply point assuming that all the flow is supplied to the last set of pond. First supply point: Elevation of bottom = 2.10 m - (0.00001 x 150 m) -- 2.10 m Water surface elevation -- 2.10 m -4- 0.562 m -- 2.66 m Last supply point: Elevation of bottom = 2.10 m - 0.00001 x [15 x (300 m + 15 m) + 150] = 2.05 m Water surface elevation = 2.05 m -4- 0.562 m = 2.61 m Note that there is only a head loss of 5 cm (2 inches) between the first and last ponds. Therefore, this supply channel functions more like a constant head tank than an open channel. Difference in water surface elevation in the supply channel due to wind can be in the order of several inches. (H) Assuming that 70% of the remaining suspended materials will uniformly settle in the ponds, compute the average water depth of the ponds after 5 years of operation. Volume of suspended solids 0.35(4.00 m3/s x 86,400 s/day x 7 day/week x 50.1 mg/1 x 1000 1/m 3) 106 m g / k g x 1200 k g / m 3 = 35 m 3/week Total volume of solids Total area of ponds Depth of sediment Pond depth
--= ---
(35 m 3/week)(52 weeks/year)(5 years) 9200 m 3 (this is a negligible amount of sediment) (300 m)(500 m)(32 ponds) = 4,800,000 m 2 9200 m 3/4,800,000 m 2 = 0.002 m (2 mm) 1.20 m
(I) Compare the answer from Part I to what would occur if the sedimentation channel was not constructed. Volume of settled solids is 5200 m 3/week (Part C) Total volume of solids Depth of sediment Pond depth
= = -=
(5151 m3/week)(52 weeks/year)(5 years) 1,339,000 m 3 1,339,000 m 3/4,800,000 m 2 1.20 m - 0.28 m = 0.92 m
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249
Chapter 20
Summary Commandments The following are a list of basic guidelines and rules for maximizing the probability of success with seawater culture systems. They have been gained from experience. 9 Take great care in quantifying the requirements, as they will greatly affect the complexity and cost of the system. 9 Consider long-term as well as short-term requirements, even though they are more difficult to quantify. 9 Major cost underestimates are more likely to result from necessary but uncounted components and services or increased requirements rather than errors in specific items. 9 The initial cost estimates of in-water components, such as intakes and discharges, are usually greatly under estimated. 9 The proper bioengineering of the seawater system is usually the essential core of the projects of which they are a part. When dealing with architects and money people who are trying to reduce the capital costs, it is important to remind them that if the system fails it will not make any difference how much money was saved or how beautiful the building. If they cannot afford to build it fight, the cost of doing it wrong is considerably greater. 9 Due to the many critical interactions between life support requirements, site factors/elevations and seawater system design, the seawater system should be designed and laid out first, and then the building designed around it. It should be considered as a seawater system with a building rather then a building with a seawater system in it. Unfortunately, the architectural design is usually well ahead of the seawater system in the design process, often creating many serious incompatibility problems late in the process when trying to 'fit' the seawater system into the building. 9 Aquatic life support requirements are fixed by physical, environmental and biological laws, and not by management, budgetary or human schedules or dictates. 9 Consider operating approaches and procedures before the design is fixed. Significant input from operational personnel is needed in the design and construction phases. 9 Demands for services (seawater, compresses air, etc.) usually increase in quantity and quality with time. If possible, provide extra floor space, access to piping, access to drains and provisions for electrical power for potential anticipated future retrofits. 9 Remember that the key to low risk and high performance systems is large amounts of high quality seawater. In short, maintain very conservative biomass loading relative to the available water quality. If a system is working well, increasing the biomass will increase the risks. 9 Anticipate probable failures and plan accordingly to minimize the consequences. 9 Water flows downhill. The design and layout of the seawater system on a specific site involves numerous and diverse considerations, many of a nontechnical nature and independent of the seawater system requirements. Trying to circumvent this gravitational fact will lead to considerably greater system complexity, cost and risk.
250 9 Provide redundant equipment to back up critical functions in emergencies. Resist temptation to use backup equipment in normal operations just because it is available. 9 Responsibilities and decision-making procedures for emergencies should be decided before crises occur, remembering that they rarely occur at convenient times. 9 Do not forget routine maintenance and inventorying necessary spare parts when operations are going well; it is twice as important when things are not going well. 9 Be extremely careful in selecting all materials and supplies used in and around seawater systems, because your organisms may be very sensitive and seawater is very corrosive. Do not forget to include the surrounding building and paints, sprays, cleaners, sealers and solvents used near culture organisms. 9 Leach all materials in running seawater for at least two weeks before use. 9 Take great care with all fittings, pipes and equipment on the suction side of pumps to avoid even the most minute air leak. Supersaturation can easily kill. 9 Make the suction-side lines as large in diameter and as short as possible to minimize suction-side frictional losses. 9 Never try to save money by reducing the size of pipes or fittings on the suction side of main pumps. This is sure to be false economy and to lead to major long-term problems and constraints. 9 Place pressure gauges on both the suction and discharge side of pumps to monitor the condition of the lines and the performance of the pumps. Watch for biofouling, especially on the suction side. Service regularly. 9 Adequately pitch all floors in wet-lab areas towards the drains remembering that concrete may shrink on drying. 9 Greatly oversize drains to take high transient flows. Drains can never be too large. Even the largest drains will occasionally clog if not maintained. 9 Expect very high suspended solids content in incoming seawater from shallow water intakes during storms or heavy waves. Solids will accumulate wherever the flow velocity drops. 9 Anticipate the need to remove accumulated sediment and debris from any parts of the system with low flow velocities. 9 Bury or otherwise make inaccessible as little of the system as possible. The inaccessible parts are inevitably the parts you will want to get at later. 9 Place all electrical outlets up high, above any unintentional water input. 9 Use ground fault interrupters on all indoor and outdoor electrical outlets. Do not underestimate the electrical hazards associated with seawater. 9 Inspect and service intake screens regularly. 9 Be careful in locating the intakes. They should not be situated so as to pick up debris, recycle drain water or ever experience breaking waves. Do not underestimate the forces of the sea on intakes and other exposed structures. 9 Remember that the piping/processing system and the pumps are highly interactive. Changes in either area will affect the other. 9 In wet-lab and mechanical areas use 'X' fittings with blanked faces where 'L's and 'T's are needed. This maximizes accessibility for cleaning and future modifications. 9 If you are on call, do not place on automatic alarm any functions or events that can wait until normal working hours.
251 9 In a field with so much misleading or incomplete information, data voids, 'experts' and variations in conditions, it is worth remembering when dealing with the unknown or uncertain that one test, under the actual conditions to be encountered, may be worth a thousand expert opinions. 9 Lighten up! This is an interesting field. You could be designing activated sludge plants or water distribution piping in Kansas.
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253
References
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Appendices
264
Appendix A
Conversions, Definitions and Seawater Properties
The purpose of Appendix A is to provide the quick reference information that may be required to interpret various sections of this book in regards to specific circumstances that may arise. This includes conversion factors, definition of terms and useful seawater properties.
A-1 Conversion factors The multitude of units that can be encountered during the design and construction of seawater systems can add considerable confusion to the process. Listed below are select parameters and relationships, which might be helpful. To get units on the fight starting with units on the left, multiply by the given number. To go the other way, from fight to left, divide by the given value.
TABLE A- 1 Conversion factors Multiply units of
By
To obtain
micrometers or microns (Ixm) micrometers or microns (Ixm) feet (ft) square feet (ft2) gallons (US) gallons (US) gallons (US) cubic feet (ft3) cubic feet/second (ft3/s) cubic feet/second (ft3/s) gallons/minute (gpm) gallons/minute (gpm) gallons/minute (gpm) cubic feet/second (ft3/s) pounds force (lb) pounds mass (lbm) pounds/square inch (lb/in 2, psi) pounds/square foot (lb/ft 2) pounds/square inch (lb/in 2, psi) pounds/gallon per minute (lb/gpm) pounds/gallon per minute (lb/gpm) pounds/square foot (lb/ft 2) pounds/cubic foot (lb/ft 3) pounds/cubic foot (lb/ft 3)
3.93 x 10.5 1.0 x 10 . 6 0.3048 0.0929 0.1337 3.7854 0.0037854 0.02832 28.317 0.02832 0.06309 3.78 6.309 x 10.5 448.83 4.448 453.59 6895 47.88 2.246 O.1198 0.001997 4.8824 16.018 157.1
inches (in) meters (m) meters (m) square meters (m2) cubic feet (ft3) liters (1) cubic meters (m3) cubic meters (m3) liters/second (lps) cubic meters/second (m3/s) liters/second (l/s) liters/minute (lpm) cubic meters/second (m3/s) gallons/minute (gpm) newtons (N) grams newtons/square meter (N/m 2, pascals) newtons/square meter (N/m 2) feet seawater head (50~ 35 ppt) kilograms/liter per minute (kg/lpm) kilograms/liters per second (kg/lps) kilograms/square meter (kg/m 2) kilograms/cubic meter (kg/m 3) newtons/cubic meter (N/m 3)
265 TABLE A- 1 (continued) Multiply units of
By
To obtain
British Thermal Unit (BTU) British Thermal Unit (BTU) horsepower (hp) horsepower (hp) horsepower (hp) watts (W) watts (W)
1055.1 252.0 550 0.707 745.7 0.239 0.0009483
joules (J) gram-calories foot-pounds/s British Thermal Unit/second (BTU/s) watts (W) gram-calories/s BTU/s
A-2 Definitions
The following terms have been selected for definition based on an assumption of a broad-based readership. Terms that might be common in one discipline might be quite confusing to someone from another. In particular, it includes both commonly encountered biological and engineering terminology.
TABLE A-2 Definitions
Acute toxicity. A short-term exposure sufficient to result in death or severe injury to an organism, generally based on 50% mortality.
Absorption. The taking up of matter in bulk by another matter, as in the dissolving of a gas in a liquid. Adsorption. The adhesion at the molecular level of a gas, solute or liquid to the surfaces of a solid body or liquid. Aerobic. Pertaining to the presence or need for oxygen. Air stripping. See foam fractionation. Anaerobic. The absence or a requirement for absence of oxygen. Anode. The more electronegative of two or more electrically conductive materials in electrical contact with each other.
Backflushing. A cleaning or rejuvenating reverse flow of a fluid, which often is, but does not have to be, of the same type as in the normal flow direction. Most commonly, a reverse flow of seawater through a piece of equipment to remove accumulated solids and debris.
Backwashing. Same as backflushing. Biofilter. Unit with high internal surface area used for biological oxidation or reduction of organic compounds. The aerobic oxidation of ammonia to nitrate (nitrification) is the most common process.
Biofouling. Biological growth on materials and equipment placed in seawater. It is highly variable in its composition and intensity.
Biomass. The total wet weight of organisms in a system. BOD or BODs. Biochemical oxygen demand. Oxygen required to oxidize organics contained within the system to carbon dioxide and water. The BOD5 is a standardized test conducted for 5 days at 20~ and in the dark.
Brackish water. Water with a salinity greater than freshwater and less than that of full strength seawater.
266 TABLE A-2 (continued)
Brood stock. Adult animals retained for reproduction. BTU. British Thermal Unit. The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. Cathodic protection. Selecting and providing a more electronegative material to be the anode in a galvanic cell. The cathode will be some equipment or structure which one wishes to protect from corrosion. Cavitation. When local pressure falls below the vapor pressure of a flowing liquid, it will flash to vapor. When these bubbles move on and encounter a higher pressure, they are no longer in equilibrium and will suddenly collapse. If these bubbles are in contact with a solid surface when they collapse, they will generate small areas of very high pressure, possibly sufficient to crater the surface. A very noisy and destructive process that can happen in pumps if they are operated under improper conditions. Chlorine residual. The remaining chlorine concentration in a discharge, usually measured in mg/1 and equal to the chlorine dose minus the chloride demand of the water. Chronic toxicity. Long-term or recurring toxicity, generally based on reduced growth or mortality. Clarifier. Sedimentation tank or basin. Closed system. A system with little or no inflow or outflow of water. Constraint. A limitation or restriction on what can be done. Denitrification. Anaerobic bacterial reduction of nitrate to nitrogen gas. Density (mass). Mass density is a measure of density with units of mass/unit volume. Usually slugs/ft 3 or kg/m 3. Confusion is possible because specific weight and specific gravity are also density parameters. Detention time. Same as residence time. Diatomaceous earth. A light, easily crumbled siliceous material derived from the skeletal remains of diatoms and often used as a fine filtering medium. Diel. Referring to a daily (24 h) cycle. Diurnal. Referring to daylight hours. DO. Dissolved oxygen, generally measured in units of mg/1. Downtime. The length of time a system is inoperative. EDTA. Ethylenediaminetetraacetate, commonly used chelating agent, increases the availability of some trace materials in solution and reduces the toxicity of others. Extensive culture. Culturing at low organism densities and low flow rates. Fetch length. Distance of open water in wind direction. Flow rate. Fluid flow per unit time. Many different units commonly used. Flow-through system. A system which has a continuous inflow and outflow of water. There is often relatively little internal water processing. Foam fractionation. The agitation of water in contact with air bubbles resulting in the adsorption of dissolved organic and particulate matter to the bubble surfaces producing foam. Removal of the foam also removes the organic and particulate matter. Galvanic cell. Corrosion of the anode when two or more electrically conductive materials in contact with each other are immersed in an electrolyte, such as seawater. Galvanic corrosion. Result of a galvanic cell.
267 TABLE A-2 (continued)
Gravity flow. The flow of a fluid by gravity alone, without any addition of mechanical power. Head. The height of a column of fluid (seawater). This can be converted to a pressure if the fluid density is known. Head box. An elevated box or tank of fluid (seawater) which produces the head (pressure) required to gravity flow the seawater to the point of use.
Head tank. Same as head box. Heat exchanger. A device that allows heat to be exchanged between two fluids without allowing any mixing of the fluids.
Horsepower. The energy per unit time (power) needed to raise 550 pounds one foot vertically in one second. Intertidal. Area between low and high tides. Intensive culture. The culture of organisms at densities well above those found in nature by the use of high-water flows, supplemental feeding and water processing.
LC50 (LD50). The concentration (dose) of a toxic material that will kill 50% of a population within a stated time, usually 24, 48 or 96 h.
Mil. One-thousandth of an inch (0.001 in.). Nitrification. The biological oxidation by aerobic bacteria of ammonia to nitrite and then nitrite to nitrate. Nocturnal. Occurring during nighttime hours. NPSH. Net positive suction head (NPSH). The NPSH available is the sum of the atmospheric head minus the vapor pressure of the fluid, frictional losses and static lift on the suction side of a pump. The NPSH required is specified by the pump manufacturer for each pump model. The available NPSH must be larger than the required NPSH for reliable operation.
NPT. National pipe thread. Pipe thread system widely used even in metric nations. NTU. Nephelometric turbidity units. Measurement of turbidity by light scattering of sample. Open system. A system that uses large amounts of incoming water to maintain water quality with little or no internal water processing. pH. Negative log of hydrogen ion concentration ( - l o g {H + }) in a solution. Values under 7 are acidic and values over 7 are alkaline. Natural surface seawater values are usually around 7.8-8.1.
Plug flow. When a 'slug' of water proceeds through a system without mixing with any other water. Polyculture. The culturing of more than one species in the same system. Power. Energy per unit time. Usually in hp, W, kW, or ft-lb/s. Protein skimming. See foam fractionation. Pump efficiency. The power transferred into the water by the pump divided by the power input, expressed as a percentage. This may include the pump alone or the pump and motor together. PVC. Polyvinyl chloride. A common plastic with many forms. It may be transparent or colored, flexible or rigid and in sheets or shapes. Commonly used in water piping systems. Schedule 80 pipe has thicker walls for threaded applications (usually gray colored) and Schedule 40 for solvent welded joints (usually white) and other classes for drainage applications. CPVC (chlorinated PVC) is a variation with better properties at higher temperatures and is commonly used in hot water piping applications.
Rearing unit. A container in which the organisms are held during the culture process. This may include tanks, raceways and ponds.
268 TABLE A-2 (continued)
Residence time. The volume of a unit divided by the volumetric flow to the unit. This is the average time a water particle stays within the unit and is a measure of water exchange rate. Same as detention time.
Reuse. Similar to recycling, but sometimes limited to only aeration. Reuse ratio. Comparison of the flows needed to satisfy two specific water quality parameters (i.e., Qoxygen/Qammonia). If the ratio is larger than 1, more flow is needed to satisfy the parameter in the numerator. Reynolds number. Non-dimensional parameter used to characterize and compare fluid flow in pipes (Re). Sacrificial anode. Same as cathodic protection. Salinity. Concentration of dissolved salts in seawater. Salinity measured by grams of solids contained by one kilogram of seawater (parts per thousand or ppt, %o, g/kg). Full strength seawater is about 35 ppt.
Saturation. The maximum amount of a material which can be dissolved in a fluid under stated conditions. The material could be a gas, salt or metal.
SCFM. Standard cubic feet per minute of gas. Generally assumed to be air, at standard conditions of one atmosphere of pressure and temperature of 68~ (20~
Sedimentation. The process of allowing settleable solids to settle out of solution to form sediment. Usually achieved by providing sufficient time at low flow velocities.
Settleable solids. The volume of solids suspended (ml/1) in a fluid that will settle out under static conditions within a given period of time. Standard methods use 1 1 Imhoff cone and 1 h of settling at room temperature.
Significant wave height. The average height of the highest third of the waves in a given wave spectrum. Storm wave information usually presented as a significant wave height and it correlates well with the estimates of experienced mariners. This height can be used to calculate the height of higher and rarer waves, such as the average of the highest 1%.
Specific speed. Non-dimensional parameter used under given conditions to determine the suitability of different types of pumps.
Specific weight. The density of a fluid in units of weight (force)/unit volume, generally expressed as lb/ft 3, N / m 3 or kN/m 3.
Startup. Sequence of procedures required to activate a system or piece of machinery. May specifically refer to initial equipment activation or to any activation. Procedures the first time may be much more elaborate and controlled than subsequent startups.
Stocking density. The number or biomass of culture organisms per unit area or volume (lb/ft 2, lb/ft 3, kg/m 2 or kg/m3).
Storm surge. Increased tidal elevations due to storm winds and low atmospheric pressure. Wind directions encountered relative to the local geography are critical.
Supersaturation. Concentrations of dissolved materials in solution divided by the saturation values (for the given conditions) with resultants greater than one. This is a non-equilibrium condition. Usually expressed as % supersaturation, determined by the concentration minus the saturated value over the saturated value times 100.
Suspended solids. Suspended solids (SS) are measured by filtering a known volume of water through a 0.45 Ixm (may vary) filter and drying the solids to constant weight at 104~
TAN. Total ammonia nitrogen. The sum of the un-ionized and ionized ammonia expressed as nitrogen. TDH. Total dynamic head. The sum of the frictional losses and static lifts in a piping system from fluid source to discharge point, not including any pump that might be between these two points. Under many conditions the TDH is also equal to the head across the pump.
269 TABLE A-2 (continued) TDS. Total dissolved solids. This is a measure of the total concentration of dissolved solids and involves removable of settleable and suspended solids and evaporation of know volume of water to constant weight at a specified temperature. TDS is not equal to salinity, although the two parameters can be expressed in the same units and both measure dissolved solids. Turbidi~.. Reduced clarity or light transmittance of water caused by suspended particles and organic matter. Turnover rate. The volumetric flow to a unit divided by the volume of the unit, with units of 1/time. It is the inverse of residence (detention) time. Viscosity. Is the proportionality between the force required to shear a fluid and the time rate of strain. In short, the 'stickiness' of the fluid, which will vary significantly with temperature. There are two viscosity parameters commonly encountered. One is the kinematic viscosity and the other is the dynamic (absolute) viscosity. The kinematic viscosity is equal to the dynamic viscosity divided by the mass density of the fluid. Water hammer. Momentum of flowing fluid produces transient pressure pulse due to rapid stopping or altering of fluid flow. These pressure pulses can be very destructive to piping systems.
A-3 Seawater properties as a function of temperature and salinity Tabular values of key seawater properties are presented below in both English and SI units: Table Table Table Table Table Table
A-3a A-3b A-3c A-3d A-3e A-3f
Mass density (SI) Mass density (English) Specific weight (SI) Specific weight (English) Kinematic viscosity (SI) Kinematic viscosity (English)
All measurements are at one atmosphere of pressure. Values are much more precise than required for most calculations. The equation for calculating the dynamic (absolute) viscosity from kinematic viscosity and some relevant units and conversions are also presented: Mass
=
weight/gravitational constant (g)
--
32.2ft/s 2 -- 9.81m/s 2
Specific weight = mass density x g Absolute (dynamic) viscosity = kinematic viscosity • mass density
TABLE A-3a Mass density (kg/m3) Temperature "C ("F)
Salinity (g/kg or ppt) 0
10
20
25
30
35
0 (32) 5 (41) 10 (50) l 5 (59) 20 (68) 25 (77) 30 (Xh) 40 (104)
TABLE A-3b Mass density (slugs/ft3) Temperature "C (OF)
Salinity (g/kg or ppt) 0
10
20
25
30
35
0 (32) 5 (41) 10 (50) 15 (59) 20 (68) 25 (77) 30 (86) 40 (104)
1.9399 1.9403 1.9397 1.9386 1.9368 1.9345
1.9558 1.9556 1.9549 1.9534 1.9515 1.9492 1.9463 1.9395
1.9714 1.9709 1.9700 1.9682 1.9662 1.9637
1.9791 1.9787 1.9776 1.9757 1.9736 1.9709 1.9680 1.9608
1.9871 1.9862 1.9851 1.9831 1.9810 1.9783 1.9752 1.9680
1.9948 1.9939 1.9927 1.9906 1.9884 1.9854 1.9823 1.9752
1.9320
1.9252
1.9606
1.9536
TABI,E A-3c Specific weight ( k ~ / t n ~ ) Tempaturc "C (%)
Salinity ig/kg or ppt) 0
10
20
25
30
35
271
TABLE A-3d Specific weight (lb/ft 3) Temperature
Salinity (g/kg or ppt)
~ (~
0
10
20
25
30
35
0 5 10 15 20 25 30 40
62.414 62.427 62.408 62.373 62.315 62.241 62.160 61.941
62.926 62.920 62.897 62.852 62.791 62.714 62.620 62.402
63.428 63.415 63.383 63.328 63.264 63.183 63.084 62.858
63.676 63.663 63.627 63.569 63.502 63.415 63.322 63.000
63.933 63.907 63.869 63.808 63.740 63.653 63.550 63.322
64.181 64.158 64.113 64.052 63.975 63.882 63.782 63.550
(32) (41) (50) (59) (68) (77) (86) (104)
TABLE A-3e Kinematic viscosity (m2/s • 106) a Temperature
Salinity (g/kg or ppt)
~ (~
0
10
20
25
30
35
0 5 10 15 20 25 30 40
1.7915 1.5190 1.3072 1.1392 1.0038 0.8929 0.8009 0.6583
1.8031 1.5315 1.3201 1.1523 1.0169 0.9060 0.8139 0.6709
1.8149 1.5435 1.3321 1.1642 1.0286 0.9175 0.8251 0.6816
1.8209 1.5495 1.3381 1.1701 1.0344 0.9231 0.8307 0.6869
1.8260 1.5555 1.3440 1.1760 1.0401 0.9287 0.8361 0.6921
1.8330 1.5616 1.3500 1.1818 1.0459 0.9343 0.8416 0.6973
(32) (41) (50) (59) (68) (77) (86) (104)
a The kinematic viscosity equals the table values x 10 -6.
TABLE A-3f Kinematic viscosity (ft2/s x 106) a Temperature
Salinity (g/kg or ppt)
~ (~
0
lO
20
25
30
35
0 5 10 15 20 25 30 40
19.284 16.350 14.071 12.262 10.805 9.611 8.621 7.086
19.408 16.485 14.209 12.403 10.946 9.752 8.761 7.221
19.535 16.614 14.339 12.531 11.072 9.876 8.881 7.337
19.600 16.679 14.403 12.595 11.134 9.936 8.942 7.394
19.655 16.743 14.467 12.658 11.196 9.996 9.000 7.450
19.730 16.809 14.531 12.721 11.258 10.057 9.0597 7.506
a
(32) (41) (50) (59) (68) (77) (86) (104)
The kinematic viscosity equals the table values • 10 -6.
272
Append& B
Flow-through Seawater System Bibliography
Since it is unlikely that there exists any pure flow-through system, in the sense that there is absolutely no internal water reconditioning, selection of references is somewhat subjective. Appendix B contains those that are primarily flow-through while Appendix C has those with significant internal water processing and reuse. There are several overlaps of citations. Most of the information available on the design, construction and operation of flow-through seawater systems is from academies and research oriented groups. The literature is, therefore, not representative of relative use or common systems' characteristics. Table B-1 lists a selection of the available literature and much of this, unfortunately, is from not readily available sources. Considering the large numbers of flow-through systems in use, the literature is rather meager. The published systems tend to be more complex and more expensive than the majority of existing systems, which tend to be simpler and more straightforward. However, this is not true of some of the commercial systems, which can be quite sophisticated. Literature on commercial systems, mostly bivalve and shrimp hatcheries, would be of considerable value, if more of it were available.
TABLE B- 1 Flow-through seawater systems for culturing marine organisms Author(s) and date
Title and source
Comments
Bahner, L.H., C. Craft and D.R. Nimmo, 1975
A seawater flow-through bioassay method with controlled temperature and salinity. Prog. Fish-Cult., 37: 126-129.
System to prepare raw seawater by two step filtration (sand and cartridge), temperature control (7 kW immersion heater), salinity (add freshwater), and addition of precise amounts of test substance before distribution to tanks.
Clark, J.R. and R.L. Clark, 1964
Seawater Systems for Experimental Aquariums m A Collection of Papers, Bureau of Sport Fisheries and Wildlife, Research Report No. 63, 192 pp.
Good reference, 27 papers, 19 on flow-through systems, mostly research and aquarium systems, international coverage, also published in book form by Crown Publishers Inc., New York.
Colt, J. and J.E. Huguenin, 1992
Chapter 5, Shrimp hatchery design: engineering considerations. In: A. Fast and J. Lester (Eds.), Marine Shrimp Culture: Principles and Practices, Elsevier Science, Amsterdam, pp. 245-286.
Considerable bioengineering design and operations data relevant to marine shrimp hatcheries. Well referenced.
Davis, H.C., 1971
Design and development of an environmental controls system for culturing oyster larvae. In: K. Price and D. Maury (Eds.), Proceedings of the Conference on Artificial Propagation of Commercially Valuable Shellfish, Oct. 1969, Univ. Del., pp. 135-150.
Four 80 gpm seawater pumps (demand system), UV and ozone disinfection, salinity control with well water, temperature control (heating/cooling) using two carbon heat exchangers.
Dupuy, J.L., 1973
Translation of mariculture research into a commercial oyster seed hatchery. Proc. 9th Annu. Conf. Mar. Technol. Soc., pp. 677-685.
Temperature control (heating/cooling/pasturization) all using glass heat exchangers, UV, equipment and procedures described.
Dupuy, J.L., N.T. Windsor and C.E. Sutton, 1977
Manual for the Design and Operation of an Oyster seed Hatchery. Virginia Inst. of Mar. Sci./Sea Grant, 110 pp.
Biological and engineering data on hatchery systems, about a third on 1167 gpm system, 19,000 ft 2 floor area, glass heat exchangers, large cartridge filters, equipment details, suppliers and costs.
Ebert, E.E., A.W. Haseline and R.O. Kelly, 1974
Seawater system design and operations of the marine culture laboratory Granite Canyon. Calif. Fish Game, 60: 4-14.
150 gpm seawater, sand filtration to 15 microns, UV, temperature control (heating) using glass heat exchangers, cooling with portable units.
Harboe, T., S. Tuene, A. Mangor-Jensen, H. Rabben and I. Huse, 1994
Design and operation of an incubator for yolk-sac larvae of Atlantic halibut. Prog. Fish-Cult., 56: 188-193.
Design of an up-flow incubator to provide continuous water exchange and eliminate dead volume.
TABLE B- 1 (continued) Author(s) and date
Title and source
Comments
Hawkins, A.D., 1981
Aquarium Systems. Academic Press New York, 452 pp.
While not exclusively seawater and with emphasis on recycling, has much of value, good chapters on materials, processing equipment and seawater wells.
Hettler, W.E, Jr., R.W. Lichtenheld and H.R. Gordy, 1971
Open seawater system with controlled temperature and salinity. Prog. Fish-Cult., 33:3-11.
50 gpm, coarse sand filtration, salinity control (6.5 gpm well water), temperature control (heating only) with three Teflon heat exchangers.
Huguenin, J.E., 1975
Development of a marine aquaculture research facility. Aquaculture, 5: 135-150.
600 gpm, rapid sand filters, heating with four carbon heat exchangers, lined ponds, raceways, indoor lab, multi-trophic level capabilities, Woods Hole Oceanographic Institution's Environmental Systems Laboratory.
Huguenin, J.E., 1976
An examination of problems and potentials for future large-scale, intensive seaweed culture systems. Aquaculture, 9:313-342.
Design study for 1000 metric ton (dry)/year seaweed production facility, two seawater systems (150 gpm and 5000 gpm), microscreening, raceways, harvest through drain, bioengineering tradeoffs, data voids.
Korn, S., 1975
Semiclosed seawater system with automatic salinity, temperature and turbidity control. NOAA Tech. Rep. NMFS SSRF-694, 5 pp.
100 gpm, rapid sand filters, UV, glass heat exchangers, National Marine Fishery Service's Tiburon Laboratory.
Lasker, R. and L. Vlymer, 1969
Experimental seawater aquarium, U.S. Bureau of Commercial Fisheries Circular 334, 14 pp.
600 gpm multi-institutional system at La Jolla, CA, sand filters, UV, temperature control (heating) using glass heat exchangers.
Lawson, T.M., 1995
Fundamentals of Aquacultural Engineering, Chapman and Hall, London, 355 pp. in 12 chapters.
Good hardware information for design and operations.
Lomask, S., 1972
Ecology, reliability guide piping design for oceanography lab. Heat. Piping Air Cond., (April): 90-93.
100 gpm, considerable engineering information on Fairleigh Dickinson University's Virgin Island Laboratory.
Magnuson, J.J., 1965
Tank facilities for tuna behavior studies. Prog. Fish-Cult., 27: 230-233.
300 gpm, six circular 24 ft diameter tanks 4 ft deep, details of spray aeration device, NMFS Lab, Hawaii.
Milne, EH., 1972
Fish and Shellfish Farming in Coastal Waters, Fishing News (Books) Ltd., London, 208 pp.
Olla, B.L., W. Warren and H. Katz, 1967
A large experimental aquarium system for marine pelagic fishes. Trans. Am. Fish. Soc., 96: 143-150.
Good reference dealing with engineering aspects, mostly large outdoor commercially oriented experimental systems, international coverage. 32,000 gal. aquarium tank described, photoperiod control, shallow seawater well of 75 gpm, at NMFS Sandy Hook Lab.
Pruder, G., C. Epifanio and R. Malouf, 1973
The design and construction of the Univ. of Del. Mariculture Laboratory, Sea Grant Report DEL-SG-7-73, Univ. of Del., 96 pp.
400 gpm, temperature control (heating/cooling) using glass heat exchangers.
Robson, D.R., 1972
Criteria for the site selection and system design of a seaweed culture laboratory. Proc. Bras d'Or Lake Aquaculture Conference, June 1975, College of Cape Briton Press, pp. 197-203.
180-300 gpm, coarse filtration, sedimentation tank, piping and water processing systems and experiences over time are described.
Simon, C.M., 1981
Design and operation of a large-scale commercial penaeid shrimp hatchery. J. World Maricult. Soc., 12: 322-334.
238 gpm, filtration, aeration, raceways, considerable system and operational details, comparisons to Japanese and Galveston hatchery approaches, excellent reference.
Soderburg, R.W., 1995
Flowing Water Fish Culture, Lewis Publishers, Boca Raton, FL, 147 pp.
Primarily concerned with freshwater applications. Contains considerable relevant practical design information.
Strobes, W.J., 1972
A small bioassay laboratory designed for experimental thermal (heating) effects evaluation. Circular No. 72-1, Fish. Research Inst., Univ. of Washington, 12 pp.
100+ gpm, coarse gravel filter, temperature control using glass heat exchangers.
Wedekind, C., R. Mtiller, A. Steffen and R. Eggler, 2001
A low-cost method of rearing multiple batches of fish. Aquaculture, 192: 31-37.
Description of system for rearing large number of separate lots of fish fry using standard 300 x 600 mm sterilization bag. This new method of fry rearing reduces space needs, infrastructure and material costs by a factor of 10 or more.
White, D.B., R.R. Stickney, D. Miller and L.H. Knight, 1973
Seawater system for the aquaculture of estuarine organisms at the Skidaway Institute of Oceanography, Savannah, Georgia, Tech. Rep. Ser. No. 73-1, 18 pp.
100+ gpm, two stage filtration (gravel and sand) to 5 microns, UV, temperature control (heating) using stainless steel heat exchangers.
Williamson, M.R. and D.M. Robichaux, 1990
Nursery engineering for nori aquaculture. Aquacult. Eng., 9: 429-445.
Requirements and design of nori (Porphyra) hatchery and nursery systems.
276
Appendix C
Reuse Seawater System Bibliography
Since most seawater systems have some internal water reconditioning and some flowthrough rate, the labels of 'reuse' and 'flow-through' are not mutually exclusive. While systems often tend to one side or the other, there is in fact a continuum of possibilities and much of the equipment and processes are shared. Appendix B contains literature that is slanted towards systems having modest internal water reconditioning and Appendix C towards systems with more extensive water recycling and reuse. Because of equipment commonality or mixed content, some particularly good references (Clark and Clark, 1964; Spotte, 1979; Hawkins, 1981; Lawson, 1992) are included in both appendices. A lot of the early experience with reuse systems has been with freshwater. This is due to frequently encountered terrestrial freshwater shortages or limitations. If one is located near the sea, acquiring good quality and quantity seawater has in the past rarely been a problem. Coastal pollution and coastal water and land use constraints in many cases are dramatically changing this situation. This is a fast moving technology and a great deal of progress has been made since the first edition of this book. However, the majority of this work is still in freshwater. While the principles, equipment and procedures are the same in freshwater and seawater, there are some differences in species and in biochemistry. Many review articles do not clearly differentiate between the two environments and some of these are included in the bibliography. Generally a little seawater, if it is acceptable to the culture organism, makes the system more stable and makes management a little easier. Selection of references has been loaded towards seawater applications and many otherwise good information sources have been excluded. Some of the selected references deal with low salinity brackish water applications and are, therefore, considered to be using seawater. There are a number of good books and proceedings that include many very good papers. If the books or proceedings are cited below, the individual contained papers of particular merit are not specifically identified. They will, however, be specifically referenced in the text of Chapter 15.
TABLE C- 1 Selected references on seawater reuse systems Author(s) and date
Title and source
Comments
Brune, D.E. and J.K. Wang, 1998
Recirculation in photosynthetic aquaculture systems. Aquacult. Mag., 24(3): 63-71.
Discusses recirculation in ponds with significant photosynthetic activity taking place in system.
Chin, E., 1959
An inexpensive recirculating sea water system. Prog. Fish-Cult., 21: 91-93.
Three culture tanks each of 60 gallons, activated charcoal filter.
Clark, J.R. and R.L. Clark, 1964
Seawater systems for experimental aquariums - - a collection of papers. Bureau of Sport Fisheries And Wildlife, Res. Rep. 63, 192 pp.
Excellent reference, 27 papers, 11 on recycle systems, mostly research and aquarium systems, has been published in book form, Crown Publishers Inc., New York.
Cook, D.W., 1972
A circulating seawater system for experimental studies with crabs. Prog. Fish-Cult., 34: 61-62.
Six stacked tanks each about 1/2 ft 3, aeration by downward flow of 1-1.5 gpm, clam shell, crushed oyster shell and glass wool filter, small submersible pump for recycling to top of stack, economics and maintenance.
Forster, J.R.M., 1974
Studies on nitrification in marine biological filters. Aquaculture, 4: 387-397.
Biochemistry and operational data on marine biofilters.
Goldizen, V.C., 1970
Management of closed-system marine aquariums. Helgolander Wiss. Meeresunters., 20: 637-641.
Discussion of biochemistry and system sizing criteria.
Hawkins, A.D. (Ed.), 1981
Aquarium Systems. Academic Press, New York, 452 pp.
Not exclusively reuse or marine systems, 15 chapters, 4 directly relevant, considerable biological and species information.
Hirayama, K., H. Mizuma and Y. Mizue, 1988
The accumulation of dissolved organic substances in closed recirculation culture systems. Aquacult. Eng., 7: 73-87.
Accumulation of high molecular weight persistent organics in both freshwater and seawater systems with time, discussion of biochemistry and effects on culture organisms.
Hope, S.J., 1982
Holding Atlantic menhaden in a closed system for environmental research. Prog. Fish-Cult., 44: 50-52.
Two identical artificial seawater systems, each with a 2500 gal tank, rapid sand filter, two bone charcoal filters, gravel biofilter and air aeration with pure oxygen backup.
King, J.M., 1973
Recirculating system culture methods for marine organisms. Sea Scope, 3(1): 1, 6-8. Aquarium Systems Inc., Eastlake, Ohio.
Good review of biochemistry, well cited with 47 references.
TABLE C- 1 (continued) Author(s) and date
Title and source
Comments
Lawson, T.M., 1995
Fundamentals of Aquacultural Engineering. Chapman and Hall, 355 pp. in 12 chapters.
Chapter 10, Recirculation Aquaculture Systems, pp. 192-247 particularly relevant. Good hardware information for design and operations.
Levine, G. and T.L. Meade, 1976
The Effects of Disease Treatment on Nitrification in Closed System Aquaculture. Proc. 7th Annu. Meet. World Aquaculture Soc., J.W. Avault (Ed.), pp. 483-493.
Effects of 12 common therapeutic drugs on nitrifying bacteria and a methodology for assessing the effects of others.
Libey, G.S. and M.B. Timmons (Eds.), 1996
Successes and Failures in Commercial Recirculation Aquaculture. Northeast Regional Aquacultural Engineering Services, Cornell University, NRAES-98, 639 pp.
56 papers in 7 topic areas in two volumes; good reference.
Libey, G.S. and M.B. Timmons (Eds.), 1998
Proc. 2nd Int. Conf. Recirculating Aquaculture. Virginia Polytechnic and State University, Roanoke, Virginia, 407
75 papers in 14 topic sections; good reference.
PP. Likey, M.E., R.L. Emigh and ER. Randle, 1970
A recirculating seawater aquarium system for inland laboratories. Mar. Biol., 7: 149-152.
Three culture tanks each of about 66 gallon, cartridge filters, thermal control (heating/cooling), underground water storage.
Manthe, D.E and R.F. Malone, 1987
Chemical addition for accelerated biological filter acclimation in closed blue crab shedding systems. Aquacult. Eng., 6: 227-236.
Early additions of ammonia and nitrite reduce start-up time of biofilter by as much as 10 days or 28%.
Manthe, D.E, R.F. Malone and S. Kumar, 1988
Submerged rock filter evaluation using an oxygen consumption criterion for closed recirculating systems. Aquacult. Eng., 7:97-111.
Technique for monitoring biofilter performance by measuring dissolved oxygen in and out of the biofilter.
Meade, T.L., 1974
The technology of closed system culture of salmonids. Univ. of RI Sea Grant Program, Marine Technology Report 30, 30 pp.
Includes growout at low salinities (about 12 ppt), describes vertical 5 ft diameter silos each 10 or 12 ft high holding 1000-1500 kg of salmon, four silos, biofilters and thermal control.
Mock, C.R., R.A. Neal and B.R. Salser, 1977
Design and preliminary evaluation of a closed system for shrimp culture. Proc. World Maric. Soc., 8: 335-369.
Continuation of 1973 experiments and scale-up, raceways to about 60,000 1 (17,000 gal), various components tested include biofilters, settling tanks, and particle filters.
Mock, C.R., R.A. Neal and B.R. Salser, 1973
A Closed Raceway for the Culture of Shrimp. Proc. 4th Annu. Workshop World Maric. Soc., pp. 247-259.
Experiments using 12,000 1 (3200 gal) circulating tanks, crushed oyster shell filters, algal growth, high aeration (air stripping) and air lift pumps.
New, M.B., J.R Scholl, J.C. McCarty and J.R Bennett, 1974
A recirculation system for experimental aquaria. Aquaculture, 3: 95-103.
36 10-gal tanks in compact self-contained unit needing 36 ft 2 of floor space, useable at any salinity, thermal control, intended for experimental uses.
Otte, G. and H. Rosenthal, 1979
Management of a closed brackish water system for high-density fish culture by biological and chemical water treatment. Aquaculture, 18:169-181.
Salinity at about 8 ppt, high loading, biofilters, ozone, using tilapia and eels.
Parisot, T.J., 1967
A closed recirculated seawater system. Prog. Fish-Cult., 29: 133-139.
Two 205-gal culture tanks, settling chamber, filter made of layers including crushed oyster shell, activated carbon, coarse sand, and gravel, thermal control.
Piedrahita, RH. and J. Verreyh (Eds.), 2000
Special Issue: Developments in Recirculation Aquaculture Systems Technology. Aquacult. Eng., 22: 1-164.
7 papers.
Reid, B. and C.R. Arnold, 1994
Use of ozone for water treatment in recirculating-water raceway systems. Prog. Fish-Cult., 56: 47-50.
Ozone had no noticeable effect on ammonia and nitrite, but appeared to improve water clarity.
Rosenthal, H., 1981
Recirculating systems in Western Europe. In: K. Tiews (Ed.), Aquaculture in Heated Effluents and Recirculation Systems. Heenemann Gmbh, Berlin, pp. 305-315.
Review of existing simple and complex systems, fresh and salt, principles, design and performance, well referenced.
Rosenthal, H., 1993
Recirculation systems in aquaculture. In: Techniques for Modern Aquaculture. J.K. Wang (Ed.).
Good review with emphasis on European developments and highly loaded systems. Well referenced.
Sandifer, EA., RB. Zielinski and W.E. Castro, 1974
A simple airlift-operated tank for the closed-system culture of decapod crustacean larvae and other small aquatic animals. Helgolander Wiss. Meeresunters., 26: 82-87.
150-gal culture tank with sloping bottom, gravel filter and air lift pumps. Also published as South Carolina Sea Grant Program, Tech. Reprint Series No. 1.
Schlieder, R.A., 1984
Environmentally controlled seawater systems for maintaining large marine finfish. Prog. Fish-Cult., 46: 285-288.
Artificial seawater, total system volume 20,000 1, biofilter and environmentally controlled room.
Serfling, S.A., J. Van Olst and R.E Ford, 1974
A recirculating culture system for larvae of the American lobster. Aquaculture, 3: 303-309.
Multiple Hughes culture tanks built into larger tank with a sand and gravel filter bottom and a charcoal filter and thermal control on the pumped recycle loop.
Sharp, J.H., A.C. Frake, G.B. Hillier and EA. Underhill, 1982
Modeling nutrient regeneration in the ocean with an aquarium system. Mar. Ecol. Prog. Ser., 8: 15-23.
Aquarium biochemistry as a model of oceanic processes, elemental budgets are presented, system used multiple trays, thermal control and sand filter.
Siddall, S.E., 1974
Studies of closed marine culture systems. Prog. Fish-Cult., 36: 8-15.
Review of biochemistry, biofilter performance and means of improving performance are presented.
t'~ "-...1
TABLE C- 1 (continued) Author(s) and date
Title and source
Comments
Spotte, S., 1979
Seawater Aquariums m The Captive Environment. John Wiley and Sons, New York, 413 pp.
Excellent overall reference on reuse systems, including both processes and equipment.
Spotte, S., 1992
Captive Seawater Fishes, Science and Technology. John Wiley and Sons, New York, 939 pp.
Ten chapters, each divided into a science and a technology part.
Timmons, M.B. and T.M. Losordo (Eds.), 1994
Aquaculture Water Reuse Systems: Engineering Design and Management. Developments in Aquaculture and Fisheries Science, Vol. 27. Elsevier Science Publishers, Amsterdam, 323 pp.
Eleven chapters, excellent and comprehensive coverage of topic. Good source for essential design information.
Timmons, M.B., W.D. Youngs, ER. Bowser and G. Rumsey, 1993
Design principles of water reuse systems for salmonids. Agric. Biol. Eng. Services Bull. #462, Cornell University, 30 pp.
Good discussion of design criteria specific to salmonids including feeding and waste generation guidelines.
Yang, W.T., R.T. Hanlon, E G. Lee and EE. Turk, 1989
Design and function of closed seawater systems for culturing of loliginid squids. Aquacult. Eng., 8: 47-65.
Several systems covering all life stages including reproduction. Well referenced.
281
Appendix D
Water Quality Bibliography
Water quality criteria for various types of culturing systems may be quite different from those used for environmental protection. This is primarily due to the fact that environmental protection criteria are based on protection of a wide spectrum of species and life stages. Most culture systems contain only a single species or several closely related species and usually for only a limited part of the life cycle. Generally the order of decreasing severity in water-quality criteria are larval cultures, brood stock, aquariums, commercial grow-out and lastly holding facilities. Economic considerations may also heavily influence the selection of water quality criteria. Water quality criteria are best documented for freshwater fish, such as salmon, trout, and channel catfish. Less information is available for marine species, especially crustaceans and molluscs. Table D-1 contains selected references on the effects of environmental parameters on marine organisms and water quality criteria. The available data is far from complete in this important subject area.
TABLE D- 1 Selected water quality references Author(s) and date
Title and source
Comments
Alderson, R., 1979
The effects of ammonia on the growth of juvenile Dover sole. Solea solea (L.) and Tubot, Scophthalmus maximus (L.), Aquaculture, 17:291-309.
The results for both species showed evidence for a threshold level for un-ionized ammonia below which little or no effect on growth was evident. Above the threshold levels, growth was depressed in a linear manner.
Brownell, C.L., 1980
Water quality requirements for first-feeding in marine fish larvae I. Ammonia, nitrite and nitrate. J. Exp. Mar. Ecol., 44: 269-283.
Effects of ammonia, nitrite and nitrate on first feeding of marine fish larvae.
Brownell, C.L., 1980
Water quality requirements for first-feeding in marine fish larvae II. pH. oxygen and carbon dioxide. J. Exp. Mar. Ecol., 44: 285-298.
Sensitivity of first-feeding larvae to low dissolved oxygen and high pH.
Hampson, B.L., 1977
Relationship between total ammonia and free ammonia in terrestrial and ocean waters. J. Cons. Int. Explor. Mer, 37: 117-122.
Equations for computation of un-ionized ammonia concentrations in marine waters.
Heinen, J.M., 1998
Light control for fish tanks. Prog. Fish-Cult., 60: 323-330.
A review of light controller that can gradual on-off to avoid light-shock reactions.
Kiese, M., 1974
Methemoglobinemia: A Comprehensive Treatise. CRC Press, Cleveland, Ohio
Review of causes, consequences and treatment of methemoglobinemia. May result from nitrite exposure.
Kinne, O. (Ed.), 1970
Marine Ecology, Vol. 1. Wiley Interscience, New York.
Vol. 1 presents a 1744 pages review of environmental factors on marine organisms and is divided into three parts.
Klimly, A.E, 1993
Highly directional swimming by scalloped hammerhead sharks, Sphyrna lewini, and subsurface irradiance, temperature, bathymetry, and geomagnetic field. Mar. Biol., 117: 1-22.
It is hypothesized that hammerhead sharks navigate using the geomagnetic field. Electrical and magnetic fields may be more important in shark holding systems.
Lewis, W.M. Jr. and D.E Morris, 1986
Toxicity of nitrate to fish: a review. Trans. Am. Fish. Soc., 115: 183-195.
Review of effects of environmental and chemical parameters on toxicity of nitrite to fish.
Malone, R.E, H.M. Perry and D.E Manthe, no date
The Evaluation of Water Quality Variations in Blue Crab Shedding Systems. Louisiana Sea Grant Program Center for Wetland Resources, LA State Univ., Baton Rouge, LA.
Review of water quality requirements for commercial crab shedding facilities.
Meade, J.W., 1985
Allowable ammonia for fish Culture. Prog. Fish-Cult., 47: 135-145.
Review of literature indicates that un-ionized ammonia alone is probably not the cause of gill hyperplasia. Maximum safe concentration of un-ionized ammonia is unknown.
Poxton, M.G. and S.B. Allouse, 1982
Water quality criteria for marine fisheries. Aquacult. Eng., 1: 153-191.
A review paper.
Ruyet, J.R-L., R. Galland, A. Le Roux and H. Chartois, 1997
Chronic ammonia toxicity in juvenile turbot maximus). Aquaculture, 154: 155-171.
Thurston, R.V., R.C. Russo, C.M. Fetterolf, T. Edsall and Y. Barber (Eds.), 1979
A Review of the EPA Red Book: Quality Criteria for Water. Am. Fish. Soc., Bethesda, Maryland.
A comprehensive review of the EPA Red Book.
U.S. Environmental Protection Agency, 1976
Quality Criteria for Water. EPA, Washington, DC.
Water quality criteria for freshwater and seawater commonly referred to as the 'Red Book'.
Wickins, J.F., 1981
Water quality requirements for intensive aquaculture. In: K. Tiews (Ed.), Aquaculture in Heated Effluents and Recirculation Systems, Vol. 1, Heeneman Verlagsgesellschaft, Berlin, pp. 17-37.
Review of water quality requirements for fish, crustaceans and molluscs.
(Scophthalmus
In small adapted turbot, no major physiological disturbances were observed up to 0.4-0.5 mg/1 un-ionized ammonia-N, while large turbot were more sensitive to ammonia. Reduced growth was due to a decrease in food intake, not to poorer food utilization.
284
Appendix E
Biofouling Bibliography Biofouling and its control is an important factor in the operation of many seawater-culturing systems, especially for flow-through systems. Biofouling can occur wherever there is flowing raw seawater, including in piping, heat exchangers and on screens. In spite of its importance, there is very little literature directly associated with culturing purposes. What does exist is mostly related to tray culturing of shellfish, where biofouling can be a serious problem. Many coastal seawater using industrial activities, other than culturing applications, have similar biofouling problems. However, they usually do not have the biological and toxicity constraints of culturing systems and as a result have more biofouling-control options. This bibliography includes the modest available directly associated literature. It also includes a few selected references on biofouling mechanisms and on control measures used in other marine applications. There has been considerable recent progress in understanding the biochemical nature of biofouling and in developing non-toxic antifouling coatings. All this information must be used with some caution in aquacultural applications. Biofouling is highly variable in quantity and composition depending on site, season and a number of other factors. In addition, control methods themselves may impose risks or constraints on the culture organisms.
TABLE E- 1 Literature on biofouling and control Author(s) and Date
Title and Source
Comments
Ansuini, EJ., J.E. Huguenin and K.L. Money, 1978
Fouling Resistant Screens for OTEC Plants. Proc. 5th Ocean Energy Conversion Conf., Miami Beach, Florida, Feb. 20-22, pp. 283-294.
Methods for making large seawater intake screens using copper-nickel alloy mesh and fiberglass structurals.
Arakawa, K.Y., 1973
Prevention and removal of fouling on cultured oysters. Marine Sea Grant Tech. Rep. 56, 38 pp.
Japanese biofouling control methods, translated into English by R.B. Gillmore.
Benson, EH., D.L. Brining and D.W. Perrin, 1973
Marine fouling and its prevention. Mar. Technol., (Jan.): 30-37.
Qualitative and quantitative aspects and important environmental factors, review of control methods.
Enright, C., D. Krailo, L. Staples, M. Smith, C. Vaughan, D. Ward, E Gaul and E. Borgese, 1983
Biological control of fouling algae in oyster aquaculture. J. Shellfish Res., 3:41-44.
Use of periwinkles in shellfish trays for biofouling control.
Graham, J.W., R.W. Moncreiff and EH. Benson, 1975
Heat treatment for the control of marine fouling at coastal electric generating stations. Ocean 75 Conf. Records, Mar. Technol. Soc., San Diego, CA, Sept. 22-25, pp. 926-930.
Temperature elevations and durations needed to kill mussels, barnacles and hydroids.
Hidu, H.C., C. Conary and R. Chapman, 1981
Suspended culture of oysters: fouling control. Aquaculture, 22: 189-192.
Small rock crabs entrapped in trays with yearling oysters resulted in nearly complete absence of fouling and siltation, tests indicate that they fed selectively on mussels.
Huguenin, J.E. and EJ. Ansuini, 1975
The advantages and limitations of using copper materials in marine aquaculture. Ocean 75 Conf. Records, Mar. Technol. Soc., San Diego, CA, Sept. 22-25, pp. 444-453.
Guidelines for use of copper and its alloys in culturing applications.
Huguenin, J.E. and EJ. Ansuini, 1981
Marine biofouling of synthetic and metallic screens. Ocean 81 Proc., Mar. Technol. Soc., Boston, MA, Sept. 16-18, pp. 545-549.
Relative fouling rates on assorted meshes and rigid screens, some antifouling paints also tested.
Huguenin, J.E. and S.S. Huguenin, 1982
Biofouling resistant shellfish trays. J. Shellfish Res., 2: 41-46.
International test program using copper-nickel expanded metal mesh with trays of about 10 different designs.
Michael, EC. and K.K. Chew, 1976
Growth of pacific oysters Crassostrea gigas and related fouling problems under tray culture in Seabeck Bay, Washington. Proc. Natl. Shellfish Assoc., 66: 34-41.
Effects of biofouling on shellfish growth. t'~
TABLE E- 1 (continued) Author(s) and Date
Title and Source
Comments
Milne, EH., 1972
Fish and Shellfish Farming in Coastal Waters. Fishing News (Books) Ltd., London, 208 pp.
Chapter 2 describes biofouling tests with many different types of netting and treatments, also in World Fishing, Dec. 1969, 3 pp.
Milne, EH., 1975
Fouling of marine cages. Fish Farm. Int., 2(3): 15-19 and 2(4): 18-21.
Fouling and its control in fish cage culture systems.
Mitchell, R. and E Benson, 1981
Control of marine biofouling in heat exchanger systems. Mar. Technol. Soc. J., 15:11-21.
Review of biofouling formation, environmental factors and control measures.
Nash, C.E., 1974
Residual chlorine retention and power plant fish farms. Prog. Fish-Cult., 36: 92-95.
Review of problems with chlorine residues in aquaculture.
Parker, N. and K. Strawn, 1976
Aufwuchs and sediment fouling rates in flow-through aquaria receiving heated effluents from Galveston Bay, Texas. Proc. World Maricult., 7: 543-559.
Biofouling rates on glass, plastic and asbestos slides and sedimentation in tanks, rates effected by temperature, salinity and species cultured.
Smith, EG.W., 1946
The effect of water currents upon the attachment and growth of barnacles. Biol. Bull., 90:51-70.
Useful information in the design of flowing seawater systems.
Wood, E.T.E, 1955
Effects of temperature and rate of flow on some marine fouling organisms. Aust. J. Sci., 18: 34-37.
Useful design information for flowing systems.
Wynne, K.J. and H. Guard (Eds.), 1997
Naval Research Reviews, Four/1997. Vol. 49, Office of Naval Research, U.S. Navy.
Special issue with eight articles on biofouling coatings technology.
Zietoun, I.H. and J.Z. Reynolds, 1978
Power plant chlorination. Environ. Sci. Technol., 12: 780-783.
Review of power plant practices, effectiveness and environmental considerations.
287
Appendix F
Materials Bibliography
Materials selection for culturing purposes is a difficult and complex subject. There are two sets of constraints in selecting materials. One is from interactions of the materials with seawater resulting in deterioration or structural failure. The second involves biological acceptability of the materials to the culture organisms. Lack of biological acceptability is usually in the form of toxicity of the materials. Table F-1 contains information on both aspects of materials selection, although most documentation on biological acceptability is concerned with small-scale laboratory equipment and containers. General information on the physical and chemical properties of marine materials is well documented. These data should be used with some caution in culturing applications, as biological acceptability is usually not considered. Cost and availability will further limit the use of some of the more desirable materials. Documentation on the biological acceptability of materials is limited and sometimes in apparent conflict. The contradictions are often due to differences in test procedures, target species or variations in materials' composition. The composition of plastics, rubbers and polymers can vary widely between manufacturers and between batches from the same manufacturer. Changes in composition often occur without any notice. Published data should only be used as a guide in materials' selection. Bioassay tests with pre-leached material samples based on actual culture conditions and material lots should be carried out. Bioassays are usually carried out with the earliest life stages of the culture species, because they are usually the most sensitive to toxicity and are the easiest to test. In systems with high flow-through rates, economic or availability considerations may result in the satisfactory use of materials generally not considered acceptable in marine culturing applications. In contrast, special care should be taken with materials for static or reuse systems, as they are the most sensitive to problems of biological acceptability and will tend to accumulate some toxic substances. As general good practice, all materials should be adequately leached in seawater before use to reduce the risks. Even acceptable materials may have high initial toxicity due to surface coatings or leachable solvents. A change in conditions may make an acceptable material highly toxic. As examples, removing surface coatings or dramatic increases in temperature has lead to mass mortalities. Mass mortalities or chronic effects due to materials are often not identifiable from other possible sources of stress on the culture organisms.
]ABLE F- 1 Literature on use of materials in marine culturing Author(s) and date
Title and source
Comments
Bell, M.C., 1973
Fisheries Handbook of Engineering Requirements and Biological Criteria. Fish. Eng. Res. Program, US Army Corps of Engineers, Portland, Oregon.
Toxicities of Elements and Compounds (Chap. 13), Metals (Chap. 14), Plastics (Chap. 15) and Pesticides and Herbicides (Chap. 16), fresh and salt water.
Bernhard, M.A., A. Zattera and E Filesi, 1966
Suitability of various substances for use in the culturing of marine organisms. Pubbl. Staz. Zool. Napoli, 35: 89-104.
In English, toxicity tests of 3 detergents and 50 materials (mostly plastics and rubbers) on marine phytoplankton and sea urchin larvae.
Bernhard, M. and A. Zattera, 1970
The importance of avoiding chemical contamination for a successful culture of marine organisms. Helgolander Wiss. Meeresunters., 20: 655-675.
Toxicity tests of 80 materials commonly used in or with culture seawater on marine phytoplankton; in English.
Bernhard, M., 1977
Chemical contamination of culture media: assessment, avoidance and control. In: O. Kinne (Ed.), Marine Ecology, Vol. III, Wiley and Sons, Chichester, pp. 1459-1499.
Comprehensive review of contamination from glass, rubber, polymers, and metals, discusses both positive and negative contamination.
Blankey, W.E, 1973
Toxic and inhibitory materials associated with culture, phycological methods. J. Stein (Ed.), Cambridge Univ. Press, Chap. 14, pp. 209-229.
Presents methods for testing the toxicity of materials on phytoplankton, problem areas, and acceptability guidelines.
Bogden, J.D., E. Zadzielski and A. Aviv, 1983
Extraction of copper and zinc from rubber and silicone Stoppers. Toxicol. Environ. Health, 11: 967-969.
Butyl rubber contains considerable copper and zinc which can be released by certain chemicals, neither copper or zinc was extracted from silicone stoppers.
Brown, B.E, R.C. Dehart, S.R. Galler and J.R. Saroyan, 1969
Materials and testing. In: J. Myers, C. Holms and R. McAllister (Eds.), Handbook of Ocean and Underwater Engineering, McGraw Hill Book Co., New York, Chap. 7, pp. 7.1-7.92.
Comprehensive guide to marine materials, including metals, plastics, coatings and other synthetic materials, does not consider biological acceptability for culturing purposes.
Carmignani, G.M. and J.E Bennett, 1976
Leaching of plastics used in closed aquaculture systems. Aquaculture, 7: 89-91.
Leaching of plasticizer from three common synthetic structural materials and a polyester resin as a function of time at 30~
Dantinne, R., 1963
Note sur construction des aquariums (mat6riaux). Bull. l'Inst. Oc6an (Monaco), Numero Special 1C: 33-38.
In French; discusses use of reinforced concrete for tank construction.
Dexter, S.C., 1979
Handbook of Oceanographic Engineering Materials. John Wiley and Sons, New York, 314 pp.
Very comprehensive source on marine materials, tabulated data, does not consider biological acceptability for culturing purposes.
Dyer, D.C. and D.E. Richardson, 1962
Materials of construction in algal culture. Appl. Microbiol., 10: 129-131.
Toxicity testing of about 20 plastics and metals on freshwater phytoplankton.
Hawkins, A.D. and R. Lloyd, 1981
Materials for the aquarium. In: A.D. Hawkins (Ed.), Aquarium Systems, Chap. 6, Academic Press, New York, pp. 171-196.
Aquarium practices relative to materials, discusses components, testing, and toxicity.
Huguenin, J.E. and EJ. Ansuini, 1975
The advantages and limitations of using copper materials in marine aquaculture, Ocean 75 Conf. Record, Sept., San Diego, CA, Mar. Technol. Soc., pp. 444-453.
Advantages and guidelines for proper use of copper alloys in culturing applications.
Int. Nickel Co., 1976, 2nd printing
Materials for Seawater and Brine Recycle Pumps. Int. Nickel Co. (INCO), 1 International Plaza, New York, 10004.
Discusses properties of different materials for various pump components, and corrosion and wear mechanisms.
Justice, C.S., S. Murray, ES. Dixon and J. Scherfig, 1972
Evaluation of materials for use in algal culture systems. Hydrobiologica, 40:215-221.
Toxicity testing of laboratory materials used in precise research (tubing, stoppers, flasks) on phytoplankton.
Miller, D. and W.L. West, 1970
Glass for underwater windows. In: W. Hagen (Ed.), Aquarium Design Criteria, Special edition, Drum and Croaker, pp. 92-101, Nat. Fish. Cent. and Aquarium, Dept. of Interior., Washington, DC.
Design procedures and considerations for large viewing windows in aquariums.
Milne, EH., 1972
Fish and Shellfish Farming in Coastal Waters. Fishing News (Books), Ltd., London, Chap. 5, Selection of Materials, pp. 34-43.
Mostly on selection of netting and floatation materials for outdoor use.
Muraoka, J.S., 1971
Materials for the sea - - deep ocean biodeterioration of materials. Ocean Ind., 6(2): 21-23, 6(3): 44-46.
150 material samples (woods, plastics, synthetics) exposed at depth of 600 ft for 6.3 months.
Price, M., EJ. Harrison, M. Landry, E Azam and K. Hall, 1986
Toxicity effects of latex and tygon tubing on marine phytoplankton, zooplankton and bacteria. Mar. Ecol. Prog. Ser., 34:41-49.
Latex tubing is highly toxic to phytoplankton, zooplankton and bacteria, tygon was less toxic (especially if washed) but should be used with caution in bacterial studies, silicone tubing had no effects.
Reinhart, EW., 1968
Recent developments in thermoplastic piping. J. Am. Water Works Assoc., 60:1404-1410. The effects on the growth of fucoid algae of some synthetic materials used in the construction of culture apparatus. Bot. Mar., 23: 433-434.
Properties and standards pertinent to common plastic pipes.
Ozone application in aquaculture. Aquacult. Mag. Jan/Feb, 25(1): 58-63.
Discusses materials suitability problems around ozone. Includes useful materials table.
Schonbeck, M.W. and T.A. Norton, 1980 Singh, S. and EW. Wheaton, 1999
Vinyl tubing and fiberglass inhibited growth of germlings of four species of algae, silicone rubber sealer increased growth, soaking for 24 h reduced material effects.
TABLE F- 1 (continued) Author(s) and date
Title and source
Comments
Todd, B., F.I. Mar and EA. Lovett, no date
Selecting materials for seawater systems. Mar. Eng. Practice, 1(10) 56 pp., Inst. of Mar. Eng., Published by Marine Media Manag. Ltd., 76 Mark Lane, London.
Non-ferrous metals, corrosion mechanisms, material properties, considerations and selection for various components and standards in UK, US, Germany and Japan. Does not consider biological factors.
Tuthill, A.H. and C.M. Schillmoller, 1971
Guidelines for the selection of marine materials, presented Mar. Technol. Soc. Conf., 1965, 2nd ed. (1971) available from INCO, 1 International Plaza, New York, 10004, 38
Metals, corrosion mechanisms, material properties, considerations and selection guide for various components. Does not consider biological factors.
PP. West, W.W. and RA. Butler, 1970
Mechanical testing and bioassay of adhesive sealants for use in an aquatic environment, In: W. Hagen (Ed.), Aquarium Design Criteria. Drum and Croaker, pp. 102-103, Nat. Fish. Cent. and Aquarium, Washington, DC.
Experiences and properties of various tank sealants.
291
Append& G
Suspended Solids Removal Bibliography
Suspended solids removal is a common process in many seawater systems. This includes removal of solids from influent water and/or removal of uneaten feed or fecal matter within the system. Information on the many options used in culturing is usually buried in publications concerned with the larger total system. Much of this information is included in Appendices B and C, with solids removal, filtration or related equipment mentioned in the title or annotations. Three common processes for removal of solids in culturing applications are sedimentation, screening, and filtration. Sedimentation is the settling of solids through time in a low-flow velocity condition. The distinction between screening and filtering is not always clear, although screening usually refers to the use of meshes and the removal of larger-size particles while filtering implies the use of granular mediums. In spite of the importance and commonality of solids removal processes, there is little directly applicable data dealing with marine culturing applications. Table G-1 includes references from a number of areas that might prove useful as a starting point for further investigations.
Selected references on suspended solids removal processes Author(s) and date
Title and source
Comments
Baylis, J.R., O. Gullans Jr. and H.E. Hudson, 1971
Filtration. In: Water Quality and Treatment, 3rd ed., American Water Works Association, McGraw-Hill, New York, pp. 243-294.
Rapid sand filters for treatment of drinking water, emphasis on operational problems.
Bauman, E.R., 1971
Diatomite filtration of potable water. In: Water Quality and Treatment, 3rd ed., Am. Water Works Assoc., McGraw-Hill, New York, pp. 280-294.
Discussion of theory and use of diatomite filters.
Bergheim, A., S. Sanni, G. Indrevik and E Holland, 1993
Sludge removal from salmonid tank effluent using rotating microsieves. Aquacult. Eng., 12: 97-109.
With mesh sizes of 60-350 ~m, suspended solids removal was 63-68. Backflushing flow reduction methods and mechanical dewatering system described.
Boersen, G. and H. Wester 1986
Waste solids control in hatchery raceways. Prog. Fish-Cult., 48: 151-154.
Velocities in range 0.7-1.0 ft/s are needed to prevent settling of fecal matter, select slow areas of raceways allow for settling, solids removed by bottom drain or vacuum pump.
Boyd, C.E., 1979
Aluminum sulfate (alum) for precipitating clay turbidity from fish ponds. Trans. Am. Fish. Soc., 108:307-313.
Alum was better than ferric sulfate, hydrated lime or gypsum in removing suspended clay, a simple test was developed to determine the amount of alum needed to floc clay particles in pond water.
Chen, S., D. Stechey and R.E Malone, 1994
Chapter 3, Suspended solids control in recirculating systems. In: M.B. Timmons and G.S. Libey (Eds.), Aquaculture Water Reuse Systems: Engineering and Management. Elsevier Science Publishers, Amsterdam, pp. 61-100.
Good review of waste characteristics, removal mechanisms and eight different removal technologies. Includes six pages of references.
Cheung, E, K. Krauth and M. Roth, 1980
Investigation to replace the conventional sedimentation tank by a microstrainer in the rotating disk system. Water Res., 14: 67-75.
At surface loading of 10-15 m/h, a microstrainer can remove 90 of the suspended solids and produce an effluent of less than 10 mg/1 of suspended solids.
Culp, R.L., G.M. Wesner and G.L. Culp, 1978
Handbook of Advanced Wastewater Treatment, 2nd ed., Van Nostrand Reinhold, New York, pp. 89-165.
Practical treatment of wastewater filtration based on full-scale units.
Diaper, E.W.J., 1969
Tertiary treatment by microstraining. Water & Sewage Works, 115: 202-208.
Review of design and operations of open channel microscreens in wastewater treatment.
Hansen, S.E and G.L. Culp, 1967
Applying shallow depth sedimentation theory. J. Am. Water Works Assoc., 59:1134-1148.
Tube length, diameter, flow rate, nature and quantity of added chemicals, effect performance of tube settlers, filter rates range 3-5 gpm/ft 2.
Henderson, J.E and N.R. Bromage, 1988
Optimizing the removal of suspended solids from aquaculture effluents in settlement lakes. Aquacult. Eng., 7: 167-181.
To minimize turbulence the fluid velocity in the settling ponds (16 studied) should be less than 4 mm/min. Difficult to achieve solids concentrations less than 6 mg/1.
Hirayama, K., 1974
Water control by filtration in closed culture systems. Aquaculture, 4: 369-397.
Sand filter induced chemical changes in new and old culture water, system carrying capacity determined by using oxygen consumption during filtration as an index.
Illingworth, J., EM. Patrick, E Redfearn and D.M. Rodley, 1979
Construction, operation and performance of a modified diatomaceous earth filter for shellfish hatcheries. Aquaculture, 17: 181-187.
Modified commercial filter used in hatchery consistently removed up to 96 of suspended solids, particles down to 2.3 micron and reduced heterotrophic bacteria to 1-5 x
Lewicke, C.K., 1973
Microstraining water and waste water. Environ. Sci. Technol., 7:104-105.
Use and costs of open channel microscreen use in waste water filtering.
Metcalf and Eddy, Inc., 1991
Wastewater Engineering: Treatment, Disposal, Reuse, 3rd ed., McGraw-Hill, New York, pp. 248-276.
Excellent treatment of the design and operation of a broad spectrum of granular-medium filters.
Mudrak, V.A., 1981
Guidelines for economical commercial fish hatchery wastewater treatment systems. In: L. Allen and E. Kinney (Eds.), Proc. Bio-Engineering Symposium for Fish Culture, Am. Fish. Soc., Bethesda, Maryland, pp. 174-182.
Removal of suspended solids in three clarifiers averaged 85 during daily operations and 88 during raceway cleanout, system consisting of rectangular clarifier (30 min retention time) followed by earthen lagoon (4 h retention) was recommended.
Nickolaus, N., 1979
Cartridge filtration. In: E Schweitzer (Ed.), Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill, New York, pp. 4-85 to 4-93.
Cartridge filters can remove submicron to 40 Ixm particles but are limited to fluids with less than 0.01% solids, equipment and characteristics described.
Piedrahita, R.H., W.H. Zachritz, K. Fitzsimmons and C. Brockway, 1998
Evaluation and improvement of solids removal systems for aquaculture. In: G.S. Libey and M.B. Timmons (Eds.), Successes and Failures in Commercial Recirculating Aquaculture, Vol. 1, NRAES-98, pp. 141-150.
Review of settling basins, microscreens, granular filters and constructed wetlands for solids removal. Well referenced.
Rich, L.G., 1961
Chapter 6, Flow-through beds of solids. Unit Operations of Sanitary Engineering, John Wiley and Sons, New York, pp. 136-158.
Theory and practice of particle bed filters, applicable to sand, gravel and charcoal filters.
Scott, K.R. and L. Allard, 1983
High flow rate water recirculation system incorporating a hydrocyclone prefilter for rearing fish. Prog. Fish-Cult., 45: 148-153.
Hydrocyclone prefilters were highly effective in removing particulates prior to use of biofilter, flow of 150 1/min, considerable test data on cyclones.
102/ml.
TABLE G- 1 (continued) Author(s) and date
Title and source
Comments
Spotte, S., 1979
Chapter 8, Processing seawater supplies. Seawater Aquariums, John Wiley and Sons, New York, pp. 165-207.
Sections 8.2 (granular media filters) and 8.3 (diatomaceous earth filters), practical information based on experiences with recycling marine aquariums.
Stumm, W., 1977
Chemical interaction in particle separation. Environ. Sci. Technol., 11:1066-1070.
Good review of filtration methods (0.005-10,000 txm) and factors which effect performance, guide to best approaches based on particle size and conditions.
Weinschrott, B. and G. Tchobanoglous, 1986
Evaluation of the Parkson Dynasand Filters for Wastewater Reclamation in California. Dept. of Civil Eng., University of California, Davis, 128 pp.
With influent turbidity of less than 7-10 NTU, the dual-media deep-bed filters all produced an effluent with an average of 2 NTU or less.
Wrotnowski, A.C., 1979
Felt strainer bags. In: E Schweitzer (Ed.), Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill, New York, pp. 4-95 to 4-111.
Felt media can effectively remove particles in the 20-200 ~m size range, equipment and characteristics described.
295
Appendix H
Temperature Control Bibliography
Controlling culture-water temperature is a very common process in many seawater systems. This is particularly true of reuse systems, because of their greatly reduced inflow rates. They can more readily retain the heat (or lack of) and thereby greatly reduce the energy costs. Both heating and cooling systems are found, although heating requirements are more common. Most of the available information on such systems are contained in publications which describe the broader systems and not just the heating or cooling aspects. Many of these references can be found in Appendix B (Flow-Through Systems) and Appendix C (Reuse Systems). Many of the titles or 'comments' in regards to these references specifically mention temperature control in the context of these applications. Culture-water temperature is a parameter that is often automatically monitored and controlled. Also, see discussion and general references in this subject area (Section 14.3). These citations will not be repeated here. Instead, selected literature that specifically addresses temperature control or was otherwise not selected for the other appendices will be presented. Since salinity has little effect on the heating and cooling of water, freshwater citations are also included. Some freshwater equipment may not be useable in seawater without modifications, due to corrosion or contamination problems.
IABLE H- 1 t',3
Selected references on temperature control of culture water Author(s) and date
Title and source
Comments
Abell, ER., L.B. Richardson and D.T. Burton, 1977
Electric controller for producing cyclic temperatures in aquatic studies. Prog. Fish-Cult., 39: 139-141.
Controller to produce sine wave cyclic temperatures, 1 or 2 cycles/day, parts list, electrical schematic.
Alfa Laval
www.hvac.alfalaval.com/selection_tools/default.htm
The web-based program WebcAL TM is very useful for design and sizing of plate and frame heat exchangers.
Barnabe, G., 1974
Some heating devices for seawater aquaculture. Aquaculture, 4: 305-306.
Description of plastic-coated copper tubing and shock-resistant glass heaters for use in marine systems.
Botsford, L.W., H.E. Rauch and R.A. Shleser, 1974
Optimal temperature control of a lobster plant. IEEE Trans. Automatic Control, AC- 19:541-543.
Optimal control theory is used to determine the best and most economical temperature history.
Braren, R. and J.W. Zaradnik, 1974
The design and evaluation of an inexpensive seawater heater. Publ. No. 007-1-74, Univ. of Massachusetts, Aqua. Eng. Lab, Dept. Mech. Eng., Amherst, Massachusetts.
CPVC heat-X designed to heat 400 1/h from 0 to 21~ heat from conventional hot water heater.
Chavin, W., 1973
A reliable water temperature control apparatus for open freshwater systems. Prog. Fish-Cult., 35" 202-204.
System mixes hot and cold water supplies by use of temperature sensors, controller and automatic valves run by compressed air, system failure results in short to drain.
DeFoe, D.L., 1977
Temperature safety device for aquatic laboratory systems. Prog. Fish-Cult., 39:131.
Use of modified small aquarium electrical heaters as high and low temperature sensors; exceeding limits breaks circuit, closing valve and stopping flow.
Fain, G., 1975
The design of a marine environmental simulation system. Ocean 75 Conf. Record, Mar. Technol. Soc., pp. 931-939.
Theoretical discussion of control problems inherent with simultaneously controlling temperature, salinity, dissolved oxygen and turbidity.
Froese, R., 1998
Insulating properties of Styrofoam boxes used for transporting live fish. Aquaculture, 159: 283-292.
A better designed, cube-shaped Styrofoam box is suggested as the most promising and cost-effective measure to reduce mortalities resulting from heat loss during transport.
Fuss, J.T., 1983
Evaluation of a heat pump for an aquacultural application. Prog. Fish-Cult., 45" 121-123.
Description of liquid-liquid heat pump used to recover heat from the discharge, operational cost was 39% less than an oil-fired boiler.
Fuss, J.T., 1984
Feasibility of saltwater gradient ponds as a heat supply for hatchery rearing water. Aquacult. Eng., 3: 31-37.
Salt gradient solar collector ponds may be economical as a heat source for hatchery rearing water.
Hettler, W.F., 1974
A filter and chiller for an open seawater system. Prog. Fish-Cult., 36: 234-238.
Description of filter and Teflon heat exchanger for use with seawater.
Huguenin, J.E., 1976
Heat exchangers for use in the culturing of marine organisms. Chesapeake Sci., 17: 61-64.
Review of heat-X units and considerations, includes both industrially available and home-made types.
Jenson, N.J., 1980
System of individually temperature-regulated saltwater aquaria. Prog. Fish-Cult., 42: 166-168.
Refrigerant is passed to individual units by sensor-activated solenoid valves, 6 units, polyethylene heat-X, parts list.
Lawson, T.B., C.M. Drapcho, S. McNamara, H.J. Braud and W.R. Wolters, 1989
A heat exchanger system for spawning red drum. Aquacult. Eng., 8: 177-191.
Description and operational information on a 8.5 kW heat pump for heat transfer between the earth and the rearing units.
Lemke, A.E. and W.E Dawson, 1979
Temperature-monitoring and safety control device. Prog. Fish-Cult., 41:165-166.
Description of solid state temperature monitor with variable set point, variable variation around set point and alarm when limits are exceeded.
Regier, H.A. and W.A. Swallow, 1968
An aquarium temperature control system for field stations. Prog. Fish-Cult., 30: 43-46.
Description of system with epoxy-coated heating and cooling coils and programmable temperature controller.
Stickney, R.R., 1985
An efficient heating method for recirculating water systems. Prog. Fish-Cult., 47: 71-73.
Use of heat pump to deliver maximum of 53,000 BTU/h, reuse flow of 95 1/min, heat pump had higher initial cost but much lower operating cost than next best method (electric).
Syrett, R.E and W.F. Dawson, 1972
An inexpensive electronic relay for precise water-temperature control. Prog. Fish-Cult., 34: 241-242.
Manual selection of normally open or closed operations, 6 mA dc signal allows use of sensitive thermoregulators, can control equipment rated to 10 A, schematic and parts list.
Syrett, R.E and W.E Dawson, 1975
An inexpensive solid-state temperature controller. Prog. Fish-Cult., 37: 171-172.
Thermistor (sensitive to 0.01~ activated 12 V dc controller, operable 0-50~ activates on either a high or low temperature, schematic and parts list.
Wurtsbaugh, W.A. and G.E. Davis, 1976
Laboratory apparatus for providing diel temperature regimes for aquatic animals. Prog. Fish-Cult., 38: 198-199.
Water temperature variations provided by mixing water from different sources operated by a timer and automatic valves.
t'~
298
Appendix I
Aeration and Degassing Bibliography
The removal or addition of dissolved gases is commonly required in aquatic-culture systems. This may include oxygen, nitrogen, argon, carbon dioxide, or hydrogen sulfide. The commonest types of aerators are diffused aerators and airlift pumps. These units are easy to install and operate, but have relatively poor gas-transfer characteristics. In many applications, these units are used primarily to provide gentle mixing for algal or larval cultures. Due to the needs for high dissolved oxygen concentrations to support the respiration of aquatic animals, the transfer efficiencies of aerators in aquacultural applications is generally low. The required concentrations of dissolved oxygen are often at or near the solubility limit in water under the existing conditions. Some of the most efficient submerged aerators, due to the hydrostatic pressure of depth, can produce lethal concentrations of gas supersaturation with nitrogen from the air. Considerably more information is available on the use and design of aerators for freshwater applications than for seawater applications. Fortunately, much of this freshwater information is directly applicable to marine conditions, although corrosion problems may limit the use of some floating and submerged aerators. Aerator references applicable to marine applications are also included in Table I-1. These citations are divided into design and four categories of aerators by type. The following conversions may be helpful in sizing aeration systems. lb oxygen/hp per hour x 1.664
=
kg oxygen/kW per hour
lb oxygen per foot of paddle wheel per hour x 1.491
--
kg/m per hour
Information on gas supersaturation and degassing is contained in Table I-2. These citations are divided into production, measurement of supersaturation and design of degassing systems. Since some equipment is used for both aerating and degassing, both Tables I-1 and I-2 should be consulted.
TABLE I- 1 Selected references on aeration by category Author(s) and date
Title and source
Comments
Brown, L.C. and R. Baillod, 1982
Modeling and interpreting oxygen transfer data. J. Environ. Eng. Div., Am. Soc. Civil Eng., 108(EE): 607-628.
Recommendations for modeling, parameter estimation, and experimental design for unsteady-state clean water aeration.
Colt, J.E. and G. Tchobanoglous, 1981
Design of aeration systems for aquaculture. In: L.J. Allen and E. Kinney (Eds.), Proceedings, Bio-Engineering Symposium for Fish Culture, Am. Fish. Soc., Bethesda, MD, pp. 138-148.
Comprehensive information on design of aeration systems based on oxygen requirements of animals, oxygen consumption and oxygen transfer kinetics under culture conditions, hydraulic mixing characteristics, noise production, prevention of gas supersaturation and costs.
Speece, R.E., 1981
Management of dissolved oxygen and nitrogen in fish hatchery waters. In: L. Allen and E. Kinney (Eds.), Proceedings, Bio-Engineering Symposium for Fish Culture, Am. Fish. Soc., Bethesda, MD, pp. 53-63.
General information on use of gravity and pure oxygen aerators.
Stenstrom, M.K. and R.G. Gilbert, 1981
Effects of Alpha, Beta and Theta factors upon the design and specification of aeration systems. Water Res., 15: 643-654.
A review of measurement of Alpha, Beta and Theta factors in aeration testing and design.
Chesness, J.L. and J.L. Stephens, 1971
A model study of gravity flow aerators for catfish raceway systems. Trans. Am. Soc. Agric. Eng., 14: 1167-1169, 1174.
Average transfer efficiency for 7 types of cascade aerators in the range of 2.66-3.74 lb oxygen/hp per hour. The lattice aerator was highest but corrugated inclined plane (with holes) was recommended due to easier construction and operation.
Fridirici, C.T. and L.T. Beck, 1985
A self-supporting, inexpensive gravity aerator. Prog. Fish-Cult., 47: 248-250.
Made from 4 inch (10.2 cm) Schedule 40 PVC pipe cut length-wise and cross-slotted, data at flow of 1227 lpm and 3 vertical drops from 20.3 to 58.4 cm.
Hackney, G. and J.E. Colt, 1982
The performance and design of a packed column aerator system for aquaculture. Aquacult. Eng., 1: 275-295.
Oxygen transfer efficiencies ranged from 3.3 to 6.6 lb oxygen/hp per hour. A mass transfer model was developed for design purposes.
Design of aeration systems
Gravity aerators
~D
I/-~DLE, 1-1
tconunuea)
Author(s) and date
Title and source
Comments
Moore, J.M. and C.E. Boyd, 1984
Comparison of devices for aerating inflow of pipes. Aquaculture, 38: 89-96.
Comparison of 11 devices placed at pipe discharge for effectiveness in increasing dissolved oxygen and decreasing dissolved carbon dioxide. Dissolved oxygen above 6 mg/1 resulted from 'T' and 'L' aspirators and with a half open gate valve. None were effective at reducing dissolved carbon dioxide.
Strasburg, D.W., 1964
An aeration device for salt well water. In: J.R. Clark and R.L. Clark (Eds.), Seawater Systems for Experimental Aquariums, T.F.H. Publications, Jersey City, NJ, pp. 161-167.
Series of horizontal plates, with final design using 16 trays at 2 inch intervals and a loading of 2 gpm/ft 2.
Tebbutt, T.H., 1972
Some Studies on Reaeration in Cascades. Water Res., 6: 297-304.
Cascade weirs are more efficient than inclined planes or free fall weirs for the same drop. Design equations for cascade weirs are presented.
Gowan, R., 1986
Use of supplemental oxygen to rear chinook in seawater. Northwest Fish Culture Conference, Eugene, OR, Dec. 2-4, 1986, 6-41-6-46.
Injection of pure oxygen into pressurized water (80 psi) to increase smolt carrying capacity of holding facility.
Severson, R.E, J.L. Stark and L.M. Poole, 1986
Use of oxygen to commercially rear coho salmon. Northwest Fish Culture Conference, Eugene, OR, Dec. 2-4, 1986, pp. 6-25-6-40.
Series of 3 pressurized (30 psig) packed columns using oxygen with efficiency of about 73%. Use of pure oxygen doubles possible dissolved oxygen concentration and compared to pumping in more water is 2.5-5.5 times cheaper to operate.
Speece, R.E., N. Nirmalakhandan and Y. Lee, 1988
Design for high purity oxygen absorption and nitrogen stripping for fish culture. Aquacult. Eng., 7:201-210.
Design data and economics for use of oxygen counter-flow packed column.
Speece, R.E., D. Gallagher, C. Krick and R. Thomson, 1980
Pilot performance of deep U-tubes. Prog. Water Technol., 13: 395-407.
Operating characteristics of pure oxygen U-tubes as function of depth, gas/liquid ratio and velocity.
Speece, R.E., M. Madrid and K. Needham, 1971
Downflow bubble contact aeration. J. Sanit. Eng. Div., Am. Soc. Civil Eng., 97(SA): 433-441.
Capable of absorption efficiencies in the range of 80-90% when pure oxygen is injected at 0.5% of water flow rate.
Watten, B.J., J. Colt and C.E. Boyd, 1991
Modeling the effects of dissolved nitrogen and carbon dioxide on the performance of pure oxygen absorption systems. American Fisheries Symposium No. 10, Bethesda, MD, pp. 421-426.
A multi-component gas transfer model was used to evaluate the impact of carbon dioxide and nitrogen on oxygen transfer. Negligible carbon dioxide was removed but had no effect on oxygen transfer; desorption of nitrogen significantly reduced the oxygen transfer efficiency.
Watten, B.J. and L.T. Beck, 1985
Modeling gas transfer in a U-tube oxygen absorption system: effects of off-gas recycling. Aquacult. Eng. 4: 271-297.
Recycling of unused oxygen can result in major savings in variable and total costs with only minor increase in capital costs. Benefits increase with low oxygen flow, a minor increase in deeper depth, and low influent oxygen concentrations.
Appelbaum, S., A. Prilutsky and V. B irkan, 1999
An emergency aeration system for use in aquaculture. Aquacult. Eng., 20: 17-20.
Description of an automatic emergency device that introduces compressed air into rearing tanks when the air pressure fails.
Boyd, C.E. and D.J. Martinson, 1984
Evaluation of propeller-aspirator-pump aerators. Aquaculture, 36: 283-292.
Oxygen transfer rate ranged from 2.84 to 3.14 lb oxygen/hp per hour and was better than spray type surface aerators (2.20-2.32 lb oxygen/hp per hour) and diffuser units (1.78 lb/hp per hour) and with better mixing characteristics.
Colt, J.E. and H. Westers, 1982
Production of gas supersaturation by aeration. Trans. Am. Fish. Soc., 111" 342-360.
Supersaturation produced by submerged aerators. Since oxygen and nitrogen have similar mass transfer, units with highest oxygen transfer efficiency also produce the highest total dissolved gas concentrations.
Mavinic, D.S. and J.K. Bewtra, 1976
Efficiency of Diffused aeration in wastewater treatment. J. Water Pollut. Control Fed., 48: 2273-2283.
Oxygen transfer efficiency of a coarse bubble diffuser varied from 1 to 4% over depths of 1.75-8.75 ft. Transfer efficiency was constant at about 4.7 lb oxygen/kW per hour.
Mitchell, R.E. and A.M. Kirby, Jr., 1976
Performance characteristics of pond aeration devices. Proc. 7th Annu. Meet. World Maricult. Soc., 7" 561-581.
Evaluation of various devices in terms of transfer efficiency, operational problems and total cost.
Murray, K.R., M.G. Poxton, B.T. Linfoot and D.W. Watret, 1981
The design and performance of low pressure air lift pumps in a closed marine recirculation system. In: K. Tiews (Ed.), Aquaculture in Heated Effluents and Recirculation Systems, Heeneman Verlagsgesellschaft, Berlin, pp. 413--428.
Operating characteristics of small diameter airlift pumps.
Parker, N.C. and M.A. Suttle, 1987
Design of airlift pumps for water circulation and aeration in aquaculture. Aquacult. Eng., 6: 97-110.
Pumping characteristics of low-lift airlift pumps as function of lift, diffuser depth and air flow. No data on oxygen transfer or efficiency provided.
Scott, K.R., 1972
Comparison of the efficiency of various aeration devices for oxygenation of water in aquaria. J. Fish. Res. Board Can., 29: 1641-1643.
Efficiencies of five combinations of venturis, air stones and sprays were measured. A ventufi discharging through nozzle near bottom of tank had highest efficiency, although gas supersaturation could be a problem in a deep tank.
Submerged aerators
ta~ o
TABLE I- 1 (continued) Author(s) and date
Title and source
Comments
Sorgeloss, E, G. Persoone, E De Winter, E. Bossuyt and N. De Pauw, 1977
Air-water pumps as cheap and convenient tools for high density culturing of microscopic algae. Proc. 8th Annu. Meet. World Maricult. Soc., 8: 173-183.
Air-lift pumps provided superior mixing in algal culture systems.
Speece, R.E. and R. Orosco, 1970
Design of U-tube aeration systems. J. Sanit. Eng. Div., Am. Soc. Civil Eng., 96(SA): 715-725.
Regression equations for effluent dissolved oxygen concentration as function of U-tube depth, influent DO and air-water ratio.
Speece, R.E., 1969
U-tube oxygenation for economical saturation of fish hatchery water. Trans. Am. Fish. Soc., 89: 789-795.
Unit can economically saturate culture water with dissolved oxygen. Nitrogen supersaturation can be avoided by use of vacuum degassing unit or control of air/water ratio and U-tube depth.
Ahmad, T. and C. Boyd, 1988
Design and performance of paddle wheel aerators. Aquacult. Eng., 7: 39-62.
Paddles triangular in cross-section were more efficient than other paddle shapes. Oxygen transfer increased with paddle depth and speed but efficiency dropped. Best efficiency (4.87 lb oxygen/hp per hour) with 91 cm paddles, 12.5 cm depth and speed of 77 rpm.
Boyd, C.E., T. Ahmad and Z. La-fa, 1988
Evaluation of plastic pipe paddle wheel aerators. Aquacult. Eng., 7:63-72
Made of PVC pipe with efficiencies of 3.3-4.3 lb oxygen/hp per hour but low transfer rate (0.77-1.24 lb oxygen/h per foot length of paddle wheel). Non-corrosive materials may be of advantage in marine applications.
Busch, C.D., C.A. Flood, Jr. and R. Allison, 1978
Multiple paddlewheels influence on fish pond temperature and aeration. Trans. Am. Soc. Agric. Eng., 21: 1222-1224.
Six paddle wheels driven by 1/4 hp motors aerated 1.4 acre pond. One 2-h daytime operation removed temperature stratification and nighttime runs of more than 3 h eliminated the dissolved oxygen gradient.
Surface aerators
TABLE 1-2 Selected references on degassing by category Author(s) and date
Title and source
Comments
Production of gas supersaturation Colt, J. and H. Westers, 1982
Dehadrai, EV., 1966
Engelman, R.W., L.L. Collier and J.B. Marliave, 1984 Hughes, J.T., 1968 Kils, U., 1976/1977
Kraul, S., 1983 Parker, N.C., K. Strawn and T. Kaehler, 1976
Stickney, A.P., 1968
Renfro, W.C., 1963
Production of gas supersaturation by aeration. Trans. Am. Fish. Soc., 111" 342-360. Mechanisms of gaseous exophthalmia in the Atlantic cod. J. Fish. Res. Board Can., 23:909-914. Unilateral exophthalmos in Sebastes spp: histopathologic lesions. J. Fish Dis., 7: 467-476. Grow your own lobsters commercially. Ocean Ind., 3: 46-49. The salinity effect on aeration mariculture. Meeresforschung. 25: 755-759.
Results and hypothesis for the propagation of the grey mullet, Mugil cephalus L. Aquaculture, 30: 273-284. Hydrological parameters and gas bubble disease in a mariculture pond and flow-through aquarium receiving heated effluent. Proc. 30th SE Assoc. Fish Game Comm., pp. 179-191. Supersaturation of atmospheric gases in the coastal waters of the Gulf of Maine. Fish Bull., 67:117-123. Gas-bubble mortalities of fish in Galveston Bay, Texas. Trans. Am. Fish. Soc., 92: 320-322.
Efficient submerged aerators can create lethal levels of supersaturation as can airlift pumps and diffusers under some operating conditions. Cod may develop this condition in saturated water due to malfunctioning of the choroid gland-pseudobranch complex. Condition occurs spontaneously in five species of rock-fish held in aquaria. Bubble formation in choroidal rete mirabile was one of several mechanisms discussed. Air leaks on suction side of pump resulted in high level of supersaturation and mass mortality. Dissolution of air appears to be about 10 times faster in seawater than in freshwater. Small air leaks in marine systems maybe much more dangerous and difficult to detect as no bubbles may be present in the discharge water. Photosynthetic production of oxygen in 'greenwater' culture may result in gas-bubble disease in larval mullet. Gas-bubble disease developed in marine fish and shrimp held in heated effluents. Problem occurred primarily during winter. Degassing will be needed to use power plant effluents in aquaculture. Solar heating plus photosynthesis at times produced dissolved gas pressures sufficient to cause gas-bubble trauma in fish held in shallow aquariums. Intense photosynthesis during periods of light wind may result in supersaturation high enough to kill adult fish in shallow water.
TABLE 1-2 (continued) Author(s) and date
Title and source
Comments
Bouck, G.R., 1982
Gasometer: an inexpensive device for continuous monitoring of dissolved gases and supersaturation. Trans. Am. Fish. Soc., 111:505-516.
Description and operation of membrane-diffusion device. Ideal for fixed site monitoring of flows as it can be installed in pipes.
Colt, J., 1984
Computation of Dissolved Gas Concentrations in Water as Functions of Temperature, Salinity and Pressure. Spec. Publ. No. 14, Am. Fish. Soc. Bethesda, MD, 154 pages.
Detailed information on solubility of oxygen, nitrogen, argon and carbon dioxide in freshwater and seawater. Example problems and computer programs for HP-41CVs.
D'Aoust, B.G. and M.J.R. Clark, 1980
Analysis of supersaturated air in natural waters and reservoirs. Trans. Am. Fish. Soc., 109: 708-724.
A review and comparison of various sampling and analysis techniques for the measurement of dissolved gas supersaturation.
Dawson, D.K., 1986
Computer program calculation of gas supersaturation in water. Prog. Fish-Cult., 48: 142-146.
A short computer program for computation of gas supersaturation parameters. Written in BASIC for Apple IIe or IBM PC but can be adapted to other microcomputers.
Fickeisen, D.H., M.J. Schneider and J.C. Montgomery, 1975
A Comparative evaluation of the Weiss saturometer. Trans. Am. Fish. Soc., 104:816-820.
The Weiss saturometer, which directly measures dissolved gas pressure, was compared with a gas chromatograph. Both methods appear to have advantages in specific applications. Operator experience can have significant effect on the precision of the Weiss unit.
Krise, W.E, W.J. Ridge and L.J. Mengel, 1991
System for continuous monitoring dissolved gas in multiple water sources. American Fisheries Symposium No. 10, Bethesda, MD, pp. 495-506.
Details on the design of gasometer system for monitoring total gas pressure at multiple locations.
Measurement of gas supersaturation
TABLE 1-2 (continued) Author(s) and date
Title and source
Comments
Bouck, G.R., R.E. King and G. Bouck-Schmidt, 1984 Colt, J., 1986
Comparative removal of gas supersaturation by plungers, screens and packed columns. Aquacult. Eng., 3: 159-176. The impact of gas supersaturation on the design of aquatic culture systems. Aquacult. Eng., 5: 49-86.
Packed columns are the most efficient for degassing.
Colt, J. and G. Bouck, 1984
Design of packed columns for degassing. Aquacult. Eng., 3:251-273.
Detailed information on the operational characteristics of packed columns for degassing as a function of environmental and operating conditions.
Fuss, J.T., 1983
Effective flow-through degasser for fish hatcheries. Aquacult. Eng., 2: 301-307.
Performance and design information for a small vacuum packed column.
Fuss, J.T., 1986
Design and application of vacuum degassers. Prog. Fish-Cult., 48:215-221.
Practical design information on number of full-scale degassing systems.
Lasker, R. and L.L. Vlymen, 1969
Experimental Seawater Aquarium. Circular No. 334, U.S. Fish and Wildlife Service (now NMFS), 14 pp.
A description of the splash tower used at the NMFS La Jolla lab to degas seawater.
Marking, L.L., V.K. Dawson and J.R. Crowther, 1983
Comparison of column aerators and a vacuum degasser for treating super saturated culture water. Prog. Fish-Cult., 45: 81-83.
In waters with low dissolved oxygen, use of vacuum degassing may result in insufficient DO. Under these conditions it may be necessary to increase the DO before degassing.
Design of degassing systems
Review of gas supersaturation mechanisms, seasonal variations in different environments, and prevention of gas bubble trauma in aquatic systems.
306
Appendix J
Disinfection Bibliography Disinfection is the reduction in the concentration or number of viable pathogenic microorganisms present. Sterilization is the complete elimination of microorganisms. In aquatic systems, ozone, ultraviolet radiation, and chemical treatments are the most common means for disinfection. The efficacy of a particular method will generally depend on the concentration of the particular agent, the decay rate, contact time, temperature, the specific pathogenic organisms, and often other environmental factors. Even though the culture organisms are rarely present during treatment (exceptions include marine mammals and fish eggs), the toxicity of the disinfectant itself, its residues and possible side effects on the culture organisms must also be seriously considered. Treatments are usually in the flow lines before the culture tanks or in a recirculating loop. Problems caused by the treatments may be subtle and occur at concentrations below the detection limits of available analytical equipment. Sterilization requires either strong chemicals or high temperatures and pressures, and is mostly used on equipment such as nets, tanks and handling devices to preclude the transmission of diseases; however, sometimes there is still the possibility of residues effecting the culture organisms. Basic references on disinfection and sterilization in aquatic systems are presented in Table J- 1.
TABLE J- 1 Selected disinfection references Author(s) and date
Title and source
Comments
Amend, D.E and ES. Conte, 1982
Disinfection: necessary preventive maintenance for healthy fish. Aquacult. Mag., 9: 25-29.
Instructions on disinfecting nets, gloves, transport systems and other equipment.
Blogoslawaki, W.J., F.E Thurberg and M.A. Dawson, 1973
Ozone inactivation of Gymnodimium breve toxin. Water Res., 7: 1701-1703.
Ozone is effective against the toxin.
Brown, C. and D.J. Russo, 1979
Ultraviolet light disinfection of shellfish hatchery seawater. Aquaculture, 17: 17-23.
UV treatment of filtered seawater increased survival of fertilized oyster eggs of Crassostrea virginica.
Burkhardt, W., S.R. Rippey and W.D. Watkins, 1992
Depuration rates of northern quahogs, Mercenaria Mercenaria (Linnaeus, 1958) and eastern oysters Crassostrea virginica (Gmelin, 1791) in ozone- and ultraviolet light-disinfected seawater systems. J. Shellfish Res., 11: 105-109.
The relative elimination rates of a diverse group of indicator microorganisms from hard-shelled clams and eastern oysters were evaluated in ultraviolet light and ozone-disinfected seawater systems.
Caufield, J.D., 1991
Specifying and monitoring ultraviolet systems for effective disinfection of water. American Fisheries Symposium No. 10, Bethesda, Maryland, pp. 474--481.
Detailed procedure for the design and operation of UV systems.
Colberg, EJ. and A.J. Ling, 1978
Effect of ozonation on microbial fish pathogens, ammonia, nitrate, nitrite and BOD in simulated reuse hatchery water. J. Fish. Res. Board Can., 35: 1290-1296.
Oxidation of glucose and nitrite was rapid at low ozone concentrations with glucose and ammonia oxidation being pH-dependent. A 60 s contact time with 0.1 rag/1 ozone resulted in greater than 99% mortality of several common bacterial pathogens.
Colt, J. and E. Cryer, 2000
Ozone. In: R.R. Stickney, W. Griffin, R. Hardy, S. Johnson, E Lee, M. Rust, G. Treece and G. Wedemeyer (Eds.), The Encyclopedia of Aquaculture, John Wiley and Sons, New York, pp. 662-629.
A review of the use ozone in freshwater and marine aquaculture systems.
Fischer, W.S., E.H. Nilsen, L.F. Follett and R.A. Shleser, 1976
Hatching and rearing lobster larvae Homarus americanus in a disease situation. Aquaculture, 7: 75-80.
Increased survival through use of UV radiation and chemical treatment.
Flick, G.J. Jr., 1998
Common chemicals for cleaning and disinfecting aquaculture facilities. In: G.S. Libey and M.B. Timmons (Eds.), Proc. 2nd Int. Conf. Recirc. Aquaculture, Virginia Polytechnic and State Univ., Roanoke, Virginia, pp. 7-19.
Excellent review of all common disinfectant chemicals, their advantages and disadvantages.
Grguric, G., J.H. Trefy and J. Keaffaber, 1994
Ozonation products of bromine and chlorine in seawater aquaria. Water Res., 28: 1087-1094.
During ozonation of seawater in closed marine systems, reduced chemical species such as bromide ion and, to a much lesser degree, chloride ion may be oxidized to a
Author(s) and date
Title and source
Comments
Hnath, J.G., 1983
Hatchery disinfection and disposal of infected stocks. In: E Meyer, J. Warren and T. Carey (Eds.), A Guide to Integrated Fish Health Management in the Great Lakes Basin, Special Publ. No. 83-2, Great Lakes Fish. Comm., Ann Arbor, MI.
A guideline for hatchery disinfection.
Honn, K.V., M. Glezman and W. Chavin, 1976
A high capacity ozone generator for use in aquaculture and water processing. Mar. Biol., 34:211-216.
Describes variables affecting production. Highest ozone production 10.6 kg/kW per hour using pure oxygen and 2650 V.
Liltved, H., H. Hektoen and H. Efraimsen, 1995
Inactivation of bacterial and viral pathogens by ozonation and UV irradiation in water of different salinities. Aquacult. Eng., 14:107-122
One of few references dealing with efficacy of treatment processes.
Lohr, A.L. and J.B. Gratzek, 1986
Bactericidal and parasiticidal effects of an activated air oxidant in a closed aquatic system. J. Aquacult. Aquatic Sci., 4: 1-8.
Ozone-containing activated air oxidant named 'Photozone' tested in a closed aquatic system against selected bacteria and protozoa. Shown to significantly reduce bacteria.
Oakes, D., E Cooley, L.L. Edwards, R. Hirsch and V.G. Miller, 1979
Ozone disinfection of fish hatchery water: pilot plant results, prototype design and control considerations. Proc. World Maricult. Soc., 10: 854-870.
Ozone shown to be a better disinfectant than UV. Design of ozone system for production-oriented salmon hatchery is presented.
Qualls, R.G. and J.D. Johnson, 1985
Modeling and efficiency of ultraviolet disinfection systems. Water Res., 19: 1039-1046.
Model for bacterial disinfection using UV that takes into account complex intensity patterns, non-ideal flow and non-linear curves of survival vs. UV dose.
Rosenthal, H., 1981
Ozonation and sterilization. In: K. Tiews (Ed.), Aquaculture in Heated Effluents and Recirc. Systems, Vol. 1, Heeneman Verlagsgesellschaft, Berlin, pp. 219-274.
Comprehensive review of sterilization practices and techniques in aquaculture.
Spanier, E., 1978
Preliminary trials with an ultraviolet liquid sterilizer. Aquaculture, 14: 75-84.
UV-reduced mortality rate of experimentally wounded fish compared to controls.
Spotte, S. and J.D. Buck 1981
The efficacy of UV irradiation in the microbial disinfection of marine mammal water. J. Wildl. Dis., 17:11-16.
Bacterial counts were lowered except in remote parts, poor performance attributed to long recycle time and lack of residual effect.
Spotte, S., 1991
Sterilization of Marine Mammal Pool Waters. U.S. Dept. of Agriculture, Animal and Plant Inspection Service, Technical Bull. # 1797, 59 pp.
Good review of marine mammal pool disinfection processes and technology.
309
Appendix K
Culture Unit Shape, Size and Flow Pattern~Hydraulics Bibliography
There are many kinds of culture units. These can include tanks, raceways and ponds in a wide variety of configurations and sizes. These culture units are usually specific to a particular purpose or type of organism and have generally evolved over time in actual practice. An important factor that is often not fully appreciated is that the culture unit configuration is also dependent on scale. Dramatic changes in scale for equipment from previous practice can be very risky, even if the purposes and organisms are the same. Hydraulics of culture units can be very non-linear. In addition, culture units that have been satisfactory in previous practice can prove to be unsatisfactory if the objectives or conditions of utilization are changed. An example is a switch from research to commercial criteria. In spite of these caveats, previous practice can be a useful guide. Considering the extensive experience with many types of culture units, there are relatively little published data concerning the equipment itself. Most of what exists is abbreviated and buried in 'Equipment and Methods' sections of papers primarily concerned with other matters. Table K-1 includes selected references that deal primarily or in part with the culture unit characteristics. Salinity is not a significant factor in unit hydraulics; therefore, this Appendix should be useful for both freshwater and marine applications. There has been significant progress in this topic area since the 1st edition. Many of these developments have been motivated by post-use regulatory waste removal requirements. Solid waste problems can be greatly reduced if the settleable solids (feces and uneaten food) can be separated from the main discharge and handled with as little entrained water as possible. Labor requirements associated with cleaning of large units is also of major concern, especially for commercial applications. This has focused attention on culture unit hydraulics.
TABLE K- 1 Selected bibliography on culture unit shape, size and flow pattern/hydraulics Author(s) and date
Title and source
Comments
Backhurst, J.R. and J.H. Harker, 1988
The suspension of feeds in aerated rearing tanks: the effects of tank geometry and aerator design. Aquacult. Eng., 7" 379-395.
Testing of eight rectangular and circular tanks (minimum volume 3.5 1, maximum 43.5 1) with different bottom shapes and aerator design/placements.
Bidwell, R.G.S., J. McLachlan and N.D.H. Lloyd, 1985
Tank cultivation of Irish Moss, Chondrus crispus Stackh. Bot. Mar., 28" 87-97.
Tanks designed for easy scale-up to large sizes, air circulation, system optimized for commercial production.
Burrows, R.E. and H.H. Chenoweth, 1955
Evaluation of three types of fish rearing ponds. U.S. Fish and WildLife Ser. Research Rep., 39, 28 pp.
Tested Foster-Lucas unit (76 x 17 ft oval, 3 ft water), circular unit (25 ft diameter by 2.6 ft water) and raceway (80 x 8 ft, 2 ft water).
Burrows, R.E. and H.H. Chenoweth, 1970
The rectangular circular rearing pond. Prog. Fish-Cult., 32: 67-80.
Description of classic Burrows raceway commonly used in salmonid hatcheries in a number of variations, length 50-70 ft x width about 17 ft, 3 ft or less water.
Busch, C.D., 1980
Water circulation for pond aeration and energy conservation. Proc. World Maricult. Soc., 11: 93-101.
Mechanics of pond circulation and paddlewheel aerators.
Busch, C.D. and R.K. Goodman, 1981
Water circulation - - an alternative to emergency aeration. J. World Maricult. Soc., 12" 13-19.
Artificial circulation of 1.4 ha (3.5 acre) pond, loading, power, oxygen and circulation data.
Charters, A.C. and M. Neushul, 1979
A hydrodynamically defined culture system for benthic seaweeds. Aquat. Bot., 6: 67-78.
Tanks 3 x 0.5 x 0.3 m for seaweeds up to 3 m, circulated by submerged water jets, flow of 150 lpm, flow-through or closed cycle.
Chesness, J.L., W.H. Poole and T.K. Hill, 1974
Settling basin design for raceway fish production systems. Paper 74-5005, 14 pp., Am. Soc. Agric. Eng., Box 229, St. Joseph, Michigan.
Predictions vs. actual performance of trapezoidal settling basin, length 54 ft, 10-22 ft width, 3 ft depth, 1.2 ft3/s (0.035 m3/s) flow, 48% solids removal.
Cripps, S.J. and M.G. Poxton, 1992.
A review of the design and performance of tanks relevant to flatfish culture. Aquacult. Eng., 11:71-91.
Good review of past experiences and highly referenced. Considers wide variety of tank shapes and sizes.
Delacey, A.C., 1964
An annular tank for sea fishes. In: J.R. Clark and R.L. Clark (Eds.), Seawater Systems for Experimental Aquariums, U.S. Fish and Wildlife Ser., Res. Rep. 63, pp. 141-142.
2000-gal tank for active fish, OD 10 ft, ID 7 ft, 4 ft water depth, water current, light and temperature control.
Ellis, S.C. and W. Wantanabe, 1994
Comparison of raceways and cylindroconical tanks for brackish-water production of juvenile Florida red tilapia under high stocking densities. Aquacult. Eng., 13: 59-69.
Tests with two tank geometries, both with volume of 350 1. 'Raceway' is superior.
Heard, W.R. and R.M. Martin, 1979
Floating horizontal and vertical raceways used in freshwater and estuarine culture of juvenile salmon, Oncorhynchus spp. Mar. Fish. Rev., 41:18-23.
Five different configurations of floating units, all using plastic liner materials sewn together, largest horizontal unit with half round cross-X and 62' x 14' x maximum 7' (at centerline) dimensions.
Hughes, J.T., R.A. Shleser and G. Tchobanoglous, 1974
A rearing tank for lobster larvae and other aquatic species. Prog. Fish-Cult., 36: 129-132.
Describes classic Hughes system widely used to rear crustacean larvae, tank water capacity of 37-41 1, cylindrical with rounded bottom and central overflow pipe.
Iqbal, M., D. Grey, E Stephan-Sarkissian and M.W. Fowler, 1993.
A flat-sided photobioreactor for culturing microalgae. Aquacult. Eng., 12: 183-190.
A V-shaped transparent unit (working volume of 2 1) for the monoculture of phytoplankton under very controlled conditions.
Laing, I. and E. Jones, 1988
A turbidostat vessel for the continuous culture of marine micro-algae. Aquacult. Eng., 7: 89-96.
Construction and operation of 40 1 unit made from clear replaceable polyethylene sheet material formed about a core of six 80 W fluorescent lamps and supported by an external framework.
Larmoyeux, J.D. and R.C. Piper, 1973
Evaluation of circular tanks for salmonid production. Prog. Fish-Cult., 35: 122-131.
Discusses advantages and problems with circular units, includes very small tanks to 40 ft diameter, circulation data, and operational considerations.
Lawrence, J.M., 1949
Construction of farm fish ponds. Circular No. 95, 55 pp., Agric. Exp. Station, Auburn Univ., Auburn, AL, 36830.
Discusses all aspects of design and construction of earthen ponds.
Lawson, T.B. and F.W. Wheaton, 1983
Crawfish culture systems and their management. J. World Maricult. Soc., 14: 325-335.
Siting, construction and circulation data (with and without baffles) for earthen ponds of 2-40 ha (5-100 acres), optimum size towards lower end.
Nakamura, M., 1976
Design of an aquaculture pond with a tidal inlet. FAO Tech. Conf. Aquaculture, Kyoto, Japan, 26 June-May 2, FIR: AQ/Conf/76/E.81 5 pp.
Theoretical basis for calculating tidal exchange of ponds or tidal enclosures.
Mock, C.R., R.A.A. Neal and B.R. Salser, 1973
Closed raceway for the culture of shrimp. Proc. 4th Annu. Workshop World Maricult. Soc., 4: 247-259.
Baffled rectangular tank about 19 x 9 x 3 ft (5.9 x 2.7 x 1 m) with airlift powered circulation.
Mock, C.R., L.R. Ross and B.R. Salser, 1977
Design and preliminary evaluation of a closed system for shrimp culture. Proc. World Maricult. Soc., 8: 335-369.
Additional data on rectangular airlift circulated raceways, biggest raceway about 77 x 10 x 3 ft (24 x 3 x 0.9 m).
Robinson, W.R. and R Vernesoni, 1969
Low cost circular concrete ponds. Prog. Fish-Cult., 31: 180-182.
20 ft diameter tanks 30 in. deep, made from prefabricated concrete silo staves placed into concrete base and banded together at two elevations.
Author(s) and date
Title and source
Comments
Ross, R.M., B.J. Watten, W.F. Krise and M.N. DiLauro, 1995
Influence of tank design and hydraulic loading on the behavior, growth and metabolism of rainbow trout (Oncorhynchus mykiss). Aquacult. Eng., 14: 29-47.
Subadult trout tested rectangular plug flow (6.2 x 0.6 x 0.5 m deep), circulator (2.4 diameter x 0.4 m deep) and cylindrical cross-flow (4.6 x 1.5 x 1.1 m deep) tanks at two water exchange rates. Significant effects due to tank design were observed.
Salser, B.R. and C.R. Mock, 1973
An airlift circulator for algal culture tanks. Proc. 4th Annu. Workshop World Maricult. Soc., 4: 295-298.
Data on airlift-powered tank circulator.
Shell, E.W., 1966
Comparative evaluation of plastic and concrete pools and earthen ponds in fish-culture. Res. Prog. Fish-Cult., 28: 201-205.
Plastic wading pools 9 ft diameter and 2.5 ft deep, rectangular concrete tanks 24 x9 x 2.5 ft and earth 0.25 acre ponds, long-term experience at Agric. Exp. Station, Auburn Univ.
Shigeno, K., 1975
Shrimp culture in Japan. Assoc. for Intern. Tech. Promotion, Tokyo, Japan, 153 pp.
Information on culture units used for various stages of shrimp development.
Simon, C.M., 1982
Large-scale, commercial application of penaeid shrimp maturation technology. J. World Maricult. Soc., 13: 301-312.
Design, construct., support and operations of 3.65 m diameter x 1.1 m deep circular maturation tanks.
Simon, C.M., 1981
Design and operation of a large-scale commercial penaeid shrimp hatchery. J. World Maricult. Soc., 12: 322-334.
Information on culture units used in commercial shrimp culture and their operations.
Stabell, 1992.
A Simple System for Self-Cleaning of Fish Rearing Tanks by Periodic Increase in Water Outflow. Aquacult. Eng. 11: 47-53.
Cylindrical tank (1 m diameter • about 1 m depth) with slight (8-10 ~) conical bottom. Process siphon controlled, tank has central bottom drain.
Summerfelt, S.T., M.B. Timmons and B.J. Watten, 1998
Culture tank designs to increase profitability. In: G.S. Libey and M.B. Timmons (Eds.), Proc. 2nd Int. Conf. Recirculating Aquaculture, Virginia Polytechnic and State University, Roanoke, VA, pp. 253-262.
Discussion of relative merits of alternate tank designs for commercial fish production.
Timmons, M.B., S.T. Summerfelt and B.J. Vinci, 1998
Review of circular tank technology and management. Aquacult. Eng., 18:51-69.
Excellent, comprehensive and detailed review and well referenced. Design information on 'dual drain' systems and on minimum velocities for self-cleaning.
Vandermeulen, H., 1989
A low-maintenance tank for the mass culture of seaweeds. Aquacult. Eng., 8: 67-71.
Modification of rectangular polypropylene containers (104 • 104 • 66 cm high) for aerated 'tumble' culture of Ulva.
Watten, B.J. and L.T. Beck, 1987
Comparative hydraulics of a rectangular cross-flow rearing unit. Aquacult. Eng., 6: 127-140.
Cross-flow raceway with well mixed homogeneous properties, self-cleaning and having low frictional losses.
Watten, B.J. and R.E Johnson, 1990
Comparative hydraulics and rearing trial performance of a production scale cross-flow rearing unit. Aquacult. Eng., 9: 245-266. Nursery engineering for nori aquaculture. Aquacult. Eng., 9: 429-445.
Comparative tests of cross-flow raceway (18.4 m • 143 cm • 102 cm deep) and equivalent raceway with plug flow. Requirements and design of nori (Porphra) nursery tank, including simulation of tides and correct lighting.
Yang, W.T., 1975
A manual for large-tank culture of penaeid shrimp to the postlarval stages. Tech. Bull. No. 31, 94 pp., Univ. of Miami Sea Grant Prog.
Design, construction and operations of Japanese large-scale hatchery tank systems, '200 ton' tank is 32 x 32 x 6.4 ft ( 1 0 x 1 0 x 2m).
Zielinski, EB., W.E. Castro and EA. Sandifer, 1976
Model flow studies of a rectangular shrimp larval tank. Proc. World Maricult. Soc., 7: 583-605.
Tank about 12' x 3.8' x 3.8' deep (average)with sloping bottom and similar half-scale model tested at flows of 10-50 tank volumes/day, velocity and settling rates determined.
Williamson, M.R. and D.M. Robichaux, 1990
ta,)
314
Append& L
Feeder Bibliography
Most of the data on feeding practices are species specific. Much of it is contained in papers concerned primarily with the nutritional aspects. The vast majority of available data is on freshwater species, mostly catfish and trout. Relatively little is available on commercial feeding practices even for important freshwater applications. Commercial culturists, by and large, do not publish and the little that is available about commercial operations is primarily from academies and related agricultural (aquatic) experiment stations. This leaves the marine culturist with relatively little practical data although salinity should not be a significant factor. Table L-1 provides what information is available. It concentrates on feeding processes and survey papers. There has been no attempt to present species-specific data, which can often be found in the appropriate species literature. The intent has been to present the procedural and equipment information. An interesting development since the first edition is in the area of hydroacoustic sensors to shut-off feeding when uneaten feed is detected. These have been adopted for cage, pond and tank culturing. Also included are several references on developing techniques that show promise for practical use in culturing operations. There does exist some data on feeding devices of various kinds. Most of these are for small-scale use in research, hatcheries or larval rearing. Again, most are from academic or research oriented sources and for freshwater species. However, the feeds for marine species and those for freshwater are very similar and often identical in their characteristics. Such an example is with the use of brine shrimp, the equipment should be common and a selected bibliography is presented in Table L-2. Table L-2 concentrates on equipment and operations. The two feed forms best represented in the table are dry-pellet or flake, and live-zooplankton feeds. Delivery systems for other common possibilities, such as ground natural feeds and moist pellets, are poorly represented in the available literature.
TABLE L- 1 Literature on feeding processes Author(s) and date
Title and source
Comments
Backhurst, J.R. and J.H. Harker, 1988
The suspension of feeds in aerated rearing tanks: the effects of tank geometry and aerator design. Aquacult. Eng., 7: 379-395.
Interactions of tank geometry and aerator placement/flow with suspension of feeds needed in shrimp and prawn culture.
Brown, A., Jr., 1972
Experimental techniques for preserving diatoms used as food for larval P. aztecus. Proc. Natl. Shellfish Assoc., 62: 21-25.
Freeze-dried diatoms with and without preservatives shown to support growth, although not as good as live diatoms.
Derrow, R.W., II, S.T. Summerfelt, A. Mehrabi and J.A. Hankin, 1996
Design and testing of a second generation acoustic waste feed monitor. In: G.S. Libey and T.B. Timmons (Eds.), Successes and Failures in Commercial Recirculating Aquaculture, pp. 552-561.
Hydroacoustic feed detection adapted to a pond environment.
Halver, J.E., 1976
Formulating practical diets for fish. J. Fish. Res. Board Can., 33: 1032-1039.
Good survey paper.
Juel, J.E., D.M. Furvik and A. Bjordal, 1993
Demand feeding in salmon farming by hydroacoustic food detection. Aquacult. Eng., 12: 155-167.
Sensor to shut-off feeding when uneaten pellets are detected at bottom of feeding zone in large fish cages.
Libey, G.S. and M.B. Timmons (Eds.), 1998
Aquacultural engineering, Session 1. Feeds for recirculating aquaculture. Proc. 2nd Int. Conf. Recirculating Aquaculture, pp. 270-290.
Four papers: economic importance of feeds, digestibility of feeds, selection of pellet type and feed formulation.
Lovell, T., 1977
Physical aspects of food important in feeding fish. Commercial Fish Farmer, 3(6): 32.
Discussion of floating vs sinking, feed size and feeding strategies.
Meyers, S.E, D.R Butler and G.E Sirine, 1971
Encapsulation m a new approach to larval feeding. Am. Fish Farmer, 2(8): 15, 16, 18, 20.
Possible substitute for phytoplankton and live zooplankton, preparation methods described.
Meyers, S.R and C.W. Brand, 1975
Experimental flake diets for fish and crustacea. Prog. Fish-Cult., 37: 67-72.
Flake parameters, components and low cost preparation methods.
Oiestad, V., T. Pedersen, A. Folkvord, A. Bjordal and R G. Kvenseth, 1987
Automatic feeding and harvesting of juvenile Atlantic cod (Gadius morhua) in a pond. In: J.G. Balcher (Ed.), Automation and Data Processing in Aquaculture, IFAC Proceedings Series, 1987, #9, pp. 199-204.
Cod lured into fish trap by artificial current, dry feed and conditioned acoustic feeding signal. Fish trap then emptied with fish pump and fish taken to automatic grading facility.
TABLE L- 1 (continued) Author(s) and date
Title and source
Comments
Summerfelt, S.T., K.H. Holland, J.A. Hankin and M.D. Durant, 1995a
Hydroacoustic waste feed controller for tank systems. Water Sci. Technol., 31: 123-129.
Waste feed detection system adapted to tank culture.
Thain, B.E and M.J. Urch, 1973
Marine fish feeds in an intensive system. Fish Farming Int., 1" 106-110.
Experiences of White Fish Authority with various feed forms and marine species in Scotland.
Tsuru, S., 1972
Preservation of marine algae by means of freeze-drying. In: Proceedings of the Seventh International Seaweed Symposium, Sapporo, August 8-12, 1971, John Wiley and Sons, New York, pp. 339-342.
Methods of increasing survival of algae which are frozen or freeze-dried, substitute for dependence on fresh phytoplankton.
Walsh, M., J.E. Huguenin and K.T. Ayers, 1987
Fish feed consumption monitor. Prog. Fish-Cult., 49: 133-136.
Methods for monitoring feed ingestion by use of fluorescent tracers in feed pellets.
Webber, H.H. and J.E. Huguenin, 1979
Fish feeding technologies. Proc. World Symp. Fin Fish Nutrition and Fishfeed Technology, 1:298-316; FAO and EIFAC Symp., Hamburg, also EIFAC/78/Symp., R/10.2, May 1978, 35 pp.
Review paper with emphasis on feed forms, handling and distribution.
TABLE L-2 Literature on feeding and related practices Author(s) and data
Title and source
Comments
Anderson, E.D. and L.L. Smith, Jr., 1971
An automatic brine shrimp feeder. Prog. Fish-Cult., 33: 118-119.
Simple siphon-operated continuous feeder.
Bahner, L.H. and D.R. Nimmo, 1976
Precision live-feeder for flow-through larval culture or food chain bioassay. Prog. Fish-Cult., 38:51-52.
Timer-activated pump feeder, electronics and components described, capable of handling a number of units in parallel.
Benoit, D., R. Syrett and J. Hale, 1969
Automatic live brine shrimp feeder. Trans. Am. Fish. Soc., 98: 532-533.
Simple siphon-operated continuous feeder.
Charlon, N. and R Bergot, 1986
An improved automatic dry food dispenser for fish larvae. Prog. Fish-Cult., 48:156-158
For small-scale use, 3.3 cm diameter by 7 cm long clear plastic feed holder, as many as 10 feeders on long electrically driven shaft, controlled by cams on 10 min cycle.
Falls, W.W., 1980
Economic, automatic, dry-food feeder. Prog. Fish-Cult., 42: 240.
Premeasured feed is placed on a large horizontal circular plexiglass disk once a day, the disk is rotated past a scrapper by a timer and motor.
Huggins, W.L., M.M. Helm and D.R. Williams, 1987
Automatic control of food supply in the culture of filter-feeding organisms. Aquacult. Eng., 6: 259-275.
Design, construction and performance of IR photo cell algal cell monitor for use in marine hatcheries.
Joeris, L.S., 1965
Automatic feeder for small fish held in tanks. Prog. Fish-Cult., 27: 133-174.
Timer-activated solenoid-operated slide mechanism dispenses dry feeds from mason jar reservoir.
MacFarlane, L.R., 1976
Automatic feeder for delivery of high-fat starter food to swim-up fry of Atlantic salmon. Prog. Fish-Cult., 38: 106-107.
Food jars are attached perpendicular to rod which is periodically rotated by an electric timer and motor, one end of jar has holes and operates like a salt shaker when rotated.
Meriwether, EH., 1986
An inexpensive demand feeder for cage-reared Tilapia. Prog. Fish-Cult., 48: 226-228.
20 1 feed storage, adjustable delivery, 72% better growth over hand-fed, feed conversion and survival about same.
McCauley, R.W., 1970
Automatic food dispenser for walleyes. Prog. Fish-Cult., 32: 42.
A 2 rev./day spring motor (modified clock) rotates a horizontal disk with feed around its perimeter; as disk turns fixed brush deflects feed into tank below.
Mortensen, W. and O. Vahl, 1979
A programmed controller for automatic feeders. Aquaculture, 17: 73-76.
A system which controls the amounts and length of feeding period in six parallel units is described with circuit
~ D L ~
L-Z [contlnueu) oo
Author(s) and data
Title and source
Comments
Neill, W.H. and T.C. Byles, 1972
Automatic pellet dispenser for experimental feeding of fish. Prog. Fish-Cult., 34: 170.
Dry pellets loaded into horizontal glass tube, forced out at the end by magnet traveling in tube, magnet driven by external magnet on long worm gear, feeding controlled by photo cell.
Nicholson, L., J. Christmas and R. Lukens, 1985
A low cost live food feeder. Prog. Fish-Cult., 47: 245-248.
16 1 storage (plastic traffic cone) with compressed air circulation, cycle timer and electric solenoid operated.
Novotny, A.J. and D. Chakravarti, 1966
A versatile force feeding system for experimental use with small fish. Prog. Fish-Cult., 28:108-112.
Equipment and techniques for feed preparation and force feeding of individual fingerlings.
Perkins, EE., 1963
A gravity food dispenser for laboratory fish. Prog. Fish-Cult., 25: 56.
Four liter inverted plastic bottle containing feed mixed with water and controlled by screw clamp on discharge hose at base of bottle.
Personne, G. and E Sorgeloos, 1972
An improved separator box for Artemia, nauplii and other phototactic invertebrates. Helgol. Wiss. Meresunters., 23: 243-247. An automatic wet-food dispenser. Prog. Fish-Cult., 30: 113-115.
Design and construction of unit to separate and concentrate brine shrimp nauplii.
Pozar, D.E, 1980
An automatic fish food dispenser for use with Oregon moist and dry food pellets. Prog. Fish-Cult., 42: 45-48.
From a cylindrical reservoir feed is pushed through a slot of variable size by an electrically powered rotating paddle, timer controlled and with a blower below slot to keep the area below the slot clear.
Prentice, E.E, 1975
Automatic feeding system using live Artemia. Prog. Fish-Cult., 37: 168-169.
Timer-activated pump supplies brine shrimp to multiple parallel tanks through main seawater supply lines. This flushes the distribution lines between feedings.
Prilutzky, A., V. Birkan and S. Appelbaum, 1993
A universal inexpensive self-demand feeder for elvers. Aquacult. Eng., 12: 125-127.
No electrical or moving parts and suitable for pelleted, powder-like and paste feeds.
Rode, R., 1973
An automatic device for feeding aquatic organisms. Trans. Am. Fish. Soc., 102: 645-646.
A timer and multiple individually controllable air lifts deliver phytoplankton or zooplankton to culture units.
Schimmel, S.C. and D.J. Hansen, 1975
An automatic brine shrimp feeder for aquatic bioassay. J. Fish. Res. Board Can., 2: 414-316.
Delivers equal amounts of brine shrimp to multiple tanks, electrically powered pump, timer activated, parts and construction are described.
Schweinforth, R.L., G.L. Burton and C.M. Collins, 1984
Modified demand feeders for use with floating food in raceways. Prog. Fish-Cult., 46:211-121.
Similar to commercial feeders, for fish larger than 10 cm (4 inch), uneaten feed contained by 1 m diameter ring at surface.
Pozar, D.E, 1968
Water powered feeder for continuous distribution of ground wet-foods and disintegrating sinking feeds.
Serfling, S.A., J.C. Van Olst and R.F. Ford, 1974
An automatic feeding device and the use of live and frozen Artemia for culture of larval stages of the American lobster, Homarus americanus. Aquaculture 3:311-314.
Food cups are tipped and emptied by a revolving bar driven by a clock motor. The feeding interval, quantity and food type can be controlled.
Smith, R.A., 1974
Automatic brine shrimp feeder. Prog. Fish-Cult., 36: 133.
Inverted cone tank with air bubbler, timer-activated solenoid is turned off, brine shrimp settle to bottom, pump drawing from apex turned on after 8 min delay.
Tarrant, R.M., Jr. and J.E. Dunnahoe, 1975
An adjustable automatic feeder. Prog. Fish-Cult., 37: 108-111.
Timer- and solenoid-activated feeder useable over range of dry pellet sizes and delivery volumes, accurate to 2%.
Theis, G.L. and R.G. Howey, 1981
Dispenser for live food organisms. Prog. Fish-Cult., 43: 161-162.
Electrical timer-activated siphon feeder.
Tipping, J.M., R.L. Rathvon and S.T. Moore, 1986
Use of demand feeders on large steelhead rearing ponds. Prog. Fish-Cult., 48: 303-304.
Babington feeders, 125 lb capacity of dry feed, no feeder details, operations described, citations.
Vanderwalker, J.G. and E. Chin, 1962
A device for feeding brine shrimp to fishes. Trans. Am. Fish. Soc. 91" 230-231.
Continuous siphon feeder, using phototactic responses of brine shrimp. Only light to brine shrimp tank is through siphon.
Waite, D. and K. Buss, 1963
An automatic feeder for trout. Prog. Fish-Cult., 25: 52.
Timer-activated motor at base of inverted feed storage cone rotates agitator and rotor blades to fling feed horizontally, capacity 19 1 of feed.
Wehr, L.W. and W.M. Lewis, 1976
An electrically operated automatic fish feeder. Prog. Fish-Cult., 36: 117-118.
Timer-controlled rotating auger in base of feeder dispenses dry feeds, outdoor use, 25 kg capacity, 5% accuracy.
Wickens, J.F., E. Jones, T.W. Beard and D.B. Edwards, 1987
Food distribution equipment for individually-housed juvenile lobsters. Aquacult. Eng., 6: 277-288.
Two types, both for feeding large numbers of cells, one for dry pellets, other for water suspended live feeds.
Winfree, R.A. and R.R. Stickney, 1981
Automatic trough feeder developed. Aquacult. Mag., 7(4): 18-19.
Feed cups turned over by trip pins on rotating shaft driven by electric timer.
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Appendix M
Indexes for Equipment and Supplies
Since the first edition a number of sizable catalog companies specializing in aquacultural equipment and supplies have emerged. While manufacturers specializing in aquacultural equipment and supplies are increasing in numbers, much is still acquired and sometimes modified from other fields of endeavor. Some of these areas with crossover capabilities include wastewater treatment, agriculture and marine oceanographic/industrial pursuits. Another promising area, on the lower end of the flow-rate range, are the catalog stores. Many have 'industrial supply' or 'ranch and suburban' catalogs and are a relatively inexpensive source of plastic pipe, fittings, tanks and many other useful items. Inexpensive cast-iron pumps from industrial or farm catalogs, if the rusting can be tolerated, can give up to a few years of continuous service, even in seawater. Adopting equipment or supplies from other applications often includes risks and should be done with some care. As a general rule, the broader the application for a piece of equipment, the cheaper, the more reliable and the easier to replace, repair and service. Unless the requirements clearly demand it, custom designed and manufactured equipment should be avoided. Many of these catalog companies, both aquaculture-specialized and not, now have their catalogs on the web. National, regional and international aquaculture conferences often are associated with trade shows where equipment manufacturers exhibit their products. If they can be attended, these shows are a quick and easy means of acquiring a lot of information on availability, performance and costs of equipment. Similarly, there are a number of aquacultural magazines and newsletters that routinely carry equipment advertisements, which can form a starting point for gathering information. Listed in the following are a number of periodical indexes of equipment and supplies by type and manufacturer that might be useful. Some also list services, information sources, consultants and other types of data. Only one annual so far is specific to aquatic culturing applications (Aquaculture Magazine Annual Buyers Guide) but most of its content is primarily for freshwater applications. However, it does also have excellent contact information, at least for the U.S., for extension services, regional aquaculture centers, Sea Grant Programs and educational institutions involved with aquaculture. Aquaculture Magazine, Annual Buyers Guide and Industrial Directory (about 300 pages), and an Annual Products Issue, published by Achill River Corp., 16 Church St., Asheville, NC, 28802. Tel.: + 1 (828) 254-7334; E-mail:
[email protected]; Web: www.aquaculturemag.com AquaSearch, The Aquaculture and Seafood Directory. This one is only on the web. One of the 18 subject categories on its introduction page is EQUIPMENT SUPPLIERS; under the aquaculture subsection are listed 44 suppliers. Many of these have on-line equipment catalogs. Another subject category is EQUIPMENT with an index containing 41 alphabetized types of equipment. Each of these equipment types lists from one to many suppliers. This equipment also covers seafood processing and fishery applications in addition to aquaculture.
321 Web: www.aquasearch.net Pollution Equipment News, Annual Buyers Guide (about 440 pages), and a bi-monthly equipment newsletter of about 140 pages per issue, published by Rimbach Publishing, Inc., 8650 Babcock Blvd., Pittsburgh, PA, 15237-5821. Tel.: +1 (800) 245-3182; E-mail: Rimbach@ sgi.net; Web: www.Rimbach.com Regional Industrial Purchasing Guide, annual index of industrial equipment and supplies for individual sections of the U.S., published by Thomas Regional Directory, Co., Inc., 330 W 34th Street, New York, NY 10001. Sea Technology, Buyers Guide Directory, annually published by Compass Publications, Inc., Suite 1000, 1117 N 19th Street, Arlington, VA, 22209. Tel.: +1 (703) 524-3136; E-mail:
[email protected]; Web: www.sea-technology.com Water and Waste Digest Annual Buyers Guide (about 145 pages) and a bi-monthly equipment newspaper of about 60 pages per issue, published by Scranton Gillette Communications, Inc., 380 Northwest Highway, Suite 200, Des Plaines, IL, 60016-2282. Tel.: +1 (847) 298-6622; Web: www.waterinfocenter.com
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Appendix N
Computer Data Search
Appendix M contains leads for finding equipment, supplies and services. In contrast, this Appendix N is intended primarily to provide some guidance for acquiring scientific and technical data, although there is considerable overlap. This predominantly means finding pertinent technical papers and reports. Many of these data are species specific. Finding this material is rapidly becoming computer-based in contrast to the older library search techniques of progressing from the bibliography of one reference to find others. For some potential data sources, it is difficult to separate this search for technical data from an inundation of public relations and commercial information. However, contact with knowledgeable individuals (if they will talk to you) is still the fastest and surest way to finding the best published data available. Unfortunately, especially in areas of commercial aquaculture, a lot of the best and most current data may not be published at all. This is particularly true were efficiency of processes, operating techniques and procedures are involved. Many of the more interesting databases for technical and scientific literature are paid (licensed) services intended primarily for the libraries of academic and research institutions. For example, the University of Washington lists 360 separate databases (www.lib.washington.lib). About 50% of the databases are contractually restricted to faculty, students, and staff, or to persons physically present in the University libraries. The non-restricted databases can be accessed by anyone with web access. For university staff, students, and others using the library, all of these databases are free to the user, so a drive to a research library is an economical approach to many data searches. Most of the licensed databases are probably cost prohibitive for individuals or small companies. However, many offer a free trial period of usually a month. Most searches allow the user to save the search information on a floppy disk, or e-mail the search to the user. The vast majority of these data bases, but not yet all, have web access. They offer abstracts and often full text services. Full text accessibility is increasing rapidly but is currently a modest fraction of the total. The computer data search is in a rapid state of change. This appendix is certain to be quickly dated. It is intent only to provide the reader with an entry into the myriad interlinked sources available. Good hunting! N. 1 Traditional fee-based searches This type of literature search has been available for 15-20 years. A given computer service bureau commonly provides access to 10-20 specialized databases. Generally, the search is completed by a research librarian in consultation with the user. The user is billed individually for the cost of the search (dependent on the number of citations found and the degree of information printed). This type of search may still be available for some databases, but
323 the vast majority of databases are licensed to large institutions and accessed through the web. N.2 Internet sources The organization of internet aquaculture sites is complex and rapidly changing. Many commercial sites offer a large amount of free information. The most important parts of some sites are their links to other sites. All internet search engines (Yahoo, Excite, Altavisa, etc.) allow the user to bookmark a site. This places a copy of the site's internet address in a 'Favorites' folder and allows an easy return to the site in the future.
N.2.1 Governmental sites (and sites with a lot of free information) Alternative Farming Systems Information Center, Aquaculture-Related Internet Sites and Documents. This is the U.S. Department of Agriculture's aquaculture web site. It has a strong U.S. orientation but never the less has many links to other aquaculture organizations worldwide. It has an alphabetized directory, including a lot more than literature (organizations, career information, etc.). It has about 230 links. Home page: http://www.nal.usda.gov/afsic/ aqua/aquasite.htm#Sites; E-mail:
[email protected] Aquaculture (Norway). This site is primarily for Norway although it has many links to other aquaculture organizations worldwide. It lists companies, research organizations (including SINTEF and MARINTEK), equipment and species. It has about 110 links. Home page: http://www.nofa.net/aquaculture.html AquaSearch Directory. This free service has about 485 links involving aquaculture, seafood and fisheries. Considerable international content. Acquiring scientific and technical data from this source would be at best indirect. Most of the content is organizational and commercial information. Home page: http://www.aquasearch.net FishBase. This is a global information system on fishes. It was designed for use by research scientists, fisheries managers and zoologists and contains a number of separate data bases, including Species 2000, LarvalBase, Food Web Data, etc. FishBase was developed at the International Center for Living Resources Management (ICLARM) in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and with support of the European Commission. While it contains much free information, some services are paid and only available (at present) on CD ROM, such as FishBase 99 containing 20,000 references and information on 23,500 species. Home page: http://www.fishbase.org/search.cfm Fish Information Service (Japan). This site provides up-to-date information about the fishing and aquaculture industry. Home page: http://www.fis.com IntraFish (Norway). IntraFish was established as Norway's leading net site for the fish farming industry. The companies have now prepared a system that provides consumers with direct access to the latest quotations on the world's foremost salmon markets. Home page: http://www.intrafish.com United States Environmental Protection Agency. Office of Wastewater Management. Home page of the U.S. Environmental Protection Agency's Office of Wastewater Management, which is responsible for directing the National Pollutant Discharge Elimination System permits program. Home page: http://www.epa.gov/OWM
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N.2.2 Non-governmental sites Aquatic Sciences and Fisheries Abstracts (ASFA). This extensive data base offers more than 550,000 citations in a number of relevant topic areas, including Aquaculture, Marine Biotechnology and Biological Sciences. It is included in several other data bases mentioned in this appendix such as NISC's Aquatic Biology, Aquaculture and Fisheries Resources Data Base and Wilson Applied Science and Technology Index. This database is available on CD as well as offered on-line at many research libraries. Home page: http://www. silverplatter.cm/catalog/asfa.htm National Information Services Corporation (NISC). This is a worldwide information services organization, with offices in the USA (also servicing Europe), Mexico, India, Singapore, Chile and South Africa. These paid services are intended primarily for the libraries of academic and research institutions. It currently offers 54 data bases in a wide variety of subject areas, of which several are very relevant to this book. These include Aquatic Biology, Aquaculture and Fisheries Resources, containing about 799,000 citations and starting in 1971. This data base utilizes at least ten other data bases, including Aquatic Sciences and Fisheries Abstracts and FISHLIT. NISC's data base Fish and Fisheries Worldwide contains about 225,000 references and starts in 1972 and the Marine Oceanography and Freshwater Resources includes about 979,000 citations and starts in 1964. The data base Water Resources Worldwide is supposed to have a significant engineering content. All those above are available on the web. While a paid subscription service, free 30 day on-line trial access is available on BiblioLine. Home page: http://www.nisc.com; E-mail:
[email protected], Sales @nisc.com,
[email protected] Wilson Applied Science and Technology Index. Includes access to about 250 other databases (about 400 core publications) in a wide range of technical areas, including Marine Sciences, Engineering, Water and Food/Agriculture. One of them is Aquatic Sciences and Fisheries Abstracts. There is web access to this company, with some free services and trial access to many of the other sites. Home page: http://www.silverplatter.com/catalog/wast.htm N.2.3 Document delivery services For users that do not have ready access to a research library, document delivery services may be useful. These services may be able to fax or e-mail the article to the user to reduce delivery time. UnCoverWeb. This site provides free desktop delivery (in pdf or html) of full text articles from over 3000 journals to registered subscribers. You or your institution may register your existing journal subscriptions. Pay-per-view article option offered by many publishers, payable by credit card, with immediate desktop delivery (in pdf or html) or fax delivery of full text articles. Home page: http://uncweb.carl.org:80/; E-mail:
[email protected]
N.2.4 E-mail alerting service This type of service searches through selected databases or journal tables of contents and e-mails information on the latest articles published in your areas of interest.
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UnCoverReveal. Users may select up to 50 journal titles to receive table of contents notification and also have up to 25 search strategies run weekly against all new articles added to the UnCover database. UnCoverReveal sends citations and tables of contents listing that fit your personal subject and journal profile directly to your e-mail account once a week. Home page: http://uncweb.carl.org/reveal/ N.2.5 Society web sites
Aquacultural Engineering Society: American Fisheries Society: World Aquaculture Society: European Aquaculture Society: American Society of Civil Engineering: American Water Works Association:
www.cals.cornell.edu/dept/aben/aes www.fisheries.org/ ag.ansc.purdue.edu/aquanic/was/was.htm allserv.rug.ac.be/'~j dhont/eas/about/abouto2.htm www.asce.org www.infoXpress.com/awwa/aww/
N.2.6 On-line journals Many journals are starting to provide their journals on-line. The following journals do not charge for this service. It is likely that most journals will provide some form of on-line journals in the future. Transactions of the American Fisheries Society North American Journal of Aquaculture Canadian Journal of Aquatic Sciences
afs.allenpress.com/afsonline/?request=index-html afs.allenpress.com/afsonline/?request-index-html www.nrc.ca/cgibin/cisti/journals/w/w_desy_e?cjfas
N.3 Aquaculture information lists There are a number of sites that distribute current information and gossip on aquaculture and fishery topics. The volume of information can be overwhelming especially if you actually have a real job. One such service is provided by Dave Conley (
[email protected]); many others are available.
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SUBJECT INDEX
Activated charcoal (carbon) 207 Aeration and aerators 163, 298 Air lift pumps 168, 175, 301 Air stripping- s e e Foam fractionation Alarm systems 193 Ammonia limitations chemistry 22, 201, 281 mole fraction of un-ionized ammonia 22 toxicity 21, 281 Artificial seawater 60 Automatic control 197
chemical 184, 306 ozone 187, 306 ultraviolet radiation 190, 306 Dissolved oxygen considerations 24, 36, 39, 163 consumption (feed intake) 30, 31 consumption (weight) 30, 31 limitations 163 solubility in water 26
Beach profile 52, 78 Bead filters 204 Biofilters bead filter 204 rotating biological contactor 204 trickling filters 204 B iofouling control 82, 284 Biosecurity 4, 7, 183, 202
Feeders 212, 314 Filters bag 141 cartridge 139 continuous backflushing sand 138, 142 diatomaceous earth 140 microscreens 144 rapid sand 142, 143 slow sand 142, 143 Flow control 74, 75, 129 Flow measurement 134 Foam fractionation 202, 206, 266
Centrifugal pumps 104 Centrifuges and cyclones 142 Chlorination 27, 184 Construction cost estimating 217 Conversions 264 Cooling 151 Corrosion 119, 120 Databases 322 Dechlorination 186 Degassing 163, 178, 298, 305 Density production 29, 41 water 29, 41 Density index 34 Discharge considerations 79, 217 location 76, 79 Disinfection
Electrical safety 229
Gas supersaturation 178, 298, 303 Growth models exponential 12 A L method 12 Head 87, 93 Headbox (tank) 75, 129, 267 Heat exchangers 154, 157, 267, 295 Heating 151 Hydraulic radius 95, 98 Intake design 59, 66, 76, 219 screens 68, 70 submergence 51, 68, 77
328 Layout 54, 75, 79 Loss coefficients of fittings 93 Monitoring and control 131,133, 134, 193, 226, 295 Net positive suction head (NPSH) 108, 112, 267 Nitrification 202, 276 Open channel flow 93 Ozone treatment 187, 279 Pipe equivalent sand roughness 91 cleaning 82 fittings 93 friction 87, 89, 93, 174 in pump house 104, 108 materials 122 resistance coefficients 91 selection 81 types 91 Preventive maintenance 226 Production modeling 12 Protein skimmer 202, 206, 267 Pump considerations 76, 101,108, 110 head 87, 109, 110 materials 124 NPSH s e e Net positive suction head pumps in parallel 104, 113 selection 101 specific speed 101,268 types 101 -
Redundancy 102, 224 Reuse ratio 37 Rotating biological contactor 204 Seawater wells design 62 water quality 21 Sedimentation 145, 268 Site selection 8, 47, 56 Spare parts 224, 230
Species selection 8 Specific weight (water) 88, 268, 270, 271 Storm considerations 47, 76 waves 47, 66 System biomass density 29 biomass loading 29 elevations 75, 78 layout 73 monitoring and control 193, 295 production modeling 12 setting of requirements 6, 7, 39 start-up 220, 268 Tanks head 75, 131 rearing 43, 309 Tidal elevations 47 Total dynamic head (TDH) 109, 174 Trickling filters 201,204 Ultraviolet treatment 190 Viscosity (kinematic) 91,269 Water (properties) mass density 269, 270 specific weight 88, 268, 270, 271 viscosity (kinematic) 91,269 Water hammer 86, 269 Water quality ammonia 22, 201, 281 dissolved gases 24, 25, 26, 178, 298 nutrients 20, 24 salinity 20, 22, 26, 33, 269 suspended materials 137, 291 temperature 20, 22, 26, 29, 32, 39, 151,269, 295 trace materials 21, 28 Waves (calculations) 52, 66 Wet lab design (indoors) 211,212, 230 design (outdoors) 211,215 operations 223, 230
