Beverage Industry Microfiltration

Beverage Industry Microfiltration

Beverage Industry Microfiltration

Nathan Starbard

A John Wiley & Sons, Inc., Publication

Edition first published 2008 © 2008 Nathan Starbard Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing program has been merged with Wiley’s global Scientific, Technical, and Medical business to form Wiley-Blackwell. Editorial Office 2121 State Avenue, Ames, Iowa 50014-8300, USA For details of our global editorial offices, for customer services, and for information about how to apply for permission to reuse the copyright material in this book, please see our website at www. wiley.com/wiley-blackwell. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: 978-0-8138-1271-7/2008. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Library of Congress Cataloguing-in-Publication Data Starbard, Nathan. Beverage microfiltration : a comprehensive guide / Nathan Starbard. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-8138-1271-7 (alk. paper) ISBN-10: 0-8138-1271-2 (alk. paper) 1. Filters and filtration. I. Title. TP156.F5S73 2008 663–dc22 2008013208 A catalogue record for this book is available from the U.S. Library of Congress. Set in 11.5 on 13.5 pt Times by SNP Best-set Typesetter Ltd., Hong Kong Printed in Singapore by Markono Print Media Pte Ltd 1

2008

Table of Contents

Preface

ix

1 Introduction Introduction Principles of Filtration Beverage Contaminants Plugging Component Analysis FDA CFR 21 Guidelines

3 3 6 19 31 34

2 Cartridge Filters Cartridge Filters System Operation Common Cartridge Failure Modes

37 37 72 107

3 Sheet and Lenticular Filters Filtration Media Sheet Filters Lenticular Filters Manufacturers and Distributors

111 111 116 123 129

4 Bag Filters Bag Filters System Operation Bag Filter Manufacturers and Distributors

131 131 137 140

5 Crossflow (Tangential Flow Filtration) Systems Crossflow Systems Crossflow Formats and Media System Operation

141 141 143 148

v

vi

Table of Contents

6 Filtration System Selection and Design Determining the Filtration Stage(s) Determining the Format of Filtration System Sizing Auxiliary Equipment Design and Selection Parallel Filter Skids CIP Design System Manufacturers and Suppliers

153 154 159 160 170 173 175 175

7 General Industry Filtration Processes Bottle Washing Facilities Water Steam Microfiltration in the Lab Gas Filtration Vent Filtration CIP Solutions and Chemicals

177 177 178 179 179 181 183 184

8 Wine Industry Clarification Prefiltration Final Filtration Gas and Air Filtration Specialty Applications Process Testing: Filterability (Fining) Index Miscellaneous Considerations

187 188 193 193 194 196 201 202

9 Beer Industry Clarification and Trap Filtration Prefiltration Final Filtration CO2 Filtration Specialty Applications Miscellaneous Considerations

207 208 209 210 210 212 212

10 Bottled Water Industry Clarification Prefiltration Final Filtration

215 216 219 220

Table of Contents Cryptosporidium and Giardia Control Ozonation Specialty Products Process Testing: Silt Density Index (SDI) RO and Distilled Water Bottled Water Industry Standards

vii 220 221 222 222 227 227

11 Spirits Industries Particle Filtration Microbial Filtration Emerging Products Miscellaneous Considerations

231 231 232 233 234

12 Dairy Industry Microfiltration for Increased Shelf Life Microfiltration in Conjunction with UF and RO Specialty Applications Dairy Tank Vent Filtration

237 237 238 238 239

13 Soft and Sports Drinks Industries Soft Drinks Sports Drinks

241 241 242

14 Juice Industry

245

15 Flavor, Neutraceutical, and Niche Applications Flavorings Ready-to-Drink Teas and Coffee Beverages Sucrose and Liquid Sugar or Sugar Substitute Filtration Vinegar Peppermint and Spearmint Oils Seafood Broths and Juices Honey Olive Oil

247 247 248 248 248 249 249 249 250

Appendix Bibliography Glossary Index

251 255 257 273

Preface

There is a significant lack of understanding with respect to microfiltration processes within the beverage industry. The goal of this book is to bridge this gap in understanding. The text covers the engineering basics of filtration and gives a detailed understanding of the filtration media, filter formats, equipment, sizing, and operation of microfiltration processes. Industry-specific chapters provide in-depth knowledge with respect to each of the beverage markets. The text can be used as a: • • • • •

Learning tool Troubleshooting guide Optimization guide Process selection, design, and sizing guide Reference for new applications

This is the first text completely dedicated to microfiltration within the beverage industry. Other literature can be divided into two types — both with their own failings. Technical books related to a particular industry such as winemaking or brewing usually have only a small section devoted to microfiltration. This section is usually brief and does not give a good understanding of the technology or its application. Texts written entirely on filtration are not written for the beverage industry, typically only deal with one filtration technology, and have little in the way of application-specific knowledge. In my career I have been involved in every aspect of beverage microfiltration; first in academia with microfiltration-specific research and projects, then in industry — managing one of the largest beverage microfiltration departments and, finally, as a technical expert and beverage market manager for one of the leading filtration supply companies. ix

x

Preface

It is my goal with this text to not only provide a resource for engineers and production managers, but also for the operators who deal with filtration processes on a day-to-day basis, small producers who may not have much in the way of technical resources, and for academics and industry groups working with the industry and looking for new solutions and improvements to beverage processes.

Beverage Industry Microfiltration

Chapter 1 Introduction

Introduction Microfiltration has become a critical process in beverage manufacturing. Many beverage manufacturers do not have a clear understanding of microfiltration processes and the technologies behind them. This book is meant as a comprehensive guide to help beverage industry professionals with the understanding, selection, operation, and optimization of microfiltration stages in their plants and processes. There are major beverage manufacturers that have spent time optimizing their microfiltration processes and, as a result, are several times more efficient than comparably sized competitors in the same field. The overall operational savings that result can represent tens of thousands to hundreds of thousands of dollars. Improvements may be realized not only in direct filter spending but also with regard to product yields, downtime savings, operator usage, utilities, and so forth. This guide is meant as a comprehensive guide and learning tool with regard to microfiltration in the beverage industry. Processes vary considerably, so it is up to each person, plant, or organization to develop data and procedures relative to their own application. Views and opinions expressed in this document are those of the author and are the result of his personal experience gained through extensive work with beverage filtration processes. This work does not make any claims or representations and is not meant to replace direct engineering support. Beverage microfiltration is unique in that it falls between two vastly different groups of microfiltration processes. The biopharmaceutical market is, in terms of spending, the largest end-user of microfiltration technology. The filters and the filtration processes within the biopharm sector must undergo extensive validation and research. Regulatory agencies demand strict compliance and oversight of filtration processes 3

4

Beverage Industry Microfiltration

employed within drug and comparable biopharm processes. The filters used in biopharmaceutical plants can easily reach three to four times the cost of a comparable filter used elsewhere. Out of necessity, filtration is very well understood and is considered a major process step in most biopharm plants. Industrial users of microfiltration, including producers of paints, adhesives, chemicals, etc., use the most filters in terms of units; however, the filters they use are much less refined, considerably cheaper, and are treated as commodity items. Filters remove general debris; there are typically no microbial or health concerns and detailed attention is rarely paid to a well designed, understood, and optimized filtration process because the benefits of doing so are minimal. The beverage market does not manufacture high-value goods like the biopharmaceutical industry does. Most beverage plants cannot afford to spend millions of dollars on filtration. Many beverage production volumes are considerably higher than other industries due to sheer consumption rates. Although subject to some regulatory oversight, oversight of the beverage industry, particularly with regard to filtration, is in no way on par with the oversight associated with biopharm. Beverages are subject to health and spoilage concerns, and producers must deal with consumers who expect much higher quality from their drinks than they do from a can of paint or a tube of glue. Failure to remove harmful microorganisms from a susceptible beverage can be disastrous, even deadly. Microorganisms that cause product spoilage can be financially damaging. Most industrial products can still be sold after a failed filtration stage; most beverages cannot. This has created a situation where the beverage industry requires a semi-validated quality product that can be consistently relied upon to perform its targeted function. The product cannot be so highly designed and validated, however, that the costs aren’t in line with the market. Of the five major microfiltration suppliers in the beverage market, Pall, Cuno, and Domnick Hunter’s total business tends to lean more toward the industrial side, whereas Millipore and Sartorius have much more of a biopharmaceutical focus. The costs and quality of their filtration products typically reflect this divide. Pall may be considered the best-rounded of the five companies in terms of business focus, but the companies all meet in the center of the divide to compete in the beverage market. They are joined by countless smaller filtration companies as well as resellers and distributors.

Introduction Microfiltration

Microorganisms Suspended Particles

Ultrafiltration

Macromolecules

Nanofiltration

Sugars Divalent Salts Dissociated Acids

Reverse Osmosis

Monovalent Salts Non-dissociated Acids

5

Water

Figure 1.1.

Various filtration mechanisms.

Purposes Microfiltration often serves as a critical step in ensuring final product integrity. Microorganism removal is essential to beverages in which contamination can lead to consumer illness, as well as to those beverages susceptible to microbial spoilage mechanisms. Beverages that are not in danger from microbial contamination may undergo microfiltration for general particulate removal to ensure the aesthetic quality of the final product. Figure 1.1 depicts the different removal characteristics of fine filtration processes. Microfiltration serves many auxiliary functions throughout the beverage industry in addition to final product filtration. Ensuring process water quality can be crucial to general plant cleaning and sanitation regimens. Gases, such as carbon dioxide, are being used in many product formulations. Bulk or point-of-use filtration of these gases is often important to maintaining product quality. Selective use of microfiltration can lead to a faster, easier, and more economical process. Brewers can use microfiltration for both lees recovery and as an alternative to pasteurization. Wineries may use microfiltration for tartrate removal. Whiskey makers can remove chill haze using a filtration step. Ceramic crossflow systems allow the cleaning and reuse of caustic solution. Each plant’s individual processes, even within the same industry, may have its own uses for microfiltration. The bottled water and wine industries are the largest beverage microfiltration users in terms of spending. They are followed by the beer, spirits, and soft drink industries. Other industries that use microfiltra-

6

Beverage Industry Microfiltration

tion include juice, sports drink, energy drink, coffee and tea, neutraceutical, oils, as well as various liquid or semi-liquid product or component producers. Capabilities Microfiltration systems can be built to a process or application. There are practically no removal, size, or flow rate limitations. Oftentimes a single stage system is suitable, while other times one or more stages using several different housings or filtration formats must be used. The primary limitation of microfiltration systems is usually the service life of the filter and its associated change-out costs. More refined forms of microfiltration devices, such as membrane filter cartridges, can be hundreds of times more expensive than other filter formats, such as bag or sheet filters. It therefore becomes critical to have a multi-tiered filtration system that combines various filter media that work together in order to achieve the most economic filtration process. Filter service life is further extended through proper design, operation, maintenance, cleaning, and/or filter regeneration. The difference in operating costs between an optimized filtration process and an un-optimized filtration process can sometimes be the deciding factor in whether or not to implement microfiltration. With adequate knowledge of microfiltration processes and technologies, a facility can greatly improve the economics of filtration and may be able to implement further procedures benefiting the entire production process. Principles of Filtration A basic understanding of fluid dynamics and the mechanics of filtration can be extremely helpful when both designing and operating a beverage filtration process. It is important to understand flow dynamics, filter removal mechanisms, the differences among filtration media, as well as the contaminants being removed. Basic Fluid Dynamics of Filtration A fluid is a substance that conforms to its container. Fluids may be either incompressible, such as liquids, or compressible, such as gases. A driving force is required in order for a fluid to flow. Driving forces

Introduction

7

are based on the differences in physical parameters surrounding or involving the fluid, such as pressure, temperature, or concentration. Pressure is usually the key driving force in microfiltration. Pressure gradients can be created via height, mechanical pumps, or the positive or negative compression of a gas. Pressure is expressed most commonly in the English unit of pounds per square inch (psi) or its metric equivalent of bar or mbar. Atmospheres (atm), Pascals (Pa), or inches of water/mercury may also be used to express pressure. A value known as gauge pressure is sometimes used for liquid filtration and corresponds to the pressure in addition to atmospheric pressure. Absolute pressure — pressure relative to zero — is often used in gas filtration. Pressure Differential (Pressure Drop) across a Filter During normal flow liquid filtration the driving force used to push liquid through the filter is the pressure differential across the filter. Differential pressure or pressure drop is defined as the inlet (upstream) pressure minus the outlet (downstream) (See Figure 1.2) pressure as given by Equation 1.1. There will always be a differential pressure across a filter when there is some flow. ΔP = PIn − POut

(1.1)

In most crossflow filtration processes (also called tangential flow or TFF) the driving force is the transmembrane pressure. A principle similar to normal flow differential pressure, the transmembrane pressure is basically a correction for the fact that there is a pressure loss

Filter

Inlet Feed Upstream

Retentate

Figure 1.2.

Filter flow terminology.

Outlet Downstream Permeate Filtrate

8

Beverage Industry Microfiltration

on the feed side due to the tangential feed and retentate flow. The upstream pressure is the average of the feed pressure and the retentate pressure and is determined by Equation 1.2. PUpstream =

PFeed + PRetenate 2

(1.2)

Substituting the expression for upstream pressure into that for differential pressure yields the expression for the trans-membrane pressure (Equation 1.3). Transmembrane Pressure =

PFeed + PRetentate − PPermeate 2

(1.3)

For gases, the mass of the gas depends on the pressure of the gas. This means that the gas flow through the filter will depend on the gas pressure, because different pressures will have different masses. If all else is kept the same, there is typically a linear relationship between differential pressure and flow rate: • When flow rate increases, the differential pressure will increase. • When flow rate decreases, the differential pressure will decrease. In conditions where the filter is impacting the pump and flow rate, it is possible to see the following relationships: • When differential pressure across a filter increases, flow rate will decrease. • When differential pressure across a filter decreases, flow rate will increase (provided pumping capacity is available). A common example of this situation is a centrifugal pump feeding a bottling line. As the filter plugs and differential pressure increases, the flow rate to the bottling line will gradually decrease until there is no longer adequate flow to maintain the process. As any bottling manager knows, the flow rate is a limiting factor for many processes, so a filtration run will not only be limited by how much filter capacity is left, but also by how much flow it is capable of supplying to the downstream process. Pressure drop is a key factor when determining the filter area

Introduction

9

of a system during design. If a process’s flow rate is to be maintained at 200 gpm (45,420 lph), then the filtration area and pump that can supply that flow with an appropriate pressure drop should be selected. Fluid Viscosity The viscosity of the fluid is an important factor affecting pressure drop and fluid flow and should be taken into consideration. Increases in viscosity will increase the pressure drop. At a constant pressure, the viscosity will have a directly linear relationship on fluid flow rate through the filter. Generally, at a constant pressure, if the viscosity is doubled, the flow rate will be halved. If the viscosity is halved, the flow rate will be doubled. An example of this can be seen in comparing water and oil. Water will flow through a filter at upward of 50–70 times the flow rate of oil running through the same filter at the same differential pressure. A cold fluid will have a higher viscosity than the same fluid when heated. This can be significant. The viscosity of water will change about 4.5% per degree F (about 2.5% per degree C). Most solvents, such as alcohols, will have a lower viscosity than water. Some highly viscose products, such as maple syrup, will require heating in order to properly flow through a filtration process. Changing the temperature of a process stream will change the pressure drop per filter at a given flow rate. This is due to the increased viscosity of a cooler process stream versus a warmer one. The change, for example, from a 75 F (24 C) beer stream to one that is 36 F (2.2 C) is enough to result in up to a 75% increase in differential pressure through some wrapped, depth trap or prefilter cartridges given the same flow rate. This can have dramatic effects on system sizing. In certain open depth filters the viscosity may not always have a directly linear relationship to pressure. In this instance, a viscosity versus pressure drop chart or other data should be supplied by the filter manufacturer. Flow Rate Flux is a value used to normalize the flow rate for filters or filtration systems with different filtration areas. It is defined as the flow rate

10

Beverage Industry Microfiltration

per unit of surface area. Flux units would be expressed as l/min/m2 or gal/min/ft2 and can be obtained by simply dividing the flow rate by the filter’s surface area. The term “face velocity” is sometimes used within the filter industry to mean flux. Face velocity can be specified per filter device, such as l/min/cartridge. Lowering the filter flux or face velocity will have a positive effect upon the filter’s throughput, overall service life, and performance. Particles are removed more easily from slowmoving streams. Colloidal matters tend to more efficiently block pores at higher process speeds. Flux and face velocity are important considerations during both the design and operation of filtration equipment. Flux is used to calculate filter permeability. The permeability for normal flow filtration is expressed by Equation 1.4. Permeability =

Flux ΔP

(1.4)

The permeability for tangential flow filtration is expressed by Equation 1.5. Permeability =

Flux Transmembrane Pressure

(1.5)

Pore size will impact flow rate. A tighter pore size will increase the differential pressure given the same flow. Because of this interaction, caution should be taken when tightening down the pore size rating of a particular filtration stage. Tightening a pre-bottling filter from 1.2 μm to 0.45 μm, for example, will increase the differential pressure compared to what it had been previously. Filtration housings or pumps may have to be modified as a result. Adding depth will increase the differential pressure and, as a result, reduce flow. This means that changing a 0.5 μm surface filter to a 0.5 μm wrapped, depth filter will increase differential pressure and restrict flow. The flow equation is expressed in Equation 1.6. Flow =

(ΔP )( r )( A)(T ) (V )( L )

ΔP = Differential Pressure ρ = Pore Size

(1.6)

Introduction

11

A = Area T = Temperature V = Viscosity L = Path Thickness Pump Selection Pumps used for the filtration of beverages are either positive displacement or centrifugal. Centrifugal are common for large-scale applications. Positive displacement (PD) pumps, of which there are several types, such as rotary, peristaltic, or diaphragm, are more common for smaller applications and for such uses as chemical addition, laboratory functions, or small product batches. If a PD pump is being used for larger applications, such as filtration skid feed, it should be normally of the rotary type. The main operating difference between the two pump types is that centrifugal pumps are affected by pressure, whereas positive displacement pumps are not. As the differential pressure of the filtration stage increases, the efficiency of the centrifugal pump will decrease. The decrease in efficiency causes the flow rate supplied by the pump to decrease. Centrifugal pumps used as filtration feed pumps must be sized accordingly so that the pump can maintain the required outlet flow rate minimum up to the point (pressure) at which the filtration stages are completely plugged. This includes when there are multiple filtration stages and it is necessary to achieve the maximum throughput per filtration run. The efficiency of a positive displacement pump remains relatively the same as outlet pressure increases. An automatic pressure relief line should be installed to relieve pressure build-up if a PD pump is selected. Many processes or equipment skids will have this automatically built in. Fluid pulsation, often caused by PD pumps, also needs to be mitigated.

TIP Running a carbonated product with a centrifugal pump? If the process or line is running poorly and/or operating in hot weather, the carbon dioxide can come out of the solution in the product line. This will cause pump cavitation and lead to a loss of Continued

12

Beverage Industry Microfiltration

flow. The pump will need to be bled off and restarted. If this is a problem, try the following: • Decrease the length of hose or piping to the suction of the pump. • Elevate the hose or piping on the suction side of the pump. • Try to avoid allowing the product to sit for prolonged periods of time or to heat up.

Water Hammer and Pulsation Rapid closing of valves, certain types and operation of pumps, and vertical piping can all create pressure spikes that can severely damage filters, o-rings, gaskets, and other equipment. Water hammer is a result of the fact that liquids are incompressible and therefore any energy applied to the fluid is transmitted. Water hammer is essentially a rapid change in liquid velocity. Flow rapidly stopping, starting, or changing direction can all lead to water hammer. The most common cause is the rapid closing of a valve. The rapid closing of a valve can lead to a pressure spike as high as five times the normal operating pressure and can be calculated via Equation 1.7. PShock =

(0.070)( L )(V ) ( t + PInlet )

(1.7)

Pshock = Increase in pressure L = Length of upstream piping V = Velocity of flow t = Valve closing time PInlet = Inlet pressure Pulsation most often occurs as a result of positive displacement pumps as the liquid accelerates and decelerates. Pulsation can be observed as vibration and can lead to pressure spikes many times the normal flow pressure. Pulsation dampeners or surge suppressors — nothing more than a pressurized vessel filled with a gas — is one method of controlling the effects of pulsation.

Introduction

13

Particle Separation The particles and mechanisms by which they are removed can have a significant effect upon filtration process performance. It is always recommended to perform a detailed analysis of plugging components and particles contained within the feed stream at the onset of designing or altering a filtration process. It is relatively easy to determine the type and size of particles, and this information can be paired with trial data to determine the mechanism(s) by which the particles are being removed and/or are plugging the filter. Knowledge of particulates is also valuable in the determination of a proper filter cleaning or regeneration regimen, when applicable. Particle Types Particles can essentially be broken down into two primary categories: 1. Hard (non-deformable) particles such as dust, sand, DE, and metal fines 2. Soft (deformable) particles such as gels, colloids, microbes, clay, and carbohydrates Soft deformable particles are more difficult plugging agents than hard particles. This is because soft particles generally plug a filter via a pore blockage model, while hard particles will be more prone to plug via cake formation at the filter’s surface (See Figure 1.3). Cake formation leaves channels that, while restricting some flow, will still allow for some flow through the filter for a longer period of time. Soft particles such as gels, colloids, proteins, and gums exhibit higher fouling than microorganisms.

Hard Particle Caking

Figure 1.3.

Soft Particle Caking

Hard and soft particles exhibit different caking mechanisms.

14

Beverage Industry Microfiltration

Particle Removal Mechanisms There are six commonly recognized capture mechanisms for dealing with gases and liquids in microfiltration processes: 1. Adsorption — Removal via attractive forces between the particles and the filter matrix 2. Size exclusion or sieving — Removal of particles that are larger than the filter openings (removal at the surface) 3. Interception — Removal of particles as they flow through the filter matrix (removal within the depth) 4. Diffusion — Removal that occurs when particles move in a way as to increase their probability for a collision with the filter matrix 5. Gravitational settling — Separation when particles settle out of a moving stream due to gravity 6. Inertial impact — When a particle’s inertia causes it to be impacted on the filter matrix as flow is diverted around the filter The main capture mechanisms of a liquid filter are size exclusion, interception, and adsorption. Absolute membrane filtration is determined mostly based on size exclusion. Gas filters operate on size exclusion, diffusion, inertial impaction, and adsorption. The types of removal mechanisms employed will change based on particle type, size, and flow speed. Slow-moving streams with large particles will be more susceptible to gravitational settling, for example. Membrane Filter Plugging Every process stream will plug in a different manner. No plugging model has ever been developed that can be applied to all filter types in all processes. There are three primary models that can be used to describe filter plugging: 1. Gradual Plugging — Pores progressively plug as more volume flows through the filter and particles are removed. Gradual plugging is usually characterized by materials building up in the pores of the membrane. 2. Complete Blocking — A particle completely blocks one or more pores. Plugging is often at the surface and completely restricts flow through the pore(s).

Introduction Complete Pore Blocking

Figure 1.4.

Gradual Pore Blocking

15 Particle Caking

Pores may be blocked by one, two, or three mechanisms.

3. Particle Caking — Particles build up on the surface of the filter, not always completely blocking the pores, often leaving channels available for flow. The three methods of pore blockage are shown in Figure 1.4. It is much better for a stream to operate in a particle-caking mode than in a gradual or complete blocking mode. Plugging of filters, in reality, actually occurs by combinations of these mechanisms and usually with a great degree of randomness. Hard particles often form a cake on the surface of the membrane. This is one reason why membrane crossflow technology is increasingly being used for the rough clarification stage in certain beverage processes. The cake formed on the filter can be removed by creating fluid flow along the surface of the membrane rather than perpendicularly into it. Soft and deformable particles are more likely to completely or gradually block the membrane pores. Filter manufacturers will typically size new membrane systems based on the gradual pore-plugging model. Membrane filters are more likely to filter smaller soft and deformable particles, such as bacteria, colloids, clays, and carbohydrates, when there are upstream clarification and prefiltration steps to remove a majority of the hard particles, such as fines, silt, or general debris. Zeta Potential Zeta potential is a term that mostly relates to sheet and lenticular filters. When a depth filtering matrix is charged (normally positive for beverage filtration), oppositely charged particles will adhere better to its surface. Most particles that are removed in wine and beer filtration are

16

Beverage Industry Microfiltration

negatively charged. A problem with Zeta potential is that it takes time for it to establish and is disrupted when flow stops. It is possible for particles that were retained via this mechanism to be released when the filtration stops and restarts again. Some cartridge-style depth filters can have a slight Zeta potential effect, but this is less of a factor than when dealing with sheet or lenticular filters. Filter Efficiency and Beta Ratio Filter efficiency is sometimes reported in terms of Beta ratio (β). A filter’s Beta ratio relates to the filter efficiency through Equation 1.8. %Efficiency =

b −1 × 100 b

(1.8)

The Beta ratio is calculated based on Equation 1.9. bx =

P ( x )Upstream P ( x ) Downstream

(1.9)

β x = Beta ratio for particles of size “ X ” P(x) Upstream = Number of particles of size “ X ” upstream of the filter. P(x) Downstream = Number of particles of size “X” downstream of the filter Example A retention test is run. A filter retained 3,000 of 9,000 initial particles. b=

9, 000 =3 3,000

The Beta ratio is 3. % Efficiency =

3 −1 × 100 = 67% 3

The filter’s efficiency in this instance is 67%.

Introduction Table 1.1.

17

Example removal efficiency test data.

Particle pore size (μm)

Initial particles

Ending particles

Removal efficiency at pore size

0.22 0.45 0.65 1.0 2.0 3.0 5.0

5 5 10 10 10 10 50

5 2 1 0 0 0 0

0.00% 60.00% 90.00% 100.00% 100.00% 100.00% 100.00%

Total

100

8

92.00%

A filter will have a Beta ratio at each pore size rating, and it is important to assess the entire range. Be wary if only a single Beta ratio or efficiency is presented. Challenge and retention tests are often used to convey a message that is incorrect. Table 1.1 illustrates some theoretical retention test data. One could legitimately make the following statements regarding the challenge test presented in Table 1.1: • The filter has a 92% efficiency at 0.22 μm and above. • The filter has 97% efficiency at 0.45 μm and above (considered absolute by some). • The filter has 60% removal efficiency of 0.45 μm particles. • The filter has absolute retention at 1.0 μm and above. • The filter has zero retention at 0.22 μm. By contrasting the first and last statements, it is easy to see how challenge test data can be used misleadingly. In looking at the actual data, it is clear that no particles are being retained at 0.22 μm, and that only 60% of the particles are retained at 0.45 μm. There are instances similar to this in beverage industry documents. Actual data can be even more difficult to decipher and misleading, as there will not be 100 particles, but many thousands in some instances. Most manufacturers will have this data to provide. Depth-style filters are much more susceptible to this type of “creative marketing” than are membranes, but there is no standard set of rules when dealing with any filter.

18

Figure 1.5.

Beverage Industry Microfiltration

An SEM characteristic of depth media.

General Filter Structure Depth filter media is a random porous structure that retains particles as they pass through the tortuous and irregular flow paths. A magnified image of this type of structure is shown in Figure 1.5. The way this type of microfiltration works is similar to the way a diatomaceous earth or sand filter operates. Sheet filters, lenticular filters, bag filters, and some cartridge filters function as depth filter media. Those cartridge filters that function predominantly as depth filters are typically of either a wrapped or wound format. Cartridge filters may use non-membrane media that filter at the surface. These filters are made from materials similar to those used in depth filters and are constructed by laying multiple layers of filter media together on a support structure. The media is then pleated to increase surface area. Particles are usually retained at the surface of the media, but are also retained within the matrix of layers. They are more retentive than depth filters, less retentive than membrane filters, and have a dirt-holding capacity that is less than depth filters but greater than membrane filters. Table 1.2 shows the differences between the three types of cartridges. A membrane filter is a thin layer of a regular, porous structure. This type of structure is shown in Figure 1.6. Membranes operate mainly at the filter surface and have less dirt-holding capacity than depth or non-

Introduction Table 1.2.

Cartridge filter media attributes.

Filter type Depth Surface (non-membrane) Membrane

Figure 1.6.

19

Primary removal location

Dirt-holding capacity

Retention

Cost

Depth Surface

Highest Medium

Lowest Medium

Lowest Medium

Surface

Lowest

Highest

Highest

An SEM characteristic of membrane media.

membrane surface filters. Membrane filters can have absolute particle retention at a specified pore size rating. Production-scale membranes are available in cartridge format and as the filter media used in crossflow microfiltration systems.

Beverage Contaminants Particle sizes are expressed in terms of microns (micrometers, μm) for extremely fine filtration processes such as microfiltration. One micron equates to 10−6 meters in length, or one millionth of a meter. This corresponds to 0.00003937 inches. Common conversions are shown in Table 1.3. A human hair is about 100 microns in diameter. Microfiltra-

20 Table 1.3.

Beverage Industry Microfiltration Comparative particle size conventions.

U.S mesh

Inches

Centimeters

Microns (μm)

10 12 14 16 18 20 25 30 35 40 45 50 60 70 80 100 120 140 170 200 230 270 325 400

0.0787 0.0661 0.0555 0.0469 0.0394 0.0331 0.0290 0.0232 0.0197 0.0165 0.0138 0.0117 0.0098 0.0083 0.0070 0.0059 0.0049 0.0041 0.0035 0.0029 0.0024 0.0021 0.0017 0.0015

0.1999 0.1679 0.1410 0.1191 0.1001 0.0841 0.0737 0.0589 0.0500 0.0419 0.0351 0.0297 0.0249 0.0211 0.0178 0.0150 0.0124 0.0104 0.0089 0.0074 0.0061 0.0053 0.0043 0.0038

2000 1680 1410 1190 1000 841 707 565 500 420 354 297 250 210 177 149 125 105 88 74 63 53 44 37

tion is technically considered filtration in the 0.1 to 10 μm range but, in practice, is often thought of as dealing with particulates up to 100 μm. Generally speaking, particles under 100 μm will require some type of media filtration. Particles over 100 μm can be removed via screens or similar mechanisms. It is important to recognize the types and sizes of particulates and microorganisms when designing and running a microfiltration process. Figure 1.7 is an example of a filtration spectrum showing common materials relative to their pore size. Microorganisms There are many different microorganisms that can be present in beverage products or process streams. A stable, safe product usually requires

Introduction 0.01 µm

0.1 µm

21

1.0 µm

10 µm

100 µm

Bacteria Virus

Yeast Crypto

Colloidal Silica Gelatin Tobacco Smoke

Human Hair

Giardia

Pollen Red Blood Cells Diatomaceous Earth

Smallest Visible Particle

Figure 1.7.

Filtration spectrum of common materials.

the removal of these microorganisms. Producers of some beverage streams, such as highly alcoholic products, will not have to worry about microorganisms while others, such as producers of bottled water, must be very concerned with the health and quality aspects of incomplete removal. The microbial concerns for wineries and breweries are typically related more to shelf life than to health concerns. These concerns are equally as important to address. Protozoa Protozoa are single-celled eukaryotes. The word protozoa comes from the Greek for “first animals.” Protozoa are sometimes classified with animals based on certain characteristics. They can also be classified with certain algae and molds, or even be considered to be their own kingdom. Protozoa are usually quite large (Table 1.4) in comparison to most microbial contaminants found in beverages, and as such they are easily removed. The two most common protozoa of concern are Cryptosporidium and Giardia; images of these are shown in Figure 1.8. Failure to remove these organisms from susceptible beverages, such as bottled water, can be fatal to the consumer. Outbreaks within both bottled and drinking water supplies have led to several guidelines being

22

Beverage Industry Microfiltration Table 1.4.

Cryptosporidium and Giardia sizes.

Protozoa

Size (μm)

Cryptosporidium parvum Giardia lamblia

4–6 8–12

Giardia lamblia

Cryptosporidium parvum

Figure 1.8. Cryptosporidium and Giardia are hazardous microorganisms found in water. Photo Credit: H.D.A. Lindquist, U.S. EPA.

developed for the removal and/or elimination of dangerous protozoa. The relative difficulty in detecting Cryptosporidium and Giardia, and their resistance to some chemicals, has made the use of filtration a common recommendation for ensuring product safety. Despite their larger pore size, a 1.0 μm absolute rated filter, often a membrane, is recommended for the complete removal of Cryptosporidium and Giardia. Cryptosporidium and Giardia are typically found in surface waters or waters that have been exposed to the outdoors environment; they are not found in spring or mineral sources unless there has been some type of contamination or the water is subject to runoff or open-air collecting. Mold and Fungi Fungi are eukaryotic organisms, and mold is a form of fungus. There are thousands of types of molds and even more types of fungi. Most species are fairly large with respect to beverage microfiltration. The

Introduction

23

typical particle size is larger than 3 μm. Although some species are in the 1–2 μm range, some are bigger than 10–15 μm. Mold and fungi are commonly introduced to many beverages by way of product packaging materials, such as containers or closures. This can make filtration of the liquid product ineffective at completely ensuring final packaged product quality. Water used to rinse corks, caps, bottles, and so forth should be rinsed with water that has either been filtered or dosed with a chemical agent. It is common for quality-control personnel to immediately look at the filtration train when microbes are present in the final bottled product. Rather, the entire operation and all final components should be assessed from the beginning to ensure total quality. Algae Algae may be broken into two groups; prokaryotic and eukaryotic. The only prokaryotic algae, blue-green algae, are actually more accurately represented as a division of bacteria. The correct name for blue-green algae is Cyanobacteria. The classification confusion results from the fact that Cyanobacteria derive their energy from photosynthesis, just as plants do. Eukaryotic algae have many different forms, ranging from mono-cellular organisms to complex multi-cellular organisms such as seaweeds and kelps. Forms of eukaryotic algae include red, brown, green, glaucophytes, euglenids, chlorarachniophytes, chromista, and dinoflagellates. Algal blooms can be troublesome in some processes, particularly with bottled water, or when contaminated water is untreated and added to a susceptible product. Many municipal water supplies have frequent algae issues, but most beverage processing plants and facilities never develop problems with algae. Generally speaking, those plants with frequent algae problems must enact countermeasures against them and be prepared for periodic, or sometimes frequent, incidents. Plants that have no history of algae problems will not likely develop them unless there is a significant process or supply change. In addition to being susceptible to UV, algae can be removed via microfiltration. A 1.0 μm absolute filter will certainly remove any algae that may be present. Large-micron depth filters in the 2–5 μm nominal range are also effective at algae removal but can present problems related to grow-through and contaminant unloading if not properly maintained. For a plant trying to control algae, it is best to do so as far upstream as possible.

24

Beverage Industry Microfiltration

Filters should be located at the product or component entry point into the plant to avoid algae contamination and growth in other equipment such as RO filters or carbon towers. Microfiltration or some rough form of particulate removal prior to a UV stage helps to improve the UV performance. This is because the particulate matter in the stream absorbs some of the UV light and can shield the microorganisms. Yeast Yeasts are technically fungi, as are molds, mushrooms, and comparable organisms. For the purposes of beverage microfiltration, yeasts are largely thought of as a separate grouping of contaminants. This is partially because yeasts are among the smallest fungi, so their removal typically requires a specific filter selection. Yeasts are considered unique because of their significant presence in many processes. Yeasts are an essential component to fermented beverages and can be present in huge quantities both in the product and in the general production facility in such places as hoses, product lines, drains, and so forth. There are many different types of yeast relevant to the beverage industry. Many of the strains and genera are closely related to one another, with some being hybrids of others. In addition to the yeast strains that are either naturally present or are intentionally added, there are many strains that can be incidentally introduced and are harmful to the consumer or product. Some yeasts are considered pathogenic. The manner by which yeasts are classified is shown in Figure 1.9. The family Saccharomycetaceae contains 24 genera. Three genera stand out with regard to beverage processing, especially with fermented beverages: • Saccharomyces • Dekkera (Brettanomyces) • Zygosaccharomyces The genus of Saccharomyces contains nearly two dozen different species of Saccharomyces strains. Several are important to the beverage industry. Saccharomyces cerevisiae are oval shaped and about 5– 10 μm in diameter. It is the most common strain used industrially and is used to make beer, wine, and bread. In beer fermentation, it is normally used to make ale and stout and is considered “top” fermenting

Introduction

25

Family (Example: Saccharomycetaceae)

Genus (Example: Saccharomyces)

Species (Example: Saccharomyces cerevisiae)

Figure 1.9.

Yeast are classified according to Family, Genus, and Species.

yeast for the manner in which it separates within the fermentation tank. Saccharomyces uvarum is closely related to Saccharomyces cerevisiae. It is used in the fermentation of some lagers and is called a “bottom” fermenting yeast due to the way in which the yeast settles to the bottom of the tank after the fermentation process is complete. Saccharomyces pastorianus is another bottom-fermenting lager yeast. Saccharomyces bayanus is yet another species within the Saccharomyces genus. It is commonly used for wine and cider fermentation. Zygosaccharomyces is another genus within the Saccharomycetaceae family. It is a common spoilage-causing yeast within beverage processes. Zygosaccharomyces has a high tolerance for both alcohol and sugar and is able to withstand environments of 18% and 50–60%, respectively. It is also tolerant of sulfur dioxide, sorbic acid, and benzoic acid. There are about a dozen strains of Zygosaccharomyces. Brettanomyces (as it is commonly known), formally called Dekkera, is another genus contained within the Saccharomycetaceae family. Brettanomyces has six strains and is considered both a favorable component and a spoilage mechanism within winemaking and brewing. Even when intentionally used during wine or beer production, it is usually kept at low quantities and filtration is often used to remove the yeast before too many sensory-altering compounds are produced. The recommended pore size ratings for various yeast removal applications are given in Table 1.5.

26 Table 1.5.

Beverage Industry Microfiltration Recommended membrane pore sizes for yeast removal.

Yeast

Recommended Membrane Removal Size (μm)

Saccharomyces Zygosaccharomyces Brettanomyces

0.65 0.65 1.0

Table 1.6.

Recommended membrane pore sizes for bacteria removal.

Bacteria

Recommended membrane removal size (μm)

Brevundimonas diminuta Pseudomonas aeruginosa Bacteriophage Escherichia coli Leuconostoc oenos Pediococcus damnosus Lactobacillus hilgardii Oenococcus oeni Lactobacillus brevis

0.22 0.22 0.22 0.45 0.45 0.45 0.45 0.45 0.45

Bacteria Bacteria are the most abundant form of life on the planet. There are many dozens of different species that can be found within agricultural and beverage processing. Some of the most relevant bacteria species are given in Table 1.6 along with the required membrane pore size for absolute-rated removal from a beverage stream. Some bacteria are deliberately added to a process. Malolactic fermentation of wine is one such instance. Yogurt and cheese production, through the addition of lactobacillus species, is another common example. Industries that use bacteria within a process can encounter particularly difficult challenges in subsequent processing steps, when controlling those organisms can become critical. All bacteria can be removed through the use of a 0.22 μm membrane filter. Some industries, such as wine and beer, find that they only need to filter to 0.45 μm in order to remove bacteria of concern.

Introduction

27

Miscellaneous Organics Various organic contaminants can be present in many streams. This is often true for products that are originally plant based, such as wine and beer. These organics are typically soft, deformable particles, which can be highly plugging in nature. They are much like microorganisms in that they are fairly easily removed from filters during cleaning and regeneration through the use of hot water and/or chemical treatments. Plant-Based Organics There are many plant-based organics that can cause membrane plugging or decreased product filterability. Pectins, a heterosaccharide found abundantly in wine and juices, are a common plugging agent. Pectinase additions can be used to mitigate their effects. Pectins are intentionally added to certain beverages, which increases viscosity and decreases the filterability of the product. Pectins may be precipitated out by adding certain tannins to the product. This is used in some processes in which pectins cause rapid plugging of filters. Lignin, often resulting from some aging processes, can be found on membrane filters in alcoholic beverage industries. This is not surprising for beverages aged in wood, since lignin comprises from 1/4 to 1/3 the dry mass of wood. Carbohydrates can interact with materials present in a process stream to form a precipitate or to facilitate plugging. This is often observed in products such as wine coolers and premixed alcoholic beverages. Sugar crystals must be filtered from sugar syrup additions; sugar crystal filtering is the primary microfiltration application in the soft drink industry. Glucans are a form of complex carbohydrate. Beta-Glucans are very problematic in beer filtration and often require the addition of beta-glucanase enzyme to either the beer stream being filtered or the filter housings during cleaning procedures. Cellulose is also a form of carbohydrate. Proteins Proteins and protein hazes are common in many beverages. Oftentimes, these hazes are precipitated through interaction with other materials such as various ions or carbohydrates. Proteins and carbohydrates may interact to form effective plugging agents. Proteins may be present on filters as a result of microbiological activity. This is not always the case,

28

Beverage Industry Microfiltration

but the possibility should be understood when presented with a plugging component analysis. Chill hazes in beer are a result of the amount of high-mass proteins. The amount of chill hazes present in a product can therefore be linked all the way back to the grain selected for production. Miscellaneous Inorganics Inorganic contaminants are extremely diversified and can range from sand to processing aids to the minerals present in water supplies.

Several processes, such as bottled water and soft drinks, use various flocculents and coagulation agents for the pretreatment of water. These agents can be extremely effective plugging agents and can even rapidly block open pore size rated depth microfilters. If it is necessary to use one of these materials, and microfiltration is a downstream process, it may be necessary to first filter through a different filtration mechanism such as a sand filter.

Diatomaceous Earth (DE) Diatomaceous earth (DE, kieselguhr, or diatomite) is one of the most common medias used for large-scale industrial beverage filtration. Beer processed on a large scale is clarified almost exclusively on DE filters. Wineries and juice manufacturers are also heavy DE users. Diatomaceous earth consists of fossilized diatoms, which are ancient, hard-shelled algae. It is mined, then milled and graded for a particular application. DE used in beverage filtration is usually of a very fine grade in comparison to DE used for other applications. DE usage is being regulated increasingly across the world. The quality of worldwide DE is steadily decreasing as quantities are mined. These two issues have raised many concerns about the long-term use of DE filtration in the beverage industry. Facilities may use different grades of DE in their processes depending on the starting product clarity and desired end product clarity. The particle size distribution for a common filtration grade DE is given in Table 1.7. The particle size distribution will shift slightly based on the grade of DE used and by manufacturer or mining location.

Introduction

29

Table 1.7. Size distribution for common filtration grade diatomaceous earth. Typical medium-fine grade Size (μm)

Wt % below size

1 2 3 4 6 8 12 15* 24 32 48 65 96 125 200

2 4 5 8 15 22 36 50 65 75 87 92 97 99 100

* median particle size of 15 μm.

It can be seen that DE has a wide range of particle sizes even within a single grade. Many trap filters for DE fines removal are in the 1–4 μm range; however, even high efficiency trap filtration down to 1 μm can still allow some fines to progress downstream. Carbon Fines Carbon fines can be a difficult problem for many beverage facilities. While removing color or contaminants from the product, the carbon itself can become a contaminant. Many facilities will microfilter prior to bottling in order to remove carbon fines from the product. It is actually more efficient to locate the filtration directly after the carbon tank or carbon filtration step. This prevents a build-up of fines in the subsequent tanks and piping. The amount of carbon fines leaving a carbon tower will often increase after cleaning, particularly steam cleaning, and towers should be thoroughly flushed afterward. The majority of carbon particles will be sized in the hundreds of microns, but fines in the single-digit micron range can be present or generated.

30

Beverage Industry Microfiltration

Bentonite Bentonite is a fining agent most commonly used in wineries. Bentonite is an extremely efficient plugging agent — so much so that it is one of the most common materials used by filtration companies to simulate filter plugging in their own studies. Bentonite starts as a dry powder but hydrates and swells to form a clay-like material. The material conglomerates and, if used in a process, can bind to other materials, such as proteins. Bentonite conglomerations are typically large enough to plug any microfiltration stage. Bentonite should be primarily removed via some mechanism such as centrifugation or DE clarification. A plugging component analysis of plugged filters will determine if bentonite is causing premature filter blockage. Perlite Perlite, shown in Figure 1.10, is an amorphous volcanic glass. It is used as a filtration media and filter aid in the beverage industry. Perlite particles can serve as plugging agents to any downstream microfiltration processes. Perlite is primarily composed of about 75% silicon dioxide and 15% aluminum dioxide. Several other oxides make up the balance. While most perlite is of a fairly large particle size, fine-grade perlite used for beverage filtration will typically have a median particle size of about 17 μm.

Figure 1.10.

Perlite filter cake is used in many media filtration applications.

Introduction

31

Silt and Sand Silt and sand, as well as any other general debris, is usually large in size. Nominal depth-type filters of an open rating should be used to remove such contaminants. Mechanical separation tools such as Y or basket strainers or mesh screens can be effective for removal before any microfiltration stages. It is common for bottled water spring sources to have filters specifically for large debris removal located right at water entry to the pipeline or plant. Silicates and Carbonates Silicates and carbonates are usually introduced to the filtration process by untreated or poorly treated CIP (“cleaning-in-place”) or process water. These contaminants can be difficult to remove from filters, particularly membranes. Some carbonates can be removed by a rinse with citric acid. If silicates and carbonates are present, the best course of action is usually to treat the service water before it reaches the process filtration stages. These contaminants do not necessarily have a pore size, as do other contaminants, but rather are deposited onto the filter’s surface or within the filter’s depth. Some of these molecules, such as calcium carbonate, can facilitate microorganism growth leading to the formation of colonies or biofilms within the filtration system or the filter itself.

While not technically a contaminant, the water component of a beverage can plug the filter if it is cooled to a point at which partial freezing occurs. Beer, wine, coolers, and many specialty products are kept at a temperature just above freezing. An improper chiller set-point or other such problem can cause the filtration system to perform poorly due to ice build-up on the filter.

Plugging Component Analysis Filter manufacturers and suppliers will sometimes offer a plugging component analysis as part of their services. Many will perform the testing for free for customers, within reason. Plugging component analysis can be useful for both process troubleshooting and new product and process development.

32

Beverage Industry Microfiltration

During the new product development phase, the types of plugging agents and contaminants can be determined and used to target the point(s) in a process where a filtration stage is needed. Plugging component analysis becomes more critical in new, untested applications or in complex products because component interactions can often lead to a decrease in filterability or product clarity. The benefits of plugging component analysis as a troubleshooting tool are obvious. In determining what materials are present on the filter, the source of the materials can be pinpointed. For example, presence of carbon fines can indicate a problem in the carbon tower. DE present on the filter may indicate that a trap filtration stage is not functioning properly or, if no trap is present, a mesh screen (as in pressure leaf filters) might need repair. Component analysis can be used to determine seasonal or batch-to-batch product quality changes. An example is the decrease in filterability that results in many bottled water plants during the summer months when water levels are low, after extreme periods of rain, or in conjunction with the winter thaw in cold climates. There are three main plugging component analyses that are performed: • Fourier Transform Infrared Analysis (FTIR) • Scanning Electron Microscopy (SEM) • Energy Dispersive X-Ray Spectroscopy (EDS) Fourier Transform Infrared Analysis (FTIR) Fourier Transform Infrared (FTIR) analysis takes a sample of material from the filter’s surface and analyzes the resulting spectrum. If analyzing a depth filter, sometimes a section of media is taken and soaked in ultra-pure water. The water is then filtered through a membrane and the membrane analyzed. Comparing the sample’s spectrum to libraries of known spectra allows determination of the materials that are present on or in the filter. FTIR works particularly well with organic materials. Most product streams have many components being removed by the filtration, so the sample spectra generated are typically combinations of several plugging agents. The technician performing the analysis should be able to compare the most relevant matches to determine the individual plugging agents in a mixture. A proper analysis will take the process and product stream into consideration. Results from an FTIR test are not always straightforward

Introduction

33

and can require some reflection. Yeast present on a filter’s surface, for example, will usually be presented as “protein” material by the FTIR analysis. An FTIR analysis would not be able to identify any particular yeast strain or even whether the protein was bacteria-related as opposed to yeast-related. Scanning Electron Microscopy (SEM) Scanning electron microscopy (SEM) involves magnifying the filter’s surface and observing any foreign materials that might be present. Various magnifications can be used to see the different-sized contaminants. Specific microorganisms can sometimes be determined using SEM analysis. When SEM is used along with normal microscopy, general debris such as metal fragments, fibers, or fine particulates can be identified (Figure 1.11). Energy Dispersive X-Ray Spectroscopy (EDS) Energy dispersive x-ray spectroscopy (EDS) analysis (Figure 1.12) displays the elements present and their relative concentrations within a sample. It is effective for determining the presence of inorganic materials such as carbon, carbonates, and silicates.

Figure 1.11.

Sample SEM analysis. Bacteria on a track-etched membrane.

34

Figure 1.12.

Beverage Industry Microfiltration

Sample EDS analysis.

An EDS analysis works by polarizing a semiconductor with a high voltage. When an x-ray photon hits the detector, electron hole pairs are created that drift due to the high voltage. The resulting electric charge is collected. Since the voltage of the condensator is proportionate to the energy of the photon, the energy spectrum can be determined. The filter’s composition is incorporated into the test results, so it is important that the individual running the test knows what filter was used and what elements are the primary constituents of the filter. Peaks of carbon (C), oxygen (O), and fluorine (F) are inherent to a PVDF filter, for example. Strong carbon, oxygen, and sulfur (S) peaks are a natural result of testing a PES membrane.

FDA CFR 21 Guidelines The Federal Drug Administration (FDA) considers filters a direct food contact item. This is because the beverage passes through the filter. The FDA also considers filters an Indirect Food Additive in most situations. All wetted parts of the filter must therefore be compatible and approved for use by the FDA. Materials used in the construction of any filter components must also be approved. The FDA guidelines relating to filters generally come from CFR 21 Sections 174 to 189. The FDA uses the term “food” indiscriminately to refer to all foods and beverages. The main section numbers and headings relevant to beverage filtration are listed in Table 1.8.

Introduction Table 1.8.

35

FDA CFR 21 sections relating to filters and filter components.

Section

Name

174 175 176 177 178 180

Indirect Food Additives. General Indirect Food Additives. Adhesives and Components of Coating Indirect Food Additives. Paper and Paperboard Components Indirect Food Additives. Polymers Indirect Food Additives. Adjuvants, Production Aids, and Sanitizers Food Additives Permitted in Food or in Contact with Food on an Interim Basis Pending Additional Study Substances Generally Recognized as Safe Direct Food Substances Affirmed as Generally Recognized as Safe Indirect Food Substances Affirmed as Generally Recognized as Safe Substances Prohibited from use in Human Food

182 184 186 189

Table 1.9.

FDA CFR 21 subsections.

Subsection

Name

Topic

176.1700

Components of paper and paperboard in contact with aqueous and fatty foods Nylon resins Olefin polymers Perfluorocarbon resins Filters, microporous polymeric Filters, resin-bonded Polyethersulfone resins Polyvinylidene fluoride resins Rubber articles intended for repeated use

Regenerated cellulose

177.1500 177.1520 177.1550 177.2250 177.2260 177.2440 177.2510 177.2600

Nylon Polypropylene and similar PTFE Filter devices and materials Filter devices and materials PES PVDF O-ring and gasket materials

There are several important subsections, given in Table 1.9, that relate directly to filters or filter materials. Not all filter and filter component materials are listed in their own subsection. Materials may be listed under “Generally Recognized as Safe” or elsewhere. There are rare instances when there is a conflict between different sections. The FDA itself, or other reliable source, should be contacted in this situation. A searchable full-text listing of CFR 21 and its subsections can be found on the FDA’s website.

36

Beverage Industry Microfiltration

Filters being specifically marketed to the beverage industry should always meet FDA guidelines. If a filter is being acquired from an unreliable source or is usually used strictly in non-food and beverage industries, it may not be appropriate or approved for beverage processing. Filter manufacturers should be able to provide a letter stating that their products are FDA compliant. Manufacturers will often state compliance on filter datasheets or in the quality certificate mailed with the filter. Personal experience has shown that most compliance issues within the beverage industry typically involve one of the following: • Using a filter not at all geared toward the food and beverage market. • An overlooked component that may or may not be relevant, such as the bag the filter is shipped in. • A chemical or component present in manufacturing that is not present in the final shipped product. Compliance is rarely an issue with top-level manufacturers who are meticulous on this issue. Filter companies whose products are used in the biopharmaceutical industry or who have a substantial presence in the biopharmaceutical industry tend to be more thorough and experienced with these regulations. This is due to the significantly higher focus of the government and of end users in that market.

Chapter 2 Cartridge Filters

Cartridge Filters A “standard” cartridge-style filter, for the purposes of this book, is a cylindrical, disposable cartridge that requires a filtration housing of some type and is made of a type of media that can be wrapped or pleated, of either depth or membrane type. Standard cartridge-style filters have already become the predominant filtration device used in the beverage industry and are continuing to displace older filter formats, such as bag filters, filter sheets, and lenticular cartridges. Hydrophobicity and Hydrophilization Hydrophobicity is a measure of the degree to which a filter accepts water into its pores. Hydrophilic filters readily accept water into their pore structure. Hydrophobic filters repel water. Water placed on a hydrophobic filter will bead up, while water placed onto a hydrophilic filter will quickly be absorbed into the pores (Figure 2.1). Pressure can be used to force water into the pores of hydrophobic filters. Depending on the degree of hydrophobicity, this pressure, called the “intrusion pressure,” can be anywhere from a small amount to well over 100 psi (6.9 bar). Air and gas filters are usually hydrophobic membranes such as untreated PVDF or PTFE. Most liquid filters are hydrophilic, either naturally or through the application of a surface treatment. Liquid filters are hydrophilic due to several reasons. The main reason is their ability to wet and reliably integrity test in large beverage filtration systems without the use of alcohol solutions. Hydrophobic filters cannot be reliably wetted with only water because even after the intrusion pressure of a hydrophobic filter is met and water flow begins, there 37

38

Beverage Industry Microfiltration

Figure 2.1. Water beads up on a hydrophobic membrane (left sheet) while it is quickly absorbed into a hydrophilic membrane (right disk).

may be small portions of the membrane that do not wet, as the pressure in other sections has been relieved by flow. These dry portions of the membrane not only restrict flow but will also prevent a filter from successfully passing a standard integrity test. Hydrophobic filters can be used more successfully as liquid filters when filtering solvents or high alcohol streams in which the product wets the membrane. Solvents, such as alcohols, have a lower surface tension than water, and so these product streams will more easily wet hydrophobic membranes. An alcohol solution, such as isopropyl alcohol (IPA) in water, is normally used to wet and integrity test small gas filtration installations. Hydrophilic filters, natural or modified, exhibit lower protein binding than hydrophobic filters. A naturally hydrophobic filter, such as PVDF or PES, can be made hydrophilic via one of several processes. However, these modifications are sometimes susceptible to degradation at certain pH ranges and can limit a specific membrane’s use as a liquid filter with some streams. Three types of surface treatments are used when making a hydrophobic filter act hydrophilic. These treatments, shown in Figure 2.2, are: • Coating • Grafting • Cross-linking

Cartridge Filters Coating

Grafting

39 Cross-linking

Membrane Surface Treatment (Copolymer)

Figure 2.2. Membrane surface treatment techniques include grafting, coating, and cross-linking.

Coating is the most basic and least effective. There is no real attachment to the membrane. Grafting works such that the surface treatment compound is attached directly to the membrane. Cross-linking uses a method where the surface treatment is precipitated onto the membrane’s surface. The treatment compound on both surfaces of the membrane are (cross) linked to one another, but are not directly attached to the membrane itself. Naturally hydrophilic membranes include: • • • •

Cellulose and cellulose esters (cellulose acetate/nitrate) Polyamides (nylon) Acrylics Polyesters

Naturally hydrophobic membranes include: • • • • •

PVDF (polyvinylidene fluoride) PTFE (polytetrafluoroethylene) PES (polyether sulfone) Polypropylene Polyethylene

Pleated versus Wrapped The majority of cartridge filters can be classified as either pleated or wrapped. Pleating describes a flat sheet of material folded multiple

40

Beverage Industry Microfiltration

Figure 2.3. Wrapped depth cartridge filters have many layers of compressed media around a central core.

times in order to increase the amount of outward-facing filter media that can fit around the cartridge core. Standard membrane cartridge filters are always pleated. Surface-style non-membrane filters are also pleated. There is usually an upstream or a downstream supporting layer, or both, that is layered and pleated with the filtration media for increased strength. A pleat consists of the pleat peak (high point) and the pleat valley (low point). All of the pleats together are referred to as the “pleat pack.” Wrapped filters (an example is shown in Figure 2.3) have sheets of filter media cut so that they can be layered around the cartridge core. The number of layers in a wrapped cartridge can easily number 150 or more. Wrapped filter cartridges are considered depth media and are commonly clarification and prefilters. Increasing numbers of wrapped, depth-style cartridges are being manufactured as “graded density.” Graded density construction refers to a construction in which the layers of filter media are increasingly more retentive as they progress closer to the cartridge inner core. Layering such as this allows for higher dirt-holding capacity and a longer resulting service life.

Cartridge Filters Depth Removal

Figure 2.4.

41

Membrane Removal

Removal within the depth versus removal at the surface.

Depth versus Surface The method in which a cartridge filter removes particulates often lends itself to being called either a depth or surface filter. By definition, a depth filter removes particulates within the matrix of the filter, whereas a surface filter removes particulates directly at the filter’s upstream surface (Figure 2.4). Generally speaking, wrapped or wound filters can be considered depth filters. Pleated membranes can be considered surface. Pleated non-membrane filters, such as pleated polypropylene prefilters, are often considered surface filters but can have a significant portion of their removal take place within the depth matrix. That being said, even membrane filters have a matrix that will remove particulates, and depth filters will remove many particulates directly at the filter’s surface. Despite being only 100–260 μm thick, on average, a membrane filter has a significant depth to a microbe, which is only 0.5 μm. In actuality every filter is both a depth and a surface filter. The two important considerations to look at beyond the terms “depth” and “surface” are retention and dirt-holding capacity. A depth filter will usually have a higher dirt-holding capacity with a lower retention whereas a surface filter will have a higher retention with a lower dirtholding capacity. The filtering ability of a non-membrane pleated surface prefilter will fall between a pleated membrane and a wrapped prefilter. It therefore becomes critical to look at each filter’s retention, its required pore size rating, and its dirt-holding capacity in order to match the process requirements to the correct filter(s). Keep in mind that most processes will require at least two stages, so it may not be

42

Beverage Industry Microfiltration

necessary (or even possible) to fulfill every process requirement with a single filter. There are several manufacturers now creating pleated, depth filters. This is a relatively new type of cartridge filter. It is created by pleating many layers of wrapped media, usually polypropylene. There are fewer layers than with a conventional wrapped filter. The idea is that when fewer layers (i.e. dirt-holding capacity) are necessary for the application, the surface area can be increased by pleating. The filters usually offer a lower initial pressure drop, increased per filter flux, and often better retention. It is not possible to pleat as many layers of media as can be wrapped, so compared to more conventional wrapped filters, there is a decrease in dirt-holding capacity. Symmetry and Graded Density The terms “symmetry” and “asymmetry” are used when referring to membrane filters. Graded density is a comparable trait in depth filters. The terms both relate to the manner in which the filter media is composed as its depth progresses. Membrane filters can be either symmetric or asymmetric throughout their depth. The difference between the two is shown in Figure 2.5.

Figure 2.5. Cross-sectional view of two membranes. Symmetric membranes (left) have a relatively uniform pore structure throughout whereas asymmetric membranes (right) have a more open pore structure upstream of the final pore size rating.

Cartridge Filters

43

Symmetric membranes have pores that maintain relatively the same density and size throughout the depth matrix as at the surface. Asymmetric membranes will change throughout the depth of the membrane layer. Larger pore diameters will usually be upstream of the smaller pore diameters. The theory behind this construction is that the larger particles are retained within the upstream area of a membrane while the smaller particles are retained in the tighter matrix downstream. This will increase filter flux and capacity. The filter’s retention is rated based on the smallest pore size. Polyether sulfone (PES) filters are often asymmetric. Asymmetric membranes can be used quite successfully when a process is limited by flow rate or filter flux. It is possible for an asymmetric membrane to have as much as four times the flux as a comparable symmetric membrane device. High degrees of asymmetry can make a membrane weaker, however, and there are many reports that certain asymmetric PES filters cannot withstand the extremely rigorous processing conditions that a symmetric PVDF or nylon filter can. If a process is run properly, this is less of a concern, but it is still an issue to be aware of. Decreased strength will not be observed to be the same in all PES filters since different filters not only have different device and membrane manufacturing, but because filters will have different degrees of asymmetry. Asymmetry can lead to problems with completely wetting a membrane and carrying out a proper integrity test. Special integrity test procedures may have to be developed for some asymmetric membranes. Depth filters are often made so that they have a graded density in which the sequential layers of filter media become increasingly more particle retentive. This is common in wrapped polypropylene depth filters. The graded density allows for the filter to have a much higher dirt-holding capacity. Absolute versus Nominal The “absolute versus nominal” discussion is one that generates much confusion in the industry. In most minds familiar with filtration, “absolute” is the complete retention (not just initial retention) of any contaminants or particulates above the specified pore size rating, while “nominal” is everything else. An integral integrity testable membrane is the only microfiltration device that can truly claim absolute retention. Some manufacturers will claim that their prefilter or depth filter is

44

Beverage Industry Microfiltration

absolute. These claims are often made based on retention tests of some form. There can be unloading, bypass, or other mechanisms through which depth, clarification, prefilters and the like will see contaminants pass through the filter. Even the simple facts that non-membrane filters are not integrity testable and, therefore, bypass can occur for a reason such as improper filter installation, should illustrate the fact that such filters are not absolute based upon the common understanding of “absolute.” Filter manufacturers themselves are as much to blame for this confusion as anybody and are both benefited and hurt by the confusion surrounding this issue. Millipore tends to not use absolute or nominal designations. Occasionally a membrane filter may be called absolute in some literature, however, depth filters are never called absolute. Pall claims a filter has absolute retention if it achieves >99.98% retention by modified OSUF2 Beta ratio tests. Sartorius defines absolute retention as >99.99% retention in 100% of applicable retention tests. Cuno defines absolute retention as the pore size micron that yields an initial Beta ratio of 1000, which is 99.9% removal efficiency. These different claims and self-imposed guidelines are all used for membrane filters as well as depth filters — which are not integrity testable and are known to have potential for unloading if not properly operated or monitored. These tests do not address retention over time as a filter’s capacity is exhausted. Depth filters can have different actual observed retentions based on whether or not the filters are new or have been in process for several days or weeks. The simplest rule is that if you must retain all particles above a specific pore size rating, then a membrane is to be used with proper operating and integrity test procedures. Cartridge Filtration Housings Cartridge systems are defined by a notation in which the number of cartridges comes first followed by the word “Round” and the length of the cartridge in inches. So a 3 Round 30″ cartridge filter housing holds three 30″ long cartridges. Cartridge filter housings can be either T-line, in-line, or inverted by design (Figure 2.6). T-line housings are the most conventional; flow enters the housing at the bottom and fills the housing with fluid from bottom to top. Fluid flows through the media contained in the cartridges. There will be an inner cartridge core with an open side that is

Cartridge Filters Normal Flow Housing (In-Line) Inlet

45

Normal Flow Housing (T-Line)

Inverted Flow Housing Outlet

Inlet Outlet Inlet

Outlet

Figure 2.6. There are three cartridge housing configurations commonly in use within industry: in-line, T-line, and inverted flow.

attached to a receptacle in the housing base. The fluid enters the core and collects in a reservoir under the housing bottom (base) plate. Flow exits the housing from the bottom in the opposite direction of the inlet. In-line filter housings are such that the inlet is located at the top of the filter housing. The fluid flows into the housing, filling it. The fluid then passes through the filters, collects underneath the housing base plate, and exits the housing from the bottom. In-line housings are common with gas filtration and tank-venting applications. Inverted housings are essentially a conventional housing flipped upside-down. The flow will enter on the side toward the “bottom” of the housing. The housing will fill up from bottom to top and fluid will pass through the filters upward to the housing outlet. The filter cartridges hang down from the housing base plate so that the open end is attached to the housing and is higher than the closed end. This housing design is almost exclusive to dual o-ring locking tab cartridges. Breweries will often use inverted filter housings. Pall’s cluster beer filtration system (CFS) uses inverted filter housings and is common with some major beer producers who use final membrane filtration as an alternative to, or in conjunction with, pasteurization. Beyond marketing and sales literature, which can be questionable, there are no independent reports or data regarding the true efficacy of using such filter housings. It is said that inverted filter housings help with the elimination of air bubbles in the housing dome, which reduces or eliminates the need

46

Beverage Industry Microfiltration

for venting. Inverted filter housings have been reported to have a positive effect on cleaning and build-up of particulates during the filtration run. They also offer better wetting of membranes, particularly those that are hydrophobic. Inverted housings are more difficult to changeout and can be awkward to work with. Housing components are sealed with o-rings or gaskets. There are seals at each connection for the inlet, outlet, pressure gauges, drains, and vents. The housing dome forms a seal with the housing base. The o-ring or gasket forming this seal is often damaged during change-out and operation, compromising housing integrity, so it requires regular inspection and replacement. Housings that have a removable baseplate will have dual seals — one for the dome-to-baseplate seal and another for the baseplate-to-bottom reservoir seal. There will also be an o-ring seal, sometimes doubled, around the inlet opening in the baseplate. Sealing mechanisms are typically silicone, but other materials may be used depending on preference and compatibility. EPDM o-rings should be used when filtering very high alcohol liquids. Anti-sway plates are included with some non-inverted multi-round cartridge filter housings. The plate fits onto the top adapters of the cartridges and is designed to link the cartridges to one another in order to share any stress and prevent a single cartridge from either breaking or coming out of place. Many beverage manufacturers do not use the anti-sway plates, as the benefits of doing so are often questioned. Depth and Non-Membrane Media Clarification filters and prefilters are essentially the same by construction and usage in many applications. The term “clarification” is used when there is a second prefiltration in the process or when there is a filtration step not directly linked to the bottling process. Prefiltration and clarification media can be either pleated or wrapped. Wrapped media operates primarily using the filter’s depth matrix, while pleated filters will perform the majority of the filtration at the media’s surface. All filters actually perform their filtration using a combination of removal at the surface and removal within the depth of the filter, however. The filtration media used for depth and non-membrane surface filters can be the same material formatted differently, either wrapped or

Cartridge Filters

47

pleated, for its insertion into the filter cartridge. Resin-bonded and string-wound cartridges behave similarly to wrapped depth filters. Cellulose, Cellulose Esters Cellulose was first observed as early as 1533. The first cellulose acetate was prepared in 1865 by Paul Schützenberger, and a process for making it was patented in 1894. Henri and Camille Dreyfus began manufacturing cellulose acetate films around 1904–1910 and found many applications for it during WWI. The brothers began producing Celanese, the first cellulose acetate spun yarn, in 1919–1924. There are many forms and descriptions of cellulosic filter media. Cellulose, cellulose esters, mixed cellulose esters, and so forth are all terms used to refer to cellulose-based filter media. Trees are the raw material for all forms of cellulosic filter media. The tree is turned into chips and cooked to separate cellulose fibers from lignins and resins. The pulp is then chemically treated to further separate the desired cellulose fibers and the remaining lignins and resins. The pulp is pressed and dried. The cellulose can now be reacted with various acids and anhydrides to create cellulose esters via esterification and hydrolysis. Cellulosic filter materials were some of the first forms of microfiltration and are still heavily used throughout the industry today. Cellulose acetate and cellulose nitrate membranes are both cellulose esters. Membranes based on cellulosic materials, such as cellulose acetate, have largely given way to newer petrol-based compositions within beverage microfiltration. Polypropylene (PP) Polypropylene is the most common media used for cartridge prefiltration/clarification within the beverage industry. It is cheap, highly stable with most types of chemicals, and readily available in many different formats. The melting point of polypropylene is 320 F (160 C), which makes it temperature stable with nearly every food and beverage application. All major filter manufacturers, as well as most small ones, offer a polypropylene filter. Polypropylene cartridges are seen in both wrapped and pleated form. Wrapped filters may be graded density. Polypropylene filters on the market can be quite different from one another even when appearing to be similar. Filters may have greatly different retention properties, and it is important to study the retention characteristics

48

Beverage Industry Microfiltration

and efficiency of each filter at the desired pore size rating in order to decide whether a filter is well-suited to a particular process. Very low-quality polypropylene filters can have oils and residues present. This is common in some inexpensive filters used for industrial applications. These filters should not be used for food and beverage applications. Glass Fibers Filters made of fiberglass or glass fibers are typically pleated surface style. Some cartridges can be of the string-wound type. Fiberglass is chemically stable and can withstand extremely high temperatures. Glass fibers are also mixed with other filtration media to create a composite that has properties of several different media types. There has been some concern over glass fiber filter media causing a loss of color to some products, such as wine. This effect is lessened by using a filter that has only some glass fiber incorporated into the matrix. Glass fiber has been found to be effective at the removal of some colloidal contaminants and product hazes and is well suited to some beverages. Polyester Polyester is a fiber produced by the reaction of terephthalic acid and ethylene glycol. Polyester can be spun-bonded or melt-blown and has a higher temperature tolerance than polypropylene. A drawback of polyester fibers is their tendency to fibrillate. This may cause fiber shedding into the product at fine pore size ratings. Polyethylene Polyethylene is very similar to polypropylene. It is created through the polymerization of ethane. It has a higher temperature rating than polypropylene. Polyethylene cartridges are not commonly used in beverage industries. Resin-Bonded Cartridges Resin-bonded filter cartridges are constructed so that the outer cage of the cartridge is a solid piece of resin. The inside of the resin cage is filled with some combination of filter media such as polypropylene, polyester, or cellulose esters. Resin-bonded cartridges function as depth-style filters. The resin cage may have grooves or indents in the

Cartridge Filters

49

outer surface, which will increase the filter’s outer surface area available to flow. The cartridges can have a graded-density depth similar to a wrapped depth filter. Resin-bonded cartridges are essentially a form of clarifying depth filters. String-Wound Cartridges String-wound or “blanket media” cartridges are the least-used cartridge format in beverage processing. Soft drink manufacturers and some small water bottlers are the only beverage companies that occasionally use string-wound cartridges. Cartridges are constructed by wrapping a yarn of filter material around an inner core. The filter material can be anything from polypropylene to ordinary cotton. In some filters the yarn is first laid out as a sheet, pressed, and subsequently wrapped onto the inner core. This supposedly allows for more control over the process and a better cartridge. String-wound filters can be prone to media shedding in which fibers are released downstream into the product. Filters may be “brushed” by the manufacturer to increase filtering capability. Membrane Media There are many different membrane materials widely used in beverage manufacturing; polyvinylidene fluoride (PVDF), nylon, and polyether sulfone (PES) are the most common for normal flow liquid filtration via standard cartridges. Polytetrafluoroethylene (PTFE) is the most common membrane used for gas and vent filtration. Several other membranes are used, but not very often. Ceramic membranes are increasingly used for specialty applications such as crossflow clarification, caustic recycling, and heavy solids filtration. Steam is filtered using sintered stainless steel membranes. Typical polymeric membranes such as PVDF, PTFE, nylon, and PES are made by a process in which the polymer is first dissolved into a specific amount of solvent. The solvent is then cast into thin sheets and dried in an environmentally controlled chamber in which the solvent evaporates. This step creates the pores. Some membranes will then undergo subsequent processes, which can accomplish such things as changing the hydrophobicity of the membrane. Membranes made by this process are sometimes referred to as “cast membranes.” The

50

Beverage Industry Microfiltration

membrane is usually rolled at this point and proceeds to device manufacturing where the actual filter cartridge is assembled. Membranes are manufactured in flat sheet, hollow fiber, or tubular geometries. These geometries may then be further modified. The most common example of this is the pleating process, which occurs on flat sheet membranes in order to increase the per-cartridge filter surface area. The first beverage filtrations using membranes, performed in the 1960s, were done with round, flat disks of membrane. It was then realized that pleating the flat membrane and putting it into a cartridge device would greatly increase the filter surface area. Chemical compatibilities, retention characteristics, and flow rates can vary greatly between the various membrane types. A process using a 0.65 μm nylon filter may not be able to readily change to a 0.65 μm PVDF filter without changing other procedures, chemicals, or processes, such as cleaning methods. In most instances, however, the impact of changing the membrane type can be easily overcome with a little work.

TIP Membranes that are laminated during the manufacturing phase will have a polymeric substance adhered to a narrow part of the top and bottom portion of the flat sheet membrane stock. After subsequent pleating and potting into a cartridge the lamination greatly increases the strength of the membrane-to-end cap bond that occurs at the site of lamination.

Nylon Nylon is a common filter media, available from several manufacturers. Nylon is highly stable and is able to be caustic sanitized at high pH ranges. One aspect of nylon that differentiates it from other filter media is that the process used to manufacture nylon membranes is oftentimes not as consistent as with other materials. It is therefore possible to have individual pores that are larger than the target pore size rating of the membrane. To correct for this and to allow for truly absolute retention, some manufacturers will layer two nylon membranes with the thought that the statistical probability of having two of the errant larger pores

Cartridge Filters

51

on top of one another is so small that the dual layer membrane will have absolute retention. A drawback of this approach is that the filter flux rate will typically be lower than with a single-layer filter. Singlelayer nylon that can have the larger errant pores is sold for non-critical applications. It is important to verify whether this is the case and decide whether it is appropriate for a particular process. Pall’s nylon Ultipor N66 filters are of the double-layer type. It is important to note that regardless of some claims, a double-layer nylon membrane does not offer any greater microbial retention benefit over a single-layer membrane of well-produced PVDF, PTFE, or PES. There are some chemical compatibility concerns when nylon is used in conjuction with peroxyacetic (peracetic) acid. The specific manufacturer of the nylon membrane should be contacted if this chemical is being used or considered. It is known that nylon has higher protein binding than other final filtration media, such as PVDF or PES. This will sometimes result in a loss of flavor or color from some products. Wine and beer are two products that can be susceptible to this change. The change will typically be minimal and can be further neutralized by recycling the first portion of product or through the use of a pre-filler surge tank to allow some mixing of initial product. If the final filtration stage is very large, such as a 56 or 98 Round, the sensory changes will be more significant than if the housing is of a smaller size, such as a 5 or 12 Round. Only the first product passed through the filtration stage will experience these effects. Polyvinylidene Fluoride (PVDF) Polyvinylidene fluoride is a leading filter media, produced by several companies. It was first invented in 1970 and was introduced to the beverage market as a viable hydrophilic membrane by Millipore in the 1980s. PVDF has a high chemical compatibility and a very low level of protein binding. PVDF is a naturally hydrophobic membrane. The chemical composition of PVDF is shown in Figure 2.7. Millipore was the first to commercialize the hydrophilization process to turn the hydrophobic PVDF filter hydrophilic; this development has allowed the membrane material to be used more extensively in the beverage industry. The hydrophilization, however, is not stable at extremely high pH ranges, so the hydrophilic PVDF filters should not be caustic cleaned at a pH above 10 for extended periods of time. The

52

Figure 2.7.

Beverage Industry Microfiltration F

H

C

C

F

H

N

Chemical composition of polyvinylidene fluoride (PVDF).

higher the pH, the worse the swelling of the membrane and the faster it will degrade. A pH of 12 or higher is considered severe. When exposed to excessive pH, the hydrophilic surface of the membrane will hydrolyze to form a hydro-gel, which can swell and reduce membrane permeability. The swelling effect can be partially reversed, and membrane permeability restored, however, by treating the membrane with a low pH (2–3) or a highly ionic environment. Such a treatment will collapse the hydro-gel and restore permeability. The membrane will not usually be completely restored and will be susceptible to permeability decreases if the filters are again treated with a pH above 7 or the ionic strength is decreased. There are some processes where close monitoring of pH, temperature, and exposure time is used along with the restoration process. Nylon and PES are both caustic stable, so the extra cost and effort of using hydrophilic PVDF cartridges in a high caustic environment should be taken into account. It is worth noting that exposure to a pH lower than 3 has a similar effect on the membrane as exposure to a pH higher than 10. The rate of exposure is considerably slower and should not have time to adversely affect the membrane; however, degradation is theoretically possible with some low pH process streams such as vinegar. Hydrophobic PVDF, since it has not undergone the hydrophilization step, is perfectly compatible with caustic at any pH. Polyether Sulfone (PES) Polyether sulfone (Figure 2.8) is a relatively new membrane material that is seen as having a great deal of potential. Of the major membrane media currently being used in the food and beverage industry, PES probably has the most R&D and new product development currently in the pipeline. PES is a highly stable material that is caustic compatible. A differentiator of many PES filters is that the membranes can

Cartridge Filters

Figure 2.8.

53

SEM image of a polyether sulfone membrane.

be asymmetric in composition. The asymmetric composition allows for higher flow rates per surface area (flux) and may result in a higher dirt-holding capacity. A PES filter can easily have 3–4 times the flow rate per cartridge of a comparable filter using nylon or PVDF. This makes PES membranes ideally suited to being used for processes in which the filtration housing is grossly undersized with regard to flow rate. Not only will the housing have a higher flow rate with a lower pressure drop, but the plugging effects of face velocity will be greatly reduced, thereby increasing the filter service life. PES has quickly become the primary filter offering from several manufacturers such as Sartorius, Cuno, and Domnick Hunter. The two other major cartridge filter companies, Pall and Millipore, also have several PES offerings, but will typically lead with their nylon or PVDF lines, respectively. There is a fairly high degree of variability in performance between various PES compositions and manufacturers. One PES membrane should not be taken as identical to another PES membrane. Some PES membranes, particularly those of more open pore size ratings of 0.45 μm and above, have been prone to cracking under very high stress or long usage times. This is a potential problem to be aware of when choosing a PES membrane or evaluating process-operating conditions.

54

Figure 2.9.

Beverage Industry Microfiltration F

F

C

C

F

F

N

Chemical composition of polytetrafluoroethylene (PTFE).

The problem is in part related to the degree of asymmetry of the membrane. A greater degree of asymmetry can lead to decreased strength in the membrane as well as difficulties in being able to wet and integrity test large installations. Polytetrafluoroethylene (PTFE) Polytetrafluoroethylene is a cheap, naturally hydrophobic membrane and is the most widely used membrane for gas, air, and vent filtration. PTFE was invented by DuPont in 1938 and is more commonly known outside of filtration as Teflon. The chemical composition of PTFE is shown in Figure 2.9. Cellulose Acetate (CA) Cellulose acetate, one of the earliest membranes developed, is plantfibers based as opposed to being petrol based like membranes made of nylon, PVDF, PTFE, and PES. It was first commercially produced by Sartorius. Cellulose acetate membranes will often be more expensive than petrol-based membranes due to the higher costs associated with their manufacturing. There are also some questions as to whether they are as durable as petrol-based membranes. Cellulose acetate is sensitive to extreme pH ranges and temperatures. Cellulose acetate is produced by reacting cellulose with acetic acid and acetic anhydride. Partial hydrolysis occurs, and the acid-resin precipitates out of solution and is collected. The precipitate is dissolved in acetone and dried. There are several filter cartridges used in the beverage industry that use a cellulose acetate membrane; however, they are not nearly as widespread as the other primary membrane materials. Cellulose nitrate is a similar material that can be used as membrane. It is produced by almost exactly the same process with the only change

Cartridge Filters

55

being the final chemical reaction in the esterification step. Cellulose nitrate exhibits higher binding than cellulose acetate. Sintered Ceramic and Metal Membranes Sintered ceramic membranes are becoming more frequently used in beverage filtration applications. The membrane is manufactured by first creating a slurry containing water, binder, an anti-flocculent, and ceramic powder. The slurry is spray dried and pressed into a mold. The material is heated at a low temperature to remove the binder. The remaining material is heated to a high temperature in order to fuse the ceramic particles together. Only the final step is actually referred to as sintering. Ceramics used for membranes are usually alumina or zirconia but many more ceramics could potentially undergo the process. Ceramic membranes can have an extremely long service life and are chemically resistant. Ceramic membranes are well-suited to caustic regeneration/reuse applications. If properly maintained, many ceramic membranes have a service life that is measured in years rather than months. Ceramic membranes are much more commonly used in crossflow filters than in normal flow. Membranes may also be made of sintered metals. The process of metal sintering involves heating a metal powder to some temperature below its melting point until the particles begin to adhere to one another. The metal sintering process has several applications beyond filtration and is performed on a variety of different metals. Stainless steel is the only feasible metal for use in beverage filtration. Metals such as brass are not considered food grade and do not have the same chemical properties as stainless steel. Sintered metal membranes can withstand extremely high temperatures and pressure spikes. Sintered stainless membranes are commonly used for process steam filtration within the beverage industry. Cartridges are very expensive, as can be expected, but tend to have an extremely long service life, which offsets the initial cost. In addition, since steam is a gas, the number of cartridges required for most steam filtration applications is minimal. Track-Etched Membranes Track-etched membranes (Figure 2.10) are created by first exposing a polymeric film to high-energy ions. Channels are generated at points in which some of the ions move through the film. These channels are

56

Figure 2.10.

Beverage Industry Microfiltration

SEM image of a track-etched membrane.

different from the unaffected material so that during the etching phase, when the film is exposed to an alkali solution, precise cylindrical holes are created at the sites of the channels (tracks). Pore size ratings of track-etched membranes are typically in the tighter range of 0.05– 1.0 μm. Polycarbonate is the most common track-etched membrane used in the beverage industry. The main benefit of track-etched membranes is that all pores are nearly identical and of the desired size, with deviation usually being no more than 4–6%. Track-etched membranes remove particles almost completely by the sieving mechanism. Although track-etched membranes have a lower porosity than cast membranes, the relative thinness (~10 μm) of the track-etched membrane compensates with regard to flow rate. Washing in the reverse direction is very effective with track-etched membranes since they act completely as a sieve and nearly all particles are removed at the surface. Composite Membrane Media Many filter manufacturers are developing different forms of composite filters as a result of new applications throughout the industries that use microfiltration. Rapid expansion in the biopharmaceutical industry, one of heaviest users of microfiltration, has spearheaded this change. There has also been a recent push to create filtration processes that are specific to a particular application. This is a vast change from when only

Cartridge Filters

57

a couple of filter formats with a few media choices were available. Composite filters and media can be a difficult subject to approach because many of the benefits of these filters are often more the result of marketing than factual. Some of the composite filter designs being marketed include: • Dual-layered membranes in which a more open membrane layer is on top of the membrane of the desired final pore size rating. • A membrane or pleated non-membrane surface filter semi-wrapped with depth filter media. • A membrane layered and pleated along with a surface-type prefilter media. These filter media configurations often involve adding a prefiltration layer over the membrane layer within the same cartridge device. When two membrane layers are used, the top layer may not be integral since it is not seated directly into the cartridge device. The extra layers can restrict flow and increase cost. If a process is properly designed with adequately sized and maintained prefiltration, there will typically be no need for these configurations. Clarification and prefiltration stages are normally sized larger than final filtration stages to achieve good economics. Composite formats combining a pre- and final filtration allow for only a 1-to-1 prefilter layer–to–final filter layer ratio. That being said, there are some cases in which an extra prefilter layer, of a pore size rating between the main prefiltration stage and final filtration stage, can be beneficial and prolong the service life of the final cartridge. This is usually limited to smaller applications in which there is a particular contaminant not present in high enough quantities to warrant its own prefiltration stage. Such applications are not common in beverage processes. Non-Media Components Filter cartridges are composed of a variety of components and materials other than the actual filter media (Figure 2.11). These components can include: • Inner support cage • Outer support cage

58

Beverage Industry Microfiltration

Top End Cap Inner Core (Cage) Outer Cage Bottom End Cap

Figure 2.11.

• • • •

Cartridge components.

Bottom end cap adapter Top end cap adapter Pleated filter support layers Sealing mechanism (o-ring or gasket).

A failure in any one of these components will lead to an overall system failure just the same as would a defect in the filter media itself. Most non-media components are fairly standard throughout the industry, and many filter manufacturers source these parts from companies that specialize in them. The component manufacturers will commonly supply multiple filtration companies. A key differentiator, however, is how the components are put together. There are many patented processes and differing degrees of quality that can impact the device manufacturing. Some filter manufacturers will have much more robust and durable cartridges in certain environments than others. This can have a huge impact on the overall economics of a filtration process, as more durable cartridges will last longer and are often able to withstand more frequent and rigorous cleaning and regeneration cycles. An example of this type of development is Millipore’s patented dual viscosity end capping process for its primary beverage filter offering, the Vitipore II. By using end caps made of both high and low viscosity polypropylene, the membrane pleat pack is able to be better seated into the end caps. This greatly improves the shear stress tolerance at the

Cartridge Filters

59

membrane–end cap bond. The membrane–end cap bond location is a leading site of cartridge failures, particularly when a process uses a rigorous hot water cleaning regimen. By improving this bond, the cartridge robustness is increased, which decreases cartridge failures, increases service life, and increases tolerance of harsh cleaning procedures. Edge lamination is another process that some manufacturers use to improve end cap–to–pleat pack bonding. The edges of the membrane that are bonded to the end cap are laminated with a polymer, which improves the bond.

Many cartridges are constructed by a process of combining individual elements to create the full-length cartridge. This has greatly improved cartridge manufacturing processes and the ability for manufacturers to react to orders and have a fast turnaround of the many different cartridge codes and configurations. Processes that employ this method involve the manufacturing of many 10″ elements per batch. These 10″ elements are then stored and can be later combined to form 20″, 30″, or 40″ cartridges. The top and bottom end cap adapters are also combined at this point. The typical manufacturer will have an inventory of 10″ elements, bottom end cap adapters, and top end cap adapters that can be combined to create each cartridge configuration quickly and as needed.

Outer Cage, Inner Cage, and End Caps Not all filter cartridges have the same components or combination of components. Almost all cartridges will have an inner cage. Almost all surface or pleated filters will have an outer support cage. Wrapped depth filters may or may not have an outer support cage. All filters have some form of end cap, but the end cap styles vary considerably from filter to filter. For the purposes of function and materials there are two end caps types: • Type 1 — The end cap is a hard plastic and there is some other component such as a (1) gasket or (2) o-ring required to make a proper seal. • Type 2 — The end cap is soft and serves as the sealing mechanism under pressure. This is sometimes called a “crush seal.”

60

Beverage Industry Microfiltration

O-Ring Seal Crush End-Cap Seal Additional Gasket Seal

Figure 2.12. Cartridges have one of three sealing mechanisms: o-ring, gasket, or crush end-cap seal.

Figure 2.13. Upstream and downstream support layers add strength to the membrane pleat pack.

The three types of sealing mechanisms are shown in Figure 2.12. Polypropylene is the material of choice for most filter manufacturers in the construction of the end caps, outer, and inner support cages. Polypropylene has a melting point of 320 F (160 C) and so is able to withstand high temperatures. Polypropylene is highly chemically stable, mechanically strong, and readily available. Polyester is also used, as are other materials, to a much lesser extent. Pleated Filter Support Layers Pleated filters usually have support layers on either the upstream or downstream sides of the primary filter media, or on both (Figure 2.13). These support layers provide additional stress resistance to the filter media and do not usually serve as an additional filtration matrix. The

Cartridge Filters

61

Figure 2.14. Either o-rings or gaskets will form the cartridge to housing seal. Gaskets may be a separate component, as seen here, or the end cap itself.

support layers may or may not be bonded into the end caps. The support layers do not cover the seam where the two ends of the pleat pack are bonded together. These support layers are not the same as prefiltration layers or second membrane layers. Polypropylene and polyester are common materials used as filter support layers. O-Rings and Gaskets Cartridges form a seal with the filtration housing using either o-rings or gaskets (Figure 2.14). There are many materials that can be used in the construction of o-rings and gaskets. Common materials include silicone, Viton, EPDM, Teflon, and other comparable polymers. Due to trademark rights, an o-ring or gasket material is sometimes given a generic name as opposed to a trademarked name such as Teflon or Viton despite being an identical composition. Most o-ring and gasket materials are highly chemically compatible and thermally resistant and are perfectly suitable to beverage applications. If unsure about a material or process ask the filter manufacturer for: (1) the temperature specification on the material and (2) the chemical compatibility of the material. Having a list of chemicals and/or products that will come into contact with the filter and their respective temperatures will help. Be mindful that sometimes a chemical at room temperature is compatible, but heating that same chemical will cause it to become incompatible with many other materials. Storage requirements of the cartridge with respect to the o-rings and/or gaskets should

62

Beverage Industry Microfiltration

be verified, as they may have to be removed and stored separately if storing the cartridge in a chemical solution for an extended period of time. Cartridge Codes and Styles Filtration cartridges are available in various “codes.” These codes are designations for the end cap configuration of the cartridge. It is the end caps that fit into the filter housing, and so it is important to use the proper configuration so that the cartridge will fit correctly into the housing and form an integral system. There is some overlapping of code designations between the major filter manufacturers, but there is even more discontinuity. Each of the companies has end cap keys and pictures available to help determine the proper cartridge code (Table 2.1). Despite using different code designations, most manufacturers use the same basic configurations. A filter may be called Code F by one company, Code 3 by another, or Code 0 by yet another, all the while having the same dimensions and being completely interchangeable. It is generally recommended to avoid any non-standard filter configuration to avoid being locked into one manufacturer or risk having to reinvest in new capital should a filter change be required. Sartorius’ Jumbo format cartridge is one such example. The Jumbo cartridge is essentially one single large wrapped depth filter that fits into a specially made housing. The housing cannot be used with any other filter types

Table 2.1.

Select manufacturers’ adapter code comparison.

Description

Millipore

Sartorius

Pall

Cuno

Domnick Hunter

Double 226 o-rings, locking tab, top adapter Double 222 o-rings, flat top Double 222 o-rings, top adapter Double open end, flat gasket, or crush seal

Code 7

Code 25

Code 7

Code B

Code C

Code 0

Code 27

Code 3

Code F

Code E

Code 5

Code 26

Code 8

Code 5

Code D

Code F

Code 21

R F & RM F

Code D

Code B, L

Cartridge Filters

63

and no other manufacturer makes the Jumbo format cartridges. Millipore’s Optiseal format, which is used for small applications as well as gas or vent filtration, is another example. Cartridge Specifications There are several pieces of documentation that are available or that come with a cartridge filter. Understanding these documents and the many specifications that are listed can be a daunting task. Some of the most common filter documents available are: • Brochures and Catalogues — The most general documents available, brochures and catalogues usually give an overview of a company’s products with respect to a particular application such as “Beverage Processing” or “Wine Making.” General process flows can be shown with a basic filter recommendation or pore size rating commonly used for the application. • Datasheets — Filter-specific document that details much of the technical information regarding the cartridge. Datasheets have many cartridge specifications, list some common applications, and tell the different pore size ratings and configurations available. Part number designations are found on datasheets. Datasheets can be useful in determining filter properties or when comparing filters from different manufacturers. • Quality Certificates — Quality documents usually come with the actual filter and will have information about the filter company’s practices, facilities, and quality procedures. Sometimes more valuable information, such as details regarding challenge testing, can be found in quality documents. • Instruction Manuals — Instruction manuals vary greatly in their complexity from one manufacturer to another. Information that is commonly found can include installation instructions, wetting and integrity test procedures, and/or cleaning procedures. • Validation Guides — Validation guides are not usually made available to the general public but are sometimes given upon request or found from another source. Validation guides detail some of the more extensive testing performed by the filter manufacturer. Safety factors, real test procedures, FDA compliance, failure rates, QA acceptance rates, and data regarding stress tests beyond normal operating

64

Beverage Industry Microfiltration

conditions are some of the pieces of information that can be found in these documents. Challenge Testing Challenge tests involve measuring a known sample of particles or contaminants passed through a filter in order to determine the relative amount of removal by the filter. Challenge testing can be performed with a specific microorganism or with some general particulate such a test dust or silicone beads. A test commonly referred to by filter manufacturers is the P. diminuta challenge test. This challenge test is primarily used for 0.22 μm sterilizing grade filters when a high grade of filtration is required. Test results can be misleading because not all manufacturers will use the same challenge levels and some manufacturers will use selected cells that are on the larger scale to yield better test results. As always, due diligence is required when reviewing any test data. Other microbes, or particles, are used to challenge more open pore sizes. Saccharomyces claims are common on 0.45 μm filters used in the wine industry, for example. Filter efficiency and Beta ratio can be specified in this section. Clean Water Flow rate Clean water flow rates are given as plotted charts of flow rate (lpm or gpm) vs. differential pressure (mbar or psid). Cartridge length, pore size, and temperature will affect the specification, and these are usually listed. Clean water flow rate is useful when comparing the retention efficiency of some depth-style filters and when designing new processes that are low fouling. When comparing wrapped depth-style cartridges, the retention efficiency of one filter may be compared to another by selecting the same pore size rating and comparing the differential pressure at the same flow rate for the same cartridge length and fluid temperature. The cartridge that has the higher differential pressure at that flow rate will usually have better retention at the selected pore size rating, for comparable filters. This can be seen when comparing the pressure versus flow rate curve given in Figure 2.15 with the corresponding filter removal efficiencies shown in Table 2.2. Maximum Operating Temperature and Pressure Maximum operating temperature is the temperature at which the filter manufacturer has determined the filter can operate for an extended or

Cartridge Filters

Figure 2.15.

Table 2.2.

Filter A Filter B

65

Filter A/B differential pressure vs. flow rate curve.

Filter A/B removal efficiency at selected pore size rating. 0.5 μm

0.6 μm

0.8 μm

1.0 μm

2.5 μm

4.0 μm

>99.99 20

>99.99 45

>99.99 80

>99.99 95

>99.99 >99.99

>99.99 >99.99

indefinite period of time without failure due to heat. Cartridges will usually be able to operate intermittently or for shorter periods of time at higher temperatures. It is not uncommon for a filter manufacturer to build a 20–30% safety factor into the maximum operating temperature but, in taking advantage of this, the plant may risk filter failure. Filter manufacturers usually test filters far in excess of the release specifications as part of their initial product validation and will sometimes divulge this information to a current or potential customer. The plant can perform its own testing to determine how far they can push the specifications in their particular process. The maximum differential pressure is a specification that the manufacturer states the filter can operate up to without failure. There is usually a safety factor built into this specification as well. Maximum differential pressure is given as two separate values: forward and

66

Beverage Industry Microfiltration

reverse. Forward differential pressure is the differential pressure of normal flow from the upstream to the downstream side of the filter. Reverse differential pressure involves flow from the downstream to the upstream side of the filter and usually relates to reverse cleaning procedures. Filters will have a lower reverse differential pressure specification. Filters are sometimes significantly weaker in the reverse direction. This is especially true with some membrane filter cartridges. Differential pressure specifications are given at several temperatures. When temperature increases, the cartridge becomes weaker and has a lower differential pressure specification both in the forward and reverse directions. Differential pressure specifications, particularly in the reverse flow, are one area in which not all manufacturers are equal. Some manufacturers have significantly more robust filtration cartridges than others. Higher design safety limits sometimes mask the higher specification from the customer. This does not allow the higher tolerance to be completely taken advantage of. Personal experience has shown that Millipore is one such company whose filter cartridges can be much more durable than some competing manufacturers. There is some discontinuity with regard to maximum differential pressure when discussing depth filters. Depth filters can be prone to unloading at high differential pressures. It can be thought that the point at which significant unloading takes place should be the maximum differential pressure specification. Oftentimes, however, maximum differential pressure is related more to total filter failure. One must use caution when operating depth filters to operate them so that they do not reach the point at which significant unloading occurs. This point may be lower than the specification for maximum differential pressure. Media, Materials of Construction, Construction, and Dimensions Specifications that deal with the filtration device composition or manufacturing are fairly straightforward. Filter media is the material that is actually performing the filtration. Materials of construction usually refer to the materials that are used in the construction of the inner support cage, outer support cage, end caps and, if applicable, membrane or pleated filter supports. O-ring and gasket materials are sometimes listed in this section as well. Construction fields can vary but usually refer to the device as a whole, such as how many pieces, the

Cartridge Filters

67

type of molding process, or some other aspect of the device manufacturing process. Cartridge dimensions are the various diameters and lengths of the different parts and sections of the cartridge. The most important dimension is the cartridge length (such as 10″, 20″, 30″), but this is usually listed separately and specified upon ordering. Filtration Area Filtration area is the surface area available for filtration and is essentially the surface area of the outer most filtration media exposed to the oncoming fluid. A higher filtration area will typically mean a higher flux and a higher flow rate per filtration area — and so a higher flow rate per cartridge. This is only true for comparable filters, as the filter flux of one type of membrane cannot be directly compared to a different type of membrane based on area alone. Many polyether sulfone (PES) membrane filters, for example, will have a higher flux than other membranes such as nylon or polyvinylidene fluoride (PVDF) given the same filtration area. Dual-layer membranes will not have a higher filtration area because only one layer’s outer surface is directly exposed to the oncoming fluid. The downstream layer only accepts fluid as it passes through the first. The filtration area of depth filters should be determined by the outer surface area and not the internal matrix. The surface area of some pleated filters may be misleading in terms of fluid flow. A high surface area filter may have so many pleats that not all upstream surface area is truly exposed to the fluid as the filter pleat packs compress under pressure. This will reduce the flux from what would be expected after simply examining the filtration area. Having a higher number of pleats will typically increase the strength of a cartridge with respect to pleat pack sheer, a leading mode of cartridge failure. Compliance FDA CFR 21 compliance is the most commonly seen compliancerelated specification in the US beverage industry. Comments within the specifications regarding extractables, fiber releasing, or other issues are common. FDA compliance is almost never an issue when dealing with commonly used beverage cartridges. The only instance that may sometimes present a problem is fiber shedding in some uncommon filter types such as string-wound.

68

Beverage Industry Microfiltration

Sterilization and Cleaning Sections within the filter specification guides or datasheets that deal with sterilization and cleaning usually refer to steam sterilization or hot water sanitation. The specification is often given as the number of cycles, at a specific temperature and/or time, that a cartridge has been validated to withstand. There are safety factors built into these specifications. A facility may have to extrapolate for its process based upon actual time or temperature, because the specifications are usually only listed for a few different parameters. Data about specific cleaning chemicals such as citric acid or peroxyacetic acid may be given in literature dealing with a specific industry or application such as winery or brewery filtration. Most manufacturers try to keep datasheets as generic as possible and will not publish this information, however. Integrity Test Specifications (Bubble Point, Air Diffusion) Membrane filters will have bubble point and air diffusion specifications listed. These specifications are important when creating an integrity test procedure and test criteria. Bubble point is the pressure at which air can be forced through a wetted membrane. If a cartridge is integral, the bubble point observed during an integrity test will be the same or higher than the specification. If a cartridge is not integral, the bubble point will be reached at a pressure lower than the specification. The bubble point specification is independent of cartridge length or number but varies with pore size and filter material. Air diffusion is the amount of air that will diffuse through a wet membrane at a specific temperature and pressure over a given time. The diffusion specification is given in either cc/min or ml/min. These values are the same (1 ml = 1 cc). If a cartridge is integral, the amount of air diffusing through the membrane to the downstream side will be equal to or lower than the specification. If a cartridge is not integral the amount of air diffusing through the membrane will be greater than the specification. Air diffusion specifications are usually given on a 10″ cartridge basis. If using a longer cartridge length, the specification must be scaled up. Multiple cartridges within a housing must also be accounted for. Gases other than air can be used for integrity testing and so filter manufacturers will have specifications for other gases developed; these are not usually listed in primary literature, but will be given upon request. Integrity testing is covered in detail later in this chapter.

Cartridge Filters

69

Chemical Compatibility Most cartridges are chemically compatible with common materials and chemicals. There are some well-known compatibility issues such as PVDF with caustic, and nylon with peroxyacetic acid. If a filter cartridge isn’t compatible with something, it will typically not be listed in a datasheet by the manufacturer, so it is best to check. When determining the filtration device for a process, be sure to list all products, chemicals, temperatures, and materials that will come into contact with the filters and ask the manufacturer specifically for compatibility. It is completely acceptable to ask for compatibility test data. Most manufacturers perform extensive compatibility studies during initial product validation and are often willing to perform such testing for free if they do not have data already developed. Disposable Filter Devices Filter manufacturers have recently released product lines composed of small- to medium-sized disposable filters pre-loaded into disposable plastic housings (capsules). An example is shown in Figure 2.16. Disposable filters and housings are ideal for small manufacturers wanting to avoid capital expense or specialty processes that are infrequent or are not standard with all product batches or types. Disposable filters

Figure 2.16.

Disposable filter device.

70

Beverage Industry Microfiltration

are excellent in new product development and R&D endeavors. These filters are available in several formats, including sanitary tri-clover clamp, so that they can be easily placed into a process line, used, and thrown away. Some devices are pre-sterilized and most can be sterilized through either autoclaving or irradiation. Disposable filters work well for point-of-use gas filtration since there is no need to wet and integrity test upon installation. The filter can then be used for the specified time frame and thrown away. This eliminates hassles concerning alcohol wetting and integrity testing and the sanitation of non-product lines, which may not be properly set up with the required utilities or equipment. Manufacturers, Distributors and Resellers Filter suppliers can be broken into two categories: manufacturers and distributors. Within each category there are other differentiators such as size, markets served, and geography. Manufacturers Cuno, Domnick Hunter, Millipore, Pall, and Sartorius are the primary suppliers of filter cartridges to the beverage market. These five companies comprise an overwhelming percentage of the total microfiltration market. Each of these manufacturers is a multinational organization with a wide range of products and services supplying multiple markets (beverage, industrial, pharmaceutical, laboratory, etc.) and are filtration industry leaders. In addition to the five manufacturers listed above, there are literally dozens of smaller filter manufacturers as well as small branches of large conglomerates that do not necessarily specialize in beverage process filtration, such as GE’s Osmonics Division. These smaller organizations will often sell filters at prices below those of the large companies; however, price alone should never be the only factor in filter selection. Compromises on quality, technical service, support, reliability, and product availability can come with a discount price. Personal experience has shown that large beverage manufacturers who consume a high number of filters will benefit from the increased customer support, higher quality focus, multigeography support, and product reliability that the large filter companies offer. Large beverage

Cartridge Filters

71

customers will be able to negotiate the per filter cost to reduce the higher cost of name-brand filters. Large beverage filter consumers are sometimes able to cut the price of filter cartridges by 20–50% as part of supplier agreement negotiations. On the other hand, small beverage manufacturers will often consume so few filters that the associated benefits of the 10–20% per cartridge price difference of the smaller vendors will amount to only a few thousand dollars at most, often much less. This savings doesn’t usually justify the potential sacrifice of quality, reliability, and service that goes with choosing the smaller filter vendors as opposed to the primary suppliers. Each beverage plant should make its own best decision as to which filter manufacturer and supplier will suit its needs and budget best. Suppliers, particularly the larger ones, will oftentimes sell to the beverage market through various third-party channels, and so sales and support to the beverage customer will usually come from a combination of distributors and direct sales depending on geography, country, and/or specific market. Distributors and Resellers Due to the fragmented and widespread nature of the beverage industry, large filter manufacturers often employ skilled distributors to assist in sales and support. There are literally thousands of food, beverage, and associated companies and plants in the United States alone. Most of these customers are not large individual users of filters, so the beverage industry may not warrant the filter manufacturers keeping huge specialized sales forces. Through employing a distributor that specializes in a particular industry (brewing, for example) who represents many associated products such as other equipment, enzymes, packaging materials, chemicals, and so forth and has a pre-established customer base, the filter companies are able to better penetrate the beverage market without overloading their own in-house technical sales and service staff. This is particularly useful when dealing with a wide variety of beverage markets such as dairy, wine, beer, juice, bottled water, alcohol, etc. In exchange for their services, the distributors will apply a markup on the resale of the filters they purchase direct from the manufacturer. Manufacturers will discount the sales to the distributor so that the subsequent markup is barely noticeable to the end beverage customer. Filtration companies who employ distributors may still supplement the distributors with a few highly skilled internal staff to

72

Beverage Industry Microfiltration

provide high-level technical support and to interface with internal groups back at the manufacturer. Just as all filtration companies are not the same, so too, not all distributors are created equal. Distributors may focus on only one market, such as water or beer, or may cover the entire food and beverage sector and/or multiple industries. Some distributors are purely local, focusing solely on the large Californian wine industry, for example, while others are national or even multinational. Large distributors will represent more products — especially name brand products, and will often represent more diversified products. Top level distributors will sometimes have their own technical staff and engineers to assist in process development or support of their customers. All beverage plants interact with a distributor for some products and these relationships can often be leveraged into filtration supplies.

System Operation This section will review common procedures and issues pertaining to the operation of a typical cartridge-based microfiltration system or process. Every process is different — differences in equipment, filters, process streams, climate, facility age, operator training, acceptable chemical usage, and other factors will mean that no single guideline can be used in every facility. This review will not be all-inclusive, but it will cover many of the ins and outs of system operation as well as offer an in-depth explanation about a process that is not well understood in industry. Installation There are dozens of different types and formats of cartridges used throughout the beverage industry. There are equally as many housing styles and manufacturers. No single quick reference guide can be applied to all situations. There are generally four main types of cartridge installations. Flat End or Gasket — Double Open-Ended Cartridges Double open-ended cartridges (DOE) are a common style for prefiltration and clarification filters. Most double open-ended cartridges have

Cartridge Filters

73

end caps made of, or covered in, a flexible polymer material that functions as a sealing mechanism when pressure is applied. DOE cartridges may otherwise have gaskets at the end, which function as the sealing mechanism. Installations usually have a guide post onto which the cartridge core is placed. There is a seat cup at the bottom, and the top is held down by a pressure mechanism. This is most commonly a spring cup assembly (Figure 2.17). The spring cup assembly is a cup that fits into the inner core of the top of the cartridge attached to a spring that is compressed upon the tightening of a top hold-down plate (Figure 2.18).

Figure 2.17.

Spring cup assemblies hold double open-ended cartridges in place.

Inlet

Figure 2.18.

Double open-ended installation.

Outlet

74

Beverage Industry Microfiltration

Figure 2.19. Over-tightening of crush seal cartridges can result in splitting the cartridge end cap and bypassing of contaminants.

Installation: • Open the housing and remove used filters. • Slide the new filters to be installed over the cartridge guide posts. • Place the spring cup assembly into the top open end of the cartridge with the spring side facing upward. • Place the hold-down plate on top of the springs. • Tighten the hold-down plate taking care not to over-tighten. Overtightening of filters is common and can result in cracking or splitting of the gasket end cap material and lead to bypass (Figure 2.19). A good rule for most filters and housings is that the springs should compress 3/4 of an inch. • Reassemble the filter housing. Locking with O-Ring — Single Open-Ended Cartridges Locking tab filters with an o-ring seal (Figure 2.20) are the most dependable for proper installation. Locking tabs, dual o-rings, and single open-ended filters are fast becoming a standard with new systems and, in particular, those using membrane final filters. O-ring sizes can vary (usually between either 222 or 226) so it is important to verify the correct o-ring size and adapter dimensions of the housing.

Cartridge Filters

75

Dual Locking Tabs

Figure 2.20.

Locking tab cartridge end cap design.

The top of these cartridges may be closed with either a flat disk or an end cap that has some form of adapter such as a spear. A critical final membrane filtration step should use this style of cartridge. Installation: • Open the housing and remove used filters. • Wet the new filter o-rings and ensure that they are properly seated in the cartridge grooves. • Align the tabs on the cartridge’s open end with the tabs machined into the housing receptacle. • Press down to ensure the cartridge is fully inserted into the housing. • Twist the cartridge 90 degrees to ensure that it is locked into place. It is best to twist the cartridge from the bottom-most 10″ element to avoid placing additional stress on the element bonds. • Ensure that both tabs have been locked into place. It is a common error for one of the tabs to rise up from the receptacle when first twisting. This may create bypass or cause an integrity test failure if dealing with a membrane system. • Filtration housings such as this often have a hold-down or anti-sway plate. Place the plate on top of the cartridges if equipped. • Reassemble the filter housing.

76

Beverage Industry Microfiltration

Keep in mind that installing the filters correctly is only one part of the task. The housing must be reassembled properly and should be inspected for such things as damaged o-rings during each fresh installation. Filter installation is also a good time for a thorough rinse of the filter housing to remove any large particles that may have accumulated on the bottom plate of the housing, as this may be the only way to remove them. Flat End or Gasket — Single Open-Ended Cartridges Flat end, single open-ended (SOE) cartridges have either a flat gasket on the bottom of the filter or an end cap that acts as a crush seal. These single open-ended cartridges are not the same as single open-ended cartridges that utilize o-rings to form a seal. Flat-end SOE cartridges must be held down by some sort of pressure mechanism from the top. Guideposts and bottom seat cups help to install the cartridges and keep them from shifting. Installation: • • • • •

Open the housing and remove used filters. Slide the new filters to be installed over the cartridge guide posts. Place the hold-down plate on top of the cartridges. Tighten the hold-down plate, taking care not to over-tighten. Reassemble filter housing.

Non-Locking with O-Ring — Single Open-Ended Cartridges Non-locking cartridges with o-rings (Figure 2.21) are usually just pushed down into place. The o-rings form the seal. There may or may not be other components such as anti-sway plates that help to stabilize the cartridges. Housings with these cartridges should be assessed for the possibility of the cartridges coming out of place. Reverse flow cleaning can easily cause these cartridges to dislodge from the housing receptacle if there is not a second means of keeping the cartridge properly seated. The top of these cartridges is closed with either a flat disk end cap or an end cap with some form of spear or other component on the top. O-ring sizes can vary between cartridges, but are usually 222 or 226. There should be two o-rings per cartridge. Installation: • Open the housing and remove used filters. • Wet the new filter o-rings and ensure that they are properly seated in their grooves.

Cartridge Filters

Figure 2.21.

77

Non-locking dual o-ring end cap design.

• Align the cartridge’s open end above the receptacle and insert the cartridge. • Press down to ensure the cartridge is fully inserted into the housing. Gently twisting the cartridge may help in the insertion. • The filtration housing may have a hold-down or anti-sway plate. If so, place the plate on top of the cartridges. • Reassemble the filter housing. Non-locking o-ring–style cartridge filters should not be subjected to significant reverse flow as it may cause the cartridges to dislodge from the housing receptacles. NOTE The housing dome can be large and heavy. Some housings, particularly double open-ended, will have a top that swivels to allow for cartridge removal. The others will normally have some type of lifting mechanism attached to the dome. This is sometimes in the form of two large handles welded on the sides of the dome. Lifting lugs, pieces with circular holes, can be welded onto the top of the dome. Most large housings in high-quality operations will have some type of mechanical lifting means to avoid operator injury. This can be via a pulley, counterweights, or crane system. Counterweights are the most common. There is no standard system for removing housing domes and most are made in-house. Operation Operating a cartridge microfiltration system is mostly a matter of startup and shutdown. Sanitation and cleaning is performed outside of the

78

Beverage Industry Microfiltration

period between start-up, and shutdown is discussed separately. Differential pressure is the primary parameter to monitor for all systems. Individual processes may have other parameters such as SO2 or N2 addition at the skid or flavor additions that may require monitoring; but with regard to the filtration itself, differential pressure is the best indicator of process performance. Start-up Start-up usually occurs just following the pre-run sanitation cycle that often precedes a product run. When starting up a cartridge microfiltration train, it is important to slowly introduce flow into the housing and keep the housing vent valve open until a steady stream of liquid flows through the vent outlet and any gas is evacuated. Open the housing outlet valve before opening the housing inlet valve to avoid pressure shocks. When the system is first under pressure, either during the initial sanitation or when first running product, check the system for leaks. Start-up is a good time to record the differential pressure around each filtration stage. The first few minutes of a process run will require some monitoring and additional venting, but once the system is fully operational, only periodic differential pressure checks and venting, with some products, is required. Venting Ensuring that a microfiltration housing is properly vented is one of the most overlooked yet important aspects of operating a microfiltration train. Failing to properly vent a housing will lead to the formation of a gas bubble at the top of the housing dome (shown in Figure 2.22). As the gas bubble increases in volume, it will begin to overlap the filter cartridges and prevent flow through the upper portions of the cartridges. This will not only lead to underutilization of a system’s available filter service area but will make it appear as if the system has a higher differential pressure than it actually should, because the same amount of liquid is being pushed through a smaller filter surface area. It is easy to tell when a system is not being properly vented by one of the following methods: • Open the housing vent valve. Liquid should quickly flow through the valve if the housing is being vented regularly.

Cartridge Filters

79

Housing Vent

Gas Bubble

Inlet

Outlet

Figure 2.22. Failing to vent a filtration housing during cleaning or operation allows for the formation of a gas bubble within the housing dome.

• Filters should usually be inspected upon removal or replacement. With many cases of poor venting, it can be seen that the top elements of the cartridges are less worn or less discolored than the bottom elements. Wear should be uniform throughout the entire cartridge. • Many beverages passing through a filtration train are chilled. Condensate will often form on the outside of the filtration housings as a result. If this condensate is missing from the top of the housing dome, but present nearer the bottom, then there is likely an air bubble in place of liquid. Not properly venting microfiltration housings is a problem during cleaning and sanitation of a system. Gas bubbles are actually more common during cleaning and sanitation than during production. The biggest problem created by improper venting during cleaning/sanitation is inadequate contact: when there is a gas bubble, the flushing water or cleaning chemicals cannot reach the top portion of the cartridges or housing dome and the system is not properly cleaned or sanitized. The most important time to vent a microfiltration housing is after starting flow, either for a product run or for cleaning/sanitation, or after significant periods of downtime. It is important to periodically vent the

80

Beverage Industry Microfiltration

housings during the filtration as well, particularly if running a carbonated product or a product with a high dissolved oxygen content. Temperature can affect the frequency of required venting, as a higher temperature will be more likely to cause gases to come out of solution. Monitoring Differential Pressure Differential pressure is one of the easiest and most valuable parameters to monitor in a microfiltration process. Differential pressure over the course of a filtration run relates to the degree of filter plugging or reduction in service life a filter is experiencing. Differential pressure can alert an operator to the following: • • • • •

When a process is reaching its capacity When filters are nearing their change-out specification When filters need to be cleaned or regenerated The length of time a process can continue to run When there may be a negative impact to downstream processes by particulate breakthrough or a loss of flow

Differential pressure for normal flow cartridge filtration increases throughout the filtration cycle in a manner similar to Figure 2.23. Note the way in which the differential increases faster as the filters plug. It may take many months for the filters to reach 75% of their recommended differential pressure limit, but then only a few days to reach 90–100% of the specification.

Differential Pressure

Time

Figure 2.23. Differential pressure usually builds exponentially during a filtration cycle.

Cartridge Filters

81

Filter Regeneration

Differential Pressure

Time

Figure 2.24.

Cleaning partially restarts the filter plugging cycle.

Differential pressure can be reduced by cleaning the filters. This will not be 100% effective and even with ideal cleaning and filter regeneration there will be a differential pressure build-up over the filter service life. A filtration that was run with periodic cleaning is shown in Figure 2.24. Optimization of cleaning procedures can increase filter service life many times over the service life without cleaning. When determining a filter’s differential pressure change-out specification, it is important to factor in the starting differential pressure that is inherent to all cartridge filters. If a there is an initial differential pressure of 2 psi (138 mbar) with a filter change-out specification of 15 psi (1,034 mbar) then the filters should actually be replaced at a differential pressure of 17 psi (1,172 mbar), not 15 psi (1,034 mbar). Production time is costly. It is important to quickly diagnose which stage of a multistage filtration train is plugged. Table 2.3 may be adapted to a process and used to quickly determine which filtration stage is plugged by simply looking at the system pressure gauges. Shutdown When a product run is finished, it is almost always recommended to perform a rinse or sanitation of the filtration equipment. This not only cleans or sanitizes the system but also removes particulates and contaminants from the filters and can help to extend their service life. Industries such as alcohol production do not always perform a shutdown procedure and may simply close the filtration system inlet/outlet

82 Table 2.3.

Beverage Industry Microfiltration Fast determination of plugged stage in a multistage filtration train.

Outlet pressures (psi [mbar]) Pump 20 (1,379) 30 (2,068) 40 (2,758) 50 (3,447) 60 (4,137) 70 (4,826) 90 (6,205)

Clar. 0 30 (2,068) 40 (2,758) 30 (2,068) 40 (2,758) 70 (4,826) 60 (4,137)

Stages plugged Prefilt. 0 0 40 (2,758) 0 40 (2,758) 40 (2,758) 40 (2,758)

Clar. X

Prefilt.

Final

X X X X X

X X X

X X X

Assume: 1. Clarification stage plugs at 20 psi (1,379 mbar). 2. Prefiltration stage plugs at 30 psi (2,068 mbar). 3. Final Filtration stage plugs at 40 psi (2,758 mbar). Note: 1. Pump outlet can be read as the clarification stage inlet. 2. A centrifugal pump feeding this train should be sized so that it can meet the minimum flow requirements with up to 90 psi (6,205 mbar) outlet pressure.

valves, leaving product in the system, until the next production run. It should be realized that while this is fine with regard to the microbial stability of the system, it does nothing to clear particulate material from the filters or regenerate the filters. When performing a shutdown of a filtration system, always close the feed valve, stop the feed pump, or divert flow before closing the filtration system outlet valve. Remove the pressure contained within the housings before opening. Opening the top vent valve aids in draining the housing. Maintenance Filter housing maintenance is often a tricky issue for the plant. Many filtration systems and housings being used in industry today are old and are no longer produced. To make matters worse, many of the companies that once produced filtration housings have been bought out or otherwise no longer exist. Even if an old housing is still being made by an existing company, they may not have parts in stock, and some companies are reluctant to offer good customer service if the plant is

Cartridge Filters

83

no longer using that company’s filters. Conversely, if the current filter supplier is contacted about a housing they did not originally manufacture, they may not be able to help with parts or service for the housing. Many beverage plants have well-equipped machine or maintenance shops and will be able to create and repair common parts. Some plants will not and will have to order replacement parts. O-rings and gaskets for housings are typically easy to fabricate, but care should be taken when repairing old or broken ones. Parts such as proper cartridge guide posts or spring cup assemblies are more difficult to make in-house. All housing parts should be inspected regularly as part of a preventative maintenance program, and at least one spare for commonly broken or lost parts should be kept on hand. Most of these parts don’t cost much, but having spares can save tremendous time, effort, and money if a plant is caught in a line-down situation. Filters should be manually inspected whenever a PM is scheduled. It is advisable to schedule regular filter checks in unison with filter change-out criteria. If a filter is to be replaced every three months, for example, the filters should be visually inspected every six weeks. It is not uncommon for a plant to discover broken, warped, or damaged filters that should be replaced during these inspections. Odors, foreign materials, and other such issues can be discovered during these checks. Cleaning, Sanitation, and Storage The cleaning, sanitation, and storage of filters, particularly of membranes, is one of the most difficult subjects within the industry. While most cleaning chemicals will work to some degree, true guidance from the filter manufacturers regarding the best chemicals or solutions, or the concentration, temperature, length of cleaning, or frequency of cleaning is almost nonexistent. This is surprising given that one of the major advantages of cartridge filters over other microfiltration formats is their ability to be cleaned and reused repeatedly. Confusing the issue further are the many chemical supply companies (who are not affiliated with the filter manufacturers) who push their chemicals into beverage plants and have their own data on cleaning or sanitation with respect to filters and their products. Cleaning can be described as the removal of particles, debris, and cells from the filters to either maintain or restore performance. Clean-

84

Beverage Industry Microfiltration

ing helps to disrupt the formation of biofilms. Sanitation is specifically designed to kill microorganisms, particularly those that may be present downstream of the filters, compromising system sterility. A good program will combine regular cleaning and sanitation cycles and must take the following items into consideration: • • • • • • •

Cleaning/Sanitation fluid Temperature Frequency Concentration Contact time Contaminants present Varying of chemicals

Most of these parameters are self-explanatory, with the exception of two: contaminants present and varying of chemicals. Varying of chemicals is a solution to the fact that some microorganisms can build up a resistance to cleaning/sanitation chemicals. Many industries, particularly bottled water, find it helpful to vary the chemicals used. One week may see a peracetic acid-based cleaner used, for example, and the next a chlorinated cleaner. In terms of contaminants, it is important to understand what needs to be cleaned from the system. There are three main types of materials that are deposited onto filters: • Rigid particles • Organics • Inorganics Depth and prefilters should retain the majority of rigid particles and many organic colloids. Membrane filters should retain the majority of microorganisms. Many inorganic materials such as silicas or calcium carbonate may be present at various stages. Monitoring differential pressure during cleaning and sanitation can be more important than monitoring during production. Cleaning and sanitation is often performed with hot fluids, and filters are more susceptible to damage when hot. Differential pressure limits on cartridge filters will steadily decrease as the fluid temperature increases. Reverse cleaning or flushing of filters must be closely monitored. Many filters are considerably weaker when reverse flushed with hot fluids. Most

Cartridge Filters

85

manufacturers do not recommend hot reverse flushing except in certain situations when they are certain the plant can properly manage the system. Some manufacturers never recommend hot reverse flushing. The reason for this difference in approach is the large range of hot reverse stress tolerances between the various manufacturers’ filter offerings. Personal experience has shown that Millipore’s Vitipore II line is one of the best filters with regard to reverse stress tolerance, with some data showing as much as a 38% increase in reverse stress tolerance over some other major manufacturers’ cartridge filters.

NOTE 1. For most beverage cleaning processes, it is important to begin each cleaning or sanitation cycle with cold water rather than directly starting the cleaning cycle with a hot fluid. First rinsing with cold water prevents some materials, such as proteins, to be “baked” onto the membrane or filter. While the temperature at which this occurs varies between process streams, 130 F (54 C) is a good starting place as many of the commonly observed proteins will coagulate beginning at that temperature. 2. When changing from cold to hot water or chemicals, the temperature increase should be gradual, if possible. Quickly changing from cold to hot water and vice versa can lead to micro cracks at the media–end cap bonds. These micro cracks are a leading cause of filter failure when dealing with membrane filters. 3. Venting filter housings is sometimes more important during cleaning and sanitation than during production. Air/gas bubbles form more readily during most cleaning/sanitation cycles than during production and can prevent hot water or chemicals from reaching the top of the filters, cartridge hold-down plate, top of the housing dome, or venting apparatus. This, in effect, creates a dead leg right in the middle of the filtration process.

Water used for cleaning and sanitation is best when filtered to the same pore size rating (or lower) than the filters being cleaned. If unfiltered water is used to clean a 0.45 μm membrane, the water can be depositing just as much as it is removing. Similarly, a 0.22 μm bottled

86

Beverage Industry Microfiltration

water membrane filter, for example, should not be cleaned using 1.0 μm filtered water, as there will be a tremendous amount of material in between the two pore sizes that will be deposited onto the 0.22 μm membrane. This is the same for water used for CIP chemical makeup. There have been plants that have added filtration on cleaning and sanitation systems and experienced huge reductions in subsequent product filter spending. Cleaning and sanitation chemicals are readily available from a number of companies that specialize in them. Oftentimes these chemical suppliers work with filter companies to perform filter compatibility testing, but this is not always the case. A beverage plant should ask both the chemical supply company and the filter manufacturer if such data exists. Following the chemical manufacturers’ recommendations can be important. It is also important to realize that many of the “proprietary” or special chemicals offered by the sanitation companies are nothing more than mixtures of commonly recognized cleaning chemicals. Most solutions simply contain a mixture of sodium hydroxide, chlorine, hydrogen peroxide, acetic acid, nitric acid, phosphoric acid, and/or peracetic acid. Hot chemicals are better antimicrobial agents than cold chemicals; however, the chemical compatibility of many filters and chemicals decreases with an increase in temperature. If dealing with hot chemicals for cleaning and sanitation, make sure that the chemical compatibility studies have been performed at the maximum temperature the fluid will reach during sanitation. Ozone should not come in contact with most cartridge filters. Ozone will oxidize and degrade any polypropylene support materials. While there may be some cartridge filters that are ozone compatible, the vast majority are not. Cartridge filters made entirely of Teflon are an exception and are usually ozone compatible. It is known that UV degrades ozone, and so a very few water bottlers, whose products require heavy use of both ozone and UV, have opted to place ozone, followed by a UV lamp, prior to a microfiltration system. This is not recommended, as there is little benefit and tremendous risk should the UV system fail. Cleaning Rigid Particles Rigid particles such as sand or DE are nondeforming and must be removed from the filters. Reverse flushing to drain is one of the best

Cartridge Filters

87

Reverse CIP Flow

Forward CIP Flow

Figure 2.25. particles.

Reverse flow often outperforms forward flow in the cleaning of rigid

methods for removal. Forward flushing will not always remove these particles as they may not degrade in heat or be pushed through a filter. The difference between the two flushing methods is shown in Figure 2.25. Pushing rigid particles in the forward direction through a depth filter is not a feasible cleaning method, as it takes a high pressure, will usually take a long time, and may simply push the particles downstream to the membrane. Reverse flushing in a multistage system without sending the flow immediately to drain will prove ineffective as well, since the particles will simply plug the downstream side of the previous filter or will be deposited elsewhere in the system. In this case, the particles will end up right back on the filter when flow resumes. Rigid particles may also be removed by filling the housing and draining through a bottom drain valve on the upstream side of the filters. This is not as effective as reverse flushing to drain and does not do a good job at removing the particles from the depth matrix. Many particles will dissolve or breakdown in hot water in the forward direction. It is not always necessary to reverse clean — however, it can be beneficial in some instances or processes. Cold water is almost as effective as hot water when removing rigid particles, since it is only a matter of pushing them out of the system. This is important to remember since reverse flushing is one of the most effective means of removing rigid particles and many cartridge filters may not withstand hot water reverse flushing as well as cold water

88

Beverage Industry Microfiltration

reverse flushing. (Although using only cold water in the reverse direction will do little in the way of removing organics and miscellaneous inorganics.) It is best to perform reverse flushing of rigid particles before the filter is completely plugged. When a filter becomes completely plugged the increased differential pressure causes particulates to migrate deeper into the filtration matrix, Cleaning at 80% of the recommended change-out differential pressure is often a good starting point. Please note that this is not to be confused with 80% of the cartridge’s maximum pressure tolerance specification, which deals only with device strength. Cleaning Organics Organic particles may be broken into two groups: • Microorganisms • Colloids Microorganisms are usually removed by destroying their cell walls with hot water or a chemical (Figure 2.26). Microorganisms that form colonies are more difficult to remove than those that do not. A protective layer of secreted polysaccharides will protect the colonies from coming into contact with the hot water or cleaning chemical. Cleaning to remove microorganisms may be performed in either the forward or reverse direction with similar results. Reverse direction will usually perform somewhat better, but it requires close monitoring of reverse differential pressure, good controls, and a sound understanding of the filters in use. In either forward or reverse cleaning, it is best to send the flow to drain before it reaches either an upstream or downstream

Forward Hot CIP Flow

Figure 2.26. Hot water and/or CIP chemicals will break down many organic materials. This facilitates their removal from the filter.

Cartridge Filters

89

filter. This is not as crucial, however, as when dealing with rigid particles. If heating systems or hot water is not available in the plant, chemicals must be used to kill/break down microorganisms. Chemicals commonly employed include chlorine, hydrogen peroxide, peracetic (peroxyacetic) acid, and caustics. Organic colloidal materials may be removed either by dissolution with hot water or chemicals. Chemicals can include chlorine, hydrogen peroxide, peracetic acid and so forth. Hot chemicals are more effective than cold chemicals. Cleaning Inorganics Inorganic materials are often present on process filters as a result of poorly treated service water. Such materials are heavily present on service water filters and in some water bottling plants. Some inorganic particles can be colloidal. Carbonates present on the filters may be removed with a citric acid recirculation. Warm citric acid should be used when possible. Sanitation/Sterilization Steam sterilization of cartridges has been reported to cause a slight decrease in filter performance with each subsequent sterilization cycle. Steam sterilization can still be an excellent method to sterilize process piping, lines, and filters. Most filters have recommendations regarding the maximum number of safe steam sterilizations but, like any other cleaning or sanitation of the filters, should always be followed by an integrity test before being put into service. Steam used for filter sterilization should be filtered. Stainless steel sintered metal membrane cartridge filters are made for this application. These filters are typically expensive but will normally only require one filter and will last a number of years. Steaming a wet membrane filter can cause a rapid increase in differential pressure. Because the system is now at an elevated temperature, this increased differential pressure can easily damage filters. Filters should be steamed dry or at least partially dried to a point where they will not be damaged. Anticorrosion agents are sometimes added to central steam supplies. The compatibility of these chemicals should be verified with the filter being steamed. Few beverage plants in the United States use steam on process filters; however, this is slightly more common in Europe.

90

Beverage Industry Microfiltration

Chemical sanitations are used by many manufacturers. Care should be taken to use a sufficient chemical concentration to achieve the desired effects without using so high a concentration that the filters are negatively impacted. Remember that hot chemicals are more effective than cold chemicals; you must ensure that a chemical is compatible with the filters not only at ambient temperature but also at the maximum temperature seen in a sanitation process. Hot water at 180 F (82.2 C) or higher may be used for sanitation of the filter housings and cartridges. A proper analysis should be made concerning contact time and any potential dead legs in the system. All areas that come in contact with product should reach 180 F (82.2 C) for the desired cycle time. Cycle times vary, but are often between 15 and 30 minutes at the desired temperature. The QA/QC department of any beverage manufacturer should be actively involved in both designing and maintaining adequate sanitation regimens throughout the plant. Storage It is not always necessary to perform special storage procedures for cartridges. For the most part, the benefits of storing cartridges are antimicrobial. There are, however, instances in which such procedures can also lead to filter regeneration. This is accomplished through the addition of a special chemical or step in the storage process. Some beverage plants remove and store cartridge filters in a chemical solution. Others will fill the entire filtration housing with the storage solution when not in use. Plants may use storage procedures not only for long-term storage but also during weekend or holiday shutdowns or during periods of extended maintenance. When not being used in process, filters are susceptible to microbial growth. There are many chemicals that can be used for storage. Most storage chemicals require dilution or mixing with water. Filtered water is best. Peroxyacetic acid, ethanol, sodium metabisulfite solution, and even formaldehyde are all used. Peroxyacetic acid and sodium metabisulfite are common in the bottled water industry and for shorter-term shutdowns. Ethanol is increasingly being used for between-crush storage of filters in the wine industry. Formaldehyde is only for long-term storage and can present some health hazards, so it is rarely used. As with cleaning chemicals, the chemicals used for storage are usually available under many different trade names.

Cartridge Filters

91

Filter manufacturers sometimes recommend that, if a process is only shutting down for a day or two, hot water from the shutdown sanitation be used for storage. Wineries with tank blanketing systems may pressurize the filtration housings with nitrogen if shutting down for weekends or other short time frames. Any of the inert gases commonly used for tank blanketing such as N2, CO2, or argon would suffice. Antimicrobial activity can decrease in some chemicals over time. Peracetic acid (peroxyacetic acid) is one such chemical and requires renewing the solution every 3–4 days in periods of extended storage. Chemical compatibility studies should be more exhaustive when determining a proper filter storage solution due to the increased contact time. One day of storage can be the equivalent of many months of 30minute chemical treatments or cleanings. O-rings should be checked for their own compatibility. Most types of o-rings should be removed and stored separately if storage solutions of ethanol or those containing sodium metabisulfite or potassium metabisulfite are used for more than short time frames. Specialized Treatments Individual cleaning processes can be tailored to a specific filter plugging agent. Plugging component analysis (SEM, EDS, or FTIR) should be performed to determine what plugging components are present before and after cleaning. Targeted chemicals can then be evaluated. Perhaps the best known result of such a program is the use of beta glucanase enzyme in beer and, to a lesser extent, wine. Adding 5– 10 ppm of this enzyme to a housing volume of storage solution or rinse water and allowing it to sit for a few days has been proven to help clear various glucan-based plugging agents off of filters, particularly membranes, used in final filtration processes. Many breweries that use large scale microfiltration add beta glucanase enzyme or a mixture containing beta glucanase enzyme to the beer before clarification. This improves the subsequent filterability of the beer, which improves filter service life and the quantity of beer that can be processed in a single run. Pectinase and hemicellulase enzymes can be used to increase the filterability of juices. The recirculation of citric acid has been proven to assist in the elimination of some flavor and aroma carryover concerns in various

92

Beverage Industry Microfiltration

beverages including wine, flavored beer, and specialty malt beverages. A 1–2% solution should be sufficient.

Integrity Testing Integrity testing membrane filter cartridges ensures that the intended retention characteristics of the membrane and the system are being met. Only membrane filters can be integrity tested. Integrity testing detects errant pores within the membrane, membrane defects such as cracks or cuts, cartridge defects such as damaged o-rings or a cracked end cap, as well as filtration housing defects such as a housing leak or damaged housing o-ring or gasket. Integrity testing also ensures that the membrane cartridge has been properly installed. It is the goal of integrity testing to detect any situation that can cause particles larger than the pore size rating of the membrane to pass downstream of the filter. Integrity tests were initially designed for the pharmaceutical and biotechnology industries that use much smaller filtration housings than many beverage processes. Most pharmaceutical processes use filtration housings between 1 Round 30″ and 5 Round 30″. Even 12 Round 30″ housings are relatively uncommon in biopharmaceutical plants as compared to beverage plants. Beverage processes such as wine, bottled water, and beer, in particular, often use housings in the 36 Round 30″ to 55 Round 30″ range and can be as large as 98 Round 40″ in some major breweries. Bubble point integrity testing cannot be reliably performed on housings this size. Pressure hold or forward diffusion integrity testing is usually performed. These two tests rely on the maximum acceptable diffusion specification of the test gas through the wet membrane. This value is scaled up via one of several equations that will be presented later to determine the maximum acceptable pressure drop or allowable air diffusion during the integrity test. Sensitivity problems with pressure hold and air diffusion integrity testing of large multi-round filtration housings can occur since many integral membranes have an actual diffusion that is lower than their maximum specification. If a particular 30″ cartridge’s maximum specification is 20 ml/min and the housing is a 36 Round 30″ and 35 of the cartridges are integral with an average actual diffusion of 15 ml/min, the one remaining cartridge can appear to be integral with a diffusion

Cartridge Filters

93

of 195 ml/min. This is well beyond the single cartridge’s 20 ml/min maximum integrity specification. While most integrity failures will be large enough to detect despite this of lack of sensitivity, the issue can still be of concern to many manufacturers. While there is no complete solution to the problem, there are several options that can reduce the likelihood of a problem: • Rather than using a single large multi-round filtration housing, two or more smaller housings can be used in parallel. These housings can then be individually tested and will have a higher degree of sensitivity. This may save money, as there are fewer cartridges that need to be replaced when one housing fails integrity testing. Alternatively, some filtration systems (such as Pall’s Cluster Filtration System [CFS]) integrity test large housings in clusters, which results in an increase in sensitivity. A 98 Round 40″ beer CFS system, for example, is divided into seven 14-filter clusters for integrity testing. • Some filter manufacturers individually test every membrane cartridge during the manufacturing process. While this cannot detect defects due to installation damage, damage during processing, or improper installation, it can eliminate the possibility of errantly large pores or membrane manufacturing defects, which will more often be the smaller integrity issues that can go undetected. Cartridges damaged during installation or processing will often fail in a large enough fashion to be detected despite the decreased sensitivity. • Many manufacturers have developed average integral diffusion specifications as opposed to maximum allowable diffusion specifications. These values are not usually published in the literature and must be requested. Using the average integral diffusion specification when calculating the allowable pressure drop or maximum diffusion of a large housing will increase the sensitivity of the integrity test and reduce the likelihood of one defective cartridge being masked by many integral cartridges. Integrity Test Principles Integrity testing should be performed after installation, after cleaning or sanitation processes, and following any process runs — usually after the post-run CIP has been completed. If filtering large, continuous product batches that run over many days or weeks, it may be best to

94

Beverage Industry Microfiltration

perform intermittent integrity tests to avoid larger product holds should the cartridges fail integrity testing after the process run. In such instances it is usually optimal to develop a specialized integrity test using the product being filtered as the wetting agent, rather than water, to avoid having to clean the filtration system. This will minimize downtime due to the integrity tests. Integrity testing is based upon either measuring the capillary forces of the membrane, as in bubble point testing, or measuring the diffusive gas flow, as in pressure hold or forward diffusion testing. Both types of tests have been correlated to log reduction values (LRVs) developed for every filter using retention test methodologies. Integrity testing can be performed both manually and by using automatic integrity testers available from any of the large filtration companies. Automatic integrity testers can be expensive — the cheapest are several thousand dollars — but can save time, give a higher test sensitivity, and have other benefits such as the recording of test results. Using automatic integrity testers has disadvantages. Automatic integrity testers can yield false positives and false negatives, and the results of every test should be double checked. The most common example of a misleading automatic integrity test is leaving the outlet valve closed during a bubble point or pressure hold integrity test. Since the outlet is closed, there will be no pressure drop to measure; however, the automatic integrity tester will count this test as passing. As with most cases of automation, a trained operator should still double check the test results and not put blind faith into a piece of equipment. Bubble Point Test Bubble point is the most basic and simplest integrity test to perform. Bubble point testing does not require scaling up based on the filter area. Every membrane filter has a bubble point specification. The specification is the minimum pressure necessary to force out the fluid within the membrane pores (Figure 2.27). The bubble point specification is usually given for water. If using a wetting fluid other than water, a different bubble point will have to be used since different fluids will have different surface tensions and viscosities. Bubble points are available in terms of IPA/water solutions for hydrophobic membrane filters. Fluid temperature can affect the bubble point and will be specified with the bubble point value. Manual bubble point integrity testing is usually considered valid for up to a 3 Round 30″ filter housing. Some auto-

Cartridge Filters

95

Air Pressure

Figure 2.27. Bubble point measures the air pressure required to push water out of the pores of a fully wetted membrane.

matic integrity testers claim that bubble point tests can be applicable for up to a 6 Round 30″ filter housing when using the automated unit. Certain double-layered filters are more difficult to be integrity tested via bubble point. This is because pores larger than the specification may be incorporated into the membrane so, while layering improves retention, bubble point detects the larger pores, in some cases, and results in a failing test. Bubble point is calculated using Equation 2.1. Bubblepoint =

4 ( k )( γ )(CosΘ ) d

(2.1)

k = shape correction factor γ = surface tension Θ = contact angle d = pore diameter Manual Procedure: 1. Wet the membrane filters according to the manufacturer’s recommended procedures. Most beverage membrane filters will wet easily. Ensure that the housing is fully vented during the wetting procedure to avoid creating an air bubble. 2. Drain both the upstream and downstream sides of the filters. Open the housing vent valve to assist in draining. 3. Close all valves and drains upstream of the membrane filters. 4. One downstream outlet needs to remain open. Most filtration skids will have a downstream valve on the main outlet piping with a drain valve before the primary outlet valve. It is easiest to leave the drain valve open. Attach the opened drain valve to a piece of tubing and submerge the open end of the tubing into a bucket of water. A bucket of water can also be placed directly underneath the opened drain valve but the outlet must be submerged.

96

Beverage Industry Microfiltration

5. Attach a regulated gas supply to the upstream of the housing. 6. Set the pressure regulator so that the gas pressure is 80% of the bubble point specification. 7. Open the gas supply valve into the housing. Some gas and water will initially discharge from the outlet as the membrane pleat packs compress. 8. Slowly increase the gas pressure. Watch for rapid bubbling from the submerged outlet. 9. The pressure at which rapid bubbling occurs is the bubble point. Compare this pressure to the specification. If the ending test pressure is at or above the specification, the housing and filters are integral. Forward Diffusion Test When there is a liquid held in the pores of a membrane, gas will dissolve into that liquid. When a pressure differential is applied to the system, there will be a different gas concentration across the membrane. If this pressure is applied to the upstream side of the membrane, then the concentration of gas will be higher on the upstream side of the membrane, creating a gradient across the membrane, and resulting in gas flow through the liquid to the downstream side of the membrane (Figure 2.28). Diffusion is calculated by Equation 2.2. Diffusion =

( K ) ( PInlet − POutlet )( p)( A) ( L)

(2.2)

K = Diffusivity coefficient PInlet = Inlet pressure POutlet = Outlet pressure p = Membrane porosity A = Membrane area L = Effective path length Air Pressure

Figure 2.28. Air diffusion, and its variations, measure the diffusion of air through water contained within a membrane’s wetted pores.

Cartridge Filters

97

The overall diffusion specification is simply the number of cartridges or elements within a system multiplied by their individual diffusion specifications. If a filtration housing has five 30″ cartridges, each with a diffusion specification of 20 ml/min per 30″, then the total housing diffusion specification is 100 ml/min. If using a gas other than air to integrity test, ask the filter manufacturer for the specification for that particular gas. Specifications have been developed for most common gases. Nitrogen is often used and typically has about a 20% lower diffusion specification than air. Carbon dioxide has a higher diffusion than air or nitrogen. Test temperature, wetting fluid, and test pressure will affect the diffusion specification. The diffusion specification will change if using a wetting fluid other than water. Diffusion can change drastically with temperature. It is best if the wetting fluid is the same temperature throughout the test. Cooling of the fluid during integrity testing can lead to false values. Manual Procedure: 1. Wet the membrane filters according to manufacturer’s recommended procedures. Most beverage membrane filters will wet easily. Ensure that the housing is fully vented during the wetting procedure to avoid an air bubble. 2. Drain both the upstream and downstream sides of the filters. Open the housing vent valve to assist in draining. 3. Close all valves and drains upstream of the membrane filters. 4. One downstream outlet needs to remain open. Most filtration skids will have a downstream valve on the main outlet piping with a drain valve before the primary outlet valve. It is easiest to leave the drain valve open. Attach the opened drain valve to a piece of tubing and submerge the open end of the tubing into a bucket of water. A bucket of water can also be placed directly underneath the opened drain valve, but the outlet must be submerged. 5. Attach a regulated gas supply to the upstream of the housing. 6. Set the pressure regulator to the recommended test pressure given in the filter specifications. Be careful not to exceed the filter’s bubble point specification, as this will force the water required for the test out of the membrane. The filters will require a new wetting step if this occurs.

98

Beverage Industry Microfiltration

7. Open the gas supply valve into the housing. Some gas and water will initially discharge from the outlet as the membrane pleat packs compress. 8. Wait five minutes for the system to stabilize. 9. Place a graduated cylinder upside down, completely filled with water, into the bucket. Position the graduated cylinder so that the bubbles that periodically come out of the tube are caught by the graduated cylinder. 10. Catch the bubbles into the graduated cylinder for a timed period and relate the volume of air captured to the diffusion specification. If the air diffusion specification is 20 ml/min then there must be less than 20 ml of air in the graduated cylinder after one minute, less than 40 ml of air after two minutes, and so forth. Since gas bubbles do not always come out at regular intervals, it is more accurate to measure the flow for a few minutes rather than just one minute. Pressure Hold Integrity Test Pressure hold integrity testing is best described as a fast gross failure test for large multi-round filtration housings. Manually performing a pressure hold test is much easier than a forward air diffusion test. There is no need for tubing and measurement is simple. Pressure hold operates on the same principles as forward diffusion testing. Gas diffuses through the membrane from the pressurized upstream side of the filter to the downstream side, which must be open to the atmosphere. Pressure hold testing is different in that rather than leaving the gas pressure on, the pressure is shut off at the start of the integrity test, and the drop in upstream pressure is measured over some time period such as 10 minutes. Pressure hold testing is the most common integrity test for large beverage filtration systems. As with other forms of integrity testing, fluid type, gas type, temperature, and pressure will affect the integrity test specifications. Equation 2.3 calculates the maximum allowable pressure drop for a particular system. Pressure Drop =

( D )(t )( P ) (V )

D = System diffusion specification t = Test time

(2.3)

Cartridge Filters

99

P = Atmospheric pressure V = Upstream volume of housing and piping The diffusion specification is given by the manufacturer for a filter at a specific temperature and test pressure using a particular gas when the filter is wetted with water. If there is any deviation from any of these parameters, the given diffusion specification will no longer hold true and must be recalculated. The diffusion used in Equation 2.3 is the system diffusion, and so the number of filters must be taken into consideration. The recommended test time is usually 10 minutes. Atmospheric pressure is 14.5 psi (1,000 mbar). The upstream volume is the volume of the housing minus the volume of the filter cartridges plus any upstream piping that is pressurized during the test. Many new filtration housings come with this volume pre-calculated for use in integrity tests. If this information is not available, filling the housing with water and draining into buckets of a known volume is a simple method of obtaining the housing volume. Do not forget to subtract the volume occupied by the cartridges. A good estimate is that a 30″ standard membrane filter cartridge takes up approximately 700 ml (0.1057 gal) of space. Example Calculate the allowable pressure drop for a 36 Round 30″ filter housing using filters with a diffusion specification of 14 ml/min per 10″ element. The diffusion specification for the filter is 14 ml/min per 10″ element. The specification must be scaled up to represent the fact that 30″ cartridges are being used. Diffusion scales linearly with surface area. Multiply the 10″ specification by 3 to obtain the 30″ specification of 42 ml/min per 30″ cartridge. The diffusion of all 36 cartridges must be considered. The diffusion of the total housing is merely the per cartridge diffusion multiplied by the number of cartridges contained within the housing. The diffusion specification for the entire housing is 1,512 ml/min. A test time of 10 minutes is typically used for pressure hold integrity tests. The atmospheric constant is 1,000 mbar. The housing upstream integrity test volume is 192,000 ml. The upstream piping of the system adds another 2,200 ml to the total upstream volume of 194,200 ml. The pressure drop calculation becomes:

100

Beverage Industry Microfiltration

⎛1512 ml ⎞ 10 min 1000 mbar ( )( ) ⎝ ⎠ min pressure drop = = 77.86 mbar 194,200 ml The highest allowable pressure drop for this system during a 10 minute pressure hold integrity test is 77.86 mbar (1.13 psi). Manual Procedure: 1. Wet the membrane filters according to the manufacturer’s recommended procedures. Most beverage membrane filters will wet easily. Ensure that the housing is fully vented during the wetting procedure to avoid creating an air bubble. 2. Drain both the upstream and downstream sides of the filters. Open the housing vent valve to assist in draining. 3. Close all valves and drains upstream of the membrane filters. 4. Leave the downstream valve(s) and/or drain(s) open. 5. Attach a regulated gas supply to the upstream of the housing. 6. Set the pressure regulator to the recommended test pressure. It is important to set the pressure before opening the gas inlet valve. If the gas supply is attached and regulated to a pressure higher than the test pressure, then the pressure could surpass the bubble point of the membrane filters, which would then require rewetting of the filters. 7. Open the gas supply valve into the housing. Some gas and water will initially discharge from the outlet as the membrane pleat packs compress. 8. Wait five minutes for the system to stabilize. 9. Close the gas supply valve. 10. Monitor the upstream pressure for the specified test time. 11. If the upstream pressure has dropped by the maximum allowable pressure drop or less, the filters are integral. Wetting and Integrity Testing a Hydrophobic Membrane Hydrophobic membranes repel water. It is therefore more difficult to wet, and subsequently integrity test, hydrophobic membrane filters. Filter manufacturers recommend that an alcohol-in-water solution be used to wet the membrane. Most hydrophobic membrane filters will have bubble point and diffusion specifications readily available for such wetting solutions. The most common hydrophobic wetting solution is 60/40 IPA/water followed by 70/30 IPA/water. Some industries may use ethanol/water solutions for convenience, and this works perfectly

Cartridge Filters

101

well, providing that the correct specifications are used for the particular wetting solution and alcohol concentration. Hydrophobic membrane filters are almost always used for gas filtration and tank venting. The installations are typically small, and bubble point testing is most commonly used. The small size of these applications is a benefit for cost reasons. There are usually a small number of filters used in the application, and hydrophobic gas filters can be sourced cheaper than hydrophilic liquid filters. Many beverage manufacturers will only integrity test gas filtration housings upon initial filter installation. Filters in these applications rarely plug, can have a long service life, and require little or no cleaning and/or sanitation. Manufacturers therefore tend to use the filters for a specified length of time and simply throw the filters away after use, which limits the number of integrity tests required. Hydrophobic membranes have been used in some high alcohol product filtrations. In these applications it is easiest to simply wet the filters with product to perform the integrity test. Product-specific integrity test specifications must be developed in this instance. If, for some reason, hydrophobic membrane filters are being used in an application and alcohol solutions are not able to be used, water at very high pressure or static soaking with some surface tensionreducing fluid can be used to wet the hydrophobic filters. Such procedures will vary greatly depending on the filter and equipment setup and should be specially developed for each case. There has been some success in wetting hydrophobic membrane filter cartridges using cold water in the reverse flow. These processes involve introducing cold water slowly into the cartridge’s inner core. The outlet must be restricted so that a pressure above the intrusion pressure of the cartridge is maintained. The intrusion pressure is the pressure through which water will freely flow through the pores. The pressure for a 0.45 μm hydrophobic PVDF filter is around 20 psi (1,931 mbar). The pressure for a 0.22 μm hydrophobic PVDF filter is higher at around 85 psi (5,861 mbar). To reliably wet the cartridges with a reasonable flow, however, the pressure must be held higher than the intrusion pressure. A 0.45 μm hydrophobic PVDF membrane experiences a strong breaking point at 30 psi, and the flow and time required to wet the cartridge significantly decreases. Small filtration housings in the range of 1 to 5 Round 30″ that utilize hydrophobic membrane filters may be easily wetted in the reverse direction with a flow of 2–4 gpm (454–908 lph) per 30″ cartridge in

102

Beverage Industry Microfiltration

reverse at a pressure of 30–35 psi (2,068–2,413 mbar) for 10–15 minutes. Large filtration housings may require higher pressures or flow rates and can run into difficulties that require one or more additional steps to completely wet all of the filtration cartridges. If the filtration housing in the installation uses an inverted design, it becomes considerably easier to wet larger installations by simply holding forward flow at an elevated pressure. The reason for this is the manner in which air is evacuated from the cartridge’s inner core. Troubleshooting an IT Failure Integrity test (IT) failures can be broken into two categories: filter-related and hardware-related. Filter-related failures are due to filter integrity, filter installation, improper wetting, and any other filterrelated scenario. Hardware-related failures can only be attributed to upstream hardware such as the inlet valve, inlet drain valve, housing o-ring or gasket seal, housing vent valve, or damaged housing dome. A failure in a bubble point integrity test can only be related to the filters if the test pressure is exceeded. With regard to diffusion and pressure hold integrity testing, a simple method to determine which type of failure is occurring is to attach a tube to the downstream drain valve. Submerge the tube in a bucket of water and re-perform the integrity test. If rapid bubbling from the submerged tube occurs immediately after the housing has been pressurized to a low pressure, then the integrity failure is related to the filters. If there is little or no bubbling then the failure is related to the upstream hardware. False positive integrity tests are potentially more damaging than integrity failures. The main reason for a false positive integrity test is failure to open the downstream valve. If the downstream valve is not open, there will be no pressure drop. Another common error is failing to turn the gas off after the stabilization step of the pressure hold test. If the gas remains on, there will be no upstream pressure drop during the course of the integrity test. When processing certain beverages or beverage ingredients, various oils or similar substances can coat the membrane. If this coat is not adequately rinsed off, the surface tension of the wetting fluid (water in most cases) will be reduced by the coating substance. The reduction in surface tension will lower the bubble point of the membrane/wetting fluid and will result in a failing integrity test. It can also result in a failure of non–bubble point integrity tests, since the water will be more

Cartridge Filters

103

easily pushed out of the wet membrane pores at a lower pressure. A significant volume of flushing water may be required to remove certain oils or substances. Specialized IT processes or cleaning procedures can be adapted to fit situations such as this. Temperature change over the course of an integrity test can result in a false test result. The most common form of this is when a filter housing is not properly cooled down after a hot water flush or sanitation prior to integrity testing. The housing will continue to cool toward ambient temperature during the integrity test and will result in a loss of pressure upstream to the filters. It will therefore appear as if the filters are not integral. This is explained simply by the Ideal Gas Law (Equation 2.4) that states the following: PV = hRT

(2.4)

P = Pressure V = Volume h = Number of gas moles present upstream of the filters R = Ideal gas constant T = Temperature Ignoring the small loss of gas due to integral diffusion through the wet membrane, η will remain relatively constant. If there is indeed a leak in the filters, η will not remain constant and is the normal mechanism through which a non-integral filter fails integrity testing. R will always remain constant. The volume of the housing and upstream piping will remain constant during the test. Equation 2.4 reduces to the expression given in Equation 2.5. P=T

(2.5)

Since pressure and temperature are now directly related, and are inversely proportionate, a 50% reduction in temperature due to cooling would result in a 50% loss in upstream pressure. If the test pressure is 40 psi (2,758 mbar), and must experience no greater than a 3 psi (207 mbar) pressure drop to pass integrity testing, the system cannot cool by more than 7.5%. In other words, a housing at 160 F (71.1 C) could not cool to below 148 F (64.4 C) before the end of the test, or the test will fail. On the opposite side, heating a housing during an

104

Beverage Industry Microfiltration

integrity test might actually mask a non-integral filter or other leak in the system. Filter Change-Out Filters are changed out according to a variety of different approaches. The most common change-out strategies employed include: • Differential pressure reaches manufacturer’s maximum recommended specification • Differential pressure reaches plant’s specification • Product run does not meet minimum throughput requirements • Time-in-service guidelines • Seasonal processing • One-time usage processes • Filter integrity failure Differential Pressure Reaches Manufacturer’s Specification Manufacturers will have a maximum recommended specification for the operation and change-out for each of their filters. Sometimes this specification relates to the maximum stress tolerance, however, and not particulate unloading or flow rate concerns. The manufacturer’s specifications may be based on ideal processes, which assume adequate pumping capacity, properly sized filtration stages, and other conditions that do not exist at many plants. Specifications based upon particulate unloading (for some nonmembrane filters) or minimum flow rate will usually be lower than those based on maximum stress tolerance before cartridge failure, and these specifications should be used. It does not make sense to run a depthstyle prefilter to 30 psi (2,068 mbar) if particulate unloading begins at 15 psi (1,034 mbar) or if the flow rate falls below acceptable limits at 20 psi (1,379 mbar) due to bottling demands or pump constraints. Remember that filters will naturally have some initial clean pressure drop that can be observed upon installation. The actual change-out of the filters depends on this initial pressure as well as the recommended change-out specification. If a filter has an initial pressure drop of 2 psi (138 mbar) with a change-out specification of 15 psi (1,034 mbar), the filter change-out should actually occur at 17 psi (1,172 mbar) and not 15 psi (1,034 mbar) as stated in the specification.

Cartridge Filters

105

Differential Pressure Reaches Plant Specification Manufacturer’s recommended change-out criteria may not fit with a plant’s process. In these instances, experience has taught the plant to operate using a different specification. One such example is a high-speed bottling line in which the filler is immediately preceded by a membrane filter. The membrane filter’s recommended change-out specification is 40 psi (2,758 mbar), but the filtration skid cannot provide enough flow to properly feed the filler starting at 32 psi (2,206 mbar). It makes more sense to take action, such as cleaning the filters, than it does to run a bottling line at half speed. In some cases, however, it still might be more feasible to run the line at half speed, such as when trying to finish a product batch. Plants will often have to develop such procedures and criteria based on their actual process. Product Run Fails to Meet Minimum Throughput Required When dealing with batch processes, filtration equipment may be sized so that it can process an entire batch before cleaning. If the filters are repeatedly cleaned and re-used it may happen that there comes a batch that cannot be entirely filtered before the filters plug or some other constraint is met. Plants may change out the filters when this happens or when they feel that this may happen either later during the batch or during a subsequent batch. A filter, for example, may have a high differential pressure at the end of a successful product run. The filter could then be cleaned and put back into service, but it is felt that the filter would not make it through the next product batch without plugging. The plant decides to install a new filter. This also occurs when filters plug partially through a filtration run. Even though the filters could be cleaned and returned to service, they are replaced. In such processes it may make even more sense to use two filtration skids in parallel. In the event that one skid plugs or is unable to finish a filtration run, the other system is put online while the first filter set is either cleaned or replaced. The second system may be a smaller system designed to just finish a partial run. Time-in-Service Guidelines Beverage companies often enforce time-in-service guidelines. An example of such a guideline would be:

106

Beverage Industry Microfiltration

• Prefilters must be changed out every three months, with membrane final filters being changed every six months unless some other criteria such as plugging or differential pressure is met. Plants with low-fouling process streams such as high quality mineral water often impose such guidelines as a best practice. These guidelines are not always necessary. Filter manufacturers vary on their recommended time-in-service guidelines. Most guidelines tend to fall between 1–2 years. Filter companies will usually avoid giving a steadfast rule, as all processes behave differently and require different levels of security. Time-in-service guidelines should take into consideration microbial concerns, filter spending, and cost of change-out. Mineral water plants, again, who often impose such guidelines, can use 36–55 Round filtration housings, and so the cost of one extra change out per year can be as high as $10,000–15,000. Mineral water plants are some of the most susceptible to microbial growth and contamination as well as foul odors and other quality concerns should filters remain in place for too long. Seasonal Processing Filters used in a process that is only run seasonally will often be changed out at the end of the processing season. Wineries are a perfect example of this. Clarification filters for tartaric crystal removal are used only in the fining and stability phases of winemaking. Many wineries do not bottle year round, but rather only a few months after crush. In these instances it sometimes makes more sense to simply discard the filters at the end of the season rather than storing them in a chemical solution and attempting to reuse the filters next season. One-Time Filter Usage One-time filter usage is actually the guideline for many industries outside of food and beverage. Pharmaceutical and biotechnology companies use hundreds of millions of dollars worth of cartridge filters every year, with much of that being as one-time usage. Beverage companies will almost always use some sort of cleaning and reuse of cartridge filters due to the high costs of filtration relative to the value of product. This is perfectly fine and makes good economic sense. There are still instances of one-time filter usage in beverage applications. One

Cartridge Filters

107

of the most common examples is that of mobile bottlers. Mobile bottlers are used extensively in winegrowing regions such as Northern California to bottle the products of smaller wineries. Mobile bottlers will usually purchase new filters for each customer, building the cost of the filters into the total bottling fee, and either discard the filters after the product run or leave the filters with the customer. The customers, since they do not have their own bottling or filtration processes, simply throw the filters away. This is also practiced by some stationary contract bottlers where the product is made on site with many other products or is shipped in to be bottled. Filter Integrity Failure Some manufacturers use cartridge filters until they fail. This may allow for the maximum usage to be attained from each filter setup. The facility must have good process controls to safely operate in this manner. Filter durability and ability to be cleaned are important aspects to consider in this instance. A higher cost filter with a longer service life may be the most economical selection overall, as there will be fewer failures and, as such, fewer filter setups required throughout the year. The filter cost versus filter service life must be compared to make the best selection for the plant.

Common Cartridge Failure Modes Although there are any number of methods through which a cartridge filter can fail, some failure modes are more common than others. Most of these failure modes have already been discussed in previous sections and are being presented again here, in no particular order, due to the importance of understanding these issues. • Reverse Stress Failure — Most cartridges are extremely susceptible to failure when cleaned in the reverse direction. This is particularly true at elevated temperatures. Care should be taken when introducing both a new reverse cleaning procedure as well as a new filter into a manufacturing process that uses such cleaning procedures. • Pleat–End Cap Bond Stress — The site at which the pleat pack is attached to the end cap is one of the weakest locations on the cartridge. It is this location that may be damaged most by water hammer.

108

•

•

•

•

•

•

•

Beverage Industry Microfiltration

Rapidly heating or cooling the cartridge can lead to micro cracks at this location, which will eventually lead to filter failure. Chemical Compatibility — Too often, chemical compatibilities are not checked when changing chemicals, starting a new process, or changing filter types. While the vast majority of common chemicals are, for the most part, compatible with the vast majority of filters, there are many incompatibilities as well. High pH caustic coupled with hydrophilized PVDF or ozone in association with polypropylene are two notable incompatibilies. Improperly Regulated Compressed Gases — Compressed gases are used throughout the food and beverage industry. Oftentimes these gases are compressed to pressures well in excess of what a filter or filter housing will see in normal operation. Plants may utilize some form of blow down or product recovery process that uses compressed gases. Compressed gas supplies are also attached to housings for integrity testing. Steaming — Since steaming is a sanitation process, not a cleaning process, forward flow is always recommended. Reverse steaming of cartridges can easily lead to filter failure. Steaming wet filters can cause an excessive differential pressure in either the forward or reverse direction and, with the steam temperatures involved, can easily damage filters. O-Ring Degradation — O-rings are a weak point on many cartridges. In addition to simply rolling out of place on install, o-rings are easily nicked and cut. O-rings can also be susceptible to separate chemical compatibility issues than the main filter device or filter media, a fact that is often overlooked. Over-Tightening of DOE Cartridges — Over-tightening of the spring cup assemblies used in filtration housings containing double openended cartridges can cause the soft end cap material to split over time. This will create a means of particulate bypass within the system. SOE Locking Cartridge — Many operators damage cartridges when installing locking double o-ring type filters by leaning into the cartridge during twisting or by holding the cartridge at the top element and twisting. This creates a great deal of strain on the bonds between the elements, particularly if the cartridge has already locked into place. Filter Bag Opening — A great number of cartridge failures have been traced back to simply opening the bag a new cartridge comes in with

Cartridge Filters

109

a knife, razor, or box cutter. Membranes are extremely thin and a slight slash with a knife or razor is sufficient to cut the membrane. • Pleat Pack Sheer — Membrane pleat pack sheer due to high stress environments most commonly relates to a filter failure at either the peak or the valley of the membrane pleat itself. These failures are most commonly observed at or near the membrane seam that joins the two ends of the membrane. These failures can be caused by water hammer and pulsation but are also a result of normal high stress, high flow, long service life processing. If these types of failures are being observed, using a cartridge with a higher number of pleats reduces the pleat pack sheer and can decrease the number of cartridge failures. Failures at the pleat valleys often occur as a result of stress in the forward direction, while failures at the pleat peaks can often occur as a result of stress in the reverse direction. This can demonstrate from what direction or at what point in the process damage is occurring.

Chapter 3 Sheet and Lenticular Filters

Filtration Media Sheet and lenticular filters are primarily constructed of a random fiber matrix of cellulose. Asbestos was once used in filter sheets but, due to obvious health and safety concerns, it is no longer used. Cellulose used in the construction of sheet and lenticular filter media originates from plant cell walls of trees. Pine, birch, and beech trees are most commonly used. Woods chips are chemically treated to remove the lignin. The pulp is then washed to obtain a paste-like material. The pulp undergoes a washing stage with an alkaline solution and is thoroughly rinsed with water. The fibers are then separated so that the filter can have the desired characteristics. The cellulose is mixed at this point with any specialty materials as well as a binder, then made into sheets, dried, pressed, and cut. There are many specialty sheet and lenticular filters available, made with various constituents such as resins, activated carbon, perlite, or diatomaceous earth. Media can have polypropylene strands added to the matrix for increased strength. Carbon-impregnated filters can be used for decolorization. There are instances when carbon media can be used to correct off-flavors or tastes. Carbon-impregnated filters can be as much as 2/3 carbon by weight, with the remainder being standard depth matrix. There will often be some carbon fines that bleed through into the filtered outlet. A carbon filter should not be used as a final filtration but rather as a pretreatment step that also performs some of the filtration. A good feature for a carbon-impregnated filter to have is an outer covering. The outer covering will help to eliminate carbon fines from entering the product. It is usually made of a material such as polyester. The media used for sheet (Figure 3.1) and lenticular filters is cut by special dies. Most plate and frame filters use square-cut filter sheets. 111

112

Figure 3.1.

Beverage Industry Microfiltration

Square-cut filter sheet.

Lenticular filters are almost always round disks. Different pieces of equipment may use different shapes or sizes. Filter manufacturers should have the ability to cut different sizes or shapes of filter media upon request, and many tout the completeness of their die inventory. Special orders may be subject to a minimum quantity. Sheet and lenticular filters will often have positive Zeta potential. This refers to the fact that the filtration media is positively charged. Negatively charged particles, like many of those found in wine, beer, and other beverage streams, will better adhere to a positively charged filter. This can be a significant factor in particulate removal with sheet and lenticular filters. Constant and stable flow is required for Zeta potential to be effective. It is lost once flow stops, and it takes time to re-establish itself once flow begins again. Particles that had been retained can be released upon stopping and starting of a filtering process. It is possible to build a bypass into the filtration unit’s outlet so that the initial flow after restarting can be sent back into the suction side of the feed pump. This will reestablish the electrostatic removal and prevent liquids containing particles from proceeding downstream. Other components can be part of a lenticular filter cartridge. Metal components will always be stainless steel. Structural plastic components of stacked filters will be made from a food-grade polymer

Sheet and Lenticular Filters

113

with high temperature and chemical resistance such as polypropylene. Sealing components, such as o-rings and gaskets, are made from conventional materials like silicone, viton, EPDM, etc. There are no other components directly associated with a filter sheet. Filter Grades Sheet and lenticular filters are classified by grades. The grade selected will be determined by the desired particle retention and filtrate clarity. Grade designations can vary. Most grades will be given as some sort of description of the type and effectiveness of filtration such as “coarse,” “polish,” or “sterile.” Manufacturers may give the filters a nominal pore size rating. Each filter specification should include the recommended flow rate, the maximum flow rate, and the maximum differential pressure. Knowledgeable manufacturers will have specific recommended flow rates developed for different product types such as wine or beer. Coarser filter grades will have higher recommended flow rates than finer filter grades. Notations may vary between manufacturers but the general categories should largely be the same. One manufacturer’s “fine” grade lenticular may otherwise be called “pre-bottling” grade, or a “coarse” grade may be called “clarification.” Manufacturers will often have many subgrades of filters under each broader category. Coarse-grade filters should be used to arrest fermentations, as a rough clarification, or to remove fining agents, DE, carbon fines, and other particulate matter. Polishing-grade filters will typically remove most particulate materials and reduce the microbial load of the liquid with regard to larger microbes such as yeasts, molds, and algae. Sterile filter grades lead to a much higher degree of clarity and begin to significantly reduce the microbial load of the product. Sterile grades should not truly be considered sterile. There will not be a complete reduction of microorganisms throughout the product batch when using sterile-grade sheets or lenticulars. If complete microbial retention is required, a membrane cartridge filter must be used afterward. Sterile filter grades are sometimes referred to as pre-membrane grade. Media Specifications • Media — The media used in the construction of the filter will always be listed in the datasheet/filter description documents. The majority

114

•

•

•

•

•

•

Beverage Industry Microfiltration

of the media will be cellulose based; however, some filters will have additional components such as DE, polypropylene, PVPP, carbon, perlite, or resins. Non-Media Components — Lenticular cartridges, particularly those with a modular design, may have several components that are part of the device but not part of the filtering media. These components will generally be listed separately and can include o-rings or sealing mechanisms, inner core, support structure, spacers, and various adapters. These components will be food grade if using a filter marketed to the beverage industry and will usually be constructed of some neutral polymer, such as polypropylene. There are no other components directly associated with a filter sheet. Grade — The grade of the filter is given. Filter grades are typically broken into three categories: (1) rough or clarification; (2) fine filtration; and (3) “sterile” or pre-membrane. Filter manufacturers may offer several subgrades within each basic category. Wet Strength — The strength of the filter media during processing is often referred to as the filter’s wet strength. This is used when comparing filters and filter manufacturers. A higher wet strength is desirable because strong filters are less susceptible to media blowout during production as a result of flushing or sterilization, increased differential pressure, or water hammer or pressure shocks. Filter Size and Area — Filter size is always given. The filter area is sometimes given as well but, if not, can be calculated based on filter size. The term “active filter area” may refer to the fact that the useful filter area is smaller than what would be calculated based only on the filter size. Filter Dimensions — Dimensions of the filter, such as depth and density, can be used to calculate the dirt-holding capacity of the filter or to compare various filters from different manufacturers. Extractables — Sheet and lenticular filters will have some level of extractables. It is for this reason that it is always recommended to either prerinse filters or to recycle or mix the first portion of filtered product. Extractables levels can have a significant impact on products in which haze formation can be problematic, such as for beer or spirits. Quality filters may be designated as having low extractables. Extractables levels are not always constant between product streams. For example, the extractables level for water may not be the same as for wine. Extractables levels may increase with a higher

Sheet and Lenticular Filters

•

•

•

•

•

•

•

115

alcohol content product, so the same filter may have a higher extractables level for spirits than for beer, for example. The individual extractables level for each product type may not be given in the literature. Ash Content — Ash content relates to the mineral content of the filters. Ash content can be misleading, as it does not necessarily relate to the amounts of relative mineral extractables such as Ca, Mg, or Fe. Low ash content will often result in a lower mineral extractables level, but not always and not always proportionately. Rinse Volume — The recommended rinse volume should be given, so the filter user will have a rough idea of what volume of water is typically required to remove the bulk of the filter’s extractables. Flow Rate — The recommended flow rate of a filter is often given in the specifications section. Flow rate is sometimes expressed in terms of permeability, but conversions leading to a standard gpm or lph flow rate are usually available. Maximum Differential Pressure — The maximum differential pressure given in the specifications section is usually the pressure at which the filter risks being damaged or experiencing media blowout or rupture. This maximum differential pressure is not necessarily the recommended change-out pressure, which may be lower. Maximum Operating Temperature — The maximum operating temperature can either refer to the maximum temperature for prolonged operation or the maximum temperature the filters should be exposed to for any length of time. It is possible, with some filters, to use higher temperatures than the specification for sanitation since sanitation is only for a short period of time. This should be verified with the manufacturer. Datasheets may specify both cases. Retention Characteristics or Efficiency — Filters may have certain claims with regard to microbial removal or efficiency of removal. These claims are with respect to nominal removal only (not absolute). Retention claims may be specified by organism, such as Saccharomyces, and can be helpful when deciding on a specific filter grade or in comparing various filter grades between manufacturers. Nominal Pore Size Rating — Manufacturers will often assign nominal pore size ratings to filters so that it is easier for the beverage plant to understand the filter’s removal performance and to compare alternative processes or filter formats. These ratings can be helpful, but it should always be recognized that such ratings are nominal and no

116

Beverage Industry Microfiltration

sheet or lenticular filter can truly offer absolute or complete removal of microorganisms.

Sheet Filters Sheet filters used in the beverage industry are seen in conjunction with plate and frame filter housings. These terms are therefore often used interchangeably when referring to this type of filtration system. Technically, the filter sheet is the media that is loaded into the filtration equipment, while the plate and frame filter is the equipment or housing for the filter media. Sheet filters were a precursor to the lenticular stack and cartridge filtration systems and are still widely used among small- and medium-scale winemakers, brewers, and distillers. Other food and beverage processes such as olive oil and vinegar also rely on plate and frame filters. Most large companies have replaced sheet filters with lenticular or cartridge systems due to the many advantages of the latter two. The ability of sheet filters to handle products high in solids without first passing through a separate clarification stage, accomplished by means of a DE or comparable filter, is a benefit to small and medium manufacturers and contributes to the continued use of this filter format. Sheet filters are low cost, and small plate and frame housings can be purchased relatively inexpensively as well. Filter sheets are sized based on the dimensions of the filter. Most filter sheets will either be 20 × 20 cm, 40 × 40 cm, or 60 × 60 cm. Since this represents filter sheet area, remember that a 40 × 40 cm sheet is not twice the size of a 20 × 20 cm sheet. A 40 × 40 cm sheet will have a top surface area of 1600 cm2. A 20 × 20 cm sheet will have a top surface area of 400 cm2 or 1/4 that of a 40 × 40 cm sheet. A 60 × 60 cm sheet will have a top surface area of 3600 cm2. A 10″ membrane filter element, for comparison, will have a surface area equivalent to roughly eighteen 20 × 20 cm filter sheets, depending on the exact filter types. It is important to normalize values based on filter surface area when comparing filters or trying to determine flow rates, dirt-holding capacity, and so forth. The dirt-holding capacity of a filter sheet can be estimated by calculating the volume of the filter. A 40 cm × 40 cm sheet with a depth of 3.5 mm will have an estimated dirt-holding capacity of 560 ml

Sheet and Lenticular Filters

Figure 3.2.

117

Plate and frame (sheet) filter system.

Figure 3.3. Filter plates will vary by manufacturer, but almost all have the same basic design.

(0.1479 gal) calculated by 40 cm × 40 cm × 0.35 cm = 560 cm3 = 560 ml. Plate and frame filter holders were essentially named after the primary components of the equipment. The equipment’s frame holds a series of plates to which the filter sheets attach (Figure 3.2). The fluid inlet is on one side of the plates with the outlet on the other. A booster pump is sometimes located on the frame, as is the necessary instrumentation, such as pressure gauges. There will be a drip pan underneath the plates to collect product that leaks from the edges. The number of plates is determined by the desired flow rate and clarity. The plates are held in place and tightened by a handwheel. Turning the handwheel moves the solid end plate forward and compresses the filters and filter plates. The rod, which connects to the handwheel, usually requires regular lubrication. Filter plates (Figure 3.3) may be constructed of stainless steel, Noryl®, Rislan®, or Moplen®. Noryl and stainless steel are by far the most common plate material. Many manufacturers of plate and frame filters have a standard offering of Noryl filter plates with the option of

118

Beverage Industry Microfiltration Outlet

Inlet

Figure 3.4.

Flow diagram of plate and frame filter.

upgrading to stainless steel. Noryl filter plates are steam sterilizable up to 230 F (110 C). Sheet System Operation The operation of a plate and frame filter is more demanding than most microfiltration systems. A well-trained operator oftentimes must be present during the entire filtration cycle. Filter installation can be long and protracted. Frequent filter change-outs associated with large product runs can be time consuming and expensive. A good understanding of the filtration system is key to effective operation. The basic flow diagram of a plate and frame filter is shown in Figure 3.4. Installation Proper sheet orientation is critical during filter sheet installation. Fluid should flow from the rough side of the filter to the smooth side. Installing a sheet backward will lead to rapid plugging of that sheet. The smooth side should always face the clean side of the filter plate. The first filter will have its smooth side facing the pressure gauges/filter inlet/outlet and its rough side facing the handwheel. Each successive sheet will alternate direction. Sheet alignment is important. Ensure that the sheet is not ripped by either the filter plate or the o-ring. O-rings will occasionally be different depending on the sheet thickness, brand, and/or grade. Proper orings should be used to avoid leakage or excessive filter tightening. Sheets should be first loaded into the filter holder from the non-movable end of the filter. Plates are then moved as each filter sheet is put into

Sheet and Lenticular Filters

119

place. Some manufacturers recommend wetting the filter sheets with either water or filtered product just prior to installation. Sheets should be repeatedly tightened after the initial installation to avoid leakage. Always prerinse the filters prior to first use. Prerinsing removes loose fibers, extractable metals, and off-tastes that can sometimes be present in unused filters. Proper washers should be used for the filter plates. The use of incorrect washers is a common error that leads to edge leakage and product loss. It is advised to never mix different brands or grades of filter sheets, even when they appear similar in either brand or grade. The one exception to this rule is when the filtration system is to be divided. It is possible to divide the plate and frame filter into two sections that will have different filtrations. To do this, install a separation plate in the middle of the filter and connect the inlet/outlet of the filter appropriately. These plates are sometimes referred to as diversion plates and chambers. A diversion plate separates the plate and frame filter but does not allow for separate controlling of the two filtration stages. A diversion chamber allows for the two filtration stages to be controlled separately. Dividing the filter will effectively reduce the number of sheets for each filtration, and there will be different throughputs due to the different filter grades. If, for example, the filter is split 50/50 between two filter grades, then the tighter pore size may plug faster. If this is the case, it may be best to split the filter 30/70 in favor of the lower grade filter. Deciding this will take experience specific to a particular product, equipment, and process, and may take some trial and error along the way. This may not be possible with all pieces of equipment or setups. It is important to calculate the optimum flow rates for each stage, bearing in mind that the filter area for each partition may be different. The lower of the two stages’ recommended flow rates should be used for the process. Operation If a plate and frame filter directly feeds a bottling line, it is sometimes recommended to recycle the first portion of product to pass through the filter. This first portion of product is ideally sent back into the feed tank so that it is not wasted. Alternatively, the first bottles filled may be held and destroyed or otherwise handled as non-standard product. The first portion of product is used to push air from the system, remove leftover water from the sanitation, and possibly rinse any remaining

120

Beverage Industry Microfiltration

extractables. This product’s properties, such as color, taste, and alcohol and dissolved oxygen content, are often negatively impacted as a result. The degree of impact will vary depending on the beverage and the size of the filter or container. Unacceptable color and flavor stripping of the first portion of wine sent through the filters is common in the wine industry. All air from the plate and frame filter must be removed when first starting the filtration run. This may involve removing the various caps and plugs within the system. Plate and frame filters should come with vents at the system high points. Make sure that air is always fully vented from the system. It can help to maintain a backpressure above the equilibrium pressure to prevent gases from coming out of solution during the filtration. Monitor the clarity of the product during the filtration. This may be via a site glass on the outlet. If the clarity is noticed to have decreased, it may be possible that a filter has been broken and must be replaced. It is common for there to be some leakage of product during the filtration. A good rule of thumb is that the loss due to leakage should be less than 3–5 gallons (11.36–18.93 liters) per eight-hour shift on larger units. If there is excessive leakage, then there may be a problem due to the gaskets, compression tightness, poor lubrication, or warped/ damaged plates. Wait a few minutes after the filtration run has ended and equipment has stopped before loosening the handwheel to ensure that all pressure has been removed. Maintaining the desired flow rate per filter sheet is important in operating a plate and frame filter. The filter will have two flow rate values: (1) the maximum recommended flow rate and (2) the optimal flow rate. The optimal flow rate is usually about 80% of the recommended flow rate. The maximum flow rate is entirely determined by the filter itself. The optimum flow rate will depend on the fluid being filtered. A sheet filtering wine, for example, will have the same maximum flow rate specification as the identical filter processing beer, but the beer filter will have about a 30–40% lower optimum flow rate due to the lower filterability of beer versus wine. This is why brewers typically require nearly double the sheets than winemakers filtering product at the same flow rate. Table 3.1 compares different flow rate recommendations for various filter sizes and grades. It is extremely important to monitor differential pressure. A pressure gauge should be on the filter housing inlet and outlet as well as in the

Sheet and Lenticular Filters Table 3.1.

121

Typical maximum flow rates (gph [lph]).

Coarse filtration Clarification Sterile filtration

60 × 60 cm sheet

40 × 40 cm sheet

20 × 20 cm sheet

53–100 (201–379) 38–75 (144–284) 23–75 (87–284)

23–50 (87–189) 16–38 (61–144) 10–25 (38–95)

10–15 (38–57) 5–11 (19–42) 4–6 (15–23)

change-over plate section. If the differential pressure specification is exceeded, contaminants may be passed through the filter to the downstream side. It is also possible that the sheet matrix of the filter will be compressed, which leads to additional filter blockage. If the filters are to be cleaned, it should be done when the system differential pressure is roughly 50–70% of its maximum specification. Recommended differential pressure specifications will sometimes decrease sharply with tighter, more retentive filter sheet grades. A filter sheet manufacturer may recommend a change-out differential pressure of 35 psi (2,413 mbar) for rough clarification, for example, and 20 psi (1,379 mbar) for the tightest grade of “sterile” filtration media offered. Cleaning, Sanitation, and Storage Filters should be prerinsed prior to use. This will remove minerals and fibers. These materials can lead to off-flavors and odors in some products. Minerals can lead to haze formation. If prerinsing is not possible, it is sometimes necessary to recycle the first portion of filtered product. Water used should be clean and preferably filtered. If filtering large volumes into a holding tank, there will usually be sufficient mixing in the holding tank so that one small portion of product is not adversely affected. When scaling up the recommended rinse volume, remember that the rinse volume should be determined based on filter area and not size designation. A 40 cm × 40 cm sheet will usually require four times the recommended flushing volume of a 20 cm × 20 cm sheet, not double. Water used for prerinsing should be pH neutral. Slightly acidic water may be used if that is the only water available; very acidic or basic water should be avoided. Filter sheets should be stored in a cool, dry place prior to use. Sanitation cycle parameters can be dictated by the system components rather than by the filter sheet. If the system is to be steam

122

Beverage Industry Microfiltration

sterilized, the plates can be made of stainless steel or Noryl. Some filters will have an increase in extractable components following steam sterilization. If a filter is prerinsed to remove materials and then steam sterilized prior to start-up, it may be possible that the first portion of product must be still be recycled despite the filter having been prerinsed with the recommended rinse volume. This is not the case with all filters. When steaming the filters, it is usually best to start the steam cycle with all vents, valves, and sampling ports open to avoid steam shock of the filters. Chemical compatibilities should be checked when using chemical sanitants. Hot water sanitation of the filter sheets is common. Some manufacturers recommend the use of dilute citric acid solutions (3–5% v/v) heated to around 113 F (45 C) to sanitize the filters. This solution would need to be recirculated through the filter for about 15 to 20 minutes and subsequently rinsed from the system. It is possible to use other solutions, such as very dilute phosphoric acid. Other materials, such as iodofor, can be difficult to rinse from the filters and are not recommended. Sodium hydroxide can attack cellulose. Sheets that are fully supported by the filter holder may sometimes be backflushed. Manufacturers may not recommend backflushing of filters for critical applications, such as sterile or pre-membrane filtration. Many manufacturers never recommend backflushing — in any circumstance — while a few use the ability of their filters to be backflushed as a strong competitive advantage. The wet strength of the filter is very important when deciding whether or not to backflush. Backflushing should be done before the filter has reached its recommended change-out differential pressure. If a filter’s recommended change-out pressure is 22 psi (1,517 mbar), then the filter should be backflushed at around 10–12 psi (690–827 mbar), not after clogging at 22 psi (1,517 mbar). Water used for backflushing the filters should be clean, without prior contaminants. The filters are cleaned much better by maintaining some counter-pressure during reverse flow. A brief cold-water rinse should be first. When the outlet water from the cold rinse is clear, then hot water is sent. The majority of contaminants will be cleaned using hot water. The temperature should be increased in 2–3 degree increments until reaching the final, desired temperature. This desired temperature can be as high as 180 F (82.2 C) depending on the filter type and manufacturer. It is important to not immediately start the backflush cycle with 180 F (82.2 C) water, as some materials will

Sheet and Lenticular Filters

123

be “baked” onto the filter. Temperature increases should be gradual or made in increments when going higher than 131 F (55 C). The backflushing can be stopped when the outlet water is clear. A slight increase in temperature, if not already at the maximum specification, will show if materials are still present on the filter. In other words, if the cleaning is taking place at 120 F (49 C) and the outlet water is clear, briefly increasing the temperature to 140 F (60 C) and observing the outlet clarity will show if there are still materials present on the filter. More materials are removed from the filters as the cleaning water temperature increases.

Lenticular Filters Although lenticular filters have assuredly found a place within the beverage industry, they represent something of a midpoint in filter evolution. Lenticular cartridges evolved from filter sheets to provide an enclosed, more efficient, and easier-to-use filter format. Lenticular filter cartridges have since given way to even easier to use and more efficient cylindrical cartridge filters (now called simply a “cartridge filter”). The filter media used in lenticular cartridges is nearly identical to that used in filter sheets. Lenticular filters are sometimes called “filter modules,” “pad filters,” “stack filters,” or “filter stacks.” Compared to plate and frame filters, lenticular filters offer lower labor costs, lower maintenance costs, less product loss, and lower initial capital costs. Lenticular filters use a fully enclosed system, so there is no leakage, as there can be with plate and frame filters. A basic process flow schematic of the system is shown in Figure 3.5. Lenticular filters are considerably easier to use and require little attention from an operator during a production run. Lenticular stack “cartridges” use housings similar to cartridge filter housings. Design benefits of using lenticular filters over sheet filters include: • • • • • •

Much easier usage Faster turnaround times Elimination of edge leakage Lower product losses Smaller space requirements Lower initial capital cost, relative to flow rate

124

Beverage Industry Microfiltration

Inlet

Figure 3.5.

• • • • •

Outlet

Lenticular housing flow diagram.

Higher flow rates Ability to operate at higher pressures Easier and more efficient cleaning and regeneration Increased throughput as stacks are left in housings and reused Ability to recover product via inert gas blowdown

The only real drawback to using lenticular cartridges over sheet filters is that they have higher media costs. This is easily offset, however, by the other benefits. The change-over from one system type to another can be costly from a capital purchasing aspect, but it is usually justifiable for most processes. There are two basic types of lenticular filters: • Basic design • Modular design The first lenticular cartridges are referred to as “basic” design (Figure 3.6). The filters are very similar to sheet filters. The filter media is die cut into the shape of a doughnut. The circular media is placed onto a metal insert (supporting plate), which functions as a flow channel. There will normally be a rough side and a smooth side to the media. The rough side should be facing away from the metal spacer and is the fluid inlet side. Flow enters the housing, passes through the filter media, and exits the housing through an inner core. Each pad is inserted into the housing separately. Change-out of this type of lenticular cartridge can be time consuming and may be prone to errors; care

Sheet and Lenticular Filters

Figure 3.6.

125

Basic-type lenticular filters.

should be taken to ensure that the pad is installed with the proper alignment. Most new lenticular filters are of the preassembled, modular stack design. Preassembled stacks are multiple filter disks connected to one another in a single device. There are gaps for flow in between each of the filter disks. There is also an internal chamber within each filter disk. Fluid will flow through the depth filtration media and into the inner chamber where it will flow toward the center of the disk. The center of the disk connects to an inner core of the stack. This inner core leads to the filtration housing outlet. The top of the inner core is usually closed by some sealing mechanism. There are sometimes additional flow channels within the individual disks. There are partitions within the inner chambers to prevent the filter disk sides from compressing in on one another. This reduces the possibility of increased differential pressure causing the two sides of the media to close in on one another. Module-designed lenticular filters offer several benefits over basicdesigned filters. They are more likely to be able to be backflushed and regenerated. Module-based lenticulars are changed out faster and are more robust. The media is often protected by plastic supports, as opposed to being completely exposed. This can reduce media blowout. It is more common for basic-design lenticulars to have the filter media

126

Beverage Industry Microfiltration

damaged in shipping, handling, or storage. Flow channels and other module components can offer better flow normalization to allow for all filter media to be uniformly used during filtration. Lenticular systems are based on filter surface area. Every disk and/or stack has a given filter surface area. The filter will have an established recommended flow rate related to the filter grade. A filter grade is selected based on the desired product clarity. The filter grade’s flow rate per filter surface area is then related to the process flow rate or desired volumetric output to obtain the total required filter surface area. This is what dictates how many filter disks are used or how high the filter stack will be. Lenticular cartridges are common in the wine, beer, and spirits industries. Applications include rough clarification, pre-bottling clarification, DE trap filtration, and carbon fine removal. Lenticular cartridges operate on a depth-filtration basis and have a high dirt-holding capacity. Lenticular filters are also used in the juice industry and anywhere else depth filtration media is required. Lenticular System Operation The main driver for the use of lenticular filters has been their ease of operation compared to plate and frame sheet filters. Lenticular cartridges can, for the most part, be quickly installed and changed out. They can subsequently be put online with only the turning of a few valves. Housings do not need to be closely watched during production, with the exception of periodic venting and monitoring of differential pressure. There is little product loss compared to a plate and frame filter holder. Installation The housing canister must be lifted and old filters removed before new filter installation. Lenticular filters that are not part of a preassembled stack will usually be layered with metal disks that function as flow channels and spacers. If the filters have internal flow channels leading to the inner core, they will be placed directly on top of one another. Filter disks, if applicable, should be oriented so that the rough side faces outward, toward flow. Preassembled modular lenticular filters should be placed in the housing in the same orientation as the old media is being removed.

Sheet and Lenticular Filters

127

There are slight variations between the manufacturers. The housing will usually have a centering and mounting adapter at the center of the bottom plate. Place the stack so that the bottom forms a seal with the machined housing base. This is usually accomplished by o-rings. New modular filters will have double locking tabs and o-rings similar to a cartridge filter. The top of the stack will sometimes be open. There is an adapter, which must be placed on top to create a seal and ensure that there will be no bypass during production. This seal is often through the use of o-rings. There is sometimes a locking mechanism as well. Although there are many subtle differences within the different stack designs and manufacturers, most stacks are fairly straightforward to install, provided close attention is paid to ensuring a proper seal across all connections. Lenticular housing components such as the dome-to-base sealing o-ring or gasket should be checked upon each new filter installation. Operation After the filters have been installed, system operation essentially becomes the monitoring of differential pressure. Differential pressure will increase as particulates build up within the filter. The filters must be either cleaned or replaced when the maximum recommended differential pressure is reached. Every filter (or stack) will have a differential pressure change-out specification for the point at which the filters must be either cleaned or replaced. A common specification is 35 psi differential. Plants may use a lower specification, if desired, and doing so may be beneficial if the filters are to be cleaned and reused. Filtration housings may need to be periodically vented during start-up, operation, and cleaning/sanitation to prevent gas build-up within the housing dome. It is possible to blow down the filtration housing using a compressed gas to recover any product remaining in the housing at the end of the production run. An inert gas such as nitrogen is best. Compressed air or carbon dioxide is also used. The gas should be clean, oil-free, and may be filtered. Cleaning, Sanitation, and Storage Lenticular cartridges will have some degree of extractables. Filters should be rinsed with the recommended rinse volume to eliminate the possibility of leeching undesirable contaminants into the product.

128

Beverage Industry Microfiltration

16”

12”

Figure 3.7. An increase in diameter does not result in the same percent increase in surface area.

Water should be clean and preferably filtered. When scaling up the recommended rinse volume, it must be realized that the rinse volume should be determined based on filter area and not size designation. A 16″ round disk will require about 56% more volume than the recommended flushing volume of a 12″ disk, not 33% more, as the size designation might lead one to believe (Figure 3.7). The area of a lenticular disk may be calculated using Equation 3.1. A = 2 × Π × R2

(3.1)

A = Area R = Radius Hot water is recommended for sanitation of lenticular cartridges and is the most common treatment observed in the beverage industry. Typical cycles are 180 F (82.2 C) for 20 minutes in the forward flow. Chemicals, either hot or cold, may also be used. Sodium hydroxide can attack cellulose. Not all lenticular cartridges should be steam sanitized. The different cartridges are often marked either “chemically sterilizable” or “steam sterilizable.” Those marked steam sterilizable may usually be chemically sanitized, but not vice versa. Steam sterilization may increase the filter’s level of extractables. This can be a problem if the prerinse cycle is carried out, followed by a steam sterilization, and then production.

Sheet and Lenticular Filters

129

In this case, the first portion of filtered product may require recycling or dilution with follow-on product. Not all lenticular filters will present this problem. Backflushing is an issue of debate for manufacturers and beverage processors alike. The non-stacked older type of lenticular cartridges should almost certainly not be backflushed. With regard to newer modular stacked designs the rules about backflushing will vary by manufacturer. A few manufacturers recommend backflushing as a method of reclaiming product hold-up volume or of more efficiently clearing debris from the filters during cleaning. Improper backflushing may cause the media located on the top cells of the filter to rupture. Even when backflushing is permitted, the maximum pressure and flow rate specifications in the reverse direction will be lower than in the forward direction. Wet strength is an important filter characteristic when deciding whether or not to backflush. Unused basic-design lenticular filters should be stored standing upright (vertically). Storing the filters flat on their side can put weight on the disks and may cause damage. This may not be an issue with some preassembled stacks. The filters should be stored in a cool, dry place before use. Lenticular filters can sometimes pick up odors, so they should not be stored in an area where unpleasant odors can be imparted to the filters.

Manufacturers and Distributors Pall (Seitz), Cuno, Domnick Hunter, Filtrox, and Sartorius sell sheet filters. Pall, Cuno, Filtrox, and Domnick Hunter sell lenticular filters. They often use distributors for the beverage industry. Gusmer Enterprises manufactures and distributes sheet/lenticular filters to the beverage industry, predominantly in the United States and Canada. Begerow is a well-known supplier in Europe that also has some distribution in Latin America. There are many companies producing sheet and lenticular filters around the world. Many local and regional industry suppliers will resell filters even if not an authorized or exclusive distributor of that manufacturer. More detailed company listings may be found in the Appendix. Plate and frame filter holders are often manufactured and sold by different companies, which may or may not produce filter sheets. It

130

Beverage Industry Microfiltration

may be possible to obtain both the sheets and the plate and frame filter holder from the same company. Pall supplies plate and frame filters, as does Begerow. Spadoni, Filtrox, Della Toffala, and Padovan are other examples of equipment manufacturers who produce plate and frame filter holders and, while being located in Europe, have distribution in the United States and elsewhere.

Chapter 4 Bag Filters

Bag Filters Bag filters are extremely inexpensive, but they also exhibit poor performance in most filtration processes as compared with other filtration formats. A typical bag filter can cost between $2–$20 per bag. This cost is far lower than the base cost of other filtration formats for a given product flow rate. Despite the low media purchase costs, bag filters do not have a high degree of reliability, are not able to be cleaned and reused, and can require many change-outs with every process run. The actual production costs of using bag filters will often be higher in the long run when compared to lenticular or cartridge filter formats. There are some products and processes, however, for which only bag filters can fulfill filtration requirements. A basic process schematic of a bag filter housing is shown in Figure 4.1. Bag filters are most often used with highly viscose fluids, such as oils, honey, and syrups. Processes that are extremely high in rough particulate matter may benefit from the high dirt-holding capacity of bag filters. Bag filters can be used as a means of clarification prior to more efficient filtration technologies. There are currently many applications in the beverage industry that use filter bags. The estimated viscosities of a few food and beverage related products are given in Table 4.1. Viscosity will change dramatically with temperature and specific product formulation. Filter bag sizes are specified according to a few different conventions. Most filter bags are given size designations 1, 2, 3, or 4. The overall bag sizes, from smallest to largest, are 3, 4, 1, and 2. Sizes 3 and 4 will have a diameter of roughly 4–4.3 inches (10.16–10.92 cm). Sizes 1 and 2 will have a diameter of about 7–7.3 inches (17.78–18.54 cm) (Table 4.2). 131

132

Beverage Industry Microfiltration Filter Bag Inlet

Housing Filter Basket

Outlet

Figure 4.1.

Bag filter flow diagram.

Table 4.1. Relative viscosities of common products. Water Corn oil Olive oil Yogurt Honey Mayonnaise Chocolate syrup Corn syrup

Table 4.2.

1 cP 65 cP 85 cP 1,000 cP 2,000 cP 7,500 cP 9,000 cP 15,000 cP

Standard filter bag sizes and dimensions.

Bag size #

Diameter (in [cm])

Length (in [cm])

Surface area (sq ft [sq m])

1 2 3 4

7 (2.76) 7 (2.76) 4 (1.57) 4 (1.57)

16 (6.30) 32 (12.60) 8.25 (3.25) 14 (5.51)

2.0 (0.19) 4.4 (0.41) 0.5 (0.05) 1.0 (0.09)

Filter bag manufacturers may use a convention of “standard” or “mini” for bag diameter, followed by “single,” “double,” or “triple” for bag length. The smallest bag using this nomenclature would be a mini/ single and the largest would be a standard/triple. It is common for a

Bag Filters

133

bag to be slightly different in size than others of the same designation despite the industry appearing to be fairly standard. For example, a size #1 length from a particular manufacturer may be 16.5″ as opposed to 16″. Slight size variations will not usually matter, since it would preclude the manufacturer’s products from being used in competitive housings. There are some manufacturers who are now producing cartridgestyle filters that are the correct size and have the necessary adapters to fit into bag filter housings. This has led to cartridge-style filters replacing some bag filter applications. Pall’s Marksmen filter line is a successful example. Filter bags are used for air and vent filtration as a means of removing particulates; removing dust is the most common usage. Within beverage manufacturing, the use of filter bags for air or vent filtration is typically for aesthetic or general cleanliness purposes, as it will not generally affect the beverage itself. Specific applications include: • Ventilation, heating, and air conditioning systems • Diatomaceous earth handling and delivery systems • Corker dust removal The use of bag filters for air and vent filtration is well documented in other industries. Filter Bag Media and Construction Filter bags (Figure 4.2) are generally made of felt, mesh, or microfibers. Mesh filter bags may be either multifilament or monofilament. Figure 4.3a and 4.3b shows the differences between mesh and felt media. Monofilament will be stronger and more durable than multifilament. Both mono and multifilament bags are woven together in the same fashion. As their name implies, monofilament bags have a single strand of material in each weave, whereas multifilament will have several smaller strands. Felt and microfiber filter bags are on the tighter and more efficient side, with pore size ratings between 1 and 150–200 μm in size. Mesh filter bags are usually offered in the 45–50 μm to the 1,000–1,500 μm pore size ranges.

134

Beverage Industry Microfiltration

Figure 4.2. Filter bags are used for rough clarification and the filtration of highly viscose products.

b

a

Figure 4.3a and 4.3b.

Mesh (left) and felt (right) filter bag media.

Felt filter bags can be comprised of a variety of materials, including polypropylene, nylon, polyester, and Nomex. Polypropylene and polyester are the most common, followed by nylon. Mesh filter bags are often constructed of polyester or nylon. Microfiber is usually constructed of either polypropylene or polyester. Felt polypropylene bags are the predominant filter bag in industry today. These bags are stable

Bag Filters Table 4.3.

135

Chemical compatibilities of common filter bag media.

Material

Max. Temp (F [C])

Solvents

Weak alkali

Strong alkali

Weak acid

Strong acid

Polyester Polypropylene Nomex Nylon

275 (135) 200 (93.3) 400 (204.4) 275 (93.3)

Good Fair Good Good

Good Excellent Excellent Excellent

Bad Excellent Excellent Excellent

Very good Very good Very good Excellent

Good Excellent Bad Bad

chemically and can withstand temperatures of up to 200 F (93 C). If temperature resistance above 200 F (93 C) is required, then either polyester or nylon filter bags, most of which have operating temperature limits of 275–300 F (135–149 C), should be used. The chemical and temperature compatibilities of materials used in filter bag construction are compared in Table 4.3. The filter bag attaches to the bag filter housing by way of a ring, constructed of either steel or plastic. Bags with plastic rings are usually less expensive. Chemical and heat compatibilities of the processing fluid and chemical agents should be studied if using a plastic ring. Bag filters are sometimes disposed of by incineration. If this is being considered, then steel rings can present a problem. Filter bags can come with a drawstring rather than a ring. Some have an optional handle. Scrim versus Self-Supported Felt filter bags can have a support material called a “scrim.” This support material is a fabric that is worked into the felt for additional strength. Self-supported bags do not have scrims and many times, with modern technologies, they do not suffer a significant loss in strength as a result. Do not automatically decide that a bag is mechanically weaker if it is self-supported. It will often be just as strong as a comparable scrim-supported bag, but can cost less. Sewn versus Welded The two ends of the filter bag’s seam will either be sewn or welded to create the seam. The top sealing ring may also be sewn into place. It was once thought that sewn filter bags were stronger and more resistant to breakage. This is no longer true in many cases, and a wellmanufactured filter bag with welded seams can be just as strong as one

136

Beverage Industry Microfiltration

with sewn seams. A concern with sewn filter bags arises when the holes created by the needle during the sewing process are larger than the pores or openings of the filter bag. Needle holes can be in the 1,000 μm range. This creates potential for bypass, which will allow undesired contaminants to pass downstream of the bag. If a sewn bag is chosen, verify that the thread used is food grade and accepted by the FDA. Outer Surface Treatments Filter bags should have an outer surface that is either glazed or singed. These processes ensure that the fibers of the filter fabric will not enter the filtered downstream liquid and cause contamination. Filter bags once had outer coverings that performed this function. This has been made obsolete by new processes, and glazed bags should usually be chosen. Filter Bag Specifications Bag filters have few relevant product specifications. Most information about the filter is given as a product discussion or is simply an inherently simple product choice, such as bag size. Choices can include: • Filter Media — This is the material the bag is constructed of. The media configuration such as felt, microfiber, or monofilament is usually specified in this field as well. • Pore Size Rating — Pore sizes are always nominal with bag filters and can vary anywhere from 1 micron to microns in the hundreds or thousands. • Bag Size — The available bag sizes, with specific length and width dimensions, are specified. • Surface Treatment — Whether or not the bag has a surface treatment or covering and the type of treatment or covering. • Sealing Mechanism — The specifications section should discuss the sealing mechanism used on the bag seam. The choice will be between sewn or welded construction. Auxiliary information, such as the thread used, should be specified. • Ring Type — The material used for the ring’s construction and any special considerations with ring design. If a non-standard ring design is used, there will often be a picture or discussion regarding the manner in which the ring attaches to the housing.

Bag Filters

137

• Miscellaneous Options — There are sometimes options related to the filter format or construction that are not listed in other categories. These options can relate to the handles or loops of the bag, special bag considerations such as prerinsed or washed, or various designs that are not standard within the industry or are innovations by the supplier.

System Operation Filter bag systems are considerably simpler to run than other filtration processes. Bags are easy to install. There are no filter-bag cleaning, sanitation, or regeneration cycles. Change-out is dictated by differential pressure. Filter bag housings operate so that the flow is introduced at the top portion of the housing. The liquid flows down into the bag with particulates accumulating inside of the bag. Filtered liquid passes through the bag and collects within the housing. The filtered fluid outlet is at the bottom of the housing. Installation Bag filter housings are typically comprised of an outer shell with a perforated filter basket located inside of the outer housing. The bag filter is installed so that it rests inside of the filter basket. The top ring of the filter bag will be located at the top end of the filter housing. The ring usually snaps into a groove at the top of the housing. There are other adapter types for attaching the filter bag to the bag filter housing, but these are used less often. The filter bag housing will close via a top lid that is sealed with a flat gasket. Figure 4.4 shows a cross-sectional view of the housing-to-bag connecting area. A specialty bag connection or housing adapter is required in some instances when a particular bag will not fit into an existing housing. Manufacturers may offer special services that can produce filter bags with the appropriate adapters. Operation The bag filter will remove contaminants from the fluid. Particulates will build up on the inside of the bag during the filtration cycle. Fluid

138

Beverage Industry Microfiltration Filter Bag Ring Filter Housing Filter Bag

Filter Basket

Figure 4.4.

Cross-section diagram of filter bag sealing area.

will leave the bag in all directions and proceed to the filter housing outlet. Bag filters are not used in industries where absolute microbial elimination is required, so the operation of a bag filter process becomes the following steps: 1. 2. 3. 4.

Install filter bag. Start product flow. Monitor differential pressure. Stop product flow when change-out differential pressure is reached. 5. Replace filter bag. This series of steps can occur many times over the course of a production run or even over the course of a day. Excepting installation, bag filter operation consists entirely of monitoring differential pressure during the filtration cycle. Differential Pressure Bag filter service life is based on how many particulates and contaminants are being removed from the process stream. When processing clean streams, the bag filter can have a long service life. With highfouling process streams, a bag filter may plug quickly and/or repeatedly over the course of a single filtration run. Differential pressure is the only process parameter to monitor in order to determine when a filter bag change-out is required or will soon be required. As particulates

Bag Filters

139

Change-Out Occurs

Maximum Differential Pressure

Differential Pressure

Filtered Volume

Figure 4.5. is met.

Filter bags are changed out when their differential pressure specification

build up on the inside of the filter bag, the differential pressure across the filter bag housing will increase. A differential pressure of 8–12 psi (552–827 mbar) will usually indicate that a filter bag’s capacity is at or nearing its end. Bag change-out will occur at some point beyond this pressure, normally in the 15– 20 psi (1,034–1,379 mbar) range. These pressures will vary based on processing conditions and filter bag specifications and should be verified with the manufacturer for each case. The filter bag manufacturer will have a maximum specification for which the bag can be used without failure. This is not usually the same as the change-out specification but, unlike other filter formats, the two specifications may be close. The bag is replaced and the cycle restarted when the change-out differential pressure of the bag has been reached. Figure 4.5 depicts the build-up of differential pressure as the filtration run progresses. It important to closely monitor the differential pressure around a bag filter housing. If the maximum differential pressure of a filter bag is exceeded, the bag may rupture and send contaminants downstream. Cleaning, Sanitation, and Storage Filter bags are not meant to be cleaned and reused. Cleaning filter bags can result in stretching of the material. The stretching will increase the size of some of the filter bag pores, which results in the desired particulate removal not being achieved. As some of the pores are

140

Beverage Industry Microfiltration

stretched and become larger, others will be pulled together and get smaller. This may result in the undesirable removal of some components or premature filter plugging.

Bag Filter Manufacturers and Distributors Domnick Hunter and US Filter are the only “major” filtration companies to offer filter bags. There are dozens, if not hundreds, of small filter manufacturers and suppliers that offer filter bags. The nomenclature between the manufacturers is largely the same, so selecting a filter bag supplier is usually fairly straightforward. Many local or regional beverage distributors that handle other equipment or filtration supplies do not normally deal with filter bags because of the low profit margins and markup relative to the amount of time and service often involved. It is simply not worth their time — especially when considering the number of small manufacturers that supply direct. A distributor with a 10% commission or resale value would have to sell almost 67,000 $7.50 filter bags just to cover the $50,000 base salary of one additional employee.

Chapter 5 Crossflow (Tangential Flow Filtration) Systems

Crossflow Systems Normal flow filtration (NFF) systems are designed so that the flow is directly conveyed perpendicularly into the filter. Particles are either retained on the surface or within the depth of the filter. In crossflow (or tangential flow filtration [TFF]) systems, the fluid flow is across — and so tangential to — the filter’s surface. An applied pressure forces some of the fluid to pass through the filter. Particles are retained according to their size, similar to normal flow filtration. The retained particles, however, are removed by the fluid stream and do not build up on the filter’s surface (Figure 5.1). Crossflow systems within the beverage industry have recently been used with success in the filtration of high-fouling process streams. Many of these applications are still considered specialty uses, such as the reuse of caustic solution or the recovery of tank bottoms. Crossflow systems are being installed as a viable replacement to existing clarification techniques such as diatomaceous earth (DE, or kieselguhr) filtration in wine and beer. This is perhaps the largest untapped microfiltration market within the beverage industry. Nearly every appreciably sized winery or brewery uses or has used at least one stage of DE filtration. There are enormous costs associated with these processes in terms of material purchasing, handling, storage, and delivery. There are also sizable product losses that occur due to the saturation of product into the filter media. The sludge that results must also be disposed of. Add the fact that DE is a carcinogen in its powder form and that many governments are regulating its disposal, and crossflow clarification becomes an attractive alternative. The increased 141

142

Beverage Industry Microfiltration

Crossflow

Normal Flow

Figure 5.1. Operating in the crossflow results in material being swept away from the membrane surface. This helps to prevent particulate build-up.

regulatory pressures on DE usage and disposal, particularly in Europe, have put a great deal of pressure on large wineries and breweries to replace DE. The fact that the quality of DE available to the world market is steadily decreasing further exacerbates the regulatory and production quality issues. The bottled water industry has recently begun using crossflow systems as a clarification step prior to final filtration for mineral and spring water sources that cannot be RO (reverse osmosis) filtered. This has proven invaluable as a cost-effective means of microfiltration, which allows high-fouling spring water to retain its spring or mineral water classification while still being microfiltered to remove microbes and particulates. These advances in crossflow usage come after several years of failure by crossflow technology to win widespread acceptance within the industry. It now appears as if crossflow technology will continue to have a substantial — and growing — presence within beverage processes. Beverage crossflow systems dealing with streams heavy in solids sometimes require the feed to be passed through a centrifuge first. This is true with beer crossflow systems used as a replacement for DE clarification. Wine undergoes many racking and fining stages, so a centrifuge is not always required. However, prior to clarification, many wine processes already have one or more centrifuge steps that will enhance crossflow performance. Sartorius and Pall have both partnered with leading centrifuge companies, Alfa Laval and Westfalia, respectively, to provide the option of a combined centrifuge/crossflow filtration system. A strong benefit to using crossflow systems is the increased filterability of product with regard to any downstream filtration processes.

Crossflow (Tangential Flow Filtration) Systems

143

Wineries and breweries that have changed from DE clarification to crossflow clarification have seen as high as 2–3 times more throughput through subsequent final bottling filtration stages.

Crossflow Formats and Media The membrane media and formats used in beverage crossflow systems can be extremely varied. In composition, the membrane material itself is essentially the same as the membrane material used for cartridgebased systems. It is the membrane format, device, and filtration equipment that varies between normal flow and crossflow filtration systems. Systems may use cast polymeric membranes such as PVDF or PES assembled in a hollow fiber, cassette, or spiral-wound format. Many systems use sintered ceramic or metal membranes. In TFF, the device determines as much about the filter as the media does. This is in contrast to other microfiltration technologies that use essentially the same devices within their technology, but the actual filtration media differs. A depth cartridge is essentially the same device as a membrane cartridge; they simply employ different filtration media. But hollow fiber and spiral-wound TFF devices are very different even when both membranes are made of PES. Filters used in TFF systems are normally built to have a fairly long service life and to be reused many times. Cassette-format filters are the exception and have a much shorter life span compared to other formats. Manufacturers may quote timeframes upward of 10 years for replacement of certain filters. This service life is necessary because the filters, especially ceramic or sintered metal, are expensive to replace. The service life will be partially dependent on how much product is filtered and the frequency and effectiveness of cleaning cycles. Most membranes used in TFF systems are in the 0.1–0.8 μm pore size range. A problem with crossflow systems is that each of the manufacturers makes their own equipment and filters, so designs vary. Crossflow filtration equipment and media are not interchangeable between manufacturers. Once a specific system is purchased, the user is locked into that manufacturer’s equipment, filters, and support. A confusing aspect of media selection for crossflow systems is that the TFF media pore size may not necessarily be the same as that of the

144

Beverage Industry Microfiltration

media used during NFF for similar applications or products. Beverage crossflow systems normally use a 0.1 or 0.2 μm membrane as opposed to the 0.45 or 0.65 μm membrane that would be used for the same product if filtered via normal flow filtration. This does not usually harm the product since the beverage itself will just as easily pass through the 0.1 μm pores without much additional filtration as compared to a 0.45 μm filter. Another incorrect assumption often made is that the filter will clog more quickly since it is 0.1 μm instead of a higher pore size. Processors often ask: “Why am I using a 0.1 μm membrane when the microbes I need to remove are completely retained by a 0.45 μm membrane? Won’t that cause additional blockage?” In fact, a 0.1 μm membrane in a crossflow system is more efficient. The reason for this is that the submicron surface of the membrane will be smoother and flatter. Open pore sizes are more prone to having peaks at the membrane’s surface; these can trap material on the surface that would otherwise be swept away by the tangential flow mechanism. Ceramic Membranes Ceramic membranes, typically comprised of a sintered ceramic oxide such as alumina or zirconia (and sometimes also containing titanium or titanium oxides), are perhaps the best materials with regard to durability in process and their ability to handle high solids loading and unpredictable process streams. They are also some of the most resistant to chemical and harsh cleaning treatments. Ceramic membranes are the most expensive of the media formats. Although fairly durable once in process, the ceramic membranes can be brittle, and it is always possible for the membrane to be damaged by rough handling or during installation. Ceramic systems are most often comprised of a stainless steel outer casing (housing). The ceramic membrane module will be located inside the housing. The membrane module is typically engineered to fit exactly within a particular housing. There will be several hollow flow channels for the liquid within the membrane module. These flow channels (tubes) will normally be in the 2–8 mm range. Figure 5.2 shows a crosssectional view of the housing and media. When properly cared for, ceramic crossflow membranes have some of the longest service lives of all microfiltration devices. It is even possible that the manufacturer will guarantee a membrane for as many

Crossflow (Tangential Flow Filtration) Systems

145

Outer Shell (Housing) Ceramic Module Permeate Flow Channel

Figure 5.2. Ceramic TFF systems have several flow paths (channels or tubes) within the membrane module. The entire module is encased within a stainless shell.

as 5–10 years after install. A few ceramic systems are used in wine manufacturing as a replacement for DE filtration; however, the vast majority of systems are used for specialty applications, such as caustic or product recovery. A reason for this is that ceramic filters possess a very long flow path through which the filtrate must pass. This tends to increase the temperature of the filtrate, sometimes significantly, which can be damaging to some products, including wine. Wine temperature will often be significantly increased as a result of ceramic membrane processing. Hollow Fiber Membrane Hollow fiber membranes are made from cast polymer materials such as PVDF or PES. The tubes are extruded. The outer casing is filled with many tubes (Figure 5.3). The tubes can be smaller than 1 mm in diameter. Hollow fiber membranes are becoming common in both bottled water and wine. Many tubes comprise a filter module. Multiple different modules can make up a single filter unit. Hollow fiber systems can have a high flow rate and excellent throughput. The media is generally not as long lasting as ceramic and is not as durable as ceramic when rigorous cleaning regimens are employed. Hollow fiber membranes, when used with highly fouling process streams, often require some rough clarification process beforehand.

146

Beverage Industry Microfiltration Outer Shell (Housing)

Flow Channel

Figure 5.3. Hollow fiber crossflow systems will have many hollow membrane tubes in the 1 mm range. The filtrate collects outside of the tubes within the shell of the module.

This can be done using a centrifuge, for example. Large particle sizes can be problematic for hollow fiber membranes due to the small tube diameters. It may be necessary to choose a tube diameter based on the maximum particle size observed during filtration. Hollow fiber membranes are the most commonly used TFF format as a replacement to DE filtration in wine and beer. They are also increasingly common within the bottled water industry as a clarification stage. Spiral-Wound Membrane Spiral-wound membranes are constructed so that two membrane layers are wrapped spirally around a collection tube. There is a mesh layer separating the two membrane layers. The mesh is usually stainless steel or an inert polymer, such as polypropylene. The mesh serves as a spacer to maintain flow between the membrane layers. The membrane edges are sealed to one another to prevent flow from entering the filtered permeate stream. Spiral-wound filters can operate at high pressures. Depth prefilter media can be incorporated into the spiral to improve filter performance. A couple specialty high-volume applications exist for spiral wound systems in the beverage industry. A few soft drink plants in Europe use

Crossflow (Tangential Flow Filtration) Systems

147

spiral membranes for the filtration of large volumes of RO water, for example. Clear juices and bottled water may be processed on occasion by spiral-wound systems. Sintered Metal Membranes Sintered metal membranes, which are made of stainless steel (sometimes with a titanium oxide layer), are not used much within the industry, but have some application in processing extremely high-solids streams as well as corrosive or otherwise harsh streams. Sintered metal membranes have practically no temperature or pressure limitations for beverage plants or processes. Sintered metal TFF systems will generally function similarly to a sintered ceramic system, but with more open (larger diameter) channels. The sintered metal channels can be 2–3 times as wide as ceramic channels, so sintered metal membranes can be more effective if dealing with large particulates or materials that form a sludge or heavy cake. Tank bottoms or lees recovery may use a metal membrane. Cassette Format Cassette TFF devices (Figure 5.4) are used extensively on lab-scale applications and within the pharmaceutical industry. It is only recently

Figure 5.4.

Lab-scale TFF cassette.

148

Beverage Industry Microfiltration

that cassette devices have started to move into larger-scale beverage processing. Sartorius’ crossflow systems targeted at the wine and beer industries use cassette format filter media. A few European breweries have replaced their diatomaceous earth filters with these crossflow units. Filter cassettes are typically a flat sheet or series of sheets contained within a preassembled plastic device with an inlet and outlet connection. Molded components inside of the cassette create flow paths. Large units must stack many cassettes together. The actual membrane is a cast polymeric membrane, such as PVDF, polypropylene, or PES. Cassette systems will require some type of prior clarification for most feeds. These systems will have the lowest per unit flow rate, can require large installations, and are the only crossflow format used in beverage processing that requires fairly regular media change-outs. The media is less expensive than the other formats, so the media costs versus change-out frequency must be assessed in each specific instance. Personal experience has shown that current cassette systems are not well suited to beverage processes, and that an alternative format of crossflow filtration, such as hollow fiber or ceramic, should be used in most instances.

System Operation Crossflow systems within the beverage industry are extremely different from one another. There has been no attempt at standardization. The many different filter formats, extremely varied from one another, have further complicated the field. It is therefore impossible to create any standard set of guidelines for installation, operation, cleaning, sanitation, and so forth. Manufacturers have been fairly good at generating specific operating manuals for their equipment, something severely lacking with other microfiltration technologies. Installation The initial filter install will usually be performed by the vendor as part of start-up services. Most filters rarely require changing and, as a result, are often covered in the parts and services agreement, if one is purchased. Detailed installation guidelines for a specific system should be given with every new equipment and filter purchase.

Crossflow (Tangential Flow Filtration) Systems

149

Operation Crossflow filtration systems are usually designed to be complete turnkey installations. The systems are largely a matter of starting and stopping flow and will take little manpower to operate. Large industrial installations can operate with as few as one operator per 4 or 5 units. Differential pressure, which is called “transmembrane pressure” for crossflow filtration, should not significantly increase over the course of a filtration run as with other filter formats. If the filter becomes plugged during operation, the run should be stopped and the filter cleaned. The system should be designed and sized so that this happens rarely. There may have to be some adjustments to the retentateto-permeate ratio exiting in the filtration stage in order to improve yield. Crossflow systems will operate so that the retentate (solidscontaining stream) will be recycled back into the feed tank. The filtered permeate, also called the filtrate, will proceed into the finished product tank. This process is shown in Figure 5.5. Since filtered liquid is being removed and solids are being re-collected in the feed tank, the percent solids in the feed will gradually increase. The filtration is stopped when the percent solids in the feed reaches a certain level. Perhaps the most important aspect of both choosing and running a crossflow system is the monitoring of feed solids and the ability of the unit to handle incoming solids. The ability of the unit to handle solids directly relates to the amount of residual solids (lees) left in the feed tank. This, in turn, will determine the amount of product lost with the solids. The material remaining in the feed tank at the end of the run should be as high in solids as possible to maximize yield. This material may then be further processed, in some instances, for additional product

Retentate Feed Tank

Feed

Figure 5.5.

Product Tank

Crossflow Unit Permeate

Process flow of crossflow filtration stage.

150 Table 5.1.

Beverage Industry Microfiltration Yield comparison between crossflow feed limits of 20 and 30%.

Inlet

Feed stops at 30% solids

Feed stops at 20% solids

Volume of product

10,000 gal

Solids in product

5% vol. %

Density of product

8.5 lb/gal

Density of solids

12 lb/gal

Mass of product Mass of solids Total mass in

80,750 lb 6,000 lb 86,750 lb

Percent solids in product Ending percent solids feed Mass solids in feed tank Mass liquid in feed tank Density of product Volume of product lost Process yield (volumetric)

0

0

20% wt %

30% wt %

6,000 lb

6,000 lb

24,000 lb

20,000 lb

8.5 lb/gal 2,824 gal 72%

8.5 lb/gal 2,353 gal 76%

recovery. A yield comparison showing the results from two systems with different maximum feed solids inlets is given in Table 5.1. This shows that the yield is higher with a better ability to handle more feed solids. Bottled water manufacturers that use crossflow systems will operate slightly differently due to the low cost of water. The crossflow unit should be located as far upstream within the plant as possible to minimize value-added steps such as resin or carbon filtration or other treatments. This ensures that water that will eventually be rejected with the retentate is as minimally processed as possible. In general, even with poor-quality water, the amount of particulates within the water recycle stream will be minimal. The retentate stream can be recycled back into a feed silo with little impact. The silo should then be periodically flushed and/or drained. The unit may also be operated so as to maximize the permeate stream as much as possible and send the retentate to drain if excess water capacity or disposal is not an issue. Operating most crossflow units at a lower flow rate will decrease electrical consumption. Lowering the speed of the crossflow reduces the amount of product heating that occurs. In certain industries, such as wine and beer, these extra few degrees can mean a big difference. A large industrial crossflow unit can typically be expected to heat the product between 1 and 6°F (roughly 0.5 to 3°C).

Crossflow (Tangential Flow Filtration) Systems

151

Module-based crossflow units can be designed so that the overall unit can run with one or more crossflow modules locked out. This helps in a variety of ways including: • Module(s) can be independently cleaned while others continue operating • Module(s) that fail integrity testing can be locked out until the membrane is replaced Cleaning, Sanitation, and Storage Filters should be cleaned regularly. Check with the manufacturer regarding specific recommended cleaning regimens and compatibilities. Find out if the cartridges can be cleaned in the reverse direction and, if so, what the tolerance and reverse specifications are. Crossflow units should be sanitized upon start-up, the same as for any other piece of equipment. All systems will tolerate hot water sanitations. If chemicals are to be used, the compatibilities should be verified with the manufacturer. Ensure that chemical compatibilities have been tested over a long enough period of time, because many crossflow membranes may be used for years. Chemical compatibility testing should reflect this service life. Ceramic and stainless membranes are effectively cleaned with a caustic solution and are completely compatible with such a treatment. A benefit of ceramic and stainless systems is their tolerance of aggressive cleaning regimens. Hollow fiber, cassette, or spiral formats that utilize PVDF should not be cleaned with caustic solutions in excess of pH 10. PES membranes are caustic resistant. Crossflow systems should have a high rate of regeneration such that the filter’s capacity and efficiency is almost completely restored upon proper cleaning. Crossflow filter modules are designed so that they may be left in place within the equipment after being rinsed and cleaned. Some manufacturers may recommend a storage solution be brought into the system for prolonged periods of downtime. Many of the systems currently used in beverage processes are fairly new and heavily automated, so they often come with pre-programmed automatic cleaning cycles. Automatic cleaning cycles are often more effective than manual cleaning. Cycles may incorporate both forward and reverse cleaning, pulsating flow, and other procedures that make cleaning more effective. The manufacturer develops the protocols to

152

Beverage Industry Microfiltration

be used, allowing the plant to simply ensure the proper CIP lines are attached, valves opened, and any required chemicals are available. Crossflow filters are reusable and should be cleaned if or when they plug. The criteria for actual filter replacement should be discussed with the specific manufacturer, as these vary greatly due to the differences in filter configuration and media. Some crossflow filters can easily last several years, so a filter change-out should not be undertaken unless necessary, particularly when considering the high cost of filter replacement.

Chapter 6 Filtration System Selection and Design

Filtration processes vary considerably between industries. They vary substantially even among individual plants within the same industry. Prior to installing any equipment, it is important to understand the ultimate goals of the filtration, economics of each alternative, and impact to the overall process. Several steps need to be completed in the selection and design phase of implementing any filtration process. The following must be determined: • What the filtration is designed to remove • Whether removal needs to be absolute or, if not, the removal efficiency • The number of stages for filtration • The filtration type for each stage • The filter media and/or manufacturer • Process constraints and output requirements, such as filler intake or production timetables • Sizing of each stage of the filtration • Supporting equipment, such as pumps or surge tanks • Operational details and procedures such as cleaning, sanitizing, operating, and properly maintaining the filtration systems Each of these items should be checked and rechecked against one another to ensure that nothing is in conflict. The desired filter may not be compatible with the plant’s required cleaning regimen, for example. A different filter selection may then be required and the housing size changed as a result of the new filter’s media and specifications. All aspects of a filtration process should work cohesively toward the plant’s best overall performance. 153

154

Beverage Industry Microfiltration

Filter vendors and/or manufacturers should be brought into the process early on for input. Often, it is beneficial to work with multiple suppliers to get a better idea of what needs to be done and the capabilities of each company’s products. Remember that vendors are there to sell their product. If a particular company does not have a crossflow system, for example, they may push a lenticular stack or depth cartridge filter that may not provide the best solution to the plant’s problem.

Determining the Filtration Stage(s) Filtration stages are typically categorized into three types: clarification, prefiltration, and final filtration. Clarification and prefiltration are essentially the same thing, with the exception being that the term “prefiltration” is reserved for the stage directly before the final filtration step. There can be zero or many clarification steps, either zero or one prefiltration step, and only one final filtration step for each product. Clarification Clarification is carried out most often using depth filters, but can be performed using non-membrane surface filters for higher retention performance. Clarification stages are essentially a rough filtration stage and are often targeted at a specific contaminant at a particular step in the process. Trap filtration following a brewery DE filtration is an example. The trap filtration is a clarification stage for the specific removal of DE fines. Tartrate crystal removal during wine stabilization processes is another example. Many clarification stages will have nothing to do with the bottling process and will serve only as intermediary filtration processes (Figure 6.1). It is also common to locate a clarification stage directly before the prefilter in the final pre-bottling filtration process (Figure 6.2). Adding a clarification stage at this point allows for an additional step down in pore size and retention to better protect follow-on filtration stages and is commonly used for less filterable streams. An example of this would be wine filtration in which there might be a 1.0 μm clarification stage followed by a 0.65 μm prefiltration stage, which then leads into a 0.45 μm final membrane filtration. A three-stage filtration train such

Filtration System Selection and Design

Storage Tank

Figure 6.1.

Clarification

155

Storage Tank

Clarification stages may have no direct impact on bottling.

Clarification

Prefiltration

Final Filtration

Figure 6.2. A clarification stage may directly precede the prefiltration stage in some filter trains.

as this allows for better use of the characteristics of the various filter media. The clarification stage will use depth media, which has a high dirt-holding capacity. The prefiltration stage may then use another depth media with higher retention, but less dirt-holding capacity or may use a non-membrane surface filter for high retention where more capacity isn’t as necessary due to the previous clarification stage. The final membrane filtration will then act as the absolute barrier for product quality assurance. Staging the filtration processes usually allows for the best overall process economics. Filter prices are such that the more open and less retentive filters are the cheapest. Depth filters are less expensive than surface filters. Lenticular, sheet, and bag clarification filters are much less expensive than cartridge clarification filters. Membrane filters are the most expensive. This pricing becomes critical when deciding on the filter change-out criteria and operating procedures previously discussed. It illustrates that putting extra effort into the clarification stages can lead to considerable savings down the road in final filter spending. Filtration stages do not necessarily have to be in the same filter format.

156

Beverage Industry Microfiltration

Clarification

Figure 6.3. clarification.

Clarification

Prefiltration

Final Filtration

Multiple sequential clarification stages are all referred to as

Prefiltration

Final Filtration

Figure 6.4. Final filtration always refers to the last filtration step before bottling. This step is normally preceded by a prefiltration stage.

Many processes will have a depth sheet or lenticular filter clarification stage followed by a depth cartridge prefiltration and a membrane cartridge final filtration. It is possible to have several sequential clarification stages (Figure 6.3). Prefiltration Prefiltration is a clarification stage that is specifically designed to protect the final filters (Figure 6.4). This is especially true when the final filters are membranes. The cost of a final membrane filter is usually at least 3–4 times that of a prefilter (cartridge), so it becomes important that the prefiltration step performs the majority of the filtration, as opposed to it being done in the final filtration step. Prefiltration stages will often be sized larger than final filtration stages. A good rule of thumb is that there should be 1.5 times the prefilter surface area as compared to the final filter surface area. This can vary depending on the process and amount of particulate loading. Filtration processes that are sized almost exclusively on flow rate and that involve low particulate loading are more likely to have an equal prefilter-to-final filter surface area ratio.

Filtration System Selection and Design

157

The pore size rating of a prefiltration stage should be determined as a function of (1) frequency of prefilter change-out and (2) length of final filter service life. A well-optimized prefiltration stage will usually see a change-out frequency 2–3 times that of the subsequent final filtration stage. While it may seem counterintuitive, more frequent prefilter change-outs will often lead to better process economics because the final membrane filters are much more expensive than the prefilters. Put simply, the prefilters should do the majority of the filtration work with the final filters serving as a final removal step and guarantee of product quality only. If a cartridge membrane is used in the final stage, a cartridge prefilter is typically used, since it will offer the best protection to the final membrane. It is possible to use fine- or sterile-grade sheet and lenticular filters, but these will not offer protection that is as good for the final filters. It is not uncommon for some applications to have a depth or non-membrane surface filter as the final bottling filtration stage. Spirits industries, for example, will often only use a depth media for particulate removal just prior to bottling. Any filter format could be selected to offer acceptable protection of the final filter in this instance. Prefiltration stages are used before reverse osmosis and ultrafiltration membrane filtration processes. This prefiltration can be crucial to ensuring RO or UF membrane protection and longevity. Final Filtration Final filtration is sometimes used synonymously with membrane filtration. This is not necessarily true for all industries. Wine, beer, and bottled water, which use microfiltration for final product sterility, will usually have a final filtration stage that uses membranes; however, it is common in other industries, such as spirits, to have a depth or surface filtration as the final stage. By definition, the final filtration stage is simply the last filtration step in a process. The final filtration stage should be selected so that it retains the desired amounts of contaminants. It is often best to start the design process by first sizing and selecting the final filtration based on the desired end-product quality. The prefiltration is then selected to protect the final filtration. If additional clarification processes are required, these are designed after the prefiltration and final filtration stages are decided on.

158

Beverage Industry Microfiltration

Prefiltration

Final Filtration

Redundant Final Filtration

Figure 6.5. It is possible to have two identical final filtration stages. The second of these is referred to as a redundant final filtration.

Redundant final filtration uses two identical filtration housings and filters in series (Figure 6.5) and is used by some beverage manufacturers. If using an integrity-testable membrane final filter, and if the plant is properly monitoring and controlling the process, this is not normally necessary. A final membrane does not allow contaminants larger than its pore size rating to bypass the filters when integral. Membrane integrity can be checked by a variety of tests, both manually and automatically, and should be performed on start-up, shutdown, and after cleaning or sanitation cycles. If a plant does not have good controls over integrity testing procedures, sanitations, or general filtration principles, then a redundant final filtration does add an extra layer of product protection, but it should be recognized as a point of possible future optimization. Redundant membranes have considerably lower rates of plugging since the previous membrane is removing the relevant contaminants. It is still possible for the redundant membrane to plug, however, as there are some reformable colloidal materials present in many streams, as well as issues with protein binding (not necessarily filtration) and service water contamination. Redundant non-membrane systems can be used when there are concerns about contaminant bypass or unloading. Non-membrane systems cannot be integrity tested, so bypass is possible due to filter damage, improper installation, and other factors. Depth filters may be subject to unloading if differential pressures are not properly monitored. Water hammer and pressure spikes can also cause unloading. A redundant filtration stage will mitigate these effects and make it less likely for contaminants to enter the finished product.

Filtration System Selection and Design

159

Determining the Format of Filtration The size, type, and quantity of plugging components will dictate which filtration stages and filter formats to use. Filter pore size ratings can be stepped up or down to either increase or decrease a stage’s particulate loading based on particulate size. The filter format may be based on particulate loading in that a high-fouling stream will require increased use of lenticular or depth-style filters and may require increased clarification or prefiltration stages in terms of both stage sizing and number. The type of plugging components will further influence the decision and may warrant additional steps targeted at a specific contaminant. A detailed plugging component analysis of all streams to be filtered should be the first step in designing a filtration process. These analyses are often simple and can be performed on the lab or bench scale. The majority of microfiltration systems currently in use in the beverage industry are either based on cartridge or sheet/lenticular design. Sheet design came first and was later adapted into lenticular filter format. Sheet filters are used in plate and frame housings. Lenticular filters are constructed from the same media as sheets; however, they are constructed in a manner that makes them easier to use and are made stackable to more easily create larger filter surface areas. Lenticular filters are encased in filter housings similar to filter cartridges. The two housing types are not interchangeable. Sheet and lenticular filters are only available as non-membrane depth filters. Sheet filters are commonly the final filtration stage for some smaller wineries and breweries as well as a few other industries. Lenticular filters may be used by medium to larger producers. As a facility grows, it is less likely to use sheet filters and, after further growth, less likely to use lenticular filters. Cartridges can be produced with depth media, so there can be overlapping as to which format (sheet, lenticular, bag, or depth cartridge) to use for some clarification and prefiltration applications. The vast majority of new systems being operated and installed are of the cartridge filter design. This design allows for much easier use, faster turnaround times, increased cleanability and regeneration, lower product losses, increased throughputs and, most importantly, the use of integrity-testable membranes for absolute particulate and microbial removal at a selected pore size

160

Beverage Industry Microfiltration

rating. Cartridge and crossflow systems are the only microfiltration formats that can use membrane filter media. Bag filters are used in highly viscose streams that do not require a great degree of microbial quality assurance. Bag filters are also common for facilities applications or the filtration of product components. Bag filters require the use of filter housings similar to lenticular and cartridge filters. Bag filters are the cheapest filtration media available; however, the costs of frequent change-outs, product losses, etc., will often preclude their use based on total operating costs. Bag filters should only be used for particulate removal and not for microbial removal in a process stream susceptible to spoilage or health issues arising from microorganisms. Crossflow filters are currently used for specialty applications or as a clarification stage where flow will be sent into a subsequent filtration process.

System Sizing Once the goals and formats of the filtration stages have been determined, it is necessary to size the filtration process. Each filtration company has many different guidelines for sizing filtration systems. This has led to a lot of variability within the industry. Outlet flow rate (i.e., to bottling) is a common starting point. The equipment sizing will then have to be adjusted based on other process considerations, such as batch time, cleaning frequency, particulate loading, variability of the process stream, temperature, and so forth. There is no straight formula for accurately determining the size of beverage microfiltration stages. All product and operating conditions must be considered in order to correctly develop the best process. Cartridge The sizing of a cartridge filter housing depends on many factors, including the filter type, pore size rating, flow rate, feed filterability, cleaning regimens, and process stability. There has never been a standard sizing method in any beverage industry. Each filter manufacturer has its own guidelines — and, in many cases, doesn’t have any true guidelines. There is tremendously wide variability in housing sizes between facilities within the same or comparable industries. There are

Filtration System Selection and Design

161

even large differences observed with regard to geography. Many European filtration housings tend to be grossly oversized by American standards, for example. That being said, there have been some trends observed, so some data exists to point a manufacturer in the right direction in selecting correctly sized cartridge housings. Most logical sizing methods are presented on the basis of feed flow rate per filter unit or surface area. The reason behind this is that the process outlet is often fixed by some constraint such as bottling or production outputs or acceptable time through a process step. Sizing is also based on flow rate because of face velocity. Face velocity is an important consideration that is often not well understood. To put it simply: one can filter 300,000 gallons at 50 gpm much more easily than 300,000 gallons at 150 gpm. The latter will typically prove more difficult to filter and will cause filter blocking earlier than if the filtration had been run at a lower flow rate, provided the same number of cartridges are used. The process outlet is usually set by external factors, so the final output cannot be lowered to extend filter life. As a result, the only viable means of reducing filter face velocity is by increasing the filter surface area to reduce the per filter (or per surface area) flow rate. This not only effectively reduces per filter face velocity but also decreases the amount of filtered volume per filter. By reducing the filtered volume per filter, the time until plugging and the required cleaning frequency is further extended. When a filtration train is feeding into an actively running filler, the filler becomes the process constraint. A filtration stage may only be partially plugged when the filler begins to be restricted on product flow. This often occurs even if the filtration train was initially sized based on minimum filler outlet. Filtration trains before a filler are therefore sized larger, given the same batch volume and output requirements, as compared to filtration trains not directly feeding a filler. Fillers sometimes demand a real flow rate 30–50% higher than the normal process capacity. The sizing flow rate of the filtration train is calculated from the filler output according to Equation 6.1. Q × V × Z = FSizing Q = Filler bottle output per unit time V = Bottle size

(6.1)

162

Beverage Industry Microfiltration

Z = Flow rate modifier ( between 1.3 to 1.5) FSizing = Flow rate to be used for filtration train sizing Example If the filler operates at a speed of 12,000 bottles per hour, the size per bottle is 750 ml, and assuming a 30% higher flow rate to obtain the necessary feed flow rate through the filtration skid, then the flow rate to use in sizing the filtration train is calculated as in Equation 6.2: 12, 000

bottles L × 0.75 L × 1.3 = 11, 232 hour hour

(6.2)

The filtration train should therefore be sized using a flow rate of 11,232 lph as opposed to 9,000 lph, which is the actual output, in liquid volume, of the filler. If sizing a low-fouling process stream (Note: Most wine and beer streams are considered high-fouling), the clean water flow rate curves supplied with the filters can be used. Mineral or spring water sources with acceptable filterability (SDI ≤3) may use these curves with a good degree of reliability. To use the clean water flow rate curve for sizing, follow these steps: • On the clean water flow rate curve, find the line for the particular filter selected, bearing in mind that most curves will have multiple filters or pore size ratings shown. • Trace the desired initial pressure drop horizontally until the selected filter line is met. The desired initial clean water pressure drop across a cartridge filter housing is normally around 1–2 psid (69– 138 mbar). This may be a little higher with some retentive wrapped, depth filtration cartridges and is sometimes lower with membrane cartridges. • Follow this point vertically until the x-axis is crossed. The point at which the x-axis is crossed represents the flow rate per cartridge. • Divide the desired process output by the flow rate per cartridge to obtain the number of cartridges required. If the desired process flow rate output is small enough so that it is represented on the graph, it is possible to work backward by tracing

Filtration System Selection and Design

163

the flow rate to the filter line and across to the differential pressure on the y-axis. This differential pressure may then be divided by the target to obtain the number of cartridges. These curves are completely linear and may be extended off of the graph’s scale. Always check the filter size of the curve because 10″ and 30″ cartridges will have different curves, although the results may be scaled later. If presented in 10″ elements, just divide the results by 3 to get the number of 30″ cartridges. Clarification stages have the most variability in filter requirements because they deal primarily with the bulk removal of contaminants and particulates from high-fouling streams. A standard number cannot usually be applied because it depends on how dirty the stream is upon entering the filtration and how clean it is required to be following the filtration. Sizing of new clarification stages almost always requires bench or pilot product testing. An exception is when a process step is well grasped and somewhat consistent from plant to plant, such as beer trap filtration. Spring and mineral water source clarification is another example. Clarification stages not attached to a bottling process can often be sized based on bulk particulate removal requirements rather than flow rate. In these cases the housing is sized so that it can filter a set amount of particulates from a known product batch size before plugging. Bench or pilot scale testing is best suited to this type of system sizing. Run the test filters until the change-out or cleaning criteria is met, a differential increase of 10 psi (690 mbar) for example, while recording filter throughput. Relate the test filter throughput to the future batch size to obtain the number of filters, or filter area, required to process the batch. Be mindful that dirt-holding capacity can decrease with each cleaning cycle and so, if reuse is desired, it might be best to oversize. It is possible for a tank to develop different layers of particulate loading. The end-of-run tank bottoms of many processes is considerably less filterable than other areas of the tank. There are instances where oxygen contact can cause film layers toward the top of a storage tank. Many beverage batch filtration processes are underdesigned based on tests performed with the first bit of product pulled from a batch, which leaves the system to quickly plug toward the end of the run when less filterable material remains. When sizing the final bottling filtration train, the general rule is that the clarification stage (if present) should be sized larger than the

164

Beverage Industry Microfiltration

prefiltration stage, which is sized larger than the final filtration stage. If a clarification stage is present, then the prefiltration stage may not be sized much larger than the final filtration stage. If only prefiltration and final membrane filtration stages are present, it is common to size the prefilter 50–100% larger than the final filter. The first step in sizing is to determine (1) the smallest microorganism to be retained by the final filter prior to bottling or (2) the smallest particle to be retained at a given processing step. After the pore size rating has been selected and the filter type is known, size based on flow rate or, if sizing a bulk removal step outside of the filling line, size based on filter dirt-holding capacity. Then adjust or modify sizing based on the following process considerations: • • • • •

Type and amount of contaminants in the feed stream Real flow rate required at filtration output Batch volume requirements Face velocity by filter element Cleaning frequency and methods

A good rule of thumb is that final membrane filters in spring water plants should be sized around 7–9 gpm (1,590–2,044 lph) per 30″ cartridge (if filtered to 0.22 μm). Brewery final filters (0.45 μm) that follow trap and prefilters are often sized in the 2.5 gpm (568 lph) per 30″ cartridge range. Wineries vary considerably because of the vast differences in cellar processing. Some major wineries size in the 10– 15 gpm (2,271–3,407 lph) per 30″ cartridge range, while others are closer to 4 gpm (908 lph) per 30″ cartridge (if using 0.45 μm). Changes in pore size rating and differences in filterability will dramatically affect these values and so the above guidelines should only be used as comparison. Filter suppliers may use lab-scale tests that use 47-mm disks and small volumes of product to size cartridge filtration systems. These tests were initially designed for extremely high-fouling streams, such as in a direct fermentation outlet, as seen in the pharmaceutical industries. Many pharmaceutical companies treat filters as a one-time use item. Food and beverage companies do cleaning and regenerations to reuse cartridge filters. Small-format tests do not take this into account.

Filtration System Selection and Design

165

Food and beverage manufacturers use considerably larger filtration housings than do pharmaceutical and biotechnology companies, which do not lend themselves well to being scaled up from 47-mm disks. Small-format tests such as this do not usually work well with beverage process streams. Pilot filterability tests with an actual process stream are, perhaps, the best means for sizing a filtration stage. These tests should be performed with at least a 10″ cartridge for accuracy and proper scalability. Gas and air filters will always be membrane cartridge types. The membrane used should be PTFE for almost every application. The pore size rating is almost always 0.22 μm. Gas and air filters will be sized smaller than liquid counterparts. A couple of guidelines to use for sizing a 0.22 μm membrane gas filtration application are: 1. The initial pressure drop of the combined housing and installed filters should be less than 1 psi (69 mbar). 2. The maximum flow per 10″ element should be limited to 100 SCFM (170 Nm3/h) or below. Tank vent filters or fermentation tank vent filters should be sized differently than standard gas filters. Sizing these filters will often require tank properties such as materials of construction and wall thickness and/or additional gas properties to be taken into consideration and can require considerably more involved calculations. A professional designer from a filtration supply company should be consulted on such applications. A basic rule of thumb is that the maximum flow rate per 10″ element should be 50 SCFM (85 Nm3/h) or below for these applications; however, this will depend on tank properties, pumping rates, and gas properties. Sheet (Plate and Frame) Plate and frame filters are sized according to flow rate. Once the desired outlet flow rate of a process has been selected, divide by the recommended flow rate per filter to determine the number of filters required by the process. The recommended flow rate per filter will vary with grade, desired clarity, process fluid, and manufacturer. The number of filters directly relates to the number of plates required. Once the number of filters/plates has been determined, simply choose the piece of

166

Beverage Industry Microfiltration

equipment (filter skid) that can hold that number. If the selection is close to two different skid sizes, it is best to use the larger size since it will allow the addition of more plates later on if needed. It may be necessary to modify the manufacturer’s recommended flow rate for a particular filter sheet based on incoming product clarity, desired product clarity, and exact product being filtered. If a filter has a recommended flow rate of 10 gpm (2,271 lph) for unclarified red wine, for example, a centrifuged red wine may work well with a flow rate of 14 gpm (3,179 lph). Desired batch size should be taken into consideration. Filter sheets will have a rough value established for the amount of volume that can be filtered for a given product and incoming clarity. It may be possible to meet flow rate requirements in sizing, but then not be able to filter an entire product batch or tank. In this instance the filtration skid and number of plates/filters should be increased to allow for processing of the complete batch. This may not always be possible, however, and it is common for a product batch or tank to require multiple setups before completing a run when using sheet filters. Lenticular Lenticular filter housings are sized based on recommended filter surface area. Each filter disk has a filter surface area, and this is compared to a value obtained by preliminary filterability tests. Lenticular cartridges have been widely used in some applications, such as winery and brewery filtration, so most suppliers will have some guidelines that will preclude the need for preliminary testing. If this is not the case, the housing may be sized by running a product sample through a small-scale representation of the lenticular cartridge. Record the pressure drop across the filter during the test filtration run. This may be done with either small-scale pressure gauges or pressure transducers on the filter inlet and outlet. Record the volume of product filtered at the point when the filter’s maximum recommended differential pressure is met. Divide this volume into the desired volume of the product batch to be run in the production-scale filtration. Multiply this number by the surface area of the test filter to obtain the total filter surface area required by the production-scale system. Divide the total surface area required by the per filter surface area given in the filter literature to obtain the number of filters required to process

Filtration System Selection and Design

167

the desired product volume. Equation 6.3 illustrates this sizing calculation. Filters Required =

VBatch ( ATest )(VTest )( AProduction )

(6.3)

VBatch = Product batch size (in production ) A Test = Test filter surface area VTest = Throughput of test filter A Production = Surface area of production-scale filter Keep in mind that oversizing may be necessary if cleaning and regeneration of the filters is to be performed. There will be some loss in filter capability over the course of cleaning cycles. Sizing based on the optimal first run filter capacity may leave the filters plugging before subsequent product batches have been completely filtered. Bag Filters Bag filters are typically sized based on the recommended initial system pressure drop. New bag filter processes should have a pressure drop of less than 3 psi (207 mbar) at the specified process flow rate. This includes both the pressure drop associated with the bag and the housing. Some manufacturers recommend an initial pressure drop of 2 psi (138 mbar) or less, while others may allow a higher initial pressure drop; in such a case, it is best to check with the bag filter manufacturer for a recommendation. Bag filter efficiency begins to severely drop off at around 8–12 psi (552–827 mbar), with change-out occurring after that. Bag pressure drop will be dependent on the bag size, pore size rating, process flow rate, and the viscosity of the fluid. Bag filter literature should come with the necessary curves and correction factors to calculate pressure drop. Housing pressure drop will increase linearly with flow rate for a specified housing. Housing pressure drop can sometimes be ignored from the equation. This may be the case if observing one of the two following scenarios: • The selected bag is of a tight pore size rating, such as 1 or 5 μm. The housing pressure drop will often be insignificant compared to the bag pressure drop.

168

Beverage Industry Microfiltration

• The process flow rate is low. Housing pressure drop increases linearly with flow rate, so a low process flow rate will result in a low housing pressure drop. This is often the case with standard housing sizes and flow rates of less than 50 gpm (114 hl/h). Follow these steps when calculating system pressure drop: 1. Locate the flow rate per pressure drop curve for the bag being considered. Make sure the correct pore size rating is selected. Select the system flow rate and find the matching bag pressure drop. 2. The flow rate curves are given as a function of water. If the viscosity of the process fluid is close to that of water, the pressure drop found on the curve can be used. If the viscosity of the fluid is much higher than that of water, a correction factor must be used. The manufacturer should have a table of viscosity correction factors for the filters. Viscosity correction factors for bag filters are usually fairly consistent between manufacturers. An example is shown in Table 6.1. Multiply the proper correction factor by the selected pressure drop. Remember that viscosity changes with processing temperature. 3. Bag size must be corrected for. Water flow rate curves are given based on either the filter’s surface area or on the filter’s size. Table 6.1. Example viscosity correction factors for sizing bag filter processes (source: Hayward Industrial Products). Viscosity (cps)

Correction factor

1 (Water) 50 100 200 400 600 800 1000 2000

1.0 4.5 8.5 16.6 27.7 38.9 50.0 56.2 113.6

Filtration System Selection and Design

169

• If the flow rate curve is specific to a filter’s size, and that size is being selected, then no calculation is required. • If the flow rate curve is given based on a specified unit of surface area, such as 1 square foot, this must be related to the surface area of the filter size selected. • If the flow rate curve is given for a specific filter size, and this size is not being used, the pressure drop supplied by this curve must first be divided by the surface area of the table’s size and then multiplied by the desired filter size’s surface area. 4. If the housing cannot be ignored, find the flow rate versus pressure drop curve supplied with the housing. Select the process flow rate and locate the corresponding pressure drop. If the curve for a specific housing cannot be located, it is usually sufficient to find a corresponding curve for a similar housing. Many manufacturers will publish these curves in housing literature. The viscosity of the fluid will affect the housing pressure drop. If the viscosity of the fluid is much greater than that of water, multiply the pressure drop obtained from the curve by a viscosity correction factor. Housing viscosity correction factors are not the same as those used for bag filters and can vary more by manufacturer than can bag correction factors, which are fairly consistent. Housing viscosity corrections are not as large as bag correction factors, however, and they will usually amount to less than a 2 times increase, whereas bag correction factors can amount to increases of over 100 times. 5. Add the housing pressure drop to the bag pressure drop to obtain the system pressure drop. 6. There is no steadfast method for correcting for a fluid stream’s particulate loading, batch size, or other plant process requirements. These items are nonetheless important and must be considered. If it is known that a fluid stream is very high in particulates, it may be necessary to oversize. If a batch size is a 50,000 gallon (1,893 hl) tank and it is desired to process the entire tank on one filter set, then the filtration step may need to be increased. Crossflow Systems Crossflow filtration systems are usually modular. The crossflow system manufacturer will have standardized systems available with specific numbers of modules. Each module will have a recommended flow rate

170

Beverage Industry Microfiltration

for a particular product or inlet/outlet product clarity. The system size is selected by dividing the desired flow rate (determined by the plant’s process) by the recommended flow rate per module. The calculation yields the recommended number of modules for the application. The system with the closest number of modules is chosen. It is always better to round up rather than down, and the cost of an additional module is usually nominal compared to the initial costs of the system. Some systems are such that the filtration skid or membrane holders are sized for a particular range of modules. This is comparable to the way in which plate and frame filter skids are designed. With these systems it is sometimes best to purchase the larger skid/frame so that there is room for expansion. This will usually mean a slightly higher initial capital cost but, if a process expands, having an undersized filtration stage is avoided. If four modules are initially required, it is usually better to purchase an 8-module skid that is half full as opposed to a 4module skid that is completely full and cannot be upgraded later. Not all crossflow systems are built in this manner.

Auxiliary Equipment Design and Selection Auxiliary equipment design and selection can play an important role in the overall performance of a filtration process. Pumps, surge tanks, CIP piping, and other items will contribute to the sanitation of the system, the ease of use, and the general performance. Feed Pumps Bottling line feed pumps must be selected such that the feed pump is able to reach the minimum flow demanded by the filler after filtration at the maximum allowable pressure drop through the filtration stages. If a cartridge system, for example, is feeding a bottling line, the pump must be able to supply the minimum flow required by the bottling line when there is a pressure drop of roughly 70–90 psi (4.8–6.2 bar) with two filtration stages, or roughly 100–120 psi (6.9–8.3 bar) when there are three filtration stages. These pressures estimate the maximum pressure drop that may occur when all filtration stages are simultaneously plugged. The above estimates include one stage that is a

Filtration System Selection and Design

171

membrane. The actual pressure drops that may occur will vary among systems but can be easily determined. Non-bottling line feed pumps are selected such that they can maintain the minimum desired outlet flow up to the maximum pressure drop experienced by the filtration system. It is important to not grossly oversize pumps when dealing with depth filtration stages so as to not force contaminants through the depth filter matrix and into downstream processing stages or filtration steps. Pumps and valves should be operated in such a manner to avoid shock waves or water hammer, as these are common causes of both filter damage and, in the case of depth filters, material being pushed through the filters and proceeding downstream in the process. Note that bag filters are susceptible to rupturing under pressure spikes. Several types of pumps can be used. Both centrifugal and positive displacement pumps can operate with the pressure drop requirement. Positive displacement pumps may require a bypass with pressure regulation, which should be achieved by means of a spring, not weights. In some applications it is necessary to use a non-shearing or low shear pump. This will avoid high sheering forces, which can sometimes break up matter and cause a turbidity increase of the filtrate. Many new bottling lines operate with automatically controlled variable speed pumps that can be tied to filler operation or another process parameter. There are many pump vendors experienced with fluid flow who can properly determine the correct pump for each system. More information regarding pumping can be found in the Chapter 1 section, “Basic Fluid Dynamics of Filtration.” Surge Tanks Surge tanks are important for a variety of different reasons, depending on the process line. Surge tanks can allow for more constant operation, particularly with older fillers that have a small filler bowl reservoir. Constant operation through the filter train has a positive effect on filter performance over time. It is better to run the filtration process at a slower, consistent rate as opposed to an intermittent, faster rate. Surge tanks help in this matter. Surge tanks can serve other functions within specific industries. The bottled water industry typically locates a tank after the final membrane filter, so it serves as both a filler surge tank and as an ozone contact

172

Beverage Industry Microfiltration

tank. In operations with dissolved gases or gas additions to a fluid, using a surge tank after the filtration train can reduce foaming in the bottle after filling. Using certain surge tanks in the correct location can aid with dissipating pressure shocks or water hammering and reduce associated damage. Not all operations require a surge tank, and the necessity for one should be assessed on a case-by-case basis. Large filler bowls can reduce the necessity for some bottling line surge tanks. Valves Most filtration systems use a combination of butterfly and ball (spherical) valves. Diaphragm valves are also used, but can be cost prohibitive. Remember that only butterfly and diaphragm valves are truly sanitary. There are various designs of ball valves that can be more easily sanitized, but this generally requires an extra step. Most often the inlet to a filtration system is a ball valve and all other valves within the system, except the outlet, are of the butterfly type. A small vent valve, usually a simple petcock valve, should be located at all system high points to evacuate any trapped air. A check valve (no-return) should be installed immediately after the final filtration housing leading to downstream processes. Additional check valves may be required depending on the process and operation of the skid or auxiliary CIP processes. When there are multiple flowpaths into one tank or process piping, there is potential for backflow when one of those flows discontinues and the other(s) does/do not. Unintended backflow can be damaging to filtration systems. Automated valves should fail in the closed position to avoid product mixing, water dilution, or cleaning chemicals from potentially being introduced into the product stream. Care should be taken with all valves to avoid water hammer within the filtration system. Fillers tied to the feed pump are useful in this respect. Automatically throttling valves can be used to reduce the likelihood of water hammer and improve fluid flow through the filtration system. Instrumentation Pressure gauges must be located on the inlet and outlet of each housing or stage in a filtration system in order to monitor differential pressure.

Filtration System Selection and Design

173

This is true for all filter formats. Automated systems and skids can have pressure gauges communicate with the system programming or controls for easier and more accurate display, trending, recording, or monitoring of spikes. It can be useful to have differential pressure alarms, which sound as the filters are nearing their change-out or cleaning specification. Flowmeters can be useful for monitoring system throughput. There are instances when flowmeters can work in conjunction with automated pumps and valves to regulate flow and/or maintain constant flow through the system. Temperature probes or indicators can be useful for cleaning purposes. They will ensure that water and cleaning solutions meet the minimum temperature requirement and, if controls around the facilities water are inadequate, that the hot fluids are not hotter than called for in the cartridge specifications. Many filtration skids are increasingly automated. It is important that automated components be intelligently designed. Carbon dioxide or nitrogen additions should come after domed-type filtration housings. This will prevent the need for frequent venting of gases. Additions that may cause additional filter plugging but do not require the same filtration should be located after the filters. Avoid dead legs and ensure all components can be properly sanitized.

Parallel Filter Skids In large facilities that operate year-round on 24/5 or 24/7 bottling schedules, it is possible to find two identical filtration skids on each bottling line in parallel (Figure 6.6). This is typical in industries where there are many product types run on a particular line, frequent product changes, or when there is a need for regular cleanings or sanitations of the process. Having two identical skids in parallel is beneficial in that when one either plugs or is down for cleaning, sanitation, maintenance, filter change-out, or any other reason, the second set can be immediately brought on-line with either zero or little downtime to the filler and bottling/packaging processes. The initial capital is obviously larger, as is the initial filter spend, however the annual operating costs are decreased when considering the labor and downtime costs of the bottling and packaging departments. Follow-on filter spend will be

174

Beverage Industry Microfiltration Train 1 CIP

Prefilter #1

Final Filter #1 Outlet to Bottling

Inlet

Prefilter #2

Final Filter #2

Train 2 CIP

Figure 6.6. train.

Parallel filtration skids offer several benefits over having only a single

lower over time, as parallel filter skids allow for more thorough and more frequent cleaning and regeneration cycles which, in turn, allows for the filters to be used for longer periods of time. There are other benefits to using parallel filter skids in addition to alternating flow for continuous bottling and longer non-bottling–impact cleaning regimens. Parallel filter skids run together at the same time can offer a step up of flow depending on product. Using multiple skids in parallel has some positive implications for the sensitivity of membrane integrity testing. An integrity test performed on two 12 Round 30″ housings, one after another, is much more sensitive than an integrity test performed on one 24 Round 30″ housing. There are also fewer filters at risk for early change-out should a single filter cause an integrity failure of an entire housing. A multiple train skid can be equipped with different filtration alternatives for the same bottling line. A fine red wine, for example, may not undergo a membrane final filtration, whereas the winery may want to membrane filter a white wine on the same line.

Filtration System Selection and Design

175

CIP Design Filtration systems must be regularly cleaned, just as any other process equipment. Cleaning prevents the growth of microorganisms and removal and prevention of biofilms, as does the cleaning and regeneration of filters. The cleaning system should be designed based on the process’ needs. One of the most important aspects of CIP design is determining which parts of the process or system may require individual cleaning. Fillers, for example, should usually be configured so that there is the option of separate cleaning from the filtration train. If parallel filtration trains are used, it is crucial to have the ability to clean each train independently of the other. Piping should be checked for dead legs. High points on the system should have vents so that trapped air can be removed. Venting trapped air is necessary for eliminating air pockets, which may block portions of the system from being adequately cleaned. Check valves should be incorporated on CIP line inlets to prevent backflow. Cleaning should not only take into consideration the equipment and piping, but also filter regeneration, if applicable. CIP water and/or chemicals may require a separate filtration so that they do not damage or plug the primary product filters. It may be necessary to build a bypass into the filtration skid so that harsh chemicals can be used to clean the piping, surrounding equipment, and filler without negatively impacting the filters.

System Manufacturers and Suppliers Large filtration companies have systems groups that sell stand-alone filter housings, standard filtration systems, and custom-built systems. This is often the easiest method for a beverage plant to procure a filtration system. It is not the cheapest. The filter manufacturers produce filters — they do not have large steel casting and fabrication facilities to produce housings. They do not manufacture valves, pumps, tanks, etc. These products will be sourced from other manufacturers, assembled, priced at what can be a considerable markup, and sold to the beverage plant. In most situations, the filter manufacturer also sells systems through their beverage industry distributor who will add a second markup.

176

Beverage Industry Microfiltration

Plants can see considerable savings by acquiring the parts and using a local shop, in-house personnel, or some other means of assembly. This can be easiest when the plant already has contacts with reliable distributors for things such as valves, piping, and fittings. Even just directly purchasing housings can be a tremendous savings to the plant as these are often the most expensive single item on the filtration skid. Plants that are using basic filtration systems as opposed to complex automated skids complete with automated CIP, addition lines, and more, will benefit even more from directly sourcing the housings. With a little extra work, it is easily possible to see a 20–30% or more savings on a filtration skid, depending on the number of middlemen. With some of the larger and more automated complete systems coming in anywhere from $50,000–$500,000, this savings can easily justify the extra effort, especially if multiple lines or systems are involved.

Chapter 7 General Industry Filtration Processes

Bottle Washing Many containers, both new and (especially) recycled, will require some cleaning or sanitation prior to filling. Industries that require a high degree of microbial stability will need to rinse with water that contains some chemical or solution to ensure product quality. Industries that do not necessarily need microbially stable containers will still rinse containers to remove dust and debris for aesthetic purposes. Filtration is an important consideration when designing the bottle-washing step of packaging. Filtration of the water can ensure that no microorganisms are introduced to the product via the rinse water. Filtration also ensures that no particulates enter the final container and product. Particulate filtration is important when the facility’s water, most of which isn’t considered critical, passes through pretreatment stages such as carbon or multimedia beds. Algae is commonly introduced to product via unfiltered municipal water used for bottling rinsing. Returnable containers often require a higher degree of cleaning and/ or sanitation since the plant cannot know how the bottles were used when under the control of the customer. Many bottled water plants that bottle 5-gallon home and office containers will have special devices called “sniffers” to help detect if a container has been contaminated. It is not uncommon for human or animal waste or other hazardous materials such as motor oil or chemicals to be present. Breweries may steam kegs to ensure product quality. In this instance, steam filters should be used. Filters used for rinse water vary greatly among different applications. If only particulate removal is required, then a 1.0 μm or higher depth filter will be sufficient. If microbial contamination is a concern, then a 1.0 μm, 0.45 μm, or 0.22 μm membrane filter is recommended. The use of 1.0 μm filters for Cryptosporidium and Giardia removal is 177

178

Beverage Industry Microfiltration

more common if using surface water supplies as a source for rinse water. When using a membrane final filter for rinse water, it is usually beneficial, but not always required, to have a prefilter.

Facilities Water There are many times when it is helpful for general process water to be filtered: • When water is used to clean filters. When this is done, the water should be filtered to the same degree as the final product filtration. If filters in use are 0.45 μm then the water used for cleaning and sanitation should be filtered to 0.45 μm. This ensures that process filters are not damaged or further plugged during cleaning. • When water is used to make cleaning solutions for filters. When this is done, the water should be filtered to at least the same pore size as the filters themselves. • When facilities water is used for sensitive applications, such as rinse water, water for cleaning filling rooms, or water used for cleaning closures and/or closure equipment. • When surface water is being used in the plant and it is possible for Cryptosporidium and Giardia to be of concern. • When there is a known issue with the water supply, such as algae. • When it is necessary to remove certain odors or tastes; carbon impregnated filters may be used to do this. • When there is an accumulation of particulates at any point in the process due to facilities water. An example would be if incoming water passes through a carbon bed. Carbon fines can bleed through into the process water and accumulate in storage tanks or piping and be subsequently picked up by the product or become an additional cleaning problem. A number of beverage plants have benefited greatly from installing filtration systems on incoming plant water supplies. There can be dramatic increases in general plant cleanliness, decreases in ambient microorganism presence, and reduced overall filtration costs due to increased process filter service life.

General Industry Filtration Processes

179

Many spring and mineral water bottlers using 0.22 μm membrane final filters, in particular, have found it necessary to add a separate filtration process for CIP water to avoid plugging and degrading final bottling filters. This is due to the fact that most municipal water sources used for CIP are much less filterable than spring water sources. Unless filtered prior to filter cleaning, the CIP water will plug all production filters and result in a considerable cost increase for production. Reverse osmosis can be used for this application as well. It is possible to further optimize process water filtration by separating streams by application. Incoming water can be split into three streams: a stream that does not require filtration, a stream that requires only depth filtration for particulate removal, and a stream that requires membrane filtration for microbial stability. Splitting streams in this fashion will usually be a little more expensive initially, due to an increase in the number of housings required, but filter and operating costs will be lower over time. Filter selection will be based on each individual plant, its processes, water source, and applications.

Steam Steam does not introduce microbial contamination, but it can often contain hard particles that can contaminate product, piping and lines be damaging to filters if steam sanitation is used. Sintered stainless steel membranes with stainless steel cages are used for steam filtration. Stainless steel filters are expensive when compared to other process filters. This cost is relative, however, as stainless steel filters have a long service life, require little maintenance, and need only rare periodic cleanings in most cases. Steam is a gas, and contamination is usually minimal, so few filters (often only one) will be required for most plant steam supplies. Steam filters are sometimes sized based on mass flow rate. They can also be sized using conventional flow rate versus pressure drop curves. Stainless steel steam filters are often rated 1.0 μm. Microfiltration in the Lab The majority of food and beverage plants will perform some type of microbial monitoring of the product and/or process equipment

180

Beverage Industry Microfiltration

surfaces. Microbial testing of beverages usually involves taking a sample of the beverage at particular points in the process. The liquid sample is drawn through the appropriate membrane filter via a vacuum source or separate vacuum pump. The membranes used are made of the same material as process filtration membranes, but in 47-mm round disk format. The membrane pore size is usually the same as that of the final membrane filtration step in a process. Culture media is applied after filtration. Culture media that will facilitate growth of the desired microorganism on the membrane is selected. If testing is to be done on several different types of microorganisms, separate filters are used and each are cultured with the media of choice for that particular microbe. Wineries, for example, will usually have at least two tests per sample — one for yeast/mold and another for bacteria. After the culture media is applied, the sample is incubated for a set period of days, determined by the test microbe. The colonies that form on the membrane surface are counted and represented as Colony Forming Units (CFU’s) (Figure 7.1). The number of colonies varies based on the size of the liquid sample originally filtered, so the sample size should be kept constant for all samples and should be correlated to the specified microbial limit of the product. Bottled water plants will often use membrane filters to test for E. Coli and/or total coliform. The following guideline regarding this procedure is taken from FDA CFR 21 Sec. 165.110:

Figure 7.1.

Yeast and mold grown on a 47-mm disk after filtering wine.

General Industry Filtration Processes

181

Membrane filter method: Not more than one of the analytical units in the sample shall have 4.0 or more coliform organisms per 100 milliliters and the arithmetic mean of the coliform density of the sample shall not exceed one coliform organism per 100 milliliters.

Air monitoring is used in filling rooms and other sensitive areas. The old fashioned method of air testing was to leave a Petri disk out in the room in hopes that any microbes present would settle on the disk and show up in the subsequent testing. There are now more sophisticated devices that will draw a specified sample of air through a membrane filter, impacting the microbes on the filter’s surface. The filter may then be tested using the appropriate culture media and incubation time. Filter disks chosen for each lab application should be of a correct pore size rating to retain all of the microbes of concern. A yeast and mold filter can often be 0.65 μm or 1.0 μm, for example, but tighter 0.22 or 0.45 μm filters must be used when bacteria are being tested for. Most beverage processes will use the same pore size rating on lab filters as on production-scale filters to mirror the same removal. This can be especially important when there aren’t capabilities for species differentiation.

Gas Filtration Gases are used heavily in the beverage industry. Carbon dioxide is added to many finished products. Bottles and product lines are blown dry with compressed air. Nitrogen is used to blanket storage tanks or to reduce the dissolved oxygen content of the final product. Each of these applications and the dozens, if not hundreds, of others that exist within beverage processes may require a gas filter. Not all gas applications require filtration, and it will be up to the individual plant to decide the level of protection for a particular product or process. Gas filtration systems may be either point-of-use or centralized. Point-of-use gas filters are located directly where the gas is used in the process. Each point of use will require its own filter. Centralized gas filtration systems are usually located after the compressor, before or after the storage tank, or wherever the gas is introduced to the plant.

182

Beverage Industry Microfiltration

Centralized gas filtration systems will only have one filtration housing to install and maintain. Centralized gas filter housings will be larger than those of point-of-use systems. The problem with centralized gas filtration systems is that all of the gas lines and drops throughout the plant must now be cleaned and sterilized for the filtration to have any true purpose. Point-of-use gas filtration systems do not require the gas transport lines to be cleaned or sterilized since the upstream side of the filter is now irrelevant and the downstream side is cleaned along with the main process line or equipment. The drawback of using point-of-use systems is that many smaller filter housings are required. Gases entering the filters need to be dry and oil free. It is important for the gas to be dry since the gas filter used will be hydrophobic and excess moisture may blind the membrane. Oil can be a problem since it can be present in large amounts and will form a layer on the surface of the membrane, resulting in complete blockage of those pores it covers. There are compressor filters that are specifically made for oil removal from compressed gas. In the absence of oil and excess moisture, most particulates removed from a gas stream are hard particles. These hard particles will form a permeable cake on the membrane surface and will offer little obstruction to flow. The maximum allowable differential pressure for the filter is used to size the system. Many manufacturers offer gas filters (hydrophobic PTFE) in small formats such as 1″, 2″, 3″, 4″, and 5″ in addition to the standard 10″ element. This is because point-of-use gas filtration processes can be very small. Disposable filter devices are becoming increasingly popular for point-of-use gas filtration applications. The filters are used for a specified amount of time and disposed of. These filters eliminate the need for an extra stainless steel filter housing. The filters can come presterilized and even pre-integrity tested. This eliminates the need for pre-use sterilization and integrity testing. As gas filters are hydrophobic and generally require wetting with an alcohol solution to properly integrity test, the benefits of avoiding this are obvious. The filters can simply be attached in-line, often with sanitary tri-clover clamps, used, and thrown away. The majority of beverage applications for gas filtration use a hydrophobic PTFE membrane 0.22 μm rated filter.

General Industry Filtration Processes

183

Vent Filtration Vent filtration is required when a product is highly susceptible to contamination and spoilage or if it is to be stored for extended periods of time. Vent filtration is most common in the dairy industry. Beverage storage tanks all have a vent on the top of the tank. This vent gives a pathway for the air that is displaced during filling. The vent also allows for air to displace the liquid when the tank is emptied. The vent is open to the atmosphere, so it is possible for there to be product contamination through the vent. Adding a vent filter will prevent contamination of the tank via the vent. A hydrophobic membrane made of PTFE is the most common membrane material for this application. Because tank vent filters are only filtering air, they rarely plug. Tank vent filters require few cleanings and, in fact, many beverage plants simply use vent filters for a specified period of time and then discard them. If this procedure is to be adopted, it becomes necessary to use an economical tank vent filter supplier. A pore size rating of 0.22 μm is almost always used for vent filtration. Care must be taken not to wet the membrane by overfilling the tank or adding pressure beyond the wetting pressure of the membrane. If a tank is full, and enough pressure is applied, the hydrophobic membrane can be forced to wet. The vent filter will not function as a vent if it is completely or substantially wetted because air flow will be restricted. The membranes are hydrophobic, so things like rain or rinse water will not pose a wetting risk due to the lack of pressure. If a tank vent filter is inadequately sized, there will be insufficient air flow through the vent. This can result in tank implosion. Tank vents must be separated into two types for vent filter sizing. Low-pressure tank vents are found on standard storage tanks. Tank dimensions such as height, diameter, and wall thickness must be known. The rate of pumping in and out of the tank must be considered. Tank vent filters for high-pressure applications, such as fermentation tank inlet and exhaust, are sized using the gas properties such as inlet pressure, temperature, and flow rate as well as the flow rate versus pressure drop curves for the particular filter type. High-pressure tank vent filters will be larger than low-pressure tank vent filters. Some basic sizing guidelines have already been presented in Chapter 6.

184

Beverage Industry Microfiltration

CIP Solutions and Chemicals Cleaning chemicals used in sensitive areas of the plant, such as the microfiltration train, may require some type of filtration prior to use. This filtration will help to prevent particulates from damaging the process filters during cleaning. However, many cleaning solutions are filtered by the chemical supplier and this should be checked before adding a redundant filtration step. When selecting filters for chemical filtration, it is important to check chemical compatibilities. The chemicals may be more concentrated than what is used during process cleaning. Chemical contact times will be much longer than normal. It is therefore recommended to verify the criteria used by the manufacturer during the chemical compatibility testing. Compatibility testing is usually performed up to a certain concentration and/or time, such as 1% for 40 hours. These test parameters are normally designed with a typical filter cleaning regimen in mind and not for filters that are specifically filtering the cleaning chemical. Filters may see much higher concentrations and contact times when functioning specifically for CIP filtration. If cleaning chemicals are filtered, it will usually be with a depth-style filter. A common problem that arises when using cleaning chemicals is the formation of precipitates after the chemicals are added to the CIP make-up water. Since the water in some plants is filtered prior to chemical addition, these precipitates may be unknowingly passed to the downstream filtration processes, causing filter blockage and/or degradation. If this occurs, the CIP filtration process should be moved to after the point at which the chemical is added to the make-up water. When changing or developing cleaning regimens, an easy test to perform is to make up a sample of the CIP solution and filter it through a membrane of the relevant pore size rating. The membrane may be compared to one that had filtered the current CIP solution to determine if a change has taken place. A membrane is best used for the test, even if the downstream filtration processes are not performed with a membrane, so that the plugging components can be more easily determined by plugging component analysis. Many food and beverage plants use caustic as part of their cleaning regimen. Frequently using large amounts of caustic can be costly to a plant. Disposal of the spent caustic can be both costly and challenging. It is possible to process used caustic through a microfiltration system

General Industry Filtration Processes

185

in order to reuse the solution. A ceramic membrane is typically used. Sintered stainless steel membranes can also be used. Pore sizes are in the 0.05–0.1 μm range. Some suppliers, such as Pall, now have complete turnkey systems designed specifically for this application. The membranes used are extremely durable and can last years in process. The process economics and payback of such a system is often clearly favorable when more than small amounts of caustic are used.

Chapter 8 Wine Industry

With regard to microfiltration, the wine industry has been one of the fastest growing beverage markets in recent years. Its growth is second in the United States only to bottled water. The trend has continued despite a once perceived degradation or “stripping” effect of membrane microfiltration on a wine’s color or sensory attributes. Most of those wineries that have tested microfiltration have found that no appreciable degradation occurs and have moved to membrane filtration for their products. Wineries that currently perform microfiltration include nearly all of the major US and international wineries such as E. & J. Gallo Winery, Bronco Wine Company, The Wine Group, Beringer Blass Wine Estates, and Constellation Brands. At these facilities, and at the majority of others within the United States and Australia, 0.45 μm membrane filtration is typically the end goal. Many of the mobile bottlers that service smaller wineries in the United States incorporate microfiltration into their mobile bottling lines. Final filtration pore size ratings of 0.65 or 1.0 μm are sometimes used for specialty or high-end red wines. European wineries have been less accepting of the 0.45 μm standard, and many do not currently membrane filter below either 0.65 or 1.0 μm, particularly on red wines. Many wineries have been reluctant to use any membrane filtration and prefer sterile-grade pads or sheets instead for clarification or to remove a majority of yeast. Prefiltration and clarification filters vary greatly among wineries and countries. Crossflow microfiltration as a replacement to DE or sheet filter clarification has seen a significant surge recently. Sheet and lenticular filters are still common with small and medium producers but continue to be replaced by cartridge filters. Microfiltration is starting to be adapted by wineries for more non-conventional applications, such as tartrate removal, cleaning waste streams for wine/alcohol recovery, and caustic reuse. 187

188

Beverage Industry Microfiltration

Clarification The use of clarifying microfiltration stages has not been well defined within the wine industry. Some wineries use clarification filters at a number of stages within the process, while others have never used a clarification stage. Southern European wineries, for example, use microfiltration for clarification a great deal, whereas many Californian wineries do not. California wineries are still more likely to use a centrifuge, settling tank, or DE filter as opposed to sheet, lenticular, or cartridge microfiltration device for most clarification applications.

A new clarification application emerged in 2007. E. & J. Gallo’s G3 Enterprises has partnered with Filtrox to create a patent pending sheet filter, Fibrafix TX-R, which can remove the effects of TCA contamination from wines.

Tartrate Removal The use of clarification filters for the removal of tartaric acid crystals during the stabilization phase of winemaking has recently become a solid application at some wineries. Through the use of clarification filters, the tartrate removal step is shortened in length. Using clarification filters also frees up chillers that might otherwise get clogged with tartrates, and it can reduce tank lees, which lead to decreased product yields. There are several considerations when designing this filtration step. If the tartrate is currently being recovered, or if it is desired to recover this by-product, there will have to be additional recovery processes designed. Sheets are used to remove tartrates in small and medium wineries. A typical 10,000 gallon (379 hl) batch of wine will require on the order of 120 medium-grade 40 cm × 40 cm sheets. Variations in filter grade and the level of wine clarity will have an impact on the number of filters required to process a batch. Cartridges are used to remove tartrates in some wineries. Inverted filtration housings have been reported to perform better than standard housings due to the filtration mechanism and the manner in which the tartrates are removed. Housing size should be on the larger end of the

Wine Industry

189

range due to the sheer mass of material being removed. Both wrapped, depth- and non-membrane surface-style cartridge filters have been used. Due to the variation and newer nature of this application, pilot testing should be performed to determine the exact filter type, pore size rating, and housing size before proceeding. Pore size ratings to try should be in the 1.0–2.0 μm range. Large wineries may run into difficulty processing tanks in the 50,000–100,000 gallon (1,893–3,785 hl) plus range with any size housing. The removal is most effective when combined with an onboard or local chiller that allows for increased precipitation. DE Trap Filtration There are wineries that have taken after the brewing industry and have installed DE trap clarification filters. DE filtration processes are prone to poor performance. DE bleed-through is a common symptom that can cause significant problems to downstream microfiltration processes. Pressure leaf filters, in particular, are prone to DE bleed-through as the mesh screens that comprise the leaves can develop holes or cracks over time. These defects are most common at the weld joints and can be difficult to detect. Many wineries use blowdown procedures to recover wine remaining in the shell of the filter housing. These blowdown procedures, performed with a gas such as CO2, can cause DE bleed-through or bypassing of contaminants. A wrapped, depthstyle prefilter in a pore size rating of between 1.0 μm and 5.0 μm is best suited to this type of filtration. Lenticular filters are and can be used, but a cartridge-based system is recommended for new installations. Medium- to fine-grade lenticular filters should be selected if using that format. Adding a filter aid to the pre-coat of the DE filter can help to improve the performance of the DE filter and reduce the amount of particulates in the outlet. Pre-Bottling Filtration A clarification stage is sometimes built into the main pre-bottling wine filtration train. If the primary clarification stage is performed with sterile- or fine-grade sheets or lenticulars, crossflow, or a good, working DE filtration, then a pre-bottling clarification stage is often redundant. If the primary clarification is not of a high grade or the wine is subject

190

Beverage Industry Microfiltration

to further processing, additions, or prolonged storage after the primary clarification, then this additional clarification stage can be beneficial. Prefiltration stages in wineries are usually pleated surface-type filters for higher retention and better final filter protection. Adding a depthstyle filter as a clarification stage can greatly increase the overall dirtholding capacity of the total filtration process. Adding another pleated surface-style filter as a clarification stage can be beneficial, as it can be of another type or pore size rating. This splits up the filtration and adds to the overall economics. Perhaps the second filter will be one that has a higher efficiency for colloidal materials as opposed to hard particles, for example. Having both a clarification and prefiltration stage prior to final filtration allows for an extra step-down in pore size rating, which will decrease the individual stage particulate loading. Depending on the desired pore size rating of the final filtration, the clarification filters should be between 1.0 and 2.0 μm with the first being used with 0.45 μm membrane filtration and the latter being used when 0.65 or 1.0 μm final filtration is the end goal. Pre-bottling clarification stages become more important if wines are subject to long storage times, mixing between tanks, or temperature fluctuations after the DE or primary clarification step. Sheet (plate and frame) and lenticular filters are commonly used for primary clarification steps. Small and medium wineries will often filter through a plate and frame filter, as opposed to a DE filter, prior to the final bottling train. Many mobile bottlers require this level of clarity prior to the cartridge filter systems in place on their bottling lines. In these cases there should still be a prefiltration stage before the final membrane. Bag filters are used very rarely. Cartridge-style filters are recommended for better performance and economics. Wineries that hot fill, with the bottle filler being placed after a pasteurization step, will still filter prior to the pasteurizer using either sheet, lenticular, or non-membrane cartridges. It is possible to filter via a more open membrane, such as 1.0 or 1.2 μm and use a lower or shorter heat setting on the pasteurizer. Spanish wineries often used pasteurization up until recently; some still do. Crossflow (Tangential Flow) Clarification Crossflow filtration systems are now employed as an alternative to DE clarification in many wineries. Systems of this type are of a higher

Wine Industry

191

efficiency and will usually result in a cleaner wine stream entering the pre-bottling filtration stages. Crossflow systems do not require a trap filtration directly afterward. There have been reports that some winemakers have found crossflow filtration to be gentler on their wines than DE filtration, particularly with respect to maintaining the wine’s aromatics. Other winemakers have given crossflow systems a more negative review. Cellar staff who have tried or operated good crossflow filters are overwhelmingly in support of crossflow systems. Crossflow systems are greatly improving the processes of many wineries and represent a major advance in winemaking and wine production technology. Processes should be designed so that the crossflow system feeds into a bottling holding tank or surge tank, if immediate bottling is desired, which will then feed into a prefilter and final filter before bottling. Most processes are such that the crossflow will feed into a short- to mediumterm bottling storage tank, which is then fed to the bottling line when desired. Some plants assessing whether or not crossflow clarification should be instituted within their process make the incorrect assumption that a final membrane filtration is no longer required. It is still required if absolute microbial stability is desired. The costs of this filtration will now be lower, however, as the wine entering the final filtration should be cleaner. Although crossflow units can handle high solids, lees should not typically be sent into the unit unless the crossflow system is specifically design for this purpose. Tanks should still be racked after fining treatments. Wine crossflow clarification systems can be sized to fit any process. The membrane format used can be hollow fiber, ceramic, cassette, or spiral wound and can be cleaned using a wide variety of chemicals. Hollow fiber membranes can be PES or PVDF and are by far the most common crossflow format used in the wine industry, followed by ceramics. Ceramic crossflow filters can produce problems with too much heating of the wine. This is a result of the longer filtrate flow channels of ceramic membranes as opposed to hollow fiber membranes. Crossflow membranes will have a long service life compared to conventional filter devices and can often be guaranteed, with proper operation, for anywhere between four to seven years by the manufacturer. Manufacturers with crossflow systems specifically marketed to the wine industry include: Pall, Koch Membrane, Velo, Bucher Vaslin,

192

Beverage Industry Microfiltration

Della Toffola, TMCI Padovan, and Sartorius. These manufacturers are usually represented by distributors within the wine industry. Some manufacturers can produce isobaric units for sparkling wine (champagne) clarification. Isobaric units are a variation on their standard equipment that can be run at higher pressures. Do not assume that a unit can perform this function unless specifically stated. Not all systems have been proven acceptable to all winemakers and for all wines. Some winemakers in the field have greatly preferred a particular system over others and a winery looking to implement crossflow clarification should test multiple units for their particular applications and wines. Pall currently has the largest number of units in operation in the United States; Bucher Vaslin has the second largest number. These two companies comprise the vast majority of the current market share of the wine industry, with over one hundred combined units in operation in the United States. This includes several of the top wine companies. There will normally be some concentration of wine components in the retentate stream of the crossflow system. Unless small batches of wine are being processed, this concentration is usually not enough to affect the final product. Crossflow systems should always feed an intermediary tank or surge tank prior to bottling, which will allow for mixing of the wine. It is possible to recover the concentrated retentate stream, process it, and use it for other applications such as flavorings or colorings. It may be possible to pass the retentate stream through another specially designed crossflow system to recover more wine from the retentate. A couple of companies market small systems to this effect. One of the best justifications for the changeover from DE clarification to crossflow microfiltration is the increase in product yields. Roughly 1.25 lbs (567 g) of wine is absorbed into every 1.0 lb (454 g) of DE used for filtration. This absorption can represent a tremendous product loss to a winery. Sludge disposal costs, DE purchasing costs, and DE storage and handling equipment further enhance the economics of using crossflow microfiltration as a replacement to DE clarification. It is usually these savings that will justify the change; however, the increased final cartridge filter performance and service life should not be overlooked. Crossflow units can be effective as a means of stopping fermentation. It is sometimes necessary with DE filters to perform a stop fer-

Wine Industry

193

mentation filtration several times on a batch. This wastes time and money, hurts the quality of the wine, and causes unnecessary wine loss. A crossflow unit should be able to completely stop the fermentation with a single pass. The wine may have to be racked at a higher point in the tank if sending to a crossflow, as opposed to a DE filter.

Prefiltration The goal of prefiltration is to protect the final filtration in order to enhance the overall process economics. If a membrane final filtration is used, then the prefiltration should be with a cartridge-style filter. A pleated surface-type prefilter with a pore size rating just above that of the final membrane filter is best suited to this task. If a 0.45 μm final membrane filter is used as the final filtration stage, either a 0.5 μm or 0.65 μm pleated prefilter will provide optimum protection. Wrapped, depth-style prefilters can and are used; however, they will not usually have as high of a retention efficiency as compared to pleated prefilters. If a membrane is not used as the final filter, then there is more freedom in selecting the prefiltration. If, for example, only a plate and frame sheet filter or lenticular filter is used for a final filtration to reduce yeast counts, then there may not be a need for prefiltration. Prefiltration stages should almost always be sized larger than final filtration stages. The prefiltration stage should be doing the majority of the total filtration.

Final Filtration The final filtration stage of a wine process will be determined by the level of microbial stability desired by the winery. Most US and Australian wineries have moved to a 0.45 μm membrane filter standard. Facilities may use 0.65, 0.8, and 1.0 μm final filters for premium wines and wines in which only yeast or Brettanomyces removal is desired, however. The final filtration stages employed by European wineries are much more diverse. Many more wineries in Europe will only filter to either 0.65 or 1.0 μm. This is particularly true with red wines. Many

194

Beverage Industry Microfiltration

South American wineries use membrane filtration, including most of the large Argentinean wineries. While sheet filters may advertise absolute removal or sterile filtration, only an integrity-testable membrane cartridge filter offers absolute or guaranteed microbial removal at its selected pore size rating. Many winemakers have chosen not to undergo sterile membrane filtration for fear of removing some sensory component of the wine. Even the winemakers who are the most ardently against filtration agree that this sensory change is very minimal and is rarely observed in blind sensory panels. The cost of not properly filtering wines is obvious and can be seen in the many wines that develop Brettanomyces character or other off-flavors, experience decreased shelf life, or must otherwise be held, destroyed, or reprocessed. Even if a winemaker detects a minimal sensory change as a result of filtration, this change is often noted to dissipate a short while after bottling. Historically, either PVDF or nylon membranes have been used for most winery final filtration. Cellulose acetate is also used. Polyether sulfone (PES) membranes are now offered by several filter manufacturers as their primary filter offering to the wine industry, so usage of PES is steadily increasing. PVDF and PES membranes currently comprise a majority of the total market share. Within the United States, Millipore has the lion’s share of the final filter market, followed by Sartorius, and then Pall at number three. These top three companies hold an estimated 80% of the total market share. The durability of the filter device (cartridge) is as important as the membrane material. This is especially true in the wine industry, where processing conditions can severely stress the filter cartridge. Final membrane cartridge failures should be analyzed in consultation with the filter manufacturer when necessary. A plugging analysis should be conducted when a final filter plugs prematurely. These steps will help to ensure a process is running smoothly and any upsets are known and either corrected or prevented.

Gas and Air Filtration There are several common gas applications in the wine industry. These are shown in Table 8.1. It is easy, and common, for contaminants to be added to the wine by way of a gas addition or even by contact with the

Wine Industry Table 8.1.

195

Winery gas applications.

Carbon dioxide

Air or atmosphere

Nitrogen

• Bulk cellar tank addition • Carbonated product vessel counter-pressures (i.e., surge tanks, filler reservoirs, return tanks) • Addition at the filtration skid • Sparkling wine tank counter-pressure during bottling

• Bottle blower • Wine line blowdown (to remove CIP/ flushing water) • Bottling storage tank venting • Long-term storage tank venting

• Bottling tank blanketing • Bottling tank sparging to lower dissolved oxygen

• Bag-in-box air evacuation

• Surge tank and filler bowl counter-pressure • Bottle sparging

• Addition at the filter skid to lower dissolved oxygen

ambient atmosphere. Applications such as the bottle blower, filtration skid additions, and filler bowl counter-pressure are critical because the gas comes into direct contact with the product. The contact may even occur after the final filtration. Filtration of these gases is recommended, with the filter choice being a hydrophobic 0.22 μm PTFE membrane filter. It is possible to use a 0.45 μm membrane in most processes; however, 0.22 μm PTFE gas filters are so much more common that the tighter membrane is less expensive due to the quantities produced. Disposable filter devices (capsules) may be a worthwhile option for some applications. If a process is infrequently used and/or the filter is simply used and thrown away without cleaning or integrity testing, then a capsule may be the easiest alternative. Capsule devices will tend to be slightly more expensive per unit but will save money upfront, as a stainless steel filter housing does not need to be purchased and installed. NOTE Remember that carbonated products should have carbon dioxide as the pressurizing gas and that adding nitrogen to sparge a carbon dioxide–containing product will quickly decrease the level of carbonation.

196

Beverage Industry Microfiltration

Specialty Applications As wineries have become more sophisticated and diverse, so have their products and the processes used to produce them. There are a few microfiltration applications that are selectively used within the industry. Wine Coolers Products considered as “wine coolers” can either be wine or malt based. Wine-based coolers are processed generally the same as standard wine, with the exception of various flavor additions. However, wine-based coolers can be more difficult to filter than standard wine alone, due to the interaction between the sugar and flavor additions with the wine base. The additional carbohydrates will often combine with the proteins in the wine to form a potent plugging agent. High– sugar-content wine coolers are prone to higher levels of microbial growth. Various flavorings can interact to create a higher tendency to plug microfilters. Malt-based wine coolers (technically, flavored beers) can either be tank blended or in-line blended. Tank-blended wine coolers will usually be processed in the same general pathway as a typical wine, with the exception that the DE or other primary clarification stage is sometimes, but not always, bypassed, since the product is often clean enough to be sent directly to the main pre-bottling microfiltration skid. Tank-blended wine coolers should have cloudifier added after the microfiltration train since cloudifier will quickly plug the filters. In-line malt wine beverages have different filtration options available. Because the various components are added directly before, or at, the microfiltration skid just prior to bottling, either the product as a whole or the individual components may be filtered. Separate filtration of some or all of the additives and components has some benefits over filtration of the entire product at once. Typical components of the wine beverage include: water, malt alcohol, liquid sugar, liquid flavorings and colorings, cloudifier, and powdered flavorings and colorings. The water used is often RO water and, in any case, should be filtered at least to 0.45 μm. The water can be filtered down to 0.22 μm, if desired. These filters will experience little pluggage since they are only filtering RO water. Liquid sugar may be filtered down to 20 μm with a

Wine Industry

197

depth-style prefilter to remove sugar crystals. The malt alcohol stream requires only particulate removal with a depth- or surface-style prefilter, as the stream will have no microbial concerns. Liquid flavorings and colorings will vary depending on the quality and desired removal. Cloudifier in alcoholic products does not require a filtration and should not pass through a microfiltration stage, as it will quickly plug the filters. Many suppliers of these components filter prior to shipment, so it may be possible to eliminate redundant filtration at the plant. Flavorings used in wine coolers may coat the surface of a membrane filter and reduce the wetting fluid surface tension. They can also change the contact angle of the gas. This will result in not being able to perform an accurate integrity test. If a flavoring in the process is causing this, it may become necessary to flush with large volumes of water or another agent, such as citric acid, to remove the film before a successful integrity test can be performed. Not all membrane types and symmetries will react the same way to particular flavorings or components. Starter Cultures The hectic process of picking, crushing, and fermenting grape juice before either the environment or wild fermentation is able to damage the product is an ever-present problem in wineries. Fermentation tanks are often a severe bottleneck within the crush and fermentation process. Building additional fermentation tanks can be costly and is not always possible. Starter cultures are used as a means of speeding up fermentation tank throughput. Adding small quantities of actively fermenting juice into a freshly crushed tank speeds up the fermentation and better allows the preferred yeast strain to take preference over wild yeast that may be present. Filtration and pasteurization can both be used to stabilize the juice, which is later used for the starter culture (Figure 8.1). Filtration has several benefits over pasteurization. Microfiltration requires significantly lower capital than pasteurization, is able to be better tailored to a process, does not involve adding steam capabilities, has much lower utility costs, does not change the sensory characteristics of the wine/ juice, and the equipment can be used elsewhere in the process, such as for bottling filtration or clarification. Pasteurization is less susceptible to particulate loading, however, and microfiltration, even when only for yeast removal, will often require some prior clarification stage.

198

Beverage Industry Microfiltration Microfiltration

Starter Fermentation

Primary Fermentations

Figure 8.1. Microfiltration may be used to remove or reduce wild yeast and/or bacteria, as well as to stop fermentation already in progress prior to a starter fermentation. The starter may then be used to inoculate many larger, production-scale fermentations, allowing for faster throughput and better fermentation control.

Crossflow systems are well suited to this application and can handle a higher solids load in the juice. Cartridge filtration systems can be used for this task and can be effective, since there are generally low volumes of juice involved. Alcohol Recovery Grape-based alcohol is an expensive material due to its limited supplies and government regulations surrounding grape alcohol products. Alcohol used for many grape-based products such as brandy, cognac, grappa, various dessert wines, and true wine coolers must have originated from the fermentation of sugar from a grape. This is one reason that most bulk wine coolers such as Bartles and Jaymes and Seagram’s are technically “flavored beer”; their alcohol is malt based and not grape based. Grapes are an expensive raw material, so grape-based alcohol becomes a costly source of alcohol. Alcohol recovery within a winery can therefore be very profitable. Those wineries that recover grape alcohol for either their own usage or to sell will often recover the alcohol from high-solids-containing waste streams. The waste stream must be processed prior to being sent to most stills for distillation and alcohol recovery. Hearty microfiltration devices such as ceramic or sintered stainless steel membranes are used to clean these waste streams prior to further processing or distillation.

Wine Industry

199

Reverse Osmosis Prefiltration Reverse osmosis is used in wineries as a means of either removing color or alcohol from the product. Wines often have a portion of their alcohol removed to meet alcohol requirements for tax purposes. Wines may also undergo de-alcoholization to qualify as a non-alcoholic beverage. RO filters typically require some form of prefiltration. This can be successfully accomplished with plate and frame or lenticular filters or other clarification steps but is more commonly accomplished by means of a depth-style cartridge filter. Cartridge filters for these applications are usually in the 3.0 to 5.0 μm range. Prefiltration requirements of an RO filter can be determined by the RO manufacturer, and microfiltration housings for this task are often built right onto the RO skid.

Long-Range Transport Globalization of the wine industry has meant that long-range bulk wine transport has become a common phenomenon. It is common for some of the large wineries to bulk transport wine that is crushed and produced in one country to another for final blending and bottling. The United States, in particular, has become the main receiving hub for these wines, with shipments from France, Italy, Germany, South Africa, New Zealand, Australia, and elsewhere. E. & J. Gallo’s Ecco Domani is one of the more prominent shipped brands. The wine is produced in Italy and transported to California to be bottled. Californian wineries have begun shipping containers of wine to Asia for bottling for that market. When such long journeys are involved, it is easy for wine to spoil if it has not been microfiltered prior to shipment. Regardless of whether preservatives are added and the wine kept cool during transport, adding a microfiltration step greatly improves the microbial stability and quality of the wine (Figure 8.2). On the opposite end of the supply chain, wines that have been received typically require a filtration by the receiver as well, even if the wine was well clarified prior to shipment. Putting received wine directly into the pre-bottling microfiltration train can often result in fast blockage of those tighter filters if the wine was not reclarified. A few companies have begun writing shipment quality terms into their wine purchase agreements due to the poor quality of some received wine. Microfiltration

200

Beverage Industry Microfiltration Storage

Microfiltration

Transport

Microfiltration

Storage

Figure 8.2. Microfiltration before, and sometimes after, bulk transport of wine is key to maintaining product quality and microbial control.

specifications in this agreement will give the receiving plant additional control over the quality, microbial stability, and filterability of the wines they receive. Centralized bottling facilities tied to warehousing and shipping operations are another way in which wine may be bulk transported. As the wine industry is consolidated and wineries expand to new grapegrowing regions, it becomes more cost effective to bottle, package, warehouse, and ship wines from one central location as opposed to many smaller facilities. Truck-based tankers are used to ship liquid wine from crush locations to bottling facilities for this purpose. The filter used for this application will depend on the quality of the wine. It is not always necessary to use a membrane. A highly retentive pleated surface filter may be used to drastically reduce yeast and bacteria counts. This will not achieve complete removal, but it will be significantly less expensive and may be necessary if the wine is not well clarified prior to microfiltration. Membranes of 0.45, 0.65, and 1.0 μm are all used for this application when the plant desires higher removal. Sanitization of the storage container becomes more important when membranes are used, since it is pointless to meet the extra cost of completely removing microbes from the wine and then use a poorly sanitized container where the wine will almost assuredly pick up some contamination. Stop Fermentation Wines may not be allowed to complete fermentation as a means of leaving some residual sugar (RS) in the wine. Centrifuges have been used with considerable success at stopping fermentation. It is possible, particularly with small wine batches, to use filtration as a means of stopping an active fermentation. A multi-pass nominal depth filtration can be used. Since the depth filtration is nominal, one pass will not

Wine Industry

201

usually remove all yeast present in the wine, so several passes are required to ensure adequate removal. Crossflow membrane systems are being used for this application as well. The benefit of using crossflow membrane systems is that they can handle much greater levels of solids in the wine feed than other filtration formats. It may still be necessary to pass the wine through a membrane cartridge afterward to ensure complete yeast removal, but the service life of a cartridge after crossflow is much greater than without crossflow. Crossflow systems used in this manner may sometimes require a rough clarification of the feed. Fermentation Lees Wine Recovery Sintered stainless steel or ceramic membranes operated in the crossflow direction can be used to recover wine from fermentation lees. The lees must be pumpable. Thin or light lees may be pumped directly from the fermentation tank to the filtration system, while heavier lees that are strongly compacted may require sluicing with wine to be pumped. Sluice wine may be taken from the filtration system outlet and recycled back to the fermentation tank. This is a good method for recovering wine, as the sintered stainless membranes are robust and have a long service life. The membranes may be caustic cleaned. These filtration systems usually have a fairly high start-up cost and very high electrical costs. Care must be taken during operation to avoid extreme heating of the wine. Wine resulting from the process is not typically suitable for bottling by itself but may be used for blending into other finished products. Membranes for this application are in the 0.1 μm to 1.0 μm pore size range. A channel that is open enough to avoid rapid blockage by solids must be used.

Process Testing: Filterability (Fining) Index There have been several versions of filterability, or fining, indexes developed for use in wineries. These tests are basically a measure of how clean a wine is relative to the final membrane filter. UC Davis developed one process that is in use by a few wineries. The test involves filtering a sample of wine through a 47-mm disk of the same membrane and pore size rating as the final membrane in the process, at a set

202

Beverage Industry Microfiltration

pressure (usually 30 psi [2,068 mbar]). The time to filter a specified volume is recorded as the initial flow rate. After some elapsed time, another flow rate measurement is taken. Different tests use different formulas to obtain the filterability index. Some tests will use the same volume for each flow rate measurement and simply compare to determine the flow rate decay. Other filterability tests will have the second flow reading taken using double the volume. Generally, the lower the filterability index, the easier it is to filter the wine. Filterability index testing is, for the most part, not accurate within the wine industry for a variety of reasons: tanks will have strata of differing filterabilities, 47-mm disks are not very relatable to largeprocess filter housings, membrane plugging is usually a function of both soft and hard particles, wine types vary tremendously in their filterabilities, and so forth. The only benefit of filterability testing is advance knowledge that a product batch is not perfectly filterable. It does nothing to prevent the causes of reduced filterability, and no winery would discard a tank of wine due to low filterability, so the product will inevitably end up passing through the microfiltration train regardless. It may be possible to take the advance knowledge of poor filterability and process the wine batch through another method of clarification such as centrifugation or DE clarification, but the costs of doing so may be prohibitive, and effects may be limited as these processes will not always remove the plugging components of concern to the microfiltration stages.

Miscellaneous Considerations Properly running an optimized wine filtration process can lead to tremendous production savings in both time and money. Each plant and process will have its own areas requiring optimization, some of which are covered in the following paragraphs. Older winery fillers may have overflow piping. The overflow piping takes wine from the filler and recirculates it back into the filtration skid, usually first through a surge tank, prior to the prefilter. If the filler overflow is not properly managed, the filter throughput (as measured by filler output) can be effectively decreased by 10–30%. If, for example, a tank of 50,000 gal (1,893 hl) is to be bottled through a filler that averages around 20% recycled overflow, the filtration train will

Wine Industry

203

re-filter 10,000 (379 hl) of the initial 50,000 gal (1,893 hl), 2,000 (76 hl) of the refiltered 10,000 gal (379 hl), 400 (15 hl) of the 2,000 gal (76 hl) and so on. The filter will have an actual filtered volume of over 62,000 gal (2,347 hl) despite the filler output being only 50,000 gal (1,893 hl) of product. If this overflow were eliminated, the filtered volume would go down by almost 25% and could represent a significant increase in filter service life and reduction in filtration costs. Wine is one of the most difficult beverages for which to optimize and run an efficient filtration process. One of the reasons is the degree of variability among wines — and even among vintages of the same wine. The many different processes and equipment configurations used to produce wine has an impact on the product’s filterability. Several processing methods that can lead to a wine with decreased filterability include: • • • •

Not treating the must with proper enzymes Creating a wine with unripe grapes Keeping the wine on lees Wine resulting from pressing, as opposed to free-run, with decreased filterability occurring with increased pressing • Creating wines from severely macerated grapes • Creating wine with grapes that have been affected by rot. Grapes that have been affected by rot can produce wines that are particularly difficult to filter. This is due to beta-Glucans that are secreted by Botrytis cinerea, a fungus responsible for grape rot. A concentration of even a few milligrams per liter of beta-Glucans in wine can have a significant impact on certain filtration processes. Enzymes to break down the glucans can be added to greatly improve the filterability of the wine. Reclaim wine is wine that is recovered at various points within a process and either added back into the primary product or sent to a lower wine program. Typical sources of reclaim include half-filled bottles, the first round of bottles from a filler, wine left over in the filtration housings, damaged bottles, such as those with broken corks or scuffed labels, leftover wine in the filler or surge tanks, and so forth. It is important to properly manage reclaim wine and control where it is sent within a process. If a wine is sent to reclaim as a result of a glass defect, for example, the wine should not be sent back into the

204

Beverage Industry Microfiltration

filtration train prior to the prefilter, as there might be glass shards or other material present that could damage the filters. A mesh screen installed on the reclaim line would provide some protection against foreign debris in this instance. If a product has cloudifier added after the microfiltration train, there should be no reclaim put back into the filtration system. The DE or crossflow membrane clarification stage should be carried out at the lowest temperature seen in the filtration/filling stage. If the DE filtration is carried out at a particular temperature and the wine is subsequently cooled in the bottling tank or just prior to microfiltration, there will be additional materials that can precipitate and/or form in the wine. This is a common cause of membrane blockage that can be avoided. Avoid topping off or mixing tanks just prior to microfiltration and bottling. Separate tanks — even if the same wine type and vintage — are not entirely the same. It is common for wineries to put the leftovers of one bottling tank into another that is to be bottled next. Sometimes non-vintage wines are blended or reclaim wine from different types, tanks, or vintages are combined into a single tank. Mixing like this, right before the final pre-bottling microfiltration train, is not recommended. There will often be interactions that can cause precipitates or other materials to form that will lower the filterability of the wine. If a large mixing process is done on a bottle-ready tank, the tank should be reclarified by the main clarification stage whether via DE clarification, crossflow microfiltration, or a plate and frame filtration. Many varietals, such as Sauvignon Blanc or Chardonnay, are now being carbonated to a slight degree. Filtration housings must be frequently vented if running a carbonated product, due to the gas bubble that forms at the housing dome. If allowed to become large enough, this gas bubble will begin to restrict flow through the cartridges and reduce filter surface area. Frequent venting becomes more important when running wine coolers or similar heavily carbonated products. If the bottling tank is not equipped with a tank blanketing system, there will often be a surface film layer that forms on the top of the wine. This surface film can lead to plugging of the final membrane filter. While there is little that can be done to prevent this from occurring (beyond installing a tank blanketing system), it can be helpful to understand that when a tank is emptying, there will usually be a sharp decrease in the wine’s filterability.

Wine Industry

205

TIP If there is no tank blanketing system installed on the bottling tank, pitch some dry ice into the bottom of the tank prior to filling with wine. The dry ice will melt, leaving a layer of carbon dioxide on top of the wine. Although this layer will not last indefinitely, it will help to prevent the formation of surface films, inhibit microbial growth, and help the filtration process.

Chapter 9 Beer Industry

It was once thought that the brewing industry would become one of the largest microfiltration markets in the food and beverage segment. While brewery microfiltration spending is still regarded as significant, it has certainly not become what was hoped for. Plate and frame filters are used by many small, medium, and craft breweries. Lenticular filters can be used as a trap filtration or as the primary clarification. Kieselguhr (DE) filtration remains the most prominent method of both clarification and pre-bottling filtration. Sheet and lenticular filters currently process approximately three times as much beer volume as cartridges. DE trap filtration is the most common application for cartridge filters and is used by many large breweries. Most breweries pasteurize beer rather than sterile filter prior to bottling, despite the increased sensory quality of filtered beer versus pasteurized beer. The only major brewing group in the United States to use large-scale microfiltration as an alternative to pasteurization is SABMiller; its breweries sterile filter (0.45 μm) only their keg line draft beer. The Japanese beer market, which is quite large despite serving only one country, has been more accepting of pre-bottling membrane filtration. Asahi, Suntory, and Kirin sterile filter beer with either 0.65 or 1.0 μm membrane cartridge filters. These breweries usually operate a process in which heat treatments are combined with microfiltration. Latin American breweries use cartridge filtration on an appreciable scale, including a few with membrane final filtration. The beer industry is now experimenting with crossflow microfiltration systems as a replacement to DE clarification. A few small breweries have already changed over, particularly in Europe, but the level of success that crossflow technology is experiencing in the wine industry has yet to be observed in brewing. 207

208

Beverage Industry Microfiltration

Clarification and Trap Filtration Clarification in the brewing industry typically refers to either (1) small to medium breweries and craft brewers that use either plate and frame filters or lenticular filters or (2) the large-scale brewers that use a trap filtration stage after the primary DE clarification. Small and craft breweries often use plate and frame filters as the primary beer filtration. Some medium-scale breweries also use plate and frame filters. Lenticular filters are used as a primary clarification by small, medium, and craft breweries. A mid-grade sheet or lenticular filter for polishing is the likely choice for many small brewers. Using either plate and frame or lenticular filters eliminates the need for larger, more expensive DE filtration systems as well as DE purchasing, handling, and disposal, which can be costly and difficult for smaller facilities. Since most small-scale beer manufacturing is either regional or for fast consumption, producing products with a particularly long shelf life is not always necessary. This has meant that plate and frame and lenticular filters provide adequate microbe removal and visual clarity. Keep in mind that beer style can greatly affect throughput and filter grade selection when dealing with sheet and lenticular filters. A lager beer, for example, may see 2–3 times the throughput per filter sheet than a typical ale. DE filters, such as pressure leaf and candle filters, can be prone to DE bleed-through. The leaves of a pressure leaf filter are particularly susceptible because cracks often form at the welds and can be difficult to detect and repair. The pasteurizer offers nothing in the way of particulate removal. A trap filter prevents these particulates from entering the final product. Lenticular filters are used by breweries as a post-DE filtration trap filter. Depth-style cartridge filters are commonly used by large breweries for this application. The filters selected should have a pore size rating small enough to capture these particulates and are usually in the 1.0–5.0 μm range, but can be as high as 10.0 μm. Adding a filteraid to the precoat of the DE filter can help to improve the performance of the DE filter and reduce the amount of particulates in the outlet. Crossflow Clarification Diatomaceous earth is a hazardous material in some respects and is regulated in many countries. It can be expensive to dispose of and is

Beer Industry

209

difficult to handle, sometimes requiring special delivery systems. The beer absorbed in DE represents a significant product loss over the course of many filtration cycles. There can be 1.15–1.35 lbs (522– 612 g) of beer absorbed per every 1.0 lb (454 g) of DE used during the filtration. Processes that are poorly operated can result in higher cake moisture and, subsequently, more beer loss. Crossflow technology can eliminate these difficulties and costs. Most beer crossflow systems require the beer to be first passed through a centrifuge. Sartorius and Alfa Laval have partnered together to provide a joint centrifuge/crossflow system (Sartoflow) for breweries. Pall and GEA-Westfalia have partnered together to create the ProFI centrifuge/crossflow membrane system. It is possible that the overall beer stabilization process performed via PVPP, hydrogels, or xerogels will be less effective when using crossflow clarification, as opposed to DE filtration. If using a crossflow system, these agents should be added before the centrifuge and not directly before the crossflow unit. Crossflow microfiltration better prepares the beer for subsequent sterile filtration prior to bottling. Processes that could not initially be run economically using a membrane filtration step with DE clarification may find it more feasible with the use of crossflow clarification. This creates an all-round more economical and higher-quality process, as the costs of filtration are much lower than the costs of pasteurization in most cases.

Prefiltration If a brewery is not using membrane filtration as an alternative to pasteurization, there will be no prefiltration step. When breweries decide to use membrane filtration, the membrane filters must have prefiltration to reach acceptable throughputs. If a 0.45 μm final membrane filter is used, the prefiltration should be either 0.5 or 0.65 μm. If a higher pore size membrane is used, such as a 0.65 or 1.0 μm, the next higher pore size rated prefilter, with good retention efficiency at that rating, should be used as a prefiltration step. Many well-clarified beers see a significant increase in membrane plugging particulates at around 0.5 to 0.8 μm. Using a prefilter higher than this range, followed by a 0.45 μm final membrane, will lead to fast blockage of the membrane.

210

Beverage Industry Microfiltration

Most installations that use a final membrane cartridge filter will use a cartridge format prefilter. There are a few facilities that have chosen to use lenticular filters as the prefilters for final membrane cartridges. This is usually due to leftover lenticular equipment being available at the plant. It is generally recommended to use a cartridge as the prefilter when a final membrane cartridge is involved. Wrapped, depth-style prefilters are used more frequently than pleated surface-style prefilters due to the high particulate loading of beer. Pleated surface-style prefilters, particularly those of polypropylene, are observed in industry, however. If only a plate and frame or lenticular filter is used it is generally referred to as a clarification step and is covered within that section.

Final Filtration Final membrane filtration is an excellent alternative to pasteurization (Figure 9.1). This is particularly true if crossflow filtration is used as the clarification stage. The initial capital requirement for pasteurization equipment is much greater than that of filtration equipment. Filtration also lends itself to a fresher-tasting product. However, filtration does take more work and better controls to ensure proper microbial reduction and a smoothly operating bottling line. Membrane filters used as a final filtration can be as low as 0.45 μm for complete removal of relevant bacteria, yeasts, and molds. A 0.45 μm membrane will result in microbially stable beer with the longest possible shelf life. Breweries may choose to use 0.65 or 1.0 μm membrane filters to remove larger organisms such as yeast, molds, and some bacteria. Brewers that filter to the more open pore sizes sometimes combine filtration with a moderate heat treatment step. The heat treatment does not reach temperatures as high as those seen in conventional pasteurization. If there is no heat treatment and only a 0.65 or 1.0 μm membrane filtration is used, there may, on occasion, be some issues with long-term shelf life related to bacteria.

CO2 Filtration Nearly all breweries use CO2 addition in some form. Usage at the bright beer tank for final product carbonation, yeast propagation, tank

Beer Industry

211

Storage

DE Clarification

Trap Filtration

Pasteurizer

Bottling

Storage

DE Clarification

Trap Filtration

Sterile Filtration

Bottling

Storage

X-Flow Clarification

Pasteurizer

Bottling

Storage

X-Flow Clarification

Sterile Filtration

Bottling

Figure 9.1. Beer may be clarified and rendered microbially stable by one of several pathways.

blanketing, or air removal of product lines are some of the more common industrial uses. Bulk CO2 is usually shipped to the brewery where it is stored in a central holding tank and piped to drops or areas located throughout the plant. There are potential contamination sources associated with gas shipment, storage, and final delivery to the plant. Sterile filters can be placed at the storage source, within the delivery lines, or directly at the gas point of use. There are several items to be considered when determining filter placement. If the filter is placed at the delivery point, storage tank outlet, or in the various delivery lines, it may become necessary to sanitize all or part of the CO2 delivery lines. If the filters are placed at the point of use, it is not necessary to sanitize the storage tank (although periodic tank cleanings are always recommended) or the delivery lines. Point-of-use placement will typically require more filters to be used. Most gas filters are inexpensive

212

Beverage Industry Microfiltration

and have long service lives. A 0.22 μm hydrophobic PTFE membrane is used. Specialty Applications Beer and Yeast Recovery from Bottoms It is possible to use a crossflow microfiltration system to recover beer from the tank bottoms that are very high in solids. These systems also yield a retentate highly concentrated in yeast. The recovered beer stream may be recombined for a significant yield improvement to the brewery. Breweries may choose to use the recovered yeast stream (filter retentate) as a further cost-saving measure. Wort Filtration Wort may be filtered by means of microfiltration after the mashing and steeping process and prior to fermentation. Other means of separation such as decanting, centrifugation, and so forth are more common; however, microfiltration is perfectly feasible and is used within the industry. A very open depth filter is used. Flavored Beer Breweries that produce different types of flavored beer can impart these flavors by adding ingredients during or after fermentation in the beer production. Juices are often added post-fermentation, just prior to bottling. If the brewery is using microfiltration, juice or flavor additions can cause a significant decrease in the filterability of the end-beer product. It may be necessary to add pectinase to juices to break down some of the filter-plugging pectins. Ensure that the flavoring or juice addition does not have cloudifier added by the supplier. Hazes or precipitates may form as a result of mixing the beer base and flavoring components. A follow-on clarification stage may be required to specifically deal with this haze formation. Miscellaneous Considerations There are a few considerations that can help to improve beer microfiltration processes:

Beer Industry

213

• Adding beta glucanase enzyme prior to the microfiltration step will improve the filterability of beer. Glucans are one of the primary plugging sources in beer. They are colloidal in nature, so breaking them down will greatly increase filter throughput. Membrane filters in particular benefit from the addition of beta glucanase and, in some instances, the enzyme is required if beer, which has a low filterability, is to be filtered economically. Beta glucanase enzyme is available from many brewery suppliers and may be sold under various tradenames. Beta glucanase enzyme can be added to a cleaning regimen in order to help regenerate and clean the filters post-production. Beta-Glucans tend to plug membranes more efficiently when combined with certain other agents, such as certain proteins or tannic acid. • Beer “lace” can be an effective plugging agent. Lace forms when the beer foam climbs the package release tank located before the prebottling filtration system. The foam dries on the tank wall. Subsequent batches of beer help to build up layers of the foam that dry on top of one another. When the foam layer gets too heavy to stay on the tank wall it falls into the beer where it proceeds to pass downstream and plug the filters. Adding foam stabilizers or procedures designed for removing or minimizing the effects can help with this problem. Small amounts of dried foam, not necessarily just build-up on the tank, can block filters over the course of a filtration run. • Precoating too quickly can lead to DE bleed-through. Various filter aids are available that improve the performance of the DE filtration. Improved DE filter performance will lead to better performance of the downstream filtration systems including the trap filtration.

Chapter 10 Bottled Water Industry

The bottled water industry’s recent explosion has created one of the largest markets for microfiltration products and technology. The shear volume of bottled water now produced and consumed in the modern world and the fact that bottled water is highly susceptible to a vast range of harmful microorganisms has lent itself to the current microfiltration spending levels. There are numerous safeguards in place to protect the quality of water threatened by such microorganisms as E. coli, Cryptosporidium, and Giardia. Absolute rated microfiltration to a pore size of either 1.0 or 0.22 μm is one of these safeguards. A pore sizing rating of 1.0 μm is recommended by the International Bottled Water Association (IBWA) for the removal of Cryptosporidium and Giardia, harmful organisms that are typically found in surface waters. The pore size rating of 0.22 μm is a best practice adopted by some companies and ensures that all potentially harmful bacteria and microbes are removed from the water. Although filtration is never seen as the sole barrier to microorganisms, it is often one of the most crucial. Microfiltration serves as a complementary backup to other quality safeguards such as ozonation and ultraviolet light. Microfiltration is used as an effective prefiltration for RO and distilled water products, such as those produced by PepsiCo (Aquafina) and Coca-Cola (Dasani). It is a best practice to follow even an RO unit or still with a pre- and final filtration stage just prior to bottling for added protection. The recommended process flow diagrams for different bottled water product options are shown in Figure 10.1. The relative youth of the industry has lent itself to being fairly technically uniform and advanced with regard to microfiltration technology. Excluding RO filters, cartridge microfiltration dominates the industry, with almost no instances of sheet or lenticular filters being used. A very few facilities use bag filters. Facilities with hard-to-filter 215

216

Beverage Industry Microfiltration RO or Distilled (Purified) Pathway

1. Silo 2. RO/Still Prefilter 3. Reverse Osmosis / Distillation 4. Prefiltration (Best Practice)* 5. Final Filtration (Best Practice)* 6. UV 7. Ozone 8. To Bottling

Spring or Mineral Pathway

1. Source Filter 2. Silo 3. Pretreatment (Carbon, Resin, Etc) 4. Prefiltration 5. Final Filtration 6. UV 7. Ozone 8. To Bottling

Figure 10.1.

Spring or mineral and purified bottled water process flow diagrams.

water supplies use crossflow clarification systems as a means of improving water quality prior to plant entrance and subsequent microfiltration and bottling.

Clarification Clarification filters are often used in bottled water facilities as the first step in reducing microbial and particulate matter before water enters the plant. Many facilities will incorporate rough depth filtration cartridges directly at the water source or spring before any tanker loading or pipeline transport. These filters can vary in size depending on the water quality and amount of particulate matter present but are generally in the 2.0–5.0 μm range. The filters can be as low as 1.0 μm depending on water quality and proximity to bottling location. The filters should

Bottled Water Industry

217

be wrapped, graded-density polypropylene depth filters or other type of depth media, such as resin bonded. When transport tankers or long pipelines are used for water delivery to the plant, it is common to use a depth filter either on the pipeline outlet or at the tanker unloading station. These filters are usually located before any water silos to prevent silo contamination or particulate build-up. This reduces the need for silo cleanings. If tanker contamination is a common issue at a plant, then filters located directly after tanker unload and before plant entry can be important to improving overall plant microbial control. These filters can be used in conjunction with source filters and, if so, are of a more retentive pore size, such as 1.0 μm. If there is no source filtration, however, it may be necessary to use a more open pore size such as a 2.0 μm or 3.0 μm. TIP Due to intermittent flow through tanker unload filter housings and the air that is constantly entrained within the system, unload filter housings will commonly experience a rapid build-up of air bubbles within the housing dome. Unload filter housings should be frequently vented. This is often overlooked because unload housings can be located outside of most production. The sporadic and uncontrolled nature of truck unload processes adds further difficulty. A check valve should be located on the system inlet.

Clarification filters can be used after water pretreatment steps commonly prone to problems. Carbon towers are the most common example. Carbon towers are susceptible to microbial growth if not properly sanitized. Carbon towers can be prone to carbon fine bleed-through if not adequately flushed after steam or chemical cleaning. Carbon fines can quickly plug a prefiltration or membrane final filtration step. If a plant has the need for large carbon towers and they are prone to bleedthrough or other concerns, it may be the most cost effective solution to install clarification filters to take the brunt of the damage in order to extend the service life of the downstream (often more expensive) filtration stages. Depending on the previous clarification stages, a filter used in this application could range in pore size from 0.5–2.0 μm.

218

Beverage Industry Microfiltration

Clarification prior to carbon filtration can reduce the particulate loading of the carbon tower. This will enhance the performance of the carbon tank and lengthen the carbon tank’s operating life. This can be accomplished by means of mechanical filtration, bag filters, or depth cartridges.

NOTE If a carbon tower is a suspected cause of premature filter plugging, ask the filter manufacturer to perform a plugging component analysis. The analysis should be able to easily determine if there are significant fines present on the filter. Black specs present on the filters can be an indicator of an unusually high amount of carbon bleedthrough, but these cannot always be observed.

When sizing clarification filters for applications such as source filtration, pipeline filtration, tanker unload filtration, or as a precautionary or remediation stage after a pretreatment step, it is important to size based on both flow rate and filter capacity. It is not uncommon to see large filtration housings, such as 55 or 60 Round 30″ high, for such applications in the 150 gpm (34,065 lph) range. It may be necessary to first size on flow rate and then scale up if the process has considerable particulate loading. Crossflow (Tangential Flow) Systems Crossflow filtration systems are being selectively used throughout the bottled water industry for those plants that have highly variable or generally poor water quality. The crossflow system does not replace the final pre-bottling membrane filtration stage but instead serves as a clarification stage that can vastly increase the final filter service life and throughput. This is extremely useful for spring and mineral water bottlers that cannot use RO filters and cannot economically sterile filter with normal flow microfiltration alone. The use of a crossflow system in this instance can allow the producer to maintain their spring or mineral water classification. Several manufacturers have crossflow

Bottled Water Industry

219

systems specifically designed for this application. They will normally use a 0.1 μm hollow fiber membrane, most commonly PES, and can be sold as a complete turnkey system designed for the clarification of difficult-to-filter water supplies. Systems geared toward the treatment of municipal water supplies, rather than bottled water, are also used for this application from suppliers who conventionally deal with municipal or wastewater treatment and not the beverage industry. Crossflow clarification of municipal water supplies is effective for those plants that wish to microfilter CIP and facilities water originating from municipal water sources but are not able to achieve good process economics with only microfiltration. Since CIP and facilities water is not considered final product, reverse osmosis is a good alternative that will not impact product classification.

Prefiltration Prefiltration processes are put in place to protect the final membrane filtration. The prefiltration stage becomes more important when there are no, or limited, clarification steps used. Recommended prefiltration filters will vary based on the clarification stages present upstream, water pretreatment steps, and overall plant water quality. Wrapped depth and pleated surface prefilters are both used. Highly retentive wrapped depth polypropylene cartridges are the most commonly used prefilters. If there is no clarification, or if water quality is less than optimal, it is usually better to use a wrapped depth filter due to its higher dirtholding capacity. Prefilter retentiveness is important because anything that passes the prefiltration stage due to unloading, bleed-through, or other mechanism will directly impact the more expensive final filtration stage. If selecting a wrapped, depth-style filter, check the retentiveness of all filter choices. Keep in mind that filter manufacturers use different guidelines for explaining retentiveness. Typical pore sizes for a water prefiltration stage are usually in the 0.3–1.0 μm range if a 0.22 μm final membrane filter is used. Do not be afraid to tighten an existing prefiltration stage and observe the impact on final filter service life. Prefilters should perform the vast majority of the filtration work and should therefore be changed out multiple times (2–3) for each final filter change out.

220

Beverage Industry Microfiltration

Final Filtration Absolute rated, integrity-testable membrane final filtration is one of the best methods for ensuring final product quality. Regardless of whether or not a plant is employing a multi-barrier approach through the use of other steps, such as UV and ozonation, membrane filtration is a critical control point for both particulate matter and microorganisms. At a minimum, a 1.0 μm absolute rated pleated surface filter should be used. Industry best practice is the use of a 0.22 μm final membrane filter. It is to this standard that the world’s largest bottled water company, Nestlé Waters division, adheres to for most of its bottled water plants. Many small water bottlers use “absolute” rated non-membrane filters, such as pleated polypropylene or pleated mixed cellulose esters. These filters will meet the recommendations of the IBWA and NSF Standard 53 but cannot guarantee removal of all microorganisms and cannot be integrity tested like a membrane. The plant’s filtration costs will be considerably lower, however, when using these filters as opposed to membranes.

NOTE Bottled water filters can develop off-odors or tastes when left in service for extremely long periods of time. Filters should be periodically checked for this. An appropriate maximum service life — six months or a year for example — may need to be adopted by the plant. Such guidelines are often necessary in bottled water plants due to the low filter fouling observed with some water supplies that are especially clean.

Cryptosporidium and Giardia Control The NSF, FDA, and IBWA have established guidelines regarding Cryptosporidium and Giardia control. These guidelines were a direct result of several outbreaks in which consumers even lost their lives. Giardia and Cryptosporidium are fairly large (>1.0 μm) and are usually found in surface waters. A difficulty has been that Cryptosporidium has

Bottled Water Industry

221

proven to be resistant to disinfection treatments employed within the industry. It takes a 1,000 ppm dosage of chlorine, for example, to achieve complete kill. This is well above acceptable dosage limits. A 1.0 μm absolute rated filtration step in a properly monitored and controlled process is sufficient for removal of these microorganisms. A depth or prefilter should not be used if the potential for Cryptosporidium and Giardia is known to exist, regardless of whether or not the filter manufacturer claims “absolute” removal for the filter at 1.0 μm. Some manufacturers offer special systems designed specifically for the removal of these organisms; however, a typical microfiltration stage ending with any membrane of a pore size rating of 1.0 μm or less will ensure complete removal.

Ozonation The use of ozone (O3) is common in bottled water facilities due to its effectiveness as an antimicrobial agent. Ozone negatively impacts nearly all cartridge filters currently on the market. This is due to the fact that ozone is not compatible with polypropylene and will cause the oxidation and subsequent degradation of filters with materials constructed of polypropylene. The outer cage, inner cage, and end caps of most cartridge filters, which are constructed of polypropylene, are usually thick enough so that they will be able to withstand some exposure. The support layers of pleated filters are also constructed of polypropylene. These layers are much thinner than the other components and will quickly degrade (often in a matter of hours or days), which will leave the membrane without proper support and lead to filter failure. The membrane is often ozone compatible as a material by itself. Ozonation should always occur after the filtration stages, and there should be no recirculation of ozonated water back into the upstream side of the filtration process. It is common knowledge that UV can destroy ozone. A few facilities have opted to place ozone, followed by UV, before the filtration process. This is not recommended, as any failure in the UV stage will cause degradation and integrity failure of the filtration process. Such a failure would not only lead to filter replacement expenses but also to costly product holds for product that cannot be relied on to meet quality standards. Cartridge filters that are 100% PTFE (Teflon) are compatible

222

Beverage Industry Microfiltration

with ozone. There has not been any significant adoption of these filters within the industry, but if improvements with hydrophilization are made, they may become an inexpensive and viable filtration device. The use of ozone has been scaled back in recent years due to the formation of bromate (BrO3-) in those water sources that have naturally occurring bromide (Br-). Filtration becomes much more important as a microbial removal tool when ozone levels must be reduced.

Specialty Products Specialty products produced as part of the bottled water industry are relatively new processes and are quite varied between manufacturers. Many exact processes and formulations are still guarded. Specialty water products are commonly flavored waters, mineralized waters, or waters that have been artificially carbonated. There are an increasing number of products geared toward such things as diet supplement containing water or caffeinated water. In most respects these specialty products will filter exactly the same as standard bottled water, but many will be more susceptible to microbial growth, which makes filtration even more important. Products that are carbonated should have a 0.22 μm point-of-use gas filter located at the point of carbonation. Flavorings are sometimes filtered separately prior to addition. There may be additional blending tanks for mineralization or flavor addition. There is usually no need for tank vent filtration due to the fast bottling and low in-tank storage times. Mineral additions can sometimes cause precipitates or deposits that will reduce filterability. Most specialty products will have a filterability that is lower than the water used to make it. The lower filterability may or may not be appreciable but should be considered when sizing new systems. It may be beneficial to size systems slightly larger than those used for conventional bottled water elsewhere in the plant.

Process Testing: Silt Density Index (SDI) Silt density index (SDI) testing (also called fouling index) was originally developed in the 1970s and is used in the industry. It is essentially

Bottled Water Industry

223

a standardized filterability test used for site assessment, water quality monitoring, and process troubleshooting. SDI testing is common in other water applications, such as municipal treatment and those applications that employ reverse osmosis. SDI testing is an effective means of gauging water quality throughout the year and alerting the plant to any water quality upsets due to environmental factors, such as drought, winter thaw, or heavy rains. It is possible to see spikes in particulate loading after certain environmental events that are not seasonal or otherwise predictable. A facility should first establish a baseline SDI throughout the year to which subsequent SDI test results can be compared.

A bottled water plant in California sees its filterability sharply decrease every time rocks shift or break off within the spring. This can be caused by natural erosion, earthquakes, tremors, and so forth. Light tremors are common in the area. The root cause was determined to be a powdery clay within the rock formations that is released and quickly hydrates to form a gel when it comes into contact with water. Given the size of the plant, each of these occurrences could result in tens of thousands of dollars in filter replacement costs. The only course of action is close monitoring of events and regular SDI testing. If the filterability drops, a back-up water source must be used while the primary line is flushed to remove the clay.

SDI testing can be used to gauge the effects of process changes that may affect filterability, such as an addition or removal of a pretreatment step. Addition of a carbon bed may decrease filterability, for example. The same is true for various coagulants or other chemical treatments that may be applied. Performing SDI tests after unexpected or rapid filter pluggage can be a method of quickly determining and troubleshooting the problem. By working backward from the plugged filtration stage, it is possible to compare the SDI test results after each stage in a process to see where the breakdown has occurred. Performing an SDI test on the water as it enters the bottling plant will quickly tell if it is a processing or a water source issue.

224

Beverage Industry Microfiltration

Equipment used for pH adjustment can sometimes change the water stream’s level of fouling. An SDI test should be run both with the equipment on and then with the equipment off to gauge whether or not this is having an effect on the microfiltration performance. Dissolved solids coming out of solution as a result of pH adjustment can sometimes lead to increases of 3–5 times the non–pH-adjusted SDI. SDI Test Equipment The equipment used for performing an SDI test is comprised of an adapter to attach to the appropriate outlet or drain valve. The adapter feeds into a pressure regulator. There should be a pressure gauge on the regulator. A valve is located after the regulator. The valve leads into a 47-mm filter disk holder. The 47-mm filter holder can have a vent valve built in for easy venting. The filter holder outlet can have a fitting to direct flow. Figure 10.2 shows such an apparatus. There are companies that offer an automatic SDI test unit.

Figure 10.2.

Silt density index (SDI) test apparatus.

Bottled Water Industry

225

SDI Test Procedure 1. Ensure that pretreatment steps and any other conditions are operating consistently with what is observed at the filtration train. If, for example, a step is only performed at certain times and is suspected of causing poor filterability, then run the test when this step is occurring. 2. Flush the sample line for a few minutes before attaching the SDI test apparatus. 3. Ensure that the SDI apparatus is well rinsed. 4. Place a 47-mm 0.45 μm MCE membrane filter into the apparatus with the upstream side of the membrane facing the inlet. 5. Connect the SDI apparatus to the sampling line. 6. Set the pressure regulator to 30 psi (2,068 mbar). 7. Partially open the inlet valve and vent any air that may be trapped within the tester. Some testers have a vent built in, while other testers will require that the holder be loosened slightly and tilted up so that the air can escape. If the air has not been completely vented from the upstream side of the filter, there will be white patches on the filter’s surface where air bubbles blocked the flow of water. If testing a low-fouling stream, such as most spring waters, continue testing by following the standard procedure below to complete the test. If testing a high-fouling stream, such as some municipal water or poorly treated surface water supplies, continue by following the second procedure to complete the test. Procedure 1 (continued): Standard 1. Place a graduated cylinder below the tester outlet to collect flow. 2. Open the inlet valve completely and measure the initial flow rate. Initial flow rate is defined as the time it takes to fill a 100 ml graduated cylinder. 3. Record the flow rate after 5, 10, and 15 minutes. It is possible to ignore the 5- and 10-minute intervals and only record the 15-minute flow rate for the purposes of calculating the index. The 5- and 10minute intervals are recorded so that the gradual pluggage of the membrane can be observed and the accuracy of the final 15-minute flow rate can be gauged. If the filter plugs and flow stops before 15

226

Beverage Industry Microfiltration

minutes, record the time at which flow stopped. Flow stopping is defined as the point at which flow first breaks. Procedure 2 (continued): Highly plugging streams 1. Open the inlet valve. 2. Record the time at which flow stops. The point at which flow stops is defined as the point at which steady flow first breaks. Two or more SDI tests should be performed to confirm results with a third run if large differences are observed between the first two. Calculating the Index Silt density index is calculated using Equation 10.1. SDI =

% Pluggage Time

(10.1)

The percent pluggage must be calculated using Equation 10.2 for tests that run the entire 15 minutes. % Pluggage =

TEnd − T0 × 100% TEnd

(10.2)

TEnd = Fill time after 15 minutes T0 = Initial fill time If a test stops before 15 minutes, then 100% pluggage is assumed. Example 1 An SDI test is run. The initial fill time was 10 seconds. The ending fill time was 104 seconds. The test ran for the entire 15 minutes without flow stopping. % Pluggage = SDI =

104 sec − 10 sec × 100% = 90% 104 sec

90% = 6.0 15 min

Bottled Water Industry

227

Example 2 An SDI test is run. Initial fill time is 65 seconds. Flow stopped after 6.5 minutes. SDI =

100% = 15.4 6.5 min

Interpreting SDI Results The results of SDI tests will usually be compared to the already established base lines for a particular facility. A general rule of thumb is that an SDI of 3.1–5.0 is considered acceptable. An SDI result of 3 or below is considered good; however, an SDI in the 0.5–2.0 range will achieve the best process economics. Bear in mind that even occasional spikes in SDI (water quality) can be damaging to the filtration process.

RO and Distilled Water Reverse osmosis and distillation processes themselves are outside the scope of this text. It is necessary to prefilter RO and still feed. The prefiltration is performed with a depth-style cartridge filter in the 1.0– 5.0 μm pore size range. RO and distilled water that is bottled will still sometimes pass through a pre-bottling filtration skid to ensure product integrity and safety. This is a best practice and typically has a low associated cost as the filters will have an extremely long service life. Water pretreated via RO or distillation has an extremely low-fouling tendency. RO prefiltration is one of the few places in beverage microfiltration where resin-bonded cartridges are common. They will function almost identically to wrapped, depth-style filters, which are more commonly used for this application.

Bottled Water Industry Standards The IBWA and NSF International both have standards relevant to microfiltration in the bottled water industry. Although not required by law, some bottlers have decided to adopt either one or more NSF

228

Beverage Industry Microfiltration

Standards or the IBWA Model Code. Adherence to the IBWA Model Code is a requirement for IBWA members. NSF International NSF International (www.nsf.org) is a leading organization dealing with consumer health and safety. NSF Standard 53 applies to the suppliers of technologies to the bottled water market designed for Cryptosporidium and Giardia control. Microfilters and microfiltration systems fall under this category. The filter supplier can apply for NSF Standard 53 certification. The NSF has a series of criteria that the filter must pass in order to be certified. The NSF audits the filter production facility to ensure that proper GMP procedures are in place. Many filter manufacturers will say that their filters are NSF 53 “compliant” or wording similar to that effect. This means that they are not certified and have not undertaken the certification process. Most filter manufacturers will not go through the certification because of the associated costs. A five-year filter or filtration system certification would cost the manufacturer over $50,000 for every product. This cost recurs every five years. Considering that most manufacturers have many, perhaps even a dozen or more, products for the bottled water industry, the cost is simply not justifiable by the limited benefits of using “NSF Certified” on marketing literature and being listed on the NSF website as certified. Not having such a certification does not necessarily reflect on the supplier’s filter quality and does not mean that the supplier’s filters would not pass the certification process if applied for. Consumers can search the NSF website to determine which suppliers and products have been certified. International Bottled Water Association (IBWA) The International Bottled Water Association (www.bottledwater.org) is a non-governmental entity that establishes best-practice guidelines for many water bottlers and the companies that supply the water industry with equipment or services. The IBWA “Model Code” was first established in 1982 when US FDA regulations were much more limited in scope than they currently are. It is the responsibility of all IBWA member companies to adhere to the guidelines set forth in the IBWA Model Code. Several Model Code guidelines and recommendations deal with microfiltration including:

Bottled Water Industry

229

• “All bottled water products shall be free of coliform bacteria, including E. coli” (IBWA Model Code October, 2007, effective January 1, 2008) • “Bottled water production, including transporting, processing, packaging, and storage, shall be conducted under such conditions and controls as are necessary to minimize the potential for microbiological contamination of the finished product.” (IBWA Model Code October, 2007, effective January 1, 2008) • “Water intended for bottling must be from a source approved by the applicable regulatory agency. If treatment is necessary to reduce, remove or prevent growth of microbial contaminants, chemical, physical and/or radiological substances (including multiple barrier treatments such as filtration, disinfection, reverse osmosis, etc.) of that water during processing, the finished bottled water product shall be safe and suitable for consumption. These treatments can be used singularly or in combination as multiple barriers. A hazard analysis (such as HACCP) should be undertaken to provide the basis for determining the appropriate combination of control measures to reduce, eliminate or prevent, as necessary, hazards (microbiological, chemical and radiological) for the production of safe bottled water.” (IBWA Model Code October, 2007, effective January 1, 2008) • “When necessary, treatment of waters intended for bottling, to reduce, remove or prevent growth of microbial contaminants, may include the application of chemical processes (such as chlorination, ozonation, carbonation) and physical agents or processes (such as high heat, ultraviolet radiation, filtration). These treatments can be used singly or in combination as multiple barriers. Treatments vary in their effectiveness against specific organisms. When necessary, treatments to remove or reduce chemical substances may include chemical and particulate (mechanical) filtration such as achieved with surface filters (e.g., pleated membrane filters) or depth filters (e.g., sand or compressed fiber [cartridge] filters), activated carbon filtration, demineralization (deionization, water softening, reverse osmosis, nano-filtration), and aeration. These treatments for chemicals may not adequately reduce or remove microorganisms and, likewise, treatments for microorganisms may not adequately reduce or remove chemicals and particulate matters.” (IBWA Model Code October, 2007, effective January 1, 2008)

230

Beverage Industry Microfiltration

• “Water intended for bottling shall not be stored, transported, processed, or bottled through equipment or lines used for milk, other dairy products, non-beverage foods, or any non-food product. Nondedicated beverage equipment and lines used for other beverages shall be sanitized using a hot clean-in-place (CIP) process, or equivalent. The process must be addressed in the plant’s sanitization standard operating procedure (SSOP) manual and HACCP plan, and shall include provisions for monitoring, critical limits, appropriate corrective action, and records.” (IBWA Model Code October, 2007, effective January 1, 2008)

Chapter 11 Spirits Industries

Alcoholic beverage industries will typically use microfiltration as a means of particulate removal. It may also be necessary to remove various precipitates and colloidal materials, such as chill haze, from the product. As the industry expands into nonconventional markets, such as premade drinks, flavored and mixed drinks, and drinks that have a lower alcohol content than conventional products, it becomes necessary to use microfiltration for microbial control as well.

Particle Filtration Beverages will pick up various particulate matters during production and/or transport. Many alcoholic products such as vodka, whiskey, tequila, and so forth need a clear transparent finish, so any particulates must be removed from the product prior to bottling. Many particulates will come from pretreatment stages, such as ion exchange or carbon treatment. Carbon filtration is commonly used on several types of alcohols. Vodka, for example, may be passed through a carbon filter 6–12 times in order to remove organic impurities while maintaining a steady ethanol content. This is done both by recirculation through one or more filters or by single passes through a series of filters. Carbon fines can appear in the product as a result and require a subsequent filtration to ensure product clarity. Depth- or surface-style filters may be used for particulate removal. Membrane filters can be used at an additional cost. Most conventional alcoholic beverages are typically so clear at bottling that membrane plugging is of little concern, and the filters will have very long service lives. The change-out expense of membrane filters is considerably higher than that of depth filters or surface filters, and this may prove 231

232

Beverage Industry Microfiltration

to be a deterrent regardless of service life. If the final filter choice is between a depth-style filter and a surface-style pleated filter, the surface filter should be used unless there is very high particulate loading. The surface-style filter will have increased retentiveness and less likelihood of particulate unloading should the maximum recommended differential pressure be exceeded. If there are large amounts of particulate material present, it may be better to use a wrapped, depth-style filter for its increased dirt-holding capacity. If higher retentiveness is still desired, then a surface-style pleated filter could be used afterward. The cost of non-membrane cartridge filters is fairly low, so adding a second step would be minimal from a cost perspective. Lenticular and sheet filters are used for particle filtration of spirits. Many distilleries use only sheet or lenticular filters for final product filtration. It is also common for sheet and/or lenticular filters to precede more efficient cartridge filters in a process. Bag filters are rarely used on clear liquids, but some syrups and thick alcoholic products may use bag filters for particulate removal. Sheet and lenticular filter media can be specially designed so that they remove the precursors to haze formation, including fatty acid esters. It is optimal to remove medium- to long-chain fatty acid esters while leaving the short-chain fatty acid esters, which are responsible for some aroma profiles of the product. Some lenticular and sheet filters will release calcium and magnesium ions during the first portion of the filtration run. These ions can lead to precipitates and haze formation, so a filter that has low ion release is best. Many alcohol products will develop various hazes as a result of metal ions, crystal precipitation, chemical interactions, aging processes, or flavor additions. Undesirable hazes can be removed by filtration.

Microbial Filtration If the alcohol of a product is sufficiently high, there will be little concern about microbial contamination and growth. Premixed drinks and products with low alcohol content can be susceptible to microbial spoilage. Those drinks with high sugar content are at a higher risk of spoilage. If there is at least a decent concentration of alcohol, then a 0.45 μm filter can be used to remove microorganisms that may cause product spoilage. It may be possible to use a higher pore size rating

Spirits Industries

233

than 0.45 μm to have a shelf-stable product, depending on the alcohol content and target microorganisms.

Emerging Products Nonconventional products within the alcoholic beverage industry have grown to be a fair portion of the industry’s total produced volume. Such products include the many different premixed drinks that are modeled after long-time drink favorites. There are increasing numbers of flavored low alcohol malt beverages on the market. These products, as long as there is some appreciable alcohol content, will not usually be prone to microorganisms that pose a health concern, but they will be vulnerable to microorganisms that cause spoilage and decreased shelf life. Filtration of the product to 0.45 μm will remove spoilage-causing microorganisms. If the alcohol content is high enough, only a particle filtration may be required. Many brand name alcoholic cocktail mixtures use sheet and lenticular filters for a final filtration. A coarse to medium-fine grade is often used with a filter flux of about 0.37–0.49 gpm/ft2 (9–12 hl per hour per m2) for the coarser grade and 0.25–0.37 gpm/ft2 (6–9 hl per hour per m2) for the medium grade. Product variability should be taken into consideration when designing and sizing these stages. Most spirits (whiskey, vodka, gin, etc.) are relatively uniform with regard to sizing; however, alcoholic cocktail mixtures can vary greatly. A large variance in product viscosity is one common difference that can affect filtration processes. It is sometimes more cost effective to filter the product components separately. The higher alcohol base may only require a particulateremoving depth filtration. This is also true for many of the flavors and sugar additions. Some liquid flavorings or juices may require a microbial filtration step. RO water will usually require prefiltration (3.0– 5.0 μm) prior to the RO filter and may have a subsequent membrane filtration (0.22–0.45 μm) after the RO system. Cloudifier must be added after the various microfiltration steps. The final product may require a filtration since there can be interactions that occur after the final product has been blended. There are often significant decreases in filterability when combining a conventional alcoholic base, such as vodka or whiskey, with flavors

234

Beverage Industry Microfiltration

or sweeteners. Products that are oak aged, such as whiskey and brandy, for example, will sometimes see a haze form when sugars and flavors are added. This is due to the oak-extracted components interacting with the artificially added components. The resulting haze will have a low filterability and will usually require an additional clarification stage specifically targeted at removing the haze prior to final filtration. Sometimes hazes or dissolved materials will only be observed after cooling to a specific temperature. If this is the case, and it is expected that the product will either be cooled to that temperature in storage, transport, or by the customer, the final product filtration(s) should be carried out at that temperature to remove the material. Flavorings should be considered for their filterability prior to being added. Changes in ingredient suppliers should be preceded by a filterability analysis of the new product. A change in an ingredient or supplier for materials such as caramel coloring or sugar syrup will oftentimes lead to a rapid plugging of the filters and leave the plant wondering why. There are many considerations when producing nonstandard alcoholic beverages that are normally not involved when producing highalcohol products. Filters must be cleaned regularly for microbial control and filter regeneration. If the product is to be carbonated, a 0.22 μm point-of-use CO2 filter should be used. Proper sanitation procedures become more important. Long downtimes may require filter storage procedures. The new product lines will sometimes have more in common with other industries than with the alcoholic beverage industry and this should be recognized. Other industries, such as wine, water, and beer, should be looked at when determining equipment and procedures.

Miscellaneous Considerations • Do not neglect cleaning of the filters. Some alcoholic beverage plants simply leave product in the lines following shutdown and then restart production on the next shift without cleaning or sanitation. Although microbial control may not be a concern with high-alcohol products, contaminants such as proteins, colloids, scale, carbon fines, and so forth will still build up on the filter surface. The contaminants need to be removed in order to achieve maximum filter service life.

Spirits Industries

•

• •

•

235

A simple cold-water flush in the reverse direction, with exit flow to drain, will often be the only cleaning requirement. Hot water may help to break down some organic colloidal materials and facilitate removal. Hot water flushes in the forward direction are more effective at removal than cold water in the forward direction. Nonalcoholic mixers are essentially juices, as opposed to alcohols. Some of these mixers are even pasteurized to ensure microbial stability. It is perfectly feasible to use microfiltration as a means of ensuring product quality. If there is no alcohol content, it may be necessary to use a membrane final filtration of 0.22 μm or of at least a 0.45 μm. Individual component filtration can work well if the mixer is nothing more than RO water, flavorings, and sugar. Some depth filter sheets have a high absorbing capacity for fusel oils. Carbon-impregnated media is often used for the decolorization or removal of organic contaminants and impurities of various spirits. Filter sheets, lenticular filters, and cartridge filters are all available with carbon-impregnated media. Many conventional polymers used for sealing mechanisms, such as gaskets and o-rings, are not compatible with long-term processing of very high-alcohol content products. Silicone and viton should not be used, due to excessive swelling of the material. EPDM, PTFE, or Buna-N should be used instead, with certain high-alcohol products.

Chapter 12 Dairy Industry

The dairy industry has become a large consumer of ultrafiltration and reverse osmosis equipment. While it was once thought that microfiltration would replace pasteurization in the dairy industry, it has not. Health concerns associated with properly producing milk and other dairy products have prevented the widespread use of microfiltration. It is very easy to heat pasteurize and ensure that there are no hazardous microbes present. While microfiltration can be equally effective, it can be more prone to errors within the process, for example, inadequate integrity testing of membranes. The tight pore sizes required for complete removal of microbes presents an issue with regard to membrane fouling and undesired removal of some components. Microfiltration is being used for some specialty applications and in conjunction with other technologies for producing a safe, shelf-stable product.

Microfiltration for Increased Shelf Life Microfiltration has been proven capable of increasing the shelf life of dairy products. Microfiltration enhances the sensory characteristics of the product as compared to conventional heat pasteurization. Microfiltration has, despite this, seen extremely little success as the primary mode of ensuring microbial stability of the dairy product. Skim milk has been successfully microfiltered at larger pore size ratings for removal of spoilage causing bacteria and spores. This has allowed for an increased shelf life of the microfiltered product. Milk has been treated with a combination of larger-pore microfiltration and heat treatments to produce stable products. It is possible to separate the milk into two streams. The first stream will pass through a microfilter, while the second stream is pasteurized. The first stream is typically skim milk 237

238

Beverage Industry Microfiltration

in which the fat globules are retained by the microfilter. The two milk streams are later combined and will have an increased shelf life and fresher taste than if the entire batch had undergone pasteurization.

Microfiltration in Conjunction with UF and RO Ultrafiltration and reverse osmosis of dairy products has become increasingly common. Microfiltration can be used effectively in support of these applications. Specific uses of RO include the concentration of milk and the demineralization of lactose. UF is used to concentrate whey proteins. UF can be used to remove water, lactose, and ash from the milk, while RO allows only water to pass through the membrane. UF and RO are used to concentrate unpasteurized milk for shipment. For a fraction of the cost of regular milk, concentrated milk can be safely transported from the farm to the processing facility where it is reconstituted, stored, pasteurized, and packaged. This process was approved by the FDA and is presently in use. The water used to reconstitute the concentrated milk will be RO water. The water will usually require prefiltration before the RO unit and may require subsequent sterile filtration following the RO filter. RO concentrated milk can also be used in ice cream processes. Microfiltration is used as a prefiltration stage prior to RO and UF filters. Pore size ratings will be fairly open, in the 3.0–5.0 μm or larger range. Specialty Applications Milk can be crossflow microfiltered at 0.1 μm to remove many constituents but still retain much of its casein. The resulting filtered milk is ideal for cheese-making processes. This application has been successful in cheddar cheese production. The protein concentrates that result from the microfiltration of skim milk can be separated into betalactoglobulin, alpha-lactalbumin, and lactoferrin. These materials have applications in various neutraceutical uses and as food ingredients in both dairy and nondairy products. The milk soluble proteins in the microfiltration permeate of skim milk can be used in milk beverages to replace milk casein. This process will maintain the same total level of protein, calcium, and lactose of the beverage. Ceramic crossflow

Dairy Industry

239

filters are used within dairies for many water reuse and specialty process recovery applications. An example is the concentration or removal of fat from some waste or side process streams.

Dairy Tank Vent Filtration The most common application of microfiltration within the dairy industry is the use of tank vent filters. Nearly all dairy storage tanks will have a tank vent filter. The filter is a 0.22 μm PTFE hydrophobic membrane, and it prevents contamination of the tank via the tank vent, which must remain open to the atmosphere. Disposable filter devices (capsules) are readily available and can be used effectively as presterilized disposable tank vent filters.

Chapter 13 Soft and Sports Drinks Industries

The vast majority of soft drinks do not undergo final filtration of the blended product. Sports drinks are usually pasteurized, although some facilities in Europe are successfully using microfiltration as an alternative to pasteurization of sports drinks. The major applications of microfiltration within the soft and sports drink industries are sugar syrup clarification, filtration of the make-up water, and gas filtration.

Soft Drinks Sugar syrup must be filtered to remove particles and sugar crystals. This filtration is usually accomplished by means of a wrapped polypropylene depth filter in a pore size rating of around 20–25 μm. The actual specification for some large soft drink manufacturers for sugar syrup clarification is complete absence of 40 μm particles and 90% or greater removal of 20 μm particles. Other manufacturers may use tighter specifications. On a per plant basis, sugar clarification is not usually a large cost for the manufacturer. The average 30″ wrapped polypropylene filter will have a product throughput of roughly 35,000 gallons (1,325 hl). A 30 Round 30″ high filtration housing should therefore have a throughput of approximately one million gallons (37,850 hl). The filters used for sugar syrup clarification are fairly inexpensive. Lenticular stacks are used by some soft drink bottlers for syrup filtration. By volume, water makes up approximately 90% of most soft drinks. Water quality is therefore very important to the final product. If the water is not properly treated, it can impart negative taste or odor to the final product. Municipal water supplies can be highly variable and experience quality fluctuations. Municipal treatments are different 241

242

Beverage Industry Microfiltration

among locations. This can be problematic for multi-plant or multilocation operations attempting to manufacture the same product. It is also possible for there to be contamination between the municipal treatment and the plant. Industry best practice is to use RO, distilled, or a combination of RO and distilled water for product makeup. Reverse osmosis is much more common and cost effective. RO filters and distillation units used on product water makeup will have a prefiltration stage prior to the RO filter. These filters are normally in the 1.0–5.0 μm pore size range and are typically either wrapped polypropylene, resin bonded, or, on rare occasion, string wound. Carbon dioxide can be filtered using a 0.22 μm hydrophobic PTFE membrane filter. Soft drinks may or may not undergo a final particulate filtration prior to filling. This may be accomplished with either a depth or surface-style filter. Many soft drinks, such as colas, are inherently microbially stable. This is due to the combination of carbonation and low pH.

Sports Drinks Sports drinks are extremely susceptible to microbial contamination. If microfiltration is used as an alternative to pasteurization, care must be taken to ensure proper microbial control throughout the bottling area. Rinse water should be filtered. All gases coming into contact with the product or product containers should be sterile filtered to 0.22 μm. Storage and surge tanks should have 0.22 μm tank vent filters. It is a good practice to filter each component prior to blending and the final product just prior to filling. This is true even if the product is blended in-line directly before filling. The final product filtration should be down to 0.22 μm. Redundant final 0.22 μm filtration stages in series will result in extra product-quality assurance. It is common for sports drinks to have a cloudifier added to the final product. It is important that, when microfiltration is involved, this cloudifier be added after any microfiltration stages, as it will quickly plug the filters. No recycling or product returns feeding back into the filtration train may be used when running cloudifier-containing product. One might ask why a plant would ever microfilter a sports drink rather than use pasteurization. The answer lies in the fact that sports

Soft and Sports Drinks Industries

243

drinks are a fast-growing market that is seeing more and more volume of product produced each year. Sports drinks are very low-fouling products that will typically have a low cost of filtration on a per gallon basis. Compared with the energy costs and capital expenses of pasteurizing millions of gallons of product, microfiltration can be an especially economical alternative if properly carried out.

Chapter 14 Juice Industry

The juice industry pasteurizes the majority of its products. While there has been a recent focus regarding “non-thermal pasteurization” technologies, these have largely excluded microfiltration. Ultra-high pressure, pulsed electric fields, and other novel technologies have taken the forefront of this debate. The problem with microfiltration of juices resides in the fact that, unlike beer and wine, it is often desirable to filter juice to 0.22 μm in order to ensure that no dangerous microorganisms are present in the product. In this respect juices are similar to bottled water but with considerably worse filterability, which makes microfiltration not as economically attractive. This is particularly true when considering the increased risks associated with nonthermal processing. There are juice facilities that microfilter to 0.45 μm. A pore size rating of 0.45 μm will retain E. coli bacteria. Bag filters are used within some facilities as a means of rough particulate removal only and work well for this task. Microfiltration can be used most effectively with clear juices, such as apple or grape. A prefiltration stage must be used. A clarification stage will be beneficial to the overall process. Crossflow clarification is effective and offers a good pretreatment prior to cartridge microfiltration. Cranberry juice manufacturers sometimes use clarification via microfiltration. Pulpy juices will require that the solids be removed and processed separately. The juice solids may be recombined after microfiltration. Juice plants that use aseptic storage will require both tank vent filtration and point-of-use gas filtration for the blanketing gas. These filtration steps should use a 0.22 μm hydrophobic membrane filter. When RO and UF membranes are used, it becomes a possibility to use microfiltration as a form of prefiltration/clarification prior to these stages. De-bittering of citrus juice is one such example. RO and UF processes 245

246

Beverage Industry Microfiltration

are becoming more common throughout the juice industry. Juices that are high in pectins may require the addition of pectinase enzyme to increase filterability. Cloudifier should not be added to juices until after all microfiltration stages. Crossflow microfiltration systems have some potential uses in rough juice clarification. Since juice, which is currently rough clarified by processes such as centrifugation, press filters, or DE filtration mechanisms, is heavy in solids, the microfiltration crossflow system may have to be paired with a centrifuge or comparable technology to be an effective replacement. Koch Membrane markets systems to certain juice industries for clarification. There has yet to be a specific or widespread push into the juice industry with crossflow clarification.

Chapter 15 Flavor, Neutraceutical, and Niche Applications

The flavor and beverage-related neutraceutical industries are highly variable with regard to filtration. Most of the various materials being produced are either proprietary or only being produced by one or a few manufacturers, so there is little knowledge sharing or commonality, even when it might be possible. Many flavor and neutraceutical companies will only use filtration to remove particles, as their products are inherently microbially stable to begin with. A common use of microfiltration in these industries is the removal of hazes or other forms of colloidal materials. Products that are susceptible to microbes are filtered to remove such contaminants.

Flavorings Flavorings may be filtered by either depth or surface cartridge filters. They may also be filtered by bag filters. Due to the large numbers of different flavorings on the market, generalizations about filtration processes cannot be made. Some flavor processes will employ filtration down to 1.0 μm, while other processes may be in the 20 μm range. Many flavorings are susceptible to both hard particles and the formation of hazes. Multiple filtration stages may be used to remove the different types of contaminants. If a product is seen as susceptible to the formation of hazes, the filtration should be carried out at the lowest temperature at which the hazes will form. Many flavorings are not susceptible to microbial contamination or growth, so a membrane final 247

248

Beverage Industry Microfiltration

filter is unnecessary. Determining whether or not a product is susceptible to microbes will be one of the most important considerations when designing a filtration process.

Ready-to-Drink Teas and Coffee Beverages Ready-to-drink teas and specialty coffee beverages are fast-growing markets. Some of these beverages are pasteurized. Many are not. Prefiltration of RO water is a common microfiltration application within these processes. Filtration of the final produced product is also done. Products of this nature can have a desired solids content in which some solids are to be left with the final product. This can present a problem for microfiltration in that pore size ratings designed to remove microorganisms will also remove these solids. Pasteurization may be necessary in these cases. Solids may be re-added after the final product filtration, but this must be carried out aseptically. Sucrose and Liquid Sugar or Sugar Substitute Filtration Sucrose can be filtered using either depth-style cartridge filters or bag filters. The pore size rating should be about 20–25 μm. Some manufacturers may filter to much more open pore size ratings in the 100 μm range. Filters used for soft drinks should have a high removal rating for particles down to 20 μm, with at least a near-absolute removal of particles in the 40–50 μm range. Sugar substitutes such as aspartame are also filtered. Each product using liquid sugar can have its own filtration specifications that need to be developed. Vinegar In traditional vinegar production, the wine used for the vinegar may be microfiltered according to typical wine production. After the secondary bacterial fermentation, large-scale vinegar production has several additional possible needs for microfiltration. Most large-scale vinegar is clarified through a DE filter similar to those used for wine or beer. A pad or lenticular filter may be used for clarification in lieu of DE filtration at smaller production facilities or with smaller batches.

Flavor, Neutraceutical, and Niche Applications

249

Vinegar may be microfiltered via cartridges following DE, pad, or lenticular clarification prior to bottling. Microfilters may run into chemical compatibility issues with long-term vinegar filtration, so chemical compatibilities of filters should be verified when designing a process.

Peppermint and Spearmint Oils Natural peppermint and spearmint oils can be filtered by depth cartridge filters and, more commonly, by bag filters. These products often require dual-stage clarification consisting of both prefiltration and final filtration housings. The final filtration can be in the 30 μm range, while the prefiltration stage should be in the 70 μm range. The large difference in pore size rating between the prefiltration and final filtration stages relates to the types of materials present and the fact that prefiltration media at larger pore size ratings do not have large relative differences in retention efficiency as compared with media at smaller pore size ratings.

Seafood Broths and Juices Seafood broths such as clam juice or fish stock may be microfiltered prior to bottling or canning. These products are usually filtered with either bag or depth cartridge filters. Pore size ratings are often in the 25 μm range. Pore size ratings can be higher depending on the liquid clarity and visual quality desired.

Honey Honey can be passed through a very open filter to remove particulate material, such as wax and propolis, without removing pollen, which is sometimes retained for use in various health foods. Honey may also be filtered to a finer degree to remove all solids and pollen grains. Honey filtered to this finer degree is what is most often seen in grocery stores because it has higher clarity and a longer shelf life due to slower crystallization. Honey is filtered using bag filters.

250

Beverage Industry Microfiltration

Olive Oil Olive oil can be filtered with a lower-grade sheet in a plate and frame filter device. These grades are usually designated as “refining” or “rough clarification” or something else to that effect. The capacity per sheet will be significantly lower than with other plate and frame applications, such as wine. When installing the filter sheets, remember to wet the sheets with oil rather than water just prior to beginning filtration. It is sometimes recommended to install two sheets in the place of one sheet when filtering olive oil. Check with the manufacturer regarding this issue.

Appendix Filter and Filtration Equipment Manufacturers and Suppliers (Partial Listing)

Cartridge Filters Name

Website

Bea Technologies Begerow Cuno (owned by 3M) Domnick Hunter (owned by Parker) Filtrox Flow Solutions FlowTech Corporation FSI (Filter Specialists, Inc.) GE (Osmonics) Graver Technologies Gusmer Enterprises Millipore Pall PTI Technologies Roki Sartorius Scott Labs Vintner’s Supply Company Whatman

www.bea-italy.com www.begerow.com www.cuno.com www.domnickhunter.com www.filtrox.ch www.flowsolutions.com www.flowtechfilters.com www.fsifilters.com www.gewater.com www.gravertech.com www.gusmerenterprises.com www.millipore.com www.pall.com www.ptitechnologies.com www.rokitechno.co.jp www.sartorius.com www.scottlab.com www.vintnerssupply.com www.whatman.com

251

252

Appendix

Cartridge and Lenticular Filter Housings Name

Website

3L Allegheny Bradford Alteco Bea Technologies Begerow Cuno Della Toffola Domnick Hunter (owned by Parker) Filtrox FlowTech Corporation FSI (Filter Specialists, Inc.) Graver Technologies Millipore Pall Sartorius Scott Labs Spadoni Vintner’s Supply Company

www.3lfilters.com www.abccorporate.com www.alteconet.com www.bea-italy.com/ www.begerow.com www.cuno.com www.dellatoffola.it www.domnickhunter.com www.filtrox.ch www.flowtechfilters.com www.fsifilters.com www.gravertech.com www.millipore.com www.pall.com www.sartorius.com www.scottlab.com www.spadoni.it www.vintnerssupply.com

Sheet and Lenticular Filters Name

Website

Begerow Cuno (owned by 3M) ErtelAlsop Filtrox FlowTech Corporation Gusmer Enterprises Pall/Pall Seitz Sartorius Scott Labs Vintner’s Supply Company

www.begerow.com www.cuno.com www.ertelalsop.com www.filtrox.ch www.flowtechfilters.com www.gusmerenterprises.com www.pall.com www.sartorius.com www.scottlab.com www.vintnerssupply.com

Appendix

253

Plate and Frame Filter Housings Name

Website

Begerow Della Toffola ErtelAlsop Filtrox FlowTech Corporation Prospero Scott Labs Spadoni TMCI Padovan Velo Vintner’s Supply Company

www.begerow.com www.dellatoffola.it www.ertelalsop.com www.filtrox.ch www.flowtechfilters.com www.prosperocorp.biz www.scottlab.com www.spadoni.it www.padovan.com www.velo-group.com www.vintnerssupply.com

Bag Filters Name

Website

3L Domnick Hunter (owned by Parker) FlowTech Corporation FSI (Filter Specialists, Inc.) Hayward Industrial

www.3lfilters.com www.domnickhunter.com www.flowtechfilters.com www.fsifilters.com www.haywardindustrial.com

Bag Filter Housings Name

Website

FlowTech Corporation FSI (Filter Specialists, Inc.) Hayward Industrial Scott Labs

www.flowtechfilters.com www.fsifilters.com www.haywardindustrial.com www.scottlab.com

254

Appendix

Beverage Crossflow Systems Name

Website

Bucher Vaslin Criveller Della Toffola Filtrox Gusmer Enterprises Koch Niro Pall Sartorius Spadoni TMCI Padovan Velo

www.buchervaslin.com www.criveller.com www.dellatoffola.it www.filtrox.ch www.gusmerenterprises.com www.kochmembrane.com www.niroinc.com www.pall.com www.sartorius.com www.spadoni.it www.padovan.com www.velo-group.com

Bibliography

Bird, David. 2005. Understanding Wine Technology. DBQA Publishing. Dairy Management, Inc. 2000. Opportunities for Membrane Filtration of Milk. Innovations in Dairy. International Bottled Water Association. 2007/2008. IBWA Model Code. McCabe, John T. 1999. The Practical Brewer, 3rd ed. Master Brewers Association of the Americas. McCabe, Warren L., Smith, Julian C., Harriott, Peter. 2001. Unit Operations of Chemical Engineering, 6th ed. McGraw-Hill. Meier, Peter et al. 1995. Investigation of Plugging Colloids on Microporous Membrane Filters. MBAA Technical Quarterly. 1:25–34. Modrok, Alexander et al. 2006. Crossflow Filtration of Beer — The True Alternative to Diatomaceous Earth Filtration. MBAA Technical Quarterly. 43(3):194–198. Pregler, Bill. 2006. Crossflow Filtration Systems. Wine Business Monthly. Shachman, Maurice. 2005. The Soft Drinks Companion. CRC Press.

255

Glossary

Absolute (Absolute Rated)

Adapter

Algae

Asymmetric

Backflushing

Bacteria

The complete removal of contaminants of a size above the specified pore size rating. Definitions of “complete” removal will vary by manufacturer. The bottom end cap of a cartridge or module lenticular filter that attaches to the housing and forms the filter to housing seal. Organism that is a contamination concern with beverages. Commonly found in surface and municipal water supplies. Often introduced via packaging or facility water. Membrane property in which the pore size and density is progressively tighter through the membrane’s depth. Often leads to increased filter flow rate and dirt-holding capacity, but may also cause potential issues with filter wetting and durability depending on the degree of asymmetry. Only the final portion of the membrane possesses the stated retention. The act of cleaning a filter in the reverse direction. Not all filters are able to be reverse cleaned. Smallest nonviral microorganism. Absolute removal of all bacteria requires a 0.2 μm membrane filter. 257

258 Bag Filter

Base Plate

Bentonite Beta Ratio

Binding

Bleed-Through

Bubble Point

Cage (Outer/Inner)

Caking or Cake Formation

Capsule

Glossary Nominal-rated filtration device used for very rough clarification or filtration of highly viscous fluids. The part of the filter housing to which filter cartridges or lenticular filters attach. It separates unfiltered product from filtered product. Some base plates may be removed, while others are permanently attached to the housing. Fining agent used in the wine industry. It is a very effective plugging agent. Numerical expression for the removal efficiency of specific particles at a particular pore size rating. Affinity of certain filter media to remove components from the filtered product by a mechanism other than filtration. Usually possesses a negative connotation as this removal is often undesired and can affect color or sensory attributes. Particulates progressing through a filtration stage by means of a defect or malfunction in the process. Membrane integrity test in which the housing and wetted filters are gradually pressurized until the water contained within the membrane’s pores is forced out and rapid bubbling occurs. Plastic structural components of cartridge filters designed to add strength and protect the filter media. The gradual build-up of particles, first upon the filter and then upon each other, which leaves some flow channels available for flow between the built-up particles. Most often associated with hard particulates. Disposable filters that are a complete unit and require no separate housing.

Glossary Carbon Fines

Carbon (Impregnated) Media

Cartridge Filter

Cassette

Cast(ing)

Cellulose (Cellulosic, adj.) Cellulose Acetate

Change-Out Clarification

259

Small particulates originating from carbon beds or carbon-containing filter media that can progress downstream of the pretreatment stage and cause product contamination or subsequent filter plugging. Media incorporated into the matrix of some filters for the removal of certain attributes such as color or odor from the filtered product. Versatile filtration device that can employ a variety of filter media and configurations. Most common microfiltration format currently in use within the beverage industry. Tangential flow device that uses a flat sheet membrane encased in a hard plastic shell. Common to pharmaceutical applications but prone to plugging and poor performance in many beverage applications. The primary production process of polymeric membranes is referred to as casting. Petrol-based or polymeric membranes are sometimes referred to as cast membranes as a result. Base material, originating from plants, used in the construction of sheet and lenticular filters as well as some cartridge filters. Membrane originating from cellulose as opposed to being petrol-based. First membrane developed. The replacement of used filters. Filtration stage or type of filtration associated with the removal of large particulates or the targeted removal of a specific contaminant at some point in the overall process. Examples would include spring source filtration, DE trap filtration, or the removal of carbon fines.

260 Coating

Code Colloidal

Contaminant

Crossflow

Cross Linking

Datasheet

Deformable

Depth Filter

Glossary Surface modification technique that can change the hydrophobicity of a membrane. Least effective technique in which there is no permanent attachment of the substrate. Designation for the adapter and sealing configuration of cartridge filters. Group of soft, deformable contaminants found in many beverages. Very effective plugging agents. Undesired material in the fluid being filtered. Often the reason for filtration. Contaminants can be microorganisms, general debris, organic or inorganic particles. Filtration process in which fluid flow is parallel to the surface of the filter thereby improving filter performance with regard to solid handling and rate of blockage. Alternative name for Tangential Flow Filtration (TFF). Surface modification technique that can change the hydrophobicity of a membrane. Most effective technique in which the substrate surrounding the membrane is bonded. Most common piece of filtration literature. Discusses key properties and specifications of the filter. Property of certain particles that allows them to change shape. Often allows certain particles to fit downstream of a filter that otherwise would be unable to. Deformable particles are typically more effective at filter blockage than nondeformable particles. Filter utilizing media that removes particulates predominantly in the filter matrix as opposed to at the filter’s surface.

Glossary Device, Filter

Diatomaceous Earth

Differential Pressure

Diffusion, Forward or Air

Dome, Housing

Downstream

Efficiency Electron Dispersion Spectroscopy (EDS) Electron Scanning Microscope (ESM) End Cap

Extractable

261

Considered the entire filter unit including any support material, adapters, and filter media. Filter media used for rough clarification of certain beverages. Common plugging agent found in many microfiltration processes. Expression for the difference in pressure between the two sides of a filter. Calculated as inlet minus outlet pressure. Membrane integrity test in which the housing is kept at a constant pressure and the diffusive gas flow through the wetted membrane is measured at the housing outlet. Upper shell (bell) of cartridge and lenticular filter housings that surrounds the filters. The filtrate side of the filter. A fluid is on the downstream of a filter after passing through it. Effectiveness of a filter at removing specific particles from a fluid. Analysis that yields the elements and their relative concentrations present on the filter. Microscope that is able to magnify at resolutions high enough to observe filter structures and contaminants. Cartridge filter component that forms the ends of the device and facilitates sealing. Dictates compatibility with the filtration housing. Material that may be released or leeched from a filter during the filtration. Typically refers to minerals in sheet and lenticular filters or certain oils or chemicals in other filter types that may or may not be present. May require preuse flushing to remove.

262 Felt

Filter Filter Grade

Filter Plate Filterability

Filtration

Final Filtration

Fines

Flow Rate Fluid Flux

Format, Filtration or Filter

Glossary Media type used in the construction of filter bags. Felt material can include polypropylene, polyester, nylon, or Nomex. Device designed for the removal of components from a fluid stream. Rough characterization of removal efficiency and target application for sheet and lenticular filters. Part of a plate and frame housing that holds the filter sheet in place. Quantification of the ability of a fluid to be filtered. The higher a fluid’s filterability, the easier it is to filter that fluid. Filterability is an important characteristic of a product and should be calculated relative to each filter and filter rating being considered. The act of removing a component from a fluid stream by passing the fluid through a filter. The last, and usually most retentive, filtration stage that a fluid will undergo. Often associated with bottling, as many plants will locate a final filtration just prior to bottling to ensure product quality. Small particulates often originating from a larger pretreatment step such as a carbon tank, resin bed, or DE filtration stage. The speed of a fluid. Typically given in gallons per minute or liters per hour. Either a gas or a liquid. The subject of filtration. Defined as flow rate per filter area. Useful expression when comparing the performance of different filters. Term often used to denote a filtration technology such as cartridge, bag, or sheet filtration.

Glossary Fourier Transform Infrared (FTIR) Gas Gasket

Glass Fiber

Graded Density

Grafting

Hard Particle Haze

Headspace

263

Analysis able to determine compounds present on the filter’s surface or within the filter’s depth. Compressible fluid such as air, nitrogen, or carbon dioxide. Sealing mechanism used for both filtration devices and filtration equipment. Constructed of a pliable, chemically and thermally stable polymer. Clarification and prefiltration media used in both depth- and surface-style filtration cartridges. It is typically mixed with other filter media. Characteristic of certain depth filters in which the retention of subsequent layers increases throughout the depth. Increases flow rate and dirt-holding capacity. Surface modification technique that can change the hydrophobicity of a membrane. Moderately effective technique in which the substrate is attached to the membrane. Nondeformable particulates such as sand, silts, rocks, and metal fines. Plugging agent found in many beverages. Can be brought on naturally or as a result of the process. There are many different types resulting from various causes that can usually be traced back to the source. The portion of a container that lies between the upper liquid’s surface and the top of the container. Often a site for contamination or oxygen pickup in many beverages. Headspaces may be filled with inert gases to minimize their effects upon the beverage.

264 Hollow Fiber

Housing

Hydrophilic Hydrophobic Integrity Test

Lenticular

Liquid

Macrofiltration

Matrix Media

Membrane

Glossary Crossflow technology in which the membrane is extruded into the shape of a narrow tube. Many of these tubes are bundled together and form the filter module. Many modules can make up a filtration unit. Filtration equipment used in conjunction with cartridge, bag, and lenticular filters. Holds the filter(s). Readily accepts water; able to be easily wetted. Repels water. Method for verifying that a membrane is free of defects and that the only flow path through the system available to the fluid is through the membrane. Eliminates the possibility of a defective or damaged membrane, improper filter or housing sealing, or improper filter installation, all of which can lead to bypassing of contaminants. Depth filtration device that evolved from sheet filters. Commonly used in many beverage industries. Incompressible fluid. The beverage being filtered is a liquid. Process water and chemicals are other liquids that are also filtered in the beverage industry. The removal of large particulates typically above 10 μm. Some macro and microfiltration technologies overlap. Term referring to the filtration media as a whole and the space that it occupies. The material performing the actual filtration. Examples include cellulose, nylon, and polyether sulfone. Porous filter media that primarily operates via a sieving mechanism to remove most contaminants at the surface. Membranes

Glossary

Mesh

Microfiber

Microfiltration

Mold

Monofilament

Nanofiltration

Nomex Nominal

265

are either petrol based, cellulosic, or made from sintered ceramics or metals. Cartridge and crossflow filters are the only microfiltration devices currently able to utilize membranes. Media configuration used in the construction of filter bags in which either monofilament or polyfilament fibers are woven together to create the filter. Media type used in the construction of filter bags. The microfiber material is usually either polypropylene or polyester. The removal of particulate matter between 0.1 μm and 10 μm. This text focuses on technologies in this range, even when specific devices or applications may call for a pore size rating of higher than 10 μm. There is an overlap between some technologies and what is considered micro and macrofiltration. Contaminant common to many beverages. Often introduced via packaging or facilities water. A single strand of media woven to create the final filter matrix. Refers to bag filter construction. Filtration stage between ultrafiltration and reverse osmosis. Removes sugars as well as some acids and salts. Media commonly used in bag filters. Removal that cannot be guaranteed. Nominal pore size ratings are often given as a guideline; however, particles smaller than the pore size can be allowed to pass. Bag, lenticular, and sheet filters are generally always considered nominal and most non-membrane cartridge filters should also be considered nominal, but this is not always the case.

266 Normal Flow Nylon

O-Ring

Particulate Perlite Permeate Plate and Frame

Pleat

Plugging Point-of-Use

Polyester

Polyether Sulfone

Glossary Filtration process in which fluid flow is perpendicular to the surface of the filter. Material used for non-membrane bag filters and as a membrane in cartridge filters. It can also be added to the matrix of some lenticular and sheet filters for increased strength and filter performance. Sealing mechanism used for both filtration devices and filtration equipment. Constructed of a pliable, chemically and thermally stable polymer. Term for nonmicrobial contaminant. Often the subject of filtration Alternative to diatomaceous earth. The portion of fluid that passes through the filter. Filtration equipment for use with sheet filters. Plates hold the sheets while the frame holds the plates. Fold of some cartridge filter media. Consists of the pleat peak (high point) and the pleat valley (low point). All of the pleats together are referred to as the “pleat pack.” The blocking of a filter by components being removed from the fluid stream. Filtration located directly at the final location of usage as opposed to at a central supply tank or unloading area. Typically associated with gas or air filtration but also relevant to some flavor and chemical additions as well as some CIP applications. Material that is used as a filter bag media and also as a support layer for some pleated cartridge filters. Membrane material that can have an asymmetric pore structure and has very good chemical compatibility. Common membrane used for crossflow systems in addition to cartridges.

Glossary Polyfilament

267

Many strands of media are woven together to create one strand, which is then woven into the final filter matrix. Refers to bag filter media construction. Polypropylene Very versatile material. Used as the filter media for many depth filtration cartridges. Used as a bag filter media. Polypropylene can also be molded and is used for many filter components such as cages, end caps, and support materials. It may be added to the matrix of some sheet and lenticular filters for increased strength and filter performance. It can be both pleated and wrapped when used in cartridge filters. Polytetrafluoroethylene, Membrane material that is most commonly PTFE (Teflon) used for gas, air, and vent filtration applications. Polyvinylidene Naturally hydrophobic membrane material Fluoride, PVDF that is often turned hydrophilic and is heavily used in the beverage industry. Pore The openings in the surface and throughout the depth of a membrane filter. Nonmembrane filters may have a pore size rating, but this is misleading as they do not have an actual “pore” structure. Prefiltration Filtration stage with the specific purpose of protecting a subsequent downstream filtration, such as a more retentive and/or expensive final filtration or RO filter. Pressure Hold Membrane integrity test in which the upstream side of a filter is pressurized, gas inlet closed, and the gradual drop in pressure monitored over the test time. Protozoa Potentially harmful group of microorganisms commonly found in surface waters. Cryptosporidium and Giardia are the most relevant examples. Several filtration guidelines have been adopted in the bottled water industry specifically concerning these organisms.

268 Pulsation

Qualification (Qualified)

Receptacle

Regeneration

Resin Bonded

Retentate Retention Reverse Osmosis

Sanitation Sheet Filter

Sieving Sintering

Glossary Condition of elevated pressure that can lead to filter damage or particulate unloading. Process that many manufacturers put their filters through in which exhaustive studies are performed on such parameters such as retention, extractables, and device tolerances. The machined hole in the housing base plate into which the cartridge filter is inserted. Ability of a filter to be partially or completely restored, typically through cleaning, so that it can be effectively reused. Type of cartridge filter that consists of a hard, but permeable, outer plastic shell filled with filtration media. The portion of fluid that does not pass through the filter or is retained by the filter. The ability to remove a contaminant or component from a fluid stream. Membrane filtration that is capable of removing all components from water including monovalent dissolved salts. Highest degree of liquid filtration possible. The destruction and removal of microorganisms and contaminants. Early form of microfiltration still heavily used within the beverage industry. Requires a plate and frame filter housing to hold the media in place during filtration. Removal mechanism in which exclusion occurs primarily at the filter’s surface. Process used to create metal and ceramic membranes. The primary step involves heating a powder form of the material until the molecules begin to adhere to one another.

Glossary Soft Particle Specification Sterilization

String Wound

Support Layer

Surface Filter

Symmetric

Tangential Flow Filtration (TFF) Track-Etch(ing), (ed)

Trap Filtration

Turbidity

269

See: Deformable. Filter property, such as heat or pressure tolerance, or device dimensions. The complete removal of organics and microbial contaminants. Term often used interchangeably with sanitation, but has a stronger connotation of effectiveness. Crude cartridge filter that employs a thick strand of material wrapped around a central core. These filters are not commonly used in the beverage industry, nor should they be. Can be prone to fiber migration. Nonfiltering layer added to the pleat pack of pleated cartridges to increase stress tolerance. Filter in which removal occurs primarily at the top layer of the filter, facing upstream, opposite the direction of flow. Membrane property describing pore structure that is relatively uniform throughout the depth of the membrane. See: Crossflow. Membrane fabrication technique in which a polymeric film is first exposed to highenergy ions and then exposed to an alkali solution. This process creates a filter with a very tight and uniform pore size range with little deviation. Filtration directly after a diatomaceous earth (or perlite) clarification stage targeted at the removal of fines. Analytical measurement designed for quantifying the rough amounts of particulates and foreign materials present in a liquid stream. This measurement does not relate well to filterability and is often subject to a great degree of unreliability and uncertainty.

270 Ultrafiltration

Unloading

Upstream

Vent Valve Venting

Viscosity

Water Hammer

Wetting

Glossary Filtration in the range of about 0.005 μm to 0.1 μm. Removes viruses, proteins, and most macromolecules. Units are often expressed in terms of Daltons rather than microns. The release of contaminants retained in depth filter media when the media is either ruptured, operated past its recommended differential pressure, subjected to pressure spikes or shocks, or loses its adsorptive potential. The direction from which flow originates. Fluid is upstream of the filter before it passes through the filter. Valve located at the high point in filtration equipment used for air or gas removal. The act of air or gas removal during filtration. Certain products require regular venting in order to effectively operate a filtration process. The ability or resistance of a fluid to flow. A higher value indicates less ability to flow and, subsequently, a more difficult filtration. Shock usually associated with fast closing of valves or poor pump operation that can cause a rapid and violent pressure build-up that can be damaging to filters and filter processes as well as cause particulate unloading in certain filters. The process of flowing water through the filter. Most important with membrane filters, as they may be hydrophobic or hydrophilic and must be completely wetted in order to be integrity tested. Gas and air filters are hydrophobic to prevent undesired wetting.

Glossary Yeast

Zeta Potential

271

Common microorganism used throughout the beverage industry for fermentation. Absolute removal of all strains is at about 0.65 μm. There are a great many different types of yeast. It is a spoilage mechanism and contaminant when undesired. Adsorptive property of certain depth filtration media to attract and retain particles.

Index

A Absolute pressure, 7 “Absolute” rated non-membrane filters, small water bottlers and, 220 Absolute vs. nominal discussion, cartridge filters and, 43–44 Acrylics, in hydrophilic membranes, 39 Activated carbon, 111 Adapter code comparison, for selected manufacturers, 62t Adapters, SDI testing and, 224 Additional gasket seal, 60 Adsorption, 14 Air diffusion, 68 calculating, 96 integrity testing, 92 purpose of, 96 Air filters, sizing of, 165 Air filtration bag filters for, 133 wine industry and, 194–195 Air monitoring, 181 Alarms, differential pressure, 173 Alcoholic beverage industry emerging products in, 233–234 microfiltration used by, 231 miscellaneous considerations related to, 234–235 Alcohol recovery, wineries and, 198 Alfa Laval, 142, 209 Algae, 23–24, 177, 178 Alpha-lactalbumin, 238 Anti-sway plates, 46 Aquafina (PepsiCo), 215 Area, filter, 114 Asahi, 207

Ash content, 115 Asymmetric membranes, 42, 42, 43 Atmospheres (atm), 7 Automatic integrity testers, disadvantages with, 94 Automatic pressure relief lines, 11 Average integral diffusion specification, 93 B Backflushing, 122, 129 Bacteria in beverages, 26 final filtration in breweries and, 210 removal of, recommended membrane pore sizes for, 26t Bag filter housings, manufacturers and suppliers for, 253t Bag filters, 6, 18, 131–140 cost of, 131, 155 filtration format and, 160 flow diagram, 132 honey filtration and, 249 manufacturers and distributors of, 140 manufacturers and suppliers of, 253t media and construction of, 133–135 peppermint and spearmint oil filtration and, 249 sizes of, 131–133, 132t, 167–169 specifications for, 136–137 system operation for, 137–140 cleaning, sanitation, and storage of, 139–140 installation of, 137 operation of, 137–139 uses for, 131

273

274

Index

Ball valves, 172 Bartles and Jaymes wine coolers, 198 Basic design lenticular filters, 124, 125 Basket strainers, 31 Batch size, 166 Beer beta glucanase enzyme and, 91 clarification of, 211 flavored, 212 organic contaminants and, 27 pasteurization of, 207 Beer industry, 207–213 beer and yeast recovery from bottoms by, 212 clarification and trap filtration used in, 208 crossflow clarification, 208–209 CO2 filtration and, 210–212 final filtration and, 210 flavored beer, 212 miscellaneous considerations in, 212–213 prefiltration and, 209–210 wort filtration and, 212 Beer “lace,” 213 Begerow, 129, 130 Bench testing, system sizing and, 163 Bentonite, 30 Beringer Blass Wine Estates, 187 Beta glucanase enzyme, 91 Beta-Glucans beer filtration and, 27, 213 in wine, 203 Beta-lactoglobulin, 238 Beta ratios, 16–17, 44 Beverage contaminants, 19–31 algae, 23–24 bacteria, 26 bentonite, 30 carbon fines, 29 diatomaceous earth, 28–29 microorganisms, 20–26 mold and fungi, 22–23 perlite, 30 plant-based organics, 27 proteins, 27–28 protozoa, 21–22 silicates and carbonates, 31

silt and sand, 31 yeast, 24–25 Beverage crossflow systems, manufacturers and suppliers for, 254t Beverage manufacturing, role of microfiltration in, 3 Biofilms, 31 cleaning and, 84 removal and prevention of, 175 Biopharmaceutical market, microfiltration technology and, 3–4 “Blanket media” cartridges, 49 Blue-green algae, 23 Booster pump, plate and frame filter system, 117 Botrytis cinerea, 203 Bottle blower application, wine industry and use of, 195 Bottled water, protozoa in, 21–22 Bottled water industry, 215–230 clarification used by, 216–219 crossflow (tangential flow) systems, 218–219 Cryptosporidium and Giardia control by, 220–221 final filtration and, 220 growth in, 187 ozonation and, 221–222 prefiltration and, 219 process testing: silt density index, 222–227 calculating silt density index, 226–22 interpreting SDI results, 227 SDI test equipment, 224 SDI test procedure, 225–226 reverse osmosis and distilled water, 227 specialty products in, 222 spring or mineral and purified bottled water process flow diagram, 216 standards in, 227–230 International Bottled Water Association, 228–230 NSF International, 228 youth of, 215–216 Bottle washing, 177–178 Bottling facilities, wine industry, longrange transport and, 199–200

Index Bottling lines, sheet system operation and, 119–120 Bottom end cap, in filter cartridges, 58, 58 Brettanomyces, 24, 25 character or off-flavors, wines and, 194 removal of, from wines, 193 Breweries final membrane filter sizing in, 164 flavored beers produced by, 212 inverted filter housings and, 45 microfiltration use by, 5, 207 Brochures, for cartridges, 63 Bromate formation (BRO3), ozone and, 222 Bromide (Br), 222 Bronco Wine Company, 187, 192 Bubble point, 68 calculating, 95, 95 integrity testing, 92 failures in, 102 manual testing of, 94–96 Bucher Vaslin isobaric units, 192 wine crossflow systems, 191 Bulk filtration, of gases, 5 Buna-N, 235 Butterfly valves, 172 Bypass, 44 C Caffeinated water, 222 Caking mechanisms, particle types and, 13, 13 California wineries clarification applications used by, 188 long-range transport issues and, 199 CA membranes. See Cellulose acetate membranes Candle filters, DE bleed-through and, 208 Capsule devices, wine industry and use of, 195 Capture mechanisms, 14 Carbohydrates, 27 Carbon, 114 Carbonated products carbonated waters, 222 centrifugal pumps and, 11–12 wine products, 204

275

Carbonates cleaning and, 89 silicates and, 31 Carbonation, breweries, CO2 and, 210–212 Carbon dioxide (CO2), 5, 181, 195 breweries and use of, 210–212 soft drink filtration and, 242 Carbon filtration, alcoholic beverages and, 231 Carbon fines, 29, 178 Carbon-impregnated filters, 111 Carbon-impregnated media, filtration of, 235 Carbon towers, 217–218 Cartridge failure modes, common, 107–109 Cartridge filter housings manufacturers and suppliers for, 252t sizing of, 160–165 Cartridge filters, 18, 37–109 A/B differential pressure vs. flow rate curve, 65 A/B removal efficiency at selected pore size rating, 65t absolute vs. nominal discussion about, 43–44 attributes of, 19t codes and styles of, 62–63 compliance and, 67 depth and non-membrane media, 46–49 depth vs. surface, 41–42 disposable filter devices, 69–70 distributors and re-sellers of, 71–72 filtration area in, 67 housings for, 44–46 hydrophobicity and hydrophilization and, 37–39 installation of, 72–77 integrity testing for, 92–104 integrity test specifications for, 68 manufacturers and suppliers of, 70–71, 251t media, materials of construction, construction, and dimensions of, 66–67 membrane media, 49–57 non-media components, 57–62, 58

276

Index

Cartridge filters (cont.) operation, 72, 77–83 maintenance, 82–83 monitoring differential pressure, 80–81 shut-down, 81–82 start-up, 78 venting, 78–80 pleated vs. wrapped, 39–40 specifications for, 63–69 standard, 37 sterilization and cleaning of, 68 symmetry and graded density, 42–43 Cartridge prefilters, 157 Cartridges length of, 67 manufacturing of, 59 Cassette TFF devices, 147, 147–148 Cast membranes, 49 Catalogues, for cartridges, 63 Caustic processing, cleaning regimen and, 184–185 Celanese, 47 Cellulose, 27, 47 in hydrophilic membranes, 39 in sheet and lenticular filters, 111 Cellulose acetate, 47 Cellulose acetate membranes, 54–55 Cellulose esters, 47 Cellulosic filter media, 47 Centralized gas filtration systems, 181–182 Centrifugal pumps carbonated products and, 11–12 pressure drop requirement and, 171 Centrifuge/crossflow filtration systems, 142 Centrifuges, stopping fermentation and, 200–201 Ceramic crossflow filters dairies and use of, 238–239 wine crossflow clarification systems and, 191 Ceramic crossflow systems, 5 Ceramic membranes, 49, 144–145 caustic processing and, 185 fermentation lees wine recovery and, 201

Ceramic TFF systems, flow paths of, 145 CFS. See Cluster Filtration System (Pall) CFUs. See Colony Forming Units Challenge tests, for cartridges, 64 Chardonnay, 204 Check valves, 172 Cheese-making, milk crossflowing and, 238 Cheese production, lactobacillus and, 26 Chemical compatibility, 108 crossflow systems and testing of, 151 sheet system operation and, 122 vinegar filtration and, 249 Chemical sanitation, of cartridges, 90 Chill haze in beer, 28 removing, 231 Chocolate syrup, relative viscosity of, 132t CIP process. See Clean-in-place process Citric acid, 91 Citrus juices, de-bittering of, 245 Clam juices, filtration of, 249 Clarification, 154–156 of beer, 211 bottled water industry and use of, 216–219 brewing industry and use of, 208 crossflow systems and, 141, 142 juice industry and use of, 245–246 maximum flow rates for, 121t stages in, 155, 156 filter requirements and, 163 prefiltration stage preceded by, in some filter trains, 155 sugar, soft drinks and, 241 of vinegar, 248–249 wine industry and use of, 188–193 Clarification filter grade, 114 Clarification filters, 46, 106 Clarity, filtration and, 120 Cleaning of alcoholic beverage filters, 234–235 beverage cleaning process, steps in, 85 bottle washing, 177–178 of cartridge filters, 68, 83–89 inorganics, 89 organics, 88–89

Index purpose of, 83–84 rigid particles, 86–88 of crossflow systems, 151–152 of filter bags, 139–140 filter plugging cycle and, 81 of filtration systems, 175 of lenticular cartridges, 127–129 sheet system operation and, 121–123 specialized treatments in, 91–92 of valves, 172 Cleaning chemicals, filtration and, 184 Clean-in-place, 31 design, 175 solutions and chemicals, 184–185 Clean-in-place process, bottled water sanitation and, 230 Clean-in-place water, separate filtration process for, 179 Clean water flow rates, cartridges and, 64 Cloudifiers, 233 juices and, 246 sports drinks and, 242 Cluster beer filtration system, 45 Cluster Filtration System (Pall), 93 Coarse filter grades, 113 Coarse filtration, maximum flow rates for, 121t Coating, membrane surface treatment via, 38–39, 39 Coca-Cola, 215 Cocktail mixtures, 233 Codes, cartridge, 62–63, 62t Coffee beverages, specialty, 248 Cold water flushes, of alcoholic beverage filters, 235 Colloidal materials, removal of, 88, 89, 231 Colonies, 31 Colony Forming Units, 180 Compatibility testing, CIP solutions and, 184 Complete blocking, 14, 15 Compliance, FDA CFR 21, 67 Composite membrane media, 56–57 Compressed gases, improperly regulated, 108 Compressor filters, 182 Constellation Brands, 187, 192

277

Construction fields, cartridge filters and, 66–67 Corn oil, relative viscosity of, 132t Corn syrup, relative viscosity of, 132t Crossflow clarification brewing industry and use of, 208–209 juice industry and use of, 245–246 Crossflow feed limits, of 20 and 30%, yield comparison between, 150t Crossflow filtration stage, process flow of, 149 Crossflow systems, 141–152, 142 crossflow formats and media, 143–148 cassette format, 147, 147–148 ceramic membranes, 144–145, 145 hollow fiber membranes, 145–146, 146 sintered metal membranes, 147 spiral-wound membranes, 146–147 high-fouling process streams and, 141 stop fermentation and, 201 system operation, 148–152 cleaning, sanitation, and storage, 151–152 installation, 148 operation, 149–151 system size selection, 169–170 Crossflow (tangential flow) clarification, wine industry and use of, 190–193 Crossflow (tangential flow) systems, bottled water industry and use of, 218–219 Crosslinking, membrane surface treatment via, 38–39, 39 Crush end-cap seal, 60 Crush seal, 59 Crush seal cartridges, over-tightening of, 74, 74 Cryptosporidium, 21–22, 22 bottled water industry safeguards against, 215, 220–221, 228 filters for removal of, 177–178 sizes of, 22t Cuno, 4, 44, 53, 70 adaptor codes, 62t sheet and lenticular filters manufactured by, 129 Cyanobacteria, 23

278

Index

D Dairy industry, 237–239 dairy tank vent filtration, 239 microfiltration in conjunction with ultrafiltration and reverse osmosis, 238 for increased shelf life, 237–238 specialty applications in, 238–239 Dairy tank vent filtration, 239 Dasani (Coca-Cola), 215 Datasheets, for cartridges, 63 DE. See Diatomaceous earth DE filtration beer and improving performance of, 213 wineries and, 204 Dekkera (Brettanomyces), 24, 25 Della Toffola, 130, 192 Depth filter media, 18, 18 Depth filters, 17, 41 bottled water industry and use of, 216–217 clarification and use of, 154 cost of, 155 maximum differential pressure and, 66 retention and, 44 rigid particles, organic colloids and, 84 Depth media clarification stage and, 155 non-membrane media and, 46–49 SEM characteristic of, 18 Depth removal, membrane removal vs., 41 Depth vs. surface, in cartridge filters, 41–42 DE trap clarification filters, wine industry and use of, 189 Diaphragm pumps, 11 Diaphragm valves, 172 Diatomaceous earth, 111 common filtration grade, size distribution for, 29t regulation of, 208–209 usage and disposal issues with, 141–142 uses for, 28–29 Diatomite, 28

Differential pressure alarms, 173 bag filter service life and, 138–139, 139 flow rate and, 8 lenticular system, 127 manufacturer’s maximum recommended specification for, 104 microfiltration process and monitoring of, 80–81, 81 monitoring of, during cleaning and sanitation, 84–85 plant specification and, 104, 105 sheet system operation and monitoring of, 120–121 Diffusion, 14 Diffusion specification, example of, 99–100 Dirt-holding capacity, 41 of filter sheet, 116–117 Disposable filter devices, 69, 69–70, 182 Distilled water microfiltration and, 215 reverse osmosis and, 227 Distilleries, particle filtration and, 231–232 Distributors, filter, 71–72 Diversion plates, 119 Documentation, for cartridges, 63–67 DOE cartridges. See Double open ended cartridges Domnick Hunter, 4, 53, 70 adaptor codes, 62t filter bags, 140 sheet and lenticular filters, 129 Double-layer nylon membranes, 51 Double open ended cartridges installation of, 72–74, 73 over-tightening of, 108 Downstream support layers, membrane pleat pack and, 60 Downstream valves, false positive integrity tests and, 102 Dreyfus, Camille, 47 Dreyfus, Henri, 47 Drip pan, plate and frame filter system, 117 Driving forces, 6–7

Index Dry ice, wine filterability and, 205 Dual-layered membranes, 57, 67 Dual o-rings, 74 DuPont, 54 E E. coli bottled water safeguards against, 215, 229 membrane filters and testing of, 180–181 E. & J. Gallo Winery, 187, 188 crossflow clarification and, 192 Ecco Domani brand, 199 Earthquakes, drops in water filterability and, 223 Edge lamination, 59 EDS analysis. See Energy dispersive x-ray spectroscopy analysis Electron scanning microscope, 33 End caps cartridge codes and styles for, 62 in cartridge filters, 58, 58–59 types of, 59 End cap-to-pleat pack bonding, 59 Energy dispersive x-ray spectroscopy analysis, 33–34 sample, 34 EPDM, 61, 235 Equations beta ratio calculation, 16–17 filter permeability calculation, 10 flow, 10 flow rate in sizing filtration train, 162 pressure spikes and rapid closing of valve, 12 silt density index calculations, 226–227 sizing calculations, 167 sizing flow rate of filtration train, 161–162 tangential flow filtration permeability, 10 upstream pressure determination, 8 Erosion (natural), drops in water filterability and, 223 ESM. See Electron scanning microscope Eukaryotes, 21 Eukaryotic algae, forms of, 23

279

European breweries, crossflow microfiltration systems in, 207 European wineries final filtration stages used by, 193 microfiltration use and, 187, 188 Extractables lenticular cartridges and, 127 levels of, 114–115 F Face velocity, 10 sizing methods and, 161 False positive integrity tests, 102 Federal Drug Administration (FDA), 220 CFR 21 compliance, 67 CFR 21 guidelines, 34–36 relating to filters and filter components, 35t subsections in, 35t Feed flow rate, sizing methods and, 161 Feed pumps, design and selection of, 170–171 Felt filter bags, 133, 134 components of, 134–135 Felt filter bags, scrim and, 135 Fermentation stopping, wine industry and, 200–201 wine industry and, 198 Fermentation lees, wine recovery from, 201 Fermentation tank vent filters, sizing of, 165 Fiberglass fibers, filters made of, 48 Fibrafix TX-R, 188 Filler bowl counter-pressure, wine industry and use of, 195 Fillers, CIP design and, 175 Filterability (fining) index, wine industry and, 201–202 Filter bags cartridge failures and opening of, 108–109 common media for, chemical compatibilities of, 135t cross-section diagram of sealing area, 138 outer surface treatments for, 136 scrim vs. self-supported, 135–136

280

Index

Filter bags (cont.) sewn vs. welded, 135–136 specifications for, 136–137 uses for, 134 Filter change-out, 104–107 differential pressure reaches manufacturer’s specification, 104 differential pressure reaches plant specification, 104, 105 filter integrity failure, 104, 107 one-time filter usage, 104, 106–107 product run fails to meet minimum throughput required, 104, 105 seasonal processing, 104, 106 time-in-service guidelines, 104, 105–106 Filter cleaning, with water, 178–179 Filter efficiency, beta ratio and, 16–17 Filter flow terminology, 7 Filter grades, 113 flow rate per filter surface area for, 126 Filter housings cartridge, 44–46, 45 venting of, 85 Filter integrity failure, 104, 107 Filter media, 66 Filter modules, 123 Filter permeability, calculating, 10 Filter plates construction of, 117–118 design of, 117 Filter-related failures, troubleshooting, 102 Filters ash content, 115 compliance issues within beverage industry and, 36 dimensions of, 114 disposable, 69, 69–70 extractables levels for, 114–115 FDA CFR 21 sections relating to, 35t flow rate for, 115 maximum differential pressure for, 115 maximum operating temperature for, 115 media specifications for, 113–116 nominal pore size rating for, 115–116

pressure differential across, 7 retention characteristics of, 115 rinse volume for, 115 size and area of, 114 Filter service life, extending, 6 Filter sheets, 116 Filter stacks, 123 Filter structure, general, 18–19 Filtrate, crossflow filtration systems and, 149, 149 Filtration. See also Microfiltration basic fluid dynamics of, 6–11 bottle washing, 177–178 determining format of, 159–160 of make-up water, soft and sports drink industries and, 241 various mechanisms of, 5 Filtration area, for cartridge filters, 67 Filtration cycle, differential pressure and, 81 Filtration principles, 6–17 Filtration skid additions, wine industry and use of, 195 Filtration skid feed, 11 Filtration skids, automated, 173 Filtration spectrum, of common materials, 21 Filtration system selection and design, 153–176 for auxiliary equipment, 170–173 feed pumps, 170–171 instrumentation, 172–173 surge tanks, 171–172 valves, 172 CIP design, 175 filtration stages, 154–159 clarification, 154–156 final filtration, 157–158 prefiltration, 156–157 format of filtration, 159–160 key factors in, 153 parallel filter skids, 173–174 system manufacturers and suppliers, 175–176 system sizing, 160–170 bag filters, 167–169 cartridge, 160–165

Index crossflow systems, 169–170 lenticular, 166–167 sheet (plate and frame), 165–166 Filtration train, sizing flow rate of, 161–162 Filtrox, 130 sheet and lenticular filters manufactured by, 129 Final bottling filtration train, sizing, 163–164 Final filtration, 156, 157–158, 164 bottled water industry and, 220–221 breweries and, 210 of peppermint and spearmint oils, 249 redundant, 158, 158 two identical stages of, 158 wine industry and, 193–194 Fine filtration grade, 114 Flat end, single open-ended cartridges, 76 Flat sheet geometry, 50 Flavored beers, 212 Flavored beverages alcoholic, filtration of, 233, 234 drinks, 231 waters, 222 Flavorings, 247–248 in wine coolers, 197 Flowmeters, 173 Flow rate, 9–11, 115 differential pressure and, 8 pore size and, 10 Flow rate curve, bag filter sizing and, 168–169 Flow rate values, sheet system operation and, 120 Fluid dynamics, of filtration, 6–11 Fluid inlet and outlet, plate and frame filter system, 117 Fluid pulsation, 11 Fluids, defined, 6 Fluid viscosity, 9 Flux, 9–11 Flux units, expressions of, 10 Foam stabilizers, beer “lace” and, 213 Forward differential pressure, 65–66 Forward diffusion integrity testing, 92 Forward diffusion tests, 94, 96–98

281

Forward flow, reverse flow vs., in cleaning of rigid particles, 87, 87 Fouling index, 222 Fourier Transform Infrared analysis, 32 Frame filters, sizing, 165–166 FTIR analysis. See Fourier Transform Infrared analysis Fungi, in beverages, 22–23 Fusel oils, 235 G Gas bubbles, within housing domes, 78– 79, 79 Gases, 6 mass of, 8 Gas filters breweries and use of, 211–212 sizing of, 165 Gas filtration, 181–182 soft and sports drink industries and, 241 wine industry and, 194–195, 195t Gaskets, 61, 61–62, 66, 113, 235 in filter cartridges, 58 housing components sealed with, 46 integrity testing of, 92 Gauge pressure, 7 GEA-Westfalia, 209 General Electric, Osmonics Division, 70 Giardia, 21–22, 22 bottled water industry safeguards against, 215, 220–221, 228 filters for removal of, 177–178 sizes of, 22t Glass fibers, filters made of, 48 Globalization, of wine industry, 199–200 Glucans, 27 beer microfiltration and, 213 Grade, filter, 113, 114 Graded density cartridge filters and, 42–43 construction, 40 Gradual plugging, 14, 15 Grafting, membrane surface treatment via, 38–39, 39 Grape-based alcohol, 198 Grapes, rot and, 203 Gravitational settling, 14

282

Index

G3 Enterprises (Gallo), 188 Gusmer Enterprises, 129 H HACCP plan, 230 Hand-wheel, plate and frame filter system, 117 Hard particles, 13, 13, 15 Hardware-related filter failures, 102 Hazes flavorings and, 247 formation of, 121 removal of, 231, 232, 234 Hemicellulase enzymes, 91 Hollow fiber crossflow systems, 146 Hollow fiber geometry, 50 Hollow fiber membranes, 145–146 wine crossflow clarification systems and, 191 Honey filtration of, 249 relative viscosity of, 132t Hot chemicals, cleaning organics and, 88–89 Hot reverse flushing, 85 Hot water cartridge storage and, 91 lenticular cartridge sanitation and, 128 Hot water flushing, of alcoholic beverage filters, 235 Hot water sanitation of filter housings and cartridges, 90 of filter sheets, 122 Housing components, sealing of, 46 Housing domes, 77 gas bubbles within, 78–79, 79 Housing pressure drop, bag filter sizing and, 167–168 Housings bag filter, 132 cartridge filter, 44–46 inverted, 44, 45, 45–46 lenticular system, 127 maintenance of, 82–83 multi-round, integrity testing and, 92–93 o-ring sizes and, 74 unload filter, venting of, 217

Housing viscosity corrections, bag filter sizing and, 169 Hydrophilic membranes, 37–39 water beaded up on, 38 Hydrophilization, cartridge filters and, 37–39 Hydrophobic filters, 37–39 Hydrophobicity, cartridge filters and, 37–39 Hydrophobic membranes, 51 cold water in reverse flow and wetting of, 101–102 using, 101 water beaded up on, 38 wetting and integrity testing of, 100–102 I IBWA. See International Bottled Water Association Ice build-up, on filter, 31 Ideal Gas Law, 103 Incoming plant water supplies, filtration systems for, 178 Inertial impact, 14 Inlet, 7, 7 In-line filter housings, 44, 45, 45 Inner support cages, in filter cartridges, 57, 58, 59, 60 Inorganic contaminants, in beverages, 28–31 Inorganics cleaning, 89 filters and, 84 Instruction manuals, for cartridges, 63 Instrumentation, design and selection of, 172–173 Integrity testing, 44 of membrane filter cartridges, 92–104 bubble point tests, 94–96 forward diffusion tests, 96–98 pressure hold integrity tests, 98–100 principles related to, 93–94 troubleshooting failures, 102–104 wetting and: for hydrophobic membranes, 100–102 Integrity test (IT) failures, troubleshooting, 102–104

Index Integrity test (IT) specifications, for cartridge filters, 68 Interception, 14 International Bottled Water Association, 215, 220 Model Code of, 227, 228–230 Intrusion pressure, 37 Inverted housings, 44, 45, 45–46 IPA. See Isopropyl alcohol Isobaric units, 192 Isopropyl alcohol, 38 J Japanese beer market, pre-bottling membrane filtrations and, 207 Juice industry, 245–246 Jumbo format cartridge (Sartorius), 62–63 K Kieselguhr, 28, 141, 207 Kirin, 207 Koch Membrane, 246 wine crossflow systems, 191 L Lab-scale TFF cassette, 147 “Lace,” beer, 213 Lactobacillus species, 26 Lactoferrin, 238 Lactose, demineralization of, 238 Lamination, 50 Latin American breweries, cartridge filtration used in, 207 Lees, fermentation, wine recovery and, 201 Length, cartridge, 67 Lenticular cartridges, non-media components in, 114 Lenticular disk, area calculation for, 128, 128 Lenticular filter housings manufacturers and suppliers for, 252t sizing, 166–167 Lenticular filters, 18, 123–130 brewing industry and use of, 207, 208 clarification in wineries and, 190 composition of, 111 cost of, 155

283

design benefits of sheet filters vs., 123–124 extractables and, 114–115 filter grades, 113 filtration format and, 159 filtration media and, 111–116 manufacturers and distributors of, 129–130 manufacturers and suppliers of, 252t particle filtration of spirits and, 232 in round disk formats, 112 types of, 124 Lenticular system operation, 126–129 cleaning, sanitation, and storage, 127–129 installation, 126–127 operation, 127 Lignin, 27 Liquid filters, hydrophobicity of, 37–38 Locking tab cartridge end cap design, 75 Log reduction values, 94 Low-fouling process stream, sizing of, 162 LRVs. See Log reduction values M Maintenance, of filter housing, 82–83 Malt-based wine coolers, 196–197 Malt beverages, low alcohol, 233 Manufacturers of bag filter housings, 253t of bag filters, 253t of beverage crossflow systems, 254t of cartridge and lenticular filter housings, 252t of cartridge filters, 251t of filters, 70–71 of filtration systems, 175–176 of plate and frame filter housings, 253t of sheet and lenticular filters, 252t of wine crossflow systems, 192 Marksmen filter line (Pall), 133 Maximum differential pressure filters, 115 Maximum flow rates, 120 typical, 121t Maximum operating temperature and pressure, cartridges and, 64–66

284

Index

Mayonnaise, relative viscosity of, 132t mbar, 7 Media, in filter construction, 113–114. See also Membrane media Media blow-out, reducing, 125 Media configuration, filter bags, 136 Media specifications, 113–116 Membrane blockage, avoiding, 204 Membrane cartridge filters, pleated, 40 Membrane crossflow technology, 15 Membrane-end cap bond, 59 Membrane filter cartridges, 6 integrity testing of, 92–104 Membrane filter plugging, 14–15, 15 Membrane filters, 18–19 cost of, 155 retention and, 44 Membrane media, 49–57 cellulose acetate, 54–55 composite, 56–57 manufacture of, 50 nylon, 50–51 polyether sulfone, 52–54 polytetrafluoroethylene, 54 polyvinylidene fluoride, 51–52 SEM characteristic of, 19 sintered ceramic and metal membranes, 55 track-etched membranes, 55–56 types of, 49 Membrane plugging, plant-based organics and, 27 Membrane removal, depth removal vs., 41 Membrane surface treatment techniques, 38–39, 39 Mesh filter bags, 133, 134 Mesh screens, 31 Microbial filtration, spirits industries and use of, 232–233 Microbial testing, of beverages, 180 Micro cracks, 85, 108 Microfiber filter bags, 133 Microfiltration, 5, 19. See also Filtration before and after bulk transport of wine, 200 alcoholic beverage industries and, 231 bottled water industry and, 215 brewing industry and, 207

central role of, in beverage manufacturing, 3 in conjunction with UF and RO for dairy products, 238 formats, 159–160 for increased shelf life of dairy products, 237–238 industrial users of, 4 of juices, 245–246 in the lab, 179–181 purposes of, 5–6 soft and sports drink industries and, 241, 242–243 of vinegar, 248–249 wine industry and, 187, 197, 198 Microfiltration housing, venting, 78–80 Microfiltration systems, capabilities of, 6 Microns, 19 Microorganisms in beverage products or process streams, 20–26 removal of, 5, 88–89 Milk, microfiltration and, 237–238 Millipore, 4, 44, 51, 53, 66, 70 adaptor codes, 62t final filter market share by, 194 Optiseal format, 63 patented dual viscosity end capping process, 58 Vitipore II line, 85 Mineral bottled water process flow diagram, 216 Mineralized waters, 222 Mixed cellulose esters, 47 Mixed drinks, 231 Mobile bottlers, one-time filter usage and, 107 Modular design lenticular filters, 124, 125–126 Module-based crossflow units, 151 Mold, 178 in beverages, 22–23 on disk after filtering wine, 180 final filtration in breweries and removal of, 210 Monofilament, 133, 136 Moplen®, filter plates constructed of, 117 Multifilament, 133

Index Multi-pass nominal depth filtration, stop fermentation and, 200–201 Multi-stage filtration train, fast determination of plugged state in, 82t N Nanofiltration, 5 Needle holes, sewn filter bags and, 136 Nestlé’s Waters Division, 220 NFF systems. See Normal flow filtration systems Nitrogen, 181 Nomex, in filter bags, chemical compatibilities of, 135t Nominal vs. absolute, cartridge filters and, 43–44 Non-alcoholic mixers, 235 Non-locking cartridges, with o-rings, installation of, 76–77 Non-locking dual o-ring end cap design, 77 Non-media components, in filters, 114 Non-membrane media, depth media and, 46–49 Non-membrane pleated surface prefilters, filtering ability of, 41 Non-thermal pasteurization technologies, 245 Normal flow filtration systems, 141, 142 Noryl®, 122 filter plates constructed of, 117–118 NSF International, 220 bottled water industry standards, 227, 228 Nylon, 49 in filter bags, chemical compatibilities of, 135t filter media, 50–51 O Oak aged products, haze formation and, 234 Off-odors, bottled water filters and, 220 Olive oil filtration of, 250 relative viscosity of, 132t One-time filter usage, 104, 106–107

285

Optimum flow rate, 120 Optiseal format (Millipore), 63 Organics cleaning, 88–89 filters and, 84 hot water and/or CIP chemicals and removal of, 88 O-rings, 61, 61–62, 66, 113, 235 degradation of, 108 in filter cartridges, 58 housing components sealed with, 46 integrity testing of, 92 lenticular cartridges, 114 lenticular system, 127 non-locking cartridges with, installation of, 76–77 sheet system operation and, 118 storage of, 90, 91 O-ring seals cartridge, 60 locking tab filters with, 74–75 Outer support cages, in filter cartridges, 57, 58, 59, 60 Outlet, 7, 7 Outlet flow rate, system sizing and, 160 Overall diffusion specification, 97 Overflow piping, wine filtration process and, 202–203 Ozonation, bottled water industry and use of, 215, 220, 221–222 Ozone (O3), 86, 221 P P. diminuta challenge test, 64 Pa. See Pascals Pad filters, 123 Padovan, 130 Pall, 4, 44, 51, 53, 70, 142, 185, 209 adaptor codes, 62t final filter market share by, 194 isobaric units, 192 Marksmen filter line, 133 sheet and lenticular filters manufactured by, 129 wine crossflow systems, 191 Parallel filter skids, benefits with, 173– 174, 174 Particle caking, 15, 15

286

Index

Particle filtration, spirits industries and use of, 231–232 Particle separation, 13–17 filter efficiency and beta ratio, 16–17 membrane filter plugging, 14–15 particle removal mechanisms, 14 particle types, 13 zeta potential, 15–16 Particle sizes comparative conventions for, 20t expression of, 19 Particulate removal, depth vs. surface, 41–42 Particulate unloading, manufacturer’s specification and, 104 Pascals, 7 Pasteurization of beer, 207 of dairy products, microfiltration and, 237–238 of juice products, 245 wine industry and, 197 PD pumps. See Positive displacement pumps Pectinase, 91 Pectinase additions, 27 Pectinase enzymes, juices and addition of, 246 Pectins, 27 Peppermint oils, filtering of, 249 PepsiCo, 215 Peracetic acid, nylon membranes and, 51 Peristaltic pumps, 11 Perlite, 30, 30, 111, 114 Permeate, crossflow filtration systems and, 149, 149 Peroxyacetic acid, cartridge storage and, 90, 91 PES. See Polyether sulfone Petcock valves, 172 pH adjustments, SDI testing and, 224 Pilot scale testing, system sizing and, 163 Piping, CIP design and, 175 Plant-based organics, in beverages, 27 Plate and frame filter holders, 117 manufacture of, 129–130 Plate and frame filter housings, 116, 117 manufacturers and suppliers for, 253t

Plate and frame filters brewing industry and use of, 207, 208 flow diagram of, 118 Plate filters, sizing, 165–166 Pleated, depth filters, 42 Pleated cartridge filters, wrapped cartridge filters vs., 39–40 Pleated filters, surface area of, 67 Pleated filter support layers, 60–61 in filter cartridges, 58 Pleated membranes, as surface filters, 41 Pleated polypropylene prefilters, 41 Pleated surface-style prefilters bottled water industry and use of, 219 breweries and use of, 210 Pleat-end cap bond stress, 107–108 Pleating process, 50 Pleat pack, 40 Pleat pack sheer, filter failure and, 109 Plugged stage, in multi-stage filtration train, fast determination of, 82t Plugging carbon towers and, 217–218 membrane filter and, 14–15, 15 redundant membranes and, 158 Plugging component analysis, 31–34, 91 energy dispersive x-ray spectroscopy, 32, 33–34 filter format choices and, 159 final filtration in wine industry and, 194 Fourier Transform Infrared, 32–33 scanning electron microscopy, 32, 33 Point-of-use gas filtration systems, 5, 181, 182 Polishing-grade filter, 113 Polyamides, in hydrophilic membranes, 39 Polycarbonate, track-etched membranes and, 56 Polyester fibers, 48 in filter bags, chemical compatibilities of, 135t filter support layers and, 61 in hydrophilic membranes, 39 Polyether sulfone, 49 filters, 43, 52–54 filtration area and, 67

Index membranes final filtration in wine industry and, 194 hydrophobic, 39 SEM image of, 53 Polyethylene cartridges, 48 in hydrophobic membranes, 39 Polypropylene, 113, 114 in filter bags, chemical compatibilities of, 135t filters, 47–48 filter support layers and, 61 in hydrophobic membranes, 39 ozone and, 221 sealing mechanisms and use of, 60 Polytetrafluoroethylene, 49, 235 chemical composition of, 54 in hydrophobic membranes, 39 membranes, 54 Polyvinylidene fluoride, 49 chemical composition of, 52 filter media, 51–52 filtration area and, 67 in hydrophobic membranes, 39 membranes of, final filtration in wine industry and, 194 Pore blockage, 15, 15 Pore size for bottled water prefilters, 219 brewery final filtration and, 210 crossflow systems and, 143–144 flow rate and, 10 microfiltration and, 180 prefiltration stage and, 157 vent filtration and, 183 Pore size rating for bottled water, 215, 217 dairy products and, 238 for filter bags, 136 microbial filtration of spirits and, 232–233 nominal, 115–116 peppermint and spearmint oils and, 249 prefiltration in wine industry and, 193 seafood broths and juices and, 249 selecting, 164 soft drinks and, 241

287

sucrose filtration and, 248 tartrate removal from wine and, 189 Positive displacement pumps, 11, 171 Pounds per square inch, 7 PP filters. See Polypropylene, filters Pre-bottling filtration, wine industry and use of, 189–190 Prefilters, 46, 178 Prefiltration, 156, 156–157, 164 bottled water industry and, 219 breweries and, 209–210 clarification stage preceding, in some filter trains, 155 juice industry and, 245 peppermint and spearmint oils and, 249 reverse osmosis, wineries and use of, 199 wine industry and, 193 Pre-made drinks, 231 Pre-mixed drinks, microbial spoilage and, 232 Pressure, 7 intrusion, 37 maximum operating, cartridges and, 65–66 Pressure differential (pressure drop), 8–9 across filter, 7–9 bag filter sizing and, 167 forward diffusion test and, 96 pressure hold integrity tests and calculation of, 98–100 system, calculating, 168–169 Pressure gauges, 172–173, 224 Pressure hold integrity tests, 92, 94, 98–100 Pressure leaf filters, DE bleed-through and, 189, 208 Pressure regulators, SDI testing and, 224, 225 Pressure spikes rapid closing of valves and, 12 unloading and, 158 Primary fermentations, wine industry and, 198 Product yields, crossflow microfiltration and, 192 ProFI centrifuge/crossflow membrane system, 209

288

Index

Prokarayotic algae, 23 Proteins, in beverages, 27–28 Protozoa, in beverages, 21–22 psi. See Pounds per square inch PTFE. See Polytetrafluoroethylene Pulsation, water hammer and, 12 Pump cavitation, 11 Pump selection, 11–12 Purified bottled water process flow diagram, 216 PVDF. See Polyvinylidene fluoride PVPP, 114 Q Quality certificates, for cartridges, 63 R Ready-to-drink teas, 248 Reclaim wine, 203–204 Recycled containers, cleaning/sanitation of, 177 Redundant final filtration, 158, 158 Removal efficiency test data, example of, 17t Re-sellers, filter, 71–72 Residual sugar, in wine, 200 Resin-bonded cartridges, 47, 48–49 Resins, 111, 114 Retentate, crossflow filtration systems and, 149, 149 Retentate flow, 8 Retention, 41 Retention characteristics filters, 115 Retention ratings, 43, 44 Retention tests, 16 Retentive filters, cost of, 155 Reverse cleaning/flushing, of filters, 84–85 Reverse differential pressure, 66 Reverse flow, forward flow vs., in cleaning of rigid particles, 87, 87 Reverse osmosis, 5 bottled water industry and use of, 215 of dairy products, 238 distilled water and, 227 soft drink industry and, 242 Reverse osmosis prefiltration, wineries and use of, 199 Reverse steaming, of cartridges, 108

Reverse stress failure, 107 Rigid particles cleaning, 86–88 filters and, 84 reverse flow vs. forward flow in cleaning of, 87, 87 Ring type, filter bags, 136 Rinse volume, 115 Rinse water, filters for, 177–178 Rislan®, filter plates constructed of, 117 RO. See Reverse osmosis Robustness, cartridge, 59 Rotary pumps, 11 Rough filter grade, 114 Rough juice clarification, 246 RS. See Residual sugar S SABMiller, 207 Saccharomyces, 24, 25 Saccharomyces cerevisiae, 24, 25, 25 Saccharomyces claims, challenge tests and, 64 Saccharomyces uvarum, 25 Saccharomycetaceae, 24, 25 Sand, 31 Sanitation of cartridge filters, 83 of cartridges, 89–90 of crossflow systems, 151–152 of filter bags, 139–140 of lenticular cartridges, 127–129 of non-standard alcoholic beverages, 234 purpose of, 84 sheet system operation and, 121–123 Sanitation standard operating procedure manual, 230 Sartoflow, 209 Sartorius, 4, 44, 53, 54, 70, 142, 209 adaptor codes, 62t crossflow systems by, 148 final filter market share by, 194 Jumbo format cartridge, 62–63 sheet filters sold by, 129 wine crossflow systems, 192 Sauvignon Blanc, 204 Scanning electron microscopy, 33, 33

Index Schützenberger, Paul, 47 Scrim, self-supported bags vs., 135–136 SDI. See Silt density index Seafood broths, filtration of, 249 Seagram’s wine coolers, 198 Sealing mechanisms for filter bags, 136 for filter cartridges, 58 for housing components, 46 types of, for cartridges, 60, 60 Seasonal processing, 104, 106 Self-supported bags, scrim in felt filter bags vs., 135–136 SEM. See Scanning electron microscopy Service life, of bottled water, 220 Sewn filter bags, welded filter bags vs., 135–136 Sheering forces, 171 Sheet alignment, sheet system operation and, 118–119 Sheet filters, 6, 18, 116–123 clarification in wineries and, 190 composition of, 111 cost of, 155 design benefits with lenticular filters vs., 123–124 dirt-holding capacity for, 116–117 extractables and, 114–115 filter grades, 113 filter sheet sizes, 116 filtration format and, 159 filtration media and, 111–116 manufacturers and distributors of, 129–130 manufacturers and suppliers of, 252t particle filtration of spirits and, 232 Sheet system operation, 118–123 cleaning, sanitation, and storage, 121–123 installation, 118–119 operation, 119–121 Shipping of bulk CO2 to breweries, 211 of wine, 199–200 Shut-down procedure, for filtration equipment, 81–82 Silicates, 31 Silicone, 61

289

Silt and sand, 31 Silt density index, 222 calculating, 226–227 Silt density index testing apparatus, 224 development of, 222–223 equipment for, 224 interpreting results of, 227 procedures for, 225–226 highly plugging streams (procedure 2), 226 standard (procedure 1), 225–226 uses for, 223 Single-layer nylon membranes, 51 Single open-ended cartridges, flat end or gasket, installation of, 76 Single open-ended filters, installation of, 74–76 Single open-ended locking cartridges, 108 Sintered ceramic membranes, 55 Sintered metal membranes, 147 Sintered stainless steel membranes, 55, 179 caustic processing and, 185 Size filter, 114 filter bags, 136 Size exclusion or sieving, 14 Skids automated, 173 parallel filter, 173–174 Skim milk, microfiltration of, 237 “Sniffers,” 177 SOE cartridges. See Single open-ended cartridges Soft drinks, 241–242 Soft particles, 13, 13, 15 South American wineries, membrane filtration used by, 194 Spadoni, 130 Spearmint oils, filtering of, 249 Spiral-wound membranes, 146–147 Spirits industries, 231–235 emerging products, 233–234 microbial filtration, 232–233 miscellaneous considerations, 234–235 particle filtration, 231–232 Sports drinks, 241, 242–243

290

Index

Spring bottled water process flow diagram, 216 Spring cup assemblies, 73, 73 Spring water plants, final membrane filter sizing in, 164 Square-cut filter sheets, 111, 112 SSOP manual. See Sanitation standard operating procedure manual Stack filters, 123 Stainless steel membranes, fermentation lees wine recovery and, 201 Stainless steel sintered metal membrane cartridge filters, 89 Starter cultures, wine industry and use of, 197–198 Starter fermentation, wine industry and, 198 Start-up, cartridge microfiltration train, 78 Steam filters, 177 Steam filtration, 179 Steaming, 108 Steam sanitation, 121–122 Steam sterilization of cartridges, 89 of lenticular cartridges, 128 Sterile filter grades, 113, 114 Sterile filtration, maximum flow rates for, 121t Sterilization of cartridge filters, 68 of cartridges, 89–90 Storage of cartridge filters, 83, 90–91 of crossflow systems, 151–152 of filter bags, 139–140 of lenticular cartridges, 127–129 sheet system operation and, 121–123 Streams of water, splitting, 179 String-wound cartridges, 47, 49 Sucrose filtration, 248 Sugar crystals, 27 Sugar substitute filtration, 248 Sugar syrup clarification, soft and sports drink industries and, 241 Suntory, 207 Suppliers of bag filter housings, 253t of bag filters, 253t

of beverage crossflow systems, 254t of cartridge and lenticular filter housings, 252t of cartridge filters, 251t of filtration systems, 175–176 of plate and frame filter housings, 253t of sheet and lenticular filters, 252t Surface filters, 41 Surface treatment, of filter bags, 136 Surface vs. depth, in cartridge filters, 41–42 Surge suppressors, 12 Surge tanks, design and selection of, 171–172 Symmetric membranes, 42, 42, 43 Symmetry, cartridge filters and, 42–43 System sizing, 160–170 bag filters, 167–169 cartridges, 160–165 crossflow systems, 169–170 lenticular filter housings, 166–167 sheet (plate and frame), 165–166 T Tab filters, o-ring seals and locking of, 74 Tangential flow, 7, 8. See also Crossflow systems Tangential flow filtration, permeability for, 10 Tank blanketing systems, wine filterability and, 204, 205 Tank-blended wine coolers, 196 Tank implosion, 183 Tanks, separate, wineries and, 204 Tank vent filters, sizing of, 165 Tank vent filtration, juice plants and, 245 Tartrate removal, 5 wine industry and, 188–189 during wine stabilization process, 154 Tastes, bottled water filters and, 220 TCA contamination, removing effects of, from wine, 188 Teas, ready-to-drink, 248 Teflon, 54, 61 Teflon cartridge filters, 86 Temperature, maximum operating, cartridges and, 64–66

Index Temperature probes or indicators, 173 Tequila, particulate removal and, 231 TFF. See Tangential flow TFF systems, filters used in, 143 Time-in-service guidelines, 10, 105–106 T-line housings, 44–45, 45 TMCI Padovan, wine crossflow systems, 192 Top end cap adapter, in filter cartridges, 58, 58 Track-etched membranes, 55–56 SEM image of, 56 Trans-membrane pressure, 7, 149 Transport, long-range, wine industry and, 199–200. See also Shipping Trap filtration, 154 Tubular geometry, 50 U UF. See Ultrafiltration Ultipor N66 filters (Pall), 51 Ultrafiltration, 5 dairy industry and, 237, 238 Ultraviolet light bottled water industry and use of, 215, 220 ozone destruction and, 221 Unload filter housings, venting, 217 Unloading, causes of, 158 Upstream pressure, determination of, 8 Upstream support layers, membrane pleat pack and, 60 US Filter, filter bags through, 140 UV. See Ultraviolet light V Validation guides, for cartridges, 63–64 Valves CIP design and, 175 design and selection of, 172 Velo, wine crossflow systems, 191 Vent filters, for dairy tanks, 239 Vent filtration, 183 bag filters for, 133 Venting CIP design and, 175 filter housings, 85 microfiltration housings, 78–80

291

unload filter housings, 217 wine coolers and, 204 Vinegar, clarification and microfiltration of, 248–249 Viscosities, relative, of common product, 131, 132t Viscosity correction factors, for bag filters, 168, 168t Vitipore II line (Millipore), 58, 85 Viton, 61 Vodka, particulate removal and, 231 W Water. See also Bottled water industry for backflushing, 122–123 for filter cleaning and sanitation, 85–86 percent of, in soft drinks, 241 relative viscosity of, 132t viscosity of, 9 in wine coolers, 196 Water filtration, 178–179 Water hammer avoiding, 172 pulsation and, 12 Water hammer spikes, unloading and, 158 Water temperature, reverse flushing of rigid particles and, 87–88 Welded filter bags, sewn filter bags vs., 135–136 Westfalia, 142 Wet filters, steaming, 108 Wet membrane filters, steaming, 89 Wet strength, 114 Whiskey, particulate removal and, 231 Whiskey makers, microfiltration use by, 5 Wine beta glucanase enzyme and, 91 organic contaminants and, 27 processes leading to decreased filterability in, 203 Wine coolers, 196–197 Wine Group, The, 187 Wine industry, 187–205 clarification in, 188–193 crossflow (tangential flow) clarification, 190–193 DE trap filtration, 189

292

Index

Wine industry (cont.) pre-bottling filtration, 189–190 tartrate removal, 188–189 dry ice tip, 205 final filtration, 193–194 gas and air filtration, 194–195 microfiltration and, 187 miscellaneous considerations, 202–204 prefiltration, 193 process testing: filterability index, 201–202 specialty applications, 196–201 alcohol recovery, 198 fermentation lees wine recovery, 201 long-range transport, 199–200 reverse osmosis prefiltration, 199 starter cultures, 197–198 stop fermentation, 200–201 wine coolers, 196–197 Wine recovery, from fermentation lees, 201 Wineries final membrane filter sizing in, 164 microfiltration used by, 5 prefiltration stages in, 190 Wort filtration, 212 Wound filters, as depth filters, 41 Wrapped, depth-style prefilters, breweries and use of, 210

Wrapped cartridge filters, pleated cartridge filters vs., 39–40 Wrapped depth cartridge filters, 40 Wrapped depth polypropylene cartridges, bottled water industry and use of, 219 Wrapped filters, as depth filters, 41 Wrapped media, 46 Y Yeast beer and recovery of, from tank bottoms, 212 in beverages, 24–25 classification of, 25 on disk after filtering wine, 180 mold filters and, 181 removal of final filtration in breweries and, 210 recommended membrane pore sizes for, 26t Yogurt lactobacillus and, 26 relative viscosity of, 132t Y strainers, 31 Z Zeta potential, 15–16, 112 Zygosaccharomyces, 24, 25