Processing plants and equipment

PROCESSING PLANTS AND EQUIPMENT P. BOWLES Kvaerner Process (UK), Ltd., Whiteley, Hants, United Kingdom

I. INTRODUCTION II. INDUSTRIES USING BIOSEPARATIONS A. Pharmaceuticals and Biopharmaceuticals B. Food and Beverage C Waste Water Treatment D. Chemicals and Fuels III. PROCESS-SCALE BIOSEPARATIONS A. Selection Criteria B. Biomass Separation and Primary Recovery C. Product Purification and Final Isolation IV. PROCESS-SCALE CONSIDERATIONS A. Materials of Construction and Mechanical Design B. Automation C. Safety and Biosafety D. Location E. GMP and Validation F. Hygienic Design V. SUMMARY REFERENCES

INTRODUCTION The diversity of industries which involve bioseparations has led to the development of a wide range of techniques and unit operations for the efficient processing of biological materials. The objective of this chapter is to aid the scientist or engineer in selecting a method of bioseparation which will be suited to the particular requirements of the process and the product at a commercial scale of operation. The complexity of biological processes generally requires many stages to produce a final, purified product from a particular composition of raw materials. Although a typical bioprocess consists of two main parts: upstream fermentation and downstream product recovery, it is not unusual to have between 10 and 20 steps in the overall process. This reflects the complex Separation Science and Technology,

Volume 2

Copyright © 2000 by Academic Press. All rights of reproduction in any form reserved.

633

634

p. BOWLES

nature of a typical fermentation broth, which will consist of an aqueous mixture of cells, intracellular or extracellular products, unreacted substrates, and by-products of the fermentation process. From this mixture, the desired product must be isolated at a given purity and specification, and all of the unwanted contaminating materials must be removed. The choice of a bioseparation technique will depend on a number of factors, including the initial location of the product inside or outside the cell as well as the product size, charge, solubility, chemical, or physical affinity to other materials, and so on. Economic factors also come into play, including the value of the product, the regulatory environment in which the product is manufactured, and the balance between the capital cost of the bioseparation equipment and the operating cost of running it. In moving from laboratory- or pilot-scale processing to full-scale manufacture, it can be difficult to scale up certain types of bioseparation equipment easily, for example high g centrifuges are available as bench mounted units (using test tubes), but an equivalent industrial machine with a similar g force is unlikely to be a cost effective solution, even if it is possible to build a suitable unit. It would not be realistic to consider 10 or 100 identical units as a realistic alternative. Compromises are therefore required as a process is commercialized to ensure that it remains technically and economically feasible. In this chapter, guidance is provided concerning the choice of industrial bioseparation equipment which is available, and the issues which must be taken into account when selecting a suitable system to meet both technical and economic objectives.

II. INDUSTRIES USING BIOSEPARATIONS In this section, the wide range of industries using bioseparation techniques are briefly reviewed. A. Pharmaceuticals and Blopharmaceuticals Bioseparations are essential in the manufacture of high-volume, low-value bulk pharmaceuticals and nutraceuticals such as antibiotics and vitamins, where economies of scale are used to ensure commercial competitiveness. At the opposite end of the pharmaceutical product spectrum, genetically engineered therapeutic proteins of extremely high value are produced at very small scale. These different products share a common requirement for a large number of bioseparation stages to isolate the product at an acceptable level of purity. This is particularly important in the pharmaceutical industry where product manufacturing is closely regulated and controlled at all stages to ensure that the medicines produced are effective and safe to use. Product consistency between batches must also be achieved. Manufacturers are obliged to make great efforts to demonstrate these requirements while developing and operating pharmaceutical manufacturing processes, and a later section in this

PROCESSING PLANTS AND EQUIPMENT

635

chapter discusses validation and good manufacturing practice (GMP) in more detail. B. Food and Beverage The majority of food and beverage products are based on biological materials, although not all are produced using fermentation techniques. Dairy products such as yoghurt and cheese; beverages including beer, fruit juices, and v^ine; and single-cell proteins for human or animal consumption all involve bioseparations. As with pharmaceuticals, the food industry is highly regulated and food hygiene considerations are paramount in any manufacturing process. Many food production processes are based on batch rather than continuous manufacturing, with the need to dismantle and clean equipment between batches. Cleaning in place, or CIP, is increasingly important in pharmaceutical and food processes to reduce labor requirements for manual cleaning and to improve levels of cleanliness, in particular, the repeatability of cleaning between different batches. The competitive nature of the food and beverage industry and the need for continued improvements in cost-effective manufacturing have provided an impetus for companies to develop and use new bioseparation techniques at very large scales, for example, freeze-drying in coffee production and continuous centrifugation in brewing. Many food industry innovations are now slowly being adopted by pharmaceutical manufacturers as they also come under increasing pressure to help reduce health care costs. C. Waste Water Treatment Many waste water treatment processes involve biological processes to reduce the concentration of a wide range of contaminants including organic materials, nitrogen, and phosphates. Activated sludge, aerobic and anaerobic digestion processes are used for industrial and municipal effluent treatment. Generally these processes require subsequent bioseparation of the microorganisms from the treated waste water. Examples of commonly used bioseparations include sedimentation, coagulation, and filtration. The scale of operation for such bioseparation processes is considerable, because of the volumes of effluent which are processed and the throughputs required. Proprietary aerobic digesters such as the Deep Shaft process may use centrifugation to recover biomass from the treated effluent for recycle as an inoculum for the digester or to reduce the quantity of water before sending the solid material either to incineration or land fill. D. Chemicals and Fuels There is an increasing trend toward the production of fine and commodity chemicals on a very large scale using fermentation processes followed by downstream bioseparation and purification. This trend is being driven by the

636

p. BOWLES

availability of renewable feedstocks for such processes, with a positive effect on the environment, the possibility of processing at near ambient conditions, compared with the high temperatures and pressures required for chemically synthesised equivalents, and the isolation and commercialization of more efficient microbial strains which can convert raw materials to useful products. Citric acid and vitamin C are examples of very large scale fermentation processes where the subsequent product isolation involves several bioseparations, including filtration, precipitation, evaporation, crystaUization, and drying methods. The scale of operation requires careful choice of equipment which is robust, efficient in separating product from unwanted by-products, and cost effective to be competitive. There are continuing efforts to develop cost-effective processes for fuel alcohol production, although the economics are often dependent on the availability of subsidized feedstocks to compete with traditional fuels derived from oil. The pretreatment and fermentation of such feedstocks, derived from corn, sugar cane, and even municipal waste, yields a dilute aqueous solution of ethanol which must be separated from a complex mixture of waste materials and then concentrated by distillation to remove water. Both batch and continuous production processes have been developed, with the requirement for effective bioseparations during both the pretreatment and ethanol recovery parts of the process. The development of genetically engineered plants offers the prospect of pharmaceutical production from crops as well as improved yields for cereals, vegetables and other agricultural products. The challenge will then be to find suitable bioseparations to enable the efficient isolation of such products.

III. PROCESS-SCALE BIOSEPARATIONS The industries described are diverse but all require bioseparations at various scales. Although not all such manufacturing processes involve fermentation, it is possible to identify common types of bioseparations which are required at particular stages. A typical process will include the following bioseparation steps: Biomass separation of insoluble from soluble material, with either phase being retained depending on the location of the product as intracellular or extracellular material. Examples of unit operations commonly used include centrifugation, filtration, and sedimentation. Primary recovery of the active ingredient from the solid or liquid phase to remove large quantities of unwanted waste materials, which may themselves be processed further. Suitable techniques include solvent extraction, precipitation by chemical or physical changes to the product-containing solution, and ultrafiltration or microfiltration to separate products above a particular size. Work done on combined biomass separation-primary product recovery processes such as expanded-bed adsorption are now being commercialized in the pharmaceutical industry.

PROCESSING PLANTS AND EQUIPMENT

637

Purification of the product and removal of specific impurities by suitable methods, based on the size, charge, or solubility of the materials being separated. Chromatographic techniques are widely used for these types of purification steps, as well as adsorption and crystallization. Final product isolation in a form suitable for further processing into the final dose form of the pharmaceutical, e.g., as a tablet or an injectable solution. Secondary production of this type is sometimes done in a separate facility, with the raw material referred to as the bulk product or, more recently, the active pharmaceutical ingredient. Examples of unit operations at this stage of processing include lyophilization, precipitation, or crystallization followed by solid isolation using filtration and drying techniques. In some cases, the final product must be produced in a sterile form, which introduces additional compHcations when selecting suitable process equipment.

A. Selection Criteria

For all of the bioseparation types last referred to, there are a number of selection criteria to be considered when developing a commercial scale process. [. Location and Nature of Product

The product may be located inside a microorganism (intracellular) or outside in the growth medium (extracellular), or alternatively, the product could be the whole cell material. The nature of the product may be solid or dissolved in the aqueous phase. For example, the product is found in the aqueous phase for a fuel ethanol fermentation, within the cell for a therapeutic protein, while the product is the whole cell in the case of single cell protein. The location of the product influences the choice of a bioseparation method which may favor the efficient recovery of either the solid or liquid phase. The relative difficulty of separating intracellular products from other unwanted insoluble materials may influence the subsequent processing steps once the solids phase has been recovered from the fermentation broth. The cell line from which the product is derived will also play a part in the decision-making process, because bioseparation techniques are likely to be needed depending on whether the fermentation is based on mammalian, microbial, fungal, or yeast cells. Different fermentation broths demonstrate varying characteristics of viscosity, density, particle size, and charge which may enable exploitation of a difference in that characteristic between the phases to be separated. ii. Production Scale, Quality, and Regulatory Environment

In the industries using bioseparations described above, there is a great variation in terms of production scale and product quality between waste water treatment and pharmaceutical production. This will obviously affect the choice of equipment for the process, although in many cases the principle on which bioseparation is based will be common. For example, centrifuga-

638

p. BOWLES

tion techniques are widely used in both industries, ahhough the size, design of the equipment and type of centrifugation method are different. Where small-scale bioseparations have been developed, particularly in the biopharmaceutical industry, there has been a tendency to retain laboratory type equipment even if this results in more labour and capital intensive processing. The reason for this is often to avoid the need for extended periods of process development work with new equipment designs, which might delay the launch of a product where competitors are not far behind. Manufacturers are also wary of adopting new bioseparation techniques for processes if there is any risk that regulators such as the U.S. Food and Drug Administration (FDA) will require more evidence that the equipment is fit for the purpose. This conservative tendency is understandable and may influence the choice of bioseparation equipment for pharmaceutical manufacturing in particular. The required product quality and therefore the value of the product to the consumer will also influence the choice of bioseparation technique. Usually a more efficient or specific bioseparation technique will have higher cost, and so it would obviously be uneconomic to consider a series of chromatography columns to treat a very low value waste water stream to remove some specific impurities. High- and medium-value products such as pharmaceuticals and foods are manufactured within a regulated environment which imposes various legislation and guidelines on manufacturers. These regulatory constraints will also influence the choice of bioseparation equipment. For example, to maintain appropriate levels of cleanliness or sterility for certain products requires specialized equipment at a premium cost. Apart from regulations aimed at product quality, there are also issues concerned with the safe operation of certain processes, for example, where genetically modified or pathogenic microorganisms are being handled. In such cases, the bioseparation process is normally contained; in other words, the potential for release of hazardous material is minimized by various methods. Many bioseparations also involve the use of solvents which must be handled in appropriately designed equipment and facilities with proper explosion protection. Again there are cost implications associated with these types of processes which must be identified at the outset of the development phase. iii. Waste Production and Disposal

In most bioseparations, a waste stream will be generated which has no commercial value. Depending on the nature of this waste stream, it may not be possible to dispose of the material easily without further processing. For example, solvent-rich mother filtrates in antibiotics production are usually distilled to separate the solvent and aqueous phases so that the aqueous phase composition is acceptable for discharge to the sewer and the solvent phase can be reused or incinerated as a smaller volume of material. Biologically hazardous material must always be inactivated before it can be disposed of, or even removed from the production facility. This will normally require a validated heat or chemical deactivation system for aque-

PROCESSING PLANTS AND EQUIPMENT

639

ous materials, or autoclaving for solid materials, to ensure that no live organisms remain after treatment. It is important to identify the relevant environmental and regulatory constraints affecting the disposal of material from bioseparations, so that any additional steps are allowed for within the overall manufacturing process. iv. Cost and Program Issues All process-scale bioseparations will have implications for project cost and program when developing a new process. It is important to consider both the capital costs associated with designing, purchasing, and installing a piece of bioseparation equipment and the operating costs of maintenance; utilities such as electricity, steam, and compressed air; labor; and any raw materials. In most cases, there will be a trade-off between capital and operating cost which may favor a particular type of equipment, depending on the desired initial capital investment and the economics of the process. The complexity of many industrial bioseparation equipment items means that the design and construction can be time consuming, particularly if process development is required to test the equipment on a typical product to see if it will work at the larger scale. It is not unusual to have 6 to 9 month delivery periods for this type of equipment, and even when delivered, it will be necessary to install, commission, and validate it. Therefore, the project program must recognize the long duration for introducing commercial bioseparation equipment. B. Biomass Separation and Primary Recovery In a bioprocess the desired end product may be present as whole cells or intracellular or extracellular material at the end of a fermentation. Therefore in this first bioseparation stage, it may be necessary to recover either the solid or aqueous phase, with as much of the unwanted phase removed as possible, and with minimal loss of the desired material to maximize product yield. After biomass removal has been achieved if appropriate, the main objective of the primary recovery stages is to isolate the product from significant impurities which will generally be in the same phase. At this stage of bioseparation, it is necessary to exploit some difference between the product and impurities such as solubility (in water or an organic solvent), particle size, surface affinity, charge and so on. Since many unit operations are common to cell separation and primary recovery, the possible options for process-scale equipment are discussed in the following. i. Pretreatment Depending on the nature of the product, pretreatment of the feed material may be desirable to improve the separation characteristics. Possible techniques are based on chemical or physical treatment and include thickening, flocculation, and coagulation. A simple heat treatment process where the temperature of the broth is elevated and held for a period of time can reduce

640

p. BOWLES

the broth viscosity by breaking down the microbial structure or promoting cell lysis (breakage). The addition of chemicals including polymeric flocculants or filter aids can increase the particle size prior to the bioseparation stage or reduce the resistance of the solids phase (usually biomass) on the filter medium. An example of the latter pretreatment is in antibiotics manufacture where rotary vacuum filtration of fermentation broths, where the filter is precoated to improve the separation of biomass from the clarified filtrate containing the crude product. ii. Sedimentation

In sedimentation processes, the major driving force for separation is the difference in specific gravity between the liquid and solid phases. This can be enhanced by increasing the g force, by using a centrifuge device, or by increasing the size and density of particles by flocculation. Gravity sedimentation systems are relatively cheap at high throughputs and are well suited to low-labor, continuous operation. Even if sedimentation does not achieve complete phase separation, it can be a useful first stage of bioseparation process to reduce the quantity of material to be handled in subsequent processing stages. Settling time is a key parameter for choice of sedimentation equipment, together with the feed slurry solids concentration. Gravity sedimentation techniques are used commonly in effluent treatment processes for separation of activated sludge from aqueous solutions, in fuel ethanol production for recovery of yeast cells from aqueous ethanol solutions for recycle to the fermenter, and in the pharmaceutical industry for separation of solvent and aqueous phases in product recovery and isolation of impurities. Equipment types range from simple circular tanks, equipped with rake arms for large thickeners used in effluent treatment, through lamella type thickeners, which are fitted with inclined plates to increase the solids handling capacity, to flotation tanks where particles are caused to rise to the surface of the tank through natural low density or the use of gas bubbles or chemical flocculating agents. iii. Filtration Processes a. Pressure Filtration

Conventional pressure or vacuum filtration techniques are widespread in industry for separating cells and other biological materials from a liquid phase which can be solvent based or aqueous. A pressure differential between the dirty and clean sides of the filter, created with over pressure or vacuum, provides a driving force for the liquid to be forced through the filter material which retains solids above a particular size. This type of filter is often used in conjunction with a precoat material on the filter to improve the separation characteristics. Solids in the range 0.1 to 10 /xm are typically removed by this type of bioseparation, which is generally used where the sofid material retained by the filter is the unwanted by-product, and the desired product is dissolved in the liquid phase.

PROCESSING PLANTS AND EQUIPMENT

64 I

b. Gravity Filter

Gravity filters are seldom used in the process industries because they offer low filtration rates, however, simple Nutsch filters are sometimes found in the pharmaceutical industry at pilot scale. The Nutsch filter is a tank with a perforated base on which a filter cloth can be supported. The feed slurry liquid filters through the cake and cloth under its own weight. Although these units are low cost, they are labor intensive to operate, cannot be contained for protection of the product or the operator, and are slow. c. Pressure Filter

Pressure filters are operated above atmospheric pressure at the slurry surface using a slurry pump or compressed gas, typically between 0.5 and 4.0 bar gauge. Usually they are suitable for batch operation only. Pressure filters have several advantages including faster filtration rates, a large filter area for a given floor space, and the flexibility to operate at different stages within a batch manufacturing process. However, they are labor intensive and expensive to operate in a contained manner. Examples of pressure filters include the plate and frame filter press, which gives a variable filter area depending on the number of plates installed on the frame, improving flexibility. Cake washing is also possible with this type of filter. High-pressure contained-plate and frame filters are now available where separations are more difficult or where solvents are being handled. The Rosenmund filter is a specialized type of pressure filter in the form of an agitated vessel with a flat base and a perforated false bottom on which a filter cloth can be mounted. The agitator can be used to spread the filter cake evenly, carry out reslurrying, and assist with cake washing and delumping. A rotary screw is used to discharge the solids from the filter. It is possible to combine filtration and drying operations within the Rosenmund filter to contain filtration, washing, and drying operations within one single piece of equipment. Minimal liquid hold-up and very efficient cake washing can also be achieved, and these filters are commonly used for final recovery of bulk pharmaceutical products following crystallization or precipitation. The Funda filter is another type of pressure filter with a stack of rotating circular horizontal leaves within a cylindrical vessel, with the filter medium on the upper side of each leaf. Filtrate is drawn through the leaves and removed while solids are deposited on the upper surface of the leaf. It is possible to blow compressed gas through the filter to help dewater and dry the filter cake; cake washing is also feasible. SoUds are discharged by rotating the filter at a sufficient speed to throw them off the filter medium, such that the solids fall to the bottom of the housing and can be removed through a slide valve. d. Vacuum Filtration

In this type of filter, the pressure differential across the filter is achieved by imposing a vacuum on the downstream side, rather than pressure on the upstream side. Both batch and continuous vacuum filters are widely used in

642

p. BOWLES

the process industries, for example, in pharmaceuticals manufacture and waste water treatment. e. Rotary Drum Filter

This equipment consists of a horizontal axis revolving drum. The surface of the drum is segmented, with compartments fitted with drainage pipes leading inside the drum to a common manifold and a rotary valve located at one end of the drum. A filter medium is attached to the external surface of the drum. When the drum is mounted with part of its surface in a tank of slurry, the application of a vacuum behind the filter medium pulls the filtrate through. The solid material is retained on the filter surface and, as the drum turns slowly past a knife, is dislodged into a collection hopper for disposal or further treatment. The filter medium may be precoated by placing the precoat solution in the immersion tank before being replaced by the process slurry. Generally precoated filters must operate on a semicontinuous basis because after a period of time the precoat layer will deteriorate and must be replaced. Filters without a precoat can be operated continuously. Rotary vacuum belt filters are a similar type of filter with the added advantage of being able to continuously filter, wash and dry the filter cake as it travels along an endless belt. Precoat is not needed on this type of filter. Although the belt filter is in many ways superior in performance to the drum filter, it does rely on an easily filterable cake being used and requires a large area within a production building. Containment of solvents requires a complex enclosure design to minimize fume losses. f. Centrifugal Filtration

Centrifugal force, rather than pressure differential, is used to throw the solid phase against the filter medium and force liquid through the filter medium and cake. The filter medium may be wire mesh, perforated metal or cloth and is not usually used in a precoat manner. Centrifugal filters can be either batch or continuous operation. Higher gravitational force centrifuges are not considered in this section since they do not involve any filtration, but are described in detail below. g. Basket Centrifuge

The basket centrifuge is operated in batch mode and comprises a rotating basket within a housing, onto which the drive unit is fixed and driven from the top or bottom of the unit. Solids discharge may be from the top or bottom of the machine. Typically, these machines are operated at speeds of 400 to 600 rpm for slurry feeding and washing, but up to 1100 rpm for cake dewatering. A special sofids plough is used to push the cake off the filter medium. They are very flexible machines capable of handling a wide range of solids, but are relatively labor intensive to operate. h. Continuous Centrifuge Filters

Continuous centrifugal filters are available as truly continuous or batchcontinuous units. Conical screen centrifugal filters consist of a perforated

PROCESSING PLANTS AND EQUIPMENT

643

conical screen which rotates in either the vertical or horizontal plane. Feed slurry is introduced at the cone angle end, and liquid passes through the screen, while the solids slide down the cone and are thrown off at the end. The cone angle is important for the correct operation of this type of filter. They are best suited to high solids concentrations and uniform particle size so that liquid will drain easily while avoiding screen blockage. Pusher (reciprocating) centrifugal filters enable filtration, cake washing, and drying as sequential operations, hence they are batch-continuous units. Cake formed on the screen is pushed sideways by an advancing annular ring and thrown off the edge of the spinning basket. Multistage baskets can be used. Pusher centrifugal filters can be automated to a high degree. Peeler centrifuges are also batch-continuous machines where the cake is removed by a plough. Different solids content feedstocks can therefore be handled in this type of unit, provided that they do not clog up the filter medium. A high degree of automation can be achieved with this type of unit. I. Cartridge Filtration

These are housings of metal or plastic containing one or more replaceable and renewable cartridges which contain the active filter element, usually based on a polymeric filter medium or in some cases, sintered stainless steel. They are useful as polishing filters where the level of solids to be removed is relatively low, to prevent the filter from blocking up. A most important application of cartridge filters is in sterile (absolute) filtration of gases and liquids either as part of a fermentation process or during final purification stages for a bulk or sterile pharmaceutical liquid product. In such processes, the filter and housing will usually be sterilized in an autoclave or in place using steam before filtration starts. Integrity testing of filters is important to demonstrate that the ability of the filter to remove all particles above a certain cut off point has not been compromised, to ensure that sterile solutions do not contain harmful contaminating microorganisms or viruses which could affect the product and ultimately the patient. /. Cross-Flow Filtration

Although this technique is not limited to the initial cell recovery stages of a downstream process, cross-flow filtration is commonly used for product recovery operations, particularly in lower volume processes where stringent hygiene requirements apply, as in the pharmaceutical and food industries. Cross-flow filtration is also referred to as tangential flow filtration or microfiltration, but all three terms refer to a process by which membranes are used to separate components in a Hquid solution (or suspension) on the basis of their size. The development of robust membranes in polymeric and ceramic materials has provided a powerful new technology for bioseparations, which is already widespread in the process industries as well as for water treatment processes. The principle of operation for a cross-flow filtration system is to recirculate a hquid solution or suspension, usually using a positive displacement pump, through the membrane module, which may be arranged as multiple tubes, a spiral wound sheet or in a plate and frame configuration. The use of

644

p. BOWLES

several membrane modules enables flexibility in designing a cross-flow filtration system to suit a particular application. The pressure imposed on the feed side of the membrane creates a driving force which forces material of smaller size than the membrane through to the clean side. This is referred to as the transmembrane pressure, the clean material passing through the membrane as permeate, and the remaining material not passing through the membrane as retentate. The transmembrane pressure tends to be higher as the pore size decreases. Cross-flow filter performance is often characterized by a flux rate, which equates to the permeate flow rate per unit area of membrane surface. The flux rate in most biological separations is reduced by a fouling phenomenon called gel polarization, which tends to concentrate material at the surface of membrane to impose an additional resistance to transmembrane flow. The deterioration in flux rate must be well characterized for a commercial bioseparation process to ensure the correct size for the cross-flow filtration unit and avoid hold-ups at this processing stage. Cross-flow filters can be operated in three different modes according to the nature of the product to be recovered and the stage in the processing. Concentration mode enables a product in either soluble or insoluble form to be reduced in volume prior to further processing, provided that the product size is greater than the membrane pore size, so that the material cannot pass through the membrane. This is useful when there is a large volume of aqueous material to be removed as waste in order to reduce the batch size for downstream purification operations. Typical, a concentration stage can be used immediately after fermentation, especially for mammalian cell cultures, or following an elution stage from a chromatography step which has increased the product solution volume. Diafiltration (see later) can be used to wash further soluble impurities from the concentrated product fraction if desired. Clarification mode enables a product in soluble form to be separated from larger sized solid or dissolved impurities, by passing it through a suitable size membrane and collecting the filtered liquid as permeate. There will usually be a limit on the volume reduction which is possible before the membrane surface becomes badly fouled. To avoid losing a significant proportion of product in the retentate fraction, diafiltration can be used (see later). Diafiltration is essentially a washing step which can be used either to remove more impurities as part of a concentration process, or to increase yield by recovering more product as permeate in a clarification process. The feed volume is maintained at a constant level by adding a suitable solvent to the feed tank as permeate is removed through the membrane. Several volumes of feed solution can be added as diafiltrate according to the processing requirements. There is usually a point beyond which diafiltration becomes uneconomical, due to the marginal reduction in impurities or increase in product recovery achieved for a given volume of diafiltrate. Cross-flow filtration systems are suitable for aqueous and solvent based solutions and suspensions, provided that electrical equipment is appropriately specified to meet relevant hazardous area classifications. Most systems are

PROCESSING PLANTS AND EQUIPMENT

645

suitable for cleaning in place and, with a suitable membrane material, for sterilization in place (SIP) using saturated steam. If SIP is not possible, a chemical solution, typically sodium hydroxide, is commonly used to sanitize the membrane system and minimize any microbial growth. They are therefore well suited to the hygienic and sterile applications found in the food and pharmaceutical industry, as well as for contained operation if hazardous materials are being processed. Commercial cross-flow filtration units are often supplied as packaged units where the membrane modules, feed pumps, feed and permeate tanks, heat exchangers, pipes, and controls are all arranged on a frame, or skid, which is preassembled and tested in the fabricator's workshop. It is possible to provide these units with a high level of automation and control, depending on the application. Cross-flow filtration systems are attractive when a high-quality filtrate or permeate is required, where washing is needed, and if contained operation is desirable for safety or hygiene reasons. It is also a useful technique in heat-sensitive processes where dewatering is required, and where other techniques such as evaporation could damage the product. They may be less attractive where the feed solution is highly fouling, or where an acceptable product recovery requires a large amount of diafiltration, thus diluting the product concentration significantly. It is not possible to use these units to recover dried products, but they may be useful in reducing the quantity of material to be handled in a downstream bioseparation process, for example, a spray dryer or an adsorption process. iv. Centrifugation

In centrifugal separation, the sedimentation rate of a particle is increased many thousands of times compared with gravitational forces, to enable efficient separation of particles with relatively small differences in density or size. Centrifugal bioseparations are an important group of available industrial techniques and are found in most of the industries described earlier for concentration and washing of solid phase material, countercurrent extraction of soluble products, and removal of solid phase impurities to clarify a product in solution. They are most commonly found in the early cell recovery and primary product separation stages of a bioprocess and are capable of handling relatively high liquid throughputs, solids concentrations, and a wide range of particle sizes. However, the choice of industrial centrifuge will be influenced by these parameters, as well as the need for sterility, containment, batch or continuous operation, and the nature of the product as solid or liquid phase material. In most cases, it will be necessary to carry out centrifuge trials using a typical feed material and pilot-scale version of the candidate machine so that the effectiveness of the chosen type can be verified. a. Tubular Centrifuge

Tubular centrifuges are small diameter, vertical axis machines running at high g forces up to 15,000 rpm and feed rates between 0.4 and 4.0 m^/hr.

646

p. BOWLES

They are best suited to liquid-liquid separations and clarification duties, but not high solids concentrations due to the limited solids hold-up capacity. They can handle small-density difference separations and best suited to batch processes. They are difficult to clean, and as large-scale laboratory units, best avoided unless another type of centrifuge design will not work. b. Solid Bowl Centrifuge

Solid bowl centrifuges are similar to tubular centrifuges, but with a larger diameter bowl and running at slower speeds. Feed rates can be as high as 10 m^/hr, provided that the solids concentration in the feed is not too high, as the solids hold-up is again limited. c. Disk Stack Centrifuge

These versatile machines are used for liquid clarification, concentration of light slurries, and liquid-liquid separation. They are capable of continuous operation even with high soHds concentrations, since the solids phase can be discharged periodically if desired. They can also be arranged as hermetically sealed units for handling hazardous materials or in sterile applications. The centrifuge contains a stack of conical disks spaced between 0.5 and 2 mm apart. The feed is supplied through a pipe to the center of the bowl at the base of the machine and is distributed into many thin layers. The different phases therefore have only a very short distance to travel to free themselves from each other. Once the solids have contacted the underside of the disks, the settling process is over and the solids move to the periphery of the disks, where they are thrown off the edge onto the bowl wall. Feed rates of up to 250 m^/hr can be handled by this type of centrifuge, with g forces in the range 5000 to 10,000 rpm. If the solids phase is fairly small, then disk stack centrifuges can be configured as the solids retaining type. If necessary, bowl liners can be fitted to assist with product removal and cleaning. Alternatively, solids discharging types are available in two configurations, either the nozzle type, which ejects solids continuously, or the solids ejecting type, where intermittent discharge through valves on the nozzles avoids excessive liquid loss or dilution of the slurry. This type of centrifuge is well suited to CIP and some models can also be sterilized in place as part of a hygienic or contained bioseparation process. d. Decanter Centrifuge

The decanter centrifuge is a horizontal axis machine comprising a long rotating cylindrical bowl which contains a screw conveyor rotating at a slightly different speed in the same direction. Typically, the bowl rotates at 5000 to 8000 rpm, and the screw rotates 50 rpm more slowly. If the bowl is tapered at one end, dewatering of the solids on a "beach" is possible before discharge. The angle of the tapered section, the relative length of the beach and the remainder of the bowl, and the differential speed between the bowl and the scroll are all important parameters which must be fine-tuned to a particular process.

PROCESSING PLANTS AND EQUIPMENT

647

Decanter centrifuges are well suited to high solids concentrations at feed rates between 1 and 100 m^/hr. They cannot achieve such high standards of separation as a disc stack machine, and are more difficult to engineer as truly hygienic or contained units. They are suitable for continuous operation and can discharge solids continuously. V. Sorption Processes

Adsorption and ion-exchange processes involve contacting a solution with a rigid and durable particulate phase which is able to selectively take up either the product or one or more specific contaminants. Generally, after the column has been loaded with the product or an impurity, another solvent is used to elute the material back into solution, possibly with an intermediate washing stage if some impurities are likely to be taken up along with the product. The particulate phase must then be regenerated and possibly sanitized using suitable solutions. Bioseparations using sorption processes have a number of advantages over alternative methods, including mild operating conditions of temperature and pressure, low energy consumption, high specificity, simple equipment, and the possibly for separation and recovery of the product essentially in the same physical and chemical state. However, sorption processes are usually run in batch mode with consequently high labor requirements. They tend to have a relatively slow "reaction" rate and the product hold-up per unit volume of packing is low, also large volumes of effluent are generated in the washing and regeneration stages. The attachment of particular solute molecules to the surface of the particulate sorption packing material can be achieved by a number of different methods, which are outside the scope of this paper. There are a large number of different sorption materials and complex physical and chemical interactions which must be considered. The most common sorption materials are activated carbon, silica gel, activated alumina, molecular sieves, and ion exchange resins. This chapter deals with the industrial aspects of handling these materials and operating process-scale equipment, but does not look at the choice of sorption material for a particular process. vi. Packed-Bed Systems

In most cases, apart from the expanded-bed systems discussed earlier, sorption processes tend to be based on packed-bed configurations where the material is loaded into a suitable column and remains static during the sorption process. Operation can be batch, with one column or several in series, or continuous, with two or more columns in parallel. When designing sorption columns, important process parameters include the pressure drop across the packing, especially if fouling might occur, and velocity and flow through the bed to achieve the correct residence time for adsorption. Large columns often have problems of poor flow distribution, since preferential channeling via the path of least resistance can reduce the ability of the sorption material to take up the product. Some packing materials will expand by up to 20% when wetted and this must be accounted for in the column sizing. The handling of different solution types and

648

p. BOWLES

quantities is also important: How will the solutions be made up at the correct volume, how will they be disposed of, and what operating conditions are required? The loading and unloading of particulate material from the column must also be considered: Can the sorption material be regenerated, how many times before change is needed, and how will this operation be done when several tonnes of material could be involved? Backwashing of some packed beds is practiced to remove impurities and to regenerate the sorption material. It may also be necessary to chemically sanitise the column to minimise the build up of microorganisms. Examples of sorption processes using packed beds include recovery of crude antibiotics from fermentation broth filtrate, heavy metal removal from product streams, and separation of amino acids from solutions. vii. Expanded-Bed Adsorption

This is a relatively new technique which is now becoming commercialized. It combines the cell separation and primary product separation stages in a single unit operation, to reduce equipment costs, improve product yields and reduce processing times. The principle of operation is a column of suitable adsorptive material showing affinity toward the product. Due to the fouling nature of most fermentation broths, which contain a large amount of solid phase material, the adsorption bed would quickly become fouled if operated in a classical packed-bed mode. To get around this problem, the bed is fluidized using the liquid flow, so that the particles expand and move away from each other, enabling debris and cell material to pass through the bed without causing blockage, while the product can still be adsorbed onto the packing. A clean product solution can then be eluted from the adsorption bed, for further processing. The advantage of this technique is that it can avoid the need for two separate process stages to first separate the product from cells, perhaps using a centrifuge, and then a second adsorption stage using a packed bed or chromatography column to isolate the crude product. However, it is best suited where the product is in the aqueous phase as dissolved material, and requires careful control of the expanded bed to give good product recovery while maximizing the removal of impurities. viii. Cell Disruption

Cell disruption techniques are used to recover materials produced within the cell, for example, industrial enzymes and some pharmaceutical proteins. Generally this stage of bioseparation will follow cell recovery, for example, by centrifugation, and precede the isolation of the desired product from the cell debris which is also produced during the disruption process. There are a range of physical and chemical methods available at laboratory scale for cell disruption which involve the use of reagents or temperature and pressure changes to break the cell wall to release the desired products. However, at an industrial scale it is more common to use a mechanical disruption technique, and a number of companies have developed efficient

PROCESSING PLANTS AND EQUIPMENT

649

cell disruption equipment suitable for yeast and bacterial cells. Mammalian cells with fragile cell walls do not generally require this type of treatment. Since cell disruption is a relatively specialized technique with specific difficulties depending on the organism being handled, it is worth obtaining assistance from the equipment manufacturer at an early stage, and possibly using a small-scale version of the apparatus to carry out pilot scale tests. When carrying out cell disruption operations it is often necessary to provide cooling of the cell concentrate due to the high pressures developed in the equipment. An additional consequence of high-pressure operation is that cell disruption equipment can generate aerosols which may be undesirable, particularly for biologically hazardous organisms. In these cases, the ability to steam sterilize the equipment is required, for decontamination, and some type of secondary containment may also be required, such as an isolator or a contained area within a facility to which access is controlled. Mechanical cell disruption techniques are based on high shear effects as fluid is forced through a narrow orifice, or a chamber containing rotating disks and glass beads to break up the cellular material. Both techniques enable some control over the extent of cell disruption. C. Product Purification and Final Isolation Following the initial stages of product recovery from a fermentation broth, a number of purification stages will be required in all but the simplest industrial processes. In the case of high-purity pharmaceutical products, a large number of separation stages are usually required to remove all impurities from the desired final product. By identifying some difference between the product and its impurities, either physical or chemical, the desired bioseparation can be achieved. i. Chromatographic Separation Chromatography is an effective bioseparation technique suitable for low-volume, high-value products such as pharmaceutical proteins. In chromatographic separations, an aqueous or organic solution containing the product is passed through a packed column containing a separation matrix. Differences in chemical or physical properties between the product and its impurities are exploited to achieve the separation. In most industrial purification processes, several stages of chromatography are required to achieve the required product purity, generally with a concentration step using ultrafiltration to reduce the volumes of liquid handled from stage to stage. At industrial scale, various chromatographic techniques are available: adsorption chromatography, which uses physical binding effects which are dependent on pH or salt concentration; affinity chromatography, where a specific binding between a molecule and the matrix is achieved; and partition chromatography, where product and impurities move through the bed at different rates. Typical stages in a chromatographic separation process are first loading of the column with the product while impurities pass through, various

650

p. BOWLES

washing stages to further purify the product, then elution where some change to the column operating conditions removes the product from the matrix into the solvent phase. After the product has been removed, the column is cleaned, sanitized, and regenerated. All of these stages involve the passage of buffer solutions though the column, this term being a general description for any aqueous or solvent-based solution usually containing organic or inorganic salts. The scale-up of a chromatographic process to industrial scale can be difficult to achieve while maintaining an acceptable throughput and yield of product. Problems may occur which are not met at the laboratory scale, for example, the flow distribution pattern through a large-diameter column, excessive pressure drop in a longer column due to compression of some matrices, and the need to maintain equipment cleanliness over an extended number of purification cycles. Since most chromatographic stages are found toward the end of the production process, and because very few matrices are suitable for steam sterilization, product protection must be ensured by locating the equipment within a clean room environment. Often, the temperature of the process must be controlled, typically at 4°C, and so the entire clean room may be cooled to avoid the need for local process cooling. At an industrial scale, the preparation of buffer solutions and the loading of the column with a matrix is also more difficult. Large volumes of solutions must be prepared ready for use, requiring vessels for dissolution, mixing, and storage. The larger volumes of matrix required in a large-diameter column require special equipment for packing to avoid channeling and consequential poor flow distribution. These two requirements may create the need for dedicated clean rooms where buffer preparation and column packing can be carried out. As a general rule, the use of organic solvents in chromatographic processes should be minimized, because of the requirement for specialized flameproof equipment which can be extremely costly compared with the equivalent item for a "safe" area. Where unavoidable, a separate flameproof room for handling solvent-based materials is recommended, with the appropriate specification for mechanical and electrical equipment, controls and room fittings including lights, switches, and telephone systems. ii. Crystallization Crystallization is an important unit operation at industrial scale found commonly in both the food and pharmaceutical industries. It is capable of producing highly pure solid materials in a form suitable for sale. For example, bulk antibiotics and sugar are two biologically derived products which are crystallized at the end of their manufacturing process. The crystallization step enables the removal of unwanted impurities by a convenient route and, coupled with subsequent washing of the crystal slurry on a filter, produces a highly pure end-product. As a widely used unit operation throughout the process industries, there is a wealth of scientific and engineering literature which underpins this important separation technique, beyond the scope of this section. The com-

PROCESSING PLANTS AND EQUIPMENT

65 I

plex heat and mass transfer problems associated with crystaUization have meant that such processes have sometimes been considered a "black art." Also, the need to recover the soHds from a liquid slurry by filtration and subsequent drying requires a more complex train of process equipment at an industrial scale. For foods and pharmaceutical products, the handling of slurries and solids at industrial scale presents problems where the product is exposed on filters and in dryers, rather than being enclosed within a pipe or vessel as a liquid. Contamination of the crystalline material can occur, and the product itself or the solvent phase it must be removed from might be toxic. Various types of equipment have therefore been developed to enable wet crystalline "cakes" and dry powders to be handled in a contained manner, using specially designed booths, isolators, and pack off systems to protect the product from its environment (and vice versa for highly potent materials). Both batch and continuous crystallization equipment are available at industrial scale, although batch operation is normally favored for pharmaceutical products where batch integrity must be maintained for quality control reasons. Continuous crystallization is suited to higher throughputs and enables more energy efficient operation. Batch crystallization vessels can be agitated or unagitated, and may use either cooling or evaporation to cause crystallization, sometimes with "seeding" required. In some cases, very smooth surfaces are required to enable the crystals to form in the desired form, and this can be achieved using purposebuilt glass-lined vessels and stirrers. iii. Thermal Separations

Thermal separations are commonly required for biological products to reduce or remove unwanted solvents, most commonly water, from a liquid or wet soHd material. Evaporation produces a more concentrated liquid while drying results in a product with lower moisture content. Such processes are energy intensive at industrial scale and so it is important to investigate possible alternatives such as reverse osmosis for concentration of a liquid, or preliminary filtration by mechanical means before final product drying, so that more liquid is removed from the feed material. Dried products are generally more stable and suited to storage for extended periods, compared with liquids or wet solids where there may be potential for microbial growth to occur especially for nonsterile products. Drying conditions for bioseparations may be milder than for other types of products, but still require the removal of liquid from between the interstices of the solid and as droplets on the solid surface, as well as from within the bulk of the particle either in pores or encapsulated within the particle surface. a. Thermal Dryers

Industrial drying equipment is available in many different forms for both batch and continuous duties, using hot air or a combination of indirect heating and vacuum to remove the liquid.

652

p. BOWLES

Tray dryers, the simplest type of dryer, are commonly used for batch drying of biological materials, where the wet solids are placed on trays which are then transferred into a chamber. The chamber may have a heating jacket, heated tray supports, or a hot air supply. Vacuum may be applied to reduce the temperature at which the liquid evaporates, preserving heat labile products. These are well suited to low-volume products or flexible plants where a number of different products with different characteristics must be dried. They are relatively inefficient to operate, difficult to clean, and labor intensive to operate. The product is exposed when being loaded and unloaded, so the dryer may need to be located in a clean room or area for pharmaceutical products. Various types of agitated dryers are available, again operating in batch mode, with vacuum and indirect heating to increase the drying rate. The dryer chamber may be a horizontal cylinder, a pan, or a vertical cone. These units are more efficient and offer faster drying rates due to the constant turnover of solids within the chamber. They can be loaded and unloaded in a contained manner where product or operator protection is required. However, they are still relatively difficult to clean and operate on a batch basis with a relatively low possible throughput. For vacuum dryers, a solids filter between the drying chamber and the vacuum pump is required to collect any "fines" from the dried product. Combined filter-dryer units are available in a number of different configurations including the Funda filter, Titus-Nutsche filter dryer, Rosenmund filter, and Seitz-Wega filter. These equipment types enable filtration and drying in a single piece of equipment to reduce the amount of product exposure and the necessity to transfer wet cake from one plant to another. However, the time required to process a batch of material through filtration and drying stages means that this equipment may create a bottleneck to production unless several units operate in parallel, at a higher capital cost. Hence a balance must be made between contained processing needs and plant capacity and flexibility. b. Spray Dryers

Spray dryers are operated continuously and commonly used for foods, enzymes, and pharmaceutical intermediates and products. Most if not all of the solvent phase can be removed provided that the feed slurry is converted to a fine spray to maximize the surface area for heat and mass transfer. Spray dryers have a relatively large space requirement in a plant and have a high energy consumption. They can be difficult to clean effectively but are well suited to single products where continuous operation is desirable. Again dust can be a problem and contained pack off systems are recommended to maintain a clean environment around the spray dryer unit. c. Freeze-Dryers

Freeze-drying is a specialized process by which moisture is removed from a wet solid, usually placed on trays or in small containers, by sublimation under high-vacuum conditions. This is an energy-intensive procedure even compared with conventional drying processes but is used in a number of industries where heat causes damage to the product, reduces its yield, or

PROCESSING PLANTS AND EQUIPMENT

653

spoils the presentation of the product. Examples of freeze-dried biological materials include instant coffee granules and high-value pharmaceutical proteins such as growth hormones. Freeze-dryers are large and expensive items which require a large amount of supporting equipment for heating, vacuum production, and condensation.

lY. PROCESS-SCALE CONSIDERATIONS A. Materials of Construction and Mechanical Design At industrial scale, careful consideration of the materials of construction for the bioseparation equipment is vital to ensure that the product does not become contaminated, by rust, for example, and also to assure long plant life with good reliability to maximize throughput. Materials that were suitable on a laboratory or pilot scale may no longer be appropriate, where the process and mechanical demands on the equipment may be greater. For example, the plant could be located outside where there are greater extremes of temperature in summer and winter, or equipment may need to be steam sterilized in situ rather than being autoclaved. Mechanical design conditions refer to the range of temperatures and pressures that are encountered during bioprocessing. The equipment supplier will add a margin to the stated design conditions to ensure that failure will not occur in normal operation, and test the equipment before delivery under the most stringent conditions. Where high pressures or vacuum conditions are encountered, a recognized pressure vessel code such as ASME VIII in the United States or BS 5500 in the United Kingdom will be followed, and particular construction techniques and testing requirements will be either optional or mandatory, according to these codes to suit a particular application. The chemical and physical nature of the products being processed will also be important, especially high or low pH and chloride content, which can mean that even some grades of stainless steel could corrode. For example, pharmaceutical chromatographic separations involve aqueous buffer solutions containing sodium chloride as a sanitizing agent, and under certain conditions of concentration and temperature, chloride-induced stress corrosion cracking may occur. Cleaning chemicals can also attack certain materials and so any requirement for cleaning, sanitizing, decontaminating, or flushing the equipment with chemicals other than those used in the processing operation must be clearly defined and checked for compatibility. It is therefore important to draw on the experience of the equipment supplier and to fully define all anticipated operating conditions for the bioseparation equipment. It is also vital that any other components such as gaskets, O-ring seals, instruments, and other parts are checked for compatibility with the products to avoid failure in service and possible product contamination or equipment downtime for repairs to be made.

654

p. BOWLES

B. Automation To increase production capacity, to give more repeatable process conditions, or to reduce labor costs, it may be advantageous to automate certain bioseparation processes rather than relying on manual operation. For example, a decanter centrifuge could be controlled from a local PLC (programmable logic controller) so that sterilization, separation, and cleaning operations are automatically monitored and controlled using on-off and modulating control valves and appropriate instrumentation. Automated plant is also useful in semicontinuous and continuous processes to make the control of the plant more stable. Hov^ever, there are several disadvantages with automated bioseparation systems, including cost, development time, and the need for complex validation activities if the equipment is being supplied as part of a regulated production facility, for example, for pharmaceuticals production. In such cases, specific guidelines have been developed for computer system validation known as GAMP (good automated manufacturing practice). A further disadvantage is that suppliers may offer only one specific type of hardware a n d / o r software, which may be incompatible with a company's standards or with other equipment in the plant. The operation of a particular bioseparation step often involves unique features which require specialized software to be written rather than an "off-the-shelf" system, with consequent delays for testing and implementation. It is recommended that a careful analysis of costs is made before making the decision to automate a particular process, looking at capital and operating costs (such as man power), and to compare the process with existing plants or competitors to see if there is an industry benchmark.

C. Safety and Biosafety In all industrial processes, the safety of operators and staff, as well as the general public in surrounding areas, is of paramount importance. Every effort should be made during design and construction to ensure that the bioseparation plant is safe to operate with all risks identified and minimized through appropriate precautions. Hazardous features to be considered will include pressure relief; handling of hazardous materials such as acids and alkalis; protection from steam and other high-temperature fluids; and electrical classification for handling solvents or protection from water ingress, high speed rotating machinery, and noise levels. A unique feature in biological separations in the potential presence of biologically hazardous materials, in particular pathogenic or genetically modified microorganisms. Where these are being handled, specific safety guidelines are mandatory both in Europe and the United States, depending on the level of hazard presented by the microorganism. Formal safety reviews such as Hazops (Hazard and Operability reviews) may be required during the design of a new facility or the modification of an existing plant. It is recommended that specialist help be sought in carry-

PROCESSING PLANTS AND EQUIPMENT

655

ing out such reviews to ensure that all potential hazard are identified at an early stage in the project where the appropriate protective measures can be specified. D. Location Equipment and plant location can vary from an outdoor, exposed site, as in the case of an effluent treatment plant, to a clean room with controlled climate and air quality, for example, in biopharmaceuticals manufacture. The specification for bioseparation equipment will depend on its location, for both mechanical and electrical components. The need to weatherproof a piece of equipment and protect it from rain, wind, and temperature extremes will require specific provision to be made. Equipment located indoors will not necessarily require such features, although cleaning down of plant areas with hoses, as is common in the food industry, requires some degree of protection against water ingress for electrical items such as motor drives, control panels, and instruments. E. GMP and Validation For pharmaceuticals and foods, the safety and efficacy of the product is strictly regulated to ensure that consumers are protected. Both the European Union (EU) and the United States have regulatory bodies who are responsible for food and drug safety. The U.S. Food and Drug Administration and their European counterparts provide high-level regulations and directives for manufacturers of foods and pharmaceuticals. Good manufacturing practice, or GMP, encompasses this legislation plus more detailed guidelines which have been prepared to help the industries operate to a consistent standard. It is important to identify the markets where the product may be sold and to understand the prevailing GMP regulations and guidelines which will apply. Even if a manufacturing facility is outside the United States, the FDA must inspect the facility and license its products for sale if products are to be sold within the country. During the earliest stages of product and process development, facility design, and planning, due consideration must be given to ensure that GMP requirements are satisfied and the product or products will be approved. Validation is the process by which a facility is demonstrated to be compliant with GMP and fit for the manufacture of a particular product. Validation within the pharmaceutical industry normally falls into three or four parts: Design qualification (DQ) is the validation of a design to ensure that all GMP requirements are met at an early stage in the life cycle of the project, while there is still an opportunity to make changes relatively easily. Installation qualification (IQ) is where the construction of the facility and equipment is checked against the design specifications to ensure compliance with the original design intent.

656

p. BOWLES

operational qualification (OQ) then enables the functionahty of the faciUty and equipment to be tested against the design specifications. Finally, performance qualification (PQ) ensures that the actual product can be manufactured within the required specification and quality parameters which are claimed. Usually, three batches of product must be produced and carefully documented to demonstrate the repeatability of the process and the consistent specification of the product. The cost and complexity of vaUdation is often underestimated and can cause delays in bringing the product to market. Validation requirements for a project should be identified as early as possible in the project life cycle to ensure that adequate time and cost is allowed to complete them successfully. It is particularly important to establish the documentation required from suppliers and contractors working on the project, and the extent to which they will be required to play a part in the validation process. For example, if material certification is required for equipment components, these must be ordered from the supplier's own stockholders with the raw materials, and cannot be obtained retrospectively. It is particularly important to put in place quality control procedures for the development of hardware and software for plant automation. Good automated manufacturing practice provides a systematic and structured approach to the development of these systems including change control and validation methods. F. Hygienic Design For the pharmaceutical and food industries, surface finish is very important to enable effective cleaning and sterilization or sanitization. Equipment should be specified with a polished internal finish, possibly with electropolishing for critical applications, and designed with a minimum of crevices or dead spaces where dirt can collect. Welds must be finished to the same standard as the plates and ground flush with the internal surface and must be pinhole and crevice free. External surface finish may also be important for visual reasons and to enable cleaning down for surface decontamination in clean room locations. Where steam sterilization is required, the equipment must be self-venting and draining so that condensate drains to a single low point where it can be removed, and air which is trapped at high points can be displaced by steam.

V. SUMMARY In this chapter, a brief overview of the approach required when selecting and specifying industrial bioseparation equipment has been provided. Because of the range of industries involving bioseparations, it has been possible to give only general guidelines and advice. Each industry and product type will have particular requirements which will determine the choice of suitable processing plant and equipment.

PROCESSING PLANTS AND EQUIPMENT

6!>/

A holistic approach to the selection of bioseparation equipment is vital, so that the unit operation is not considered in isolation, but in relation to the whole process, the facility or site where it will be located, the nature of the product, and the operating and capital costs. Only then can an informed decision be made to find the right balance between product quality and yield, processing costs and capital investment. REFERENCES Atkinson, B., and Mavituna, F. (1983). "Biochemical Engineering & Biotechnology Handbook." Macmillan, New York. Bailey, J. E., and OUis, D. F. (1986). "Biochemical Engineering Fundamentals," 2nd ed. McGraw-Hill, New York. Lydersen, B. K., D'Elia, N. A., and Nelson, K. M., eds. (1994). "Bioprocess Engineering Systems Equipment and Facilities." Wiley, New York. Perry, R. H, and Green, D. (1984). "Perry's Chemical Engineer's Handbook," 6th ed. McGrawHill, New York.