Bioprocesses membrane processes

In bioprocesses, a variety of apparatus that incorporate artificial (usually polymeric) membranes are often used for both separations and bioreactions. In this chapter, we shall briefly review the general principles of several membrane processes, namely, dialysis, ultrafiltration (UF), microfiltration (MF), and reverse osmosis (RO). 

Schafer, A., Hossain, M. M. (1996). Extraction of organic acids from kiwifruit juice using a supported liquid membrane process. Bioprocess Biosyst. Eng., 16, 25-33. 

Sintered glasses are commercially used as filters, carrier materials in bioprocessing, biomedical processes and also for thermal insulation, sound proofing and fire protection [166,177,466]. Porous glasses are used in separation processes, as supports for immobilised enzymes, as carriers for solid phase synthesis, for the immobilisation of biologically active materials and in membrane technology or for studying matter in confined spaces [263,264]. 

The application of whole-cells or enzyme-based catalysts was protected in two different bioprocess patents ([56] and [57], respectively). The patent specifies the process [57] involving a sulfur-specific reactant with membrane fragments, an enzyme, or a composition of enzymes having the ability to selectively react with sulfur by cleavage of organic C—S bonds, derived from R. rhodochrous strain ATCC No. 53968 or B. sphaericus strain ATCC No. 53969. 

Identifying an environment that avoids induction of undesired enzymes and repression of desired ones and implementing bioreactor control systems that maintain these desired conditions in a bioprocess are subjects of future importance. For example, accumulation of a product in the cell environment can often repress synthesis of some of the enzymes required for production of that compound. Product repression and inhibition phenomena have motivated special interest recently in combined bioprocessing operations which accomplish separation simultaneously with bioreaction. By continuously removing a product that inhibits its own synthesis, production of that material is improved. Development of new selective membranes and other process strategies for accomplishing these separations is an important area for future research. 

It is indeed impossible to capture aU current and future applications, and uses in any one publication. What follows here is a selective presentation from the large number of possible membrane-based processes of relevance to bioprocess industries. 

Membranes are particularly suited for bioprocesses involving the cultivation of microorganisms or cells as biocatalysts, in which the product of interest is produced extracellularly. Such processes are becoming increasingly attractive when compared to those in which the products accumulate intracellularly. Some of the reasons for this include the use of novel expression systems which favor higher product concentrations, and the ease of purification as compared to an intracellular bioproduct route. One of the drawbacks remains that extracellular protein products are produced in dilute concentration. Extracellular-product based-processes require cell separation, product recovery and concentration. The use of ultrafiltration and microfiltration membranes has become a method of choice in such process schemes. 

In bioprocessing, gas-phase pressure measurements are utilized for evaluation of the partial pressures of various gaseous components, to monitor the performance of outlet gas filters, and to control sterilization procedures. Since they are compatible with the aseptic requirements of biotechnological processes, membrane-type pressure sensors are most commonly used. 

Mohammad AW, Ng CY, Lim YP, and Ng GH. Ultrafiltration in food processing industry Review on application, membrane fouling, and fouling control. Food Bioprocess Technol. 2012 5 1143-1156. 

First applications of membrane reactors can be foimd in the field of bioprocess engineering using whole cells in fermentations or enzymatic bioconversions [6, 7]. Most of these processes use polymeric membranes, as temperatures seldomly exceed 60 °C. The development of inorganic membrane materials (zeolites, ceramics and metals) has broadened the application potential of membrane reactors towards the (petro) chemical industry [8]. Many of these materials can be applied at elevated temperatures (up to 1000°C), allowing their application in catalytic processes. 

Most phannaceutical substances are manufactured in batch processes by (a) chemical synthesis, (b) fermentation, (c) isolation and recovery from natural sources, and (d) a combination of the above. Fermentation broths are usually very dilute and contain many complex compounds as given in Table 3.3 [23]. Because of the dilute and impure nature of the broths and sensitivity to operating conditions, MF, UF and NF are weU-suited for downstream processing, i.e., separation, isolation, purification and recovery of the product. Several membrane applications in bioprocessing are illustrated in Figure 3.24 [23] including gas separation (GS). 

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