Bioprocessing membranes

R. van Reis and A. Zydney, Bioprocess membrane technology. Journal of Membrane Science 297 (2007) 16-50. 

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. 

A key consideration in development of all multi-step bioprocesses is the type of bioreactor it may be necessary to accommodate a range of conditions including compartmentalization of the enzymes, cofactor recycle, adequate oxygen supply, variable temperature and pH requirements, and differential substrate feed rates. Examples described below include a range of different reactors, of which membrane bioreactors are clearly often particularly useful. 

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). 

The principles, sampling systems, control of the measuring device and application of MS for bioprocesses have been summarized by Heinzle [157,158] and Heinzle and Reuss [162]. Samples are introduced into a vacuum (< 10 5 bar) via a capillary (heated, stainless steel or fused silica, 0.3 x 1000 mm or longer) or a direct membrane inlet, for example, silicon or Teflon [72,412]. Electron impact ionization with high energy (approx. 70 eV) causes (undesired) extensive fragmentation but is commonly applied. Mass separation can be obtained either by quadrupole or magnetic instruments and the detection should be performed by (fast and sensitive) secondary electron multipliers rather than (slower and less sensitive) Faraday cups (Fig. 21). 

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. 

Entrapment of enzymes and cells has played an important role in developing bioprocesses. Applications of entrapment technology to biosensors and bioanalysis have mainly been focused on udlizadon of cells and, to a smaller extent, on enzymes (24). Combining covalent coupling and entrapment cross-links enzymes and inert protein to form a protein membrane that covers the sensitive part of the electrode dp in bioanalytical applications (25). Entrapping enzyme aggregates is another variadon of this methodology (26). 

Groot WJ, Soedjak HS, Donck PB, ban der Fans RGJM, Luyben KCAM, and Timmer JMK, Butanol recovery from fermentations by hquid-hquid extraction and membrane solvent extraction. Bioprocess Engineering 1990, 5, 203-216. 

Bowen WR, Electrochemical aspects of microfiltration and ultrafiltration, in Howell JA, Scanchez V, and Field RW (Eds.), Membranes in Bioprocessing, Chapman Hall, Cambridge, 1993, pp. 265-292. 

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. 

Recently, studies on biofouling have appeared in the hterature [36-38] while membrane optimization has been more extensively studied in the field of bioprocess [39—45]. 

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