Microfiltration 15 microporous hollow fibre membrane has been used for the purification of bovine growth hormone from Escherichia coli lysate(Tutunjian, 1985). Although the growth hormone as partially rejected from the membrane, this could be recovered using diafiltration such at over 99% recovery from the original lysate was possible. Kroner et al.(1984)used MF to recover a range of soluble enzymes from cell debris, although they concluded that the separation was not satisfactory due to high retention of the enzymes in the feed Transmission of enzymes through microporous membranes is rather anomalous. Le and Billigheimer(1985)found that transmission of arylamidase increased rapidly over the first 5-10 minutes of processing and then declined steadily. This was ascribed to adsorption of protein to the membrane surface during the initial phase, to form a monolayer lining. Transmission of the enzyme occurred when the surface was saturated and subsequently declined due to the formation of a secondary membrane of cell debris and proteinaceous matter. In general, careful manipulation of pressures and flow rates can be used to optimise protein transmission through MF membranes Alternatively, valuable extracellular biotechnological products can be separated from cell suspensions by MF. Raehse et al. (1986)employed polysulphone tubular membranes with a pore size of 0.3-0.5 um to separate alkaline protease from a fermentation broth The ratio of the mean pore diameter of the membrane to the size of the microorganisms was between 0. 15 and 0.85, which gave a rapid separation suitable for large-scale A combination of CMF with affinity chromatography provides an innovative develop ment for purifying biochemicals from fermentation broths or other aqueous media, such s trypsin from pancreatic extract. The principle is to bind the biochemical to a macroligand and remove contaminants by CMF. Following dissociation, the purified material can then be recovered by CMF, and the macroligand recycled (Luong et al 1987) It is possible to incorporate MF membranes into membrane reactors. In this way a continuous process can be developed in which the membranes are retentive to the cells (or other biocatalyst), but permeable to the reaction products. Most reported develop- ments in this field have been on laboratory scale, and use UF rather than MF membranes One promising report with MF is the incorporation of zirconia membranes into a continuous fermentation system with cell recycle for production of alcohol which ermitted very high yeast concentrations to be used (Lafforgue et al., 1987). This has led to the possibility of extremely high alcohol production capacity (possibl 50 kg m-2h-) 5.4 CONCLUSIONS MF has made significant advances in new applications in the food and biotechnology ndustries. However, the technique has not yet realised its full potential, largely due to the severe problems of flux decline due to fouling. It is believed that further developments in membrane design and a greater knowledge of fouling mechanisms will result in greater application in the future, especially in the field of downstream processingMicrofiltration 151 microporous hollow fibre membrane has been used for the purification of bovine growth hormone from Escherichia coli lysate (Tutunjian, 1985). Although the growth hormone was partially rejected from the membrane, this could be recovered using diafiltration such that over 99% recovery from the original lysate was possible. Kroner et al. (1984) used MF to recover a range of soluble enzymes from cell debris, although they concluded that the separation was not satisfactory due to high retention of the enzymes in the feed. Transmission of enzymes through microporous membranes is rather anomalous. Le and Billigheimer (1985) found that transmission of arylamidase increased rapidly over the first 5-10 minutes of processing and then declined steadily. This was ascribed to adsorption of protein to the membrane surface during the initial phase, to form a monolayer lining. Transmission of the enzyme occurred when the surface was saturated, and subsequently declined due to the formation of a secondary membrane of cell debris and proteinaceous matter. In general, careful manipulation of pressures and flow rates can be used to optimise protein transmission through MF membranes. Alternatively, valuable extracellular biotechnological products can be separated from cell suspensions by MF. Raehse et al. (1986) employed polysulphone tubular membranes with a pore size of 0.3-0.5 pm to separate alkaline protease from a fermentation broth. The ratio of the mean pore diameter of the membrane to the size of the microorganisms was between 0.15 and 0.85, which gave a rapid separation suitable for large-scale applications. A combination of CMF with affinity chromatography provides an innovative develop￾ment for purifying biochemicals from fermentation broths or other aqueous media, such as trypsin from pancreatic extract. The principle is to bind the biochemical to a macroligand and remove contaminants by CMF. Following dissociation, the purified material can then be recovered by CMF, and the macroligand recycled (Luong et al., 1987). It is possible to incorporate MF membranes into membrane reactors. In this way a continuous process can be developed in which the membranes are retentive to the cells (or other biocatalyst), but permeable to the reaction products. Most reported develop￾ments in this field have been on laboratory scale, and use UF rather than MF membranes. One promising report with MF is the incorporation of zirconia membranes into a continuous fermentation system with cell recycle for production of alcohol which permitted very high yeast concentrations to be used (Lafforgue et ul., 1987). This has led to the possibility of extremely high alcohol production capacity (possibly 150 kg m-2 h-I). 5.4 CONCLUSIONS MF has made significant advances in new applications in the food and biotechnology industries. However, the technique has not yet realised its full potential, largely due to the severe problems of flux decline due to fouling. It is believed that further developments in membrane design and a greater knowledge of fouling mechanisms will result in greater application in the future, especially in the field of downstream processing