Microfiltration of protein mixtures and the effects of yeast on membrane fouling

The effects of yeast cells on membrane fouling by a protein mixture were st udied in dead-end filtration. A 0.2 mu m cellulose acetate membrane was use d with a 1 g/l protein mixture consisting of equal amounts of bovine serum albumin, lysozyme, and ovalbumin. Yeast cells were used either in suspensio n or as preformed yeast cakes on top of the membrane. A small concentration of 0.022 g/l yeast cells in suspension enhanced the permeate flux and main tained protein transmission at nearly 100%, compared with a 60% reduction i n the protein concentration in the permeate obtained after 3 h for the prot ein mixture filtered alone. Higher suspended yeast concentrations of 0.043 and 0.18 g/l resulted in lower fluxes and intermediate values for the prote in transmission. For the three different thicknesses of preformed yeast cak es studied (0.025, 0.05, and 0.10 cm), the cake with intermediate thickness resulted in protein transmission of nearly 100% and the highest permeate f lux. The thinner yeast cake resulted in a lower permeate flux, but it maint ained protein transmission at nearly 100%, whereas the thicker cake resulte d in a reduction in both permeate flux and protein transmission. The mechan ism proposed to explain the results is based on the formation of a secondar y membrane by the yeast cells on top of the original membrane. This seconda ry membrane entraps protein aggregates, which would otherwise cause membran e fouling and reductions in permeate flux and protein transmission, (C) 199 9 Elsevier Science B.V. All rights reserved.