Reversibility of heterogeneous deposits formed from yeast and proteins during microfiltration

Formation of heterogeneous deposits of particulates and macromolecules occurs frequently during membrane filtration. Removal of these deposits is important in maintaining flux and preventing retention of valuable species. In this paper, the effect of interaction between bovine serum albumin (BSA) and yeast particles on the reversibility of cake formation during microfiltration was studied. Critical flux and hysteresis of flux-transmembrane pressure curves are evaluated using flux stepping experiments. Intermittent filtration was used to observe cake dispersal and re-establishment. Washed yeast formed reversible, low resistance cakes even above the apparent critical flux. At a low yeast concentration of 0.3 g/L, the introduction of 1 g/L protein into the feed solution reduced the apparent critical flux significantly. However, at higher concentrations of yeast (0.8 and 1.45 g/L), the introduction of protein had little effect on the apparent critical flux. It was observed that even 0.1 g/L BSA was sufficient to introduce irreversibility in the cake formation with 0.8 g/L yeast. The rate of fouling appeared lowest for pH 3.0 for these mixed systems, suggesting that rapid binding of BSA at the top of the cake due to electrostatic attraction prevented further penetration of the particles into the void space of the yeast cakes.