Effect of ionic environment on the crossflow microfiltration behaviour of yeast suspensions

In this study, the effects of various metal ions, Al3+, Cu2+, Ni2+, Pb2+ and Na+, on the transient and steady-state crossflow microfiltration behaviour of dilute yeast cell suspensions are investigated. It is observed that in the presence of Pb2+ and Al3+ specific cake resistance decreases, while steady-state permeate flux increases. At the same concentration levels, cake resistance for Al3+ is lower compared with Pb2+. Microscopic examinations of the yeast suspension indicate higher levels of yeast cell aggregation in the presence of Al3+ than Pb2+. The specific cake resistance increases with increasing concentrations of Na+, Ni2+ and Cu2+ ions whereas the steady-state fluxes decrease. In these cases, cell aggregation is not present except when the concentration of Cu2+ is 0.4 mM. Consequently, at this concentration level, significant decrease in specific cake resistance is present. The order of the binding affinity of the metals to yeast cell is Al3+ > Pb2+ > Cu2+ > Ni2+ which is also reflected in the metal ion rejection under identical processing conditions. (C) 2002 Elsevier Science B.V. All rights reserved.