Yeast cake layers as secondary membranes in dead-end microfiltration of bovine serum albumin

Abstract

Dead-end filtration of bovine serum albumin was performed in a phosphate buffer through a yeast cake layer deposited on an asymmetric, polysulfone microfiltration membrane having a nominal pore size of 0.2 μm. Yeast cake layers of varying thicknesses were preformed in two ways - by gravity settling prior to the onset of filtration and by vacuum filtration. The role of the cake layer of rejected cells as a secondary membrane for reducing protein transmission and affecting permeate flux was studied. The steady-state flux was found to be higher in the presence of a thin cake layer than in the absence of a cake layer. This is thought to result from the yeast cake serving as a filter-aid to remove membrane foulants from the protein solution. Due to the micro-channeling effects, higher fluxes were observed for filtration through a cake layer preformed by vacuum filtration, as compared to the corresponding values for a cake layer of equal dry mass preformed by gravity settling. The protein transmission studies revealed three types of fouling - membrane fouling due to the internal pore deposition of protein, protein adsorption through the entire cake depth, and surface filtration leading to protein rejection at the cake surface.