Effect of adsorbed protein on the hydraulic permeability, membrane and streaming potential values measured across a microporous membrane

Abstract

The effect of the adsorption of a protein, bovine serum albumin (BSA), on the membrane potential, flux reduction and streaming potential measured across a microporous polysulphone membrane with different NaCl solutions and pH values is studied. From electrokinetic phenomena, information about the electrical properties of the membrane (fixed charge concentration and ionic transport numbers) or the membrane/solute interactions (streaming and zeta potentials) can be obtained. The influence of pH and ionic strength on volume flux and streaming potential values is considered. Results show that hydraulic permeability decreases strongly when the pH decreases, having its minimum value at the isoelectric point of the protein; the apparent zeta potential values are also dependent on both pH and salt concentration. Differences in the streaming potential coefficient determined for two membranes fouled under different experimental conditions may be attributed to different mechanisms for the adsorption of proteins in the membrane: (i) a protein deposition on the membrane pores; (ii) an adsorbed layer of protein on the membrane surface. In this latter case, the whole membrane system can be considered as a “composite” or two-layer membrane, and a comparison of the results obtained with both microporous polysulphone and “composite” (microporous+BSA layer) membranes could permit us to determine some parameters related to the protein sublayer.