Use of hydrodynamic and electrical measurements to determine protein fouling mechanisms for microfiltration membranes with different structures and materials

A comparison of membrane fouling caused by filtration of a protein (BSA) through two macroporous membranes, one polymeric (polysulfone) and other ceramic (ZrO2/Al2O3), is carried out. Clean and fouled membranes were characterized by SEM micrographs, water permeability, streaming/zeta potential and impedance spectroscopy measurements. SEM micrographs show BSA on the polymeric and ceramic membranes surfaces but only the polymeric membrane is completely covered, while trans-membrane (or through membrane) zeta potential results indicate protein deposition on the pore walls of both membranes; moreover, differences in time evolution of permeate flow, protein rejection and water permeability for both membranes were also obtained. According to these results, two different main fouling mechanisms can be assumed: a cake layer on the surface of the polysulfone membrane and pore narrowing for the ceramic sample. Impedance spectroscopy measurements allow the estimation of membrane electrical resistance and a reduction in membrane porosity associated to protein deposition was estimated considering a simple system of non-conducting cylindrical capillaries filled by the (conducting) electrolyte solution.