Protein fouling of ultrafiltration membranes — investigation of several factors relevant for tertiary wastewater treatment

The fouling of two different ultrafiltration membranes by solutions of three globular proteins with different molecular weights and isoelectric points was investigated at low concentrations relevant to secondary effluents (10 mg·L^–1). The results reveal the increased fouling potential of macromolecules being small enough to enter the membrane pores due to the resulting blockage and (or) constriction of the pores, compared to a moderate increase of the filtration resistance due to gel layer formation by larger compounds. Differences between the applied membranes in terms of fouling behaviour, protein retention, as well as attachment of macromolecules to membrane surface and pore walls demonstrate the impact of pore size distribution, zeta potential, surface roughness, and hydrophobicity of the membranes on the fouling mechanism. Comparative ultrafiltration experiments using two different pumps indicate the influence of type and dimensioning of the pumping system on membrane fouling due to structural changes of solutes by pump-induced shear forces.