A zwitterionic block-copolymer, based on glutamic acid and lysine, reduces the biofouling of UF and RO membranes

In this study, the anti-fouling ability of coating ultrafiltration (UF) and reverse-osmosis (RO) membranes with a block copolymer of polystyrene (PS) bound to an alternating lysine–glutamic acid peptide PS-b-(KE)₁₅) was analyzed. The PS-b-(KE)₁₅ coating had no effect on membrane permeability. Membrane fouling experiments were conducted with extracellular polymeric substances (EPS) extracted from the biological sludge of a membrane bioreactor, which treats municipal wastewater. The mechanism responsible for the anti-fouling behavior, of the modified membranes was found to be the hydration of the coating – attributed to the adsorption of electrolytes – as detected by quartz crystal microbalance with dissipation monitoring (QCM-D). The hydration of the coating was observed in the presence and absence of calcium. However, fouling of the modified membranes with EPS was mediated and enhanced by calcium, and the presence of calcium abolished the anti-fouling effects of the PS-b-(KE)₁₅ layer on both UF and RO membranes. The interaction between EPS and the bare, uncoated membrane area in the presence of calcium likely eliminated the anti-fouling capabilities of the PS-b-(KE)₁₅ layer. Membrane coating may be further improved by designing a continuous, denser layer of PS-b-(KE)₁₅.