Assessing Biofouling Resistance of a Polyamide Reverse Osmosis Membrane Surface-Modified with a Zwitterionic Polymer

Reverse osmosis (RO) is a technology that can help increase clean water supply in today's world. However, mitigation of biofouling of RO membranes is a remaining challenge towards a wider use of this technology. It was suggested that a promising way to control membrane biofouling could be surface modification, e g., using low-fouling zwitterionic polymers. Published studies demonstrated that zwitterionic coatings can indeed improve the resistance of polyamide (PA) membranes to the initial bacteria adhesion, however, no long-term experiments with real water effluents were conducted. In this report a commercial PA RO membrane was surface-modified with a zwitterionic polymer and its propensity to biofouling was tested in both short-term bacteria adhesion experiments and longer filtration tests conducted using real treated wastewater effluents spiked with a small level of nutrients. The obtained results showed that, initially, there was a clear improvement in the biofouling resistance of the modified membranes and their permeation flux remained stable, in contrast to the non-modified counterpart. However, eventually, the permeabilities of the two membranes declined to a similar degree. The results indicate that antifouling coatings might not promise a better membrane performance in long term. The analysis of the biofilms grown on the pristine and the modified membranes suggested that adaptation capabilities of biofilms overcame the favorable changes in surface properties of the membrane achieved by the modification. The presented results emphasized the importance of long-term filtration experiments as an ultimate test for assessing biofouling resistance of the modified desalination membranes.