One-Step Covalent Coating By Zwitterionic Polymers for Superior Fouling-Resistant Reverse Osmosis Membranes

Fouling is one of the major concerns in the membrane desalination process. Attachment of inorganic and organic foulants from the feed solution onto the membrane surface can cause significant flux decline, which leads to increased operating pressure and frequent physical/chemical cleaning. To reduce the operational cost and increase energy efficiency of the current system, proper antifouling strategies are critical. Existing methods reported in literature to modify reverse osmosis (RO) membranes for enhanced anti-fouling properties usually involve two or more complicated reactions on membrane surface and toxic chemicals, which are difficult to scale up. One-step and environmentally friendly approaches are strategically important for the upsize and commercialization of any new types of antifouling RO membranes.

In this study, block copolymers containing zwitterionic monomers and anchoring monomers that can react with trimesoyl chloride were synthesized by free radical polymerizaiton in water. After the routine interfacial polymerization by m-phenylenediamine and trimesoyl chloride on the inner surface of hollow fiber membranes, the copolymer solutions were flown through the fiber immediately for a few minutes to complete the anti-fouling modification. The resulted modified membrane showed both higher water flux and salt rejection than the pristine thin film composite (TFC) membranes. The water flux reached to ~ 6 LMH/bar and NaCl rejection is > 98%, which is good for low-pressure RO applications. When mixed solutions containing calcium and alginate were used as the feed, the modified membranes did not show any fouling after 24 h, while the flux of pristine membranes dropped by 30%. Moreover, no significant fouling was observed for the modified membrane in a 10-day test using the feed solution from a local RO plant.