3D zwitterionic brush-grafted ultrafiltration membranes for fouling-resistant effluent pretreatment and improved reverse osmosis desalination

Ultrafiltration (UF) membranes are promising options for reverse osmosis (RO) desalination pretreatment, but membrane fouling limits their broad application. This study presents a three-dimensional (3D) poly(sulfobetaine methacrylate) pseudo-bottlebrush-grafted polyethersulfone UF membrane with excellent antifouling properties during the filtration of secondary wastewater effluent, providing an effective pretreatment to reduce fouling during RO desalination. Membrane characterization confirmed successful grafting and also demonstrated that extended polymerization (2–6 h) increased surface hydrophilicity, reduced charge and roughness, and improved antifouling performance. Filtration of secondary wastewater effluent for 5 days at 95 % water recovery using the modified membrane resulted in only 24 % increase in transmembrane pressure (TMP). Surface characterization and quartz crystal microbalance with dissipation (QCM-D) measurements indicated enhanced antifouling properties owing to low bacterial deposition and reduced organic matter adsorption. Effluent treated with the modified membrane was of superior quality compared to that treated with conventional tertiary treatment, and using modified membrane-treated effluent as a feed for RO desalination led to better performance than the conventionally treated effluent, as demonstrated by the stable TMP over 12 h desalination. These findings highlight the potential of grafted UF membranes to minimize fouling and increase RO efficiency, thus helping to produce potable water in water-scarce regions. • 3D Pseudo-bottlebrush grafting is achieved via two-step polymerizations. • 3D zwitterionic brush-grafted PES UF membrane has excellent antifouling properties. • Brush thickness increase with grafting time confirms pseudo-bottlebrush structure. • 3D zwitterionic brush grafting reduces foulant adsorption and bacterial deposition. • UF pretreatment enhances RO performance over conventional tertiary treatment.