Zwitterion grafted polyethersulfone ultrafiltration membranes integrated with coagulation process for fouling mitigation in sewage wastewater treatment

Abstract

The study investigated the use of zwitterion-grafted polyethersulfone (PES) membranes integrated with polyelectrolyte coagulation process for the remediation of sewage wastewater after physical screening stage from a wastewater treatment plant (WWTP). The zwitterion (sulfobetaine methacrylate, SBMA) brushes were grafted onto the PES polymer backbone using free radical polymerisation in aqueous medium to improve its hydrophilic properties and therefore reverse its fouling tendencies. The successful synthesis of poly(sulfobetaine methacrylate-grafted PES (pSBMA-g-PES) polymer composite was confirmed using FTIR and TGA, as well as gravimetric method. The resulting polymer composites were used to fabricate zwitterion-containing membranes using the non-solvent induced phase separation (NIPS) method. The performance parameters of the fabricated membranes were all enhanced, i.e., pure water flux, fouling resistance, improved quality of produce water, as well as increased mechanical strength. The observed fouling resistance improved with increasing zwitterion content demonstrating its role in delaying or inhibiting foulant adhesion. The fabricated membranes were used to treat sewage water from WWTP, the results indicating improved performance with increasing zwitterion content. In order to further reduce fouling and increase the useful lifespan of the membranes, pretreatment of the sewerage water with alum was integrated with the filtration process. This was repeated in a six filtration-wash cycles to demonstrate increased reusability of the membranes with improved fouling profile. The produce water qualities was evaluated using pH, turbidity, TDS, TOC, and EC, which were all below the standards required for reuse. The incorporation of zwitterions resulted in increased membrane hydrophilicity and surface charge modulation that explain their comparatively higher antifouling and rejection qualities in comparison to the pristine membrane. The zwitterionic membranes also showed exceptional flux stability and recyclability, indicating a longer lifespan potential.

Keywords

• Coagulation
• Grafting
• Polyethersulfone
• pSBMA
• Ultrafiltration
• Zwitterionic membrane