Strategic optimization of silver nanoparticle and PDA modified spacers in spiral-wound nanofiltration for sustainable mitigation of single and composite fouling

Membrane fouling in spiral-wound nanofiltration is intensified by coexisting microorganisms, organic matter, and metal ions in real wastewaters, yet most mitigation strategies focus on membrane surface modification while overlooking the role of feed spacers in regulating in-channel fouling. In this study, silver nanoparticle-polydopamine (Ag-PDA) modified spacers were prepared on commercial polypropylene spacers via a two-step coating process. Optimized spacers exhibited AgNP size of ~40 nm at surface loading of 0.99 wt%, reduced contact angle from 87° to 72°, and achieved > 99.99% antibacterial efficiency. Across microbial, organic, and inorganic fouling systems, permeate flux improved by 24–89% with concurrent rejection enhancements, and AgNP leaching remained below 0.1%. In municipal, micro-polluted source, and electroplating wastewaters, the modified spacers delivered 80–92% flux recovery and 91–94% reductions in membrane-surface bacterial counts. These results establish Ag-PDA modified spacers as a robust, cost-effective, and environmentally sound antifouling strategy for spiral-wound nanofiltration under complex real water conditions.