Drinking Water Treatment Using PES/ZnO Mixed Matrix Membranes: Enhanced Antifouling Performance and Rejection at Low Nanoparticle Loadings

Poly(ether sulfone) (PES) ultrafiltration mixed matrix membranes containing zinc oxide (ZnO) nanoparticles were fabricated and evaluated for drinking water treatment, with emphasis on fouling control and pollutant rejection. Unlike most studies that use model foulants, membranes were tested with organic-rich surface water from the Guarapiranga Reservoir, enabling a realistic assessment under drinking water conditions. Membranes (0–1.0 wt % ZnO) were prepared by nonsolvent-induced phase separation and characterized (SEM, AFM, porosity, hydrophilicity, zeta potential, permeability). Crossflow experiments with raw water included resistance partitioning, Hermia model analysis, and foulant extraction. Low ZnO loadings (0.25–0.50 wt %) delivered the best performance, reducing total fouling resistance by about 84% relative to pristine PES and achieving flux recovery above 96%. Improvements were linked to a more negative surface charge (−26 to −31 mV) and favorable pore structure that promoted electrostatic repulsion and reversible deposit formation. Membranes in this range also showed higher rejection of natural organic matter, with greater removal of color, TOC, and UV254 than both pristine PES and higher ZnO loadings. By contrast, the 0.75% ZnO membrane, despite its highest pure water permeability, exhibited greater irreversible fouling and lower rejection, while the 1.0% ZnO membrane behaved similarly to unmodified PES. Combining physicochemical characterization with real water tests, the study addresses practical and scale-up barriers to applying mixed matrix membranes. Findings indicate that PES-ZnO membranes with minimal nanoparticle loadings (0.25–0.50 wt %) offer a cost-effective and scalable strategy to improve flux stability, fouling control, and pollutant rejection in drinking water production.