Inclusion of nanofiltration as a robust barrier against municipal effluent impacts in drinking water treatment

The growing prevalence of unplanned potable reuse presents significant challenges to drinking water safety. However, the adverse effects of effluent organic matter (EfOM) from upstream secondary effluents (EF) on downstream drinking water treatment efficiency remain poorly understood. To address this gap, this study has systematically evaluated the influence of varying EF proportions on feedwater properties through comprehensive dissolved organic matter (DOM) characterization. The results revealed the limited efficacy of conventional coagulation (C) in removing EfOM and confirmed the superior performance of coagulation-nanofiltration (CNF) as a dual-barrier strategy. Molecular-scale analysis demonstrated complementary mechanisms, with coagulation preferentially removing aromatic, high-molecular-weight (MW) oxidized NOM, and nanofiltration targeting low-MW saturated EfOM. This process combination not only mitigates EfOM-induced water quality problems, but also enhanced operational sustainability by reducing membrane fouling. Furthermore, the CNF process exhibited complete resilience to EF ratios below 30 %, maintaining THM formation potential, HAA formation potential, and toxicity levels comparable to or better than those of conventional treatment (coagulation) of EF-free feedwater. These findings confirm CNF as a robust water treatment solution for utilities managing increasing wastewater contributions in source waters.