Distinct Sorption and Rejection Behavior of Hydrophobic Endocrine-Disrupting Compounds by Chlorinated Polyamide Nanofiltration Membranes: Mechanisms and Implications

Effective removal of hydrophobic endocrine-disrupting compounds (EDCs) using polyamide nanofiltration (NF) membranes remains a challenge in membrane-based water treatment. A common belief is that the sorption of hydrophobic EDCs is key to their rejection, while high sorption often leads to low rejection. However, this study reported distinct sorption-rejection behavior of EDCs by various chlorinated polyamide membranes. Specifically, the chlorinated NF90 membrane exhibited significantly reduced sorption and, thus, enhanced rejection for EDCs. This is primarily attributed to the enhanced hydrophilic carboxyl groups through chlorination-induced hydrolysis, which can suppress the hydrophobic interactions between the membrane and the EDCs. More interestingly, the chlorinated VNF1 membrane demonstrated higher sorption but also higher rejection of EDCs than that of the virgin membrane. The high sorption can be attributed to the strong hydrophobic interaction between EDCs and the hydrophobic chlorine attached to the membrane. Meanwhile, the large size of chlorine also strengthened membrane size exclusion, thereby enhancing its rejection of EDCs. Such enhanced size exclusion overperformed the impact of increased sorption, thus leading to enhanced rejection. These findings elaborate the existing membrane sorption-rejection framework and offer valuable insights for the rational design of advanced NF membranes aiming for the effective elimination of EDCs in water and wastewater treatment.