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Nanoplastics-mediated interfacial processes controlling perfluorooctanoic acid transport in forward osmosis
Summary
Researchers examined how polystyrene nanoplastics with different surface chemistries affect PFAS removal in a forward osmosis membrane system, finding that nanoplastic fouling promotes accumulation of PFOA near the membrane surface — especially for positively charged particles — worsening concentration polarization and complicating PFAS removal from contaminated waters.
Forward osmosis (FO) has gained attention as a low-pressure treatment option for removing per- and polyfluoroalkyl substances (PFAS). PFAS frequently coexist with micro and nanoplastics (NPs) in contaminated waters, yet their combined influence on membrane separation remains insufficiently understood. In this study, a UiO-66-NH modified antifouling FO membrane was fabricated to investigate how NPs affect the rejection and transport of perfluorooctanoic acid (PFOA). PFOA removal was evaluated under different membrane orientation, pH of the feed solution, draw solution salinity, coexisting PFAS species, and the presence of polystyrene-based NPs with different surface chemistries (PS, PS-NH, PS-COOH). The membrane showed high PFOA rejection efficiency, which increased under alkaline conditions but declined at high draw-solution concentration due to reverse salt diffusion and charge screening. Coexisting PFAS with different chain lengths and pKa values altered PFOA rejection through competitive interactions at the membrane interface. Experimental evidence further showed that NP-related fouling strengthened external concentration polarization and promoted extra accumulation of PFOA near the membrane, with the extent of accumulation strongly dependent on NP surface chemistry, particularly electrostatic attraction for PS-NH and weaker interactions for PS and PS-COOH. These results demonstrate that NPs play an important role in PFAS transport during FO filtration and should be considered when evaluating mass-transfer behavior in complex waters. This work provides insights into the dual impact of coexisting PFAS and NPs on FO membrane performance and highlights the importance of mitigating cake-enhanced polarization in designing antifouling membranes for wastewater treatment.