Deciphering the role of commercial nanofiltration membranes in removing 30 per-and polyfluoroalkyl substances: performances, mechanisms and implications

Per- and polyfluoroalkyl substances (PFASs) are bioaccumulative and highly stable in ecosystems, posing potential toxicity risks to human health. Membrane treatment has become a critical research area in current treatment technologies for PFASs. In this study, we selected five commercial nanofiltration (NF) membranes to investigate the performance of the membrane structure on treating 30 PFASs in simulated and industrial wastewater. The results indicated that the rejection of 30 PFASs exceeded 65% for all membranes. The performances of NF90 and DK membranes were better than others, whereas the treatment efficiency of the NF270 membrane was the lowest for most PFASs. Under the experimental conditions, NF90 membrane exhibited the highest surface negative charge and the lowest molecular weight cut-off (MWCO), resulting in relatively stronger electrostatic repulsion and size exclusion effects, which were the key factors influencing PFASs removal efficiency. For all membranes, the rejections were higher for PFASs with long carbon chains and strong hydrophobicity. The treatment efficiencies were higher for PFSAs with smaller pKa and LogKow, compared to PFCAs with the same carbon chain length, showing that electrostatic repulsion and hydrophobic interactions resulted in better efficiency. Furthermore, coexisting pollutants in the actual wastewater could have different impacts on the treatment outcomes by influencing factors such as pH and blocking membrane pores. This work presents an environmentally friendly and efficient method for removing PFASs from wastewater and provides insights into the separation mechanism of NF membranes for dozens of PFASs.