Rejection of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) by severely chlorine damaged RO membranes with different salt rejection ratios

Removal of per- and polyfluoroalkyl substances (PFAS) from water use cycles has now become an urgent task due to their wide spread in water environment and associated adverse health effects. Despite the effectiveness of nanofiltration (NF) and reverse osmosis (RO) for PFAS removal, the high cost related to the high pressure operation and membrane replacement mostly limit the application in the actual drinking water treatment. In this study, we investigated the rejection of the two most typical PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) by the chlorine treated RO membranes (Dow FILMTEC (TM) SW30HR) with five different salt rejection ratios from 12% to 66%, which simulated the used membranes upgraded for the permeability. The damaged membranes were further characterized for their contact angle and zeta potential, and elemental composition was analyzed by X-ray photoelectron spectroscopy. The lab-scale cross-flow filtration tests demonstrated that the damaged RO membranes with 39 similar to 66% salt rejection ratios achieved over 85% rejection of both PFOA and PFOS, which was comparable or even superior performance to that previously reported for NF membranes. Characterization of damaged membranes suggested that electrostatic repulsion and size exclusion both played an important role in the rejection of PFOA and PFOS by the damaged membrane. The present study provides new insights into the energy-efficient and material-saving, thereby economically sustainable, membrane process for the removal of the legacy PFAS.