Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water

Abstract

Ion exchange (IX) is a promising technology to remove legacy anionic per- and polyfluoroalkyl substances (PFAS) from water. As increasing numbers of per- and polyfluoroalkyl ether acids (PFEA) and other emerging PFAS were detected in the environment, it is necessary to understand how well IX resins remove these emerging PFAS for drinking water treatment. In this study, nine commercially available IX resins were tested to treat a drinking water source spiked with 40 legacy and emerging PFAS at 600 ng/L, including PFEA, perfluoroalkyl carboxylic and sulfonic acids, fluorotelomer sulfonic acids, perfluoroalkane sulfonamides, perfluoroalkane sulfonamidoacetic acids, and zwitterionic species. With limited contact time (15 min), PFAS properties such as the fluorinated chain length, charge, and functional groups all affected PFAS adsorption to resins. However, the impact of PFAS properties on PFAS removal became less pronounced when the contact time increased beyond 2 h, while the resin polymer matrix became the critical factor for PFAS removal. All five tested polystyrene-divinylbenzene (PS-DVB) resins achieved more than 90% removal in 24 h of 35 PFAS compounds, while polymethacrylate and polyacrylic resins achieved >90% removal for less than half of the compounds. Regenerating PS-DVB resin was investigated using different salt species, regenerant pH, brine concentrations, and methanol contents. Sodium chloride and ammonium chloride were found the best brines for regenerating the tested resins. Increasing brine concentrations enhanced the regeneration efficiency, especially for short-chain PFAS. Using simple salt regenerants, up to 94% of selected short-chain PFAS was released from resins designed for general water treatment, but no meaningful regeneration was achieved for long-chain PFAS or PFAS-specific resins when the organic solvent content was less than 20%.