Competitive Removal of Per- and Poly-Fluoroalkyl Substances (PFAS) in Multi-PFAS Component Systems by Ion Exchange Resins: Effects of Resin Matrix, PFAS Property, and Sulfate

To meet the mounting regulations on per- and poly-fluoroalkyl substances (PFAS) in drinking water, ion exchange (IX) has become one of the most widely used technologies. However, the effects of resin characteristics and effects of common water matrix ions (sulfate) on the competitive uptake of PFAS of varying chain lengths and functionalities in multicomponent systems are not well understood. In this study, two commercial strong-base IX resins were tested for competitive removal of 10 PFAS. This study demonstrates that polystyrene matrix (IRA900) IX significantly outperforms polyacrylic matrix (A860) IX in the removal of PFAS due to both electrostatic and hydrophobic interactions. More effective removal in IX was found in longer-chain PFAS and perfluoroalkyl sulfonic acids (PFSAs) than in perfluoroalkyl carboxylic acids (PFCAs). PFAS removal was effective over a broad pH range of 4–8.5 except for short-chain PFCAs, which were competed with hydroxide ions. The uptake of IRA900 decreased with the increase in sulfate concentration and the decrease was profoundly in shorter-chain PFAS. In kinetic tests, the PFAS removal for IRA900 was ~85% without sulfate and ~80% with sulfate within 48 h. Moreover, it was confirmed that the presence of sulfate suppressed shorter-chain PFAS and PFCA homologues. IRA900 was regenerated using NaCl, methanol (CH3OH), and a combination. A decrease by 10.7–12.6% after first regeneration was attributed to PFCA.