Cyclic Removal and Destruction of Per- and Polyfluoroalkyl Substances from Water Using Ion Exchange, Resin Regeneration, and UV/Sulfite Reduction

Abstract

Ion exchange (IX) can effectively remove per- and poly-fluoroalkyl substances (PFAS) from drinking water sources at ng/L to µg/L levels. However, adsorbed PFAS on spent resins should be further destructed for detoxification. Traditional resin incineration or landfilling may cause secondary pollution to the surrounding environment and cannot achieve resin reuse. This study explored three variations of a PFAS treatment train, aiming to completely defluorinate PFAS with different chain lengths and functional groups at environmentally relevant levels (ng/L) and to reuse the resins and solvents. The optimized treatment train includes IX, resin regeneration with 5wt% NaCl and 60% v/v methanol, distillation of waste regenerant, and advanced reduction by hydrated electrons (eaq−) generated during the ultraviolet/sulfite (UV/sulfite) treatment of still bottoms. Such a treatment train achieved nearly 100% PFAS removal from surface water and groundwater using either PFAS-specific or generic resins, and almost 100% defluorination of PFAS except a few short-chain fluorinated sulfonates and ethers. Regenerated resins had comparable PFAS removal to the pristine resins over three cycles. The generic resins (e.g., Dupont AmberLite™ IRA910) are easier to regenerate and thus are recommended for the treatment train over PFAS-selective resins (e.g., Purofine® PFA694E). Direct heterogenous defluorination on resins loaded with perfluorooctane sulfonate (PFOS) was ineffective, potentially due to the consumption of UV light/eaq− by the resins and insufficient contact between the UV light/eaq− with PFOS on the resin surface. Distillation of the waste regenerant successfully concentrated PFAS in the still bottoms, reduced the waste volume, and removed excess methanol, all essential for effective UV/sulfite treatment. Meanwhile, the produced condensate with high methanol contents and low PFAS levels can be reused for the next regeneration cycle. Findings from this study provide a timely and sustainable solution to the stringent and evolving regulations on PFAS and the resultant production of PFAS-laden resins as hazardous wastes.