Remove Per- And Polyfluoroalkyl Substance From Water By Combined Ion Exchange and UV/Sulfite Treatment

Abstract

Per- and polyfluoroalkyl substances (PFAS) are contaminants of concern in North Carolina. Ion exchange (IX) is effective in separating PFAS from contaminated drinking water, but incapable of chemically breaking down the contaminants. Thus, waste streams from IX, including spent resins and regenerant, contain high levels of PFAS and are challenging to be disposed of safely. This project addresses this problem by strategically combining IX and resin regeneration via chemical PFAS degradation. We hypothesize that in this treatment train, PFAS can be separated from contaminated water and subsequently mineralized for safe and feasible waste management. With the goal of sustainable and cost-effective management of IX wastes for PFAS removal, this project includes tasks of determining the most suitable chemical treatment for IX wastes, optimizing the treatment conditions, and assessing the feasibility of the treatment train for water treatment practice.

In this project, we proposed and evaluated several variations of a treatment train for PFAS removal and defluorination for water treatment. The most effective option for the treatment train design we identified in this project combines IX, NaCl/methanol regeneration, distillation, and UV/sulfite defluorination. Using this treatment train, PFAS at environmentally relevant levels (ng/L) can be captured by IX to near 100% by either PFAS-specific or generic resins. The spent resins can be regenerated using 60% methanol/5% NaCl solutions and reused in the following treatment cycles, with much better regeneration performance from the generic resins than PFAS-specific resins. The waste regenerant can be distilled to separate methanol for reuse, with simultaneous PFAS enrichment and volume reduction of the waste stream. Finally, the concentrated waste (still bottoms) can be treated with UV/sulfite to transform PFAS into nontoxic fluoride. This process is effective for most PFAS with almost 100% removal and >75% defluorination, although a few short-chain sulfonates and GenX are more challenging to treat. The generic resins (e.g., IRA910 tested in this project) are recommended for the treatment train over PFAS-selective resins and can be reused for treatment over multiple cycles. All the detailed conditions for each treatment step were optimized. Overall, PFAS with different chain lengths and functional groups can be effectively removed and eventually defluorinated in different water matrices using the proposed treatment train.