Perfluoroalkyl acid transformation and mitigation by nNiFe-activated carbon nanocomposites in steady-state flow column studies

The ongoing contamination of groundwater with per-and polyfluoroalkyl substances(PFAS)has resulted in a global and rapidly growing interest in PFAS groundwater remediation. Preferred technologies that lead to PFAS destruction are often limited by not addressing all PFAS, being energy-intensive or not being suited for in-situ application. We developed nNiFeactivated carbon(AC) nanocomposites and demonstrated varying degrees of PFAS reduction and fluoride generation with these nanocomposites in batch reactors for several PFAS. Here we explore nNiFe-AC’s effectiveness to transform perfluoroalkyl acid acids(PFAAs) under steady-state flow(0.0044 to 0.15 mL/min) in nNiFe-AC:sand packed columns. Column experiments included, two perfluorooctane sulfonate(PFOS) in deionized water and two PFAA mixtures in deionized water or bicarbonate buffer containing five perfluoroalkyl carboxylates(PFCAs, C5-C9) and three perfluoroalkyl sulfonates(PFSAs, C4, C6 and C8) at temperatures of 50 or 60℃ were evaluated. PFOS transformation was similar in PFOS-only and PFAA mixture column experiments. Overall, % PFAA transformation under flow conditions exceeded what we observed previously in batch reactors with up to 53% transformation of a PFAA mixture with ～ 8% defluorination. Longer chain PFAS dominated the PFAAs transformed and a bicarbonate matrix appeared to reduce overall transformation. PFAA breakthrough was slower than predicted from only sorption due to transformation; some longer chain PFAS like PFOS did not breakthrough. Here, nNiFe-AC technology with both in-situ and ex-situ potential application was shown to be a plausible part of a treatment train needed to address the ongoing challenge for cleaning up PFAS-contaminated waters.