Direct regeneration of ion exchange resins with sulfate radical-based advanced oxidation for enabling a cyclic adsorption – regeneration treatment approach to aqueous perfluorooctanoic acid (PFOA)

Abstract

Per-and poly-fluoroalkyl substances (PFAS) challenge traditional water treatment and reuse. Although ion exchange (IX) is a technically effective option for removal of aqueous PFAS, it cannot serve as an ultimate solution without PFAS detoxification and sustainable resin regeneration. On the other hand, sulfate radical (SO4●−)-based advanced oxidation processes (SR-AOPs) have proven effective for destructing certain PFAS, but are rarely applied to realistic treatment, primarily because SR-AOPs can excessively increase total dissolved solids and decrease pH in treated water. Here we proposed and tested a cyclic treatment approach for addressing perfluorooctanoic acid (PFOA), a representative PFAS. Each cycle included IX for purifying considerable PFOA-polluted water and concentrating trace PFOA on a small quantity of resins; and direct regeneration of PFOA-sorbed resins with heat activation of peroxodisulfate (PDS) for detoxification and resin regeneration. Results show that cumulative PFOA removal was linearly increased with the cycle number for regenerated resins. Despite slight resin destruction, regeneration with a low PDS dose could effectively recover the adsorption capability. However, a too high PDS dose could seriously damage the resins, causing an irreversible loss of the adsorption capacity. The approach can purify substantial water and detoxify PFOA, while producing a small quantity of non-hazardous regenerant, thereby enabling a cost effective design for treatment of PFOA-polluted water. Equally important, the study demonstrates a new strategy for on-site regeneration of exhausted IX resins in water and wastewater treatment.