Cyclic sorption/regeneration of ion exchange resins and UV/sulfite treatment for complete perfluorooctane sulfonate removal

Per- and polyfluoroalkyl substances (PFAS) are being detected frequently in water, raising health concerns. While anion exchange resins (IERs) are effective in removing PFAS contamination in water to below regulatory limits (often in the ng/L range), their regeneration efficiency is typically low, requiring high-salinity brines that generate substantial secondary waste and limit reuse over multiple cycles. This study used cationic cetyltrimethylammonium bromide (CTAB) to desorb perfluorooctanesulfonic acid (PFOS), introducing a novel solution for the regeneration of PFOS-laden IERs and enabling their reuse for at least five cycles without compromising efficiency. The concentrated PFOS eluent could be directly subjected to a subsequent UV/sulfite degradation process, avoiding CTAB separation, unlike organic solvents. Using 1 mM CTAB solution, PFOS desorption reached ∼82.6 % for A860 and ∼54.4 % for A600 at ∼50 mg/g PFOS loading on IERs, which is significantly higher than conventional desorbents. XPS analysis revealed a stronger reduction in F 1s and S 2p signals, along with partial restoration of quaternary ammonium groups and Cl − exchange sites after PFOS desorption. Molecular dynamics simulations and radial distribution function analyses supported experimental evidence that CTAB facilitates PFOS desorption from IERs. Weaker hydrophobic and electrostatic interactions within PFOS and IERs, compared to those with CTAB, lead to preferential displacement of PFOS. UV/sulfite treatment of the PFOS-CTAB eluent achieved ∼99.9 % PFOS degradation and ∼90.3 % defluorination, demonstrating that CTAB does not hinder the process. Twelve perfluorinated intermediates were identified, including six new ones identified for the first time. Based on this, defluorination, desulfonation and C C bond cleavage were proposed as the major degradation mechanisms, breaking the PFOS molecule into smaller fragments. This CTAB-driven regeneration of PFOS-loaded IERs introduces a novel approach for cyclic PFAS treatment in practical applications. • Introduced CTAB as a regenerant for PFOS-laden IERs, enabling reuse for 5 cycles • At 50 mg/g loading, 82.6 % PFOS desorption from A860 and 54.4 % from A600 was achieved. • PFOS desorption driven by hydrophobic/electrostatic interactions and micelle formation • UV/sulfite degraded ∼99 % PFOS in CTAB eluents with ∼90 % defluorination efficiency. • Identified twelve PFOS degradation intermediates, including six newly reported ones