Efficient and low-energy degradation of PFAS in complex waters via enhanced hydrated electron generation using a VUV/sulfite process

Per - and polyfluoroalkyl substances (PFAS) are environmentally persistent, and conventional treatment methods often suffer from low degradation efficiency and high energy consumption. This study developed a vacuum ultraviolet/sulfite (VUV/SO 3 2− ) advanced reduction process to degrade perfluorooctanoic acid (PFOA), a representative PFAS. Under optimized conditions, the system achieved a defluorination efficiency of 75.68% and a degradation rate exceeding 95% within 2 h. The degradation mechanism is driven by the synergistic action of hydrated electrons (e aq − ) from VUV photolysis and hydroxyl radicals ( • OH) from sulfite activation, which promote stepwise cleavage of terminal C F bonds. Computational results further support that electron attachment at the terminal C F sites initiates defluorination. The system exhibits strong resistance to Cl − and PO 4 3− , while CO 3 2− , NO 3 − , and humic acid inhibit degradation by scavenging active species. The electrical energy per order (EE/O) was measured at 8.89 kWh/ m 3 , significantly lower than traditional UV-based systems. Additionally, the proposed “Energy Consumption per unit Defluorination” metric highlights the energy efficiency of fluoride removal, demonstrating the potential of the VUV/SO 3 2− process for practical PFAS remediation.