Far-UVC (222 nm) Enhances the Advanced Reduction Process for Per- and Polyfluoroalkyl Substance (PFAS) Destruction

The UV-based advanced reduction processes (ARPs) have emerged as an effective strategy to degrade PFAS contaminants in water. This study investigates PFAS degradation by integrating far-UVC irradiation at 222 nm with sulfite-based ARPs. Comparative analysis of UV222/sulfite and conventional UV254/sulfite revealed that UV222/sulfite systems significantly improve the performance by generation of more hydrated electrons (e_aq ^-), the primary reactive species driving PFAS degradation, and exhibit superior energy efficiency, characterized by lower electrical energy per order (<i>E</i> _<i>EO</i> ). The higher efficiency of UV222/sulfite can be attributed to stronger light absorption of sulfite and higher photon energy at 222 nm. Under optimized stepwise sulfite dosing conditions, the UV222/sulfite ARP achieved high perfluorooctyl sulfonic acid (PFOS) removal efficiency, nearly 85% reduction in parent compound and 66% defluorination within a 6 h period, while the degradation of shorter-chain PFHxS and PFBS was slower. Real water matrix components can influence treatment efficiency. The impacts of nitrate/nitrite were transient and diminished after rapid photolysis at 222 nm, while dissolved organic matter and carbonates exerted strong reactive species scavenging effects. This study establishes UV222/sulfite ARP as a promising strategy to enhance PFAS degradation. Careful optimization of UV222/sulfite system parameters and water matrices will increase the adaptability for environmental PFAS remediation.