Reductive Control of Refractory Contaminants in Water by Far-UVC Photolysis of Sulfite

The emergence and risks of oxidant-resistant contaminants necessitate the adoption of advanced reduction processes (ARPs) for their remediation. Conventional UV-based ARPs, however, face limitations in real-world applications due to inefficient light and chemical utilization as well as low yields of hydrated electrons (e_aq^-). In this study, we demonstrate that shifting the UV irradiation wavelength from 254 nm (UV₂₅₄) to 222 nm (UV₂₂₂) in the UV/sulfite ARP enhances the e_aq^- yield by 48.67-fold. Leveraging experimentally determined parameters, including the molar absorption coefficient of sulfite (1145 ± 11 M^-1 cm^-1) and its quantum yield for photolysis (0.104 ± 0.0070 mol Einstein^-1) at 222 nm, we developed a kinetic model to predict e_aq^- concentrations in the UV₂₂₂/sulfite system under diverse environmental and operational conditions. Using real tap water and surface water matrices, we show that the UV₂₂₂/sulfite ARP reduces energy consumption by a factor of 4.19-16.18 compared to the conventional UV₂₅₄/sulfite process during the degradation of halogenated contaminants, including perfluorooctanoic acid (PFOA). Additionally, the UV₂₂₂/sulfite system decreases cytotoxicity in natural organic matter (NOM)-laden water by 28% following chlorination, which is mainly attributed to the suppressed formation of dichloroacetonitrile (DCAN).