Enhanced Photolysis of Sulfite by Far-UVC (222 nm) and Efficient Photoreductive Degradation and Dehalogenation of Halogenated Organic Pollutants

UV/sulfite technologies offer promising advanced reduction processes (ARPs) for the degradation and dehalogenation of halogenated organic compounds (HOCs), but are limited by the low absorption of sulfite at a conventional wavelength of 254 nm (UV254). This study introduces a wavelength-optimized far-UVC KrCl* lamp (UV222)/sulfite as transformative ARPs. Sulfite exhibited 45.6-fold stronger absorption at 222 nm compared with 254 nm, coupled with a higher innate quantum yield (Φ_innate) of 0.128 mol·Ein^-1 versus 0.115 mol·Ein^-1. This wavelength optimization generated 29.2-fold higher steady-state concentration of e_aq^-, with optimal performance at basic pH (>9) and moderate sulfite dosages (0.4-0.75 mM). HOC degradation and dehalogenation showed clear structure-dependent patterns. The enhancive effect of UV222 over UV254 negatively correlated with HOCs' susceptibility to UV photolysis due to competitive absorption between sulfite and target compounds. Electron-withdrawing halogens significantly favored reductive degradation over oxidation, enabling UV222/sulfite to outperform UV222/H₂O₂ by 1.3-37.1 times in degradation and 1.9-48.6 times in dehalogenation efficiency, with prominent enhancement particularly for polyhalogenated HOCs. In real water matrices, nitrate and nitrite inhibited HOCs' degradation through UV absorption and e_aq^- scavenging. Compared with UV254/sulfite, UV222/sulfite reduced energy costs by 92.7% and required lower sulfite doses. This study provides insights into the wavelength-matching mechanism for UV/sulfite, offering an economical and efficient solution for the remediation of recalcitrant HOCs.