Synergistic reductive dechlorination and oxidative mineralization of chlorinated organic compounds in a UV-anaerobic Fenton system: UV-driven Fe(II)/Fe(III) cycling and continuous radical generation.

The effective remediation of chlorinated organic compounds (COCs) in industrial wastewater is hindered by the high C-Cl bond dissociation energy and toxic chlorinated intermediates formation in traditional advanced oxidation processes (AOPs). This study developed a UV-anaerobic Fenton system that synergizes oxidative and reductive pathways for efficient degradation and dechlorination of p-chloroaniline (p-CA). The system achieved excellent performance with 93.5 % TOC removal and 89.8 % dechlorination within 90 min. Mechanistic analysis revealed that UV light drove Fe(III) reduction through both direct photoreduction and hydrated electrons (eaq-), ensuring rapid Fe(II)/Fe(III) cycling and sustained hydroxyl radicals (•OH) production. Critically, the anoxic environment prevented scavenging of eaq- and hydrogen radicals (•H), enabling them to serve as primary species for reductive dechlorination. The subsequently generated aniline intermediates, activated by the electron-donating -NH2 group, became highly susceptible to •OH attack, promoting ring opening and sequential oxidation to short-chain carboxylic acids, ultimately achieving complete mineralization. Furthermore, the broad applicability of the system was verified by extending to typical COCs such as p-nitrochlorobenzene (p-NCB), trichloroethylene (TCE), trichloromethane (TCM), and trichloroacetic acid (TCA). By systematically elucidating a reduction-dominated pathway synergistically coupled with oxidative degradation, this study challenges the conventional oxidation-centric paradigm in Fenton chemistry. It provides experimental evidence to support the theoretical development of inherent advanced reduction processes in AOPs and offers a scientific foundation for optimizing the advanced treatment of chlorinated organic wastewater.