UVC/sulfite-based ARPs for trifluoroacetic acid defluorination in water: Performance, kinetics, and mechanism

Rapid defluorination of TFA in water is achieved using the anoxic UVC/S(IV) system. • UVC-induced S(IV) photoactivation generates hydrated electrons for C–F bond cleavage. • Key operational parameters for the defluorination process are optimized. • Kinetic simulation verifies stepwise hydrated-electron-mediated defluorination pathway. Trifluoroacetic acid (TFA), a representative ultrashort-chain PFAS, is highly mobile, persistent, and difficult to remove by conventional water treatment. In this study, an anoxic UVC/S(IV) system was developed for rapid TFA defluorination through sulfite photoactivation and hydrated-electron-induced C–F bond cleavage. The individual roles of UVC irradiation, sulfite, and dissolved oxygen (DO) were first examined, followed by evaluation of operating factors and water-matrix components. Negligible defluorination occurred with UVC or sulfite alone, whereas their combination induced rapid fluoride release, confirming the essential role of sulfite photoactivation. DO strongly inhibited defluorination by scavenging hydrated electrons, indicating that oxygen exclusion is necessary. Under baseline conditions of pH 11, 20 mM sulfite, and 0.2 mM TFA, approximately 90% defluorination was achieved within 30 min. Temperature, pH, sulfite concentration, and photon flux were the main factors governing fluoride release. Ca 2+ , Mg 2+ , NO 3 − , and humic acid markedly inhibited TFA defluorination, while Na + , K + , Cl − , and SO 4 2− showed little effect. A kinetic model incorporating sulfite photoactivation, hydrated-electron reactions, stepwise defluorination, and S(IV) depletion reproduced the experimental trends. Overall, this work clarifies the operating conditions and matrix limitations of an anoxic UVC/S(IV) process for TFA defluorination. Download: Download high-res image (261KB) Download: Download full-size image