Bromate abatement with ultraviolet light-emitting diode/thiosulfate advanced reduction processes: Mechanisms,...

Bromate, a possible carcinogenic byproduct of ozonation, is potentially removed by the ultraviolet (UV)/sulfite advanced reduction process (ARP), with hydrated electrons playing a major role. However, this process becomes less efficient under acidic to neutral pHs and remains limited to the use of conventional mercury UV lamps. To address these issues, a UV-light emitting diode (UV-LED)-based ARP was studied for bromate removal using thiosulfate as an alternative reducing agent and UV-LEDs emitting at 265 nm and 280 nm as a radiation source. The UV-LED₂₆₅/thiosulfate process effectively reduced 100 ± 0.0% of the initial bromate concentration (4.0 μM) at pH 6.4 ± 0.1, following the pseudo first-order rate constant of 1.3 × 10^-2 min^-1. Meanwhile, the UV-LED₂₆₅/sulfite process attained only 11.6 ± 1.4% bromate degradation efficiency. Results of electron paramagnetic resonance and scavenging experiments indicate that hydrated electrons and sulfite radicals derived from the UV-LED₂₆₅/thiosulfate process played a significant role in bromate degradation. The process demonstrated optimal performance within a pH range of 5.8-6.4, with higher thiosulfate doses accelerating the bromate removal efficiency. Furthermore, excessive chloride and bicarbonate concentrations interfered with the bromate removal. Comparable energy consumption (electrical energy per order of 27.4 kWh/m³) with UV/sulfite processes has demonstrated the potential of UV-LED₂₆₅/thiosulfate ARPs for effective bromate degradation, using a sustainable UV radiation source and compatible with acidic ozone-treated water.