Bromate abatement with ultraviolet light-emitting diode/thiosulfate advanced reduction processes: Mechanisms, affecting parameters and applications

Abstract

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-LED<inf>265</inf>/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-LED<inf>265</inf>/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-LED<inf>265</inf>/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-LED<inf>265</inf>/thiosulfate ARPs for effective bromate degradation, using a sustainable UV radiation source and compatible with acidic ozone-treated water.