New insights into bromate removal by UV/sulfite process: Influencing factors, mechanism, and energy efficiency

In recent years, the UV/sulfite process has shown high superiority in removing toxic halogenated organic compounds and oxyanions. Herein, the reduction of bromate (BrO₃ˉ) in this process was reinvestigated. The reduction of BrO₃ˉ in this process was influenced by some key coexisting species. A significant inhibition on the reduction of BrO₃ˉ was observed in the presence of dissolved oxygen (DO). Nevertheless, increasing sulfite dosage could effectively mitigate the negative impact of DO on the reduction of BrO₃ˉ. Humic acid (HA) could influence the reduction of BrO₃ˉ through the enhancement of hydrated electron (e_aqˉ) yield or the scavenging of e_aqˉ. It should be noted that the presence of Cl⁻ and HCO₃⁻ had an insignificant influence on the reduction of BrO₃ˉ. In this process, besides e_aqˉ, sulfite radical (SO₃^•−) also contributed to the reduction of BrO₃ˉ, which was evidenced by scavenging experiments and fitting of a kinetic model. Moreover, the energy efficiency of this process for BrO₃ˉ removal was found to be enhanced by increasing sulfite dosage, as indicated by calculation of electrical energy per order (EE/O). Meanwhile, this process was proven to be economical for BrO₃ˉ removal. This study might provide a new outlook on the UV/sulfite process for real applications.