An overview of bromate formation in chemical oxidation processes: Occurrence, mechanism, influencing factors, risk assessment, and control strategies

Chemical oxidation processes have been extensively utilized in disinfection and removal of emerging organic contaminants in recent decades. Some undesired byproducts, however, are produced in these processes. Of them, bromate has attracted the most intensive attention. It was previously regarded as a byproduct that typically occurred in ozone-based oxidation processes. However, for the past decade, bromate formation has been detected in other oxidation processes such as CuO-catalyzed chlorination, SO4--based oxidation, and ferrate oxidation processes. This review summarizes the occurrences, mechanisms, influencing factors, risk assessment, and control strategies of bromate formation in the four oxidation processes, i.e., ozone-based oxidation, chlorine-based oxidation, SO4--based oxidation, and ferrate oxidation. Besides, some unresolved issues for future studies are provided: (1) Clarification of the relative contributions of SO4- and Br to the oxidation of bromine for bromate formation in SO4--based oxidation processes; (2) evaluation of the role of different reactive species in the bromate formation in the process of UV/HOCl; (3) quantification of the dual role of alkalinity in bromate formation during ozonation; (4) assessment of the risks of bromate formation in SO4--based oxidation processes for practical applications; and (5) exploration of strategies for inhibiting bromate formation in SO4--based oxidation, UV/chlorine, and metal oxide-catalyzed chlorination processes. [Display omitted] •This work reviewed the formation of bromate in four chemical oxidation processes.•The occurrences and mechanisms of bromate formation were discussed and compared.•The influencing factors of bromate formation were comprehensively analyzed.•The risk assessments and corresponding control strategies of bromate were compared.•Five main unresolved issues of bromate for future studies were made.