Enhancing Ferrate Oxidation of Micropollutants via Inducing Fe(V)/Fe(IV) Formation Needs Caution: Increased Conversion of Bromide to Bromate

This study explores the formation of bromate (BrO ) in the copresence of Fe(VI) and bromide (Br ). It challenges previous beliefs about the role of Fe(VI) as a green oxidant and highlights the crucial role of intermediates Fe(V) and Fe(IV) in the conversion of Br to BrO . The results show that the maximum concentration of BrO of 48.3 μg/L was obtained at 16 mg/L Br and that the contribution of Fe(V)/Fe(IV) to the conversion was positively related to pH. The study suggests that a single-electron transfer from Br to Fe(V)/Fe(IV) along with the generation of reactive bromine radicals is the first step of Br conversion, followed by the formation of OBr which was then oxidized to BrO by Fe(VI) and Fe(V)/Fe(IV). Some common background water constituents (e.g., DOM, HCO , and Cl ) significantly inhibited BrO formation by consuming Fe(V)/Fe(IV) and/or scavenging the reactive bromine species. While investigations proposing to promote Fe(V)/Fe(IV) formation in Fe(VI)-based oxidation to enhance its oxidation capacity have been rapidly accumulated recently, this work called attention to the considerable formation of BrO in this process.