Bromate formation during the oxidation of bromide-containing water by ozone/peroxymonosulfate process: Influencing factors and mechanisms

Previously, we proposed a novel advanced oxidation process combining ozone (O₃) with peroxymonosulfate (PMS), which simultaneously produces sulfate radical (SO₄^{rad -}) and hydroxyl radical (^radOH) and significantly enhances the removal of organic matter. However, bromate formation is poorly understood during the oxidative treatment of bromide-containing water by O₃/PMS process. In this study, factors influencing bromate formation were explored during the O₃/PMS process, including the influences of solution pH, PMS dosage, and bromide concentration in distilled water and in actual water samples. Furthermore, the bromate formation mechanism was also clarified by monitoring the intermediate hypobromous acid (HOBr/OBr^-), calculating the change of bromide species at different pH levels, and was further confirmed by adding radical scavengers. Generally, the O₃/PMS process significantly promotes bromate formation compared with ozone treatment alone. During the O₃/PMS process, increasing the PMS dosage and bromide concentrations promoted bromate formation, which was also significantly improved by raising the pH from 4.0 to 10.0. Bromate formation was a result of the combined effect of molecular ozone, ^radOH, and SO₄^{rad -}, and the HOBr/OBr^- was the essential intermediate species. Bromate formation was inhibited in the actual water sample due to the competitive effect of natural organic matter, bicarbonate, and reaction of HOBr/OBr^- with ammonia. Therefore, the bromate formation should be evaluated as applying the O₃/PMS process for organic matters abatement in bromide-containing actual water.