Quantitatively assessing the role played by carbonate radicals in bromate formation by ozonation

[Display omitted] •Bicarbonate enhances the bromate formation by ozonation due to the role of CO3−.•The role played by CO3− in bromate formation was quantitatively evaluated.•CO3−-involved bromate contributes a large fraction of the total bromate formed.•The main role of CO3− is the oxidation of bromine to BrO in the bromate formation.•A model was developed and was shown to predicted the CO3− -involved bromate well. Bicarbonate scavenges OH to form CO3− that enhances the bromate formation by ozonation. However, the role of CO3− in the bromate formation during ozonation has never been quantitatively investigated. Herein, we establish a quantitative approach for evaluating the role played by CO3− based on the detection of CO3−-involved bromate and CO3− exposure. Experiments demonstrated that the CO3−-involved bromate was responsible for 33.7–69.9% of the total bromate formed with bicarbonate concentrations from 0.5 mM to 4 mM. The CO3− exposure was two orders of magnitude higher than the corresponding OH exposure during ozonation. These results demonstrate that CO3− plays a comparable or even more pronounced role in the oxidation of bromine during bromate formation than OH. A model was developed based on the ratio of bromine oxidized by CO3−, which could predict the CO3−-involved bromate formation well. Modeled and experimental results illustrated that the contribution of the CO3−-involved bromate to the total bromate decreased with increasing pH or initial bromide, but almost remained unchanged at different ozone dosages. Moreover, the presence of humic acid led to an increase in this contribution during ozonation. The results of this study provide a more in-depth understanding of the mechanism of bromate formation during ozonation.