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

Bicarbonate scavenges OH to form CO that enhances the bromate formation by ozonation. However, the role of CO in the bromate formation during ozonation has never been quantitatively investigated. Herein, we establish a quantitative approach for evaluating the role played by CO based on the detection of CO-involved bromate and CO exposure. Experiments demonstrated that the CO-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 CO exposure was two orders of magnitude higher than the corresponding OH exposure during ozonation. These results demonstrate that CO 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 CO, which could predict the CO-involved bromate formation well. Modeled and experimental results illustrated that the contribution of the CO-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.