Implications of bromate depression from H₂O₂ addition during ozonation of different bromide-bearing source waters

Minimizing bromate formation by adding H₂O₂ is one major option for bromide-containing source water when applying ozone in drinking water. However, difference in background water quality can have a significant influence on bromate depression. In this study, three bromide-bearing source waters (YZ, HR and HP) were selected to investigate bromate depression during the H₂O₂-ozonation process. The results showed that there was strong correlation between bromate formation and molecular ozone consumption during ozonation process for the three waters. Compared to YZ and HR, ozone was consumed quickly within about 10 min for HP water, inducing lower bromate formation during ozonation process. In the initial step of bromide oxidation, molecular ozone oxidation was responsible for more than 80% of oxidation, much higher than that by hydroxyl radicals. Specifically, 94% of the oxidation of bromide occurred with ozone for YZ water, which might be attributed to the low concentration of organic matter in the water. The residual molecular ozone would be a restrictive factor and affect the bromate formation significantly. For YZ and HP water, as H₂O₂/O₃ (g/g) increased to 0.5, the ozone decomposition rate increased 61 times and 7.2 times respectively, which resulted in difference in bromate depression performance when applying H₂O₂. Humic acid and tyrosine in water were confirmed to have effects on bromate formation and depression after H₂O₂ addition. This study could elucidate the different bromate depression effects occurring in different source waters when adding H₂O₂, which will provide an informative guide for bromate control in drinking water treatment.