H₂o₂/o₃ Advanced Oxidation Technology For Bromate Control During Ozonation Of Yellow River Water

Ozone-Biological Activated Carbon (O₃-BAC) is a widely-used advanced watertreatment technology. However, carcinogen bromate is formed during ozonation ofbromide^-containing water, which has become a serious problem in O₃^-BACtechnology at present. In this study, characteristics of ozone depletion and bromateformation of Yellow River water were investigated and bromate formationmechanisms were proposed. Based on this, H₂O₂/O₃ advanced oxidation processes(AOPs) were applied for bromate control during ozonation and its controlmechanisms were revealed subsequently. In addition, the influences of waterconditions and treatment methods on bromate control were also discussed. Theresults showed that:Ozone decomposition accorded with first order reaction in pure water system(145μg/L Br^- and no organic matter). A two-step first-order reaction kinetic modelwas employed to simulate the same process in Yellow River water. During ozonationof this water, about 65% of bromate was formed through the following pathway:Batch experiments showed that H₂O₂/O₃ AOPs turned out to be feasible forbromate control and with the ozone dose of 2⁴mg/L, a decrease of 30%⁶0% inbromate formation has been observed. When the molar ratio of H₂O₂/O₃ was 1.5,bromate concentration reached the minimum. The bromate control mechanisms ofH₂O₂/O₃ AOPs were as follows: O₃ was transformed to·OH with H₂O₂ addition andthis has remarkably inhibited the oxidation of Br^- by O₃. In the meantime,·OH wasmainly consumed by organic matter instead of Br^-, so it did not increase bromateformation evidently.When H₂O₂/O₃ AOPs were applied in bench scale experiments, a decrease of70% in bromate formation could be expected averagely with the ozone dose of2.88⁴.30mg/L. When the molar ratio of H₂O₂/O₃ was 1.5, the bromateconcentration reached the minimum as well, and could be restricted below 10μg/L to satisfy the existing drinking water standard with an ozone dose below 3.72mg/L. More than 50% of UV254 was removed in H₂O₂/O₃ AOPs. Besides, the direct cost of H₂O₂/O₃ AOPs application was only RMB 0.015 Yuan / m³ water more than independent ozone oxidation. Therefore, it is economically feasible to use H₂O₂/O₃ AOPs in the existing O₃-BAC processes.