| Bromate is the most concerned disinfection by-product in drinking water treatment. According to the new Chinese Standards for Drinking Water Quality, the maximum contaminant level for bromate is10μg·L-1. Bromate is mainly formed in ozonation processes from the oxidation of bromide through a combination of ozone and· OH radical reactions. Bromate concentration control is realized through minimization of Bromate formation in treatment processes and bromate elimination after its formation. Ammonia addition, pH depression and chlorine-ammonia process are feasible measures in control of bromate formation; several physical and chemical methods have been studied as options to remove Bromate already existed.Ozone oxidation of bromide ion in water solution reaction research was investigated via two different experimental methods of continuous inlet ozone and intermittent adding saturated ozone water. The effects of reaction time, the ozone dosage as well as pH value on the reaction process of bromide ion and ozone. The results show that, with feeding ozone continuously into bromide containing water, the initial concentration of Br-was488μg·L-1, the concentration of bromine in bromate accounted for11%of total bromine concentration, accounted for17%to the oxidation bromine concentration; the concentration of bromine in the intermediate product accounted for50%of total bromine concentration, accounted for83%to the oxidation bromine concentration. With the Br-initial concentration of155.2mg·L-1, the concentration of bromine in bromate accounted for24%of total bromine concentration, accounted for63%to the oxidation bromine concentration; the concentration of bromine in the intermediate product accounted for14%of total bromine concentration, accounted for37%to the oxidation bromine concentration. While adding saturated ozone water into Br-containing water, with Br-initial concentration of5mg·L-1, the decrease in the concentration of Br-were2.06mg·L-1, the increase concentrations of BrO3-were only0.31mg·L-1, the concentration of bromine in the bromate accounted for10%of the oxidation bromine concentration. At the same time, the pH value had no significantly affect on the reaction of ozone and bromide ion in aqueous solution. The results also demonstrated that the final products of the oxidation reaction were identified to be Br2and Br3-except for BrO3-. The formation of Br3-which was yielded from the reaction of Br2with Br-was the major process in the reaction of Br-attacked by O3. The characteristic absorption spectrum of Br3-with an absorption peak at260nm as well as the molar absorptivity of Br3-of3.4×104L·mol-1·cm-1were also investigated.Hydrogen, ferrous sulfate and sodium sulfite are selected in this research as reductants to study the effects of chemical reduction on bromate elimination. Under normal temperature, pressure and typical pH range in drinking water treatment, hydrogen cannot react with Bromate. Ferrous sulfate can remove bromate but is not a realistic option due to its easy reactivity with dissolved oxygen and potential hazard brought by ferric ion. Sodium sulfite is a feasible option to reduce bromate and the removal rate is higher in alkaline condition than in acidic condition. A preliminary research is conducted on the capability of granular activated carbon to remove bromate. At the room temperature of20℃, in the pH range of5.5-8, The adsorption equilibrium profile is given; the adsorption capability is12mg·g-1; at a dosage of3g·L-1, the removal rate can reach as high as99.1%. The adsorption isotherms are also studied and analysed using several models. BET adsorption isotherm is the most suitable to describe experimental results, and theoretical one-layer adsorption capacity is calculated to be9.61mg·g-1The results may provide helpful information about the mechanism of the oxidation reaction of Br-with O3and fate of Br-or its derivatives in the environment by the oxidation processes, meanwhile, provide data basis for bromate removal in aqueous solution. |
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