Environmental analytical methods

Bromate ion formation in dark chlorination and ultraviolet/chlorinationprocesses for bromide-containing water

HUANG Xin , GAO Naiyun , DENG Yang


Received April 15, 2007,Revised September 30, 2007, Accepted , Available online

Volume 20,2008,Pages 246-251

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Bormate (BrO3??) is a carcinogenic chemical produced in ozonation or chlorination of bromide-containing water. Although its formation in seawater with or without sunlight has been previously investigated, the formation of bromate in dilute solutions, particularly raw water for water treatment plant, is unknown. In this article, the results of bench scale tests to measure the formation rates of bromate formation in dilute solutions, including de-ionized water and raw water from Yangtze River, were presented in dark chlorination and ultraviolet (UV)/chlorination processes. And the e ects of initial pH, initial concentration of NaOCl, and UV light intensity on bromate formation in UV/chlorination of the diluted solutions were investigated. Detectable bromate was formed in dark chlorination of the two water samples with a relatively slow production rate. Under routine disinfecting conditions, the amount of formed bromate is not likely to exceed the national standards (10 g/L). UV irradiation enhanced the decay of free chlorine, and, simultaneously, 6.6%–32% of Br?? was oxidized to BrO3??. And the formation of bromate exhibited three stages: rapid stage, slow stage and plateau. Under the experimental conditions (pH = 4.41–11.07, CCl2= 1.23–4.50 mg/L), low pH and high chlorine concentration favored the generation of bromate. High light intensity promoted the production rate of bromate, but decreased its total generation amount due to acceleration of chlorine decomposition.

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