Bromate ion formation in dark chlorination and ultraviolet/chlorination processes for bromide-containing water.
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 effects 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 microg/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.
Huang
Xin
X
State Key Laboratory of Pollution Control and Resource Reuse, Tongji University Shanghai 200092, China. byronxin@yahoo.com.cn
Gao
Naiyun
N
Deng
Yang
Y
D001959:Bromates / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry* / Q000528:radiation effects*; D002713:Chlorine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D012973:Sodium Hypochlorite / Q000737:chemistry; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000528:radiation effects*; D018508:Water Purification
D001959:Bromates; D001965:Bromides; D014874:Water Pollutants, Chemical; D002713:Chlorine; D012973:Sodium Hypochlorite