[Bromate ions formation in UV/chlorination processes for bromide-containing solutions].

Bromate ions formation in UV/chlorination processes was systematically investigated. Experimental conditions were explored, such as pH, initial concentration of NaOCl, dissolved oxygen, UV light intensity and water temperature. The results showed impalpable changes of the H2O-NaOCl-Br(-) system was observed in dark, whereas in UV/chlorination processes free chlorine was continuously reduced and a considerable ratio (6.6 - 32 percent) of bromide was oxidized to bromate. The chlorine decomposition followed pseudo-first order rate equation when the reaction conditions, including pH, temperature and UV light intensity, was nearly fixed. Within the light intensity range of 610 - 1 896 microW/cm2 and temperature range of 12.2 - 36.1 degrees C the pseudo-first order rate constants had a linear relationship with temperature and light intensity, respectively. Bromate formation could be divided totally into three stages: quick-form stage, slow-form stage and plateau stage. In slow-form stage the production of bromate had a good linear relationship with the amount of decayed chlorine, of which the regression coefficients were higher than 0.96 in most cases. Under the conditions in these experiments (pH 4.41 - 11.07, DO 1.5 - 9 mg/L, Cl2 1.23 - 4.50 mg/L), production of bromate was favored under the circumstance with low pH value, low DO value and high chlorine concentration. Both increasing temperature and increasing light intensity improved the creation of bromate, as well as reduced the duration of bromate forming process because of the acceleration of chlorine decomposition.