Pilot Study On Formation And Inhibition Methods Of Bromate During Ozonation For Bromide- Containing Water

Ozonation process application in drinking water treatment has increased all over the world, by-products like bromate formed upon ozone disinfection received more concern. Bromate has been classified as a possible class II-B carcinogen by the International Agency for Research on Cancer (IARC). The maximum level of bromate content in drinking water had been set at 10μg/L, according to the drinking water standards released by China EPA on November 29th,2006. Simulation studies in pure water were conducted to investigate the influential factors and inhibition methods (i.e. inhibitors like NH₄⁺/H₂O₂ and catalytic ozonation in presence of nano-metal oxides) of bromate formation during ozonation of bromide-containing water, in order to synthetically control the bromate formation during ozonation process. Main research conclutions are as follows.When other water parameters were kept unchanged, bromate formation increased as ozone dosage increased and continuous ozone dosing method could decrease about 46.5 percent of bromate formation when compared with instantaneous ozone dosing method. Furthermore, under the constant ozone dosing conditions, bromate formation had a linear correlation with the initial bromide concentration, and more than triple bromate were formed as the temperature increased in the range of 15 - 26℃. The increase of pH value in the range of 6.0 - 7.8 led to more bromate formation and faster degradation of dissolved ozone in water. Also, bromate formation decreased as humic acid concentration in water increased in the range of 0 - 3 mg/L. Total bromine in solution was found conserved throughout the ozonation process.Researches showed that ammonia addition could decrease bromate formation obviously, and had no measurable influence on ozone degradation in water. Excess addition of H₂O₂ could inhibit the formation of bromate as well, but accelerated ozone degradation in water. When ammonia and excess H₂O₂ were added together, bromate formation decreased when compared with the situation that only excess H₂O₂ was added, but increased when compared with the situation that only ammonia was added.It was also shown that both nano-SnO₂ catalytic ozonation and nano-TiO₂ catalytic ozonation could inhibit the formation of bromate during ozonation process, and the inhibition ability of nano-TiO₂ catalytic ozonation was found better than that of nano-SnO₂ catalytic ozonation. Light condition had no measurable influence on the inhibition ability of nano-TiO₂ catalytic ozonation. The inhibition ability of nano-TiO₂ catalytic ozonation increased as nano-TiO₂ dosage was enlarged, especially when nano-TiO₂ dosage was in the range of 0– 100 mg/L. Increment of ozone dosage and reaction temperature could augment the inhibition ability of nano-TiO₂ catalytic ozonation as well, while the rise of initial bromide concentration and pH value could impair the inhibition ability of nano-TiO₂ catalytic ozonation. As humic acid concentration in water increased, the inhibition ability of nano-TiO₂ catalytic ozonation increased at first and then decreased.