Bromate(BrO_3) is a disinfection by-product in drinking water, and its removal is very difficult especially at low levels.60 Co gamma rays were used to remove BrO_3in aqueous solution in this study. The effects of absorbed doses, BrO_3initial concentration, gas saturation, p H value and coexisting anions(Cl, NO 3, SO2 4and HCO 3=CO_3^(2 -))on BrO_3reduction were evaluated. After 4.0-k Gy irradiation of air-equilibrated solution of 30.7 lg/L BrO_3, the residual BrO_3was 8.3 lg/L, which is below the maximum contaminant level of drinking water. The BrO_3reduction rate increased with the dose, in the order of N2[ air [ O_2[ N_2O atmosphere under similar conditions. The results also show that high p H favored the BrO_3removal. According to the experimental results, it can be concluded that the efficiency of decomposing BrO_3by reactive species followed the order of e aq[ H [ HO_2 [ O_2. Coexisting Cl, HCO 3=CO_3^(2 -)and SO2 4ions have little effect on BrO_3removal, whereas NO_3can inhibit its removal as a result of competition with BrO_3for e aq.
The formation of bromate,a classified potential carcinogen,is of great concern when disinfection processes are used for treating high-bromide drinking waters.Bromide-containing aqueous solutions with various additives were irradiated by ^(60)Co γ source.With a 2.0 kGy irradiation of N_2O-saturated solutions at initial bromide concentrations of 180.2μgl^(-1),416.9μgl^(-1),663.1μgl^(-1) and 823.9μgl^(-1).79.5%,84.0%,87.3%and 88.3%of bromide ions were transformed to bromate,respectively.Addomg CO_3^(2-)/HCO_3^- or NO_3^- ions into N_2Osaturated bromide solutions,the amount of bromate ions formed decreased with increasing concentrations of the additives.On the other hand,the bromate concentration was all below the detection limit of 1 μgl^(-1) whenever N_2O was not added to quench e_(aq)^- and H.The results indicated that γ-rays irradiation could be used as a disinfection process,instead of ozonation,to comply with upcoming more stringent regulations,especially in waters containing high concentrations of bromide.
