Bromate Formation In Ozonation Coupled With Common Inorganic Reducing Agents

The process of ozone oxidation of bromine water will produce carcinogenic bromate,and the mechanism of its formation has been discussed completely.According to the pathway of bromate formation,ozone and hydroxyl radicals play important roles in this process.Generally,inorganic reducing agents can react with ozone and hydroxyl radicals to inhibit the formation of bromate.But when a certain type of reducing agents added,the concentration of hydroxyl radicals increases.There has not been studies on whether the concentration of bromate increases after adding these type of reducing agents yet.In this work,the formations of bromate after inorganic reducing agents added into the ozone system were studied.We compared the effects of inorganic reducing agents-sodium nitrite,sodium sulfite,hydroxylamine and sodium thiosulfate on the formation of bromate at different inorganic reducing agent concentrations,p H,bromide concentration,ozone concentration and temperature under the sa me experimental conditions.It was found that sodium sulphite and sodium nitrite did not affect the formation of bromate under various influencing factors and inhibited the formation of bromate.But when a certain concentration of hydroxylamine and sodium thiosulfate added,the formation of bromate was promoted.So the effect of hydroxylamine,sodium thiosulfate on the ozone system bromate formation was analyzed in detail.In the experiment of bromate formation in ozonation coupled with hydroxylamine,when the hydroxylamine was added into system,the bromate was produced a lot at low p H,and the concentration of bromate was 2.06 ?M which is the largest under 30 ?M of hydroxylamine at p H=3.0.The phenomenon was attributed to the effective ?OH formation in the ozone/hydroxylamine system at acidic p H.Based on the evolutions of the formed concentrations of HOBr/Br Oand the hydroxyl radical,we proposed that bromide was initially oxidized by OH to form ?Br,which was then further oxizide by ozone and formed bro mate eventually in the ozone/hydroxylamine system at acidic p H.In the experiment of bromate formation in ozonation coupled with sodium thiosulfate,when the sodium thiosulfate was added into the ozone system,the bromate was produced fast.The concentration of bromate was the 0.80 ?M,89.9% of the whole concentration of bromate,which is highest under 25 ?M of sodium thiosulfate at p H=7.0.The concentration of bromate was much greater than that of ozone alone,and it did not change significantly with p H at p H=3.0~7.0.However,according to the evolutions of the formed concentrations of HOBr/Br Oand the hydroxyl radical exposure,the bromate formation in ozone/sodium thiosulfate system depended mainly on hydroxyl free radicals.In real water,increasing the concentration of sodium thiosulfate can prevent the f bromate forming.