Practical Studies of the Electrolysis and Volatilization of the Bromide from Drinking Water to Minimize Bromate Production by Ozonation

In four recently published articles, a process for the oxidation of bromide to bromine and the volatilization of bromine from drinking water sources was presented. This process was shown to be able to remove up to 35% percent of the bromide found naturally in the California State Water Project. Although bromide itself is quite harmless, it has been shown to react with commonly used disinfectants to produce compounds or disinfection by-products (DBPs) of suspected carcinogens. Bromide reacts with ozone to form bromate. This article presents two studies of pilot scale, flow-through electrolytic reactors that oxidize bromide to bromine and volatilize bromine at <pH 3.5, which occurs at the anode as a result of the oxidation of water. One reactor had 14 anodes that were 91 cm deep and the other had 13 anodes 1.2 cm deep. The bromide removal rates were studied at several different water flows and power settings for different bromide concentrations for both reactors. The results show removal of bromide is impacted by water flows and power settings for different bromide concentrations. Effluent from the deep reactor did show some reduction in bromate concentration as compared to control samples but the results were inconsistent. This appeared to be caused by significant differences in the ozone demand produced by different experimental conditions, difficulty determining the concentration of chlorine, and the use of hydrogen peroxide as a dechlorinating agent. Using the shallow reactor, these difficulties were overcome by developing a more consistent determining chlorine concentration, using much larger ozone doses to overwhelm the ozone demand, and by using ascorbic acid instead of hydrogen peroxide. With these changes, it could be shown that the electrolytic reactor not only lowered the concentration of bromide in the water but when ozonated, the amount of bromate formed was reduced in direct proportion to the amount of bromide removed for an equal dose of ozone.