Ozonation of waters containing moderate to high levels of bromide at ambient pH can form bromate at levels that may exceed the United States maximum contaminant level (MCL) of 10 μg/L. A proven technology for minimizing the formation of bromate is ozonation of the water at a reduced (typically acidic) pH. However, in waters with moderate or high alkalinity, the cost of acid and base addition to lower and subsequently raise the pH of the water can be higher than the cost of generating the ozone. To lower costs (minimize the amount of acid and base addition), Metropolitan Water District of Southern California has been conducting a long-term evaluation of alternative bromate-control strategies. Test results indicate that, depending on a utility's by-product goals, that the addition of chlorine/ammonia, ammonia/chlorine or chlorine dioxide upstream of the ozone can be used to significantly minimize bromate formation. This paper provides new insights into emerging bromate-control strategies, as well as potential fatal flaws-the increased formation of other by-products of concern (chlorate, trihalomethanes, N-nitrosodimethylamine) in treated water.

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