A drinking water utility's perspective on bromide, bromate, and ozonation

Application of ozone in drinking water treatment plants in the US is growing because of ozone's multiple benefits. Ozone functions as a powerful oxidizing agent and disinfecting agent, it improves finished water quality by reducing turbidity, it reduces the formation of many halogenated disinfection by-products, and it is capable of treating chlorine resistant organisms like cryptosporidia. However, when bromide ion is present, e.g. from the geology, runoff, or sea water intrusion, ozone will convert some of the bromide to bromate depending upon the treatment reaction conditions. Bromate can also be introduced into drinking water as a contaminant in the chlorine used for disinfection. The current maximum contaminant level (MCL) in the USA is 0.010 mg/L, and the maximum contaminant level goal (MCLG) is zero, because of the possibility that bromate may function as a genotoxic carcinogen. The level of the MCL, especially if it is lowered, will significantly impact the ability of many water suppliers to utilize ozone in their water treatment processes and also raise the costs of those applications.