Full-Scale Evaluation of the Ammonia-Chlorine Process as a Bromate Control Strategy

摘要

Ozonation of water containing moderate to high levels of bromide (0.1-0.3 mg/L), such as California State Project water, can form bromate at levels that exceed the maximum contaminant level of 10 μg/L. A proven technology to minimize the formation of bromate is to add acid to reduce the pH of ozonation. However, in waters with moderate or high alkalinity, the cost of acid and caustic to lower and subsequently raise the pH of the water, respectively, can be higher than the cost of producing ozone. To lower costs, the Metropolitan Water District of Southern California conducted a demonstration-scale evaluation of the addition of ammonia and then chlorine (ammonia-chlorine process) to form chloramines prior to ozonation as an alternative bromate control strategy that did not require operation at an acidic pH. Full-scale testing at Metropolitan’s Henry J. Mills Water Treatment Plant was initiated to determine if this technology would be a viable option. Results showed that the ammonia-chlorine process consistently controlled bromate to 5 μg/L or less at ambient pH (7.7) with bromide as high as 0.30 mg/L.