The ozonation process was successfully implemented to provide primary disinfection for Giardia and viruses and to
control tastes and odors. Raw water ozonation has also shown to provide microflocculation benefits, including lower
ferric sulfate and lime use and improved filtered water quality. Approximately 2. 5 mg/L ozone is typically required to
meet disinfection requirements. Ozone residuals are maintained to achieve a City disinfection inactivation ratio goal of
1. 5. The raw water bromide levels, coupled with relatively high pH, are in a range that could lead to excessive bromate
formation following ozonation.
The City did not monitor bromate at the Eagle Mountain WTP until the Stage 1 Disinfectants/Disinfection By-Products
Rule (DBPR) was finalized in 1999. At that time, the City began monitoring the treated water for bromate and found
that levels near or slightly exceeding the 10 µg/L were being produced.
Findings from the report, Strategies to Control Bromate and Bromide (1999, order #90751/project #156) proved to
be very useful in selecting the best strategy to minimize bromate formation. That study showed that ammonia addition
prior to ozonation could reduce the formation of bromate by the formation of bromamines. Bromamines would be less
reactive to the ozone and not form as much bromate.
As a result of examining the Foundation study, the City began feeding ammonia gas into the raw water, upstream of
the ozone contact basins. It was determined that an ammonia dose of approximately 0.1 to 0.12 mg/L limits bromate
formation in the treated water to levels typically below the detection limit of 5 µg/L when the ozone dose is maintained
at approximately 2. 5 mg/L and the raw water pH is approximately 8.0.
Using a low dose of ammonia in the raw water has enabled the Eagle Mountain WTP to control bromate
formation and meet the regulatory limit of 10 µg/L. However, the bromide levels have been consistently above
0.200 mg/L for the past two years requiring the plant staff to closely monitor the ozonation process to keep
bromate levels below the regulatory limit.