AWWA ACE95270

In preparation for a more stringent disinfection byproduct regulation, the District embarked on a comprehensive pilot scale ozonation study. The goal of the study was to evaluate the impact of ozonation on formation of bromate and reduction of taste and odor causing compounds. The effect of variable ozone dose, bromide concentration, ozone contactor configuration, and ozone feed gas concentration on the formation of bromate and reduction of geosmin and MIB were also tested. Ozone was applied at the minimum dose required to meet the C x T criteria for disinfection, and at higher doses required for taste and odor control. Ozone was added to the water at two different contactor configurations, at 40/20/20/20 and at 60/20/20/20 percent splits. The raw water was spiked with geosmin and MIB, and varying concentrations of bromide. Ozone residual, raw settled and finished TOC, UV254, alkalinity, hardness, turbidity, color, pH, geosmin, MIB, bromide and bromate were measured. The results of the study show that settled water ozonation produces lower bromate levels than raw water ozonation, even at comparable pH. Bromate levels for the settled water ozonation were consistently below the 10 ug/L level, at ozone doses required for 1.0 log inactivation of Giardia. Ammonia addition and pH reduction methods reduced bromate formation for both application points. Raw water ozonation was more effective in the reduction of geosmin and MIB than settled water ozonation. Higher ozone feed gas concentration resulted in higher finished water bromate levels. The preliminary results for ozone dose splitting were inconclusive. Additional data will be gathered to obtain more information on the impact of ozone contactor configuration on bromate formation.