Empirical modeling of bromate formation during ozonation of bromide-containing waters

Empirical bromate formation models were developed from observed batch ozonation data to simulate the effects of important water quality characteristics and treatment processes on bromate formation. Data generated from true batch ozonation studies with an orthogonal matrix design, served as the base for development of empirical models for bromate formation. The variables examined include pH, initial bromide concentration, alkalinity, ozone dose, ammonia and dissolved organic carbon level. This array of variables was selected to evaluate the effects of important water quality characteristics and treatment processes on the formation of bromate ion during water ozonation. Limited temperature variation data were also generated. Isolation and fractionation of natural organic matter (NOM) by ultrafiltration and reverse osmosis membrane techniques allowed assessment of source water variations and the role of molecular size on bromate formation. Multiple linear regression of logarithmic transformations was used to generate the models. Results obtained from the empirical models indicate that bromate formation is favored at high pH, initial bromide concentration, alkalinity and high ozone dose. On the other hand, increasing DOC and ammonia concentration decreased bromate formation. The models also indicated that NOM isolated from different water sources have a strong influence on bromate formation upon ozonation of model solutions composed of different membrane isolates. Both internal and external validation of the models demonstrated that the bromate models predicted bromate formation well. Finally, the models indicated that acid addition (pH depression) strategies can be used to control bromate formation.