AWWA WQTC71618

This powerpoint presentation begins by providing a brief overview of drinking water disinfection and emerging challenges for water treatment. Ultraviolet (UV) irradiation is presented as a promising alternative, along with photolysis of chlorine, the role of bromide during UV/chlorine process, and concerns for halate formation during UV/chlorine process. Study objectives were to: explore the effects of bromide ion on the photolysis of free chlorine; characterize halate formation during UV/chlorine coexposure process with the presence of bromide; and, evaluate contamination level of halate in simulated drinking water after UV/chlorine process. Materials and methods included: natural organic matter (NOM) source - Suwannee River NOM (SNOM solution); free halogen source - NaOCl: Cl₂(gas) + 0.01M NaOH. UV system configuration is presented, along with analytical methods. Conclusions indicate that: the presence of bromide did not significantly change the observed photolysis free chlorine; upon UV irradiation, chlorine is always far more efficient in achieving higher [OH]_SS than bromine; BrO• and BrO₂^- may serve as decisive intermediates during bromate formation; the scavenging of BrO₂^- by excessive free chlorine could hinder the bromate formation from •OH-dominated multistep oxidation; and, from a practical point of view, when the bromide ion concentration in raw water exceeding 1 mg/L, the UV/chlorine process may induce the potential risk of bromate exposure by breaking its MCL of 10 µg/L; on the other hand, the chlorate formation was minor considering the provisional guideline value of 700 µg/L. Includes figures.