University of Massachusetts - Amherst
Environmental Engineering Seminar Presents:
Speaker: Dr. Urs von Gunten
Topic: Ozonation of Drinking Water:
A Balancing Act Between Disinfection and Bromate Formation?
Date: April 20th, 2001, 3:35 pm
Place: Marston 132
The expanded use of ozonation for the disinfection of drinking water has resulted in a growing concern over disinfection byproducts of ozonation. One such disinfection byproduct of ozonation that has been identified is bromate. Bromate has been classified by the International Agency for Research on Cancer (IARC) as having sufficient evidence of carcinogenicity in laboratory animals. In 1993, the World Health Organization (WHO) set a provisional value of 25 µg/l in their drinking water guidelines. The USEPA has proposed a maximum contaminant level (MCL) of 10 µg/l for bromate.
Most drinking water sources contain some level of bromide. Both ozone and hydroxyl radicals, a decomposition product of ozone, contribute to the formation of bromate. A direct reaction with ozone is responsible for the oxidation of bromide (Br-) to hypobromite (BrO-), and the oxidation of bromite (BrO2-) to bromate (BrO3-). The intermediate steps may be carried out through indirect reactions with hydroxyl radicals (OH·) and other secondary oxidants.1
Disinfection versus Bromate Formation
Ozonation in drinking water facilities is used for disinfection. A certain amount of CT is required and regulated for the removal of pathogens. At higher CT values, bromate concentration increases and can exceed the MCL. Therefore, a conflict between disinfection requirements and bromate MCLs exist. It is of great importance to understand the mechanisms and chemistry between bromate and ozone in order to minimize bromate formation while still being able to achieve the required CT for disinfection.
1von Gunten, Urs et. al. “Bromate Formation in Advanced Oxidation Processes”, Journal AWWA, June, (1996).