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.
References
1von Gunten, Urs et. al. “Bromate Formation in Advanced
Oxidation Processes”, Journal AWWA,
June, (1996).