BROMATE REDUCTION BY DENITRIFYING BACTERIA

In the presence of bromide, ozonation as applied in water treatment re sults in the formation of bromate, an ion with carcinogenic properties . The reduction of bromate by mixed bacterial populations as well as p ure cultures was studied under laboratory conditions. Bromate was redu ced to bromide by a mixed bacterial population with and without a prec eding nitrate reduction step in an anaerobically incubated medium with ethanol as the energy and carbon source at 20 and 25 degrees C. The p redominating bacteria isolated from the batches showing bromate reduct ion were identified as Pseudomonas spp. Strains of Pseudomonas fluores cens reduced BrO3- to Br- but at a much lower rate than the mixed bact erial population did. Nitrate is a preferred electron acceptor for the bromate-reducing bacteria. Bromate reduction did not occur in the pre sence of NO3-, and the rate of bromate reduction was at least 100 time s lower than the rate of nitrate reduction. Bromate was completely con verted to Br-, indicating that intermediates, e.g., BrO2-, did notaccu mulate during bromate reduction.