|Chee Sanford, Joanne|
Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2001
Publication Date: N/A
Citation: Interpretive Summary: Bromate can be formed as a disinfection by-product when bromide-containing water is treated with ozone, which is a process to remove residual organic compounds in water treatment systems. Ingestion of drinking water containing bromate can cause tumors. Biologically active carbon (BAC) filters are becoming more attractive in the U.S. for treatment of very low residual concentrations of toxic disinfectants and by-products, and depends on the activities of microorganisms associated with the filters. In this study, we evaluated the conditions that were critical for biological bromate removal to occur. The system was sensitive to high oxygen and nitrate concentrations, but was not affected by sulfate concentrations. Oxygen, nitrate, and sulfate are likely to be present in water prior to treatment and discharge at treatment facilities. The type of organic compounds naturally present in water also affected the amount of bromate removal. Maintaining pH conditions close to neutral was also more effective. This study demonstrated that effective bromate removal could be achieved if key conditions are controlled.
Technical Abstract: Biological removal of the zonation by-product, bromate, was demonstrated in biologically active carbon (BAC) filters. For example, with a 20-min EBCT, pH 7.5, and influent dissolved oxygen (DO) and nitrate concentrations 2.1 and 5.1 mg/l, respectively, 40% bromate removal was obtained with a 20 mu g/l influent bromate concentration. In this study, DO, nitrate and sulfate concentrations, pH, and type of source water were evaluated for their effect on bromate removal in a BAC filter. Bromate removal decreased as the influent concentrations of DO and nitrate increased, but bromate removal was observed in the presence of measurable effluent concentrations of DO and nitrate. In contrast, bromate removal was not sensitive to the influent sulfate concentration, with only a slight reduction in bromate removal as the influent sulfate concentration was increased from 11.1 to 102.7 mg/l. Bromate reduction was better at lower pH values (6.8 and 7.2) than at higher pH values (7.5 and 8.2), suggesting that it may be possible to reduce bromate formation during zonation and increase biological bromate reduction through pH control. Biological bromate removal in Lake Michigan water was very poor as compared to that in tapwater from a groundwater source. Bromate removal improved when sufficient organic electron donor was added to remove the nitrate and DO present in the Lake Michigan water, indicating that the poor biodegradability of the natural organic matter may have been limiting bromate removal in that water. Biological bromate removal was demonstrated to be a sustainable process under a variety of water quality conditions, and bromate removal can be improved by controlling key water quality parameters.