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Research was conducted at Metropolitan (at a demonstration-scale plant) on the effects ofchlorine dioxide (or its byproduct chlorite) on bromate and chlorate formation and disinfection(CT) credit during subsequent ozonation. Pre-oxidation with 0.5 or 1.0 mg/L chlorine dioxidejust prior to ozone addition resulted in reduced bromate formation and increased Giardiainactivation credit from ozone. The addition of chlorite only (0.7 mg/L) reduced bromateformation and disinfection credit. The results suggest that the presence of chlorite reacts rapidlywith ozone, reducing the amount of ozone available for either bromate formation or disinfectioncredit. Alternatively, the addition of chlorine dioxide in these tests appeared to satisfy more ofthe oxidant demand than that exerted by the chlorite produced, resulting in a net benefit inbromate control and increased disinfection. In these tests, chlorite was oxidized to chlorate,which needs to be considered if chlorate is regulated in the future (currently there is an actionlevel of 0.8 mg/L for chlorate in California).In additional tests, low-pH ozonation (6.5) reduced bromate formation below its maximumcontaminant level of 10 g/L. Combinations of chlorine dioxide pre-oxidation and low-pHozonation further reduced bromate formation. This paper discusses the relative merits of eachapproach for controlling bromate formation and meeting disinfection goals. Includes 13 references, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 10File Size: 1 file , 690 KB