Controlling nitrification is essential if chloramines are to be a viable alternative disinfectant scheme for distribution systems in all types of environments. This article reviews problems associated with nitrification and presents laboratory and field evidence for using the chlorite ion (ClO_2-)to control nitrification in distribution systems. Laboratory experiments in this study showed that even low dosages of ClO_2 (0.05 mg/L) can inactivate 3-4 logs of ammonia-oxidizing bacteria (AOB) over several hours.Higher concentrations of ClO_2-inactivate all of the AOB in as little as 30 minutes. Field investigations at five Texas water utilities showed that the presence of ClO_2- in the distribution system resulted in less loss of chloramines and ammonia-nitrogen and thus less nitrification than in those systems in which ClO_2-was not present. The ease of use of ClO_2-is compared with other, more traditional nitrification control measures.
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