AWWA JAW71769

Microbial acceleration of chloramine decay makes maintaining adequate residual in large tanks and reservoirs a challenge for utilities. In the Sydney Water distribution system in Australia, a major tank regularly experienced nitrification, resulting in near zero residuals during summer and autumn. To combat the problem, the authors developed a control cycle based on the microbial decay factor, a relatively new quantitative tool that separates the contribution of chemical and microbial processes to overall chloramine decay. The approach provides a sensitive indication of the onset of accelerated chloramine decay and requires early action and ongoing adaptive management of chloramine using simple measurable parameters. Although traditional indicators of nitrification (e.g., ammonia, nitrite) provide valuable information, they do not show the effect of nitrification on chloramine decay characteristics. Measurement of these characteristics via the microbial decay factor method and better insight into the microbial and chemical decay present can help utilities assess system status and consequently better manage the residual. Includes 14 references, tables, figures.