Role of nitrification in accelerating chloramine decay through application of microbial decay factor (F_m) method

Chloramine is widely practiced as a secondary disinfectant in many utilities, including that in Australia and US. Utilities face challenges in maintaining adequate disinfectant residual. Usually, nitrification is thought to be responsible for instability of residual and hence mostly measurement targets nitrification indicators. To prove/disprove this belief, the authors analyzed two different types of samples using the microbial decay factor (F_m) method: mildly and severely nitrifying samples. Microbial decay in mildly nitrifying samples was heavily dependent on total chlorine residual rather than nitrite levels in the sample and it took place without any signs of nitrification. In severely nitrifying samples suspected soluble microbial products accelerated chloramine decay much more than the process of nitrification, i.e. production of nitrite or subsequent drop in pH. Therefore, other processes were found to be more significant in accelerating chloramine decay than the nitrification process. For proper control of chloramine residual, measurement of chloramine decay characteristics is recommended. 2011