011218 Harrington The objective of this research project is to develop a model integrating the chemical and microbiological phenomena that occur in chloraminated drinking water systems. As chloramines decay, disinfection potential decreases and the ammonia formed by the decay is converted to nitrites by ammonia-oxidizing bacteria (AOB). This causes two problems: first, nitrite is a public health concern and second, nitrite accelerates the decomposition of the chloramine residual, further reducing disinfection potential and creating more ammonia for the AOB to nitrify. In general, nitrification will occur when the growth rate of AOB (due to the presence of ammonia) is larger than the inactivation rate of AOB (due to the presence of chloramines). The specific objectives of this research are to: 1) Develop a food-to-biocide ratio indicative of nitrification potential and evaluate the ability of this ratio to predict the time to onset of nitrification in various chemical environments within the distribution system, 2) Evaluate the microbial ecology of AOB and nitrite-oxidizing bacteria in chloraminated distribution systems and determine the chloramine resistance of representative strains isolated from the distribution systems and 3) Interconnect the chemical and microbiological fundamentals of nitrification in chloraminated distribution systems using a mathematical model that simulates nitrification in model distribution systems. The development of a nitrification potential indicator may help utilities establish criteria to minimize nitrification episodes. Furthermore, the evaluation of the onset of nitrification under different environmental conditions will provide relevant information to formulate strategies for nitrification control. The microbial ecology studies and the isolation of relevant chloramine resistant strains will provide the means to explore the mechanisms of disinfectant resistance. ***
