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Nitrification 1.0 Introduction The goal of this document is to review existing literature, research and information on the potential public health implications associated with Nitrification. Nitrification is a microbial process by which reduced nitrogen compounds (primarily ammonia) are sequentially oxidized to nitrite and nitrate. Ammonia is present in drinking water through either naturally -occurring processes or through ammonia addition during secondary disinfection to form chloramines. The nitrification process is primarily accomplished by two groups of autotrophic nitrifying bacteria that can build organic molecules using energy obtained from inorganic sources, in this case ammonia or nitrite. In the first step of nitrification, ammonia -oxidizing bacteria oxidize ammonia to nitrite according to equation (1). NH3 + 02 --> NO2-+ 3H++ 2e (1) Nitrosomonas is the most frequently identified genus associated with this step, although other genera, including Nitrosococcus, and Nitrosospira. Some subgenera, Nitrosolobus and Nitrosovibrio, can also autotrophically oxidize ammonia (Watson et al. 1981). In the second step of the process, nitrite -oxidizing bacteria oxidize nitrite to nitrate according to equation (2). NO2 + H2O —> NO3" + 2H+ +2e (2) Nitrobacter is the most frequently identified genus associated with this second step, although other genera, including Nitrospina, Nitrococcus, and Nitrospira can also autotrophically oxidize nitrite (Watson et al. 1981). Various groups of heterotrophic bacteria and fungi can also carry out nitrification, although at a slower rate than autotrophic organisms (Verstraete and Alexander 1973; Watson et al. 1981). Speciations of nitrifying bacteria in drinking water systems (Wolfe 1990 and 2001) suggest that the number of heterotrophic nitrifiers in drinking water systems may be negligible compared to autotrophic nitrifiers. In comparison, heterotrophic nitrification occurs in wastewater applications (Grady et al. 1980). Chloramines are produced in a reaction between free chlorine and ammonia. Chloramination is commonly used for secondary disinfection purposes to control microbial growth in finished water. Chloramines include monochloramine, dichloramine, trichloramine, and organochloramines. For disinfection purposes, monochloramine is the preferential form. Chloramine use is expected to increase in the near future as a result of more stringent disinfection by-product (DBP) maximum contaminant levels (MCLS) associated with the Stage I and Stage II Disinfectant/Disinfection By -Product Rule (DDBP Rule). Review of the Information Collection Rule (ICR) database indicates that 33% of 353 treatment plants use chloramines. The draft regulatory impact analysis prepared for the Stage 2 Microbial and Prepared by AWWA with assistance from Economic and Engineering Services, Inc. 3