Occurrence of nitrification in chloraminated distribution systems

Utilities in the United States that chloraminate were surveyed to evaluate the incidence of nitrification in distribution systems and determine whether nitrification can be predicted from basic system and water quality data. An estimated two thirds of medium and large US systems that chloraminate experience nitrification to some degree. About every fourth surveyed utility reported moderate to severe nitrification problems. In addition, every fourth utility did not know the extent of nitrification in its system. The incidence of nitrification was more frequent during summer or when the temperature was greater than 15 degrees C (59 degrees F); nevertheless, several sites sampled under cold water conditions-i.e., below 10 degrees C (50 degrees F)-also evidenced nitrification. No one water quality parameter by itself may be a good indicator of nitrification, but several important factors should be evaluated collectively-nitrite, nitrate, chloramine dosage and residual, ammonia, pH, heterotrophic bacterial counts, and dissolved oxygen.