AWWA JAW56654

Nitrification affects many water utilities that use chloramine as the finished water disinfectant, but traditional nitrification control strategies are not always effective. Although the utility can change from chloramine disinfection to free chlorine to control nitrification, the disinfection byproducts (DBPs) produced by free chlorination are just as problematic as the nitrification. With increased use of chloramination to meet the requirements of the Disinfectants/DBP Rule, nitrification will become an issue for more utilities. Skadsen reviewed historical water quality data and the occurrence of nitrification in the Ann Arbor, Mich., water system and saw a correlation between high pH and low occurrence of nitrification. If this correlation held true during full-scale operation at the Ann Arbor water plant, raising the pH of finished water might be a relatively simple alternative for preventing nitrification. Successful experiments prompted the utility to set an operational goal of pH 9.3 for its finished water and to conduct an eight-year assessment to evaluate the effects of the higher pH on the occurrence and degree of nitrification. The elevated pH significantly improved the control of nitrification but did not completely eliminate it. This experience indicates that raising finished water to pH 9.3 is a practical step for controlling nitrification, although additional control methods may be required in some cases. Includes 32 references, tables, figures.