AWWA JAW24264

Nitrification occurred in two covered finished-water reservoirs in Southern California following a change from free chlorine to chloramine disinfection. The proliferation of autotrophic ammoniaoxidizing bacteria was suspected to be the cause. Adverse water quality effects caused by the nitrification episodes included a rapid decline in the total chlorine and total ammonia-nitrogen residuals and elevated levels of nitrite and heterotrophic plate count bacteria. As a result, the reservoirs were taken out of service and break-point chlorinated. This article examines the conditions leading to the development of nitrification in reservoirs containing chloraminated water, along with the measures that can be used to control the process. Includes 39 references, tables, figures.