AWWA WQTC65946

Unintentional nitrification occurs in nearly 67% of all utilities practicing chloramination. Nitrification has been linked to distribution systems and storage tanks with long detention times. Excess ammonia during chloramination promotes ammonia-oxidizing bacteria that emit nitrite and form biofilms within distribution systems. Utilities can control nitrification in two ways. First, they can increase the chlorine to ammonia molar ratio (Cl₂:NH₃) to reduce free ammonia in the distribution system. Second, they can practice breakpoint chlorination to leave a free chlorine residual that hinders biofilm growth and then reapply chloramines downstream. The former strategy increases the formation of dichloramine (NHCl₂), while the latter forms a series of reactive intermediates. The effect of both strategies on the formation of nitrogenous byproducts has not been examined. We conducted experiments to study the impact of Cl₂:NH₃ molar ratios > 1 on the formation of three toxic nitrogenous disinfection byproduct families, nitriles (e.g., cyanogen chloride), nitramines (dimethylnitramine) and nitrosamines (e.g., NDMA). For these experiments, we used dimethylcyanamide as a model nitrile, dimethylnitramine as a model nitramine, and NDMA as a model nitrosamine. Includes 5 references, figures.