Seasonal Chlorination Practices and Impacts to Chloraminating Utilities

Utilities that have difficulty maintaining free chlorine residuals in their distribution systems, or that are unable to attain the minimum DBP concentrations set by regulation, often switch to chloramines as secondary disinfectants. Unfortunately, chloraminated distribution systems are biologically unstable in that they may promote nitrifying bacteria growth. The prevention and control of nitrification is a concern for chloraminating utilities as it is identified with disinfectant loss and facilitation of heterotrophic biological growth. This study has shown that a periodic switch from a chloramine residual to a free chlorine residual may not be sufficient for long-term control of nitrification within a chloraminated distribution system. Given the higher levels of DBPs observed following a switch to free chlorine, utilities may be better served by careful maintenance of their ammonia feed such that nitrification episodes are minimized.