The Role and Behavior of Chloramines in Drinking Water

Chloramination has been used in drinking water treatment since the early 1900s, but its use has been low compared to that of chlorine. In recent years, a large number of utilities have switched from chlorine to chloramine as a secondary disinfectant, primarily to comply with the U.S. Environmental Protection Agency’s (EPA) Stage 1 and Stage 2 Disinfectants and Disinfection ByProducts Rules (D/DBPR). Chloramines are a class of oxidants formed by the reaction of chlorine and ammonia. In drinking water treatment, chloramines are primarily used as a secondary disinfectant to provide a residual in the distribution system. The three major forms of chloramines are mono-, d-, and tri-chloramines. The ratio at which chlorine and ammonia are fed determines the species of chloramines produced. Monochloramine is the preferred species, as it is more effective and less likely to cause taste-andodor problems. Chloramines provide an effective disinfectant residual while reducing the formation of regulated disinfection by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs). Chloramines are also more stable than chlorine and therefore last longer in the distribution system. Chloramination can be a complex process and improper management can lead to unintended consequences including nitrification, formation of non-regulated DBPs, and deleterious effects on some elastomeric materials used in the distribution system. Since chloramine use has been increasing, water professionals need to understand the various aspects of chloramination with the goal to better manage and operate their systems and minimize unintended consequences. Since the mid-1980s, the Water Research Foundation has funded more than 70 research projects that examine chloramine-related issues, such as making the switch to chloramines, nitrification events, formation of disinfection by-products, and lead and copper release as related to chloramine use. What follows is a summary of the relevant chloramine-related WRF reports.