chloramination

Chloramination is a water treatment disinfection method that forms chloramines—mainly monochloramine—by combining chlorine with ammonia. It is commonly used in drinking water distribution systems to maintain a residual disinfectant as water travels through pipes.

In typical operation, chlorine reacts with ammonia to form monochloramine (NH2Cl). If chlorine remains in excess or pH shifts, dichloramine (NHCl2) or trichloramine (NCl3) can form. The relative amounts depend on pH, temperature, and the chlorine-to-ammonia ratio. Monochloramine is more stable and persistent than free chlorine, but it is a weaker disinfectant.

Advantages include a longer-lasting residual disinfectant, reduced formation of disinfection byproducts such as trihalomethanes and haloacetic acids, and often improved taste and odor in treated water. It can also reduce corrosion in some distribution systems. Disadvantages include lower immediate disinfection power, the potential for nitrification if ammonia is not carefully controlled, and the need for careful monitoring of pH, chlorine, and ammonia levels.

Applications and considerations: Chloramination is commonly used for municipal drinking water in many countries. Systems may adopt chloramination as a pre- or post-chlorination strategy or switch from free chlorine to chloramine for residual maintenance. Chloramines require careful monitoring to avoid nitrification and to ensure regulatory compliance; certain applications, such as dialysis, require dechlorination of water.