monochloramine

Monochloramine is an inorganic chemical with the formula NH2Cl. It is a chloramine used primarily as a disinfectant in water treatment. In aqueous solutions it forms when ammonia is treated with chlorine under controlled conditions, and it is favored at moderate pH levels. Monochloramine is colorless and soluble in water, and it serves as a relatively stable, residual disinfectant in drinking-water distribution systems.

Production and properties

Monochloramine is produced by the controlled chlorination of ammonia, typically via the reaction NH3 + HOCl → NH2Cl + H2O. The process aims to minimize formation of other chloramines such as dichloramine and nitrogen trichloride by adjusting the chlorine-to-ammonia ratio and pH (often near neutral to mildly basic conditions). In water, monochloramine is less reactive with organic matter than free chlorine, which results in lower formation of certain disinfection byproducts such as trihalomethanes. It provides a longer-lasting residual disinfectant in pipes, though it is a weaker oxidant than chlorine and can slowly decays over time or with exposure to light and heat.

Applications and safety

Monochloramine is widely adopted in municipal drinking-water treatment to maintain disinfection throughout distribution and to reduce byproduct formation. It can also be used in some industrial cooling and process waters. Benefits include a more persistent residual and lower reactivity with organic contaminants; drawbacks include potential taste or odor concerns and irritation at higher concentrations. It is typically stored and handled as an aqueous solution; dry monochloramine is not commonly used due to stability concerns. Proper management is required to avoid formation of other chloramines and to ensure safe discharge and environmental protection.