Formation of Hydrazine as a Chloramine By-Product

Hydrazine, N2H4, has been used widely since the 1950s in a variety of industrial applications. Hydrazine is a potent carcinogen and is classified by the USEPA as a probable human carcinogen with a 10-6 risk level of 10 ng/L in drinking water. While hydrazine is manufactured by the reaction between monochloramine and ammonia, there is no mention in the drinking water or wastewater literature of concerns about hydrazine formation as a by-product of chloramination. This project produced a modified analytical method for hydrazine with a detection limit <5 ng/L. The project found that hydrazine formation was not significant (<5 ng/L) under conditions typical of most water treatment applications (pH <9.0, NH3-N <0.5 mg/L as N). The project also identified conditions under which hydrazine formation may be significant, including pH >9.0 in combination with the presence of free ammonia and chloramines, which may result from chloramine decay in the distribution system or poor control of chemical dosing. Hydrazine may form in the distribution system even if it is not -detectable in water leaving the plant.