Modeling the Decomposition of Disinfecting Residuals of Chloramine

Chloramines have long been used to provide a disinfecting residual in distribution systems when it is difficult to maintain a free chlorine residual. In spite of a long history of chloramine use, however, the fate of chloramines in distribution systems as well as characteristics and processes which influence its stability are largely unknown. The notion of chloramine stability remains vaguely defined although dosage requirements are frequently determined by the rate and extent of chloramine loss in a distribution system. In this study, chloramine decay was studied using chloramine concentrations from 0.01 mM to 0.1 mM as Cl2 (0.71 to 7.1 mg/L as Cl2), a range important in drinking water treatment and where no previous kinetic investigations have been conducted. Experimental results compared well with the output from a comprehensive reaction model that incorporates 10 reactions. Also a simple coefficient of use in defining the limit of chloramine stability is presented.