Inactivation of Mycobacterium avium with monochloramine

Batch experiments were performed to study the inactivation kinetics of Mycobacterium avium in the presence of monochloramine at 5-30 degrees C, pH 6-10, and 0.30-42.3 mg Cl2/ L. For each temperature and pH investigated, limiting high and low inactivation rates were observed for high and low disinfectant concentrations, respectively, within the range investigated. The rate of inactivation transitioned from high to low over a relatively narrow range of intermediate monochloramine concentrations. The observed temperature dependence of inactivation was consistent with an Arrhenius expression with activation energies of 58.0 and 71.7 kJ/mol for the high and low concentration ranges, respectively. The rate of inactivation increased with decreasing pH, consistent with trends reported for the reaction of monochloramine with protein thiols. Experiments performed at pH approximately 3.5 showed that dichloramine was a weaker disinfectant than monochloramine, and that its contribution to the overall inactivation of M. avium with combined chlorine was negligible at pH 6-10. A kinetic model incorporating disinfectant concentration, temperature, and pH effects was used to illustrate that monochloramine efficiency to inactivate M. avium in water could vary broadly from adequate (e.g., 99.9% inactivation efficiency in 32 min at 5 mg Cl2/L, pH 6, 30 degrees C) to impractical (e.g., 99.9% inactivation efficiency in 9 d at 1 mg Cl2/L, pH 9, 5 degrees C).