AWWA WQTC62502

Listed on the US Environmental Protection Agency Contaminant Candidate List 2, Mycobacterium avium is an opportunistic human pathogen found in municipal drinking water systems. Its survival and presence in drinking water has been attributed to its resistance to chemical disinfection by single applications of chlorine, chloramines, ozone, and chlorine dioxide. However, current disinfection strategies exist that employ the use of a primary and secondary disinfectant. Inactivation kinetics of M. avium with monochloramine has demonstrated the presence of an adaptive response triggered by pre-exposure to relatively low concentrations of monochloramine (<1 mg/L). Subsequent inactivation by monochloramine at higher concentrations (>5 mg/L) proceeds at a slower rate compared to that without the pre-exposure. With some utilities using both free chlorine and monochloramine, the objective of this study was to elucidate any synergistic and/or adaptive responses exhibited by M. avium to sequential treatment. In addition, while free chlorine inactivation kinetics has been reported in the literature, a comprehensive study on the effects of water quality parameters is still needed. Despite the fact that M. avium is often found within biofilms, this study focused on the inactivation kinetics of M. avium as suspended cells in order to provide the baseline kinetics for future work with biofilms. The experimental results presented here are for single-step free chlorine and sequential free chlorine/monochloramine as a function of pH, temperature, and disinfectant concentration. Includes 5 references, figures.