Inactivation of Nitrosomonas europaea and pathogenic Escherichia coli by chlorine and monochloramine

The purpose of this study was to measure the chlorine and monochloramine inactivation kinetics of Nitrosomonas europaea at 21°C in the presence and absence of particles. The inactivation kinetics rates were compared with those obtained with Escherichia coli O157:H7. The results show that, in pure water, the use of free chlorine produced 4 log₁₀ of N. europaea inactivation at a CT value of 0.8 mg.min l⁻¹, whereas monochloramine yielded 4 log₁₀ of inactivation at CT values of approximately 9.9–16.4 mg.min l⁻¹. With E. coli, chlorine produced approximately 4 log₁₀ of inactivation at a CT of 0.13 mg.min l⁻¹, whereas monochloramine resulted in 4 log₁₀ of inactivation at a CT of approximately 9.2 mg.min l⁻¹. These results suggest that N. europaea is more resistant to monochloramine and chlorine than E. coli. Corrosion debris, soil material and wastewater had no statistically significant (p < 0.05) impact on the inactivation of N. europaea by either chlorine or monochloramine. It seems likely that the CT values present in distribution systems would be sufficient to control suspended cells of these two organisms, especially under conditions of breakpoint chlorination, which could be used to control nitrification. Adequate disinfection should prevent the growth of these organisms in a distribution system.