Influence of chlorine-to-nitrogen ratio on the inactivation of heterotrophic bacteria in bulk water during chloramination.

Comparative experiments were conducted to determine the inactivation efficiency of chloramines on heterotrophic bacteria in bulk water. The impact of pH, concentrations of organic compounds, turbidity, and chlorine-to-nitrogen (Cl/N) ratio on inactivation efficiency was studied. Experimental results showed that inactivation efficiency was best at a 4:1 Cl/N ratio, while the lowest efficiency occurred at a 3:1 ratio. The inactivation rate increased with decreasing pH in the range of 6.0-9.0. Higher levels of organic matter and turbidity seemed to weaken the inactivation ability of chloramines. In comparison with results obtained for two other Cl/N ratios studied, a maximum chloramine residual was maintained at a 4:1 Cl/N ratio. A positive correlation was found between the inactivation rate of heterotrophic bacteria and chloramine residual. These observations support the hypothesis that the differences observed in inactivation rates can be attributed to the chemical species distribution of chloramine at various Cl/N ratios.