This study was conducted to investigate the characteristics of chloramination as a secondary disinfection in a drinking water distribution system. At the range from pH 6 to pH 8, monochloramine was predominant with a trace of dichloramine, and the free chlorine was detected after breakpoint. At 25℃, the breakpoints of pH 6, 7 and 8 appeared when the weight ratios of chlorine to ammonia nitrogen were 11:1, 9:1 and 10:1 respectively, and the peak points on the breakpoint curves at pH 6, 7 and 8 were in the Cl2 / NH3-N ratio of 9:1, 6:1 and 5:1 respectively. As pH increased from 6 to 8, maximum point of monochloramine on the breakpoint curve was moved from 7:1 to 5:1 in the weight ratio of chlorine to ammonia nitrogen. The maximum concentration of monochloramine was formed at the pH values of 7～8 and in the Cl2 / NH3-N ratio below 5:1. As the Cl2 / NH3-N ratio increased and the pH lowered, chloramines decay proceeded at an increased rate, and residual chloramines lasted longer than the residual free chlorine. The monochloramine and the dichloramine were formed at pH 6, and then the dichloramine continued increasing with contact time.

This study was performed to evaluate the inactivation and microbial regrowth of heterotrophic and nitrifying bacteria using chloramine as a secondary disinfectant for drinking water distribution system. Three sets of the three reactors filled with the Cl2/NH3-N ratio of 3:1, 4:1 and 5:1 were used in these experiments. Chloramine concentration were applied to each set of the reactors with 1㎎/ℓ, 2㎎/ℓ and 3㎎/ℓ, respectively. For the set with 1㎎/ℓ was applied, all the reactors showed that the residual chloramine concentration gradually decreased with elapsed time and reached to zero level after 7 days. Heterotrophic bacteria remarkably increased and nitrification occurred after 11 days. For the sets with 2㎎/ℓ and 3㎎/ℓ, however, the residual chloramine was maintained through the experimenatal period (21 day). Furthermore the regrowth of heterotrophic bacteria and nitrification were not found. More than 2㎎/ℓ of chloramine with Cl2/NH3-N ratio of 3:1, the nitrification could be inhibited by 2 days of contact time.