Author(s): Qianyi Zhang; Evan G. R. Davies; James Bolton; Yang Liu
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Keywords: Monochloramine; Dissipation; Stormwater sewers; Total active chlorine
Abstract: Many municipalities in Canada and all over the world use chloramination to disinfect drinking water. However, the long-lasting monochloramine (NH2Cl) disinfectant can pose a significant risk to the environment when it drains from outdoor uses into municipal stormwater systems, and ultimately into fresh water sources. Although NH2Cl is more stable than free chlorine, it can still auto-decompose by a complex set of reactions. Its auto-decomposition rate depends on the pH, the initial free ammonia -) and natural organic matter concentration, and other factors. Further, NH2Cl can react with nitrite (NO2 (NOM) in the stormwater. In this study, field samples were collected from stormwater pipelines under residential, park, industrial, and commercial neighbourhoods in Edmonton, Canada. The average concentrations of total active chlorine (TAC) monitored in the stormwater sewers were between 0.14 mg/L and 0.24 mg/L, values significantly higher than the Canadian Council of Ministers of the Environment’s (CCME) guideline for in-stream concentrations of 0.02 mg/L for the protection of aquatic life. The evaluation of NH2Cl dissipation under various environmental conditions indicated that natural organic - matter (NOM) is the dominant factor controlling NH2Cl dissipation in stormwater. Initial NO2 concentration was also found to affect the NH2Cl dissipation rate in stormwater sewers, while alkalinity and ammonium nitrogen (NH4 +-N) showed no significant effect on NH2Cl dissipation in stormwater samples. The impact of pH was not determined because of the similarity of pH values between the stormwater samples.
Year: 2016