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Field data analysis of active chlorine-containing stormwater samples
Qianyi Zhang1, Mohamed Gaafar1, Rong-Cai Yang2
1Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada.
Journal of Environmental Management
|October 23, 2017
Summary
Chloramination used for drinking water can harm aquatic life. Stormwater monitoring in Edmonton found high total active chlorine (TAC) levels, exceeding limits in 2015, but lower in 2016 due to increased rainfall.
Area of Science:
- Environmental Science
- Water Quality Management
- Ecotoxicology
Background:
- Chloramination is a common secondary disinfectant for drinking water, aiming to reduce disinfection byproducts.
- The disinfectant monochloramine (NH2Cl) can enter freshwater systems via storm sewers, posing risks to aquatic ecosystems.
- Understanding the fate of monochloramine in stormwater is crucial for environmental protection.
Purpose of the Study:
- To measure total active chlorine (TAC) concentrations in stormwater discharges in Edmonton, Alberta.
- To assess the impact of weather conditions on TAC levels in storm sewers.
- To investigate factors influencing monochloramine decay in stormwater.
Main Methods:
- Field sampling of stormwater in Edmonton during summer 2015 and 2016 under varying weather conditions.
- Analysis of total active chlorine (TAC) concentrations in collected samples.
- Laboratory experiments to determine the effect of dissolved organic carbon (DOC) on monochloramine decay.
- Analysis of physicochemical and biological characteristics of stormwater and sewer biofilm.
Main Results:
- TAC concentrations in 2015 ranged from 0.02 to 0.77 mg/L, exceeding the 0.02 mg/L effluent limit.
- TAC concentrations were significantly lower in 2016 (0-0.24 mg/L), potentially due to higher precipitation reducing water use.
- Higher densities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in residential biofilms correlated with ammonium and nitrite levels, possibly aiding TAC decay.
- Dissolved organic carbon (DOC) was identified as the primary factor controlling monochloramine decay rates in laboratory experiments.
Conclusions:
- Stormwater discharges can contain significant levels of active chlorine from chloramination, posing a risk to aquatic life.
- Precipitation patterns and water usage influence TAC concentrations in stormwater.
- Ammonia-oxidizing and nitrite-oxidizing bacteria in biofilms may contribute to monochloramine decay.
- High DOC concentrations, particularly from industrial sources, accelerate monochloramine decay in stormwater.
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