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Article

Effect of Ammonia Nitrogen and Dissolved Organic Matter Fractions on the Genotoxicity of Wastewater Effluent during Chlorine Disinfection

Li-Sha Wang, Hong-Ying Hu,* and Chao Wang

Environmental Simulation and Pollution Control State Key Joint Laboratory, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, PR China

Environ. Sci. Technol., 2007, 41 (1), pp 160–165

DOI: 10.1021/es0616635

Publication Date (Web): November 18, 2006

Corresponding author phone: (+86-10)6279-4005; fax: (+86-10)6277-1472; e-mail: hyhu@tsinghua.edu.cn.

Abstract

Chlorine is a widely used disinfectant which prevents the spread of harmful pathogens when reusing wastewater, but harmful byproducts might be formed and cause adverse ecological and health effects. In this study, the potential effects of chlorination on the genotoxicity of different biologically treated wastewater samples were investigated using the umu test. For the first time, ammonia nitrogen (NH₃N) was found to significantly influence genotoxicity during wastewater chlorination. After chlorination, the genotoxicity decreased in wastewater with a low NH₃N concentration (<1020 mg/L), but it increased notably in wastewater with a high NH₃N concentration (>1020 mg/L). By fractionating the DOM (dissolved organic matter) in wastewater into different fractions, it was found that the hydrophilic substances (HIS) fraction of DOM was the key fraction involved in decreasing genotoxicity during the chlorination of wastewater with a low NH₃N concentration, while the hydrophobic acids (HOA) fraction of DOM was the key fraction involved in increasing genotoxicity during chlorination of wastewater with a high NH₃N concentration. Furthermore, fluorescence spectroscopy analysis on different fractions indicated that some free or combined aromatic amino acids might produce highly genotoxic byproducts during the chlorination of wastewater with a high NH₃N content, and this was then demonstrated through experiments on the chlorination of free aromatic amino acids.