Effect of ammonia nitrogen and dissolved organic matter fractions on the genotoxicity of wastewater effluent during chlorine disinfection

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 (< 10 similar to 20 mg/L), but it increased notably in wastewater with a high NH3N concentration (> 10 similar to 20 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.