Effects of chlorination on the properties of dissolved organic matter and its genotoxicity in secondary sewage effluent under two different ammonium concentrations

Recently, NH4+ has been reported to induce potential risks during wastewater chlorination. Thus, the effects of chlorination on genotoxicity and fluorescence spectra of secondary sewage effluents, were investigated in this study before and after adding a high NH4+ quantity. Chlorination decreased the genotoxicity of secondary sewage effluent, while the presence of a high level of NH4+ inhibited this decrease. By further ultrafiltration following XAD-8 resin fractionation, it was found that, with a high NH4+ concentration, the genotoxicity in the fraction of hydrophobic acids (HOA) increased after chlorination and a sub-fraction of HOA with molecular weight less than 1 kDa was the key fraction resulting in this increase. Similar to genotoxicity changes, NH4+ was also found to influence the changes in fluorescence spectra during chlorination. After chlorination, the fluorescence intensity of the dissolved organic matter (DOM) notably decreased, and the emission band of DOM fluorescence spectra shifted to a lower wavelength. However, the presence of NH4+ inhibited both the decrease in intensity and shift. The changes in fluorescence spectra suggested that the fluorescent structure of secondary effluent may decompose during chlorination, but NH4+ could inhibit this decomposition.