Influence of different flow conditions on the occurrence and behavior of potentially hazardous organic xenobiotics in the influent and effluent of a municipal sewage treatment plant in Germany: an effect-directed approach

Flow conditions in the sewer systems are particularly important for the chemical and toxicological characteristics of raw and treated wastewater. Nevertheless, this topic has not been thoroughly investigated to date. In this study, composite wastewater samples were taken daily from the influent and effluent of a municipal sewage treatment plant. Polarity-based fractionation of the samples was carried out through sequential solid phase extractions. Biological testing of single and recombinant fractions was performed using bioluminescence inhibition assay according to DIN EN ISO 11348-2. Selected compounds (pharmaceuticals and polycyclic aromatic hydrocarbons) were also included in the chemical analysis by liquid chromatography coupled with tandem mass spectrometry and gas chromatography coupled with mass spectrometry. By analyzing different flow conditions, this study clarifies how these fractions contribute to the total toxicity of organic substances in wastewater. Additionally, it demonstrates the extent to which the potentially hazardous effects of the fractions can be reduced at the examined sewage treatment plant. Results Summarizing, medium to highly polar organic compounds were particularly relevant for the total toxicity of organic xenobiotics. For rising wastewater flow under wet weather conditions, we observed a significant decrease in the overall toxicity of the organic pollutants and specifically in the toxic effects of the moderately polar fraction 2. Conclusions The results provide the starting point for an important risk assessment regarding the occurrence and behavior of potentially toxic xenobiotics by differentiated polarity in municipal wastewater for varying flow conditions.