| Summary: | The decentralized treatment of wastewater and its on-site infiltration is common practice, especially in rural areas. However, uncertainties exist on the degradation potential of treated wastewater constituents mixed with additional infiltration of large quantities of water originating from precipitation. The intermixture of these waters is causing a reduction of residence times of the treated wastewater as well as an increased water saturation within the unsaturated soil zone. This can lead to a negative influence on the purification efficiency. Laboratory-scale 1D column experiments, accompanied by numerical simulations of water flow using the software code HYDRUS 1D, have been performed to evaluate the risks for a reduction of the degradation efficiency. Water content measurements and analysis of relevant organic substances in samples taken at different depths were the basis for evaluating the influence of the joint infiltration on the purification efficiency. The results highlight that a joint infiltration of treated wastewater and additional water originating from precipitation is not affecting the degradation efficiency for treated wastewater constituents. Degradation rates under these conditions were similar to the infiltration of treated wastewater alone. Timeframes with high water saturation were limited to the duration of the precipitation event.
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