CASE 1: Retention soil filters in urban catchments

Partner in charge: RWTH

Location: Aachen, Germany

The figure on the right shows that the full-scale RSF Aachen-Soers is currently being constructed near the Wastewater treatment plant (WWTP) Aachen-Soers and will be in op- eration in 2022. The RSF has a surface area of 14,600 m2 and a retention volume of 36,800 m3 and is divided into six filter cells. Two or more filter cells are filled depend- ing on the spilled volume of the combined sewer overflow (CSO). Most of catchment is drained by the combined sewer system. The pilot RSFs are situated on the WWTP Aachen-Soers nearby the full-scale RBF in a ventilated greenhouse to control precipitation. The pilot consists of an equilibration tank to mix raw water of the desired qual- ity by blending drinking water and effluent of the primary clarifier. The effluent of the equilibration tank is used to feed two one-stage RSF (RSF1 and RSF2) and one two-stage RSF (RSF3a and RSF3b).

Current Status Case Study + Needs for Improvement:

The full-scale retention soil filter is under construction to further protect the receiving river Wurm from the com- bined sewer overflow emissions. The quality of the receiving water is intensively monitored and the addition of the RSF is expected to show benefit effects. Based on the experiences in the pilot-scale, further development of the RSF technology is planned to produce a more compact version for locations with space constraints.

Activities - Technical configurations and envisaged improvements

The RSF will be equipped with coarser filter material for smaller space footprints in urban areas while accepting slightly lower water quality. Further development is planned for an RSF version which uses biologically de- gradable flocculants to further reduce the footprint while maintaining high water effluent quality. Furthermore, it’s use as a drainage layer under existing roads for infiltrating runoff is being considered. Suspended solids, fine particles (AFS63), nutrients, heavy metals, micropollutants and microplastics will be measured.

Ambition until the Project End and Beyond

To develop and implement a prototype of RSFcompact system will be monitored and compared to a conventional full-scale RSF version for treatment effectiveness. Recommendations for further development and application of the use of RSF and RSFcompact systems will be made and disseminated to end-users.

Waste Water Treatment Plant WWTP Aachen-Soers (orange) and Retention Soil filter RSF (red) and B. C: RSF Aachen-Soers with six filter cells, Influent from left to right.