Model-based assessment of in-sewer heat recovery potentials considering wastewater treatment-specific temperature limits

Due to the ongoing climate and energy crisis, wastewater is becoming increasingly important as a source of renewable energy. In urban areas, heat recovery from the sewer is considered a promising approach, as the locations of supply and demand are close to each other. In this context, it is crucial that negative impacts on temperature-sensitive processes in the downstream wastewater treatment plant are strictly avoided. To support the necessary planning and authorization, this paper presents a model-based approach to assess the thermal energy level of the wastewater at any given location in the sewer, taking into account the influent temperature constraints of the wastewater treatment plant. The entire modelling is based on the open-source software SWMM 5, which was extended by a temperature model. The concept showed its practicability and informative value during a full-scale field application in the sewer systems of the Austrian city of Graz. All modelling is based on freely available software, which makes the approach easy transferable to other cities with comparable infrastructural boundary conditions.