Modelling temperature dynamics in sewer systems - comparing mechanistic and conceptual modelling approaches

The vast majority of the energy consumed for urban water services is used to heat tap water. Heat recovery from wastewater is consequently an area of rapidly growing concern, both in research and by commercial interest, promoting the path towards a circular economy. To facilitate a system-wide evaluation of heat recovery from wastewater, this paper compares two one-dimensional models (mechanistic and conceptual) that can describe wastewater temperature dynamics in sewer pipe systems. The models are applied to successfully predict downstream wastewater temperature for sewer stretches in two Swedish cities (Linkoping & Malmo). The root mean squared errors for the mechanistic model (Linkoping Dataset1 - 0.33 degrees C; Linkoping Dataset2 - 0.28 degrees C; Malmo - 0.40 degrees C) and the conceptual model (Linkoping Dataset1 - 0.32 degrees C; Linkoping Dataset2 - 0.20 degrees C; Malmo - 0.44 degrees C) indicate that both models have similar predictive capabilities, encouraging the use of conceptual models to reduce data requirements and model calibration efforts. Both models are freely distributed and can be easily integrated with wastewater generation and treatment models to facilitate system-wide wastewater temperature dynamics analysis.