Modelling heat recovery from urban wastewater systems - case study from Malmö

Abstract: The purpose of this thesis is to estimate how much heat can be recovered from the sewer system in Malmö, Sweden, and determine the best location for that heat recovery. In fulfilling that purpose, this thesis covers the process of modeling wastewater flows and temperature changes in the sewer system in Malmö, the results of those processes, and the estimated amount of heat that can be recovered from the sewer system. The methods used to complete this study included primary data collection through in-sewer equipment installation and field data measurements, along with the use of two different models (one for a city-wide wastewater flow rate prediction and the other regarding heat transfer in the sewer network). Extensive secondary research was also conducted. The results from this study included the estimation of different amounts of heat from the sewer system. For example, a scheme of heat extraction of 36,000 kW during a 12-hour period was analyzed during the same time frame where flow and temperature data was collected. That number would always keep a temperature at the wastewater treatment plant over 9 ºC and corresponds to 6.3% of the total district heating consumption per year in Malmö. Also, a 1% difference between the real and modeled wastewater flows for one of the catchments on the city was obtained. Finally, the temperature modeling process delivered differences between 0.1 and 0.3 ºC for one of the studied places.