Heat recovery potential from treated wastewater at the Daugavgrīva WWTP

The Daugavgrīva Wastewater Treatment Plant (WWTP “Daugavgrīva“) is the largest wastewater treatment facility in Latvia, where municipal and stormwater from Riga and the surrounding areas are treated. After the treatment process, the water is discharged into the Gulf of Riga; however, it still contains a significant amount of thermal energy that is currently unused.

In 2025, a study was launched within the ENABLE DHC project to evaluate the possibilities of recovering this residual heat and integrating it into the district heating system using industrial heat pump technology. The study analysed treated wastewater flow and temperature parameters as well as the heat demand of the Daugavgrīva and Bolderāja district heating zones in order to determine a technically and economically justified solution for heat recovery and integration into the district heating network.

Daugavgrīva Wastewater Treatment Plant in Riga. Photo: Rīgas ūdens / rigasudens.lv

Wastewater heat potential at the Daugavgrīva WWTP

Flow and temperature data of treated wastewater were analysed during the study. The average wastewater flow at the plant reaches approximately 5800 m³/h, while the temperature remains relatively stable throughout the year within a range of approximately 8 to 22 °C.

Based on these parameters, the available heat recovery potential in treated wastewater was assessed. The analysis indicates that the potential reaches approximately 380,000 MWh per year, corresponding to a heat capacity ranging from 34 MW during winter to up to 54 MW in summer.

The flow and temperature data from WWTP “Daugavgrīva“ show that the available residual heat potential significantly exceeds the heat demand of the Daugavgrīva district heating zone. To utilise this potential, the integration of an industrial heat pump system into the district heating network is being evaluated.

District heating zones and heat pump scenario analysis

To determine the optimal system solution, EKA Baltic carried out a technical and economic scenario analysis within the study, evaluating different heat pump capacities and possible district heating zone configurations.

The analysis considered the individual Daugavgrīva and Bolderāja heating zones, as well as a combined heating zone. Scenarios were compared based on technical and economic indicators, including net present value (NPV), investment payback period, and system load under different seasonal operating conditions.

The results indicate that the optimal system configuration for the combined district heating zone is a heat pump system with an installed capacity of approximately 6 MW, providing the best balance between system utilisation and economic performance.

Contribution to the development of district heating

The study demonstrates that the thermal energy contained in treated wastewater can represent a significant resource for district heating systems. By evaluating different technical and economic scenarios, a system configuration was identified that allows the efficient use of the available heat potential from WWTP “Daugavgrīva“ and its integration into the district heating network.

Such a solution enables part of the heat demand to be covered by the energy potential of treated wastewater that would otherwise be released into the surrounding environment, thereby reducing the reliance on traditional heat generation sources.

“EKA - Naturally sustainable engineering solutions”