Heat recovery from municipal wastewater in Joensuu -two heat pumps have been installed and oil used for thermal drying of the sludge has been replaced by biogas
Two heat pumps (in total 250 kW) have been installed to wastewater treatment plant of Kuhasalo in Joensuu. Water flow for the evaporators is 25 l/s.
Temperature of purified wastewater is typically from 8 to 14 degrees Celsius. Heat pumps can recover 3 to 4 degrees from it.
Heat is stored in a 10 m3 water tank. Warm water (60 º C) is used in different phases and buildings at the WWTP.
Oil used for thermal drying of the sludge has been replaced by biogas from the digesters. Biogas and oil was earlier used for heating up the buildings on site.
Oil is only needed during very low temperatures and they save even 250 000 € annually.
The main stakeholders and beneficiaries are the taxpayers of the municipality, because of the annual savings generated. Practice also decreases demand of the oil transport to the area and CO2 emissions. This way it also improves complacency of the people resident at the area.

Resources needed

Investment costs were 1 100 000 € and estimated payback period 6-7 years.

Evidence of success

System creates 600 000 kg CO2e / year less than original Plant. The average savings because of decreasing oil use is 160 000 € annually.

Potential for learning or transfer

Wastewater management is an existing issue in all urban areas in Europe. Especially in Northern Europe where the climate is cold in wintertime this kind of system is useful for decreasing oil use and recovering energy from the wastewater. The system is also scalable so that it can be used in small or larger scale depending on the need.
Main institution
wastewater treatment plant of Kuhasalo in Joensuu
Pohjois- ja Itä-Suomi, Finland (Suomi)
Start Date
January 2013
End Date
December 2013


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