Heat pump at a wastewater treatment plant in Kalundborg, Denmark
NIRAS assisted Kalundborg Utility to use heat pumps to utilise energy from waste water.

heat pump solution

Waste water turned into district heating

With an innovative heat pump solution, Kalundborg Utility utilises wastewater from a sewage treatment plant to produce district heating. The sewage treatment plants have the potential to become the energy producers of the future, a report by NIRAS shows.

Kalundborg is a Danish municipality covering 604 square kilometres in the north-western part of the island of Zealand. The company Kalundborg Utility provides water to all households in the area and is responsible for the district heating and treatment of all wastewater in the municipality.

Kalundborg Utility has installed a heat pump to extract the excess heat from the wastewater. The heat pump is the largest installed in a sewage treatment plant in Denmark and is capable of providing district heating to local customers.

NIRAS advised Kalundborg Utility about heat pumps and managed the planning, tendering and contracting of the main contractor for the construction and implementation of this innovative solution.

The heat pump utilises excess heat

The heat pump system replaced two old oil-fired district heating plants. The new system has a combined heat capacity of 10 MWt (34mmBTU/hr). The heat pump utilises the excess heat and energy available from the wastewater. The wastewater is 30°C (86°F), and it is this heat that the heat pump utilises when it heats the supply water in the district heating network supplied to customers.

Even though the heat pump is driven by electricity, it still has a significant environmental advantage as more than 50 percent of the electricity produced originates from sustainable energy, such as wind turbines.

The future supplier of heat

One of the most significant findings of NIRAS’ report was that technologies for efficient energy production from sewage treatment plants are the key to a successful transition from energy consumer to future energy producer for utility companies. The report was prepared by NIRAS for the Ministry of the Environment and Food and was based on interviews with 62 of the largest sewage treatment plants in Denmark.

Knowledge from the report was used to advise Kalundborg Utility in their transition from the oil-fired district heating plant to one driven by a heat pump.

The new development of sewage treatment plants becoming energy generators has already taken off. Several plants in Denmark are already actively taking steps to become energy suppliers instead of energy consumers.

Huge potential

In total, there are 674 sewage treatment plants in Denmark, and they are facing a paradigm shift from primarily focusing on cleaning wastewater to also working with resource utilization.

The report from NIRAS shows that the wastewater sector has the potential to not only being able to supply itself with energy – but also to be able to supply 130 GWh (443000mmBTU) of heat or electricity to customers.