Researching wastewater heat as a sustainable energy solution
Hoogheemraadschap Delfland is one of the twenty-two water authorities in the Netherlands and responsible for water management in the region. Together with the municipality of The Hague they agreed to initiate research on how purified wastewater can be used as a sustainable heat source. Currently, purified wastewater with a temperature of around 20°C flows from the Houtrust wastewater treatment plant through large pipes directly into the North Sea. By extracting heat from this water before it reaches the sea, the warmth can be reused.
"I'm proud of this collaboration with Hoogheemraadschap Delfland. The energy transition in The Hague requires all local sustainable sources. The potential for using treated wastewater is enormous. So, we're eager to work with Hoogheemraadschap to further explore where and how we can utilise this heat."
How it works
This technique, aquathermie — is the use of thermal energy from water. By extracting heat from treated wastewater and upgrading it with heat pumps, the temperature can be raised to a level suitable for heating homes and providing hot tap water. Surplus heat generated in summer can be stored underground and reused during colder months, creating a stable, year-round energy source.
Building the foundation for a new urban heat source
Turning this potential into reality is not without challenges. The infrastructure required to extract heat from large volumes of water takes up space—something that is scarce in a compact city like The Hague. The study therefore focuses on identifying suitable locations for installations and determining the most effective points along the wastewater pipeline to capture the heat.
At the same time, researchers are mapping which neighbourhoods could benefit most from aquathermal heating. Current estimates suggest that up to 20.000 homes could eventually be heated using this method.
Local involvement
Residents are already closely involved. In the Vruchtenbuurt, the local initiative Warm in de Wijk is actively participating in the research. The group sees aquathermie as a promising and realistic alternative to fossil fuels for their neighborhood. If the study confirms the technical and spatial feasibility, the first aquathermal heat from wastewater could become available after 2030.
Working towards a climate-neutral region
For Hoogheemraadschap Delfland, the project fits squarely within its broader mission. As one of the Netherlands’ twenty-two water authorities', Delfland is responsible for water safety, water quality and water management in one of the country’s most densely populated and economically active regions.
"Delfland believes it's important to reduce the use of fossil fuels by switching to sustainable heat sources. The heat in wastewater we treat is one such sustainable source. Delfland is eager to collaborate with regional partners, such as the City of The Hague, to explore how we can utilise this heat source. In this way, we can work together towards a climate-neutral region."
Delfland Water Board
Delfland’s working area stretches from the North Sea to the outskirts of Zoetermeer and Wassenaar, covering more than 41.000 hectares. Around 1,4 million people live and work in the region, alongside some 40.000 businesses and an internationally renowned glasshouse horticulture sector. Water resilience, protecting this area from rising sea levels while ensuring clean and safe water is central to Delfland’s role.
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