Cleaning wastewater with energy surplus

With the help of Danfoss drives, the Aarhus water treatment plant in Denmark not only ensures clean water – it also produces more electricity and heating than it consumes.

Water and wastewater facilities account for the largest consumption of electricity in most municipalities, typically 25-40% of the local authorities' total energy use. In the Danish city of Aarhus, the local water company has managed to transform the wastewater facility from being just a wastewater plant to also functioning as a combined heat and power plant.

In 2014, the wastewater plant in Aarhus produced 140% electricity and 2.5 GWh excess heat, which is led into the district heating system in the city, thereby reducing its carbon footprint. The heat and electricity production combined equals energy production of 190-200%, which is 90% more than the facility consumes. 

This is achieved through advanced process optimization and by using more than 120 VLT® AQUA Drive variable speed drives from Danfoss as control handles on almost all rotating equipment. The drives enable the wastewater facility to adapt to the change in load during the 24-hour cycle and save energy. Done optimally, this also creates the maximum amount of sludge/carbon for the digester, creating gas which is used for both electricity and heat production.

The vision for Aarhus Water is to extend energy generation even further to achieve so much surplus energy from its wastewater treatment plants that it can also meet the energy requirement of the city’s potable water supply. This will transform the single largest electricity consumer in the municipality into an energy-neutral party.

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VLT® drives for water and wastewater applications