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Lyonnaise des Eaux-GDF SUEZ reuses the heat from wastewater to heat a public building – The city hall of Valenciennes

4. Environment

Energy / Greenhouse Gases (GHG)


As part of the Climate Plan and Agenda 21, the city of Valenciennes, the Eaux et Force company, and the S.I.A.V. (Syndicat(Union) Intercommunal Assainissement(Sanitation) Valenciennes), have implemented an innovative way to recover thermal energy from sewage. This environmentally friendly process is intended to heat buildings in Valencienes’s City Hall while responding positively to the requirements of the European Union  


The recovery of wastewater calories can produce energy savings


“Degrees blue” is a process developed by Lyonnaise des Eaux and installed by its subsidiary Eaux et Force in 2010 for the city of Valenciennes.

The principle of “Degrees blue” is to capture the heat from the effluents flowing into the sewers to heat buildings. This environmental and economical process promotes energy autonomy in communities through using an untapped a local resource. “Blue degrees” constitutes true green energy that meets the environmental challenges of tomorrow.

The technology used is relatively simple: an exchanger is placed at the bottom of the water piping. This heat exchanger is made of stainless steel plates that transfer the heat from waste water to the calorie carrier fluid inside it. This heat transfer fluid consisting of glycol recovers calories and directs them to the heat pump. It circulates in a closed loop inside the heat exchangers of the boiler room of the Town Hall building.

The heat pump then multiplies the calories taken and raises the temperature until it is sufficient to heat the building.


- New technology for communities
- Contribution to sustainable development policy
- Spreading phenomenally to other communities


Results achieved:
- Decrease of 45% of the energy bill from the city of Valenciennes
- CO2 emissions divided by 3 (200 tonnes of CO2 saved per year)

147 200 collaborateurs
81,3 milliards € (2013)


1-2, place Samuel de Champlain
92930 Paris la Défense

Mise à jour le 23/05/2016

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