Exona-Evry: Green Energy from Wastewater

The Local Public Company (SPL) Confluence Seine Essonne Energie, keen to innovate in energy resource management and strengthen its ecological commitment, has chosen Stereau to realize its ambitious energy recovery project. This initiative aimed to convert the sewage sludge from the wastewater treatment plants of Evry-Courcouronnes and Corbeil-Essonnes into biomethane, a green and renewable energy source, thus marking a decisive turning point for the ecology and local economy of the territory.

The challenges

In March 2021, the SPL “Confluence Seine Essonne Energie” was established, resulting from a collaboration between Grand Paris Sud and the SIARCE, to jointly manage the two wastewater treatment plants in Evry-Courcouronnes and Exona. Challenge: Transforming sewage sludge into biogas, thus marking significant progress in the ecological transition of Grand Paris Sud.

  • Biomethane production from sludge, thereby reducing waste and increasing energy efficiency.
  • Conversion of biogas into marketable biomethane for the city gas network.

Our solutions

The biogas treatment process implemented by Stereau, leading the consortium with Gazfio, Travaux Publics de Soisy (TPS), and Destas & Creib, was structured in three main stages:

  • Methanization: sewage sludge is processed to produce biogas, which is captured and stored after dehumidification.
  • Purification: the biogas undergoes activated carbon pretreatment for filtration and is then converted into 98% pure methane (biomethane), meeting GRDF standards.
  • Injection: the purified methane is then injected into the gas network.

In parallel, a heat recovery system was installed to optimize energy use and reduce the electrical consumption of the unit.


  • Production of 1.2 million Nm3 of methane per year, equivalent to the gas consumption of 330 households or 73 gas-powered buses.
  • Reduction of sewage sludge volume by 30%, thereby improving air quality on-site and in the surrounding area.
"Turning wastewater into a new resource: the Exona-Evry project embodies our commitment alongside local authorities to clean energy and sustainable resource management."
346 000
population equivalents
14 millions
of kWh produced per year
97 Nm3
Biomethane production

Other achievements

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