Aubenas (Ardèche)

Aubenas: wastewater to green energy 

Consisting of the five municipalities of Aubenas, Saint-Etienne-de-Fontbellon, Saint-Sernin, Saint-Didier, and Mercuer, the Bourdary Joint Association initiated the construction of a new wastewater treatment plant in June 2019 to replace the outdated Bourdary and Tartary treatment plants. By producing and utilizing biogas derived from the anaerobic digestion of sewage sludge in the GrDF network, the new wastewater treatment plant, designed and constructed by Stereau, is a unique example in Ardèche. This valorization of wastewater into renewable green energy exemplifies an innovative approach in sanitation and contributes to the energy transition of the region.

Bourdary wastewater treatment plant - Aubenas (Ardèche). Biogas production from wastewater - Stereau

The challenges

  • To have a modern, efficient, and environmentally friendly facility capable of treating, for the next 30 years, the effluents from 49,000 population equivalents.
  • To treat and valorize sludge resulting from wastewater treatment into biogas, which, after filtration, is transformed into injectable biomethane in the GrDF network.

Our solutions

The strong expectations of the community regarding environmental respect and greenhouse gas emissions reduction were integrated from the very beginning of the design.
All the motors in the plant operate on frequency inverters, allowing their power to be adjusted to the specific needs of the equipment, in order to save energy. The screening treatment of the influents at the entrance of the plant enables the recovery of sand and gravel for reuse after washing, in construction activities. The centrifuges, which remove water from the sludge, help reduce the amount of materials to be disposed of in landfills, as well as the associated traffic for their disposal.

Special attention has been given to controlling all nuisances, both odorous and noise-related. Air treatment using Stereau’s green deodorization process, Lanodor®, prevents any olfactory discomfort at the plant and its surroundings. The installation of sound insulation on walls and ceilings in all areas containing the loudest equipment ensures satisfactory working conditions.


  • Production of locally sourced renewable green energy, consumed locally.
  • 200,000 m3/year of biomethane injected into the GrDF network, equivalent to the consumption of 200 households.
  • Reduction of over 60% in the quantities of sludge to be transported and treated.
  • Elimination of 50 25-ton semi-trailers between Ardèche and Gard for sludge disposal.
  • Savings in drinking water: The Bourdary wastewater treatment plant solely utilizes the industrial water available at the facility.
"An exemplary circular economy project, unique in Ardèche."
A daily flow rate of
population equivalents
m3 of air treated daily through the Lanodor® deodorization solution.

Other achievements

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