SIAAP and SUEZ unveil France’s largest biogas unit

SIAAP (Greater Paris Sanitation Authority) and SUEZ have officially inaugurated a new state-of-the-art biogas production unit at the Seine Aval wastewater treatment plant in the Paris metropolitan area.
Treating the wastewater of over six million residents, the Seine Aval plant is the largest of its kind in Europe.
The newly inaugurated unit, led by a consortium headed by SUEZ, forms a central pillar in the ongoing modernisation of the site and reinforces SIAAP’s mission to deliver more efficient, sustainable wastewater services.
“This new biogas production unit, the largest in France, is a key part of our wider modernisation programme at Seine Aval,” said François-Marie Didier, Chairman of SIAAP.
“It enables the conversion of 130,000 tonnes of sewage sludge into both agricultural fertiliser and local, renewable energy. As France’s largest biogas producer, this facility addresses key challenges around safety, performance, and environmental stewardship.”
Xavier Girre, CEO of SUEZ, hailed the successful delivery of the project: “SUEZ is proud to have led this transformative project in collaboration with trusted partners. The new unit will improve the plant’s environmental footprint while enhancing its performance. It reflects our deep expertise in sludge recovery and long-standing partnership with SIAAP to reshape this vital infrastructure for the energy transition.”
Spanning seven municipalities in the Yvelines and Val-d'Oise departments — including Achères, Conflans-Sainte-Honorine, and Saint-Germain-en-Laye — the Seine Aval plant treats the wastewater of the Paris metropolitan population every day.
The complete reconstruction of the biogas production unit began in 2016 and was delivered by a consortium comprising SUEZ, Chantiers Modernes Construction (a Vinci subsidiary), Demathieu Bard Construction, SOGEA Environnement, and architectural firm Thetis Tanguy du Bouetiez. This redevelopment is part of SIAAP’s broader site transformation programme, underway since 2009.
The facility now has an annual treatment capacity of 130,000 tonnes of sludge and generates 350 GWh of renewable energy — making it France’s largest biogas production unit from wastewater. It supplies 56% of the plant’s overall energy needs and is fully energy self-sufficient.
Incorporating cutting-edge safety systems, a compact design, and advanced deodorisation, the new unit was engineered to adapt to fluctuations in sludge composition. Total project investment reached €401 million (excluding VAT), with €373 million allocated to the consortium. It received €32 million in grants and €16 million in interest-free loans from the Seine Normandy Water Agency.