Grésillons 1 and 2 wastewater treatment line

In Triel-sur-Seine, in the Yvelines department, Bouygues Travaux Publics participated in the design and construction of a wastewater treatment plant in two phases, carried out on behalf of the Syndicat interdépartemental d’assainissement de l’agglomération parisienne (SIAAP). The work resulted in the delivery of a facility that meets High Environmental Quality standards and serves the urban wastewater treatment needs of nearly 2 million inhabitants.

The first phase involved civil engineering work to enable the treatment of 100,000 m³ of water per day: earthworks, foundations, embankments, buildings, roads, and networks.

When it was delivered in 2007, the Grésillons wastewater treatment plant replaced the obsolete Carrières-sous-Poissy plant and relieved the Achères plant, thereby modernizing the Paris metropolitan area's treatment system. The second phase, delivered in 2013, increased treatment capacity to 300,000 m³ per day and was carried out while the plant remained in operation.

In addition to tripling capacity, this work made it possible to increase quality levels to meet European requirements, reduce the final amount of sludge produced, and improve the overall energy balance through the production of biogas.