Achères Seine Aval (Yvelines)

Achères Seine Aval: restoring the ecological state of the Seine

In 2015, Stereau was declared the winning bidder of the tender launched by the Interdepartmental Syndicate for Sanitation of the Paris Metropolitan Area (SIAAP) for the design and construction of the primary sedimentation at the Seine Aval plant located in Achères (Yvelines), the second largest wastewater treatment plant in the world and the first in Europe.
This project, which involves adding a new primary sedimentation stage between the pre-treatment and biological treatment, aims to restore the environmental
quality of the Seine River downstream of Paris up to its estuary and thus limit the pollution
l oads carried into the English Channel.

Achères wastewater treatment plant (Siaap - Yvelines)

The challenges

  • To contribute to restoring the ecological quality of the Seine River.
  • The project consists of the construction of a pumping station consisting of 16 pumps with a capacity of 2.5 m3/s, a unit of 14 screens followed by 20 lamellar settlers, operating with or without the addition of chemicals to treat a flow rate of 34 cubic meters per second. Treatment and pumping facilities complete the project.
  • To limit the environmental footprint of the facility, the installation of an odor treatment process is implemented.

Our solutions

Within the scope of this contract, Stereau has implemented the services of:

Pumping and screening: water intake from the existing pre-treatment, design and construction of an emergency overflow structure at 34 m3/s, installation of 16 pumps with a total capacity of 34 m3/s, 14 bar screens, 6 mm screening (stair-type), and compaction treatment of rejects.

Primary sedimentation: installation of lamellar primary settlers, injection of coagulant and flocculant as needed, integrated sludge thickening, pumping of sludge up to 40 g/l over a distance of 1,000 meters. 

To avoid any nuisance, the structures are covered and connected to a biological deodorization system using Stereau’s patented process,  Lanodor®, with a flow rate of 240,000 m3/h.

The heating of all buildings is achieved through the heat contained in wastewater using heat pumps.


  • Improvement in the capacity and quality of wastewater treatment, including during rainy weather
  • Enhancement of the living environment for residents through the reduction of olfactory nuisances
  • Greater protection of the waters of the Seine River
m3/day dry weather capacity
70 %
of wastewater from the Greater Paris area
m3/s settling flow

Other achievements

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