World News

Veolia and SIAAP Inaugurate New Primary Settling Unit for Wastewater Treatment, Combining Industrial Performance and Environmental Preservation at the Seine Aval Site

asianwater
  • As SIAAP’s historic facility and Europe’s largest treatment site, Seine Aval serves a crucial role in the Paris region’s sanitation, treating wastewater from 6 million inhabitants daily.
  • The site achieves a significant milestone in its modernisation with the inauguration of a new primary settling unit, delivering more agile, efficient and energy-saving wastewater treatment while reducing nuisances.
  • Constructed by Veolia, this new facility can treat up to 34 m3/s of wastewater — equivalent to more than 50 Olympic swimming pools — making it Europe’s largest treatment capacity installation.

SIAAP (Greater Paris Interdepartmental Sanitation Authority) and Veolia inaugurated a new primary settling unit at the Seine Aval plant (78) on 18 March 2025. The ceremony was attended by Estelle Brachlianoff, Veolia Group CEO, François-Marie Didier, SIAAP President, and Anne Le Guennec, Veolia Senior Executive Vice President of Worldwide Water Technologies, along with elected officials and state representatives.

In the Paris region, efficient wastewater treatment is particularly critical due to the high population density and substantial volumes of wastewater requiring treatment. With millions of inhabitants, treatment plants must operate efficiently to prevent system saturation and minimise pollution in waterways such as the Seine and Marne rivers. Additionally, since the region frequently experiences heavy rainfall, the primary settling system is designed to handle flow variations by treating up to 34 m3/s — equivalent to more than 50 Olympic pools per hour. This helps preserve water quality and ensure sustainable sanitation for the region’s residents.

As part of commitments made to comply with European water directives, the new installation complements existing systems and enables better wastewater treatment by eliminating fine particles, reducing carbon and phosphorus content, and optimising the water purification process.

This inauguration marks a significant milestone in the extensive modernisation project of Seine Aval, initiated in 2009. As SIAAP’s historic facility and Europe’s largest treatment site, it plays a vital role in the region’s sanitation, treating wastewater from 6 million inhabitants daily.

A new installation with exceptional performance
Primary settling represents a critical phase in wastewater treatment. Following the pre-treatment stage, it focuses on removing suspended matter and phosphorus ahead of biological treatment. This essential step conditions the water for subsequent purification processes.

The new primary settling unit, which complements existing installations, stands as Europe’s largest such facility and marks a significant breakthrough in wastewater treatment for the Paris region. Completed after three years of work, the project required an investment of EUR511 (USD552.01) million, with EUR498 million allocated to the Veolia-led consortium.

It relies on several major innovations to:

  • Better distribute effluents based on flow rates and pollution loads.
  • Improve the quality of water discharged into the Seine River through advanced technologies including lamellar settlers that remove ultra-fine waste particles and treat dissolved phosphorus and carbon pollution.
  • Reduce odour nuisances for residents through fully covered installations equipped with an odour treatment system.

A model of energy and environmental efficiency
The new primary settling reduces its environmental impact while maximising its performance:

  • A heat recovery system has been installed on treated water (Energido™).
  • The settlers benefit from an elaborate washing system ensuring better sludge quality enabling optimised biogas production.
  • Energy and reagent consumption (Predifloc™) is optimised through predictive and real-time control using latest-generation digital tools.

Furthermore, biodiversity protection is enhanced through preservation measures for local fauna and flora.

This new primary settling unit demonstrates that industrial performance, environmental protection and residents’ quality of life can be successfully harmonised, paving the way for a new generation of water treatment facilities.

Since 2019, the Seine Aval site, Europe’s largest treatment plant, has undergone continuous modernisation. SIAAP’s primary focus remains improving industrial safety and treatment performance across its facilities. The new primary settling unit, built by Veolia and its partners, fully achieves these goals. It will provide SIAAP with a new facility that concentrates technologies perfectly suited to the challenges of its activity and mission in service of water and the environment.

François-Marie Didier, SIAAP President

“We are very proud to inaugurate today, alongside SIAAP, this new primary settling unit at the Seine-Aval site,” added Estelle Brachlianoff, Veolia CEO. “Through this landmark project, Veolia reaffirms its commitment to operational excellence and innovation serving territories and their inhabitants. This partnership, leveraging our know-how and expertise, not only meets growing regulatory requirements but also the legitimate expectations of elected officials and residents regarding environmental performance. It perfectly embodies the vision we carry within our GreenUp strategic programme: bringing cutting-edge solutions to address current and future societal challenges.”