A major project for MEL’s ecological and climate transition

Commissioned in 1986 and renovated in the early 2000s, the Wattrelos wastewater treatment plant currently treats the wastewater of nearly 417,000 population-equivalents across 15 MEL municipalities and the city of Mouscron (Belgium).
With this extension and reconstruction project, its capacity will increase to 511,500 population-equivalents by 2031, representing a rise of more than 20%.

The future plant will deliver enhanced performance:
Treatment capacity increased from 3.3 m³/s to 10.3 m³/s, thanks to the creation of a new 7 m³/s rainwater treatment line,
A 30,000 m³ storage basin—equivalent to 10 Olympic swimming pools—for improved stormwater management,
Potential integration of water reuse (REUSE) for local applications, along with exemplary landscaping, including 4 hectares of wildflower meadows and strengthened hedgerow networks to foster biodiversity.

The project will be phased to minimize impacts on the environment and local residents. A group of 20 to 40 residents will also be involved to regularly discuss progress and share feedback.

An exemplary, energy-positive plant

The new Wattrelos–Leers plant is designed as a model of efficiency, performance, and circular economy.
It will be a net energy producer thanks to a unique combination of technologies:
Sludge methanization generating 11 GWh/year of biomethane—the equivalent of the annual consumption of 2,800 residents,
Energy potential from dried sludge amounting to 14 GWh/year.
• Recovery of waste heat (2.2 GWh/year), covering the plant’s needs and equivalent to heating 1,500 homes.
• 6,000 m² of photovoltaic panels and hydroelectric turbines, supplying more than 10% of the plant’s electricity needs.

In addition, the plant will be powered entirely by 100% green electricity.

Thus, the plant will become one of the largest energy-positive facilities in France, fully contributing to MEL’s Climate Plan objectives and the decarbonization of essential services.

Environmental protection and quality of life

The wastewater treatment plant will incorporate innovative measures to enhance comfort and quality of life for local residents:
Source-level odor capture and treatment
Enclosure of noisy equipment
Entire process supplied with recycled water
Optimized sludge drying, reducing transport volumes by more than 1,000 truckloads per year

These features will help reduce nuisances, preserve resources, and strengthen the metropolitan policy for sustainable stormwater management, in line with the Local Urban Plan and efforts to combat urban heat islands.

A large-scale construction project

The project represents a total investment of nearly €293 million:
€200 million dedicated to construction works,
€93 million for 12 years of operation entrusted to Saur France.

Financing includes support from the Artois-Picardie Water Agency (€45 million in grants and €30 million in repayable advances) and from the ERDF (€6 million for the energy component).

The project is being carried out in phases to ensure continuity of public service:
2025: launch and preparatory works
2026–2028: construction of new facilities
2029–2030: phased commissioning
2031: operation of the modernized plant

Statements

Damien Castelain, President of the Métropole Européenne de Lille:
“With this €200 million project, the Métropole Européenne de Lille is undertaking one of the largest wastewater treatment plant modernizations in France. It is a structuring project that will increase treatment capacity by 20% and ensure a modern, efficient public sanitation service for hundreds of thousands of residents.
Beyond the technical dimension, this project reflects our decision to invest in the future, to strengthen the attractiveness of our region, and to improve the daily lives of our residents. MEL is leading by example, placing investment and innovation at the service of the common good.”

Élise Le Vaillant, Vice President, Saur France North-East:
“With the Métropole Européenne de Lille, we are undertaking a project that concretely illustrates the water transition: a plant capable of treating wastewater for nearly half the territory’s population, while producing more energy than it consumes. It is a forward-looking achievement, designed to adapt to regulatory changes, climate variability, and the needs of future generations.”

Hugo Bardi, President of Saur Water Engineering and Stereau:
“This groundbreaking marks the launch of a large-scale project. Engineering, innovation, and stakeholder engagement come together to create one of the most efficient and exemplary wastewater treatment plants in France. This project highlights the expertise of our teams and the consortium’s commitment alongside MEL.”

Bruno Parent, Deputy Managing Director, NGE Group:
“This groundbreaking ceremony marks the launch of a major project for which NGE Group is mobilizing its expertise in large-scale civil engineering, built on numerous references in France and internationally. Alongside MEL, local officials, and our partners, we are helping to sustainably protect water resources and strengthen actions in support of the ecological transition of the Métropole Européenne de Lille.”

Consortium
Lead contractor and operator: Saur France
Wastewater engineering: Stereau
Civil engineering: NGE GC, a subsidiary of NGE Group
Architects: HB Architectes Associés and Atelier 9.81
Project management consultant (PMC): Artelia

Total contract value: nearly €300 million, including €200 million for construction and €93 million for 12 years of plant operation by Saur France.