La Roche-sur-Yon: rethinking infrastructure for a sustainable future

In La Roche-sur-Yon, the upgrade of the wastewater treatment plant embodies a profound transformation: that of an infrastructure becoming a driver of the ecological transition, an energy producer, a haven for biodiversity and a place for engagement with the local community. This case study illustrates the ability of public infrastructure to evolve, adapt and create lasting value for the climate, nature and local communities. A tangible demonstration of SUEZ’s expertise in supporting local communities and the ecological transition.

In a context of energy price volatility and the need to reduce greenhouse gas emissions, local authorities are seeking to limit the energy dependence of their infrastructure while ensuring the continuity of essential public services. Wastewater treatment plants, historically energy-intensive, represent a key area for improvement.

In La Roche-sur-Yon, the upgrade of the wastewater treatment plant aims to optimise its energy performance and enhance the recovery of resources produced on site. The integration of the Cleargreen® process notably reduces energy consumption, thereby helping to improve the plant’s overall environmental footprint.

The biogas generated from sludge digestion through anaerobic digestion is upgraded and injected into the gas grid using the Methanis® Grid process, producing approximately 4,800 MWh of biomethane per year, equivalent to the annual consumption of around 2,000 households.

In addition, a turbine installed on the treated water stream enables energy to be recovered directly within the treatment process, further enhancing the site’s energy self-sufficiency. The plant is also equipped with 2,100 m² of photovoltaic panels, generating approximately 300 MWh of electricity per year.

Thanks to this on-site energy production, the wastewater treatment plant is energy self-sufficient and produces more energy than it consumes, generating an annual surplus of approximately 400 MWh.

In the face of climate change, resource scarcity and biodiversity loss, reducing the environmental footprint of infrastructure has become a key challenge. Beyond this, infrastructure can also contribute to biodiversity conservation and ecological continuity. For local authorities, this means designing facilities that combine operational performance with respect for ecosystems while ensuring their integration into the surrounding natural and landscape environment.

In La Roche-sur-Yon, the new wastewater treatment plant was designed with this approach in mind. It incorporates eco-design and landscape integration principles, considering the site’s topography and soil characteristics. Measures have also been implemented to support vegetation and biodiversity.

These measures include the renaturation of certain areas, tree planting, the installation of a vegetative screen at the site entrance, and the use of eco-grazing over 13,000 m². Green roofs also help improve the thermal comfort of the buildings.

In addition, the use of compact processes and multi-storey buildings helps limit the site footprint and retain more areas that support biodiversity.

Today, public infrastructure is no longer judged solely on technical performance. It is also expected to make its services visible and foster dialogue with residents. Long seen as purely technical facilities, wastewater treatment plants are now the focus of initiatives aimed at improving understanding of how they operate and their role in water management.

In La Roche-sur-Yon, the wastewater treatment plant, which serves approximately 120,000 population equivalents, fully reflects this approach. Designed as infrastructure that is open and connected to its local community, it offers both physical and digital visitor experiences, enabling schools, residents and other stakeholders to better understand wastewater treatment and the associated challenges. This public engagement also helps raise awareness of the role of wastewater services.

The construction of this new infrastructure has also generated local economic benefits through the involvement of local businesses and the creation of direct and indirect jobs. The construction phase also incorporated a strong social inclusion component, with 17,000 social inclusion hours delivered.