WWTPs

-30%

Sludge volume reduced through anaerobic digestion
(source: GRDF)

2

TWh/year: Biomethane production potential from wastewater treatment plants in France
(source: ADEME)

9%

Biomethane injection facilities source from non-hazardous waste landfills and wastewater treatment plants (source: GRDF)

Wastewater treatment plants: an overlooked renewable energy source?

Historically, wastewater treatment plants (WWTPs) focused on improving the quality of wastewater discharges. They have undergone a profound transformation since the 1990s, shifting from simple sanitation treatment to a circular economy approach.

Sewage sludge, long considered costly waste to dispose of, is now recognized as a valuable resource. Through anaerobic digestion, this sludge is converted into biogas, a green energy source used to produce electricity and heat or purified into biomethane for injection into the natural gas pipeline grid.

Anaerobic digestion of wastewater sludge has expanded significantly since the early 2000s. This biological process not only reduces the volume of sludge requiring treatment (up to 40% for primary sludge) but also produces usable biogas thanks to efficient filtration.
Initially limited to local thermal or electrical uses, energy recovery has expanded with the injection of biomethane into public networks since 2014.

Production and utilization of biogas in wastewater treatment plants

Biogas from wastewater treatment plants (WWTPs) is primarily composed of methane (CH₄) and carbon dioxide (CO₂), with traces of problematic compounds such as sulfur compounds (H₂S, mercaptans) and siloxanes.

Biogas is produced in anaerobic digesters, where organic sludge is biologically degraded under controlled conditions.

Energy recovery occurs in two main forms:

Cogeneration: simultaneous production of electricity and heat with overall efficiencies of around 80-90%
RNG upgrading: purification of biogas into pipeline-quality biomethane for injection into the natural gas grid, with high efficiencies of around 90%

For both types of recovery, it is necessary to remove contaminants such as H₂S and siloxanes from the biogas.

Environmental and economic benefits

Reduced volume of sludge requiring treatment, facilitating its management and land application as a nutrient-rich digestate
Significant reduction in greenhouse gas emissions through the substitution of fossil fuels
Contribution to the circular economy by transforming waste (sludge) into an energy resource
Improved energy self-sufficiency of treatment plants (up to 100% for some facilities)
Reduction of odor emissions and a positive impact on the community acceptance of the facilities

The valorization of biogas in wastewater treatment plants is a key pathway to meeting decarbonization and net-zero goals by 2050 (Paris Agreement, Green Deal, National Low-Carbon Strategy). By combining advanced technologies and sustainable management, these facilities are positioned as key infrastructure for circular resource management and local energy resilience.

With a filtration service offered by DELTALYS filtration further improves operational reliability and environmental performance of RNG production at the facility.