Reusing residual treatment sludge and effluents
Making better use of wastewater treatment by-products makes a positive contribution to developing regional circular economies. It also facilitates the energy transition by investing in new energy recovery processes that boost the overall contribution made by renewables.
- Recovery and re-use for agriculture by
composting and/or spreading
- Heat recovery
- To produce biogas for injection into the mains gas supply grid
- To generate electricity
- Ongoing research and development around processes for the hydrothermal gasification of biomass
At Cherbourg on the Channel coast of France, energy is recovered from the sludge produced by the wastewater treatment plant using several stages of treatment. By combining ultrasound with mesophilic digestion, the Digesthane® process reduces the volume of sludge, and produces biogas that is then used to heat the plant and generate electricity in a cogeneration plant. Sold and injected into the grid, the amount of electricity generated annually is sufficient to meet the needs of 250 households.
At Saint-Etienne in the Auvergne-Rhône-Alpes region of France, sewage sludge is methanised. Biogas from sludge fermentation can be reused on site or recovered after treatment to be converted into biomethane for injection into the mains gas supply grid. The volume of biomethane injected in this way is sufficient to meet the annual heating demand of 800 households.
Hydrothermal gasification of biomass: advancing innovation in the bioenergies
Hydrothermal gasification makes it possible to transform wet biomass, such as sewage sludge, into synthetic methane, hydrogen and carbon. At the same time, treats the sludge by isolating the individual elements within the biomass.
This process also promotes the recycling and recovery of the chemical compounds separated from the material: fertilizers, phosphorus, etc., which can then be returned to the soil.