Les avantages économiques et environnementaux de la méthanisation : avis de nos experts

Methanization is a biological phenomenon, based on “the degradation of organic matter by microorganisms,” explain experts from the Agency for Ecological Transition. This fermentation produces biogas, mainly composed of methane and carbon dioxide. “An industrial methanization project represents a certain cost. However, it is an investment with expenses that are recovered,” adds Sébastien Papouin. Indeed, the benefits of this installation are economic. The biogas purified into biomethane can be sold to GRDF or reused internally. “The company then creates its own source of energy,” summarizes our expert.

 

Indirectly, this helps reduce the use of the wastewater treatment plant. The cost of its operation, in terms of energy and labor costs, is lower. In addition, the amount of sludge is reduced by half thanks to the fermentation process. There is therefore less waste. The discharged water, on the other hand, is of better quality and the treated water can be reused. “It is thus possible to halve the water consumption of a factory,” adds Yann Balem, project manager. Finally, the sludge from methanization can be sold to farmers as a fertilizer. “Thus, waste, in addition to being reduced, becomes a product. It is a virtuous circle,” continues the engineer.

 

The interest is also environmental. As the Ministry of Ecology points out, “the biogas sector fully contributes to the objectives of energy transition for green growth, namely the development of renewable energies, the reduction of greenhouse gas emissions, and the development of a circular economy with the recovery of digestates from methanization in agriculture.” [2] Thus, optimization is as much economic as environmental. “This biogas, produced internally, emits ten times less CO2 than imported natural gas. 1 kW of locally consumed biogas is 1 kW of natural gas not used.

This also increases the resilience of a territory and a company,” specifies Yann Balem.

The methanization circuit includes an additional basin, smaller than the buffer basin. After these basins, the effluents are directed to a physico-chemical type flotation unit. The addition of reagents allows the separation between the dirty water, which goes to the WWTP, and the sludge, which is directed to the digester. Material losses and waste are also integrated into this reactor where fermentation occurs. During this digestion, microorganisms will break down the organic and biodegradable matter, thanks in particular to the absence of oxygen in this module. The biogas is then recovered. The digested sludge is concentrated, stored, and then valorized by agriculture. As for the dirty water sent to the WWTP, it will be recovered by the clarifier from which clean water will emerge.

 

“Currently, we are in the pre-project phase. This concerns the regulatory aspect,”

explains Yann Balem. “The file is more complex because the procedure for classified installations for environmental protection (ICPE), to be submitted to the prefecture, also concerns the methanation project.” Dametis supports the client and builds this environmental authorization request file (DDAE). “For this, Dametis has surrounded itself with experts. Namely the SET Environnement and GES engineering firms.”

 

Two distinct phases are then carried out. One concerns the new Wastewater Treatment Plant (STEP), with the transfer of water, the buffer tank, and the physico-chemical, biological, and tertiary treatment. The other focuses on the methanizer and hygienization. “There is no subcontractor mastering both methanization and the STEP,” explains Yann. “Dametis is therefore the equivalent of the conductor. From the call for tenders to the analysis of the files, including project monitoring, we are the sole contact for our client.”

The start-up thus plays a crucial role in advising, designing, and implementing this large-scale project. A service all the more important with the current rise in energy costs and the price of water set to increase as of 2023.