Methanization is a mature process for producing biogas, which involves promoting the breakdown of organic matter, both animal and/or plant-based, to generate a gas mixture made up of 50 to 65% methane. Agricultural methanization is a rapidly growing sector as it lies at the intersection of local and circular economies and the energy transition.
Methanization is a technological process that, under controlled conditions, produces both biogas and digestate.
It is based on the natural breakdown of organic matter by microorganisms in the absence of oxygen (anaerobic fermentation).
Organic matter can come from a variety of sectors: agriculture, industry, food waste, municipal waste, organic waste, gas from non-hazardous waste storage facilities, and more.
Once collected and transported to the methanization site, the organic matter is sorted, mixed, and heated for several weeks in a digester or methanizer (an oxygen-free chamber).
The biogas produced can be used solely for heat (by burning it in a boiler) or for both electricity and heat (through cogeneration). It can also be purified to reach the quality of natural gas, in which case it is referred to as "biomethane."
Methanization also produces a byproduct called digestate, which is a natural organic fertilizer.
Several types of organic matter, also called inputs, can be used to run a biogas/biomethane production facility.
Slurries (a mixture of animal waste) and manure (a combination of slurry and animal bedding) make up the majority of livestock effluents.
Crop residues are the above-ground parts of plants that are not harvested and left in fields or orchards after harvesting (stems, stubble, leaves, pods, etc.).
An energy cover crop is a crop planted and harvested between two main crops in a crop rotation.
The agri-food industry generates various materials during production. When these materials are used for anything other than a final product, they are called “byproducts,” such as apple pulp, downgraded fruits and vegetables, recipe mistakes, eggshells, and more.
The use of animal waste is subject to European regulation (EC No. 1069/2009) to maintain a high level of hygiene. This regulation requires specific pre-treatments for different types of animal waste before methanization.
These are crops primarily grown for energy production. Their use in methanization units is strictly regulated to avoid competition between energy production and food supply.
This refers to waste from households, municipal services, sanitation waste, and street cleaning waste.
Green waste refers to plant material resulting from the maintenance and renewal of green spaces (parks, gardens, sports fields, etc.) from local authorities, public and semi-public organizations, private companies, and individuals.
This includes sludge treated in urban wastewater treatment plants, as well as sludge from the agri-food industry, which is liquid waste from slaughterhouses, dairies, cheese factories, bakeries, breweries, canneries, and more.
Depending on the type of input, the methanization process may vary significantly, especially regarding the moisture level of the organic matter, such as in wastewater treatment plant sludge (WWTP); this is known as non-WWTP methanization or WWTP methanization.
Source : ENGIE, Renewable Gas Europe, 2024
