Lighting, heating, transport... thanks to our waste? It’s possible! Obtained via the fermentation of organic matter, biogas can be used to produce electricity, heat and even fertilizer. Purified biogas, known as biom
Lighting, heating, transport... thanks to our waste? It’s possible! Obtained via the fermentation of organic matter, biogas can be used to produce electricity, heat and even fertilizer. Purified biogas, known as biomethane, which has equivalent characteristics to those of natural gas, can be used in natural gas networks or as engine fuel. A renewable energy source as promising as it is virtuous… but the costs of which remain relatively high, thereby requiring government support.
- What is biogas?
- How is biogas produced?
- Biogas, a renewable energy source
- Biogas, benefits for the environment
- Public support required to develop the biogas sector
Biogas is usually derived from the fermentation of organic matter under the action of microorganisms. This fermentation process, which occurs spontaneously in natural ecosystems (marshland, paddy fields, soil, intestines of mammals, etc.), is known as methanization. Now, humans are able to harness the process and use it to convert our waste, replacing some fossil energy sources. The objective: to reduce our greenhouse gas emissions.
Other production options?
New biogas production methods based on the gasification of lignocellulosic resources (straw, plant stems, wood chips, etc.) or methanization (production of synthetic methane via the conversion of bio-carbon monoxide or dioxide in the presence of hydrogen) are currently in the experimental or demonstration phases. The methanization of microalgae is also being considered as a longer-term option.
All organic matter, whether of animal or plant origin, can be methanized to convert it into biogas. At present, the following types of waste are most frequently used:
- agricultural waste (animal excrement, harvest residues such as straw, etc.),
- green waste (grass clippings, etc.),
- agrifood industry waste (abattoirs, vines, dairies, etc.),
- water treatment plant sludge.
Methanization must take place in a confined facility known as a digester, in the absence of oxygen. Microorganisms naturally present in organic matter break this matter down and produce biogas, as well as a residue known as digestate.
Biogas is a mixture of:
- 50 to 70% methane,
- 20 to 50% carbon dioxide (CO2),
- traces of nitrogen, ammonia and hydrogen sulfide.
Only the methane is used, once it has been separated from the other gases (depending on its degree of purity, the CO2 could also be used).
The different types of methanization units
Methanization can be implemented on several scales. Smaller units tend to be agricultural (“farm” methanization), operated by a farmer or a group of farmers.
Bigger, collective facilities also exist, mainly converting urban or industrial waste:
• centralized units (waste of varying origin depending on the location of the facility),
• industrial units (agrifood, chemical or paper industry waste),
• units specializing in the conversion of water treatment plant sludge,
• uhousehold waste methanization units (managed by local authorities or specialist companies).
Biogas can have several uses:
- Heat production: biogas is burned in a boiler to produce heat. The latter must be used close to the production source to limit heat dissipation / loss,
- Electricity production: biogas is burned and the energy produced powers a generator that in turn produces electricity,
- Cogeneration: this involves the combined generation of electricity and heat. This is the most frequent application of biogas. Electricity is produced by a generator, while heat is recovered in the cooling system and exhaust gases and used locally,
- Vehicle fuel production: before it can be used as a fuel in a vehicle, the biogas must be purified (to remove carbon dioxide, water and hydrogen sulfide, which are corrosive for engines). The biomethane obtained is almost identical to NGV (natural gas for vehicles). This type of conversion has yet to be widely developed and primarily concerns captive fleets (urban transport, etc.).
In France, for example, buses in the northern city of Lille have been running on biomethane since 2006.
- Injection into the natural gas network: as for fuel production, the biogas must first of all be purified to give biomethane. The matter can then be injected into existing natural gas networks. This type of conversion is most frequent in Sweden, Germany, Switzerland and the Netherlands. In France, 76 methanization sites injected 0.7 Twh of biomethane into the natural gas networks in 2018. The cumulative total from the 660 projects waiting for the biomethane injection facilities to be linked up is estimated to be 14 Twh/year (source GRDF). In 2017, total natural gas consumption in France was 465 Twh.
- Residue not digested by the bacteria (digestate) can be processed (in particular, to remove pathogens) before being used as agricultural fer