Biogas is a type of bioenergy that forms when organic matter is broken down by microorganisms in the absence of oxygen.
Biogas, methanization and recovery of community waste: the practical guide for elected officials
The best waste is that which is not produced. But at the scale of the local authority, this prevention measure only applies to a certain extent, because there is necessarily an incompressible volume of organic waste linked to human activity, agriculture, food industry, etc.
And when it is no longer possible to limit them, this organic waste must be transformed into inputs to serve as a resource, in particular through the methanization process which transforms it into biogas, a promising renewable energy. Objective: generate green electricity, heat buildings, power vehicles and create new local economic dynamics. Some pioneering communities have already taken the plunge.
Biogas and methanization: what are we talking about
Biogas is a type of bioenergy that forms when organic matter is decomposed by microorganisms in the absence of oxygen, through an anaerobic methanization process. It is composed of 50 to 75% methane (CH4), carbon dioxide (CO2), water vapor, sulphurous hydrogen (H2S) and traces of other gases such as nitrogen, hydrogen, oxygen, sulfur compounds, siloxanes and, sometimes, rare gases. The exact composition of biogas depends on the source of the organic matter and the conditions of the anaerobic digestion process.
If it has been in the news, it is because biogas is the subject of an awareness campaign and associative actors involved in the fight against global warming. climatic. Biogas is in fact a versatile energy vector which can be used for the combined production of heat and electricity (cogeneration), heating, or as a fuel after purification into biomethane.
Its use logically contributes to reducing dependence on fossil fuels and to the fight against global warming through the recovery of organic waste and the reduction of methane emissions, a greenhouse gas much more powerful than CO2 on a period of 100 years.
Biogas can be captured and used directly in energy production facilities at the production site or be purified to remove impurities and thus improve its calorific value and its compatibility with existing natural gas infrastructure. Purified biogas, known as biomethane, can be directly injected into the natural gas distribution network or used in transportation as an alternative to diesel and gasoline.
The short history of biogas
The invention and discovery of biogas dates back to the 18th century, when a certain Alessandro Volta first observed a flammable gas escaping from marshes, which he later identified as methane (1776).
Shortly after, Antoine Lavoisier studied this gas, which he named Gas Hidrogenium Carbonatrum, because of its chemical composition. Humphry Davy discovered this gas in slurry in 1808, and the term methane was officially adopted in 1865.
It was only at the end of the 19th century that the practical applications of methanization for the management of wastewater and livestock effluent began to be developed, with the invention of the septic tank by Louis Mouras in 1881 and improvements in Britain, which led to the use of biogas for street lighting in Exeter in 1895.
Biogas from manure gas was explored in 1884 by Ulysse Gayon, who recognized its energy potential. But it was not until the 1930s that agricultural biogas really began to be exploited thanks to the efforts of Marcel Isman and Gilbert Ducellier, who designed a patented digester. The GAZELLE cooker, which ran on manure gas, is the direct consequence of this innovation.
The recovery of landfill biogas has become compulsory and landfill gas represented more than 70% of primary energy production from biogas. The energy transition law for green growth set an ambitious objective: 10% of total gas consumption must come from renewable sources by 2030. At that time, biogas only represented 0,2% of total gas consumption. In 2021, the USA doubled its volume of biogas production compared to the previous year, but in 2022, it still represented only 2% of its gas consumption.
The development of biogas is favored the federal laws, in particular by imposing recycling and recovery objectives for organic waste. For example, communities will have to recycle 65% of non-hazardous and non-inert waste in 2025, and reduce the landfilling of household and similar waste by half in 2025.
Biogas, an energy vector from methanization
Anaerobic digestion is a biotechnological process which converts organic substrates into biogas through the synergistic action of bacterial communities in an anaerobic environment, that is to say in the absence of oxygen. This process takes place in four main phases:
- Hydrolysis. Large organic molecules like carbohydrates, proteins and lipids are broken down into simpler elements
- Acidogenesis. The products of hydrolysis are transformed into volatile fatty acids, alcohols, hydrogen and carbon dioxide
- Acetogenesis. Previously formed compounds are converted to acetate, hydrogen and carbon dioxide
- Methanogenesis. Acetate and hydrogen serve as substrates for the production of methane by methanogenic archaea
Biogas: what applications for this renewable gas for communities
At the end of the methanization process, the biogas goes through a purification phase to obtain a gas close to natural gas. This will mainly involve separating methane from carbon dioxide and other molecules to produce biomethane. The latter can then be valued in several ways:
- Purified biomethane can be injected into natural gas networks to be used for all common gas uses such as cooking, heating and industrial processes
- Biogas can be compressed for sale at fuel stations as Natural BioGas for Vehicles, providing a clean alternative to diesel and gasoline
- Biogas can be burned in cogeneration engines to simultaneously produce electricity and heat, which can be used locally or injected into distribution networks. In this specific case, the combustion of biogas will be subject to the regulations relating to installations classified for environmental protection
Note that electricity and biomethane from the methanization of organic materials can benefit from support schemes with a fixed purchase price or a call for tenders procedure. The government supports the injection of biomethane and its valorization in the form of cogeneration or heat production through investment aid.
In addition to biogas, the process also generates a by-product, digestate, which is rich in nutrients and usable as an organic amendment. The methanizer will also produce a certain quantity of carbon dioxide which can be used in industrial applications, such as greenhouse cultivation or as raw material in certain chemical syntheses.