About Biogas
How does anaerobic digestion work?
Anaerobic digestion is a process where organic matter is almost entirely broken down into biogas by a variety of microorganisms. The resulting gas mixture primarily consists of biomethane (50-75%) and carbon dioxide (25-50%), with small amounts of hydrogen, ammonia, hydrogen sulfide, and traces of other gases.
The four main stages of this anaerobic process are:
1
Hydrolysis: Complex organic molecules are broken down into simpler soluble molecules.
2
Acidogenesis: The soluble molecules are further broken down into volatile fatty acids, alcohols, hydrogen and carbon dioxide.
3
Acetogenesis: Volatile fatty acids and alcohols are converted into acetic acid, hydrogen and carbon dioxide.
4
Methanogenesis: Acetic acid, hydrogen and carbon dioxide are converted into biomethane and water by methanogenic archaea.
At the end of the process, the primary components of the gas mixture can be utilised in various ways:
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Biogas: often burned to produce both electricity and heat.
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Biomethane: Can be injected into the gas grid or used as vehicle fuel.
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Digestate: Rich in nutrients and commonly used as fertiliser.