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How is biogas produced?
Biogas is produced when bacteria digest organic matter (biomass) in the absence of oxygen. This process is called anaerobic digestion. It occurs naturally anywhere from the within the digestive system to the depth of effluent ponds and can be reproduced artificially in engineered containers called digesters.
There are 2 main types of anaerobic digesters:
- covered effluent ponds for liquid waste, where biogas accumulates under an impermeable cover and is piped for processing
- engineered digesters for semi-liquid wastes, like fermentation tanks, where the waste is mixed and the digestion process can be controlled by heating or cooling, or by adding bacterial mix to enhance the degradation process.
During digestion, 30-60% of the digestible solids are converted into biogas.
Feedstock for the industrial production of biogas includes:
- livestock effluents and meat processing waste
- the organic components of landfills
- any other source of biomass (e.g. wastewater treatment sludge or food and beverage industry wastes).
What does biogas contain?
On average, biogas contains:
- 55-80% methane (CH4)
- 20-40% carbon dioxide (CO2).
- trace gases, including toxic hydrogen sulphide and nitrous oxide.
Methane gas is particularly important as its high energy content can be used to produce energy. Methane has 21 times the power of carbon dioxide to contribute to climate change. Rather than letting methane from natural putrefaction escape into the atmosphere, it makes sense to capture it and burn it. Combustion transforms methane into heat and carbon dioxide. In doing so, you can harvest the energy content of the gas and reduce the impact on climate change.