Biogas
What is biogas and where does it come from? How does biogas differ from biomethane? What feedstocks are suitable for biogas production? Answers to these and other questions can be found on this page.
What is biogas?
Biogas is a gas mixture that is formed when organic waste decomposes in oxygen-free environment i.e. under anaerobic conditions.
Biogas is naturally formed in landfills, for example, but in biogas plants it is produced under controlled conditions from organic waste streams which would often remain unutilized.
The most important “workers” in biogas production are microbes. They eat biomass, breaking down the carbon chains of protein, fats and sugars. The organic mass decomposes and is converted to biogas by microorganisms in about six weeks.
When microbes eat, biogas is produced.
Biogas = 50-70 % CH4 (methane) + 25-30 % CO2 (carbon dioxide)
Biogas can also contain H2O + N2 + O2 + H2 + NH3 + H2S, depending on the feedstock used.
What is the difference between biogas and biomethane?
Biogas is a gas mixture produced in a biogas plant, i.e. under controlled conditions, before its purification or other further processing (e.g. liquefaction). In biogas, the methane content usually varies between 50-70%, while the rest of the gas mixture is carbon dioxide and, depending on the feedstock material, small amounts of water, nitrogen, oxygen and various impurities.
Biomethane, on the other hand, refers to biogas from which most of the non-methane gases have been removed. In biomethane, the methane content is typically 95-99%, while the rest is carbon dioxide. Any contaminants that can damage the engine over a long period of time are removed prior to gas processing. In addition, biomethane is always odorized before its use to make it easy to detect even small leaks.
For gas car owners, biomethane as a fuel is familiar, because the “biogas” that is sold at gas filling stations and refueled in cars is biomethane.
Where does biogas come from?
The biogas plant is fed, among other things, with biowaste from households, spoiled food and sewage sludge. The biogas plant runs even on spoiled ice cream. If the reactor does not receive feedstock, biogas production will decline.
Almost all organic materials are suitable for biogas production, except for of wood, paper and cardboard.
Typical biogas plant feedstocks include:
- Household biowaste
- Manure from animal farms
- Loss fodder from arable farming
- Spoiled food items from stores
- Sewage sludge
- Fish processing waste
- Slaughterhouse waste
- By-products from the pulp and paper industry
Environmental impacts of biogas
The use of biogas as a fuel is undoubtedly a positive environmental impact. It is 100 % renewable and therefore carbon-neutral, its combustion does not generate any particulate matter and it does not contain sulfur or heavy metals.
Biogas has excellent properties as a fuel. One cubic meter of methane corresponds to one liter of diesel oil in terms of energy content, and it requires, for example, about 7-8 kg of biowaste to produce it.
Biogas refined to biomethane for use as vehicle fuel can reduce life-cycle greenhouse gas emissions by up to 85-95% compared to fossil fuels. This number takes into account the entire life cycle of the fuel, from the collection, production and distribution of raw materials to use.
Biogas production is an environmentally-friendly effort. At the landfill, methane emissions from organic waste would warm the atmosphere, as methane is a greenhouse gas 25-times more potent than carbon dioxide. Instead, at a biogas plant, renewable energy is produced under controlled conditions. The impact is significant, as landfills are one of the largest single sources of greenhouse gases worldwide. Meanwhile, biogas can replace fossil fuels, such as coal and fuel oil, nowadays used in transportation industry, manufacturing and electricity generation.