Biogas is a renewable source of energy

Biogas is a product of the decomposition of organic material. Biogas is produced when microbes break down organic matter in the absence of oxygen, with decomposition taking place through digestion by anaerobic bacteria. The final stage of this process generates methane-rich biogas as well as organic digestate that can be used as a fertiliser.

Biogas that is suitable for commercial utilisation can be produced especially from animal manure, organic industrial and community waste and wastewater treatment plant sludge. Biogas is a valuable, renewable biofuel and energy source with considerable environmental benefits.

Level of carbon dioxide high in unprocessed biogas

Biogas consists mainly of methane (CH4) and carbon dioxide (CO2) and very small amounts of other substances such as sulphur compounds and siloxanes. Small amounts of other compounds such as ammonia can sometimes also be found in biogas. Biogas usually contains 40−75% methane and 30−45% carbon dioxide (see table). By way of comparison, natural gas sold in Finland by Gasum has a methane content of around 98%.

The calorific value of unprocessed biogas is around 5.0–5.5 kWh/m3n, while the corresponding value for natural gas is 10 kWh/m3n.

Through processing biogas can be made chemically almost identical to natural gas. Processed biogas is utilised in heat and power production and can also be processed into a vehicle fuel.

Processing for more varied uses

Biogas can be used almost as it is in heat and power production.
Once processed, biogas can be used as a vehicle fuel in addition to the above-mentioned uses. During processing carbon dioxide and impurities (such as sulphur compounds) are removed from biogas.

Biogas used as a transport fuel should have a minimum methane content of 95%. The transport use of biogas also requires moisture removal and compression. Processed biogas (biomethane) can be used in transport either as a compressed product, compressed biogas (CBG), or as a liquefied product, liquefied biogas (LBG).