Biogas

Biogas is a mixture of gases produced by the decomposition of organic matter under anoxic conditions. In the absence of oxygen, decomposition occurs through putrefaction by anaerobic bacteria. In the final stage of the decomposition process, methane is produced as a result of the decomposition activity of methane bacteria.

Biogas consists mainly of methane and carbon dioxide. The composition of the gas depends on the biomass to be digested and the digestion process. For energy use, the most essential component of biogas is methane, which usually makes up 50-70% of the gas. The proportion of carbon dioxide is 30-50%. Biogas also contains small amounts of a number of other substances such as water, nitrogen, oxygen, hydrogen, ammonia and hydrogen sulphide.

Production and exploitation

Biogas is produced in a biogas reactor from biomass (including sludge, manure, waste and agricultural biomass) and landfills collect landfill gas from waste fill. Biogas can be used for heat and power generation, and can also be refined into vehicle fuel.

Other products from the biogas plant include carbon dioxide, which can be used in greenhouses, for example. The digested biomass is called digestate residue, which is almost similar in mass and nutrient composition to feed material. Its dry matter content is reduced by a few percent during the process and its pH is close to neutral.

The digestate is more homogeneous than feed, more hygienic, less odorous, and the nutrients it contains are more soluble and volatile. Thus, for example, the fertilisation properties of slurry are improved in the digestion process.

Biogas is environmentally friendly energy

Biogas contains methane just like natural gas and can be used as a substitute for natural gas. The methane content of natural gas is just higher than biogas, at around 98%. To use biogas in internal combustion engines, water and sulphur must be removed. With additional purification, biogas can also be fed into the natural gas grid or used as a transport fuel.

Methane is 20 to 70 times more powerful greenhouse gas than carbon dioxide. Therefore, reducing the landfilling of bio-waste and recovering and using the biomethane that leaks from landfills for energy production makes good environmental sense. Biogas production has clear advantages in terms of waste recovery, as digestion retains the nutrients in biomass better than composting.