Biogas can be used to substitute fossil fuels such as oil, coal and natural gas. In Denmark most of the biogas is sold to district heating plants and power plants, but the biogas can also be used for other purposes, such as transport. Biogas can moreover be used in the natural gas grid after upgrading.
For the agricultural climate budget biogas is of considerable importance, as the digestion of animal manure in a biogas plant can substantially reduce the emission of greenhouse gases.
The storage and field application of undigested slurry releases methane to the atmosphere. By digesting slurry in a biogas plant, the methane produced during digestion is extracted and utilised with the result that atmospheric emissions of methane are reduced.
Biogas is a mixture of methane and carbon dioxide and a very small proportion of other gases. Biogas is produced during the anaerobic digestion of organic material and is produced naturally in, for example, bogs.
The commercial production of biogas for human use goes back a long time. In this country, biogas plants have been built since the 1920s, but despite having a large livestock farming sector, biogas production in Denmark never really caught on.
The lack of economic profitability and technical problems associated with the production kept the interest at bay, but an increased focus on and political will to use renewable and eco-friendly energy sources have lately generated a lot of interest in biogas.
The nutrients, in particular nitrogen, remain in the slurry. The digested slurry can be applied in the field where it causes far fewer odour problems than untreated slurry. The emission of nitrous oxide, a potent greenhouse gas, is also substantially reduced compared to the application of untreated slurry. Risk of the leaching of nitrogen to watercourses is likewise reduced.
For agriculture the digestion of animal manure in a biogas plant also carries the advantage that problems with weed seeds and infectious agents are significantly reduced.
