The technological process of biogas

Biogas is produced from livestock manure, green waste, and organic waste. The functional principle of a biogas plant is simple: manure plus solids such as silage of maize, grass or grain is fed into the mixer, mixed until a homogeneous substance is obtained, and heated. Retention time at this stage is about 1.5 – 2.5 days (time required for hydrolysis). Then, the material enters the fermentation process (fermenter or digester). It remains in the digester for 30 to 45 days at a temperature of about 40°C (= in the mesophilic range). During this period, biogas is formed as a product of microbial activity. The material must be continuously agitated to prevent particles from floating and clumping on the surface or sinking to the bottom. This also facilitates the release of the gases being produced. The quantity of gas formed depends on the material, retention time in the digester, and the operating temperature. Most plants are run in the mesophilic temperature range, i.e. at about 35 to 40°C. The fermented material is finally stored.


Biogas may basically be used in all types of gas-powered appliances and machinery. A very efficient utilisation of biogas as a high-quality source of energy is the combined generation of power and heat in a cogeneration plant. In such a facility, biogas is used to fuel a converted diesel or petrol engine that drives a power generator. The heat given off by the engine is used for heating. The electricity produced is used by households or businesses, with any surplus being fed into the public grid.

Example of a standard plant


  • 10,000 tpa manure
  • 18,000 tpa solid organic residues

to generate a minimum of 1.0 MW of electrical energy

Configuration of a standard biogas plant

  1. Silo storage
  2. Feeding system for biomass and mixer
  3. Digester with agitator
  4. Post-digester
  5. Final storage with gas holder
  6. Heat user
  7. Power plant, control and surveillance system
  8. Transformer