Information on the Basic Principles concerning Biogas Plants

Particularly in Germany, the framework conditions for biogas plants in agriculture have been considerably improved through the Renewable Energies Act. Thus, the construction of a biogas plant offers the following benefits:

• Efficient use of the available biomass
• Extraction of power and heat
• Increased fertilisation action of the fermentation residue through mineralisation
• Slight emission of odour-producing substances by the fermentation residue
• Breakdown of organic acids

The fact that the extraction of biogas involves a biological decomposition process poses completely new challenges in practice.

The various phases of the decomposition process produce constantly fluctuating substrate properties. On top of this, there is the problem that decomposition processes are heavily dependent on outside temperature, and reactions of the individual groups of bacteria have also not yet been fully clarified. One other serious point is that toxic gas components such as ammonia and hydrogen sulphide are produced as by-products during the decomposition phase.

There are four distinct main phases during the production of biogas:

1) Splitting hHydrolisis)
Splitting of long-chain molecules into smaller fragments by exo-enzymes

2) Acidification  (acidogenesis)
Conversion of the original substances into organic acids

3) Formation of Acetic Acid (acetogenesis)
Conversion of the organic acids into acetic acid, carbon dioxide and hydrogen

4) Formation of Methane (methanogenesis)
Formation of methane from acetic acid, carbon dioxide and hydrogen