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What does “Biogas” mean?

Biogas is a gaseous mixture composed of methane (40-75 %), carbon dioxide (25-55 %) and trace gases (0-10 %). In anaerobic and dark environment organic material is metabolised by means of microorganisms.

Biogas is also well known as marsh gas, sludge gas, landfill gas or digester gas.
The term “Biogas” concerns the fermentation of waste materials or of renewable materials, respectively. Biogas is generated as a metabolite by methane bacteria.

How can “Biogas” be established?

The degradation of biopolymers to “Biogas” and its components is done in four interdependent steps:

1. Hydrolysis:

In the first step water-insoluble biopolymers are fractionalized into basic monomer modules or in other dissoluble fragments. This reaction is done by facultatively anaerobic microorganisms and disaggregated via exoenzymes. Carbohydrates like starch and cellulose are splitted into low saccharides, fat to glycerine and high fatty acids.
Initially proteins are splitted to poly- and oligopeptides and afterwards to amino acids by the use of peptidases.

2. Acidification:

The acidification takes place at the same time as the hydrolysis step (1st step). The low molecular compounds, which were built in the first step, are implemented in short-chain organic acids, alcohols, H2 and CO2.

During this step the facultative anaerobe microorganisms gain energy. 20 % of the total amount of acetic acid is generated.

3. Acetogenesis phase:

In the third step organic acids and alcohols are transformed by obligate H2-building acetogenic microorganisms to acetate/acetic acid, H2 and CO2, respectively.

4. Methanogenis phase:

Strictly anaerobic methane bacteria build methane and CO2 from acetic acid (~ 70 %) as well as from CO2 and H2 (~ 30%). For methane bacteria these reactions are an important energysource.

“Biogas” is made of...

Biogenic substrates like liquid manure, sewage, maize, grass, sunflower, biodegradable waste, slaughterhouse waste, vegetable and fruit waste,…..

How can “Biogas” be recycled?

There are various possibilities for the utilisation of “Biogas”.
  • electricity generation
  • production of heat
  • fuel
  • supply in natural gas network – can be useful in the future

The pros and cons of “Biogas”:

  • possibly unpleasant odour made of substrates
  • Dependence on substrate price (if substrates are bought in addition)
  • High capital investment costs

  • energetic benefit
  • reduction of fossil fuels
  • reduction of greenhouse gas
  • economisation of chemical fertiliser
  • increase of plants tolerance
  • CO2 neutral energy production
  • Environment-friendly



Brachtl, E. (2000). Pilotversuch zur Cofermentation pharmazeutischer Proteinabfälle mit Rinderjauche. Diplomarbeit, Universität für Bodenkultur Wien

Braun, R. (1982). Biogas – Methangärung organischer Abfallstoffe: Grundlagen und Anwendungsbeispiele. Innovative Energietechnik, Springer-Verlag, Wien – New York.

Schlegel, H. G (1985). Allgemeine Mikrobiologie. 6. Aufl., Georg Thieme Verlag, Stuttgart – New York.

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