Technical Background: Microorganisms in Biogas Digesters

Granted: Biogas is the result of a chemical process, but these chemical reactions are catalysed by microorganisms.

Microorganisms in the Biogas Digester and their Function:

• Bacteria digest the long-chained substrate molecules
• Bacteria continuously produce even smaller molecules (acetate CH₃ COOH, CO₂ , H₂ )
• Methanogenic archaea use these to produce methane

 

 

There are two chemical pathways for the methanogenic archaea (aka. “methanogens”) to produce methane:

Acetoclastic Methanogenesis	Hydrogenotrophic Methanogenesis
Generated from acetate (yellow): CH3 COOH + H+ → CH4 + CO2	Generated from H2 and CO2 (blue): CO2 + 4H2 → CH4 + 2 H2 O
The acetoclastic route requires only one molecule: acetate (CH3 COOH).	The hydrogenotrophic route requires five molecules: 4x H2 + CO2 .
Acetoclastic methanogenic archaea can utilise acetate directly. No other microorganisms are required.	Hydrogenotrophic methanogens depend on other species providing the hydrogen (H2 ): the so-called syntrophic bacteria.
	The proximity of hydrogenotrophic methanogens and syntrophic bacteria is crucial for the direkt interspecies electron transfer (DIET).
Per methane molecule the acetoclastic route provides approx. a quater of the energy provided by the hydrogenotrophic methanogenesis.	Per methane molecule the hydrogenotrophic route provides approx. 4-times more energy than the acetoclastic methanogenesis.
The acetoclastic route is less effective than the hydrogenotrophic methanogenesis, but robust.	The hydrogenotrophic route is more effective than the acetoclastic methanogenesis, but is less robust.

 

Our services to analyse biogas digesters can help to improve controlling of biogas digesters.

If you have questions please get in contact auf.