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Biogas production

Biogas is a type of biofuel that is naturally generated by the decomposition or breakdown of organic matter, such as food fragments, animal waste, wastewater and sewage, in the absence of oxygen. This process is called” anaerobic digestion’’. 

Anaerobic digestion is a natural form of waste-to-energy process. It is a fermentation process in which organic matter is broken down by a type of bacteria, releasing a blend of gases that are primarily methane and carbon dioxide (source:

Biogas contains a high fraction of methane (between 50-75%). Therefore, it is flammable in the presence of air and represents a source of energy that can be used to heat, cool, cook, or for regular electricity production wheen it is burnt (source:

Simplified view of biogas generation and usages

Because biogas is produced biologically (vs. natural gas which comes from fossil fuel through a geological process), it is a renewable source of energy.

Production technology

Biogas production technology refers to the development of anaerobic digestion systems that decompose organic matter using microorganisms in an oxygen free environment (source:

This technology is well-established and includes the following steps (source:

  • Organic matter or biowaste is fragmented into pieces
  • Slurrifying : liquid is added to the matter in order to make it easier to process.
  • The biowaste is heated to about 37°C, as micro-organisms need warm conditions.
  • Biogas production takes place through anaerobic digestion in large tanks for about three weeks.
  • Finally, the biogas is purified (upgraded) by removing impurities and carbon dioxide and is ready to use.

The following figure illustrates these different steps in a biogas production plant .

Biogas plant overview (source:

The following figure shows the components of a typical biogas plant (in China) using straw as a feedstock (source: Chengdu-Detong).

This figure shows how biogas is purified to get rid of its CO2 using solvents in an absorption column. The solvent is regenerated in a desorption column, where CO2 is separated from the liquid rich solution.


Biogas environmental impact

Biogas is considered to be an environmentally friendly energy source; it solves the two following important environmental issues:

  • High levels of methane released by waste generated on a global level
  • Dependance on fossil fuel energy to meet global energy demand.

In addition, biogas contributes to facing climate change issues. Because the carbon dioxide  released from biogas combustion initially came from plant matter that fixed this carbon from the atmospheric, biogas production is carbon-neutral . It does not add to greenhouse gas emissions.  Therefore, any replacement of fossil fuels by biogas will reduce carbon  emissions. 

Fossil vs biogenic CO2 emissions (source: