4.1 Biomethanation

4.1.1 What is biomethanation?

“Methane fermentation” or “anaerobic digestion” is usually used to indicate “biomethanation”. Biomethanation is a complex microbial process in which organic compounds are degraded into methane and carbon dioxide by variety of anaerobes. This biogas has a low heating value of 20-25 MJ/m3-N (5,000~6,000 kcal/m3-N) and can be used for fuel after desulfurization of hydrogen sulfide. Biomethanation is used as a technique of biofuel recovery from biomass and treatment of waste biomass. Fermented residue can be used for liquid fertilizer and raw material of compost.

4.1.2 Feature of biomethanation

First of all, organic compounds are decomposed to organic acid or hydrogen by variety of anaerobes. At the final stage, acetate or hydrogen and carbon dioxide are converted to methane. Biomethanation takes place under anaerobic conditions, especially, methanogens require absolute anaerobic conditions for methane production. Biomethanation is a microbiological process; therefore, this process proceeds under normal temperature and pressure. Biomethanation can be applied for variety of biomass compared with ethanol fermentation due to activities of complex microflora.