Biogas composition I Plant of biogas composition

Biogas typically refers to a gas produced by the biological breakdown of organic matter by bacteria in the absence of oxygen [].Although the composition of generated biogas varies a lot for different feed materials. The typical composition can be summarized as in Table 2.1.

Table 2.1 Typical composition of biogas [9]

Compound	Concentration (by volume)
Methane (CH4)	50-70 %
Carbon dioxide(CO2)	25-50 %
Nitrogen(N2)	0-10 %
Hydrogen(H2)	0-1 %
Hydrogen sulfide(H2S)	0-3 %

Principle of Anaerobic Digestion

Biogas production is a microbial process.Microbes involved in biogas productiongrow in the absence of oxygen. The most important organisms are tiny bacteria.Different groups of bacteria act upon complex organic materials in the absence of oxygen toproduce biogas. The process involved combined action of threegroups of bacteria, in three stages in the biogas plant. The first stage is thefermentation of high molecular weight substances like cellulose, starch, protein, fats, etc.present in organic materials into small molecular weight compounds like fatty acidsamino acid, carbon dioxide and hydrogen, this is brought about by a hydrolytic group ofbacteria, in the second stage the end products of the first stage are converted into acetic acid,hydrogen& carbon dioxide by hydrogen producing acetogenic bacteria. In the third stage, the methane producing bacteria convert the substances produced in the first and second stage into CH₄&CO₂.[ ]