Biogas may be described as follows :
The mixture of combustible gases obtained by the bacterial degradation of cattle dung (or any other suitable biomass) in the absence of air is called biogas. Biogas is obtained by the anaerobic fermentation of animal and agricultural wastes such as cattle dung kitchen waste etc. Biogas is not a single gas. It is a mixture of many gases.
Composition of biogas :
The actual composition of biogas depends upon the nature of biomass material used, and the method employed. Combustible components of biogas: the biogas obtained from the anaerobic decomposition of cattle dung contains methane (CH4) and hydrogen (H2) as the combustible components. Thus, the fuel value of biogas is due to presence of methane and hydrogen gases in it.
Why is biogas termed as a clean gas ?
Biogas burns with a smokeless flame and leaves no ash. As a result, the burning of biogas
Does not cause pollution of the air.
Does not pose any problem of the disposal of ash.
Therefore, biogas can be termed as a clean fuel.