Agricultural production process requires energy in the form of heat or electricity for heating, drying, powering electrical equipments etc. Heat energy obtained from burring of biomass produce greenhouse gases. Unused biomass residues can produce upto 50 % methane during natural degradation or 5-10 % methane during its open burning. Methane is also emitted by human related activities like animal husbandry, rice cultivation, biomass burning and waste management.  Methane is a greenhouse gas with a relatively high global warming potential. Each kg of methane warms up the earth 23 times as much as the same mass of CO2 when averaged over 100 years. In this regard biomethane production from organic matter by controlled digestion process for energy production is of special interest. The emission of methane could be reduced by used of controlled digestion facility and thereby reducing the GHG emissions. Therefore biomethane is not only a renewable energy source, but it also contributes to reduction of methane emission. In addition, the toxic emissions from biomethane combustion are also reduced when compared to fossil fuels.

Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat. Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles.

Composition of biogas
Compound Formula  %
Methane CH4 50–75
Carbon dioxide CO2 25–50
Nitrogen N2 0–10
Hydrogen H2 0–1
Hydrogen sulphide H2S 0–3
Oxygen O2 0–0

Biogas production process

Biogas is produced by mean of anaerobic digestion by microorganisms. Organic matter is broken down by microbial activity in the absence of oxygen. Symbiotic group of bacteria that perform different factions break down the complex organic matter in different stages of digestion process. There are four type of microorganisms involved in this process. Hydrolytic bacteria break down complex organic matter into sugars and amino acids. Fermentative bacteria then convert these products into organic acids. Acidogenic microbes convert these acids into hydrogen, carbon dioxide and acetate. Finally, the methanogenic bacteria produce biogas from acetic acid, hydrogen and carbon dioxide. The digestion time for production of biogas ranges from couple of weeks to couple of months depending upon the feedstock, digester type and digestion temperature.