The main constituent of biogas is:
methane
Biogas is produced under anaerobic conditions. The process is denominated as anaerobic digestion which involves the action of methanogens. Methanogens are the group of anaerobic bacteria which breakdown the organic compounds into methane and hydrogen gases. The major constituent of biogas is methane (55-70%). It also contains CO2 (30-45%) and some traces of gases such as H2S and ammonia.