Explanation

Biogas is a methane rich fuel gas produced by anaerobic break down of biomass with the help of methanogenic bacteria. It is a three step anaerobic digestion of animal and other organic wastes. Biogas (methane + CO₂) $\mathbf{Step - III\ } \uparrow Methanogenic\ bacteria$ Organic acid $\mathbf{Step - II\ \uparrow}Fermentive\ microbes\$ Soluble compounds or monomers $\mathbf{Step - I\ \uparrow \ }$ Proteins, fats, cellulose, hemicelloulose, etc.