- Biogas is produced through a process called anaerobic digestion, where organic matter is broken down by microorganisms in the absence of oxygen (anaerobic conditions). - The action of anaerobic microorganisms, such as anaerobic bacteria, is essential for this decomposition process, which produces biogas (primarily methane and carbon dioxide). - The presence of oxygen inhibits the anaerobic digestion process necessary for biogas production. - While organic waste (which might include leftover fertilizers) is the raw material, the mere presence of fertilizers doesn't cause biogas production; the anaerobic decomposition of organic matter by specific microbes is the key.