(4) Methane and carbon dioxide Explanation: Biogas is essentially a mixture of Methane (CH4, around 55-75%) but also contains Carbon Dioxide (CO3), around 25- 30%), varying quantities of Water (H2O) and Hydrogen Sulphide (H2S). Other compounds can also be found, especially in waste dump biogas: Ammonia (NH3), Hydrogen (H2), Nitrogen (N2) and Carbon Monoxide (CO). Methane is the valuable component under the aspect of using biogas fuel.