Biogas is the colorless , odorless combustible gas that is formed in the process of fermentation or fermentation by the organic matter of plants , herbs , dung , garbage etc. The main raw materials for making biogas are animal excreta and water. Commonly used to make dung , leaves , straw , vegetable waste and water biogas. The main component of biogas is methane gas. Biogas also contains a mixture of carbon dioxide , sulfur and other gases.