Biogas is produced from biological wastes such as landfills, industrial waste (cheese whey, slaughterhouse waste) and agricultural waste (manure, forest residues). Biogas contains CH4, it is a valuable energy source. If biogas is not recovered and burnt, CH4 is released to the atmosphere: 20 times worse than CO2 for green house effect. Although Biogas can be burnt as energy source, it contains H2S, CO2 N2 etc. To remove these contaminates can increase the heat value of biogas. Meanwhile, it can reduce the pollution when burn the untreated biogas. http://www.srisenenergy.com