The methanogens are a group of bacteria which grow anaerobically on cellulosic material and produce a large amount of methane. These microorganism are usually present in the anaerobic sludge digester during sewage treatment where they digest organic mass as well as the aerobic microbes of the slide to produce methane gas along with CO2 and H2S, the mixture of these gases and is called as biogas. Excreta of cattle is rich in cellulosic material and methenogenic bacteria. Therefore the dung can be used for generation of biogas.
