A sewage treatments plants is regarded as a giant microbial culture breading facility where the microbes are persuaded to work for our benefit.They metabolize the solid waste that passes through the treatment plant.The microbes oxidize the nutrients and during this process, they release energy in the form of heat and chemicals (phosphates, nitrates and sulphates) Gaseous by-product is also produced in the form of carbon dioxide.

Certain bacteria and cyanobacteria are nitrogen fixers.They convert atmospheric free nitrogen into ammonium form which is easily assimilated by higher plants.Thus, these microorganisms increase the fertility of soil without causing any environmental harzards and therefore, called biofertilizers.Example - Rhizobium and Anabaena.   

1. Certain bacteria which grow anaerobically on cellulosic material, produce large amounts of methane along with CO₂ and H₂. These bacteria are called methanogens (one of the common bacterium is Methanobacterium). 
2. Methanogens are commonly found in the anaerobic sludge during sewage treatment and are also present in the rumen (a part of stomach) of cattle.
3. In rumen, methanogens help in the breakdown of cellulose and their excreta called gobar, is rich in these bacteria.  Therefore, dung can be used to produce biogas commonly called as gobar gas.

1. Certain bacteria which grow anaerobically on cellulosic material, produce large amounts of methane along with CO₂ and H₂. These bacteria are called methanogens (one of the common bacterium is Methanobacterium). 
2. Methanogens are commonly found in the anaerobic sludge during sewage treatment and are also present in the rumen (a part of stomach) of cattle. In rumen, methanogens help in the breakdown of cellulose and their excreta called gobar, is rich in these bacteria.  Therefore, dung can be used to produce biogas commonly called as gobar gas.

1.Several microbes are used in preparing medicines.
2.The most important medicines for which microbes are used are antibiotics.  These are chemical compounds produced by some microbes and are used to kill or to subside the growth of other disease-causing microbes. Streptomycin, tetracycline and penicillin are some of the commonly used antibiotics. These antibiotics have significantly contributed towards the welfare of the human society.