Biomethanization of coal to obtain clean coal energy: a review

This paper entails a review on the possibility of methanization of coal using microbial tool. Biomethanization process of coal begins with biodegradation of coal by specific bacteria and fungi. As a result of this, major polymers present in coal like proteins, polysaccharides, nucleic acids and lipids are hydrolyzed to monomers like aminoacids, sugars, purines, pyrimidines and long chain fatty acids. Their subsequent fermentation forms hydrogen, CO2 and a number of reduced compounds like alcohols, short chain fatty acids, organic acids and certain aromatics. The oxidation of these reduced compounds further leads to the formation of acetate, hydrogen and CO2, methylated compounds and several intermediate compounds. Syntrophic relationship exists between fermenting bacteria and methanogens. The resultant oxidized compounds of fermenting bacteria are gradually utilized by specific methanogens to form methane. Hydrogenotrophic methanogens utilize H-2 and convert CO2 into methane. Whereas acetate is utilized by acetoclastic methanogens to generate methane. The methylated compounds are utilized for methane formation by methylotrophic methanogens.