Abstract
Anaerobic digestion is the method of wastes treatment aimed at a reduction of their hazardous effects on the biosphere. The mutualistic behavior of various anaerobic microorganisms results in the decomposition of complex organic substances into simple, chemically stabilized compounds, mainly methane and CO2. The conversions of complex organic compounds to CH4 and CO2 are possible due to the cooperation of four different groups of microorganisms, that is, fermentative, syntrophic, acetogenic, and methanogenic bacteria. Microbes adopt various pathways to evade from the unfavorable conditions in the anaerobic digester like competition between sulfate reducing bacteria (SRB) and methane forming bacteria for the same substrate. Methanosarcina are able to use both acetoclastic and hydrogenotrophic pathways for methane production. This review highlights the cellulosic microorganisms, structure of cellulose, inoculum to substrate ratio, and source of inoculum and its effect on methanogenesis. The molecular techniques such as DGGE (denaturing gradient gel electrophoresis) utilized for dynamic changes in microbial communities and FISH (fluorescent in situ hybridization) that deal with taxonomy and interaction and distribution of tropic groups used are also discussed.
Highlights
Methanogenesis is complex, redox biochemical reactions occurring under anaerobic conditions
It was found out that during anaerobic processing of sewage sludge and manure, the number of microorganisms of Methanosaeta genus decreased with increasing acetate in the environment, with simultaneous intensive growth of the bacteria belonging to Methanosarcina genus which are acetotrophic methanogens [20]
The studies on the dynamics of the population of anaerobic microorganisms participating in degradation of municipal wastes and sewage sludge indicated that Methanosaeta concilii was a dominant species among acetotrophic methanogens [22]
Summary
Methanogenesis is complex, redox biochemical reactions occurring under anaerobic conditions. Under symbiotic effects of various anaerobic and relatively anaerobic bacteria, multimolecular organic substances are decomposed into simple, chemically stabilized compounds—methane and carbon dioxide [1] This process consists of liquefaction and hydrolysis of insoluble compounds and gasification of intermediates. Digestion connected with biogas production may play a triple part It is a method of converting the energy contained in biomass into a useful fuel (biogas) which may be stored and transported. It is a method of recycling of organic wastes into stable soil additives, that is, valuable liquid fertilizer and energy. One m3 of biogas having calorific value of 26 MJ m−3 may replace 0.77 m3 of natural gas with 33.5 MJ calorific value, 1.1 kg of hard coal with 23.4 MJ calorific value, or 2 kg of firewood of 13.3 MJ calorific value [10]
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