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Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.〔National Non-Food Crops Centre. ("NNFCC Renewable Fuels and Energy Factsheet: Anaerobic Digestion" ), Retrieved on 2011-11-22〕 The process is used for industrial or domestic purposes to manage waste and/or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion. Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin sediments, where it is usually referred to as "anaerobic activity". This is the source of marsh gas methane as discovered by Volta in 1776. The digestion process begins with bacterial hydrolysis of the input materials. Insoluble organic polymers, such as carbohydrates, are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. These bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogens convert these products to methane and carbon dioxide.〔(Anaerobic digestion reference sheet ), waste.nl. Retrieved 25.10.07.〕 The methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments.〔(Meisam Tabatabaei, Raha Abdul Rahim, André-Denis G. Wright, Yoshihito Shirai, Norhani Abdullah, Alawi Sulaiman, Kenji Sakai and Mohd Ali Hassan. 2010. Importance of the methanogenic archaea populations in anaerobic wastewater treatments (Process Biochemistry- 45(8), pp: 1214-1225) )〕 It is used as part of the process to treat biodegradable waste and sewage sludge. As part of an integrated waste management system, anaerobic digestion reduces the emission of landfill gas into the atmosphere. Anaerobic digesters can also be fed with purpose-grown energy crops, such as maize.〔(Agricultural Biogas ), www.clarke-energy.com, accessed 08.11.11〕 Anaerobic digestion is widely used as a source of renewable energy. The process produces a biogas, consisting of methane, carbon dioxide and traces of other ‘contaminant’ gases.〔 This biogas can be used directly as fuel, in combined heat and power gas engines〔(GE Jenbacher Biogas Engines ), www.clarke-energy.com, accessed 15.04.11〕 or upgraded to natural gas-quality biomethane. The nutrient-rich digestate also produced can be used as fertilizer. With the re-use of waste as a resource and new technological approaches which have lowered capital costs, anaerobic digestion has in recent years received increased attention among governments in a number of countries, among these the United Kingdom (2011),〔(Anaerobic Digestion Strategy and Action Plan ), defra.gov.uk. Accessed 19.01.2012〕 Germany 〔(source needed)〕 and Denmark (2011).〔(Jyllands-Posten 29. December 2011 ). Accessed 19.01.2012 via Google Translate〕 ==Process== (詳細はbacteria (acetogens) and methane-forming archaea (methanogens). These organisms promote a number of chemical processes in converting the biomass to biogas.〔National Non-Food Crops Centre. (Evaluation of Opportunities for Converting Indigenous UK Wastes to Fuels and Energy (Report), NNFCC 09-012 )〕 Gaseous oxygen is excluded from the reactions by physical containment. Anaerobes utilize electron acceptors from sources other than oxygen gas. These acceptors can be the organic material itself or may be supplied by inorganic oxides from within the input material. When the oxygen source in an anaerobic system is derived from the organic material itself, the 'intermediate' end products are primarily alcohols, aldehydes, and organic acids, plus carbon dioxide. In the presence of specialised methanogens, the intermediates are converted to the 'final' end products of methane, carbon dioxide, and trace levels of hydrogen sulfide.〔''Adapted from'' Beychok, M. (1967) Aqueous Wastes from Petroleum and Petrochemical Plants, First edition, John Wiley & Sons, LCCN 67019834〕 In an anaerobic system, the majority of the chemical energy contained within the starting material is released by methanogenic bacteria as methane.〔 Populations of anaerobic microorganisms typically take a significant period of time to establish themselves to be fully effective. Therefore, common practice is to introduce anaerobic microorganisms from materials with existing populations, a process known as "seeding" the digesters, typically accomplished with the addition of sewage sludge or cattle slurry.〔(The biogas plant ), unu.edu. Retrieved 5.11.07.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Anaerobic digestion」の詳細全文を読む スポンサード リンク
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