NSWAI

ANAEROBIC DIGESTION

Anaerobic digestion is series of biological processes define as the biological decomposition of organic matter found in wet biomass waste (such as sewage sludge, animal manure and slurry and waste food) under anaerobic conditions with an accompanying production primarily of Methane (60%) and secondarily of other gases ,chief of which is Carbon dioxid (40%).

Anaerobic digestion (AD) is a bacterial fermentation process that operates without free oxygen and results in a biogas containing mostly methane and carbon dioxide.

The biogas can be burned directly in a gas boiler to produce heat or burnt in a combined heat and power unit to produce heat and electricity. Alternatively, the biogas can be cleaned to remove the carbon dioxide and other substances, to produce biomethane. This can be injected into the national gas grid to be used in the same way as natural gas, or used as a vehicle fuel.

The anaerobic digestion of organic material is accomplished by a consortium of microorganisms working synergistically. Digestion occurs in a four-step process: hydrolysis, acidogenesis, acetogenesis, and methanogenesis

Large protein macromolecules, fats and carbohydrate polymers (such as cellulose and starch) are broken down through hydrolysis to amino acids, long-chain fatty acids, and sugars.

These products are then fermented during acidogenesis to form three, four, and five-carbon volatile fatty acids, such as lactic, butyric, propionic, and valeric acid.

In acetogenesis, bacteria consume these fermentation products and generate acetic acid, carbon dioxide, and hydrogen.

Finally, methanogenic organisms consume the acetate, hydrogen, and some of the carbon dioxide to produce methane. Usually the methane content of biogas ranges from 40-70 percent (by volume).

Link for anaerobic digestion

http://www.waste-technology.co.uk/AD/ad.html

http://www.swlf.ait.ac.th/UpdData/Journals/ADMSW.pdf

http://www.seas.columbia.edu/earth/wtert/sofos/Verma_thesis.pdf

http://www.energyjustice.net/digesters/msw.html

http://www.foe.co.uk/resource/briefings/anaerobic_digestion.pdf

http://www.adelaide.edu.au/biogas/anaerobic_digestion/pvdv.pdf

http://www.seas.columbia.edu/earth/wtert/sofos/Ostrem_Thesis_final.pdf

http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_swm/downloads_swm/kitchen_waste.pdf

http://pubs.acs.org/doi/abs/10.1021/bk-1991-0460.ch003

http://www.swlf.ait.ac.th/IntlConf/Data/ICSSWM%20web/FullPaper/Session%20VI-B/6_BA10%20_Balakameswari_.pdf

http://ec.europa.eu/environment/integration/research/newsalert/pdf/39na4.pdf