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Anaerobic Digestion
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen.[1] The process is used for industrial or domestic purposes to manage waste 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".[2][3] This is the source of marsh gas methane as discovered by Alessandro Volta in 1776.[4][5]
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. In acetogenesis, bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide amongst other compounds. Finally, methanogens convert these products to methane and carbon dioxide.[6] The methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments.[7]
Anaerobic digestion 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.[8]
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.[1] This biogas can be used directly as fuel, in combined heat and power gas engines[9] 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 that 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),[10] Germany,[citation needed] Denmark (2011),[11] and the United States.[12]
Thetford is a market town and civil parish in the Breckland district of Norfolk, England. It is on the A11 road between Norwich and London, just east of Thetford Forest. The civil parish, covering an area of 29.55 km2 (11.41 sq mi), has a population of 24,340.[1]
There has been a settlement at Thetford since the Iron Age, and parts of the town predate the Norman Conquest; Thetford Castle was established shortly thereafter. Roger Bigod founded the Cluniac Priory of St Mary in 1104, which became the largest and most important religious institution in Thetford. The town was badly hit by the dissolution of the monasteries, including the castle's destruction, but was rebuilt in 1574 when Elizabeth I established a town charter. After World War II, Thetford became an "overspill town", taking people from London, as a result of which its population increased substantially.[2] Thetford was the headquarters of Tulip International, large-scale manufacturers of bacon, beef and pork until its closure in 2010.
Thetford railway station is served by the Breckland line and is one of the best surviving pieces of 19th century railway architecture in East Anglia.
