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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]
Reading (/ˈrɛdɪŋ/ (audio speaker iconlisten) RED-ing)[2] is a historic large market town in Berkshire, England, in the Thames Valley at the confluence of the rivers Thames and Kennet. It is on the Great Western Main Line railway and the M4 motorway, 40 miles (64 km) east of Swindon, 25 miles (40 km) south of Oxford, 40 miles (64 km) west of London, 15 miles (24 km) north of Basingstoke, 13 miles (21 km) southwest of Maidenhead and 15 miles (24 km) east of Newbury. Reading is a major commercial centre, especially for information technology and insurance.[3] It is also a regional retail centre, serving a large area of the Thames Valley, and home to the University of Reading. Every year it hosts the Reading Festival, one of England's biggest music festivals. Among its sports teams are Reading Football Club and Reading Hockey Club, and over 15,000 runners annually compete in the Reading Half Marathon.
Reading dates from the 8th century. It was an important trading and ecclesiastical centre in the Middle Ages, the site of Reading Abbey, one of the largest and richest monasteries of medieval England with strong royal connections, of which the 12th-century abbey gateway and significant ancient ruins remain. By 1525, Reading was the largest town in Berkshire, and tenth in England for taxable wealth. The town was seriously affected by the English Civil War, with a major siege and loss of trade, but played a pivotal role in the Glorious Revolution, whose only significant military action was fought on its streets. The 18th century saw the beginning of a major ironworks in the town and the growth of the brewing trade for which Reading was to become famous. The 19th century saw the coming of the Great Western Railway and the development of the town's brewing, baking and seed growing businesses, and the town grew rapidly as a manufacturing centre.
