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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]
Devizes (/dɪˈvaɪzɪz/) is a market town and civil parish in Wiltshire, England. It developed around Devizes Castle, an 11th-century Norman castle,[2] and received a charter in 1141. The castle was besieged during the Anarchy, a 12th-century civil war between Stephen of England and Empress Matilda, and again during the English Civil War when the Cavaliers lifted the siege at the Battle of Roundway Down. Devizes remained under Royalist control until 1645, when Oliver Cromwell attacked and forced the Royalists to surrender. The castle was destroyed in 1648 on the orders of Parliament, and today little remains of it.
From the 16th century Devizes became known for its textiles, and by the early 18th century it held the largest corn market in the West Country, constructing the Corn Exchange in 1857. In the 18th century, brewing, curing of tobacco, and snuff-making were established. The Wadworth Brewery was founded in the town in 1875.
Standing at the west edge of the Vale of Pewsey, the town is about 10.5 miles (16.9 km) southeast of Chippenham and 11 miles (18 km) north-east of the county town of Trowbridge. It has nearly five hundred listed buildings, some notable churches, a town hall and a green in the centre.
