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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]
Cornwall (/ˈkɔːrnwɔːl, -wəl/;[3] Cornish: Kernow [ˈkɛrnɔʊ]) is a ceremonial county and Historic County in South West England. It is recognised as one of the Celtic nations and is the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, Devon to the east, and the English Channel to the south. The largest settlement is Falmouth, and the county town is the city of Truro.
The county is rural, with an area of 1,375 square miles (3,562 km2) and population of 568,210. After Falmouth (23,061), the largest settlements are Newquay (20,342), St Austell (19,958), and Truro (18,766). For local government purposes most of Cornwall is a unitary authority area, with the Isles of Scilly having a unique local authority. The Cornish nationalist movement disputes the constitutional status of Cornwall and seeks greater autonomy within the United Kingdom.
Cornwall is the westernmost part of the South West Peninsula. Its coastline is characterised by steep cliffs and, to the south, several rias, including those at the mouths of the rivers Fal and Fowey. It includes the southernmost point on Great Britain, Lizard Point, and forms a large part of the Cornwall National Landscape. The national landscape also includes Bodmin Moor, an upland outcrop of the Cornubian batholith granite formation. The county contains many short rivers; the longest is the Tamar, which forms the border with Devon.
Cornwall had a minor Roman presence, and later formed part of the Brittonic kingdom of Dumnonia. From the 7th century, the Britons in the South West increasingly came into conflict with the expanding Anglo-Saxon kingdom of Wessex, eventually being pushed west of the Tamar; by the Norman Conquest Cornwall was administered as part of England, though it retained its own culture. The remainder of the Middle Ages and Early Modern Period were relatively settled, with Cornwall developing its tin mining industry and becoming a duchy in 1337. During the Industrial Revolution, the tin and copper mines were expanded and then declined, with china clay extraction becoming a major industry. Railways were built, leading to a growth of tourism in the 20th century. The Cornish language became extinct as a living community language at the end of the 18th century, but is now being revived.
