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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]
Hampshire (/ˈhæmpʃər/, /-ʃɪər/ (listen); abbreviated to Hants)[a] is a county in South East England on the coast of the English Channel, bordering Dorset to the south-west, Wiltshire to the north-west, Berkshire to the north, Surrey to the north-east and West Sussex to the south east. The county town is Winchester, but the county is named after Southampton. Its two largest cities are Southampton and Portsmouth which are administered separately as unitary authorities; the rest of the county is governed by a combination of the Hampshire County Council and non-metropolitan district councils.
First settled about 14,000 years ago, Hampshire's recorded history dates to Roman Britain, when its chief town was Winchester, then known as Venta Belgarum. The county was recorded in the 11th century Domesday Book, divided into 44 hundreds. From the 12th century, the ports grew in importance, fuelled by trade with the continent, wool and cloth manufacture, fishing and large shipbuilding industries. By the 16th century, the population of Southampton had outstripped that of Winchester. By the mid-19th century, the population was 219,210, double that at the beginning of the century, in more than 86,000 dwellings. Agriculture was the principal industry and 10 per cent of the county was still forest. Hampshire played a crucial military role in both World Wars. The borders of the ceremonial county were created by the Local Government Act 1972 (enacted 1974). Historically part of Hampshire, the Isle of Wight was made a separate ceremonial county and the towns of Bournemouth and Christchurch were administered as part of the ceremonial county of Dorset.
The geography of the county is varied, with upland rising to 286 m (938 ft) and mostly south-flowing rivers. There are areas of downland and marsh, and two national parks: the New Forest and part of the South Downs, which together cover 45 per cent of Hampshire.
Hampshire is one of the most affluent counties in the country, with an unemployment rate lower than the national average. Its economy mainly derives from major companies, maritime, agriculture and tourism. Tourist attractions include seaside resorts, national parks, the National Motor Museum and the Southampton Boat Show. The county is known as the home of writers Jane Austen and Charles Dickens. Hampshire is also the childhood home of Florence Nightingale and the birthplace of engineer Isambard Kingdom Brunel.
