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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]
Wales (Welsh: Cymru [ˈkəm.rɨ] (audio speaker iconlisten)) is a country that is part of the United Kingdom.[10] It is bordered by England to the east, the Irish Sea to the north and west, and the Bristol Channel to the south. It had a population in 2011 of 3,063,456 and has a total area of 20,779 km2 (8,023 sq mi). Wales has over 1,680 miles (2,700 km) of coastline and is largely mountainous with its higher peaks in the north and central areas, including Snowdon (Yr Wyddfa), its highest summit. The country lies within the north temperate zone and has a changeable, maritime climate.
Welsh national identity emerged among the Britons after the Roman withdrawal from Britain in the 5th century, and Wales is regarded as one of the modern Celtic nations. Llywelyn ap Gruffudd's death in 1282 marked the completion of Edward I of England's conquest of Wales, though Owain Glyndŵr briefly restored independence to Wales in the early 15th century. The whole of Wales was annexed by England and incorporated within the English legal system under the Laws in Wales Acts 1535 and 1542. Distinctive Welsh politics developed in the 19th century. Welsh Liberalism, exemplified in the early 20th century by David Lloyd George, was displaced by the growth of socialism and the Labour Party. Welsh national feeling grew over the century; a nationalist party, Plaid Cymru was formed in 1925, and the Welsh Language Society in 1962. Established under the Government of Wales Act 1998, the Senedd (the Welsh Parliament, formerly known as the National Assembly for Wales) is responsible for a range of devolved policy matters.
At the dawn of the Industrial Revolution, development of the mining and metallurgical industries transformed the country from an agricultural society into an industrial nation; the South Wales Coalfield's exploitation caused a rapid expansion of Wales' population. Two-thirds of the population live in South Wales, including the capital Cardiff along with Swansea, Newport and the nearby valleys. The eastern region of North Wales has about a sixth of the overall population with Wrexham being the largest northern town. The remaining parts of Wales are sparsely populated. Now that the country's traditional extractive and heavy industries have gone or are in decline, the economy is based on the public sector, light and service industries, and tourism. In livestock farming, including dairy farming, Wales is a net exporter, contributing towards national agricultural self-sufficiency.
Wales closely shares its political and social history with the rest of Great Britain, and a majority of the population in most areas speaks English as a first language, but the country has retained a distinct cultural identity. Both Welsh and English are official languages; over 560,000 Welsh-speakers live in Wales, and the language is spoken by a majority of the population in parts of the north and west. From the late 19th century onwards, Wales acquired its popular image as the "land of song", in part due to the eisteddfod tradition. At many international sporting events, such as the FIFA World Cup, Rugby World Cup and the Commonwealth Games, Wales has its own national team. At the Olympic Games, Welsh athletes compete for the UK as part of a Great Britain team. Rugby union is seen as a symbol of Welsh identity and an expression of national consciousness.
