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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]
West Yorkshire is a metropolitan and ceremonial county in England. It is an inland and, in relative terms, upland county having eastward-draining valleys while taking in the moors of the Pennines. West Yorkshire came into existence as a metropolitan county in 1974 after the passage of the Local Government Act 1972[2] and has a population of 2.3 million.
West Yorkshire consists of five metropolitan boroughs (City of Bradford, Calderdale, Kirklees, City of Leeds and City of Wakefield) and is bordered by the counties of Derbyshire to the south, Greater Manchester to the south-west, Lancashire to the west and north-west, North Yorkshire to the north and east, and South Yorkshire to the south and south-east.
Remnants of strong coal, wool and iron ore industries remain in the county, having attracted people over the centuries, and this can be seen in the buildings and architecture. Major railways and two major motorways traverse the county, which also contains Leeds Bradford International Airport.
West Yorkshire includes the West Yorkshire Urban Area, which is the biggest and most built-up urban area within the historic county boundaries of Yorkshire.
