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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]
North Yorkshire is a ceremonial county in the Yorkshire and the Humber and North East regions of England. It borders County Durham to the north, the North Sea to the east, the East Riding of Yorkshire to the south-east, South Yorkshire to the south, West Yorkshire to the south-west, and Cumbria and Lancashire to the west. Northallerton is the county town.
The county is the largest in England by land area, at 8,654 km2 (3,480 sq mi), and had a population of 1,158,816 in 2021. The largest settlements are Middlesbrough (148,215) in the north-east and the city of York (141,685) in the south. Middlesbrough is part of the Teesside built-up area, which extends into County Durham and has a total population of 376,663 in 2011. The remainder of the county is rural, and the largest towns are Harrogate (75,515) and Scarborough (59,505). For local government purposes the county comprises four unitary authority areas — Middlesbrough, North Yorkshire, Redcar and Cleveland, and York — and part of a fifth, Stockton-on-Tees. The local authorities of York and North Yorkshire are part of a combined authority of the same name, and the local authorities of the other three areas are part of the Tees Valley combined authority. The county was historically part of Yorkshire.
The centre of the county contains a wide plain, called the Vale of Mowbray in the north and Vale of York in the south. The North York Moors uplands lie to the east, and south of them the Vale of Pickering is separated from the main plain by the Howardian Hills. The west of the county contains the Yorkshire Dales, an extensive upland area which contains the source of the River Ouse/Ure and many of its tributaries, which together drain most of the county before reaching the Humber estuary in the south. The Dales also contain the county's highest point, Whernside, at 2,415 feet (736 m).
