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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]
Derbyshire (/ˈdɑːrbɪˌʃɪər, -ʃər/[2]) is a county in the East Midlands of England. A substantial portion of the Peak District National Park lies within Derbyshire, containing the southern extremity of the Pennine range of hills which extend into the north of the county. The county contains part of the National Forest, and borders on Greater Manchester to the northwest, West Yorkshire to the north, South Yorkshire to the northeast, Nottinghamshire to the east, Leicestershire to the southeast, Staffordshire to the west and southwest and Cheshire also to the west. Kinder Scout, at 636 metres (2,087 ft), is the highest point in the county, whilst Trent Meadows, where the River Trent leaves Derbyshire, is its lowest point at 27 metres (89 ft).[3]:1[4] The River Derwent is the county's longest river at 66 miles (106 km), and runs roughly north to south through the county.[5] In 2003 the Ordnance Survey placed Church Flatts Farm at Coton in the Elms (near Swadlincote) as the farthest point from the sea in Great Britain.[6][7]
The city of Derby is a unitary authority area, but remains part of the ceremonial county of Derbyshire. The non-metropolitan county contains 30 towns with between 10,000 and 100,000 inhabitants. There is a large amount of sparsely populated agricultural upland: 75% of the population live in 25% of the area.[citation needed]
