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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]
Greater Manchester is a metropolitan county and combined authority area in North West England, with a population of 2.8 million;[2] comprising ten metropolitan boroughs: Bolton, Bury, Oldham, Rochdale, Stockport, Tameside, Trafford, Wigan, and the cities of Manchester and Salford. Greater Manchester was created on 1 April 1974, as a result of the Local Government Act 1972, and designated a functional city region on 1 April 2011. Greater Manchester is formed of parts of the historic counties of Lancashire, Cheshire and the West Riding of Yorkshire.
Greater Manchester spans 493 square miles (1,277 km2),[3] which roughly covers the territory of the Greater Manchester Built-up Area, the second most populous urban area in the UK. Though geographically landlocked, it is connected to the sea by the Manchester Ship Canal which is still open to shipping in Salford and Trafford. Greater Manchester borders the ceremonial counties of Cheshire (to the south-west and south), Derbyshire (to the south-east), West Yorkshire (to the north-east), Lancashire (to the north) and Merseyside (to the west). There is a mix of high-density urban areas, suburbs, semi-rural and rural locations in Greater Manchester, but land use is mostly urban—the product of concentric urbanisation and industrialisation which occurred mostly during the 19th century when the region flourished as the global centre of the cotton industry. It has a focused central business district, formed by Manchester city centre and the adjoining parts of Salford and Trafford, but Greater Manchester is also a polycentric county with ten metropolitan districts, each of which has at least one major town centre and outlying suburbs.
Greater Manchester is governed by the Greater Manchester Combined Authority (GMCA), which consists of political leaders from each of the ten metropolitan borough councils, plus a directly elected mayor, with responsibility for economic development, regeneration and transport. Andy Burnham is the inaugural Mayor of Greater Manchester, elected in 2017. For the 12 years following 1974, the county had a two-tier system of local government; district councils shared power with the Greater Manchester County Council. The county council was abolished in 1986 and so its districts (the metropolitan boroughs) effectively became unitary authority areas. However, the metropolitan county continued to exist in law and as a geographic frame of reference,[4] and as a ceremonial county, with a Lord Lieutenant and a High Sheriff. Several county-wide services were co-ordinated through the Association of Greater Manchester Authorities between 1985 and 2011.
Before the creation of the metropolitan county, the name SELNEC was used for the area, from the initials of "South East Lancashire North East Cheshire". Greater Manchester is an amalgamation of 70 former local government districts from the former administrative counties of Lancashire, Cheshire, the West Riding of Yorkshire and eight independent county boroughs.[5] Since deindustrialisation in the mid-20th century, Greater Manchester has emerged as a major centre for services, media and digital industries, and is renowned for guitar and dance music and its association football teams.[6]
