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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]
Cambridge (/ˈkeɪmbrɪdʒ/[2] KAYM-brij) is a university city and the county town of Cambridgeshire, England, on the River Cam approximately 55 miles (89 km) north of London. At the United Kingdom Census 2011, the population of the Cambridge built-up area (which is larger than the remit of Cambridge City Council) was 158,434 including 29,327 students.[3] Cambridge became an important trading centre during the Roman and Viking ages, and there is archaeological evidence of settlement in the area as early as the Bronze Age. The first town charters were granted in the 12th century, although modern city status was not officially conferred until 1951.
The University of Cambridge was founded in 1209.[4] The buildings of the university include King's College Chapel, Cavendish Laboratory, and the Cambridge University Library, one of the largest legal deposit libraries in the world. The city's skyline is dominated by several college buildings, along with the spire of the Our Lady and the English Martyrs Church, and the chimney of Addenbrooke's Hospital. Anglia Ruskin University, which evolved from the Cambridge School of Art and the Cambridgeshire College of Arts and Technology, also has its main campus in the city.
Cambridge is at the heart of the high-technology Silicon Fen with industries such as software and bioscience and many start-up companies born out of the university. Over 40 per cent of the workforce have a higher education qualification, more than twice the national average. The Cambridge Biomedical Campus, one of the largest biomedical research clusters in the world, is soon to house premises of AstraZeneca, a hotel, and the relocated Royal Papworth Hospital.[5]
The first game of association football took place at Parker's Piece. The Strawberry Fair music and arts festival and Midsummer Fair are held on Midsummer Common, and the annual Cambridge Beer Festival takes place on Jesus Green. The city is adjacent to the M11 and A14 roads. Cambridge station is less than an hour from London King's Cross railway station.
