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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]
Ely (/ˈiːli/ (About this soundlisten) EE-lee) is a cathedral city in Cambridgeshire, England, about 14 miles (23 km) north-northeast of Cambridge and about 80 miles (129 km) by road from London. Æthelthryth (also known as Etheldreda) founded an abbey at Ely in 673; the abbey was destroyed in 870 by Danish invaders and was rebuilt by Æthelwold, Bishop of Winchester, in 970. Construction of the cathedral was started in 1083 by a Norman abbot, Simeon. Alan of Walsingham's octagon, built over Ely's nave crossing between 1322 and 1328, is the "greatest individual achievement of architectural genius at Ely Cathedral", according to architectural historian Nikolaus Pevsner. Building continued until the dissolution of the abbey in 1539 during the Reformation. The cathedral was sympathetically restored between 1845 and 1870 by the architect George Gilbert Scott. As the seat of a diocese, Ely has long been considered a city; in 1974, city status was granted by royal charter.
Ely is built on a 23-square-mile (60 km2) Kimmeridge Clay island which, at 85 feet (26 m), is the highest land in the Fens. Major rivers including the Witham, Welland, Nene and Great Ouse feed into the Fens and, until draining commenced in the 17th century, formed freshwater marshes and meres within which peat was laid down. There are two Sites of Special Scientific Interest in the city: a former Kimmeridge Clay quarry, and one of the United Kingdom's best remaining examples of medieval ridge and furrow agriculture.
The economy of the region is mainly agricultural. Before the Fens were drained, the harvesting of osier (willow) and sedge (rush) and the extraction of peat were important activities, as were eel fishing—from which the settlement's name may have been derived—and wildfowling. The city had been the centre of local pottery production for more than 700 years, including pottery known as Babylon ware. A Roman road, Akeman Street, passes through the city; the southern end is at Ermine Street near Wimpole and its northern end is at Brancaster. Little direct evidence of Roman occupation in Ely exists, although there are nearby Roman settlements such as those at Little Thetford and Stretham. A coach route, known to have existed in 1753 between Ely and Cambridge, was improved in 1769 as a turnpike (toll road). The present-day A10 closely follows this route; a southwestern bypass of the city was built in 1986. Ely railway station, built in 1845, is on the Fen Line and is now a railway hub, with lines north to King's Lynn, northwest to Peterborough, east to Norwich, southeast to Ipswich and south to Cambridge and London.
The King's School is a coeducational boarding school which was granted a royal charter in 1541 by Henry VIII; the school claims to have existed since 970. Henry I granted the first annual Fair, Saint Audrey's (or Etheldreda's) seven-day event, to the abbot and convent on 10 October 1189; the word "tawdry" originates from cheap lace sold at this fair. Present-day annual events include the Eel Festival in May, established in 2004, and a fireworks display in Ely Park, first staged in 1974. The city of Ely has been twinned with Denmark's oldest town, Ribe, since 1956. Ely City Football Club was formed in 1885.
