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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]
Wallingford (/ˈwɒlɪŋfərd/) is a historic market town and civil parish on the River Thames in Oxfordshire, England, 12 miles (19 km) north of Reading, 13 miles (21 km) south of Oxford and 11 miles (18 km) north west of Henley-on-Thames. Although belonging to the historic county of Berkshire, it is within the ceremonial county of Oxfordshire for administrative purposes (since 1974) as a result of the 1972 Local Government Act. The population was 11,600 at the 2011 census.[1]
The town has played an important role in English history starting with the surrender of Stigand to William the Conqueror in 1066, which led to his taking the throne and the creation of Wallingford Castle. The castle and the town enjoyed royal status and flourished for much of the Middle Ages. The Treaty of Wallingford, which ended a civil war known as The Anarchy between King Stephen and Empress Matilda, was signed there. The town then entered a period of decline after the arrival of the Black Death and falling out of favour with the Tudor monarchs before being called on once again during the English Civil War. Wallingford held out as the last remaining Royalist stronghold in Berkshire before surrendering after a 16-week siege. Fearing that Wallingford Castle could be used in a future uprising, Oliver Cromwell ordered its destruction.
Since then Wallingford has become a market town and centre of local commerce. At the centre of the town is a market square with the war memorial and Wallingford Town Hall to the south, the Corn Exchange theatre to the east and numerous shops around the edges. Off the square there are alleyways and streets with more shops and a number of historic inns.[2] Although it was a small town, Wallingford once had 14 churches; now, there are three ancient churches within the Parish of St Mary-le-More and St Leonard, a modern Roman Catholic church, a Quaker Meeting House dating from 1724 and Baptist, Methodist and community churches.
