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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]
Dorchester (/ˈdɔːrtʃɛstər/ DOR-ches-tər) is the county town of Dorset, England. It is situated between Poole and Bridport on the A35 trunk route. A historic market town, Dorchester is on the banks of the River Frome to the south of the Dorset Downs and north of the South Dorset Ridgeway that separates the area from Weymouth, 7 miles (11 km) to the south. The civil parish includes the small town of Poundbury and the suburb of Fordington.
The area around the town was first settled in prehistoric times. The Romans established a garrison there after defeating the Durotriges tribe, calling the settlement that grew up nearby Durnovaria; they built an aqueduct to supply water and an amphitheatre on an ancient British earthwork. After the departure of the Romans, the town diminished in significance, but during the medieval period became an important commercial and political centre. It was the site of the "Bloody Assizes" presided over by Judge Jeffreys after the Monmouth Rebellion, and later the trial of the Tolpuddle Martyrs.
In the 2011 census, the population of Dorchester was 19,060, with further people coming from surrounding areas to work in the town which has six industrial estates. The Brewery Square redevelopment project is taking place in phases, with other development projects planned. The town has a land-based college, Kingston Maurward College, The Thomas Hardye School, three middle schools and thirteen first schools. The Dorset County Hospital offers an accident and emergency service, and the town is served by two railway stations. Through vehicular traffic is routed round the town by means of a bypass. The town has a football club and a rugby union club, several museums and the biannual Dorchester Festival. It is twinned with three towns in Europe. As well as having many listed buildings, a number of notable people have been associated with the town. It was for many years the home and inspiration of the author Thomas Hardy, whose novel The Mayor of Casterbridge uses a fictionalised version of Dorchester as its setting.
