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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]
Chelmsford (/ˈtʃɛlmzfəd/) is a city in the City of Chelmsford district in the county of Essex, England. It is the county town of Essex and one of three cities in the county, along with Southend-on-Sea and Colchester. It is located 30 miles (50 kilometres) north-east of London at Charing Cross and 22 miles (35 kilometres) south-west of Colchester. The population of the urban area was 111,511 in the 2011 Census,[1] while the wider district has 168,310.[2][3]
The demonym for a Chelmsford resident is "Chelmsfordian".
The main conurbation of Chelmsford incorporates all or part of the former parishes of Broomfield, Newland Spring, Great Leighs, The Walthams, Great Baddow, Little Baddow, Galleywood, Howe Green, Margaretting, Pleshey, Stock, Roxwell, Danbury, Bicknacre, Writtle, Moulsham, Rettendon, The Hanningfields, The Chignals, Widford and Springfield, including Springfield Barnes, now known as Chelmer Village.
The communities of Chelmsford, Massachusetts, Chelmsford, Ontario and Chelmsford, New Brunswick are named after the city.
Chelmsford's population consists of a large number of City and Docklands commuters, attracted by the 30–35-minute railway journey into Central London via the Great Eastern Main Line.
