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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]
Romford is a large town in East London, England, 14 miles (23 km) northeast of Charing Cross. Part of the London Borough of Havering, the town is one of the major metropolitan centres of Greater London identified in the London Plan.[2]
Historically part of the ancient parish of Hornchurch in the Becontree hundred of Essex, it has been a market town since 1247. It formed the administrative centre of the liberty of Havering until that liberty was dissolved in 1892, and became a civil parish of its own in 1849.[3][4] Good road links to London and the opening of the railway station in 1839 were key to the development of the town.[3] The economic history of Romford is characterised by a shift from agriculture to light industry and then to retail and commerce.[3]
As part of the suburban growth of London throughout the 20th century, Romford significantly expanded and increased in population, becoming a municipal borough in 1937. In 1965, following reform of local government in London, it merged with the Hornchurch Urban District to form the London Borough of Havering, and was incorporated into Greater London.[5][6][7] Today, it is one of the largest commercial, retail, entertainment and leisure districts in London and has a well-developed night-time economy.[8][9] The population of Romford, as of the 2011 census, was 122,854.[10]
