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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]
Sandwell is a metropolitan borough of the West Midlands county in England. The borough is named after the Sandwell Priory, and spans a densely populated part of the West Midlands conurbation. According to Sandwell Metropolitan Borough Council, the borough comprises the six amalgamated towns of Oldbury, Rowley Regis, Smethwick, Tipton, Wednesbury, and West Bromwich,[3] although these places consist of numerous smaller settlements and localities. Sandwell's Strategic Town Centre is designated as West Bromwich, the largest town in the borough, while Sandwell Council House (the headquarters of the local authority) is situated in Oldbury.
Bordering Sandwell is the City of Birmingham to the east, the Metropolitan Borough of Dudley to the south and west, the Metropolitan Borough of Walsall to the north, and the City of Wolverhampton to the north-west. Spanning the borough are the parliamentary constituencies of West Bromwich West, West Bromwich East, Warley, and part of Halesowen and Rowley Regis, which crosses into the Dudley borough.
At the 2011 census, the borough had a population of 309,000 and an area of 86 square kilometres (33 sq mi).[4]
