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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]
Leicester (About this soundlisten) LEH-ster) is a city and unitary authority area in the East Midlands of England, and the county town of Leicestershire. The city lies on the River Soar and close to the eastern end of the National Forest. It is to the north-east of Birmingham and Coventry, south of Nottingham, and west of Peterborough.
The 2016 mid year estimate of the population of the City of Leicester unitary authority was 348,300, an increase of approximately 18,500 (Increase 5.6%) from the 2011 census figure of 329,839, making it the most populous municipality in the East Midlands region. The associated urban area is also the 11th most populous in England and the 13th most populous in the United Kingdom.
Leicester is at the intersection of two major railway lines—the north–south Midland Main Line and the east/west Birmingham to London Stansted CrossCountry line; as well as the confluence of the M1/M69 motorways and the A6/A46 trunk routes. Leicester is the home to football club Leicester City and rugby club Leicester Tigers.
