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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]
Salisbury (locally /ˈsɔːzb(ə)ri/ SAWZ-b(ə-)ree)[a] is a cathedral city in Wiltshire, England with a population of 41,820,[1] at the confluence of the rivers Avon, Nadder and Bourne. The city is approximately 20 miles (30 kilometres) from Southampton and 30 miles (50 kilometres) from Bath.
Salisbury is in the southeast of Wiltshire, near the edge of Salisbury Plain. An ancient cathedral was north of the present city at Old Sarum. A new cathedral was built near the meeting of the rivers and a settlement grew up around it, which received a city charter in 1227 as New Sarum. This continued to be its official name until 2009, when Salisbury City Council was established. Salisbury railway station is an interchange between the West of England Main Line and the Wessex Main Line.
Stonehenge, a UNESCO World Heritage Site, is 8 miles (13 kilometres) northwest of Salisbury.
