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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]
Canvey Island is a town, civil parish and reclaimed island in the Thames estuary, near Southend-on-Sea, in the Castle Point district, in the county of Essex, England. It has an area of 7.12 square miles (18.44 km2) and a population of 38,170.[1] It is separated from the mainland of south Essex by a network of creeks. Lying only just above sea level, it is prone to flooding at exceptional tides and has been inhabited since the Roman conquest of Britain.
The island was mainly agricultural land until the 20th century, when it became the fastest-growing seaside resort in Britain between 1911 and 1951. The North Sea flood of 1953 devastated the island, killing 58 islanders and leading to the temporary evacuation of the 13,000 residents.[3] Canvey is consequently protected by modern sea defences comprising 2 miles (3.2 km) of concrete sea walls.[4]
Canvey Island is also notable for its relationship to the petrochemical industry. The island was the site of the first delivery in the world of liquefied natural gas by container ship and later became the subject of an influential assessment on the risks to a population living within the vicinity of petrochemical shipping and storage facilities.
