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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]
Ludlow (/lʌd.loʊ/) is a market town and civil parish in Shropshire, England. It is located 28 miles (45 km) south of Shrewsbury and 23 miles (37 km) north of Hereford, on the A49 road which bypasses the town. The town is near the confluence of the rivers Corve and Teme.
The oldest part is the medieval walled town, founded in the late 11th century after the Norman conquest of England. It is centred on a small hill which lies on the eastern bank of a bend of the River Teme. Situated on this hill are Ludlow Castle and the parish church, St Laurence's, the largest in the county.[2] From there the streets slope downward to the rivers Corve and Teme, to the north and south respectively. The town is in a sheltered spot beneath Mortimer Forest and the Clee Hills, which are clearly visible from the town.[3]
Ludlow has nearly 500 listed buildings,[4] including examples of medieval and Tudor-style half-timbered buildings. The town was described by Sir John Betjeman as "probably the loveliest town in England".[5]
