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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]

​South Yorkshire is a ceremonial and metropolitan county in England. It is the southernmost county in the Yorkshire and the Humber region and had a population of 1.34 million in 2011. It has an area of 1,552 square kilometres (599 sq mi)[2] and consists of four metropolitan boroughs, Barnsley, Doncaster, Rotherham and Sheffield. South Yorkshire was created on 1 April 1974 as a result of the Local Government Act 1972.[3][4] Its largest settlement is Sheffield.

Lying on the east side of the Pennines, South Yorkshire is landlocked, and borders Derbyshire to the west and south-west, West Yorkshire to the north-west, North Yorkshire to the north, the East Riding of Yorkshire to the north-east, Lincolnshire to the east and Nottinghamshire to the south-east. The Sheffield Urban Area is the tenth most populous conurbation in the United Kingdom, and dominates the western half of South Yorkshire with over half of the county's population living within it. South Yorkshire lies within the Sheffield City Region with Barnsley also being within the Leeds City Region, reflecting its geographical position midway between Yorkshire's two largest cities.

South Yorkshire County Council was abolished in 1986 and its metropolitan boroughs are now effectively unitary authorities, although the metropolitan county continues to exist in law.[5][6][7] As a ceremonial county, South Yorkshire has a Lord Lieutenant and a High Sheriff.

South Yorkshire was created from 32 local government districts of the West Riding of Yorkshire (the administrative county and four independent county boroughs), with small areas from Derbyshire and Nottinghamshire.