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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]
St Neots /sɛnʔ ˈniːəts/[b] is a town and civil parish in the Huntingdonshire District of the county of Cambridgeshire, England, approximately 50 miles (80 km) north of central London. The town straddles the River Great Ouse and is served by a railway station on the East Coast Main Line. It is 14 miles (23 km) west of Cambridge, to which it is linked by the A428 arterial road. It is the largest town in Cambridgeshire and had a population of 30,811 in the 2011 census.[c]
The town is named after the Cornish monk Saint Neot, whose bones were moved to the Priory here from the hamlet of St Neot on Bodmin Moor in around 980 AD. Pilgrimage to the priory church and parish church brought prosperity to the settlement and the town was granted a market charter in 1130. In the 18th and 19th centuries the town enjoyed further prosperity through corn milling, brewing, stagecoach traffic and railways.
After the Second World War the town and its industry were chosen for rapid growth as London councils paid for new housing to be built to rehouse families from London. The first London overspill housing was completed in the early 1960s and new housing has continued at a slightly lower rate such that the population, including the areas transferred from Bedfordshire, is approximately four times that of the 1920s.
