Biogas
Biogas is a gaseous renewable energy source[1] produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or a bioreactor.[2] The gas composition is primarily methane (CH
4) and carbon dioxide (CO
2) and may have small amounts of hydrogen sulfide (H
2S), moisture and siloxanes. The methane can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used in fuel cells and for heating purpose, such as in cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.[3]
After removal of carbon dioxide and hydrogen sulfide it can be compressed in the same way as natural gas and used to power motor vehicles. In the United Kingdom, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel.[4] It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. Biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide. From a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released, when the material is ultimately converted to energy.
Guildford (/ˈɡɪlfərd/ (listen))[2] is a town in west Surrey, around 27 mi (43 km) southwest of central London. As of the 2011 census, the town has a population of about 77,000[1] and is the seat of the wider Borough of Guildford, which had around 148,998 inhabitants in 2019.[3] The name "Guildford" is thought to derive from a crossing of the River Wey, a tributary of the River Thames that flows through the town centre.
The earliest evidence of human activity in the area is from the Mesolithic and Guildford is mentioned in the will of Alfred the Great from c. 880. The exact location of the main Anglo-Saxon settlement is unclear and the current site of the modern town centre may not have been occupied until the early-11th century. Following the Norman Conquest, a motte-and-bailey castle was constructed, which was developed into a royal residence by Henry III. During the late Middle Ages, Guildford prospered as a result of the wool trade and the town was granted a charter of incorporation by Henry VII in 1488.
The River Wey Navigation between Guildford and the Thames was opened in 1653, facilitating the transport of produce, building materials and manufactured items to new markets in London. The arrival of the railways in the 1840s attracted further investment and the town began to grow with the construction of its first new suburb at Charlotteville in the 1860s. The town became the centre of a new Anglican diocese in 1927 and the foundation stone of the cathedral was laid in 1936. Guildford became a university town in September 1966, when the University of Surrey was established by Royal Charter.
Guildford is surrounded on three sides by the Surrey Hills Area of Outstanding Natural Beauty, which severely limits its potential for expansion to the east, west and south. Recent development has been focused to the north of the town in the direction of Woking. Guildford now officially forms the southwestern tip of the Greater London Built-up Area, as defined by the Office for National Statistics.