Crossness Sewage Treatment Works
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The Crossness Sewage Treatment Works is a
sewage treatment Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...
plant located at
Crossness Crossness is a location in the London Borough of Bexley, close to the southern bank of the River Thames, to the east of Thamesmead, west of Belvedere and north-west of Erith. The place takes its name from Cross Ness, a specific promontory on the ...
in the
London Borough of Bexley The London Borough of Bexley () is a London boroughs, London borough in south-east London, forming part of Outer London. It has a population of 248,287. The main settlements are Sidcup, Erith, Bexleyheath, Belvedere, London, Belvedere, Crayford ...
. It was opened in 1865 and is Europe's second largest sewage treatment works, after its counterpart Beckton Sewage Treatment Works located north of the river. Crossness treats the waste water from the Southern Outfall Sewer serving South and South East London, and is operated by
Thames Water Thames Water Utilities Limited, trading as Thames Water, is a British private utility company responsible for the water supply and waste water Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking w ...
. The treated effluent from the plant is discharged into the River Thames at the eastern end of the site.


History

As originally conceived the works comprised reservoirs covering 2.6 hectares designed to retain six hours’ flow of sewage. No sewage treatment was provided and the sewage was discharged untreated into the
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, s ...
on the
ebb tide Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide ...
. Following the ''Princess Alice'' disaster in 1878 a Royal Commission was appointed in 1882 to examine Metropolitan Sewage Disposal. It recommended that a
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
process should be deployed to separate solids from the liquid and that the solids should be burned, applied to land or dumped at sea. A precipitation works using lime and iron sulphate was installed at Crossness in 1888–91. Sludge was disposed of in the Barrow Deep and later in the Black Deep in the outer
Thames estuary The Thames Estuary is where the River Thames meets the waters of the North Sea, in the south-east of Great Britain. Limits An estuary can be defined according to different criteria (e.g. tidal, geographical, navigational or in terms of salinit ...
. In the year 1912/13 the Crossness works received and treated 49,534 million gallons (225.2 million m3) of sewage, and disposed of 880,000 tons of sludge. The cost of operating the Crossness works was £44,269. In 1919/20 the corresponding figures were 41,209 million gallons (187.3 million m3), of sewage, 767,000 tons of sludge sent to sea, entailing 767 sludge vessel voyages, and the costs were £52,282.


Advanced treatment

Work began in the early 1960s to install a modern treatment plant capable of treating 450,000 cubic metres per day of sewage. The cost of the works was £9 million at 1963 prices. The plant comprised storm tanks, detritus channels, primary sedimentation, mechanical aeration, final sedimentation and sludge digestion.Wood, pp.105–07 Following the 1964 upgrade the works at Crossness began to produce a nitrifying effluent whereupon sulphide disappeared from the tideway; an excess of
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
provided a safeguard against sulphide formation in the river. The practice of dumping sewage sludge at sea was banned in 1998. In that year a sludge incineration plant was commissioned, and the plant was officially opened by the
Duke of Edinburgh Duke of Edinburgh, named after the capital city of Scotland, Edinburgh, is a substantive title that has been created four times since 1726 for members of the British royal family. It does not include any territorial landholdings and does not pr ...
on 4 November 1998. The plant provides 6 MW of power for use at the treatment works.


New processes

In 2010–14 the Crossness works were upgraded at a cost of £220 million, increasing capacity by 44% to reduce storm sewage flowing into the Thames during heavy rainfall. The upgrade involved the installation of new renewable energy sources including a 2.3 MW wind turbine, a thermal hydrolysis plant, an advanced digestion plant, and an odour control treatment system. The project enabled the plant to treat 13 cubic metres of sewage per second and incorporated new inlet works, primary settlement tanks, secondary biological treatment implementing the
activated sludge The activated sludge process is a type of biological wastewater treatment process for treating sewage or Industrial wastewater treatment, industrial wastewaters using aeration and a biological floc (biofilm), floc composed of bacteria and protozoa ...
process and final settlement tanks. It also included the installation of associated sludge thickening and odour treatment facilities. The hydrolysis plant burns combustible sludge flakes created after waste water treatment to 160 °C, producing 50 per cent more
biogas Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, Wastewater treatment, wastewater, and food waste. Biogas is produced by anaerobic ...
than anaerobic digestion process. The project included the installation of eight new primary settlement tanks where sewage is collected to remove primary sludge passing through two 1.2 km-long culverts of 2 m diameter. Sewage passes through a pair of new aeration lanes into twelve final settlement tanks of 40 m diameter. The activated sludge plant includes six aeration lanes of 69 m with total volume of 86,000 cubic metres and a treatment capacity of 564,000 cubic metres per day. It includes
anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...
zone mixers, a fine bubble diffused aeration system and five centrifugal blowers giving an air flow of up to 21,000 cubic metres per hour. Additional sludge storage and thickening facilities store the additional sludge. The five raw sludge gravity belt thickeners have a capacity of 6,055 cubic metres per day each.


Crossness Pumping Station

The original sewage pumping station on the site of the treatment plant, constructed between 1859 and 1865 and featuring spectacular Victorian architecture, has been restored and is now open as a museum.


See also

* London sewer system


References

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Source

*Wood, Leslie B, (1982). ''The Restoration of the Tidal Thames''. Bristol: Adam Hilger. Thames Water London water infrastructure Sewage treatment plants in the United Kingdom Sewerage