A fatberg is a congealed lump in a sewer system formed by the combination of non-biodegradable solid matter such as wet wipes with grease or cooking fat. They have become an increasing problem in recent years, with the combination of aging Victorian drains and the rise of disposable (so-called flushable) cloths.
Fatbergs form at rough surfaces of sewers where the fluid flow becomes turbulent. Normally, in pipes and tubes with smooth inner linings the fluid near the containing wall is only slightly slower than the fluid in the central (lumen) of the pipe, and the whole volume of fluid flows smoothly and freely. When the fluid encounters an obstruction, the swirl of water helps debris to become trapped. Initially perhaps only a tiny fibre or hair attaches to the obstruction, which then swirls in the turbulent flow and increases the obstructive nature of the original defect.
Obstruction can be any type of rough surface capable of snagging debris. In brick or concrete sewers that may be surplus cement drips ("snotty noses"), damaged brickwork, loose mortar, joints damaged by land heave. Any sub-surface pipe, even of the most advanced design, penetration by foreign intrusions such as tree roots is a commonplace cause of fatberger blockage.
In sewers carrying alkaline fluids, lipids can become calcified and solid. In addition to wet wipes and fat, fatbergs may also contain other items which do not break apart or dissolve when flushed down the toilet, such as sanitary napkins, cotton buds, needles and condoms, as well as food waste washed down kitchen sinks. The resulting lumps of congealed material can be as strong as concrete, and require specialist equipment to remove.
Grease and fat blockages can cause sanitary sewer overflows, in which sewage is discharged from a sewer into the environment without treatment. In the United States, almost half of all sewer blockages are caused by grease.
Fatbergs have been considered as a source of fuel, specifically biogas. The majority of a fatberg uncovered in Whitechapel, London, in 2017, weighing 130 tonnes (130,000 kg) and stretching more than 250 metres (820 ft), was successfully converted into biodiesel.
Fatbergs can be mitigated through public awareness campaigns about flushable waste and grease traps for filtration at the source
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"Fatberg" is a portmanteau of fat + berg, modelled on iceberg. The neologism was in use among sewer managers by 2013. The word was added to Oxford Dictionaries Online in 2015. The term is in official use by authorities at Thames Water in southern England.
- 6 August 2013: A fatberg roughly the size of a bus that weighed 15 tonnes (17 tons), consisting of food fat and wet wipes, was discovered in drains under London Road in Kingston upon Thames, London.
- 1 September 2014: A collection of waste, fat, wet wipes, food, tennis balls and wood planks the size of a Boeing 747 aeroplane was discovered and cleared by sanitation workers within a drain beneath a 260-foot (80 m) section of road in Shepherd's Bush, London.
- 3 September 2014: The sewerage system beneath Melbourne, Australia was clogged by a large mass of fat, grease and waste.
- January 2015: As part of a campaign against drain blocking, Welsh Water released a video showing a fatberg in drains in Cardiff.
- April 2015: A 40-metre-long (130 ft) fatberg was reported as having been removed from underneath Chelsea, London. It took over two months to remove the fatberg, and the damage it had caused was estimated to cost £400,000 to repair.
- July 2015: A 120-metre-long (390 ft) fatberg was discovered in the city of Welshpool in mid-Wales.
- January 2016: Blockage from a fatberg near Newcastle, New South Wales, Australia damaged the Eleebana sewage pumping station. The fatberg "weighed about one tonne (1.1 tons) and took four hours to remove" by crane.
- September 2017: A 250-metre-long (820 ft) fatberg weighing over 140 tonnes (150 tons) was found under Whitechapel, London. Even with workers working seven days a week at a cost of £1 million per month, officials said it could take as much as two months to destroy it. Two pieces of this fatberg were cut off on 4 October 2017 and, after several weeks of drying, displayed at the Museum of London from 9 February 2018 as part of the museum's City Now City Future season.
- September 2017: A fatberg of congealed fat, wet wipes, and waste was discovered under the streets of Baltimore, Maryland that caused sewer spillage of 1.2 million US gallons (4.5 million litres; 1.0 million imperial gallons) into Jones Falls.
- April 2018: A fatberg discovered under South Bank in London is suspected to be larger than the one found under Whitechapel.
Fatberg boosts Museum of London attendance 
- "Monster fatberg longer than two Wembley football pitches clogging up Whitechapel sewer". corporate.thameswater.co.uk.
- "Wet wipes could face wipe-out". BBC News. 2018-05-08. Retrieved 2018-05-08.
- "Don't feed the fatberg! What a slice of oily sewage says about modern life". The Guardian. 18 Feb 2018.
- "Fatberg! Exhibiting the Monster of Whitechapel". Museum of London.
- Williams, Rob (5 August 2013). "Britain's biggest ever 'fatberg' – the size of a bus and weighing 15 tonnes – found in London drain". The Independent.
- Edwards, Jim. "Gross Photos Show Sewer Workers Battling A 'Fatberg' The Size of a Boeing 747 Under London". Yahoo/Business Insider. Retrieved 1 September 2014.
- Report to Congress: Impacts and Control of Combined Sewer Overflows and Sanitary Sewer Overflows (Report). Washington, D.C.: United States Environmental Protection Agency (EPA). August 2004. p. 4-28. EPA 833-R-04-001.
- "Kevin McCloud's Man Made Home". Channel 4.
- "Thames Water and 2OC in £200m deal to turn 'fatbergs' into energy". waterbriefing.org. 8 April 2013. Retrieved 2 June 2013.
- "'Monster' Whitechapel fatberg unveiled at London museum". BBC News. 8 February 2018. Retrieved 11 May 2018.
- "Water companies declare war on 'flushable' wet wipes". Daily Mirror. Associated Newspapers Ltd. Press Association. September 20, 2016. Retrieved 17 October 2016.
- In London’s Sewers: Less Pollution and A Smelly Form of Energy. National Geographic, 28 May 2013.
- "New words in oxforddictionaries". Retrieved 28 August 2015.
- 2013-08-06, Britain's biggest 'fatberg' removed from London sewer, BBC
- Flegenheimer, Matt (13 March 2015). "The Wet Wipes Box Says Flush, but the New York City Sewer System Says Don't". The New York Times. Retrieved 13 March 2015.
The consummate cautionary tale is that of London, where in 2013 a collection of wipes, congealed cooking oil and other materials totaled 15 tons, according to Thames Water, the utility company that removed it. It was known, like some previous occurrences, as the fatberg. "We reckon it has to be the biggest such berg in British history," Gordon Hailwood, an official with Thames Water, said at the time.
- 2014-09-01, Fatberg the size of a jumbo jet strikes central London: Eighty-metre mass of congealed fat and wet wipes under the streets of Shepherd's Bush took four DAYS to break up, Daily Mail UK
- 2014-09-01, Enormous 'fatberg' the size of an AEROPLANE found blocking sewers in London, Mirror UK
- 2014-09-03, Melbourne’s sewerage system clogged by fatberg, warns Yarra Valley Water, News.com.au
- "'Fatberg' found blocking Cardiff sewer". BBC News. 10 February 2015.
- Ratclife, Rebecca (21 April 2015). "10-tonne fatberg removed from west London sewer". The Guardian. Retrieved 21 April 2015.
- "120m fat blockage found in sewer". BBC News. 8 July 2015. Retrieved 11 October 2017.
- Cox, Dan (25 February 2016). "Wet wipes blockage weighing a tonne pulled out of sewer pipe near Newcastle". 1233 ABC Newcastle.
- "'Monster' fatberg found blocking east London sewer". BBC News. 12 September 2017. Retrieved 12 September 2017.
- News, ABC. "'Fatberg' found in Baltimore sewer system after overflow". ABC News. Retrieved 26 September 2017.
- Johnston, Chris (10 October 2017). "Fatbergs: 90% of London restaurants are contributing to problem". The Guardian. ISSN 0261-3077. Retrieved 11 October 2017.
- Adams, Tim (4 February 2018). "London's fatberg on show: 'We thought of pickling it'". The Observer. Retrieved 10 February 2018.
- Knight, Sam (9 February 2018). "A Fatberg's Journey from the Sewer to the Museum of London". The New Yorker. Retrieved 10 February 2018.
- Wells, Carrie. "'Fatberg' of congealed fat, wet wipes and waste discovered under Baltimore's streets, causing sewer overflows". The Baltimore Sun. Retrieved 26 September 2017.
- https://www.theguardian.com/uk-news/2018/apr/24/fatberg-autopsy-reveals-growing-health-threat-londoners Fatberg 'autopsy' reveals growing health threat to Londoners], The Guardian, Nadia Khomami, 24 April 2018
- Fatberg boosts museum numbers