A fatberg is a rock-like mass of waste matter in a sewer system formed by the combination of flushed non-biodegradable solids, such as wet wipes, and fat, oil and grease (FOG) deposits. The handling of FOG waste and the buildup of its deposits are a long-standing problem in waste management, with ‘fatberg’ a more recent neologism.
Giant fatbergs have blocked sewers in London, New York, Denver, Valencia, and Melbourne and are becoming more prevalent with the rise in usage of disposable (so-called ‘flushable’) cloths. Several prominent examples were discovered in the 2010s in Great Britain, their formation accelerated by aging Victorian sewers. Fatbergs are costly to remove, and have given rise to public awareness campaigns about flushable waste.
Fatbergs form at the rough surfaces of sewers where the fluid flow becomes turbulent. In pipes and tubes with smooth inner linings, fluid near the containing wall flows only slightly slower than fluid in the central channel of the pipe; thus, the whole volume of fluid flows smoothly and freely. When fluid encounters an obstruction, a resulting swirl of water starts trapping debris. Fatbergs occur in sewer systems around the globe, in cities and smaller towns.
An obstruction can be any type of rough surface capable of snagging debris. In brick or concrete sewers there may be surplus cement drips, damaged brickwork, or loose mortar joints damaged by frost heave. In any sub-surface pipe, even of the most advanced design, penetration by foreign intrusions such as tree roots is a commonplace cause of a fatberg blockage.
Fatbergs are not just the result of fats that have congealed through cooling. The lipids in fatbergs have undergone a process of saponification (the conversion of fat into soap and alcohol). Fatbergs thus require four main components: calcium, free fatty acids, FOG, and water. Comprising not only wet wipes and fat, fatbergs may contain other items that do not break apart or dissolve when flushed down the toilet, such as sanitary napkins, cotton swabs, needles, condoms, and food waste washed down kitchen sinks. The resulting lumps of congealed material can be as strong as concrete, and require specialist equipment to remove.
Fatbergs have been considered as a source of fuel, specifically biogas. Most of the fatberg discovered in Whitechapel in London in 2017, weighing 130,000 kg and stretching more than 250 meters, was converted into biodiesel.
Fatbergs can be mitigated through public awareness campaigns about flushable waste and grease traps for filtration at the source. Campaigns have been launched against wet wipes because of their effect on sewer systems, most notably by Surfers Against Sewage and the Marine Conservation Society, among other environmental NGOs, who called on the UK’s Advertising Standards Authority to end ‘misleading’ branding and packaging.
The Daily Omnivore 
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