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THE fatbergs are coming. These huge lumps of cooking oil and wet wipes lurk beneath UK streets, threatening to block sewers and put everyone off their lunch.

And they really are huge. In 2017, a monstrous 250-metre-long fatberg that weighed 130 tonnes was found under Whitechapel in east London 鈥� a piece of it still . In 2018, another rivalling it in size was found south of the river Thames and later analysed on a TV programme called , while in December that year, a whopping 800 tonnes of fat were removed from sewers in Cardiff. Even a relatively modest , made national headlines last month. So is this a new problem, or do Brits just have a new-found love of talking about it?

The word 鈥渇atberg鈥� was coined in 2008, but only when utility firm Thames Water discovered a 15-tonne blockage in London鈥檚 sewers. By 2017, the portmanteau had been added to the Oxford English Dictionary, so clearly it has caught people鈥檚 imaginations.

Tom Curran of University College Dublin, Ireland, says there has been a rise in the number of fatbergs and various factors have contributed to it: growing urban populations, ageing sewers, a rise in eating out and our increased flushing of wet wipes.

鈥淎 250-metre-long fatberg was found under east London 鈥� a piece of it still resides in a museum鈥�

Fatbergs are masses of fat, grease and oil congealed around wet wipes and other things that people shouldn鈥檛 flush down the toilet, like cotton buds and tampons. A found that, out of the solid items that could be identified, 93 per cent of the material recovered from sewer blockages were non-flushable wipes. Clearing the UK鈥檚 300,000 annual sewer blockages costs 拢100 million, it says.

Plenty of other items have been found inside fatbergs too: condoms and chocolate bar wrappers were spotted in parts of the Whitechapel monster.

This mass of solid material is a problem, but as the name 鈥渇atberg鈥� suggests, fat plays an important role in creating blockages. Cooking oil from a pan, excess gravy tipped down the sink and salad dressing rinsed off a plate all contain fats that end up in wastewater pipes.

Both commercial and domestic kitchens are culpable, but restaurants take the lion鈥檚 share of the blame because they prepare more meals and use more cooking oil than individual homes. It isn鈥檛 just places that prepare hot food: baristas who swill away coffee grounds and milk are also feeding fatbergs, says Raffaella Villa of Cranfield University, UK, who was part of the team that analysed the Whitechapel one.

We used to think that fat congealing as it cools was the main contributor to fatbergs, but a found that a key step is the saponification 鈥� turning into soap 鈥� of fats. Fats washed down the drain break into fatty acids, and those combine with calcium in the water to create hard, water-insoluble, soap-like deposits. These deposits build up around the sides of a sewer, like plaque builds up in arteries, and trap wet wipes as they grow, until you get a fatberg.

Clean-up operation

So we have an idea of how fatbergs form 鈥� but is there a reason they have drawn most attention in the UK? Blockages occur in sewers beneath towns and cities around the world, with notable fatbergs in , and in , yet the UK does seem to have cultivated a reputation for creating giant ones. 鈥淟ondon has larger Victorian sewers, which lend themselves to larger fatbergs more likely to get high profile media attention,鈥� says Michael Benke from Thames Water.

Curran says there is another factor that might be contributing to the giant fatbergs forming in UK sewers: letting food outlets off the hook.

The , which governs the nation鈥檚 sewers, doesn鈥檛 explicitly mention fats, but it does say that you shouldn鈥檛 pour away 鈥渁ny matter likely to injure the sewer or drain, to interfere with the free flow of its contents鈥�. UK building regulations also state that commercial hot food kitchens .

鈥淭he wording of legislation is not as clear-cut as it is in other places around the world,鈥� says Curran. For example, Dublin requires that waste water from restaurants doesn鈥檛 exceed a fat, oil and grease content of 100 milligrams per litre. Specific targets make it easier to enforce the rules, he says. 鈥淭here tends to be a softly-softly approach with following up with restaurants.鈥�

The Dublin example shows how to fight the fatbergs. Before 2008, the city had about 1000 sewer blockages every year. That year, it began requiring food outlets to hold waste-water licences and started a programme of inspections, sampling waste water and promoting the importance of not pouring fat out into the sewers. Since then, the number of blockages has gone down to fewer than 100 per year.

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Doing the same in the UK might not be so straightforward. UK water companies are privately owned and don鈥檛 have the power to inspect restaurants themselves, only local councils do, says Villa.

It is clear the problem needs fixing, though. Villa ran a survey of 103 restaurants in the UK towns of Reading and Bedford and found that 70 per cent had no grease management in place. 鈥淭he restaurants understand that fats are the cause of fatbergs, but they don鈥檛 understand that they are causing the problem,鈥� she says.

Addressing this misconception is essential, because once fatbergs are in the sewers, removing them is tricky. It tends to involve high-pressure water jets and weeks of manual labour to break them into smaller parts that can be taken away.

鈥淩estaurants understand that fats cause fatbergs, but don鈥檛 get that they are causing the problem鈥�

A better solution would be to monitor the sewers before fatbergs arise. Curran is working on using low-cost sensors to provide an early-warning system for fatberg formation. Ultrasonic sensors, for example, could monitor the sewage level in the pipes. If the level starts rising, that could indicate a blockage downstream. And a company called Nuron is putting fibre-optic cables through sewers to both deliver broadband and act as pressure and temperature sensors to monitor the sewer conditions in real time.

For its part, Thames Water is focusing on educational campaigns, both for households and for businesses, to stop people contributing to fatbergs. Its 鈥淏in it 鈥� don鈥檛 block it鈥� campaign, launched in 2013, encourages people to flush only 鈥渢he three Ps鈥� 鈥� pee, poo and toilet paper 鈥� and to collect cooking oil in a container that can be put in the bin, rather than down the sink.

There are signs that it is working: the number of blockages the water company has to deal with is on the decline, from 85,000 per year when the campaign started, to 75,000 in 2019. 鈥淭he number is gradually falling, but it is still a massive problem,鈥� says Benke.

Meanwhile, for those who can鈥檛 bring themselves to bin wet wipes, Water UK launched a 鈥�fine-to-flush鈥� label identifying products that will break down quickly after flushing.

Curran has first-hand experience of how problematic wet wipes can be. Before he began researching fatbergs, when his children were small, he fell prey to a brand of 鈥渇lushable鈥� wipes 鈥� and just weeks later, the sewer outside his house was blocked. 鈥淵ou can flush a lot of things down the toilet,鈥� he says, 鈥渂ut it has consequences.鈥�