An inspector stands in front of an archway in a dark sewer tunnel
A sewer inspector removes fat from sewer wall in sewage pipe in London Luke MacGregor/Reuters

“Fatbergs,” these vast bundles of congealed grease, are becoming the stuff of urban legend—but preventing their formation can be complex.

If there’s an urban problem more disgusting than the fatberg, I don’t want to hear about it. Vast, monster lumps of congealed fat stuck together with a structure of used diapers, tampons, and wet wipes, these oily excrescences are increasingly clogging urban sewers in many countries. Just this week, readers across the world have been wincing afresh at this problem after the discovery of a gargantuan fatberg beneath the streets of East London. Weighing an incredible 140 tons, this fatberg is 10 times the size than the next-biggest British fatberg, discovered in southwest London in 2013— and that one was already the size of a bus. This berg will take a team of eight workers up to three malodorous weeks to remove it.

It’s not hard to see why this giant fatberg has grabbed so many international headlines: It’s the ultimate contemporary symbol of urban consumption gone wrong, a vast mass of cooking gloop stuck together with cast-offs of people too fancy to use regular toilet paper, ever-swelling within a creaking urban infrastructure designed to manage the problems of a bygone era.

London is far from alone in struggling. Reports from China have somehow managed to make the problem sound even more disgusting: There is apparently an illicit trade there in “gutter oil” recycled from fatbergs that occasionally goes back into the cooking of the cheapest street food.

One of the biggest "fatbergs" ever seen in Britain, a ball of fat as long as three soccer pitches, is seen after it was found blocking a Victorian-era, east London sewer, in September 2017. (Reuters)

But while it’s easy to shudder at, there is no easy fix for the fatberg problem, especially in a city like London where rising population is matched with an antiquated sewer system. “London is a sort of perfect storm for the phenomenon,” says Dr. Tom Curran, a lecturer at University College Dublin’s School of Biosystems & Food Engineering department, who has studied the problem extensively. Curran says that another problem, in addition to the growing population and various utilities sharing responsibility for the sewer networks, is the burden that the commercial sector places on the aging pipes. “London has a very high concentration of restaurants, hotels, pubs and takeaways, so you have a readily available source of grease waste,” Curran says.

The materials with which cities are built exacerbate the problem, too. Urban waste water often develops a high calcium content after flowing through or over calcium-rich concrete. When that water mixes with cooking grease in the sewer, it transforms the fat into a dense lump via saponification—yes, believe it or not, fatbergs are created by the same chemical process as bars of soap.

So what’s the solution? One answer lies in tweaking consumer behavior. Ordinary citizens need to realize that wet wipes belong in the trash, not the toilet, given that they are essentially thin cloths that only biodegrade very slowly. Earlier this week, London’s Thames Water launched a public information campaign encouraging people not to flush away wet wipes and grease—which should be left to solidify in a jar and then thrown into regular trash.

Critics might write off such education efforts as buck-passing by water authorities reluctant to spend money on updating their ancient infrastructure. In Britain, however, the cost of adapting sewers would be genuinely astronomical. According to figures cited in a paper co-authored by Dr. Curran and University College Dublin colleagues, half of the United Kingdom’s sewers were built before 1945, with just under half this amount predating 1914. An estimate from 2014 placed the cost of renovating this network with broader tubes more resilient to grease at £104 billion ($138 billion).

London has already undergone a major overhaul of its water system in recent years, with £6 billion poured mainly into replacing leaking water pipes. There’s arguably little appetite for another major project. Meanwhile, the current cost of removing fatberg grease ranges between £15 and £50 million annually—still a drain, but far lower than potential reconstruction costs.

Another solution: Enlist the fatberg’s biggest contributors—not consumers, but restaurants. Unsurprisingly, London’s monster berg formed in an area that is full of pubs and takeaways. Restaurants should properly collect their frying waste in so-called grease traps, where water and fat separate and the grease can solidify and be skimmed. In the U.K., enforcement of rules around this—and agreement about the right approach—can be lax because of the splintering of responsibility between public boroughs and various privatized utility companies.

Regular inspections of restaurant grease traps can nonetheless make a huge difference. In 2008, Dublin introduced blanket inspections looking at commercial kitchen grease traps, holding 7,000 annually across a pool of 2,300 city establishments. The inspections may well have paid for themselves, as in the years following their introduction, fatberg-related sewage incidents dropped by 90 percent.

Problems with restaurant grease aren’t always a matter of calculated neglect, however. Dr. Joel Ducoste, a professor and fatberg expert at North Carolina State University, points out that restaurant kitchens have very high staff turnover and low pay, providing little incentive for staff to think about how their cooking grease could clog the city’s below-ground filth arteries. This can lead to some false steps, such as pouring overly hot liquids into the grease trap or incorrectly assuming that grease can be soaked up and dealt with just by bombing it with detergent.

Even if cities cut down on cooking oil and throw less down the drains, there will always be some used grease to deal with. In addition to the reported illicit Chinese trade in recycled oil, many restaurants sell their used cooking oil for recycling as biodiesel. While it would be tempting to see this as a suitable end use for the grease that ends up in fatbergs, the oil most commonly used for biodiesel is relatively clean oil strained directly from pans. In contrast, the fatberg grease is so-called brown grease, which has a greater water content and higher levels of contaminant.

Still, brown grease can nonetheless be recycled—in fact, Thames Water is currently negotiating with a biodiesel manufacturer to see if the Great London Fatberg of 2017 can be turned into fuel. While biodiesel is itself a creator of carbon emissions, the idea of using London’s monster fat lump to spin a thousand wheel axles has a certain ingenuity to it. But the key goal must still be to prevent these greasy monsters of the deep from forming in the first place.

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