Weird science

'Fatberg' dead ahead! 15 tons of slime and wet-naps clog London sewer

Aug. 5, 2013 at 3:52 PM ET

A CCTV still shows the 15-ton mass of wet wipes and cooking fat that was found clogging sewers under London.
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A CCTV still shows the 15-ton mass of wet wipes and cooking fat that was found clogging sewers under London.

A 15-ton "fatberg," caked with grease and fortified with wet wipes, was extracted from London sewers — in the nick of time — by an expert team of sewage flushers from the Thames Water company. 

Had the titanic mass gone undiscovered, a company press officer told NBC News, "We could have had sewage popping out of manholes all over London."

An eight-member team used shovels and jets of water to dislodge the pulpy aggregation of cooking fat and flushed wet wipes, uncovered after residents in Kingston, Surrey complained about unflushable toilets. Together, the wipes and grease formed "a congealed wet mash" the size of a bus that smelled like "the worst wet dog you can ever think of."

Thames Water spends about $1.5 million (£1 million) every month on removing odd objects from about 108,000 kilometers of underground ducts. But this "fatberg," nurtured by the delicate preferences of the wet wipers of Kingston, Surrey, was a record-breaker. 

"While we've removed greater volumes of fat from under central London in the past, we've never seen a single, congealed lump of lard this big clogging our sewers before," Gordon Hailwood, waste contracts supervisor for Thames Water said in a release. 

Wet wipes and grease: A disastrous combo in any country
For years, organizations like the North Texas Grease Abatement Council have been warning citizens about pouring away fat from a frying pan or grease from the griddle down the drain. But the new scourge of the underground are almost-flushables — moistened towelettes that will be swept away by your toilet bowl, but can lurk underground for much longer than an ordinary sheet of toilet paper. 

In fact, flushed wet wipes are overtaking solidified cooking grease as the most costly clogger of sewage piping in some parts of the U.S., Cynthia Finley, director of regulatory affairs at the National Association of Clean Water Agencies, told NBC News. USA Today reported that a truckload of cloth wipes were removed from a plant in Minnesota this spring, and in Raleigh, North Carolina, wipes are the biggest source of sewer blockages. NACWA is working with a fabrics industry organization to educate wet wipers on how to best dispose of their naps, and adjust the use directions that come with products with the "flushable" label. A combination of fat and wet wipes? That "can be very hard to deal with," Finley said.  

Meat fats like the white parts of bacon, or goose fat, or vegetable fats like Crisco, are solids at room temperature, when they're stored in a jar on the countertop. On a hot pan they turn runny and can be poured down a sink. 

But once they cool off, they turn solid and sticky once again. "Fats and wet wipes together are just a recipe for disaster," Craig Rance, press officer at Thames Water told NBC News. The stuff may disappear down the drain, but down in the sewers, "a bit of fat will catch and a wet wipe will add on to it and it will catch and catch and catch."

Britons warned: 'Bin it — don’t block it
Baby nappies, sanitary napkins, underwear and even action figures are regular visitors to the Thames River treatment plant, but wet-naps are particularly insidious because they don't come with a "Don't flush," warning. Even if some companies insist that wet wipes can be sucked away by your toilet bowl, that doesn't mean they won't cause a problem underground Rance says. 

Unlike sheets of toilet paper, which will break apart if they're dunked in a jar of water and shaken about, wet wipes last longer. Embedded in the "fatbergs" underground, they linger on for weeks. "You can reach into the fat and you can pull out a wet wipe and it will be sturdy," Rance said. 

London's 'fatberg' cleanup lasted three nights with the crew working overnight. After the mound was loosened by shovels, jets of water broke the mound into smaller fragments, which were then sucked up into a sewage tanker. The goo was then trucked off to a landfill.

In May this year, Thames Water and United Utilities joined forces to warn the public of the twin menace of grease and wet wipes. To remind Britons about the potential threat of flushed grease and wet wipes, the company has adopted the dictum: "Bin it — don’t block it."

"We’re seeing more and more fat and wet wipes, which should never be flushed even if the packaging says ‘flushable,’ ending up in our sewers," Rob Smith, Thames Water’s chief sewer flusher, said in a statement published earlier this year. 

The problem gets particularly sticky after food-related holidays, Rance said, and Thames Water gets a delayed Christmas bonus in a breakout of sewer blockages just around the new year. Rance anticipates that his American colleagues face a similar problem just after Thanksgiving. 

Nidhi Subbaraman writes about technology and science. Follow her on Facebook, Twitter and Google+. 

Video: Video from inside London’s sewer system shows a giant “fatberg” that clogged up the system. A “fatberg” is a mix of grease and wet wipes.


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