Extras » The Straight Dope

Is the fatberg apocalypse upon us?

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There seems to be an alarming increase in news stories about enormous fatbergsblobs of fat and grease accumulating in the sewers of major cities in the U.S. and Europe. Is it the Western diet, more fast-food restaurants, what? FtG

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As the Western diet continues to wreak havoc on the world’s health, you can certainly see some rich metaphorical possibilities here—hard, plaque-y, whitish deposits plugging not just our bodies' arteries but also the ones underground that sustain our cities. This past fall, London saw its largest yet: the Whitechapel fatberg, 140 tons heavy and 270 yards in length. A leviathan glob of solid fat, human waste, and trash is more than gross enough on its face, but consider too where all the sewage it's blocking will subsequently bubble up.

A recent paper in the Journal of Oleo Science reported that buildups of this kind account for 47 percent of sanitary sewer overflows in the U.S., and fully half in the UK. London attracts a good share of the attention because it’s a particularly extreme example of a common urban situation: antiquated infrastructures not designed to handle the loads they’re currently servicing. I mean that both in terms of population and what the population’s disposing of. There’s the expected verboten items—diapers, condoms, tampons—but these solids are bobbing along in a much larger waste stream: cooking grease.

We have the Brits to thank for the evocative term “fatberg,” which was added to the OED in 2015. The phenomenon is otherwise known in the sewage trade as a FOG deposit—fat, oil, and grease—and it’s the reason you don’t dump your turkey drippings down the sink after Thanksgiving dinner.

Home-scale waste isn’t the chief driver here, though: it’s restaurant waste. In research attempting to determine the source of the Whitechapel fatberg, London utility Thames Water found that not one restaurant on the street above (that’d be Whitechapel Road) used a functional grease trap—the device connected, ideally, to a commercial sink or dishwasher to screen oil content out of the waste water. A sampling of 700-plus London restaurants revealed that nine out of ten weren’t doing anything to filter out the fat headed down their drains; homes within 50 meters of a fast-food restaurant were eight times likelier to flood with sewage.

Fatberg apocalypse may be overstating it, but this is a genuinely massive problem for big-city sanitation authorities, not to mention a major physical challenge—under the streets of east London last fall, heat-fatigued crews were working in shifts to hack away at the Whitechapel berg with shovels. The BBC described fatbergs as “a form of artificial geology,” made up of “a pale, tough substance with the strength of rock.”

Or, somewhat more accurately, the strength of a mighty bar of soap. As you may recall from high-school chem class, saponification is the process wherein a fatty acid, as found in animal fat or vegetable oil, encounters some high-pH substance and turns into soap—the classic pairing is tallow and lye.

What we’re seeing in FOG situations is the fatty acids released during the deep-frying of food reacting with the calcium in the concrete sewer walls to form a monstrous cake.

As I say, there’s other stuff clogging up the works too. Solid trash in the sewers seems to play a role in fatberg formation, providing an anchor point for grease to congeal around.

The notable culprit here, now widely used by adults on themselves as well as on babies, is wet wipes; they’re typically advertised as “flushable” by their manufacturers, but sewer operators beg to differ.

Still, the wipes issue, while serious, is just the tip of the fatberg. What to do about all the grease? Getting people to give up their French fries would reduce clogging in both our vascular and sewage systems, but color me bearish on that prospect.

An alternative is to use FOG as biofuel—to power city buses, for instance—and that’s what outfits like Thames Water have been looking into. On that front, the good news is that spent cooking oil can burn 80 percent cleaner than traditional fossil fuels.

The bad news? Somebody still has to go down there and get it.

cs

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