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  • [♪ INTRO]

  • You've probably heard that it's bad

  • to throw grease down the sink.

  • And sure, that's in part because it can

  • glom onto your pipes and build up over

  • time, which can lead to long-term

  • damage and clogs.

  • But the potential harm to your plumbing is

  • nothing compared to the much bigger reason

  • you shouldn't send oils down the drain.

  • And by bigger, I mean a lot bigger.

  • Like 250 meters long, 130 tons bigger.

  • That's the size of a fatberg that London's

  • Whitechapel district had in 2017.

  • Yes, I said the word fatberg, which is a

  • giant block of fat.

  • That's a thing that we as a species

  • have to deal with now.

  • It took engineers 9 weeks to get rid of

  • the Whitechapel one.

  • And fatbergs like it are continuing to

  • grow in sewer systems around the world.

  • But, by understanding how and why they form,

  • we can figure out how to stop them from

  • sinking our infrastructure.

  • Fatbergs are more technically known as

  • Fat, Oil, and Grease deposits, or FOGs,

  • which is a less disgusting name.

  • And they're a huge problem worldwide.

  • For example, the US Environmental Protection

  • Agency estimates that some 47% of all

  • sewer backups in the US are caused by FOGs.

  • Backups are bad because they can cause

  • sewage to leak out.

  • And no one wants sewage in their home or

  • in their drinking water or on their lawn

  • or wherever else it's showing up.

  • But preventing fatbergs from forming

  • is a bit tricky.

  • You see, the problem starts because

  • bacteria in human waste generate

  • hydrogen sulfide - it's that lovely

  • compound that gives rotten eggs their smell.

  • Enough hydrogen sulfide can promote the

  • growth of other bacteria in thick coatings

  • called biofilms on the sewer walls.

  • These convert H2S to sulfuric acid, which

  • reacts with lime in the concrete to form

  • compounds like gypsum that crack and

  • corrode the walls.

  • And all of this ultimately results in

  • the release of metallic salts like

  • calcium sulfate into the wastewater.

  • This is where the fat comes in.

  • There was a lot of chemistry before the fat

  • Fats contain long carbon chains called

  • fatty acids, some of which end up

  • loose in wastewater.

  • These free fatty acids can react with

  • calcium and other metals to form molecules

  • that aren't really water soluble,

  • so they tend to form hardened masses.

  • This reaction is known as saponification,

  • which fans of Fight Club might remember

  • is the same reaction that makes soap.

  • So, instead of fatbergs, we could call them

  • soapbergs”, I guess.

  • But that makes them sound way too good

  • than they actually are.

  • Since the fats generally float, this

  • reaction largely takes place on the

  • surface of the water, particularly

  • where the water meets the wall.

  • And those corroded sewer walls, with

  • their roughened surfaces, give the

  • newly-formed soap a spot to clump or around.

  • This means that FOGs typically built up

  • in the middle of sewer walls and

  • expand from there.

  • All the non-biodegradable items people flush

  • down the toilet make the problem worse.

  • That's because items like condoms,

  • tampons, and so-calledflushablewipes

  • end up acting like glue for a giant FOG,

  • clinging onto the solidifying mass

  • and allowing new FOGs to start forming

  • on their surfaces, too.

  • But that gives us our first clue as to

  • how to prevent fatbergs.

  • Don't flush anything that isn't toilet

  • paper or human waste!

  • I don't care if it says it's flushable.

  • It isn't.

  • And it's also helpful to limit the fats

  • in wastewater in the first place.

  • Many peopleboth in residential and

  • commercial settingsdump their used

  • cooking oil and grease down the drain.

  • So, stop that.

  • Throw it away, into the trash -

  • not down the drain.

  • And places that generate a lot of

  • fatty wastelike restaurantsthey

  • should have grease traps installed.

  • These are essentially water tanks

  • where organic food waste settles

  • and the fats float, so they can both

  • be removed before entering the sewage system.

  • Traps aren't a perfect solution, mind you

  • up to 15% of the fat still escapes with

  • the waterbut sewers can handle some fat.

  • After all, our feces contain some undigested

  • fatsand fatbergs don't appear everywhere.

  • They usually appear near areas with a high

  • concentration of restaurants, like

  • shopping malls and commercial districts.

  • And the truth is, we might never be able

  • to keep enough fat from entering the sewers

  • in those areasbut there are

  • other ways to prevent fatbergs.

  • Since corrosion is a key part of the problem,

  • keeping sewers in better shape can help a lot.

  • There are coatings that can prevent corrosion

  • of the sewer walls, for example.

  • And there are chemicals that can be added to

  • wastewater that may reduce the production of

  • sulfuric acid by inhibiting the growth of

  • those biofilm bacteria.

  • But that kind of sewer maintenance isn't cheap.

  • And it adds chemicals to the water system that

  • could have negative downstream effects.

  • So, unless we distribute restaurants more

  • evenly or figure out better corrosion

  • control techniques, there will likely be

  • some fatbergs around.

  • And that means we need to figure out what

  • to do with them when they do form.

  • First and foremost, they have to be broken

  • apart into removable chunks.

  • The Whitechapel crews used pressurized water,

  • pickaxes, and shovels to chop up that

  • giant fatberg, for example.

  • And the good news about that is that while

  • these things are pretty gross,

  • we can get clean fuel out of them.

  • Scientists have found that fatbergs

  • can be converted to biodiesel, so maybe we

  • should go down there and just mine them.

  • One 2017 study found this could turn about 86%

  • of the mass into high-quality diesel, which is a

  • pretty good outcome for a nightmarish sewer clot.

  • But whether you can scale that into a

  • usable process remains to be seen.

  • And it would still be great for everyone

  • involved, especially the people who have

  • to remove them, to have fewer and smaller

  • fatbergs than we do now.

  • So we should all do our part to help

  • prevent them by properly disposing of oil

  • and grease, being careful about what we

  • flush down the toilet.

  • If it's not toilet paper and it didn't

  • come out of you, it probably

  • doesn't belong in there.

  • Because if we don't clean up our act,

  • fatbergs will keep making a big stink.

  • And maybe you're not the one down there

  • cleaning them up, but somebody is.

  • Fatbergs aren't the only messes our modern

  • lifestyle has created, of course.

  • And you can hear about some more of them

  • over on our podcast SciShow Tangents.

  • Tangents is, again a podcast, and every week,

  • some of the people who make SciShow and

  • some of the other Complexly shows get together

  • to battle for nerd cred and Hank Bucks.

  • It's very slightly competitive.

  • We are trying to amaze each other with

  • our very good science facts and

  • our very good science poems.

  • We try to stay on topic, but we're not super

  • great at that, hence the nameTangents”.

  • And if you liked learning about fatbergs,

  • you'll probably love our 30th episode where

  • we sat down with Joe Hanson from Hot Mess to

  • talk about some of humanity's biggest messes,

  • from fatbergs to molasses spills.

  • You can find it all and our other episodes

  • on your favorite podcasting platform!

  • [♪ OUTRO]

[♪ INTRO]

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B1 中級

為什麼我們的下水道會受到胖子的困擾? (Why Our Sewers are Plagued by Fatbergs)

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    林宜悉 發佈於 2021 年 01 月 14 日
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