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-called “flushable” wipes

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 people—both in residential and

commercial settings—dump 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 waste — like restaurants — they

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 water — but sewers can handle some fat.

After all, our feces contain some undigested

fats—and 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 areas—but 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 name “Tangents”.

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]