Why Our Sewers are Plagued by Fatbergs

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
There are coatings that can prevent corrosion
of the sewer walls, for example.
And there are chemicals that can be added
wastewater that may reduce the production
sulfuric acid by inhibiting the growth of
those biofilm bacteria.
But that kind of sewer maintenance isn’t
And it adds chemicals to the water system
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
of the mass into high-quality diesel, which
is a
pretty good outcome for a nightmarish sewer
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
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!

100 thoughts on “Why Our Sewers are Plagued by Fatbergs

  1. Wait you are telling me giant icebergs of fat in our fat is cloging our sewers well i needed to know that…

  2. We need to pass legislation that flat out makes it illegal to throw used grease down the drain or toilet.

  3. Soupy abortions are okay? I'm asking for a friend.

    P.s. Just dump hundreds of gallons of concentrated lye down the drain 👏 Problem solved!

  4. I was watching an episode of Younger today and couldn’t figure out where I heard the term “fatberg” before!! Scrolling through YouTube and this popped up again!!!! Thanks SciShow

  5. Did you really just give engineers all the credit? They didn't do s***. The men using the Jet-Vac trucks did all the work.

  6. I tell people on my rental properties why it is important to store and dispose of oils and grease rather than poor it down the drains…then 6 months later when they get charged a plumber's fee they look at me all pissed like they had no idea.

  7. I gre up understanding not to pour fats and Oils down the drain. I'm 6. 3My parents understood that we could be the first impacted by ouring those in the drain.

  8. Since you brought it up, the idea of intentionally naming things in a way that is repulsive to people (i.e.: moist, shart, manufacture) sounds like an effective preventative measure.

  9. I've read that some restaurants in London are not installing grease traps so that they don't have to pay the cost of labour and waste disposal cleaning them out. Essentially shifting the problem onto the sewer company instead.

  10. ok, so how are you supposed to dispose of residential waste cooking oil.

    where I live your not actually allowed to throw liquids out in the trash.

  11. in some places they would troll heavy stone or metal balls through sewer pipes to clean them out. if done on a regular basis it keeps things clear. but as always it takes money and people to stay on top of that and updating and maintaining the infrastructure seems to be one of the last things on the "to do" list for many governments.

  12. Like a recycling company for oils. You drop a bucket of oil and get some cash for it, then it gets processed for use in biodiesel?

  13. Why can't sewers be coated w/ a tough, plastic skin that doesn't corrode– or takes five millennia to corrode? Or a thin metal that won't corrode? And why aren't cities mining fatbergs in the first place? Cheaper diesel for city trucks sounds great to me.

  14. This video fails to explain that concentration of waste is more due to overcapacity from the victorian london sewer system , that from a simple chemical process. The problem is not "too many restaurants" ( blame it on the people has usual) but ovrrgrowth of cities beyonde their institucional capacity. London is a perfect example of bad government, atracting migration to a city built to acomodate in max 2,5 million people…nowdays it has 9 million , the sewer system clogs, police does not work, bombs explode and Thames is literally a open sewer . The fault is not chemistry, or toilet paper (seriously?!) Or even oil ,the problem is government incompetence

  15. Oooo, as soon as you mentioned a new SciShow (Tangents) you caught my attention! …then you said it was a podcast, and I moved on. Enough with the podcasts, Internet…

  16. Why can't you flush "flushable wipes"? They are not tampons, condoms, or diapers.
    The newer ones break down like toilet paper, and rip apart. They aren't like baby wipes, anymore!
    They can't clump if they are rip apart.

  17. Dammit I thought fatbergs where those clusters of worms stuck to the walls of sewers from a video I seen 10 years ago

  18. In Australia the courts ruled that 'flushable wipes' were false advertisment and now no wet wipes say that anymore.

  19. That 2017 study was seriously flawed, as they only used lab grown samples of the saponified fats. I used to work for a company that processed restaurant grease trap waste water etc and it was Not a cheap process. You’re lucky if you could use 20% of the used product- and even then it takes Much more time effort and money to process it than other traditional biofuel products- so it’s not a cost effective solution.

  20. in Italy used alimentary fat are gathered and can be given back to municipal collection spots also by private citizens

  21. We never put our oil down the drain we put it in a cup let it sit until hard and then we throw it away. Of corse not the cup but the oil.

  22. Thank you for giving us the goal to beat. I'm going to start petitioning our city council for a effort to beat that!

  23. As far as flushable wipes go, it's common knowledge they shouldn't be flushed. I feel like companies should not be allowed to advertise them as flushable.

  24. my Forman used to work for Sydney warter and i asked him if hes ever had to deal with this type of thing
    he said no

  25. They don't have this this problem in China because they process this sewer grease and recycle to make oil again .

  26. I once worked at a restaurant that did that soapification to the used grease so that way it would be easier to throw out as a solid.

  27. Working for a catering company, I witnessed a "fatberg" that took up an entire commercial septic tank. They don't just exist in the sewers.

  28. 4:11 Just putting it out there, why not drop a lit match down there? All that methane gas & sludge catching fire should incinerate the fatbergs. Now that I think about it, it probably wouldn't work. It would probably cause the sewer pipes to brake down that much faster, whole new set of problems. Oh well, such is life.

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