
Sound waves used to separate microplastics from laundry wastewater - elorant
https://newatlas.com/environment/sound-waves-microplastics-laundry-wastewater/
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nudgeee
Back in 2006 I was contracted to design a power amplifier prototype for the
civil engineering department of a university.

We built an adjustable 500W h-bridge based amplifier (operating between 50kHz
to 300kHz+) which was used to drive transducers to create standing waves for
waste water treatment, and it seemed to work alright in a bunch of our tests,
but at fairly low flow rates.

We passed the prototype on to the client (I think it was for a joint project
between Monash University and Melbourne Water), not sure where it ended up.
Great to see the technique being applied in consumer applications :)

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jnwatson
I use a Cora Ball [1] in my laundry for the same purpose. Studies say it is
only 26% effective, better than nothing.

1: [https://coraball.com/](https://coraball.com/)

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4ntonius8lock
Thanks for sharing that. I use a lot of polyester garments for sports and feel
kinda crumby knowing it really hurts the environment.

Hopefully these sound wave systems can be adapted to municipal water systems
so as to remove the consumer as the point of failure. Really cool to see the
technology that creates Chladni figures being applied to something so useful.

Reminds me of how things start off as entertainment many times, and eventually
make a way into an industrial application.

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maxwell
> Reminds me of how things start off as entertainment many times, and
> eventually make a way into an industrial application.

I was just thinking about this phenomenon, in terms of how it runs counter to
the criticism of "solutions in search of problems" and projects derided as
"toys".

This is a good response to those condemnations: often great ideas work in
entertainment first, then industry. The canonical example from antiquity is
Heron of Alexandria's automata.

Nowadays, roller coasters seem like a technology that future historians will
puzzle over non-utilization beyond entertainment. (The cause of course is
zoning, which halted housing and transportation innovation a hundred years
ago.)

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aSplash0fDerp
If this works like non-newtonian fluids, I imagine "finding the right shape"
or series of tones/patterns works well in bulk.

[https://m.youtube.com/watch?v=SYMvOxIsES4](https://m.youtube.com/watch?v=SYMvOxIsES4)

I don't have any hard numbers, but it almost seems like we could easily spend
a trillion dollars fixing a problem caused by a 100 billion dollar industries
by-products.

What would a carbon credit scheme look like if it were for microplastics?

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soulofmischief
The effect you're thinking of isn't relegated to just non-Newtonian fluids.

[https://en.wikipedia.org/wiki/Cymatics](https://en.wikipedia.org/wiki/Cymatics)

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aSplash0fDerp
Cool! I was thinking of granular convection using vibrations, but cymatics and
-nf's have much more entertaining videos to visualize sound.

[https://m.youtube.com/watch?v=mmPpUztcqB8](https://m.youtube.com/watch?v=mmPpUztcqB8)

> What would a carbon credit scheme look like for microplastics?

A payment plan for a ransom...(insert punchline rimshot here)

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aiphex
Very cool idea. Probably wouldn't want to do it where there is marine life
though.

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krallja
Generally, there is not marine life in the drain line of a washing machine.

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r00fus
Amusing but I think aiphex was considering the possible reuse of this tech
against the pacific gyre.

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chongli
If we cut off the microplastics at the source then the gyre will eventually
take care of itself. The problem right now is that we’re continually adding
more and more pollution.

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dwiel
What do you mean "take care of itself"?

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chongli
It'll make its way through the food chain and gradually clear up. Yes, it's
going to harm a lot of ocean life in the mean time, but there's not much we
can do about that. It's like trying to get red wine out of the white carpet
and back into the bottle.

We should stop spilling the wine or at the very least drink it somewhere
safer.

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hanniabu
Or we can attack the issue at the source and the gyre...

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kazinator
Say this has been productized and I now have a seven-year-old washing machine
equipped with this.

How do I know that the acoustic standing wave is still activating, and
separating the microplastics?

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sml156
After month's or year's you would have bucket of micro plastic.

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mrfusion
What other applications for this could there be?

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newfocogi
I worked on a project using a similar concept for concentrating micro-algae in
the water solution it is grown in. The previous method of extracting micro-
algae was filtration or centrifuges. Filters get full too quickly and need
regular attention, and centrifuges take too much energy since the density of
the particles were very close to the density of water and didn't spin out
easily.

We tried using standing acoustic waves to organize and "conclomerate" the
micro-algae in the flow and siphon off water quite similarly to the image in
the article. It "sort of" worked but only when the flow rate was really,
really low because these forces are totally dominated by drag forces and even
the smallest levels of turbulence remixes the solution.

What else could this be used for? Think of something that doesn't play nicely
with filters or centrifuges and doesn't need to be processed at really high
flow rates. Applications in the medical industry come to mind.

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nashashmi
What is it about Soundwaves that allow plastics to move in a direction?

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newfocogi
Resonant waves in a liquid can cause particles of different sizes to move
toward the nodes or anti-nodes of a standing wave. A secondary effect is the
particles can conglomerate and fall out depending on density.

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DoingIsLearning
I am more familiar with resonance in an electrical domain more so than a
mechanical one.

How do they determine at what frequency to actuate the piezos in order to
match the resonant frequency of these plastic particles? Is it just
'guestimated' or is there a more systematic way?

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newfocogi
My guess would be that they choose the frequency based on the speed of sound
in the liquid such that the nodes in the standing wave occur at a designed
location in the chamber where the separation occurs.

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makerofspoons
Or we could stop making clothes out of materials that shed microplastics. And
while we're at it, cotton too for the vast amounts of water it uses.
Industrial hemp and linen are far more sustainable options. Tencel looks like
a great replacement for cotton and uses wood cellulose.

~~~
spodek
Or we could stop making plastic.

Or at least the 90% of it making junk.

Even if we separate it, it still exists, as does basically all the plastic
we've ever produced. Even separated, at the rate we're producing it, wherever
we put it will overflow.

~~~
nitrogen
_wherever we put it will overflow._

The scarcity of landfill space is a myth sparked by the infamous "garbage
barge", which nobody accepted because it came from the NY mafia and was
getting too much attention, not because there was no room for it.

[https://en.wikipedia.org/wiki/Mobro_4000](https://en.wikipedia.org/wiki/Mobro_4000)

This Planet Money episode is a good listen:
[https://www.npr.org/2019/07/09/739893511/episode-925-a-mob-b...](https://www.npr.org/2019/07/09/739893511/episode-925-a-mob-
boss-a-garbage-boat-and-why-we-recycle)

~~~
spodek
If only it all made it to landfills, but the most polluted spots on Earth
include south sea islands thousands of miles from population centers, ocean
gyres, and so on.

Once you make something unhealthy, to suggest that (leaky) places to put some
of them are abundant misses the point. They're unhealthy and the overwhelming
majority unnecessary.

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seriesf
I've never owned a polyester garment that could be washed in water. Aren't
they all dry-clean only? Blends (like denim) I can see but in general it seems
like people just wash their clothes too often and use the machine too much
instead of hand-washing.

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14
No I just checked and many clothes like jackets, swim shorts and blue jeans
the first 2 on the list made from 100% polyester are supposed to be machine
washed. Save yourself some money and throw that clothing in the wash machine
on delicate and you should be fine.

