Sound waves used to separate microplastics from laundry wastewater | Hacker News Reader

Sound waves used to separate microplastics from laundry wastewater

newatlas.com

171 pointselorant44 comments

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 :)

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/

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.

> 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.)

The full text of the study that Cora Ball cites is available at the lead author's website: https://rochmanlab.files.wordpress.com/2019/01/mcilwraith-et...

From the paper:

> We observed no significant reduction of microfibers by weight with the Cora Ball compared to the control.

Check out figures 2, 3 and 4.

It turns out that the cited 26% number is only for the number of fibers removed. Oddly, in the same experiments, there was no significant decrease in the mass of microfibers, or the length of the remaining fibers when using the Cora ball (but there was a > 80% decrease in both number and mass of fibers when using a product that actually filters lint out of the wastewater.

My read of this study is the the 26% number may not be reliable. The reported p-value was near 0.05, which means it would not be too surprising if the difference between Cora Ball and control was due to expected experimental variation.

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

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?

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

https://en.wikipedia.org/wiki/Cymatics

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

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

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

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

Agreed, so cool! And good point. Here's to finding a way to keep micro-plastics out of the ocean altogether, for the sake of marine life, humanity and the planet.

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

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

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.

What do you mean "take care of itself"?

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.

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

Where in the FA does it talk about using it in the ocean?

washing machine waste water goes to rivers, rivers go to oceans

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?

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

What other applications for this could there be?

Filtering beer?

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.

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

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.

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?

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.

Note To Future Self:

There's an interesting Physics question posed here, which looks something like this:

If resonant waves, in this case of sound, can cause particles of different sizes to move towards the nodes or anti-nodes of standing waves, then if we consider a completely different area of physics, that is, the case of electroplating metals with electricity, that is, we have an electrode of metal A (for example, Copper), and an electrode of metal B (for example, Gold), in some electrolyte, for example, salt water, then does the electroplating procedure (via electricity) mimic what's happening to the microplastics in water, via sound waves, but just at a smaller wave scale?

In other words, maybe electricity does the same thing as what happens to the sound/microplastics -- but the electricity is a wave which is much faster in frequency, and much smaller?

Now, there's another aspect of all of this too. See, if we can get conglomeration or dissipation of microplastics via the use of sound, then perhaps this mimics the creation or destruction of matter (well, let's say 'particles' at this point, "smaller pieces of matter"), that is, the "clumps" of less rarified/more dense substances inside of more rarified/less dense substances...

Anyway, the principle at work here might be the starting point for Star Trek's food replicator... maybe this is Star Trek's Food Replicator version 0.000000001 (just applied to plastic particles in water, not food/matter particles from air, obviously... <g>)

Note: I don't claim any correctness in the ideas presented above; merely that more experimentation/research might need to be done... see the "Note To Future" self part...<g>

See Chladni plates.

https://en.wikipedia.org/wiki/Ernst_Chladni#Chladni_figures

https://duckduckgo.com/?q=Chladni+&t=ffsb&atb=v60-1&iax=vide...

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.

Cotton is softer than hemp and it's lighter than hemp. And unlike either of them, cotton is slightly elastic.

If you've ever had linen sheets you know that they get softer and looser over time.

There are companies that specialise in making clothing out of flax, but a quick look at their designs showcase just how bad linen is for clothing. The only linen garments that resemble the cut / silhouette of their standard counterparts are blouses and dresses.

I'd love to see a comparison of water required to make a square yard of cotton textile vs rayon (tencel is a form of rayon)

I don’t care about technical qualities, for me I find hemp cloth to be far more comfortable to wear. Softer on the skin, longer wearing, easier to wash and iron.

I go out of my way to get hemp clothing, especially when the options are cotton/plastic blends.

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.

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

This Planet Money episode is a good listen: https://www.npr.org/2019/07/09/739893511/episode-925-a-mob-b...

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.

Or we can chill out, enjoy the time we have left here and let nature take its course. There is no promise from nature that humanity need exist, nor that it need keep existing. Yes we can add 10% to our lifespan by getting ourselves all worked up over microplastics and climate change but the universe still wins in the long run.

I'm no expert, but I always figured that environmental sustainability would help humanity a bit more than a 10% boost in lifespan.

In Europe (yes, generalizing an entire continent) we generally avoid landfills and instead burn anything nontoxic that doesn't go to recycling. It's a great way to produce electricity and have all produced gases in one place where you can filter them. Plastic burns just fine. Obviously we try to recycle it first, but a lot of it still ends up burned. The ash that's left over is used in construction, but plastic doesn't even leave ash.

From what I've been told, that's basically the plastic industry's philosophy: it was energy that took a side trip as a bottle on the way to the furnace.

But, do what you want with that anecdote (toxic, wasteful, unsustainable, etc)

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.

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.

I'm no expert but it seems highly likely to me that you have owned polyester. Do you own socks? Jeans or shirts? A jacket? A throw blanket? So many things are poly blends or have polyester components. Unless you are explicitly checking every label, if you are just buying clothes, you are buying polyester.

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