this post was submitted on 28 Sep 2023
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Engineers at MIT and in China are aiming to turn seawater into drinking water with a completely passive device that is inspired by the ocean, and powered by the sun.

In a paper appearing today in the journal Joule, the team outlines the design for a new solar desalination system that takes in saltwater and heats it with natural sunlight.

The researchers estimate that if the system is scaled up to the size of a small suitcase, it could produce about 4 to 6 liters of drinking water per hour and last several years before requiring replacement parts. At this scale and performance, the system could produce drinking water at a rate and price that is cheaper than tap water.

https://www.cell.com/joule/fulltext/S2542-4351(23)00360-4

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[–] [email protected] 79 points 1 year ago (21 children)

Article doesn't mention what the unit does with the salt waste.

I support this 100%, but desalination presents a unique problem: what do we do with all the salt? Maybe the unit uses it for something, but otherwise it just miniaturizes a problem that we're already working on.

[–] [email protected] 39 points 1 year ago* (last edited 1 year ago) (1 children)

If this works, it's better than anything we have , which costs grid energy and dumps brine all the same. If anything, the smaller scale makes it easier to distribute and dilute the output brine.

[–] [email protected] 17 points 1 year ago (14 children)

If sea levels rise as much as they're supposed to, this will be an invaluable tool for an enormous proportion of the country. My concern comes from capitalism getting its hooks into this.

[–] [email protected] 7 points 1 year ago

Wait what country?

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[–] [email protected] 24 points 1 year ago (13 children)

Evaporate it to solid, store it if need be, or distribute it back into the sea in absorbable chunks. The water's ending up back in the sea eventually anyway, see water cycle, so it should be zero sum, just need to avoid local overloads. Seems eminently solvable.

[–] [email protected] 20 points 1 year ago

Depending on the desalination method, you can also harvest lithium while your at it.

[–] [email protected] 13 points 1 year ago (2 children)

Sounds so easy for you but what to do with the excess salt is the only real problem with desalination that we have for decades now. It's not easy to solve.

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[–] [email protected] 10 points 1 year ago (4 children)

Don’t you just dump it back in the sea? Diluting should make this a minor issue right?

[–] [email protected] 21 points 1 year ago (7 children)

That's what I always thought, but the local effects of hypersalinated water can be terrible for any nearby life

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[–] [email protected] 51 points 1 year ago (7 children)

This sounds fantastic on its face, but I seem to keep on hearing about how desalination will solve all kinds of problems and we still have this particular problem.

The missing piece, it seems, is the will for it to be used as infra at scale. Meanwhile selling bottled water taken for free from public lands for several dollars a liter in single-use bottles remains a multi-billion dollar industry. (an industry, I might add, that is aggressive about lobbying to protect its interests)

[–] [email protected] 33 points 1 year ago (1 children)

Devices like this are a lifeline for communities in developing nations. Who are the first and worst affected by water shortages and salt water intrusions into their fresh water sources.

[–] [email protected] 8 points 1 year ago

Also the poorest and least likely to get the help from the people with the resources to help.

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[–] [email protected] 37 points 1 year ago (4 children)

cool, but the real cost of desalination is transporting the desalinated water upstream, which presumably would also need to be done here

[–] [email protected] 44 points 1 year ago (2 children)

Considering how many people live near the coast it would still be a huge step forward. Right now even for most coastal cities desalination isn't cost effective and they have to import water from inland.

And by not having to deliver as much water from inland to the coast that water can be distributed more for people living inland.

Yes, it's not going to make inhospitable areas liveable but it's not just "cool".

[–] [email protected] 7 points 1 year ago (8 children)

the issue with water networks is they work great when you have the source (usually dams) upstream, water essentially is gravity fed throughout the network with only some localised pumping for certain elevated locations. wastewater again gravity fed towards treatment plants at the lowest point (usually the ocean), so usually, its fairly efficient, despite still requiring enormous amounts of energy.

this doesnt solve that. it has the source where the end point is. the desalinated water needs to be pumped up, to then be gravity fed through the network. In some places, it is worth the cost and energy due to water scarcity, and im not knocking the technology. but claiming its cheaper than tap water is patently false because the distribution cost is far higher

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[–] [email protected] 12 points 1 year ago* (last edited 1 year ago)

True...otherwise it's reverse hydro, which could be done with surplus renewables at peak times, but not at more than 10km.. This is mostly aimed at coastal communities (and sustainable floating villages 😁)

...or you could say fuck it, go full Dutch and build wind turbines and reservoirs everywhere to get water to all crops and green deserts 😊.

[–] [email protected] 11 points 1 year ago (4 children)

Since this produces distilled water, I imagine you could use it to filter any water, not just saltwater. You'd still need to boil it to make sure it was free of pathogens, in either case, and add an appropriate amount of salts and minerals back in to make it potable for the long term.

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[–] [email protected] 31 points 1 year ago (4 children)

SONOFABIT*H, I've been working on a project exactly like this with my friend for a couple years. Hella congrats they got it done and working first but damn :'( I was too slow.

Imma go sadly crush some bugles with my face stones now

[–] [email protected] 52 points 1 year ago

Keep doing it anyway. They still haven't gotten to market, and I want choices when it comes to my post apocalyptic water suitcases.

[–] [email protected] 7 points 1 year ago

Zero reason to stop. Until this is put into practice it's just another article promising a future that isn't here.

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[–] [email protected] 20 points 1 year ago (1 children)
[–] [email protected] 13 points 1 year ago (7 children)

It's just a giant plastic bag. They catch the runoff with a giant cup.

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[–] [email protected] 20 points 1 year ago (5 children)

I feel like every week we hear about some huge breakthrough that is supposed to revolutionize clean drinking water technology and save the world, but nothing ever comes of it.

I know this stuff takes time to develop, and not every idea is going to work, but it would be nice if one of these things actually did pan out and start being useful to solve our drinking water issues.

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[–] [email protected] 20 points 1 year ago (7 children)

All this stuff is like planning to colonize mars before we stop destroying earth. There is plenty of water if we just stop fucking pumping it all out and wasting it.

[–] [email protected] 28 points 1 year ago (2 children)

We're past the point where we can stop it wholesale.

We already have aquifers barely holding on, we've lost major sources of fresh water already.

I'm all for climate action, but we also need to starting developing technologies for living in the bed we've made.

Folks keep talking about climate change like it's some future event. You are living through it right now.

[–] [email protected] 11 points 1 year ago (4 children)

you know how we can stop the massive drain on the aquifers? by not allowing everyone to tap it as much as they want, farmers will have to deal with 30% fewer yields on corn, Nestle 'n Co. will lose their money printer, but that's all we would need to save the American aquifers, to STOP FARMING INT THE DESERT

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[–] [email protected] 12 points 1 year ago

Clean freshwater isn’t evenly distributed across the world and it’s not easy or cheap to transport. This kind of tech can help the people that will be most impacted by climate change to survive.

[–] [email protected] 12 points 1 year ago (1 children)

All farmers growing cotton in the middle of the fucking desert along the colorado river basin disagree with you

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[–] [email protected] 9 points 1 year ago (2 children)

Years ago they said that the screen lense from discarded projection TVs could boil/desalinate water with nothing but sunlight and discarded junk. They could literally create entire desalination plants with nothing but junkyard scrap. They never did anything with that.

I think all these "desalination" projects are nothing but worthless attempts to get free money for research

[–] [email protected] 14 points 1 year ago (7 children)

What's wrong with desalination research? Water is essential to life, and most water on Earth is salinated. The practical value of this research is apparent, both for ships on sea and coastal regions. So I don't see how these attempts are "worthless", and how it would be bad if they receive more "free money".

The article talks about what could have been a challenge faced by the junkyard scrap model, and how they solved it:

Each stage contained an evaporator and a condenser that used heat from the sun to passively separate salt from incoming water. That design, which the team tested on the roof of an MIT building, efficiently converted the sun’s energy to evaporate water, which was then condensed into drinkable water. But the salt that was left over quickly accumulated as crystals that clogged the system after a few days. In a real-world setting, a user would have to place stages on a frequent basis, which would significantly increase the system’s overall cost.

In a follow-up effort, they devised a solution with a similar layered configuration, this time with an added feature that helped to circulate the incoming water as well as any leftover salt. While this design prevented salt from settling and accumulating on the device, it desalinated water at a relatively low rate.

In the latest iteration, the team believes it has landed on a design that achieves both a high water-production rate, and high salt rejection, meaning that the system can quickly and reliably produce drinking water for an extended period. The key to their new design is a combination of their two previous concepts: a multistage system of evaporators and condensers, that is also configured to boost the circulation of water — and salt — within each stage.

I'm not sure how much money is in desalination, but it's certainly an industry. If a group comes up with a new method, and then nothing happens with it, it's probably because it's either not that great after all, or not that cost effective.

Maybe a problem is that the countries where it's needed the most are not exactly the richest countries: https://ourworldindata.org/water-use-stress#what-share-of-freshwater-resources-do-we-use

several countries across the Middle East, North Africa & South Asia have extremely high levels of water stress. Many, such as Saudi Arabia, Egypt, United Arab Emirates, Syria, Pakistan, Libya have withdrawal rates well in excess of 100 percent — this means they are either extracting unsustainably from existing aquifer sources, or produce a large share of water from desalinisation.

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[–] [email protected] 8 points 1 year ago

Delete this before Nestle sees it.

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