There is a fundamental minimum amount of energy needed to desalinate: you can't take less energy to do it,than you could gain back (from osmotic pressure) if you allowed the desalinated water to expand a cylinder containing the residual brine. This is large. This paper is a thermal method, so it doesn't have an electricity input, but to justify their efficiency claim, they should really compare against what you could do by using the same surface area for solar panels, driving a conventional setup. My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.
This paper is interesting, however, in directly producing crystalline salt, which is lower volume than brine and easier to dispose of, maybe even valuable.
The paper: [1]
They're still at lab scale in glass. They haven't built a usable system, even a small one. The big claim here is that it doesn't clog; capillary action moves the salt out of the active area to another area, where some yet to be developed mechanism removes it. That needs to be demonstrated. If they can come up with something that runs for years without clogging or replacing the active material, that's a real advance.
Laser surface preparation is known.[2] It's useful for roughening smooth surfaces in a very structured way, in preparation for painting. The result is a smooth paint surface. If you sandblast to roughen, the first paint layer is somewhat irregular. Then you need to sand and paint again to get a smooth surface. Laser roughening has been tried for auto painting, but didn't go mainstream. A good question here is whether commercial laser surface prep systems can make the material this new process uses.
It reminds me of how the Panama canal was built, and actually the first major attempt failed and they gave up. What they learned for the second attempt was that digging was not the hard(est) part to solve - it was how to move the dirt! So much dirt!
Great book on this BTW: Path Between the Seas. I couldn't put it down.
Fragility is a common problem in surface treatments, sometimes called "nanotechnology". There are super hydrophobic surface treatments that are very effective. They generate a surface which is a forest of tiny sharp points. The surface tension of water is too high to cling to such a surface. You can make something that just will not get wet. The problem is that the points are fragile, and wear destroys the effect.
Another example is ultra black coatings. Those are a forest of tiny black objects arranged so that light gets reflected multiple times and is absorbed. The commercial version is called "Vantablack". It doesn't wear well, but for optical applications such as the insides of camera lenses and telescopes, that's fine.
It's such a good book! Like any dad reading history, I have been annoying my family for years with fun facts I learned in that book. David McCullough's other books like The Great Bridge (about building the Brooklyn Bridge) are also great.
You and I are the same person apparently. Let me tell you about malaria! Or the bends! Or tetanus! Please! Wait, where's everybody going?
This is an interesting tech, but I have big doubts. In the picture you can see some salt coating the surface. Even just a little seems like too much for this type of system. I really hope they can make this work and scale this up.
This appears to be the same New Rochester article as 4 days ago with 20 comments.
>> The solar-powered system uses specially engineered black metal to absorb sunlight.
The new system replaces the earlier version that used specially engineered death metal.
Which was a big upgrade from the prior system which just used a heavy rock.
Awesome, love seeing stuff out of Rochester - RIT or UofR or any of the nearby schools.
Totally underrated area for academic pursuits.
UofR physic grad that also worked at the LLE here. Agree Rochester schools are underrated (although admittedly a little biased).
At least in the sciences you have access to lots of opportunities you don’t have at bigger name schools.
They set me up in life in a way that I don’t think would have happened elsewhere.
I had a great time at UR in the early 90’s because they had the most computing hardware per interested student in the country. I was able to relatively quickly work my way up to access to pretty much any system the school owned that I wanted, including the Cray at the LLE.
Indeed, it’s the same university that gave us room temperature superconductors.
As an RIT alum, I tend to agree.
Agree! Shout out to the Laboratory for Laser Energetics
RIT is pretty well known as a good school I believe.
I am wondering if they combined photomolecular effect[1] to make it even more energy-efficient
[1] https://news.mit.edu/2024/how-light-can-vaporize-water-witho...
So crazy question: take a dehumidifier, attach some solar panels, and deploy at scale for non-potable water suitable for crop irrigation anywhere that isn't a desert. Does it work? And if not, why?
It takes too much energy and produces water too slowly to scale. In general any area with sufficient moisture in the air to explore this also has easier access to rain and ground water.
Great point, in my case in the PNW, the water from my local well is infested with manganese (as in clogging the household plumbing in the absence of a sediment filter) and other contaminants and the water company providing it is owned by private equity. Legally, I can drill my own well for non-potable irrigation, but god forbid I filter and/or chlorinate it for my own household use. So I end up considering options like this, thanks for debunking.
You don't need to chlorinate water from your own well, unless maybe you have a cistern that you are filling for storage.
And who's going to know if you are drinking it or watering your garden?
I vacillate between trusting my well and trusting my RO (10,5,1 micron filters, plus the membrane). But it isn't healthy to drink RO all the time and I don't wanna mess with remineralization.
My well is 100' and 13 years old.
The short answer is all those problems have already been solved.
Israel desalinates 75-85% of its drinking water. The problem is political and economic dysfunction.
California for example could be doing widespread desalination with nuclear power and technology from the 1970s. They could also greatly expand reservoirs and waterways, but don’t do it. Very similar to Rome in the 400s, when people were using aqueducts built by a past civilization but lost the ability to construct them.
It "works" in the sense that this is what 99% of "Get water from air" scams are.
The reason it doesn't actually work is that it is extremely inefficient. Getting water to condense requires you to somehow reject massive quantities of heat. That's fundamental to physics.
Also, literally anywhere a dehumidifier is reasonably effective, is humid and usually doesn't have such dire water problems. Deserts have extremely low humidity and dehumidifiers working in a desert will produce very little water.
Even a good humidifier in a humid environment is burning KW to generate on the order of ten liters of water a day.
There are a couple places on earth that are essentially deserts but have an early morning humid fog roll through regularly, and those places figured out capturing that water in the air long long before we invented the refrigeration cycle.
It is literally cheaper to desalinate.
Maybe you could build giant greenhouses to fill with sea water and let the sun evaporate the water and collect that with a dehumidifier? Still absurdly inefficient. Water has such an obscene specific capacity for heat that any thermal avenue of separating it from something else will use immense energy.
The humid areas where they might work probably already have a lot of water?
What do you mean work? No, because there is no single dehumidifier on the market that will get you enough water, so you are out $80 grand, you could have just paid for water delivery.
Always wondered why the coast of the Red Sea isn't littered with channels which get flooded with seawater, which then evpporate into glassed ceilings; creating freshwater, and leaving behind salts for mining.
Sand -> Glass -> heated saltwater -> freshwater + minerals -> ??? -> profit?
Combined with some mangrove farms, surely desert coasts are able to support more life.
Wonder if this is scalable tech, and how quickly it can 'process' water. I guess if they're combined with transparent solar panels, it could be quite an epic tech.
Slightly different idea to take Red Sea water, concentrate it, and flow into the Dead Sea to stabilize the water level in the Dead Sea which is a big problem. A billion or so was spent but the project is on hold for some combination of financial, political and environmental issues.
https://en.wikipedia.org/wiki/Red_Sea%E2%80%93Dead_Sea_Water...
I love projects like this. A shame the west has handed over the baton to the Chinese and Saudis when it comes to actually being daring with megaprojects.
Some over stuff whhich are cool to read about:
Redirecting Siberian rivers into Central Asia https://en.wikipedia.org/wiki/Northern_river_reversal
Redirecting Congo basin rivers to replenish Lake Chad https://en.wikipedia.org/wiki/Lake_Chad_replenishment_projec...
Filling in a depression in Egyptian Sahara desert and fllooding it with Mediterrraanean water to generate huuuuuuuuuuuuge hydro https://en.wikipedia.org/wiki/Qattara_Depression_Project
(Similar ideas proposed for Lake Eyre, the lakes in Tunisia, and the Afar Depression in Djibouti, too).
The Saudis aren't "daring" with megaprojects. They're fucking[1] stupid[2]. Saying their megaprojects are "daring" is like saying I'm "daring" for claiming I'm going to build a catapult that will launch me to the moon.
A comparison that only works if you say it and sink a few billion into foundations for said catapult.
If you've ever been to the beach, you can smell the salt air and rotting seaweed and hear the birds.
It's all gonna get on the glass (from above and below), and eventually the salt left behind is going to build up. The salt left behind is very hard on any structure or machinery used to move it which makes repairing the large glass enclosure a pain. All this for a slow trickle of water is generally not worth it.
The Saudis were fucking around with the idea of solar domes at one point. Haven't heard anything about it for a while though (probably due to maths, lol). A shame, I've always been fascinated by Egypt and the empty expanses of nothingness. On long bus journeys around the country, the imagination can run wild.
https://www.solarwaterplc.com/featured-news/whats-inside-thi...
The issue with that idea is very simple - creating those inlets into the desert would risk soil erosion - in the desert. If your objective was to desalinate water, you're much better off using conventional desalination (there's still way more room to work around here first, like better and sustainable membranes, etc.) and offsetting your emissions by locking carbon away in mangrove reserves, which are native to those desert coasts.
They are talking about lithium recovery, but there is a less exotic byproduct I'm interested in. One tonne (≈ 1 m^3) of seawater contains about 1.3 kilograms of magnesium, equivalent to about 4 kg of magnesite ore. Typical desal prices are on the order of $1 per tonne. Magnesite ore goes for about $100 per tonne, so the crude magnesium in a tonne of seawater is worth about $0.40, which could account for a substantial fraction of the desalination cost. (These numbers are very rough.)
Now you ask: why don't we just recover magnesium from brines if it's so great? Magnesium recovery from seawater isn't that easy: typically you have to treat it with some kind of alkali (often Ca(OH)2), so the cost is dominated by the extraction process (your alkali is consumed!), and you're competing with a pretty cheap ore. But if you have a solid byproduct, instead of a liquid, the options for magnesium recovery might be a lot more efficient, potentially offsetting the cost.
The fourth-most-prevalent ion, sulfate, might also be interesting, at least in a hypothetical post-petroleum future where sulfur as a byproduct of fossil fuel extraction is no longer "free". Sulfate is also annoying to extract from seawater, but again if we have a solid, the rules change.
As for the "table" salt itself, I think we'd quickly saturate (!) the market.
Calcining Mg(OH)₂ -which is what you find in seawater - converts the soft compound into magnesium oxide, a valuable mineral commonly used in refractories, catalysts, and ceramics.The Chemical Equation: \(Mg(OH)_2 \xrightarrow{\Delta} MgO + H_2O\)Temperature Requirements: You need to heat the magnesium hydroxide to a temperature range between 500°C and 900°C. Heating at the lower end (around 500°C) yields a highly reactive, porous form of nano-MgO, while heating above 1,200°C creates "dead-burned" MgO used in high-heat industrial bricks.The Yield: The weight of your final MgO product will be roughly 69% of the original Mg(OH)₂ mass, as the evaporated water accounts for the 31% weight difference. Already energy intensive. To get to magnesium ore is another step.
>Calcining Mg(OH)₂ -which is what you find in seawater
I'm not sure what to say, because it looks like you are copy-pasting from Wikipedia or something like that. Anyway, Mg(OH)2 is not found in seawater. Mg2+ is found as a dissociated ion. When you dry it, it mostly becomes MgCl2 with a little MgSO4. Mg(OH)2 is produced from seawater by the alkaline extraction process I mentioned before, and the process in TFA is interesting because it might be better.
Also, nobody would ever make magnesite ore. I referenced magnesium ore prices to estimate the value of the magnesium-as-ore in sea salt, because using finished magnesium prices would be misleading. Magnesium is mostly consumed either as the metal or as the oxide in cements and ceramics.
…but needs a specially engineered piece of metal…
After looking at the paper, this looks like the core result:
“We collected a total of 9.3 g freshwater along with 0.343 g of sea salt from the ABF-STIC with a 9 cm2 surface area over the course of 9 hours. This is equivalent to generating 10.33 liters m−2 of freshwater and 0.38 kg m−2 of sea salt per day. The salinity of the desalinated water is found well below the WHO and EPA standards for safe drinking water.”
However the enclosure system required looks rather complicated and might be sensitive to external temperature (maybe a solar PV-powered cooling loop would help) and I imagine the cost-per-square-meter of the material is rather high, so this looks more like something for emergency response situations or maybe a desal system for a mega-yacht. If it could be scaled the idea is interesting, maybe as lithium separation from concentrated geological brines?
> The solar-powered system uses specially engineered black metal to absorb sunlight.
Brutal. 𖤐 \m/ 𖤐
If true then this might be indeed a game changer, but numerous academic publications turned out to be unfit for upscaling.
Who all has access to a femto laser? As far as I know these are all patented, and most of those patents (or at the least companies with rights to production) are in the USA, according to a professor who told us so some years ago in university (in central Europe, but he is quite old already, so I am not sure if his information was 100% up to date; but otherwise I do not doubt the validity of his claim made). So someone is going to milk rather than help. Will be interesting to see what happens to that in some years. My current guesstimate is that nothing will really happen or change.
Probably some of the best news I've seen in a while.
I’m not even going to night clicking on a title that is clearly a load of bullshit.
I suppose you could water down the ocean water it’ll was drinkable, or like just add half a teaspoon of sea water to a cup or drinking water.
Buy all work done eventually decades in to waste heat.
> without waste
...except for the huge piles of salt.
If the salt was not waste, surely people would already be extracting it from the brine and the existing methods would also be "without waste".
Persian Gulf has 20% more salt in water because of the humans which are throwing the oversalinated waste back into the sea. Dehidrated salt may be a big deal for some areas because of no waste into input.
>Persian Gulf has 20% more salt in water because of the humans
I would like to read more about this from an authoritative source.
Through the magic of Googling "Persian Gulf salinity" it seems like it's more that it's a shallow Gulf in a dry area so it has significant evaporation. Desalination does effect it but it's only a few percent of the total evaporation (which is still surprisingly big) and doesn't sound like the main driving factor or an imminent ecological concern.
https://www.frontiersin.org/journals/marine-science/articles...
https://www.sciencedirect.com/science/article/abs/pii/S14635...
Huh, looks like they process about 1/500 of the water in it every year. So enough to make a dent in the salinity eventually.
If salt and water flow in but only water flows out you will be left with salt. Same reason that concentrated brine comes out of a desalination plant, or that the dead sea is what it is.
I thought the HN-way was to be more charitable than just directly calling out obvious bullshit.
The brine is waste, and the dehydrated salt is also waste. Maybe dry waste is better, but it's still waste.
Can we please ban university press releases
why
What about removing oil from water, have we conquered that yet?
you can now extract (like mining) minerals from the ocean, sounds kind of dangerous for the ecosystem maybe? making it profitable to extract magnesium, lithium, salt... we can probably guess how this story goes.
i'm hoping it doesn't scale, honestly.
You're worried we might use all the salt in the sea for some kind of ... salt pyramids, send the water back out through sewers, and consequently leave the world's oceans diluted? That's about 1 followed by 21 zeroes, I think, in liters.
no, just take the water, remove the salt & minerals. Over time it'll dilute. Water falls again in the form of rain, obviously, but not the salt.
You're not worried? If it's for batteries? For sure they'll extract whatever they can.
Right, remove the salt and minerals. We don't need that much salt, so we'd have to build pyramids or something with it. We drink the water, but then it ends up back in the oceans. The reason I mention that part is because if it didn't, if we could destroy the water, then the remaining water would retain the same salinity, and the concern would be that we drain the ocean dry, which is silly (I refer you back to how big it is). But we don't destroy water when we use it, so instead the worry is that we dilute all the world's ocean, which is also silly (I again refer you back to how big it is). We need a lot of batteries, but the sea is not useful as a source of lithium except as a byproduct. Even if it was the only source, the old batteries themselves would soon become a better source, as concentrated stores of lithium compared to the very-much-not-concentrated lithium in the ocean. But anyway the good places to mine lithium are on land (and are dried-up bits of ancient ocean, I think).
(I checked, some deposits are old lakebeds like https://en.wikipedia.org/wiki/Salar_de_Uyuni and others are igneous.)
It's also possible - true, I bet - that all the car batteries and storage batteries 8 billion people could possibly use are equivalent to only a tiny fraction of all the lithium in the ocean, but it would be harder arithmetic to confirm that, as well as being irrelevant on account of land-based mines existing.
Someone above said 4kg of magnesium per ton of seawater. Apparently lithium is 0.18g per ton of seawater.
That still means there's billions of tons of lithium in the seas, though.
You're wildly underestimating the scale of the ocean. If we could extract all our necessary minerals from it rather than mining them that would alleviate a huge cause of environmental damage.
This reads like hyperbole:
> The brine byproduct wreaks havoc on sea life when it’s deposited back into the ocean by raising the salt level and lowering oxygen in the water.
Managing return of concentrated brine should be entirely tractable in the literal ocean.
Sure, but typically desalination plants are located in a single physical place, so a discharge pipe dumping brine 24x7 is bad for all of the things around it, as the local concentration is extremely high.
Seems like you could run a long perforated tube to diminish that effect.
I wonder what the linear diffusion gradient would look like for that. Like the perforated garden hoses or whatever for soaking soil. Aquatic organisms grow so quick though very curious on the constraints for something like this.
I liked the idea of loading it up on a ship that sails out releasing as it goes out and back. Make it solar powered or even go old school with literal sails.
Ships wouldn't need a long submerged pipe. It'd just need a small hole like a bilge drain or maybe a live well on a fishing boat. Just let the boat cruise around slowly draining back into the ocean.
As for surface life, I'm no oceanographer, but is that really the most vulnerable place? The surface is where fresh water rain meets the ocean, so that would dilute the salinity during storms. However, there's nothing to say that another pump couldn't be pulling from the ocean and mixing the brine into that so it's diluted before and not just pouring brine straight into the ocean
I like this! Though I’m not sure the math works. That page says ideal efficiency for that system would be something like 0.75 kWh/m^3. Compared to 4000 to 5000 kWh/m^3 of diesel. Now we don’t need to be efficient since the point is to use up our “fuel” and we don’t need to cary cargo for this to make sense but with numbers like that, I don’t think our boat will be able to make enough power to move at all.
And it doesn't even need to be a rigid pipe. A flexible pipe made out of, say, waterproof fabric, could be cheaply made to extend miles while remaining open due to the pressure of the water pumped into it.
Things left underwater tend to collect things on it which would make this much less porous over time.
The short version is brine is weird: it's surprisingly resistant to diffusing and tends to flow more like an immisicible fluid. So you have to put quite a lot of effort into getting it to actually disperse rather then just fall to the seafloor.
That's silly, you'd mechanically mix it with seawater rather than wait for it to diffuse. The concern would be the volume of desalinated water extracted from the local region versus the flux from ocean current. As long as that ratio is acceptable there won't be any long term problem.
Alternatively, in the absence of sensible regulations a cutthroat operator devoid of ethics constructs a plant that dumps concentrated brine in the immediate vicinity because that's the cheapest approach. Then reactionary elements raise talking points about environmental damage and pretend that it's a difficult problem to solve. Business as usual.
The brine thing is just a way to shut down conversation and let people feel superior for claiming there are no solutions to our problems except to reduce our standard of living.
It’s obvious you can safely put salt back into the ocean with enough dilution. I bet a middle schooler could design a system to do it.
It kinda depends where it's deposited, right? The expected AMOC collapse is fundamentally about salt imbalance.
depends of course, how easy does the brine dissolve, how long does it take that it is so diluted that it can't do any harm, without that information it's not easy to tell
These are often built near shallower parts along the coast where changes are more pronounced.
I mean.. we really want to permanently desalinate the ocean somewhat too so putting the brine back seems kinda stupid. Put it on land, let it dry, sell some as table salt and dump the rest into abandoned mines.
Excellent idea! The largest abandoned mines I'm aware of are salt mines, which… hang on.
Thermal methods require energy, it seems like this substrate is effective at maintaining its solar-thermal absorbing properties better than a material that will attract salts
> Testing their solar-thermal desalination technique using samples of water from the Pacific, Atlantic, and Indian Oceans, Guo and his team were able to make the surface self-cleaning. In other words, it extracted freshwater and directed the remaining salts to the passive region where they could be later collected without reducing the panel’s efficiency.
This is not "large" this is a moderate improvement. Albedo is likely only marginally affected, and the solar power input over area is the same.
Depending on this cost of this process it could very likely be a wash in terms of NPV
If this can be applied to mine effluent, you could replace the maybe with most certainly. Sulfuric acid effluent lakes leech all sorts of valuable metals out of the ground.
Brine is very easy to dispose of: you just pump it back to where it came from. Solid crystalline salt, on the other hand, is a hassle.
> Brine is very easy to dispose of: you just pump it back to where it came from.
Easy, but not necessarily good for the spot you're pumping concentrated salt back into.
If you use fat pipes that go a decent distance from shore, diluting your brine with ocean water, you’ll have a negligible impact on the ocean. The problem is if you dump lots of brine in shallow waters. Old designs did have that flaw, but it’s not that difficult to design around this constraint now that we know about it.
IMO this is an issue where NIMBYs are using environmental concerns as a smokescreen to block new desal plants from ruining the vibe at their beachfront property. Rhymes with the opposition against offshore wind farms.
I can probably be convinced pretty easily with some evidence of that, but you’ll never convince the contingent who is convinced it’ll kill sea life at any concentration or location, so, being able to shut them up by saying “we have no wastewater, we load rail cars with crunchy salt and use it for stuff” still has value.
Yeah. Worrying about salt in the sea is like worrying about oxygen in the air. Can too much oxygen in the air sometimes be a problem? Yeah, in some corner cases. Is it a major problem that we can't solve? Not at all.
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The brine came from the ocean. So just dilute it back to close to ambient salinity using municipal waste water that you are discharging anyway.
> Sure, and enriched uranium comes from the ground
Uranium can also come from the ocean water (there is, apparently, quite a lot of it in there, relatively speaking). Japan experimented with the technology in the nineties, but it really was much cheaper to just mine it from the ground, so they abandoned it.
Enriched uranium is perfectly safe to dump but it would be stupid to do so. Fission products are nasty but uranium itself is not, comparatively.
The analogy would be if you "un-enrich" it. Then it's safe. Or at least no worse than when you took it out of the ground.
except for the pharmaceuticals anyway
Actually it's easy and ok. Just mix it with the treated sewage right before it returns. Simple mass action implies the salinity hasn't changed.
But wait! There's water mass loss due to leaky pipes and outdoor pools!
Mixing salt water and brine is perfectly ok. Just use a phase diagram.
Maybe, but dumping crystalline salt is even worse to the spot you’re dumping it on.
Yes, that's my point: if you're next to the ocean, disposing of brine is extremely easy.
Even better, just package it up and eat it instead of digging underground and creating more pollution.
It's not every day that industrial waste happens to be not only edible but also tasty. Too tasty, in fact. Salt is addictive.
I wonder. It would have to dissolve, a big block of salt would take a while, kind of like the erosion of cliffs where the salt comes from in the first place. Eh, I guess you're right though, the fish wouldn't like that at all.
Why? Just build mountains out of it and maybe even open a salt-ski park in the tropics for people who don't have snow.
There are salt mountains lining most midwestern freeways as it is for winter.
I just realized that future archaeologists will be tracing our roads using the salt residue!
I think I read somewhere that salt can be used as energy storage medium? So we could get both water and batteries for renewal energy.
It’s about thermal storage, you don’t use table/sea salt for that, and you don’t need a lot of salt, because the salt is in a closed loop; it’s not being consumed.
If you read the article you sent me, you'll learn that, just as I said, you don't use sodium chloride, aka table salt, aka sea salt, for these purposes.
> Solid crystalline salt, on the other hand, is a hassle.
Just put it on your fries.
In an ideal world that crystalline salt by product could be used to offset any imported or mined salt, further reducing the environmental impact of those operations.
"Solid crystalline salt, on the other hand, is a hassle."
Just make prettier-than-Himalayan salt lamps out of it and sell it to hippies. Easy solution.
yeah, if you like to kill everything in a few 100 feet radius and kill some more in the zone of reliance.
this is delusional ecological
So, we could just dump it on the salt flats in Utah? Plenty of places are already super salty, so nothing lives there (unless it’s able to handle that).
Brine might be bad to the place you dump into, but crystalline salt is even worse.
Overall though, it’s just such a tiny concern. Ocean is huge. If we kill everything in a 100 foot radius, that’s 0.0000000008% of the ocean being destroyed. Less than a drop in a bucket.
> My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.
RO is about 2-4x the theoretical minimum, depending on how much water you're willing to reject.
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