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.
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.
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.
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.
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.
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.
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.
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.
"in mice". No, wait, that auto-reply is for cancer breakthrough.
Let me check, is that a wonderful battery ? Nope.. A promising fusion ? Neither...
Ok, so this must be the fourth kind of pseudo-wonder discovery that will maybe make it out of the lab in 20 years, if the research team managed to get scraps of funding while VC pick the next way to waste pensioners money.
Anyway, whenever they have desalinated enough water to get each researcher a pint, the round is on me.
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.
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.
I thought they tend to pipe far out and discharge as far below the surface as possible, since there is a lot of surface life and it is less damaging this way.
Ships (with long submerged pipes) would be prone to weather events and generally less reliable than an installed pipe. Perforation would be prone to clogging from build up so a nonstarter I would expect. Adding flex tubing and a relocation robot would be a maintenance headache as well. Not sure there is an easy optimization.
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.
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
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.
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.
[1] https://www.nature.com/articles/s41377-026-02315-4
[2] https://www.youtube.com/watch?v=BKYOglHYo_Y
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.
This appears to be the same New Rochester article as 4 days ago with 20 comments.
https://news.ycombinator.com/item?id=48349507
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.
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.
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.
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.
Indeed, it’s the same university that gave us room temperature superconductors.
Agree! Shout out to the Laboratory for Laser Energetics
Probably some of the best news I've seen in a while.
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.
Can we please ban university press releases
What about removing oil from water, have we conquered that yet?
> 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...
I thought the HN-way was to be more charitable than just directly calling out obvious bullshit.
So now they'll throw the dehydrated brine into the sea?
Or set up an expensive refining operation to get heavy metals, etc out?
"in mice". No, wait, that auto-reply is for cancer breakthrough.
Let me check, is that a wonderful battery ? Nope.. A promising fusion ? Neither...
Ok, so this must be the fourth kind of pseudo-wonder discovery that will maybe make it out of the lab in 20 years, if the research team managed to get scraps of funding while VC pick the next way to waste pensioners money.
Anyway, whenever they have desalinated enough water to get each researcher a pint, the round is on me.
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.
I thought they tend to pipe far out and discharge as far below the surface as possible, since there is a lot of surface life and it is less damaging this way.
Ships (with long submerged pipes) would be prone to weather events and generally less reliable than an installed pipe. Perforation would be prone to clogging from build up so a nonstarter I would expect. Adding flex tubing and a relocation robot would be a maintenance headache as well. Not sure there is an easy optimization.
If you want to be really clever about it, maybe the ship is powered by the brine.
https://en.wikipedia.org/wiki/Osmotic_power
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.
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.