Posted by speckx 1 day ago
This paper is interesting, however, in directly producing crystalline salt, which is lower volume than brine and easier to dispose of, maybe even valuable.
ps. I have no clue what I'm talking about
Animals in the ocean of course do live without fresh water. Some of them just live off of water extracted directly from their food or from metabolizing that food, which produces water. Some animals have specialized cells that excrete salt so that can take in salt water and separate out the salt.
> 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
An RO desalination plant needs electric energy to drive the pumps, which might be generated by panels which are 15-20% efficient. So, if you can have cheap thermal desalination panels, they come out ahead even if 6x less energy eficient, you avoid the whole expensive and fragile desalination plant and you gain a low skill, distributed setup.
"Desalination system could produce freshwater that is cheaper than tap water" (2023) https://www.eurekalert.org/news-releases/1002811
ScholarlyArticle: "Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer" (2022) https://www.nature.com/articles/s41467-022-28457-8
"Solar-powered system offers a route to inexpensive desalination" (2022) https://news.mit.edu/2022/solar-desalination-system-inexpens...
Easy, but not necessarily good for the spot you're pumping concentrated salt back into.
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 think that problem was known (and discarded as not important) when the first serious water desalination plants were built.
Most of the carbon we spew into the atmosphere came from the air. Ancient plants took it in via respiration.
Sure, and enriched uranium comes from the ground, but that doesn't mean it's safe to dump it back in after the enrichment process!
> So just dilute it back to close to ambient salinity using municipal waste water…
Wouldn't it generally be easier to process that municipal waste water, as is already fairly common?
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.
If you think otherwise and you're not wrong, and I think you ARE not mistaken since this isn't the first time someone other than myself mentioned it here, that means they're making bombs because we in Japanese public aren't told about it. There has only been just some routine commentaries from local mayors at most.
It's a bit weird though that they have a graph of tons of uranium hexafluoride shipped that shows the last shipment in 2018 and nothing since then.
But you're doing that with the same water you're trying to make in the first place!
A phase diagram tells you exactly how far you need to go.
You know this makes more thermodynamic sense than carbon capture, right?
Just wait for the saltwater to come back around in the sewer.
But, so what? 30% sewage is still a strong dilluant... especially when mixed with more seawater
Im shocked how many people cannot grasp that you can dilute brine's salinity arbitrarily close to seawater's with energetically cheap pumps.
The advanced treatment stages take care of it. Between UV, ozone, and nanofiltration, etc. we can remove the pharmaceuticals.
Actually the problem is the water comes out too pure out of a well designed water reuse system, to the point where the mineral content can be too low and you need to add some back in.
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.
It's not every day that industrial waste happens to be not only edible but also tasty. Too tasty, in fact. Salt is addictive.
Ohio DOT's use of road salt would allow for fresh water to be provided for somewhere in the neighborhood of 160,000 people.
On one hand, that's nowhere near enough people; it's a small drop in a giant thirsty bucket of water consumption. So we'll still need salt mountains, salt re-distribution vessels, and/or other ways to deal with excess salt.
On the other hand, 160k is a lot of humans. So perhaps we should look into doing things like this anyway.
(But we probably won't. Ohio gets road salt primarily from a mine under Lake Erie that has a very conveniently-located terminus near downtown Cleveland. The mine directly loads trucks, freight trains, and ships...and it's near the point of use already. It's pretty efficient.)
Come on guys please at least attempt to think what you’re about to type, please, I beg you.
Just put it on your fries.
Just make prettier-than-Himalayan salt lamps out of it and sell it to hippies. Easy solution.
this is delusional ecological
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.
RO is about 2-4x the theoretical minimum, depending on how much water you're willing to reject.
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.
Great book on this BTW: Path Between the Seas. I couldn't put it down.
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.
Another MIT paper on desalination from 2024 has a more conventional electrically powered system that can adjust its operating speed depending on how much power is coming in. So it can run off intermittent power sources such as its own solar panels.[3] Rather than buffering the energy with batteries, just buffer the water in a tank. This made it to field test and has some efficiency numbers.
It's annoying to see these one-off announcements with no followup. A short note a year later reporting why there's no further work would be useful to later workers.
[1] https://news.mit.edu/2023/desalination-system-could-produce-...
[2] https://drl.mit.edu/publications/journal/
[3] https://www.greenmemag.com/science-technology/breakthrough-m...
Obviously it needs to be cleaned regularly otherwise the salt encroaches into the sensitive bits. However the cleaning method doesn't require dissolving, just scraping.
The new system replaces the earlier version that used specially engineered death metal.
Totally underrated area for academic pursuits.
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.
Slow it down from trickling down a slope and you have two things: more vegetation (which also retains water) and more time for that water to penetrate the ground for local wells.
You can completely "terraform" a desertic region https://youtube.com/shorts/cfhbtgon4Nk?is=oAExB5UeMAsShBux
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.
Solar on the other hand is very cheap, and you don't need to desalinate 24/7 -- just do it when power is cheapest (which is during the sunny times if you have large amounts of solar, during windy if you have large amounts of wind, etc)
The good news in a desert: plenty of sunshine. So you can generate a lot of electricity with some cheap solar panels, there is plenty of space to put some down, and there aren't a lot of NIMBYs around to complicate the permitting process for that.
Some desert ecosystems actually depend on condensation with specialized plants and animals harvesting humidity from ocean breeze. Large parts of e.g. the Sahara border on the Atlantic ocean. Lots of water in the air but not a lot of rain. And even if humidity is low, there still is some water in the air usually.
But the simple fact of course is that there is a lot more water in water than there is in air. If you want to extract meaningful amounts of water from air, you need to process a lot of it.
And who's going to know if you are drinking it or watering your garden?
My well is 100' and 13 years old.
It also requires more infrastructure to get yield. In theory all you'd need to have is these etched metal plates, a transparent dome and a source of briny water. (and a cleaning mechanism)
The etched plates creates 100% humidity (probably more as it'll condense out)
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.
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.
https://en.wikipedia.org/wiki/Red_Sea%E2%80%93Dead_Sea_Water...
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).
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.
https://www.solarwaterplc.com/featured-news/whats-inside-thi...
[1] https://news.mit.edu/2024/how-light-can-vaporize-water-witho...