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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 yo
by ajb 4mo ago
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.
- deleted 4mo ago[deleted]
- CuriouslyC 4mo agoIf 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.
- xyzzyz 4mo agoBrine 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.
- lightedman 4mo ago"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.
- rapnie 4mo agoThat only shifts the problem. Now we need an increased supply of hippies that are hard to come by in a low hippie-tolerant environment.
- ceejayoz 4mo ago> 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.
- SoftTalker 4mo agoThe brine came from the ocean. So just dilute it back to close to ambient salinity using municipal waste water that you are discharging anyway.
- ceejayoz 4mo ago> The brine came from the ocean. 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?
- SoftTalker 4mo agoThe 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.
- ceejayoz 4mo ago> The analogy would be if you "un-enrich" it. But you're doing that with the same water you're trying to make in the first place!
- SoftTalker 4mo agoYou could just dilute it using fresh seawater, if you used enough and (maybe) spread it over a wider area. The amount of water people need for drinking is a relative drop in the ocean.
- deleted 4mo ago[deleted]
- qurren 4mo agoWhy? Just build mountains out of it and maybe even open a salt-ski park in the tropics for people who don't have snow.
- asdff 4mo agoThere are salt mountains lining most midwestern freeways as it is for winter.
- xp84 4mo agoI just realized that future archaeologists will be tracing our roads using the salt residue!
- make3 4mo agoor just you know.. asphalt residue
- Ekaros 4mo agoActually I have been thinking about this. Surprisingly straight and long cuts in rock formations might be a real thing to track. In at least some places at least some rock blasting is preferred to get aggregate for road foundations. And these tends to be rather straight and rather steep.
- ssl-3 4mo agoAssuming my constants (35g/kg of salt in seawater, 650k tons of salt dumped by the state of ohio every year, 81 gallons per day of individual domestic water usage) are correct and my napkin math isn't completely buggered, and if we look at the salt as a primary product instead of just waste: 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.)
- galaxyLogic 4mo agoI think I read somewhere that salt can be used as energy storage medium? So we could get both water and batteries for renewal energy.
- xyzzyz 4mo agoIt’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.
- galaxyLogic 4mo agoBut more thermal storage you want more salt you want, and it's gotta cost something, right? https://en.wikipedia.org/wiki/Molten-salt_battery https://en.wikipedia.org/wiki/Molten-salt_battery
- xyzzyz 4mo agoIf 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.
- aeonfox 4mo agoA better example are sodium ion batteries, which are about to take off in a big way https://www.catl.com/en/news/6812.html https://www.catl.com/en/news/6812.html
- nkrisc 4mo agoIn 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.
- RobotToaster 4mo ago> Solid crystalline salt, on the other hand, is a hassle. Just put it on your fries.
- cyanydeez 4mo agoyeah, 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
- xyzzyz 4mo agoBrine 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.
- xp84 4mo agoSo, 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).
- rtpg 4mo ago[dead]
- darksnart 4mo agoOh no, the hassle of managing the raw input for several key industrial processes that is created for free as a side product of MAKING WATER DRINKABLE WITH FREE ENERGY FROM THE SUN is TOO MUCH OF A PROBLEM! Especially considering we could instead murder millions of fish - which we then can’t eat- in the process! This entire technology is doomed! Come on guys please at least attempt to think what you’re about to type, please, I beg you.
- cyberax 4mo ago> 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.
- otterdude 4mo agoThermal 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
- aaron695 4mo ago[dead]
- cornholio 4mo agoFocusing on pure energy efficiency might be missing the point of economic efficiency. 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.
- ajb 4mo agoThis is valid for some use cases, but then it needs to be compared with other solar distillation methods, of which there are already a variety at different levels of energy efficiency, complexity, and land use.
- westurner 4mo agoScholarlyArticle: "Extreme salt-resisting multistage solar distillation with thermohaline convection" (2023) https://www.cell.com/joule/fulltext/S2542-4351(23)00360-4 https://www.cell.com/joule/fulltext/S2542-4351(23)00360-4 .. https://scholar.google.com/scholar?cites=7551078272963689346&as_sdt=5,43&sciodt=0,43&hl=en https://scholar.google.com/scholar?cites=7551078272963689346... "Desalination system could produce freshwater that is cheaper than tap water" (2023) https://www.eurekalert.org/news-releases/1002811 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 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-inexpensive-0214 https://news.mit.edu/2022/solar-desalination-system-inexpens...
- xhkkffbf 4mo agoI remember the MIT press release. I wonder if they've found any commercial success.
- pfdietz 4mo agoMIT had a spin-out company some years ago doing HDH (Humidification-Dehumidification) desalination. In thermal cycles, the problem has been in the condensation step. If there is a carrier gas present this inhibits heat/mass transfer at the condenser surfaces. The usual way of getting around this has been to operate the system with no carrier gas, but that requires pressures below atmospheric pressure, requiring strong walls to withstand external atmospheric pressure. The MIT invention was a bubble tray contactor, where air is bubbled up through trays of progressively cooler water. The water/air bubble interface provides a large surface area at low cost. One of the markets for this was cleaning up brine from fracked wells. The company, Gradiant, is still around but has evolved to involve a wider range of water treatment technologies (which is very sensible from a business viewpoint, as customers buy complete solutions, not individual technologies). https://www.gradiant.com/ https://www.gradiant.com/
- patates 4mo agoI always thought that if separating water and salt were easy, our bodies would have evolved to do it so that we'd be able to drink sea water and be fine. It must have been so expensive that searching for fresh water was worth it or there were plenty of fresh water that it was never a evolutionary pressure. Evolving kidneys capable of concentrating urine beyond 3 something percent concentration (sea water) perhaps required a massive restructuring of our internal organs and a huge constant energy expenditure, so we kept seeking fresh water. ps. I have no clue what I'm talking about
- blackoil 4mo agoSalt water fish can process sea water, no point in evolving for saltier brine if you have oceans of 3% water.
- Tagbert 4mo agoIt’s mostly that it takes energy. If fresh water is we drink that. There aren’t a lot of places where only salt water is available so, for most animals, it isn’t worth it to have evolved a way to extract water from salt water. 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.
- scythe 4mo ago>I always thought that if separating water and salt were easy, our bodies would have evolved to do it so that we'd be able to drink sea water and be fine. Unfortunately for terrestrial animals, it's just not that simple. Seawater contains a lot of microbial life, some of which can be infectious or toxic. Going to the coastline to drink is potentially hazardous, because it usually means descending a hill on a predictable route which will be attractive to predators. And you need to get pretty far into the water, usually, because of nasty stagnant runoff, which can come from decaying matter that washes ashore, and sand in the surf. That means you risk drowning. Plus, you don't just need the energy for desalination, but the infrastructure (similar problem to real life!), which means more and larger juxtamedullary nephrons in the kidney, which is already a major weak point on the back due to the high blood flow in the kidney. Meanwhile, most of your food contains a lot of water, especially if you're one of the 99.99999% of animal species that doesn't cook it.
- rtpg 4mo agoThis is a weird angle I think? Desalination brine is a real problem, so if you can eliminate that then efficiency is less of an issue (especially given that desalination plants are often in places with a lot of sunlight!). You don't want to be super duper inefficient but "no waste that has to be dumped back out" feels really big to me