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Why is desalination so difficult?
- squatdrunk 3y ago[dead]
- fareesh 3y agoI remember reading that it causes some problems related to fishing because the fish all migrate further out.
- photonerd 3y agoThat’s less the fault of the desalination, more improper/shortsighted disposal of waste byproducts
- bhhaskin 3y agoThe worry is a local increase of salinity levels, due to putting the brine back in the ocean. I think that is a solvable issue though. We can harvest some of the salt and then mix the resulting brine with reclaimed water. Then spread that out instead of dumping it in one area. We could also create inland salt deposits. The biggest issue is cost for these plants and it isn't worth spending the political capital to build them yet.
- commercialdrop 3y ago[dead]
- commercialdrop 3y ago[dead]
- User23 3y agoSolar stills are one of those basic survival tools anyone living in an arid region near a salty body of water should understand how to rig. They’re dirt simple and as easy to build as a prison still with the added bonus of only requiring the sun as an external power source. Similarly everyone should know how to rig a basic water purification system using gravel, sand, and charcoal in series. Even just as applied science experiments to do with kids they’re worthwhile. Edit: Water based solar power is generally an area I think that deserves more research. While photovoltaics have their advantages, water is cheap, clean, and reliable. Heating water with sun during the day and using it for household heating at night is the simple application that I’m most familiar with, but I wouldn’t be shocked if there’s some scale where an economically interesting Carnot cycle becomes possible.
- photonerd 3y agoWater isn’t the most efficient way of doing that but the principle is sound. There are molten salt solar arrays that work similarly.
- kjellsbells 3y agoIdle observation: do people in Materials Science feel like this is the Golden Age for their field? So many incredible paths to follow: Battery tech. Solar cells. Desalination. Carbon handling. What a time to be alive.
- deleted 3y ago[deleted]
- Animats 3y agoIt's not difficult. It's just energetically uphill. Undoing entropy costs energy. Second Law of Thermodynamics.
- deleted 3y ago[deleted]
- jonny_eh 3y agoSeparating two things isn't necessarily expensive. Think of coin sorters that just use gravity and different sized holes.
- 4rt 3y agoYou still have to lift all the coins.
- jonny_eh 3y agoSlide the coins off the table into the sorter, done!
- 11101010001100 3y agoYou need to bring the coins uphill in the first place.
- tshaddox 3y agoRight, but that’s easy. If desalination only required lifting each unit of water a few inches we probably wouldn’t say it’s particularly difficult.
- 11101010001100 3y agoEasy as in moving mass against a gravitational potential? Didn't know building a rocket was easy.
- zokier 3y agoProbably very dumb idea, but would it be feasible to just pump and sprinkle sea-water on hot, dry desert and let it naturally evaporate, and then collect it as fresh rainwater back? i.e. how much water would you need to evaporate to have a noticeable increase in rainfall?
- jareklupinski 3y agoi'd like to see the xkcd author tackle this as a "What If?"
- kneebonian 3y agoHe already has. https://what-if.xkcd.com/152/ https://what-if.xkcd.com/152/
- josephjrobison 3y agoThere is talk about pumping sea water into the Saharan desert in certain parts, which gets at that. https://www.youtube.com/watch?v=V2b7ztWvFOg https://www.youtube.com/watch?v=V2b7ztWvFOg
- samstave 3y agoWas going to say this, there are/have been many ideas to do just this - one was to build a huge canal and just then let the sea flood the area... Also - there are lots of un-earthed treasures to be found under the saharan which was once a lush environ and have been covered with sand - so prior to flooding it, we need to lidar and excavate it. What if we vaccuumed up all the sand and built a new island/continent with the material and just revealed everything underneath - then flooded it. (I believe UAE is in the market for more sand-built-land-masses)
- hinkley 3y agoOne of the more feasible ones was a linear greenhouse with a canal in it. I'm sure someone has done the math to figure out what the proper length is for such a canal, to avoid problems with scaling. And if you've ever been near an ocean for much time, you know the salt tends to get around. So I'm not sure how in a multi-year project you keep that to a minimum.
- aurizon 3y agoseveral better ways, multi stage stills and reverse osmosis are leaders of the pack, https://www.veoliawatertechnologies.com/en/technologies/multiple-effect-distillation-med#:~:text=A%20Multi%20Effect%20Desalination%20MED,to%20produce%20clean%20distillate%20water https://www.veoliawatertechnologies.com/en/technologies/mult.... https://en.wikipedia.org/wiki/Reverse_osmosis https://en.wikipedia.org/wiki/Reverse_osmosis
- mplewis 3y agoThe author specifically mentions reverse osmosis.
- aurizon 3y agoYes, RO is energetically the best, but places with geothermal excess, like iceland might choose the heat based method as they have free heat = the still warm water discharged after power still is warm enough for distillation.
- ZeroGravitas 3y agoHe also covers multi-stage stills: > My garage demo has very little going for it in terms of efficiency. It’s about as basic as distillation gets. There’s lost heat going everywhere. Modern distillation setups are much more efficient at separating liquids, especially because they can take advantage of waste heat. In fact they are often co-located with coal or gas-fired power plants for this exact reason. And there’s a lot of technology just in minimizing the energy consumption of distillation, including reuse of the heat released during condensation, using stages to evaporate liquids more efficiently, and using pumps to lower the pressure and encourage further evaporation through mechanical means.
- MarkusWandel 3y agoSome years ago I toured a maple syrup operation that has the opposite goal: Concentrate the dissolved stuff in the water. Their first stage was reverse osmosis, but only to a point. Second stage is boil, but with aggressive heat recovery from the steam to preheat the incoming liquid. All this to keep the energy cost under control.
- jeffbee 3y agoIn an operation like that, do they heat the syrup under low pressure to reduce the boiling point of water?
- philote 3y agoI'd guess that if anything they'd increase the pressure to raise the boiling point. That way things dissolve in it faster and the water doesn't evaporate away.
- tylerag 3y agoThey're concentrating maple syrup. It comes out of the tree with the sugar and flavors already dissolved in it.
- giantrobot 3y agoPart of the flavor of maple syrup is due to caramelization and the Maillard reaction of components of the sap. Just concentrating the sap would get you a syrupy substance sourced from a maple tree but it wouldn't be maple syrup.
- MarkusWandel 3y agoI've never liked the flavour of maple syrup very much. At the same maple syrup place visit, we had some, on pancakes. WTF? This is plain table sugar! What kind of stunt are you pulling here? The guy supervising the boil said don't you know? The very best grade is like that, hardly maple-y at all! Turns out it really was about the sugar all along, with the initially undesirable maple flavour coming to be prized over time as a side effect.
- dstainer 3y agoSlightly off topic, however, the post references the Carlsbad desalination facility. If you find yourself in San Diego and like oysters, I would highly recommend you checkout the Carlsbad Aquafarm. Take the tour and pick up some oysters. What's really interesting and relevant to the topic is that the oyster farm serves as a pre-filter to the desalination plant and there's an symbiotic relationship between the plant and the oyster farm.
- beembeem 3y agoThat's really cool! Thanks for pointing this out.
- aeonsky 3y agoPick up some oysters, for eating? If these oysters serve as a pre-filter for the plant, would you not want to eat them as these oysters would contain all sorts of pollution?
- the_sleaze9 3y agoA strong case for not eating any oysters at all -- but don't forget they're totally aphrodisiacs
- js2 3y agoThey clean the oysters before selling them: > This was the first oyster farm to feature an inventive “depuration and purification” process, which involves immersing the oysters in triple-filtered seawater once they reach full size. This ensures that the oysters are a completely safe, top-quality delicious shellfish product. https://www.usatoday.com/story/travel/10best/2022/08/04/how-this-southern-california-aquafarm-is-saving-the-environment-with-oysters-and-mussels/50531167/ https://www.usatoday.com/story/travel/10best/2022/08/04/how-... https://en.wikipedia.org/wiki/Depuration https://en.wikipedia.org/wiki/Depuration TIL.
- xigency 3y agoThat’s a really convoluted way to say they rinse them off in clean water. Anyway, seafood comes from the ocean. I don’t see why they would be worse than other oysters.
- fwlr 3y agoRelatively high energy cost since you’re undoing an endothermic reaction, you need to do a lot of it since we use water in large quantities… but most of all, the planet naturally does a lot of desalination for us already through various geological processes, so our “price point” for desalination is $0 per liter (infrastructure to capture rain, dam rivers, or tap groundwater isn’t literally free, but it’s pretty close - especially when it comes to the marginal cost for the next liter). It’s not difficult to desalinate per se, it’s difficult to desalinate extremely cheaply and at huge scale.
- nerbert 3y agoIn 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. If there is a real need, and a will to address it, we have everything we need to to it. https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in_Israel https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...
- ramesh31 3y ago>In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. Israel does this by burning massive quantities of fossil fuels: https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:Energy_consumption_by_source,_Israel.svg https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:E... It's not even remotely economical without huge government subsidies. Completely untenable with current technology for poorer countries, or anyone that cares at all about carbon emissions.
- tguvot 3y agoYou can't drink hydrocarbons.
- ALittleLight 3y agoCouldn't they just replace fossil fuels with nuclear and solve the emissions issue?
- SillyUsername 3y agoStupid question time, why not expose the sea water over a larger area and expose to sunshine? There's plenty of room in the UAE for this, somebody is even building a wall that could hold the water which could be dual purpose and act as cooling via evaporation...
- djent 3y agoLarger area than the oceans?
- SillyUsername 3y agoWe'll no but a super long wall facing south might do the trick...
- barelyauser 3y agoSearch for OTEC (Ocean Thermal Energy Conversion). Not necessary to build wall, just a big enough pipe to collect cold water from the depth. Then a special contraption will yield pure water from evaporation. Can be done virtually everywhere there is a deep enough ocean.
- 0xbadcafebee 3y agoI mean basically you're describing a solar pond (https://en.wikipedia.org/wiki/Solar_pond https://en.wikipedia.org/wiki/Solar_pond) or salt evaporation pond (https://en.wikipedia.org/wiki/Salt_evaporation_pond https://en.wikipedia.org/wiki/Salt_evaporation_pond). There isn't an easy way to recover the evaporated water from that process; you would effectively have to build an artificial enclosed environment and it wouldn't work as fast as exposure to the elements. Basically you would need a still (as in for alcohol) the size of 20 football fields. But sun power wouldn't be enough to power it fast enough to be practical. Maybe if you moved it into outer space...
- justsomehnguy 3y agoThis is how it is solved everywhere... but now you need to ship all this desalinetad water. And surprise! it's the second the most expensive part in the process.
- luxuryballs 3y agoCan I shower in salt water? Then all I need to do is desalinate drinking water. “Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.
- mschaef 3y ago> Can I shower in salt water? You at least need special soap: https://en.wikipedia.org/wiki/Saltwater_soap https://en.wikipedia.org/wiki/Saltwater_soap
- nickff 3y agoYes, you can shower in salt water, but you won't feel as clean in the end. You also use water for washing clothes and dishes, as well as washing your hands, watering plants, and various other tasks, for which salt water is unsuitable.
- jakear 3y agoNo. Unless you want salt-caked hair. And body. Curious, have you ever been to a beach?
- luxuryballs 3y agoyeah but I usually feel quite refreshed after coming out of the waves, but keep in mind we don’t need clean feelings to survive, we do need fresh drinking water
- jakear 3y agoSalt overexposure is liable to dry up your skin and cause rashes/cracking leading to vectors for infection.
- stOneskull 3y agoyou see that with surfers. at 30, they look like they're 50
- narag 3y agoTell that to israelis: https://www.israel21c.org/how-israel-used-innovation-to-beat-its-water-crisis/ https://www.israel21c.org/how-israel-used-innovation-to-beat...
- deleted 3y ago[deleted]
- akiselev 3y agoIs it just me, or did this article dance around the question? I am not a physicist but let me give it a stab: except for a few specialized steps like UV or oxidizing heavy metals, most filtration is mechanical. A series of filters with smaller and smaller pores capture more and more of the mess in the water like bacteria and particulates while UV breaks down viruses, the oxidizer precipitates out metals, and so on. None of those methods work with salt. Salts in general disassociate through ion-dipole interactions - the water dipoles essentially rip the ionic compound apart and surround each ion in what is called a hydration shell. They're bigger than bare water molecules but not much bigger - much too small to target with pore size. This shell also puts them in a thermodynamically stable state and it takes energy to "jostle" the water molecules away from the ions either through evaporation, distillation, or through another chemical reaction that precipitates out the ions. As it turns out, doing that takes a lot of energy, so we use reverse osmosis as a cheaper alternative: we exploit the hydration shell of the ions by putting them behind a semi-permeable membrane with very small pores, "nanopores" if you will. The pores are too small for water to cross normally, but under high pressures bare water molecules can be forced through the pores while the ions trapped in their shells remain and concentrate into a brine. It takes less energy but produces a concentrated liquid waste stream that must be disposed of. Someone please correct any mistakes I've made
- tinus_hn 3y agoTo me it doesn’t seem to make sense to first claim that you can’t filter for salt in water, and then talk about semi permeable membranes and osmosis. Those membranes are filters for salt!
- scrubs 3y agoIt danced around the question.
- eutectic 3y agoI think it's more a problem of entropy; You're taking a high-entropy mixture and trying to extract a pure substance. Think sorting red and blue lego.
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- leecarraher 3y agoI like the analogy at the end regarding nuclear power vs piping in water from freshwater sources. The upfront costs are high, but over time it would be cheaper than desalination, but due to short term governments and borders, it's hard to justify the upfront costs. So instead we are somewhat stuck with more expensive short term solutions.
- 1letterunixname 3y agoPick one 1. Steam distillation + Product can be perfect DI type 1 water - Expensive: 300+ kJ/L 2. RO membrane + Cheaper - Slow - Wastes more water - Requires regular changing of membranes The end.
- jeffbee 3y agoThe energy costs are a bit of a red herring depending on local conditions. In California we currently "curtail" i.e. discard a huge amount of renewable energy in the spring season. If we can seasonally apply that energy to desalination, and store the fresh water for later, it is essentially a huge time-shifting battery that stores excess spring energy for the summer.
- Maxion 3y agoThere's lots to unpack here why this isn't workable at scale. 1) Renewable energy product still has a cost associated with it, even if it is at times, excess. 2) That excess capacity, and the times when there's more energy produced than consumed might not match with water demand. 3) There definitely isn't, and won't be, enough excess renewable capacity to distill even a fraction of the fresh water consumed. 4) This means that you still have to calculate a per kWh cost for the energy consumed to distill salt water to fresh water. The average kWh might not be the same as the market average kWh price, since if you make your distillation plants oversized so you can utilize any spare energy production, but there will still be a price. 5) This price will most likely mean that the per gallon cost of distilled water will be higher than RO, or water pumped through a pipeline. Desalination is still an extreme measure taken when all other forms of fresh water are cost prohibitive.
- jeffbee 3y agoWith the amount of curtailed energy this year in California, using a state-of-the-art RO process, we could have desalinated about 880k acre-feet of water. This is roughly enough water for all domestic urban water use statewide for about half the year. It is already close to penciling out and our energy resources are still expanding.
- jjk166 3y ago> 1) Renewable energy product still has a cost associated with it, even if it is at times, excess. This cost is already paid for in the infrastructure. You're not going to tear down extra solar panels when demand is low just to reinstall them an hour later. > 2) That excess capacity, and the times when there's more energy produced than consumed might not match with water demand. Water can be stored very easily in large quantities and over long periods of time. Replenishing an aquifer in the summer will still help you even when the dry season is winter. > 3) There definitely isn't, and won't be, enough excess renewable capacity to distill even a fraction of the fresh water consumed. You don't need to distill 100% of freshwater, you just need to make up the difference between what is naturally available and what is used. The difference is generally small, especially when combined with water conservation methods. California's water shortfall could be covered by using just 6% of it's current annualized electricity generating capacity for desalination. > 4) This means that you still have to calculate a per kWh cost for the energy consumed to distill salt water to fresh water. The average kWh might not be the same as the market average kWh price, since if you make your distillation plants oversized so you can utilize any spare energy production, but there will still be a price. You would presumably locate your desalination plant in an appropriate location and operate it at appropriate times such that your cost per kwh is substantially below normal market rate. > 5) This price will most likely mean that the per gallon cost of distilled water will be higher than RO, or water pumped through a pipeline. RO would be desalination. A pipeline is still taking water from somewhere else, the price depending heavily on where you're getting it from and the geography between you and the source. In many cases there isn't a suitable freshwater source to pull from. Certainly there are no fresh water sources so limitless and readily accessible as the world's oceans.
- profsummergig 3y agoWhile on the issue of water: Some countries have floods in one part, and drought in the other. The floods are so bad that large numbers of people die. Here's a great challenge that should be worked on: how to capture the flood water and use it to mitigate the droughts. Could something like Elon Musk's Boring company concept fix this?
- falcolas 3y agoThat’s basically how dams and reservoirs work. It just requires a lot of space to store water.
- seunosewa 3y agoThe cost of pumping dirty water uphill ...
- NegativeK 3y agoPeople are constantly talking about using pipes to solve the US desert southwest's water crisis, as if building a water pipeline for thousands of miles isn't some gigantic logistical and engineering nightmare -- as well as a bureaucratic nightmare, since most places with fresh water don't want people in the desert literally sucking them dry.
- FreshStart 3y agoShould heat and cool it with standing soundwaves. Salty water takes the heat, cools and falls (brine-fall) rest is less salty.add membranes at intersection points..
- cratermoon 3y agoGoogly eyes on the flow meter
- hammock 3y agoBecause water is the universal solvent and NaCl is probably the most readily water-soluble salt. Reversing that state is going to take a lot of work
- emptybits 3y ago"Turning sea water into clean, drinkable water costs $2 to $5 for 1000 gallons. Less than half a penny per gallon is obviously absurdly cheap." - Elon Musk, 2023-05-07 https://twitter.com/elonmusk/status/1655262008898383872?ref_src=twsrc%5Etfw https://twitter.com/elonmusk/status/1655262008898383872?ref_...
- tibbon 3y agoI'm looking at this and unclear what he's talking about. Essentially, citation needed Elon?
- emptybits 3y agoMusk made the same "absurdly cheap" claim in a recent interview with Bill Maher. https://www.youtube.com/watch?v=oO8w6XcXJUs https://www.youtube.com/watch?v=oO8w6XcXJUs [skip to 14:45] I don't think he gave any substantiation to the claim then either. (He dismissed delivery of clean water to the world as a problem not interesting enough for him to spend time on.)
- Veserv 3y agoIsrael desalination plant profitably offering a fixed price of 1.45 NIS per cubic meter. At current exchange rates that is around 0.40$ per cubic meter (1000L). https://www.gov.il/en/departments/news/desalination_260520 https://www.gov.il/en/departments/news/desalination_260520
- infogulch 3y agoJust look at this thread for price estimates. $2-5 is pretty reasonable, even assuming a cost breakdown with energy at 10% and capital/infrastructure at 90% of the final cost.
- iudqnolq 3y agoIt's very easy to forget that we use orders of magnitude more water than comes out of our tap. A pound of beef is about 2,000 gallons, so that would be a nontrivial price increase.
- gamegoblin 3y agoI was surprised how cheap it is. Desalinated water costs ~50 cents per 1000 liters [1]. That's about the same amount of water as a typical American household uses per day. 50 cents per day for a fully desalinated water supply is... incredibly cheap. If you're interested in water policy and water management / engineering, I cannot recommend enough reading the book "Let There Be Water: Israel's Solution for a Water-Starved World". [1] https://en.wikipedia.org/wiki/Desalination#Costs https://en.wikipedia.org/wiki/Desalination#Costs
- yhgxfvx 3y ago[flagged]
- iudqnolq 3y ago*typical American household uses directly. Don't forget food, industrial, etc
- deleted 3y ago[deleted]
- bufferoverflow 3y agoYes, but you pay for that when you purchase the products. These costs are baked in.
- csours 3y agoI wonder if the brine could ever be valuable enough to extract minerals from. I keep hearing about how many tons of x mineral is in seawater.
- kylehotchkiss 3y agoIf you built a desalination system say… 500 feet under the ocean and have the pressure above pushing water through the filters, is it possible to lower the amount of required energy just a little? Then you’re more pumping water out of the system than pumping it through heavy filters
- rootusrootus 3y agoWouldn't the energy of pumping the water all the way back up to the surface completely balance out the energy provided by the weight of that water to push it through the membrane?
- function_seven 3y agoMaintenance of those filters and associated infrastructure will become crazy expensive. And now you need to pump the final product up to the land surface, adding cost there as well.
- ejz 3y agoOne thing that this article missed was that it was San Diego centric. In Israel, desalination is a much bigger part of the ecosystem. Over half of its domestic water comes from desalination. Quite a bit of the problem in California, as in almost every industrial application, is just that we make it hard to do anything with atoms.
- abotsis 3y agoWhat ever happened to desalination via ICP that the mit postdocs had working? 20wh/L iirc…
- agnosticmantis 3y agoGiven the countless environmental challenges we are facing (and causing), we should more seriously and openly consider putting a stop to exponential population growth as an (at least short-term) solution. It’s astonishing how some people preach blind faith in our ability to just find solutions for problems caused and exacerbated by never-ending population growth without identifying it as the root cause. Why is it a given that the earth can just withstand whatever we throw at it?
- mr-ron 3y agoIts not exponential. In fact its estimated to level off over the next century: https://ourworldindata.org/world-population-growth https://ourworldindata.org/world-population-growth
- egberts1 3y agoMIT solar distiller in 2020 demonstrated a gallon and a half of fresh water in one hour using a square meter of close-quarter membrane distillation process. So, 10,000 sq meter of this baby could pump 150,000 gallons of fresh water over a ten-hour solar shift. Seems like the secret sauce is 1.2cm (or is that 80mm) separation between diffuser plates thus taking advantage of solar heating/condensation/collection in one area. Of course, there remains an collection issue of brine discharge which could be removed gradually instead but in same but 3-peat manner (down to 2-3 permille, or 0.2-0.3% salinity level.) At any rate, this MIT method has leapfrogged the passive solar method ahead of reverse osmosis (RO) method by quite a bit, in terms of energy required to extra fresh water. RO still holds the insurmountable lead in base (non-fluctuating) water output rate. https://news.mit.edu/2020/passive-solar-powered-water-desalination-0207 https://news.mit.edu/2020/passive-solar-powered-water-desali...
- hinkley 3y agoI'm not sure what the full story is, but in 2019 MIT was also looking at one of the other costs. They claim it's common to pretreat the water with sodium hydroxide, which is purchased. Here they claim they have a way to regenerate it from the effluent: https://news.mit.edu/2019/brine-desalianation-waste-sodium-hydroxide-0213 https://news.mit.edu/2019/brine-desalianation-waste-sodium-h...
- michael_vo 3y agoYou could use simple pricing to influence behavior. 1100 litres a day for each American is so damn much. When you hike and stay in the mountain huts you are charged 3$ for a 4 minute shower. You could probably fix the drought situations by reducing consumption.
- flybrand 3y agoI work in microfiltration (a pre-filter step for RO), and my view is: 1/ it’s as much an energy and water storage problem as it is a technical problem. 2/ commercially, because of 1/, RO is a municipal sale. It is a civil initiative, rather than a commercial one, which means it gets crowded out by other civil decisions.
- alana314 3y agoCould we make a deep sea elevator similar to a space elevator? And if so, could we use deep sea pressures to facilitate cheaper desalination?
- dec0dedab0de 3y agoI had a dream the other day that we started generating electricity with steam engines using ocean water, then collected the steam for potable water
- barney54 3y agoIt’s not difficult, but it is very energy intensive. That was my conclusion from visiting a desalination plant.
- credit_guy 3y agoI think he fully gave the wrong answer. The main problem with desalination is capital cost. The Carlsbad plant cost one billion dollars to make. I bet very little of it is the cost of membranes, or the actual RO systems. It's simply a large plant, and building a large plant is expensive. The same problems that plague large nuclear power plants plague many other large construction projects, including large desal plants.
- throwaway14356 3y agoI was never able to find the publication again but I read an article one time about the work of 2 Australian professors (I forget which kind) who designed a giant circle shaped verical axle wind turbine with 2 tubes that suck sea water up along the sides and sprays it up in the air with the brine dropping near the turbine. An array of those they claimed could create dense clouds that produce a lot of rain at some (according to them) surprising ratio to cost.
- andy_ppp 3y agoI’ve got an idea guys! Let’s build some artificial lakes and we can just let rain and river water pool in them! We can let natural precipitation do the desalination for us!
- codedokode 3y agoThe author have mentioned that water with more than 1-2 promille of salt is considered not drinkable. But I have a bottle of carbonated mineral water from the mountains and the label says it contains 6-9 g of salts per 1 liter. So I guess it depends on which salt it is. Also, the author mentions that people in US use 1100 liters per day (which is too much in my opinion), but not all this water needs to be drinkable, one probably can not drink more than 3-4 liters per day, and the rest of the water can be salty.
- TheDudeMan 3y agoDoes one feel clean after bathing in salty water? Maybe. Not sure.
- BenjiWiebe 3y agoSalts != Salt (sodium chloride)
- reyoz 3y agoHaving a diversity of water supplies and using water fit for purpose reduces demand for drinking water. Toilet flushing, irrigation and even washing machines do not need high quality drinking water. I have 5,000L of rainwater storage that I use for toilet flushing and irrigation. Combined with a water efficient shower head (typically the largest domestic water use in my country) we use 100 L/d/person. In some areas of my city there is dual supply plumbing that delivers highly treated wastewater for these uses.
- im3w1l 3y agoInteresting. Maybe we could use an ion-exchanger to swap the salt for another one that the body is more tolerant of.
- reyoz 3y agoRO does use a lot of energy to overcome the osmotic pressure and to create flux through the membrane. An interesting concept is using the reverse process, "forward" osmosis, to extract the energy where fresh water mixes with seawater, such as a river mouth. This is called pressure-retarded osmosis (PRO) and was tried at pilot scale by Norwegian power company Statkraft. Ultimately this trial was shelved due to being uncommercial [1], perhaps future membrane development will improve the viability of FO. And yes the membranes are quite different, RO membranes are relatively thick due to the transmembrane pressures required. FO requires a much thinner support for the active layer as there is no external pressure applied to push the water through (it is drawn through by the difference in salt concentration). [1] https://www.powermag.com/statkraft-shelves-osmotic-power-project/ https://www.powermag.com/statkraft-shelves-osmotic-power-pro...
- _8j50 3y agoLate to this thread but I have always asked why nuclear powerplants can't use seawater for cooling and the condense the steam to create desalinated water? Ocean waves can be used to create electricity and it is also possible to create a dam that uses an artificial river sourced by the ocean and make hydroelectric plants to use that energy. Is it a cost issue in both cases that prevents using electricity generated that way to desalinate?
- nullcontext 3y agoThis one time on an episode of Survivorman, Kalahari iirc, I watched Les Stroud use a hole in the dirt and a clear plastic tarp covering it to act as a solar still. The condensation from his pee in said hole ran off to a collection container as pure H20 once evaporated. I just remember thinking to myself "Bear Grylls drinking his own pee is such a philistine, here is an actual pro using science to remove all the water from that pee instead first." Genuine moment of awe personally.
- DanielHB 3y agoIt is not hard, just throw the salt water in a steam turbine room and get the output through aquatuners to cool it down from 95C to 20C Put the steam turbines inside the steam room to recover some of the heat as power and you are good to go
- cies 3y agoDifficult is not an absolute. It needs to be "in comparison to something". Desalination is verrrrry easy if nature does it for us (sun on the salty sea -> clouds -> precipitation over land). Compared to this, doing it "with a machine" is hard.
- aredox 3y agoFor a blog about "practical engineering", it doesn't address the fact that in practice, saltwater isn't just "water and salt" but also all kinds of particules, pollutants and impurities that will clog any membrane after a while.
- Falell 3y agoThis is discussed at ~12:10.
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