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Freshwater from salt water using only solar energy
- Overtonwindow 9y agoDesalinization is becoming better understood, as well as cheaper, but the biggest challenge is still what to do with the leftover salt. We can't pour it back into the ocean because it will kill everything. Hopefully someday we find a way to clean and safe way to dispose of salt.
- ianai 9y agoAn abundance of salt hardly sounds like an environmental issue. By that I mean it's not a gas that's going off into the atmosphere nor a liquid seeping anywhere (on its own)
- smhg 9y agoEven assuming you have to store it like nuclear waste, the ratio of about 3.5% doesn't sound too bad to the untrained ear.
- noonespecial 9y agoBritain is using a huge old salt mine in Cheshire to store toxic waste right now. We could put all the salt... umm.. into old salt mines. Now that's a job for you to tell your kid's school class about on career day. A salt un-miner.
- andai 9y agoReminds me of XKCD 1119, "Undoing" https://xkcd.com/1119/ https://xkcd.com/1119/
- ori_b 9y ago> We can't pour it back into the ocean because it will kill everything. That's simply false. The amount of water that would need to be permanently removed from the ocean in order to measurably increase the salinity would be astounding. Let alone the amount that would need to be permanently removed to kill anything. If local salinity was a problem (which it isn't) there's an extremely easy solution: Simply pump more water, remove less salt from it. Dump it in over a wider area of shore. Let mixing take care of the rest.
- rorykoehler 9y agoGiven our track record I'd rather we didn't try find out.
- bluGill 9y agoMost of the water we desalinate gets dumped right back in the ocean, add the salt back. Even the water that doesn't get into the sewage system ends up back in the ocean again via the water cycle/rainfall. (meaning we need to worry about local salinity issues but not global) Actually most sewage systems output water that is safe to drink so we can put that water right back into our drinking water system and forget the whole problem over an over again. (If you ban lawns there might even be water left over as food is turned into water and the food probably isn't grown with city water). People generally don't like the idea of drinking sewage though so this will never happen.
- adrianmonk 9y agoLoad salt on the huge cargo ships already crossing the oceans. Build machines that dump salt overboard slowly and continuously as the ships make their voyages. The ships are probably full one direction (when traveling from countries that manufacture a lot) but relatively empty on the way back, so there's probably free space.
- dotancohen 9y agoThis idea assumes that the product consumer is the side which needs desalination. Unfortunately, in practice usually the opposite is true.
- adrianmonk 9y agoThe core of the idea is to put it on ships. Using idle capacity is just a purely optional bonus. Ignore that part if you want.
- dubyah 9y agoIt's not really a significant problem. Blending it with heated cooling water from power plants or treated effluent from waste water plants are common means of brine disposal. Provided you spread out the disposal in areas with good flow, even releasing the brine directly would have minimal impact.
- deleted 9y ago[deleted]
- toomanybeersies 9y agoWhy can't you just pour it back into the ocean? That's what's happening to the fresh water after it's used, it goes back to the ocean. It's a closed cycle. The scale of human water consumption to the volume of the sea is miniscule. Global fresh water consumption is a fraction of a percent of the volume of the ocean ( https://www.wolframalpha.com/input/?i=((total+water+consumption+*+1+year)+%2F+volume+of+the+sea)+to+percent https://www.wolframalpha.com/input/?i=((total+water+consumpt... ) There's no reason why we couldn't ship it into the middle of a desert if for some reason it couldn't go back into the sea, it wouldn't go very far once it was dumped. Conveniently, the places that rely/will rely on desalination the most happen to be desert countries.
- coenhyde 9y agoI'd imagine the problem is the concentration of salt where the dumping occurs. There would need to be a system in place to spread the salt out over a large geographical area at concentrations that is not harmful.
- jccooper 9y agoIt's not a global problem but a local one. Locally increased salinity and temperature can be a problem. You can drop a whole bunch of hot brine in the middle of the ocean to little effect, but the same is not true of a mangrove swamp or a bay.
- _ph_ 9y agoMost desalinization processes don't produce "salt", but extract a certain amount of unsalted water from the in put, leaving behind more salty water. Typically reverse osmosis at best reaches 1:1, that means you need 2 units of input water and get one unit of desalinated water and one unit of salty water. For sea water desalination 1:1 is quite optimistic though. This salty water can be safely put back into the sea. With very large scale plants you might want to make sure that you don't release the salty water at a single very concentrated spot.
- bjelkeman-again 9y agoIn the Persian Gulf there is real concern regarding the volume of brine that the desalination produces. https://www.sciencetarget.com/Journal/index.php/IJES/article/viewFile/96/25 https://www.sciencetarget.com/Journal/index.php/IJES/article...
- Salamat 9y agoIt could explain Eyewitness: Mass Dead Fish https://www.youtube.com/watch?v=70_SbAbPG_M https://www.youtube.com/watch?v=70_SbAbPG_M
- yardie 9y agoI don't know any reverse osmosis makers that are anywhere near 1:1. Current RO systems are 9.5:1. Over 90% of the saltwater is rejected as brine.
- _ph_ 9y agoThese 1:1 are the best numbers for demineralizing sweet water - I assumed that salt water desalination had much different proportions, which also means, that the relative change in salt content is pretty small and consequently the impact of putting it back into the sea.
- Cthulhu_ 9y agoAre you saying salt water kills salt water fish?
- loverofcode 9y agoof course. kind of like how oxygen can kill us.
- Overtonwindow 9y agoHey don't blame me, blame Science. Salt is a huge problem in desalinization. We can't just dump it right back into the ocean, especially if this is to be a long-term solution. https://www.scientificamerican.com/article/the-impacts-of-relying-on-desalination/ https://www.scientificamerican.com/article/the-impacts-of-re...
- loverofcode 9y agoBased on the article disposing of the double salty water "willy nilly" is the problem. We should be able to pipe a system that delivers it over a wide area. Nice info though!
- shadow_banned 9y agoSome really nice info!
- gruturo 9y agoWhat's wrong with dumping it back in the ocean? The desalinated water is also going back there eventually, so the equilibrium is unaffected
- dsfyu404ed 9y ago>What's wrong with dumping it back in the ocean Locally high concentrations of salt are bad. A little CO won't hurt you but it's not advisable to BBQ indoors.
- chrisweekly 9y agoI wonder if there's a good use to which the highly-salinated solution (the "leftover salt") could be put. It's a stretch, but I vaguely recall something about storing excess solar energy thermally, in dense piles of molten salt...
- jghn 9y agoPart of me wonders if the water could be used for fracking as a double down on energy generation, but the other part of me says that if that were possible that people far smarter and richer than I would have already been on top of this.
- logfromblammo 9y agoIn general, perform reverse osmosis (RO) until the effluent brine is up to 70 g/kg salinity. Then pump it out onto a salt pan, let the rest of the water evaporate, and sell the evaporite. Petrochem tech comes into play here, because in steam extraction of oil-sands, wastewater comes back up contaminated with silicates, and has to be treated before it can be reused. It turns out that similar processes can be used to further concentrate desalinator effluent above the 70 g/kg that regular RO tops out at, to about 130 g/kg. From there, any solar/thermal process equipment (i.e. flash distiller) can be made much smaller. For reference, seawater is typically 35 g/kg, and the top stratum of the Dead Sea averages 315 g/kg (with significant fluctuation due to local weather history). So Jordan and Israel can actually do RO on water from the Red Sea (40 g/kg), and pump the effluent to the Dead Sea. They don't have to worry about the hypersaline brine killing anything, because the Dead Sea is already dead (just like it says on the tin). And the pumping is easy, because the Dead Sea is below ocean level. A pair of siphoning aqueduct pipelines (40 g/kg and 70 g/kg) can supply a RO desalinator in every town from Aqaba to Potash City.
- rdlecler1 9y agoSolar desalination is not new. KKR invested $100b in SunDrop farms which uses solar desal that produces energy (steam) and water for greenhouses in the desert.
- ogrisel 9y agoHere is the link to sundrop farms for those not familiar with the concept: http://www.sundropfarms.com/facilities/ http://www.sundropfarms.com/facilities/
- sandl 9y ago*$100mm Source: https://agfundernews.com/how-private-equity-giant-kkr-and-sundrop-farms-are-spending-100m-on-indoor-agriculture5733.html https://agfundernews.com/how-private-equity-giant-kkr-and-su...
- smoyer 9y agoSolar desalination is not new ... I performed the same feat in the '70s during Boy Scout camp-outs in Virginia Beach (Fort Story) [0]. What is new is the level of efficiency! [0] https://en.wikipedia.org/wiki/Solar_still https://en.wikipedia.org/wiki/Solar_still
- logfromblammo 9y agoIMHO, scout troops should teach the kids how to acquire fresh water before how to make fire, but for some odd reason the kids find fire to be more interesting. Who wants to worry about wells and sump holes and and filters and bleach tabs when you can burn things?
- dredmorbius 9y agoThe general problem with membrane-based desal methods is membrane fouling and lifetime. I'm not sure that increasing the complexity of the membrane substrate itself is a positive step here, or that a complex heating mechanism offers significant wins. The alternative of more traditional membrane reverse-osmosis processing focusing on cheap substrates, whilst provisioning power separately (conventional solar PV would be suitable, and could be located on-site or remotely) seems rather more tractable.
- msl09 9y agoYeah. After the initial excitement my first thought was if using nanotechnology could make the amortized cost of a panel prohibitively expensive.
- bencollier49 9y ago6 litres / metre-squared per hour. We require 130 litres / person per day in Europe. A town of 10,000 people would require 1,300,000 litres / day = ~54,000 litres / hour = 9000 metres-squared. A facility of 100 x 100 x 1 m seems feasible. Based on those calculations, this all seems quite practical. I do wonder how frequently the filters need to be changed, though.
- Kayou 9y agoI thought 130 litres/person was quiet high and probably included things like water to grow vegetables, but no, one shower is between 30 et 50 litres and each time you go to the bathroom, it's 10 litres of drinkable water. Of course, I you have saltwater and no freshwater, you would probably use saltwater in your toilets, so that could reduce the daily usage of at least 20 litres. But then, if you consider agriculture and manufacturing, I guess that the number of 130litres/person would blow up completely.
- positivecomment 9y agoMaybe people can also shower with saltwater followed by a quick rinse in drinkable water. That would reduce the usage drastically. I couldn't find anything against showering with saltwater by skimming the results of a naive google search.
- maxerickson 9y agoYou can get about the same effect by running the water to get wet, turning it off while washing and then back on for rinsing (the infamous "navy shower"). I imagine the biggest strike against showering with salt water is that you'd need treatment, supply and heating dedicated to the salt tap. And then the salt water is busy corroding all the infrastructure devoted to it.
- dhimes 9y agoTurning off the shower while I am soaping is now second-nature to me, like turning off the water while brushing teeth. I highly recommend it.
- ajarmst 9y agoDear God, do you realize what we've done? We've invented evaporation! (Sorry, the title struck me as funny.)
- Qwertious 9y agoNot really - evaporation is used to trap the residue in the water, and dispose of the water itself. This is the reverse - dispose of the residue, keep the water.
- ajarmst 9y agoI appreciate your recognition of my plea for a refresher in middle-school science. Most people can't perceive my pain in the midst of the sarcasm.
- SubiculumCode 9y agoFrequently I hear how persons stranded at sea or on a small island die of thirst, and I wonder if they could have used the evaporation method in conjunction with the sun or fire, and a cloth set above to capture the evaporated water.
- totallynotcool 9y agoMETTC dependant, a 'solar still' could work. With the right vegetation and a plastic bag you could even collect transpiration. Off topic, but interesting nonetheless. [1] https://en.m.wikipedia.org/wiki/Solar_still https://en.m.wikipedia.org/wiki/Solar_still
- regularfry 9y agoAny particular reason you couldn't do a siphon-pumped multistage flash still with solar heating? That would be just glasswork.
- malloryerik 9y agoDumb question: would it be possible to turn the desert green? I'm imagining something done little-by-little, through farming and maybe public trusts. If this kind of technology were to continue to fall in cost, could we have farms and forests in the Sahara?
- kbart 9y agoWater is not the only problem. You'd also need soil as not much can grow in a sand.
- anotherbrownguy 9y agoLet's not forget that solar cannot be used for anything critical where reliability is expected. It requires backup from a reliable source to be practical.