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This is a great perspective check. Water is truly a near-infinite resource. If we can master desalination then humanity is in a great spot in regards to fresh
by leetharris 3y ago
This is a great perspective check.
Water is truly a near-infinite resource. If we can master desalination then humanity is in a great spot in regards to fresh water.
It also frames the challenge well. Desalinating a cubic mile gives you 120 million tons of leftovers. Another extremely difficult challenge.
- CapitalistCartr 3y agoI wonder if we could use that as a building material.
- thombat 3y agoThose leftovers are water soluble, so either you perform some interesting chemistry to convert them into something more durable or your buildings have to be in arid places (condominium in an old salt mine?)
- zdragnar 3y agoAnything that is water soluble is going to be a pretty poor building material, unfortunately. The organics floating about (protozoa, algae, fish) also generally decompose, another undesirable property. The remainder- very very fine silt and microplastics- might be useful. With all the chemical processing that would be needed to stabilize the salts, mechanical filtering and such, I think we're better off continuing to use bricks and ground sourced gravel and cement. At least the holes we dig can be repurposed into sanitary landfills.
- Blahah 3y agoCorals manage it quite effectively
- zdragnar 3y agoBut not efficiently. Scientists think the polyps absorb bicarbonate and calcium ions and deposit calcium carbonate, but they're not really sure of the bio/chemical process involved. Regardless, a polyp adds about 1mm to 1cm to the reef a year. You can get that right now just by throwing a shovel at the ground where I live.
- acidburnNSA 3y agoProbably more practical to use more chemistry and find good uses for sodium and chlorine individually.
- A_D_E_P_T 3y agoEven if we split NaCl into its constituent parts -- sodium metal and chlorine gas -- there's not a whole lot that can be done with them. Sodium is potentially useful towards two applications, off the top of my head. (1) Na2O is used in glassmaking, and it's possible that there are -- or that there can be discovered -- Na2O-enriched glasses that can be used in construction and as a filler substance, i.e. reduced to powder and added to cement. (2) Sodium-based zeolites can potentially be useful for carbon capture. Production of zeolites, however, also requires lots of alumina and silica. I struggle to think of any large-scale application for all of that chlorine, though. Maybe vinyl chloride production? But the world doesn't need that much PVC...
- tonymillion 3y agoAlso in the production of Sodium batteries, which while significantly lower in energy density compared to Lithium, they have bigger cycle counts (and as such are/can be used to buffer grid based wind/solar generation)
- Cthulhu_ 3y agoI'm a proponent of just stockpiling it, spray it onto a large basin and form a salt lake, let it evaporate to a solid as deep or as high up as it needs to be. That's a stockpile that can eventually find a use. Or not, in which case it's harmless, assuming the salt doesn't go into the ground. Or does, if it's a desert or otherwise 'dead'.
- Obscurity4340 3y agoI've read that Israel has basically already solved this problem with their desalination tech.
- tpmx 3y agoDesalination is [responsible for] around 10% of the electricity consumed in Israel. [...] more than 90% of the country’s electricity comes from fossil fuels. https://www.energymonitor.ai/tech/can-desalination-save-a-drying-world/ https://www.energymonitor.ai/tech/can-desalination-save-a-dr...
- Obscurity4340 3y agoI'm surprised they haven't jumped the solar route. Seems like that area has nothing but sun.
- gsich 3y agoDesalination is "solved". Main problem is the huge energy requiered.
- iancmceachern 3y agoSo, not solved?
- Avshalom 3y agoI'm not a physical chemist but there's probably a computable minimum energy necessary. A quick search popped up https://pubs.acs.org/doi/10.1021/acs.jchemed.0c01194 https://pubs.acs.org/doi/10.1021/acs.jchemed.0c01194 For example, desalinating seawater with a typical seawater salt concentration of 35 g L–1 (corresponding osmotic pressure of 29.7 bar) and 50% water recovery (i.e., 50% of the feed stream becomes purified water and 50% becomes brine) requires at least 1.1 kWh per cubic meter of purified water. Regardless of the desalination technology, it is impossible to desalinate water using less energy than that determined by eq 12. which a couple other searches seems to be within order unity of the current energy use
- iancmceachern 3y agoWith current membrane technology, yes. There are so many examples in our collective technical history of overcoming these types of limitations not with brute force, but with finesse. In this case, I expect it will be a combination of improved pumps, improved RO membrane technology, and finding synergies like making sea salt from the brine, collecting other useful minerals front the brine,etc. All of these things help to pay for the energy and development costs. It's not a hard physics limit like the rule if squares or the speed of light. It's a complex engineering system that has may different dynamics and interactions between those dynamics, all opportunity for improvement.
- Avshalom 3y agoGibbs Free Energy is pretty much a hard physics limit. Trying to pull gold out of the ocean to pay for pulling salt out of the ocean is --again not a chemist but-- probably thermodynamically worse.
- phkahler 3y ago>> if we can master desalination then humanity is in a great spot in regards to fresh water. Don't forget that we actually mine salt, a lot of which ends up in the sea. A million years from now we might regret that ;-)
- riffic 3y agonear infinite? there is literally a finite amount of water in this planet and it can be quantified objectively. https://en.wikipedia.org/wiki/Water_distribution_on_Earth https://en.wikipedia.org/wiki/Water_distribution_on_Earth
- anon____ 3y agoThe volume of the Pacific Ocean is 1.583x10^8 cubic miles. (https://www.wolframalpha.com/input?i=volume+of+pacific+ocean+in+cubic+miles&lang=ja https://www.wolframalpha.com/input?i=volume+of+pacific+ocean...) The world's freshwater need is about 950 cubic miles a year. (https://www.wolframalpha.com/input?i=worldwide+water+use+in+cubic+miles&lang=ja https://www.wolframalpha.com/input?i=worldwide+water+use+in+...) You can just put the leftovers back without worrying much about it.
- ninkendo 3y ago> You can just put the leftovers back without worrying much about it. Yes, just not all in one place/time. Separating seawater into pure water in one place and pure brine in another, you don’t want to let that brine out all at once in one spot, it’ll kill a lot of ocean life. Most desal plants that are attempting to do this right, will pump the brine into pipes that diffuse it over a wide area to avoid oversalinating. And it still kills a lot of ocean life.
- fiddlerwoaroof 3y agoIt might be better just to sacrifice specific spots rather than to try to spread it evenly.
- SargeDebian 3y agoIt will still need to spread from that spot.
- fiddlerwoaroof 3y agoYeah, but depending on the details and design of the sacrificed area, it might be less environmental impact overall.
- chongli 3y agoOr another solution would be just to take a hit on efficiency and not produce highly concentrated brine as a water product. If instead we extract just a bit of fresh water out and return saltwater with slightly elevated salt concentration then it wouldn’t be so lethal to marine life. Or we could have a premix station where we pump in sea water and mix it with brine at a certain ratio and then return that to the sea.
- fallat 3y agoLike others have said, there will always be a cost X to desalinate water. I think the best way to pay for X, is to use energy from an external source. External from the Earth. I'm obviously talking about the Sun. We could use the removed material as a general filler. I'm sure we can get creative about it. I think the problem is lack of incentives and misalignment of goals amongst people. I truly think if we can figure out how to how to use the most out of the Sun's rays - i.e. as most directly as possible - we will solve all our needs. The energy is truly free to the Earth.
- eru 3y agoYou can also work on making that 'X' as small as possible. There's a thermodynamic fundamental lower limit on the amount of energy needed to desalinate water, but it's absurdly small. Much smaller than the amount of energy we use in practice with current technologies. (Just like there's a thermodynamic lower limit on how much energy a computer needs. But it's also extremely low. See https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle )
- frotaur 3y agoAre you sure the thermodynamic limit on water desalination is extremely small ? I was under the impression that the salt bonds dissolved by water are quite strong and thus require a non-negligible amount of energy to reverse (for instance, if you go about it by evaporating the water, it is very much several thousands of order of magnitude above landauer levels). Edit, found in another comment : For example, desalinating seawater with a typical seawater salt concentration of 35 g L–1 (corresponding osmotic pressure of 29.7 bar) and 50% water recovery (i.e., 50% of the feed stream becomes purified water and 50% becomes brine) requires at least 1.1 kWh per cubic meter of purified water. Regardless of the desalination technology, it is impossible to desalinate water using less energy than that determined by eq 12. 1.1 KWh per cubic meter is very much NOT a negligible amount, so the landauer analogy is incorrect.
- eru 3y agoThanks for looking it up. Could you link to the sources? Thanks! I stand corrected in that case.
- csomar 3y agoThere is enough fresh water out there. The problem is that most countries are not building infrastructure to take advantage of it.
- Cthulhu_ 3y agoCost / benefit, but also, reserves are running low. Worldwide there's news about how underground aquifers are emptying out faster than they naturally restore. That's relatively easy and low cost to acquire, once that is no longer an option, water will explode in price. I'm confident that in our generation we'll see mass migrations due to water shortages in the west. California is already at risk, I gathered.
- Tangurena2 3y agoIt is also mostly in "the wrong place". I keep reading about these fantasies of pumping water from large rivers in the MidWest (like the Missouri or Mississippi) to the deserts of Utah or Arizona. The altitude difference is enormous - every drop of water would have to be pumped uphill at least one mile in altitude to get it from, say Kansas City (which is about 800 feet above sea level) up over the Rockies into the places were people should not be living. And what makes it worse is that the majority of water used in those states goes towards agriculture (82% in the case of Utah), where farmers pay less than 1% of the cost of the water they use.
- carlosjobim 3y ago> It is also mostly in "the wrong place". It's not the water that is in the wrong place. People are not supposed to live in places that can't sustain their numbers.
- eru 3y agoDesalination has become a lot better in the last decade or so. Israel even turned into a water exported thanks to the technology. See eg https://www.timesofisrael.com/how-israel-became-a-water-superpower/ https://www.timesofisrael.com/how-israel-became-a-water-supe... and https://blogs.worldbank.org/water/israel-how-meeting-water-challenges-spurred-dynamic-export-industry https://blogs.worldbank.org/water/israel-how-meeting-water-c...
- bmitc 3y agoFurther destroying the ocean's balance doesn't seem like the best idea. It literally drives life on Earth.