Engineers at MIT and in China are aiming to turn seawater into drinking water with a completely passive device that is inspired by the ocean, and powered by the sun.
In a paper appearing today in the journal Joule, the team outlines the design for a new solar desalination system that takes in saltwater and heats it with natural sunlight.
The researchers estimate that if the system is scaled up to the size of a small suitcase, it could produce about 4 to 6 liters of drinking water per hour and last several years before requiring replacement parts. At this scale and performance, the system could produce drinking water at a rate and price that is cheaper than tap water.
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Article doesn’t mention what the unit does with the salt waste.
I support this 100%, but desalination presents a unique problem: what do we do with all the salt? Maybe the unit uses it for something, but otherwise it just miniaturizes a problem that we’re already working on.
If this works, it’s better than anything we have , which costs grid energy and dumps brine all the same. If anything, the smaller scale makes it easier to distribute and dilute the output brine.
If sea levels rise as much as they’re supposed to, this will be an invaluable tool for an enormous proportion of the country. My concern comes from capitalism getting its hooks into this.
Wait what country?
Which country are you referring to?
Capitalism bad, sure, but you can’t deny it has a way of making things scalable and affordable. If some venture co started the infrastructure to mass produce this stuff and make it possible for everybody to afford it would it be that bad?
What? No, my friend you misunderstand. Mass-production makes stuff affordable and scalable. Capitalism makes it so wealth is horded and only the rich get to decide what gets made. You vote with your dollar while a billionaire votes with theirs, guess who wins.
Mass-production is not a capitalism-exclusive unlock, it’s a dlc that can be redeemed in any economic system.
Without the motivation to make a profit, few entities are both willing and able to engage in the considerable expense, risk, and effort required to spin up a mass production line.
I think “thirst” and “hunger” predate “profit” as a motive by several hundred million years.
Yeah, Neanderthals were famous for their efficient large-scale manufacturing capabilities
Weird, there was lots of mass production in the Soviet Union. Please explain.
Governments are one of the few entities that are able (and occasionally willing) to spin up a mass production endeavor without the profit motive necessarily present.
Sometimes they essentially do this themselves via federal employees, or contractors. Sometimes they achieve the ends indirectly by incentivizing private companies with subsidies and the like.
Regardless of how it gets done, everyone shows up for work in the morning motivated by something. In the Soviet Union this was often the fear of imprisonment or other such violence, which was a really shitty situation for a lot of people to be in. In the modern world, it’s typically the hope that the money made will pay for food and housing and such.
The capitalist entity was the state, the political elites the ones hoarding wealth, everyone else getting the shaft.
when, all of human history must be like 250 years old…
Right. We live in a capitalistic society though, not in another one. So either “capitalism gets its hooks” on this stuff or it stays inconvenient and unaffordable. Then we can speak about fantasy scenarios all we want…
Evaporate it to solid, store it if need be, or distribute it back into the sea in absorbable chunks. The water’s ending up back in the sea eventually anyway, see water cycle, so it should be zero sum, just need to avoid local overloads. Seems eminently solvable.
Depending on the desalination method, you can also harvest lithium while your at it.
Sounds so easy for you but what to do with the excess salt is the only real problem with desalination that we have for decades now. It’s not easy to solve.
That’s only the second part of the problem too. The first part is how do we stop the salt from building up inside the device?
You’ve got a point, but I’m going with ‘It’d eat into our profits and no-one’s making us’.
Eventually is an important word here. With the raise of temperature, the amount of vapor in the air raises too.
Hehe, adorable chunks…
Increasing ocean salinity is a very bad idea.
At the end of its cycle - after use and via sewage systems/rivers - that water will end back in the ocean, were the salt went.
In fact not putting the salt in the ocean and instead storing it as a solid on land would over time reduce the ocean salinity as the water would end back in the ocean but not the salt.
You’re correct, but so are they. In the long term and at a large scale, it balances out, but in the short term, there is a very real concern about local salinity levels wherever you’re reintroducing that salt to the ocean. Keeping up with the desalination plants will be a tricky business of logistics to avoid destroying the ecosystem around where you’re dumping that salt.
Adding the salt into water leaving sewage systems before it returns to the ocean might be a good idea, as you could basically kill two birds with one stone: put the salt back in the ocean while also avoiding damaging the local ecosystem with the fresh water of the sewage system reducing local salinity levels. But I’m no engineer or water treatment specialist, so I dunno if that’s at all a real solution.
You hit the nail in the head on that first part. People don’t realize exactly how long the water cycle takes to recover to natural levels when human intervention is accounted for. This is something that we are talking centuries to make happen, and that’s assuming we go at a steady rate rather than desalinate like we are trying to suck the oceans dry.
Increasing ocean salinity is a good idea. With all the ice caps melting, salinity is going further down. The salt makes the water denser, and that helps regulate temperatures. Also, the salinity differences between the poles and equator create a general current that cycles the water.
Plus, removing the salt and eventually returning the water is bad for ocean life. Their bodies need the salt.
You’re removing salt and water. So you are increasing salinity when returning it to the ocean.
The water too ends up back in the ocean at the end of its cycle (same as what happens with water evaporated from the ocean which ends up raining on land) after having been used.
What that paper you linked looks into (and indeed it is important) are the local effects of constantly releasing the brine in an area, since it locally increases the salinity of the water.
So yeah, it’s a valid problem, but not a “we can’t put the salt back in the ocean” (in fact we have do it, to otherwise over time the salinity of the ocean will decrease as the water gets returned to the ocean but in that scenario the salt would not) but rather a “we can’t just have some outlets discharging brine always in the same space” problem.
It’s a “polution with brine water” problem rather than a “salinity of the ocean” one.
The water does get back into the ocean sooner or later, at least most of the time, see - rivers
Someone doesn’t understand what zero sum means
Don’t you just dump it back in the sea? Diluting should make this a minor issue right?
That’s what I always thought, but the local effects of hypersalinated water can be terrible for any nearby life
Create some sort of Dead Sea salt bath / salt therapy place where people can float in the saline waters or something for cheap. Then flood a converted parking lot with the saltwater and dry it off for
rusting carsdeicing roads on the east coast.This is mostly a scale dependent issue. The size of this unit means it’s probably not a concern unless you ended up making thousands of them.
While true, I consider the issue very minor compared to getting people clean drinking water. There are no perfect solutions in society. Just a series of trade-offs, maximising benefits and minimising costs.
Yeah, that coastal community probably didn’t need any fish.
Large coastal communities don’t just go down to the local jetty and cast hooks into the water by the shore. Commercial fishing is done by large ships out in the ocean, far away from the cities.
You probably wouldn’t want to fish near a city’s sewer outflows anyway.
Depends on what you mean by far away and what kind of fish you’re talking about. Big fish like tuna are often caught far out at sea, but they’re also caught by the same small boats that do charter fishing an hour or two out from the shore. There’s plenty of inshore fishing that would be at risk, especially in bays where the salt would be less easily dispersed. I used to work at a fish market, and offhand I can think of multiple fishing industries that would be put at risk by carelessly dumping salt back in the ocean. The majority of shellfish, for example, is caught within sight of the beach. I don’t know if it’s still the case, but there used to be a ton of fishing done in Boston Harbor, and I’ve heard stories of crates of lobsters being opened only to find the lobsters carrying pieces of bodies dumped by the mob off the docks and into the harbor.
i consider 🤣 ehm ehm … I consider! I CONSIDER 😁
who the hell cares about what i consider? upvote this if you don’t give a shit about my considerations 😉
Thats the big ecological question. If we do this at scale, we’ll be releasing more briny water back into the sea than we take. Over time on industrial scales, what will this do to the oceans? Is the increased salinity negligible, even at large scales? Or will it cause marine wildlife to die out?
Think of it this way. Burning a pile of wood generates CO2. So first burning a bunch of gas or coal. A couple campfires won’t make a dent on the atmospheric composition. It’s only when we go this en masse and at industrial scales that we add appreciable CO2 to the atmosphere and cause global warming.
The ideal way to handle desalination would be for us to use the salt that’s produced, so the concentration in the ocean remains unchanged with respect to desalination.
But the water is all being returned to the ocean rather quickly. It’s not quite the same with CO2.
There’s some localized issues to deal with, but it’s not going to be a global salinity increase as we aren’t changing the form of the water and storing it, like the polar ice does.
So in fact, the ocean should already be desalinating slightly from the melting ice caps.
I thought about the ice caps, yeah. It’s just something that warrants long term monitoring and observation.
You cook with it.
Fellow Frenchman detected.
… can’t you just put i straight back into the sea?
Suitcase sized device? Only one or two of them nearby? Then that’s not a problem.
If you scale it to industrial sizes/quantities then the extra salinity in the area where you dump the waste products becomes an issue.
Eg my coastal city uses about 135 megalitres of water a day. Supplying all that from seawater requires you to put about 5 metric tons of salt somewhere, every 24 hours.
Stick 5 tons of salt a day directly in one place in shallow waters just offshore and you’ll end up with a dead zone a mile wide pretty quickly.
So now you’ve got to water that salt down into something that’s only slightly saltier than usual and that can be difficult because for my example 135 million litres of water a day, you want to dilute the waste by at least 10x that (to make it approx 10 percent saltier) and now you’re cycling a billion-plus litres a day around the place.
So this is pretty cool stuff, but just need to be careful with the side effects when it’s scaled up.
As I understand it such “waste salt” is usually returned to the ocean in the form of brine. The brine is denser than the ocean water around it so it flows down the slope of the land like a river into the deeps where it eventually dilutes back into the ambient water.
Brine flows and brine pools happen naturally in some places in the ocean already. They’re common underneath sea ice - sea ice is pure water and brines flow out of it as it forms. There are brine pools in the depths of the Mediterranean because that sea has greater evaporation than it does fresh water inflow. It’s not some new horror humanity is inflicting on the ocean. If care is taken with routing the brine it shouldn’t cause much trouble to the ecosystem.
It’s already a problem in some areas. It’s the scale that we do things at that causes the problem.
CO2 also exists in large quantities by natural process, but when you increase it on a massive scale for a century, it adds up to disaster.
Suitcase sized device? Only one or two of them nearby?
About as many as there are people living nearby.
And guess where all that water ends up?
It’s a closed circle so if you don’t transport the water far away it should just go back to the sea.
Also the sea is kind of large…
It’s not about the global or countrywide scale. It’s about the local scale. If you take a cup of salt and eat it, it’s going to end back up in the ocean eventually, but it’ll make you sick before it gets there. Dumping salt into an area is going to screw with the ecosystem in that area, in a major way. We actually have similar problems in many areas due to stuff like fertilizer runoff from people’s lawns during rainstorms, causing toxic algae blooms in ponds and around beaches.
It’s able to successfully reject the salt waste, which is a success. The question will be if it can reject enough of it.
The brine itself though is a really good question. I think there’s some existing uses for it, but we’d probably need to think of new applications for it as well.
I think the unit dumps it back into the surrounding water. I don’t think this will replace large scale reverse osmosis, but if it can produce enough for a couple people and not require external power, replacement filters, or frequent maintenance, then it’s has potential use for costal communities.
Just toss it back out in the ocean or make lots of jerky.
You put it back in the ocean. Laughable to think you would alter the ocean’s salt content this way. All of the freshwater produced would eventually end up back in the ocean anyway.
On the large scale this is true, but the problem is that the concentrated brine doesn’t instantly dilute back into the entire ocean. In large quantities, the waste outflow would damage the local coastal ecosystem before it was sufficiently diluted.
What is “sufficiently diluted” this device discharges brine at only slightly higher levels than what it takes in.
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They’re getting really good at working with tidal flow and weather to ensure they don’t cause problems, it’s just all got to be built into the system when they design it
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This sounds fantastic on its face, but I seem to keep on hearing about how desalination will solve all kinds of problems and we still have this particular problem.
The missing piece, it seems, is the will for it to be used as infra at scale. Meanwhile selling bottled water taken for free from public lands for several dollars a liter in single-use bottles remains a multi-billion dollar industry. (an industry, I might add, that is aggressive about lobbying to protect its interests)
Devices like this are a lifeline for communities in developing nations. Who are the first and worst affected by water shortages and salt water intrusions into their fresh water sources.
Also the poorest and least likely to get the help from the people with the resources to help.
Not to mention if we do this at enough scale it will raise the salinity of the ocean and, you know, kill everything.
That’s pretty unlikely, given that the water systems are more of less closed, and the volume of water in the oceans is so massive that it wouldn’t make an appreciable difference at any reasonable scale.
Keep in mind that this isn’t the creation of desalination, just making it cheaper. There are already plants that do this at a scale of 50 million gallons a day, or under 1 trillionth of the oceans.Localized salinity changes are more likely to be an issue, but for that I think they just mix that salt back in with processed waste water, making it roughly neutral.
will raise the salinity of the ocean
If care isn’t taken to avoid concentrating brine going back in just one spot, sure that could create localized problems. Buuut, you realize that the oceans constantly lose water to evaporation and their salinity is more or less stable, right? Every bit of rain or snow that falls on land (most of which returns to the ocean eventually) is water the ocean can be without and still not too salty for life.
Speaking of salinity, the Atlantic Meridional Overturning Current (which in normal conditions, is the deep/cold return current from the gulf stream -> North Atlantic) is running into a big damned problem because Greenland is melting and all that fresh water pouring off of it is disrupting the return flow of cold water to the tropics. That’s why the Gulf Stream has been so hot- it’s not getting return feed from its radiator in the North Atlantic, and meanwhile the North Atlantic is getting colder because it’s not cycling water back south, and that prevents hot Gulf Stream water from getting there.
Edit: I recently learned that concentrated brine regions in the oceans (called brine pools) are a thing. There are massive salt deposits (as much as 8km thick) under the bottom of the Gulf of Mexico today, the legacy of a time when the gulf was closed off from the oceans- when it refilled, the salt layer was covered over. Today, the deposition on top of it is heavy enough that subsidence within it squeezes the softer salt around, occasionally exposing that salt to the ocean water.
This sounds like an idea for a disaster movie!
(Yes, I know.)
Which also prevents ice from forming compounding more problems(the big massive problem) which we’re trying to avoid talking about right now.
The oceans have been collecting salt from runoff for billions of years, humans reintroducing some of that salt before the water will not affect ocean salinity.
cool, but the real cost of desalination is transporting the desalinated water upstream, which presumably would also need to be done here
Considering how many people live near the coast it would still be a huge step forward. Right now even for most coastal cities desalination isn’t cost effective and they have to import water from inland.
And by not having to deliver as much water from inland to the coast that water can be distributed more for people living inland.
Yes, it’s not going to make inhospitable areas liveable but it’s not just “cool”.
the issue with water networks is they work great when you have the source (usually dams) upstream, water essentially is gravity fed throughout the network with only some localised pumping for certain elevated locations. wastewater again gravity fed towards treatment plants at the lowest point (usually the ocean), so usually, its fairly efficient, despite still requiring enormous amounts of energy.
this doesnt solve that. it has the source where the end point is. the desalinated water needs to be pumped up, to then be gravity fed through the network. In some places, it is worth the cost and energy due to water scarcity, and im not knocking the technology. but claiming its cheaper than tap water is patently false because the distribution cost is far higher
They do this anyway…what do u think a water tower is???
Water towers are designed to provide steady pressure through demand spikes. That’s completely different from transporting the water.
you are completely missing the point mate.
desalinated water STARTS at the lowest possible point in the catchment. Rain water does not.
Bruh where I’m at the water starts underground what are u talking about???
cool, definitely not a typical network
only some localised pumping for certain elevated locations.
Sounds like this could be feasible for coastal places that are water-thirsty then? (I mean if, for example, L.A. was self-sufficient (or close to it) on water, that would mean quite a lot for its upstream/uphill neighbors). Today L.A. draws from local groundwater, canals from inland, and the Colorado River Aqueduct- and everyone that also depends on those has to make allowances for LA.
if its a relatively flat coastal location, its possible. FWIW I work for a water utility in a coastal city and we have a desal plant. Ive seen the figures. the cost of desalinated water compared to the catchment water is an order of magnitude difference. Sounds like LA it would be ideal for the environmental reasons alone though
Ground water rarely doesn’t require pumping.
A suitcase-sized, passive desalination device also sounds like a must-have for boats of all sizes, if they spend more than a few hours on sea.
True…otherwise it’s reverse hydro, which could be done with surplus renewables at peak times, but not at more than 10km… This is mostly aimed at coastal communities (and sustainable floating villages 😁)
…or you could say fuck it, go full Dutch and build wind turbines and reservoirs everywhere to get water to all crops and green deserts 😊.
Since this produces distilled water, I imagine you could use it to filter any water, not just saltwater. You’d still need to boil it to make sure it was free of pathogens, in either case, and add an appropriate amount of salts and minerals back in to make it potable for the long term.
You’re correct about readding a small amount of salts and minerals, but you may not actually need to boil it. Often the membranes used for distillation have pores that are so small that only individual atoms can go through them, which effectively filters out bacteria and virions.
minerals and salts, you get them from what you eat. you don’t need to add them to your distilled water.
You’re correct to an extent, but water is still a very useful source of minerals. Potassium, calcium, magnesium, and fluoride are all minerals and salts that we primarily get from water, and thus distilled water can cause a person to become deficient in these elements (Source).
primarily? That’s an exaggeration.
- potassium > simply a banana
- calcium > cheese, yoghurt, milk or if you’re vegan almonds and plant based milk, &c
- magnesium > chocolate (cacao), nuts, spinach
the list goes on and on. Yes, you’re right, if you drink distilled water, you have to pay attention to deficiency but it’s not a big deal. Water, unless it’s enriched artificially, has traces of these minerals.
The other issue is oversalination localized around the waste discharge when you wash away the extracted salt
SONOFABIT*H, I’ve been working on a project exactly like this with my friend for a couple years. Hella congrats they got it done and working first but damn :'( I was too slow.
Imma go sadly crush some bugles with my face stones now
Keep doing it anyway. They still haven’t gotten to market, and I want choices when it comes to my post apocalyptic water suitcases.
Zero reason to stop. Until this is put into practice it’s just another article promising a future that isn’t here.
Sounds like a great thing to include in your resume if you want them to hire you to keep working on it. Assuming theirs is better and succeeds.
Maybe you could contact them to do some joint work? If they’ve proven out the concept, the next step is scale up. And that’s a gigantic fucking step. I should think they’ll want people who are very familiar with the technology instead of people they have to train from the start. Alternatively, since this is in academia, you could work with them on commercializing it.
You’ve got options! I think it’s probably wise to consider your next moves at this point, since they’d be likely to beat you to a patent :/.
Good luck my friend, I’m rooting for you! And if I had more expertise in transient fluid and heat dynamics I’d offer some of my help.
Where’s the cheaper part?
It’s just a giant plastic bag. They catch the runoff with a giant cup.
As soon as I saw the words “powered by the sun” in the synopsis, I knew what this was. I learned this during survival training, it’s a great way to turn piss (or any other undrinkable water) into clean water. And yeah, all you need is some plastic and a cup. Let the water evaporate (power of the sun) and collect the droplets in something. Had no idea that needed a science paper.
Here’s the problem with desalination, tho: what do you do with the leftover super-brine? It’s pretty gnar stuff, like almost poison. Wide-scale desalination would produce tons of it every day. Most solutions i’ve heard are like “just dump it back in the ocean!” Which, yeah, how could that ever go wrong?
Did you read the article? You reject the slightly saltier water.
On a commerical scale the super brine may be economical to harvest the lithium. I know systems were getting close to being able to economically extract lithium from sea water. A more concentrated solution should make it easier.
Also, this would be distilled water? Or do they have some process to add the necessary minerals afterwards? I didn’t see anything about that. Because drinking distilled water isn’t exactly good for you.
There’s nothing particularly wrong with drinking distilled water as long as you are getting enough minerals and electrolytes from the rest of your diet.
True. However I would think that a system such as this would be used mostly in developing countries where getting all those minerals from your diet is not a given.
Exactly, imagine how much water can you gather in a hot climate that doesn’t evaporate untilyou get it or grow algae/fungi/protozoa/things that aren good for you.
I feel like every week we hear about some huge breakthrough that is supposed to revolutionize clean drinking water technology and save the world, but nothing ever comes of it.
I know this stuff takes time to develop, and not every idea is going to work, but it would be nice if one of these things actually did pan out and start being useful to solve our drinking water issues.
solving issues isn’t profitable
It’s unfortunately not a profitability issue, at least not necessarily. I wish that it was, because then all you need is investors like silicon valley and you can run at a loss.
What the researchers have created here is a bench top device. It needs to be scaled up for widespread commercial use, and that’s where things get difficult. Scale up is one of the things my field does, although I don’t have personal experience with it. Scale up is where a lot of projects die because of new issues developing.
This device is relying on flow patterns and convection currents. That gives me some concern actually, because these patterns can change a lot with larger vessels. A common industry problem with fluid flow in larger tanks is that you’ll get “dead zones”. The internal flow dynamics are such that some parts of the vessel see no actual flow, and it’s just stagnant. That’s a big problem when you’re relying on flow to keep your entire tank cool or to carry out precipitated salts.
Cool insight - thanks!
You’re welcome. One of the disappointing things I realized as I learned more in college wasn’t that we had easy solutions that were being suppressed by the rich, but really difficult solutions that were being discouraged by the rich.
It’s a matter of scale. You first try designs and concepts on a bench top scale in a lab. If that works, you scale the project up. And that scale up can reveal myriad problems. The internal heat and flow dynamics are going to change, and that may require a lot of adjustments. Specifically in this case, you may find that salt deposition is negligible at bench top scales, but when you start exploring larger units, salt ends up accumulating and causing issues. Scale up is part of the scientific process like any other, and it can end in failure unfortunately.
All this stuff is like planning to colonize mars before we stop destroying earth. There is plenty of water if we just stop fucking pumping it all out and wasting it.
We’re past the point where we can stop it wholesale.
We already have aquifers barely holding on, we’ve lost major sources of fresh water already.
I’m all for climate action, but we also need to starting developing technologies for living in the bed we’ve made.
Folks keep talking about climate change like it’s some future event. You are living through it right now.
you know how we can stop the massive drain on the aquifers? by not allowing everyone to tap it as much as they want, farmers will have to deal with 30% fewer yields on corn, Nestle 'n Co. will lose their money printer, but that’s all we would need to save the American aquifers, to STOP FARMING INT THE DESERT
That 30% less yields means 30% more cost for the consumer, not Nestle.
well i brought up nestle as in them just bottling free water, but a large amount of that added agriculture is used to produce corn that is inedible for human consumption and only used as animal feed, basis for fertilizer, or HFCS.
and maybe we need to put a cap on the amount of profit a company like Nestle can extract.
Pretty sure a profit cap goes against the entire concept of the stock market. It would probably collapse it.
Cool. Where do I sign up?
go to wherever fox is screaming Nazi, specifically Fox News
Yeah this is a very forward facing technology that may end up becoming a lifesaver.
All farmers growing cotton in the middle of the fucking desert along the colorado river basin disagree with you
Or how they destroyed the Aral sea for cotton
Clean freshwater isn’t evenly distributed across the world and it’s not easy or cheap to transport. This kind of tech can help the people that will be most impacted by climate change to survive.
Can you believe some people actually drink that stuff straight from the tap? It’s like they don’t even care about the golf courses at all!
why would anyone drink plain old boring water when you can get Mt. Dew from any gas station?
Brawndo, it’s got what plants crave
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What’s wrong with desalination research? Water is essential to life, and most water on Earth is salinated. The practical value of this research is apparent, both for ships on sea and coastal regions. So I don’t see how these attempts are “worthless”, and how it would be bad if they receive more “free money”.
The article talks about what could have been a challenge faced by the junkyard scrap model, and how they solved it:
Each stage contained an evaporator and a condenser that used heat from the sun to passively separate salt from incoming water. That design, which the team tested on the roof of an MIT building, efficiently converted the sun’s energy to evaporate water, which was then condensed into drinkable water. But the salt that was left over quickly accumulated as crystals that clogged the system after a few days. In a real-world setting, a user would have to place stages on a frequent basis, which would significantly increase the system’s overall cost.
In a follow-up effort, they devised a solution with a similar layered configuration, this time with an added feature that helped to circulate the incoming water as well as any leftover salt. While this design prevented salt from settling and accumulating on the device, it desalinated water at a relatively low rate.
In the latest iteration, the team believes it has landed on a design that achieves both a high water-production rate, and high salt rejection, meaning that the system can quickly and reliably produce drinking water for an extended period. The key to their new design is a combination of their two previous concepts: a multistage system of evaporators and condensers, that is also configured to boost the circulation of water — and salt — within each stage.
I’m not sure how much money is in desalination, but it’s certainly an industry. If a group comes up with a new method, and then nothing happens with it, it’s probably because it’s either not that great after all, or not that cost effective.
Maybe a problem is that the countries where it’s needed the most are not exactly the richest countries: https://ourworldindata.org/water-use-stress#what-share-of-freshwater-resources-do-we-use
several countries across the Middle East, North Africa & South Asia have extremely high levels of water stress. Many, such as Saudi Arabia, Egypt, United Arab Emirates, Syria, Pakistan, Libya have withdrawal rates well in excess of 100 percent — this means they are either extracting unsustainably from existing aquifer sources, or produce a large share of water from desalinisation.
you know, if you build a large solar still, you just have to flush it every couple cycles to deal with the salt, and it can be as big as you can make a warehouse…
How do you know that you’re flushing out all the salts with each flush? Are you able to reach every part of the reservoir with the flush? Even if you can, what do the flow patterns look like – are there dead zones with no flow?
It really isn’t as simple as you describe, although I really wish that it was.
So the fun part is, all of what you mentioned, doesn’t matter, because you don’t actually need to get every bit of salt out of the reservoir, so you just flush out a good deal of it with more salt water!
you read this paper and its complexities and assumed that the things mentioned are inherently important to the functioning of the system, but like the Tesla-trucks and acceleration, they really aren’t.
all you need for the system to work is liquid, as long as there is more osmotic pressure pulling the water away from the salt than the hydrogen bonds produce.
low tech, easy to scale, and already being done
Yes and no. I get what you’re saying. No wash is 100% efficient, nor does it have to be. It’s just going to set the number of runs the unit can do before it needs to go offline for more intensive cleaning. Short run times though lead to more expensive operation. What this work does is increase the run time by more efficiently removing salt.
Do you get what I mean? Long term salt buildup is going to cause problems, and the more slowly you can make that happen, the better.
salt is not limestone
What does that have to do with anything?
For desalination all you need is a glass bowl and two metal bowls. You put the bigger metal bowl on the ground, the smaller metal bowl in the middle, and the glass bowl over the little bowl. The salt water evaporates from the little bowl and condenses down the glass bowl into the bigger bowl. You can run this setup pretty much forever, there’s no moving parts and minimal maintenance. That’s how simple desalination is. All solar desalination projects work on this principle.
The reason we don’t use it is the same reason we don’t do so many things: there is no immediate monetary cost to destroying the environment and using up common resources, so desalination is “expensive” compared to just using up the groundwater. Once all the groundwater is used up and the rivers run dry, desalination will be very competitive.
Delete this before Nestle sees it.
“Could”. What kind of fucking title is this?
Either it does or it doesn’t.
It’s a good title. They don’t know if it will be cheaper or not until they go and actually scale it up. Based on the prototype their projections say it should but it’s very likely they would run into issues that drive up the cost.
They do say in the article that they haven’t scaled it up yet. If a large version works same as the small version it would do it. Hence “could”.
The massic heat capacity of water is
4184 J⋅kg⁻¹⋅K⁻¹. To heat one 1 Liter (1 kg) of water from 30ºC to 100ºC it would take4184×(100-30) = 2.929e5 J. We want 4 liters however, so we multiply that by 4 and get2.929e5 J × 4 = 1,172e6 JTo then turn that heated water into vapor it would require some more energy. The vaporization enthalpy of water is4,066e4 J⋅mol⁻¹, and has a molar density of1,80153e-2 kg⋅mol⁻¹(so 4 liters (4 kg) of water in moles would be4 / 1,80153e-2 = 2,22033e2 mol), which means that to vaporize the four liters of water we would need2,22033e2 × 4,066e4 = 9,028e6 J(I think I might have made a mistake here somewhere, because I don’t think it would only need 8 times more energy to completely vaporize the water, compared to the amount of energy required to heat it, but I can’t find the problem). So the total energy to heat and vaporize 30 ºC water would be9,028e6 + 1,172e6 = 1.020e7 JLet’s take a 55x40x23 cm suitcase. And let’s assume a solar irradiance of 1000 W⋅m⁻² (which is what this site says is a normal solar irradiance to be expected on a clear day on the equator). Let’s assume three faces are exposed to the sun and all equally so (three faces receive 1000 W⋅m⁻² while the other three receive none, which would not happen since on a rectangular cuboid, like a suitcase, you can’t have all three faces facing directly towards the sun). The box would be receiving
(0.55×0.40+0.40×0.23+0.55×0.23)×1000 = 438.5 W, which means that over one hour (3600 s), it would receive438.5×(3600) = 1,5786e6 J, which is less than the required1.020e7 J(by almost an order of magnitude), so it wouldn’t be possible to heat and vaporize 4 liters of water in an hour.What am I missing?
You’re assuming that all heat energy input leaves with the water once it vaporises, which is unnecessary and indeed undesirable.
If you use the incoming water to condense the output vapor, you can recover and reuse a lot of the heat energy, plus you get output water at a much more reasonable temperature.
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Nothing. These so called miracle bullshit devices shows up annually at random times to over promise under deliver so that media will talk about and gullible people lose their money on.
‘Cheaper’….desalination eats a lot of power. This is causing a huge problem over a minor inconvenience.
The article explicitly states that it is directly powered by the sun.
I’ve heard this one before and the systems never scale w/o subsidy and/or capture of the salts for industrial/rare earth use.
And how does buying panels or power make it cheaper than filtering river water?
Solar panels is an entirely other discussion about the issues they themselves bring especially with covering the earth with more black surface which is negating the point of what the ice was doing to cool the earth before it melted. Ocean water is black and solar panels are black. Albedo effect. You’re turning the earth into a cinder block.
Surely you cannot pretend this is a real problem? This is nothing compared to the loss of Albedo caused by ice melting, and also nothing compared to the fossil fuels that would otherwise go to similar purposes.
Dodge the uncomfortable fact.
Getting water to places that don’t have access to fresh water is not a minor inconvenience.
consumers already have tap water for comparison hence the title of it suggesting to be cheaper. Not as altruistic. Agreed it could help someone who doesn’t have accesss. But I disagree that simply taking it as an option of the two because one seems cheaper is not actually cheaper so much as an impact that everyone should turn to it as a sole option that is not being considered here.
If you read about this device you’ll find it’s solar powered. Solar powered desalinization boxes are nothing new, but this one doesn’t get clogged quickly like previous models have. If it scales up as well as they’re hoping this could really help a ton of people.
Solar panels also have an issue that come with it covering the earth with more black surface which is negating the point of what the ice was doing to cool the earth before it melted. Ocean water is black and solar panels are black. This is known as albedo effect.
then you have the issue of helping people. Sure, helping people who have NO ACCESS TO WATER this should definitely be an option.
But offering it to people whom already have tap water and access to water as a secondary ‘cheaper’ option is not so altruistic particularly if we don’t consider the impact as the aforementioned non reflective surface that is a much bigger impact on global warming. Hence that solar panels aren’t an all-source solution for the overall issues.
They’re not solar panels, they’re solar powered by a black sheet that heats up the box to get the water evaporating. Creating clean tap water also takes energy so unless the effect of the box’s lower albedo is greater than the environmental cost of cleaning and transporting water it’s still a net positive, especially in those parts of the world where fresh water is scarce.
Again, not arguing if it’s needed where water is scarce, So the topic is switching to a cheaper form for tap water and this is being sold as an idea to people who already have water.
I saw that more of them contextualizing how cheap it is but I could be wrong
We have destination where I live but the problem is this: the water often smells like fish. And it’s very hard because they use so many chemicals.
I don’t think desalination is the solution.
I don’t think desalination is the solution.
Solution to what?
Literally all rainwater comes from solar-powered evaporative desalination. There is nothing better than that, whatever the use.
Around half of Israel’s drinking water is desalinated, and I’ve never encountered what you describe.
Not from Israel but our entire water system is desalinated and I’ve never experienced any issue with the taste, in fact the opposite is true. Pure clean drinking water.
I will agree with the hardness aspect but other than that it’s perfectly good, i’ve tasted worse bottled mineral water.
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This circulation, combined with the sun’s heat, drives water to evaporate, leaving salt behind. The resulting water vapor can then be condensed and collected as pure, drinkable water.
This is not a chemical desalination. It’s a classic solar distiller. The output is distilled water. You actually want to cut it with a bit of seawater, because drinking distilled water pulls salts and minerals out of you, and then you die.
Drinking distilled water is actually not that dangerous, so long as you get salts some other way (food!). In order for distilled water to cause runaway deplasmolytic processes, you’d need to spend a lot of time only drinking that, afair from high school bio.
I mean you die if you only drink distilled water and never consume anything else, but the same is still true of mineral water
I was unclear - that’s exactly what I meant. I was thinking of a suitcase-sized still being used in an emergency or survival scenario, for a time anything other than “very short term.”
Producing clean water is a multi-faceted problem, your locale may require a different or multiple different solutions.
Multiple solutions are often nice cause you don’t have to rely on a single solution if one goes down or has issues.
