Submission Statements

The potential losses of existing freshwater supplies are one of the most terrifying aspects of climate change. The River Po in Italy has severely shrunk, as the snow in the Alps that feeds it, is becoming less and less due to climate change.

If that were to happen to the rivers the Himalayas feed, in India, China & SE Asia, it would be a far worse disaster.

It's hopeful to see credible tech solutions like this. As the technology works best in the sub-tropics, it could be powered by solar or wind.

But...

That water vapor becomes rain...

It's not really "free" water, that rain goes to nature and eventually human use.

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The following submission statement was provided by /u/lughnasadh:

Submission Statements

The potential losses of existing freshwater supplies are one of the most terrifying aspects of climate change. The River Po in Italy has severely shrunk, as the snow in the Alps that feeds it, is becoming less and less due to climate change.

If that were to happen to the rivers the Himalayas feed, in India, China & SE Asia, it would be a far worse disaster.

It's hopeful to see credible tech solutions like this. As the technology works best in the sub-tropics, it could be powered by solar or wind.

Please reply to OP's comment here: https://old.reddit.com/r/Futurology/comments/zx9j0b/uiuc_researchers_propose_a_new_way_to_get_fresh/j1z0fz1/

It’s a small portion of the massive amount of evaporation over the ocean surface

That’s like saying that the sunlight goes to plants so we can’t use solar panels to capture it. There is just so much of it that the small amount we are using is negligible.

You’re not serious right?

I see value in capturing the humidity there but they didn't receive the machine at all. Or did I miss it? I'm assuming it's just a standard dehumidifier at this point.

Not a lot of detail in that article. What is 210 meters wide and 100 meters in height. That diagram explains nothing.

Found the paper.

https://www.nature.com/articles/s41598-022-24314-2

The 210x100 m size of the intake is arbitrary, chosen so they can generate enough water for 500,000 people. It can be larger or smaller.

They said the main reason for the design is that it avoids generating brine from desalination.

Otherwise it is cost competitive, but not cheaper, than desalination, with the water costing around $2.20 per 1000 liters of water. (desal water is $2-$5/1000L)

Somehow I think removing moisture from above the ocean will promote evaporation in that area, which will also increase the local salinity, but I may be wrong lol.

Debbie downer probably works for Nestle?

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Lol, quick, shut down all the wind farms! We’re using up the wind.

It would slightly, but I believe the point is that by just collecting and capturing the natural water vapor that this would be no more than normal. Plus wave motion would natural refresh the water in the collection area.

I think the same could be true for pumped membrane desalination except pumping the massive amount of water needed to mix back to normal salinity would make the process more expensive.

The article even mentions:

>The researchers said one of the more elegant features of this proposed solution is that it works like the natural water cycle.
>
>“The difference is that we can guide where the evaporated water from the ocean goes,” Dominguez said.

Yep, so wherever it would have gone, it doesn't.

I didn't know that desalinization of water is in price range of $2-$5/1000L. It kinda sounds cheap/reasonable. Why it is often claimed that desalinization of water is not a good solution for world's fresh water shortage?

Two main complaints - one is that the energy required (about 5kwh per person per day) usually comes from fossil fuels, and the other is brine damaging the ocean.

The first is easily solved with solar and, with care, the second is not as big an issue as environmentalists claim - San Diego's massive salination plant (which supplies 7% of their water) has been running for 7 years and has not damaged the ocean at all.

I'm kind of a dumbass. Wouldn't that mean that less rain clouds would be created?

Also we have a HUUUUGE demand for salt as a society, so they can reuse that brine. Mostly for clearing roads at this point during poor weather, which is a whole other can of worms. (salting the earth)

Trouble is that the parts of the earth where desalination is necessary are typically very far from places where brine solution is needed to thaw roads.

Idk why people witch hunt like this. You know people genuinely don’t know right?

Do they not know about salt fog? The water vapor over the ocean is less saline than the ocean, but still saline enough to really fuck with machines that aren't designed for maritime applications.

The problem isn’t “the ocean” it’s the local environments.

The problem with brine is basically it’s toxic. You can’t really repurpose the salt and toxins that are filtered out for consumption. It’s especially bad if it happens in estuaries and small areas which really depended on fresh water. A single desal plant might help an area. The next problem is scale. Does this mean you can run 16 desal plants without issues? Not really.

I love the idea of this. Especially if there were several along the coast. Seems like it would make more sense to have the pipe carrying the harvested water to the shore plant underground. The illustration above looks a little flimsy.

Well, what I contemplated was the idea that this could potentially (if done at absolutely massive scale?) actually decrease flooding via massive rainfall and increase water in areas that need it most (something the article also alluded to). If only we could do that with wind someday too. Of course all of this boils down to temperature differences, global warming and such.

Have you been to California?

Sounds like some grad students from the middle of the country picked a project that would include travel to the coasts...

Fog is an aerosol, not vapor. Therefor it could easily be filtered out.

It sounds like a plausible idea. Someone should try it out. But know that there is no such thing as a free lunch. The process will take energy but not creating brine might make it worthwhile.

"Salt fog" is a somewhat colloquial term. Literal fog is not required for significant salt exposure.

And aerosols are not necessarily easy to filter out.

Or is a flat earther

Sure but all we’re trying to do is use less than reverse osmosis. I’m guessing it could be made more efficient by pumping so colder deep water up around the enclosure (like how those disappearing toy baby bottles work kind of) like how wastewater solids digestion is goosed by adding the FOGs captured at grease traps.

Like I said, the closely monitored environment in San Diego has not shown any ill effects.

Salt has a boiling point of nearly 1500C so it is only going to be present in air as an aerosol which again would be trivial to filter out. A coffee filter could probably get the majority of it.

Boiling and aerosols are not the only way for solids to end up in the air. For one thing, things that begin as aerosols can turn into vapor and leave airborne dust behind.

Since a storm would wipe that off the face of the earth, desalination is absolutely cheaper when you look at the cost over 20 years.

Brine buildup is only an issue in places like the black sea. Anywhere with open, circulating ocean and water currents is fine (most ocean sources).

Maybe put the discharge pipe a half a kilometre offshore and you are golden.

San Diego has access to open ocean and ocean currents. The solution to pollution is dilution in some cases. Ocean damage only happens in trapped ocean areas like the Black Sea and other dead head areas.

Brine only has 2-3x the local salt content. If you are running a giant RO system for every 1 litre of water I get out of the system I am creating around 0.5-0.6L of reject water at best. Maybe the new membranes can get down to 0.3? I don’t know what the state if the art is.

(I care for a RO system that can do 10,000L/hour).

> I believe the point is that by just collecting and capturing the natural water vapor that this would be no more than normal

I’m no expert, but isn’t it classic human folly to believe that altering one piece of the natural machine would have basically no impact?

Again, not an expert, but couldn’t something like no water vapors -> fewer rain clouds -> less rain in certain areas? Are we just punting the problem elsewhere?

A very small amount of water vapor is captured compared to the evaporation from the rest of the land and ocean.

How is this a new proposal. This is how I learned to distill salt water way back watching Voyage Of The Mimi in 7th grade.

I've read posts about this several times and they conclude that the salt that is generated by this process at scale is far more than there would be a market for and the salt that is generated is more of a sludge.

"When Praveen approached me with this idea, we both wondered why nobody had thought about it before because it seemed like such an obvious solution"

This comment within the article is ridiculous.

The capture of water vapour off oceans isn't a new concept, the material science of building a 210m x 100m tall structure sufficiently above the water that vapour is both generated and captured is challenging to say the least. While the size of the structure is of course arbitrary, you need scale to make the associated infrastructure viable.

While necessity is the mother of invention, the payback on a structure and associated infrastructure of this project is the issue... presently water is cheap, so until we are facing either a water shortage so severe that the project makes financial sense OR we decide to put people's interest above commercial gains, it just won't happen.

Vapor capture is already used in parts of northern Africa.

I haven’t read the full paper but: https://www.sciencedirect.com/science/article/abs/pii/S0025326X20308912

> A major issue of desalination is the co-produced waste called ‘brine’ or ‘reject’ which has a high salinity along with chemical residuals and is discharged into the marine environment. In addition to brine, other main issues are the high energy consumption of the desalination and brine treatment technologies as well as the air pollution due to emissions of greenhouse gasses (GHGs) and air pollutants. Other issues include entrainment and entrapment of marine species, and heavy use of chemicals.

It does suggest that depending on the type of desal, you’ll find different products and outputs. Part of it is that the water output could contain chemicals used to treat the water and other by products that still make it through the filter. The problem is that if you just blindly support desal, without considering environmental impacts, you definitely could run afoul and ruin multiple ecosystems easily. I am personally a little skeptical it can scale across the world to supply the fresh water needed for the human race without some impact to local ecosystems. I don’t think it’d impact the global ocean, so it’s kinda sus that the conversation is like “well the ocean is fine”. But the problem has always been the local environment, not a global ocean problem.

Edit:

To your comment, brine at 2-3x saltier than normal is pretty damaging to fish (and people) who aren’t used to that much brine. It’ll almost undeniably cause a lot of species to just die. That’s the problem. Life might adapt but it might not. And should we take a chance that the ecosystem will collapse?

Yeah, some solutions I've read include filling in old pit mines (many of which were dug out of salt veins because it's easy to get through), brine based storage solutions as a heat battery or ultra-cooling facilities for data centers.

Each solution has it's own problems of course, like salt leeching into ground water tables and a lack of scale to handle the possible output of brine.

Atmospheric condensation is a bit of a troublesome issue in it's own way though right, because you're altering the climate distribution of moisture. Not that we aren't altering everything all the time, but imagine if a country were to divert the flow of water from a river that historically ended in another country.

Only then imagine you're doing it with the rivers in the sky instead. Obviously it would be quite a while before capture technologies scaled up to that point, but it's not out of the realm of possibility.

There would still be a lot of water vapour if it was for small local populations but if it was scaled to produce water for millions then maybe the scale would pose a problem.

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The vapor pressure of liquids basically means that for a given pressure, temperature, etc., the liquid will produce a certain amount of vapor. The vapor will replenish itself naturally by evaporation

A few days ago I read a headline about salt based batteries being more efficient than lithium batteries. Maybe there’s a way to create batteries while also generating both power and clean water at the same time: https://energycapitalpower.com/researchers-develop-sea-salt-battery-4-times-the-capacity-of-lithium/

> You can’t really repurpose the salt and toxins that are filtered out for consumption.

Maybe we can, though:

https://energycapitalpower.com/researchers-develop-sea-salt-battery-4-times-the-capacity-of-lithium/

That’s a way different thing than desal but does present an opportunity I suppose but the problem always comes to the unpure water products that come out.

Have you been to saudia arabia

They have literal deserts of sand. I assume you could just dump it there.

*edit* Which they don't apparently. https://www.business-standard.com/article/international/saudi-arabia-s-thirst-for-water-is-creating-a-toxic-brine-problem-119010901323_1.html

If its not profitable it likely just wont happen

Yeah I think they brinier the better for those too.

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As an engineer, the project sounds insane. That is a massive structure to stick over of the ocean, and ocean water is highly corrosive so its going to take a ton of maintenance.

> Otherwise it is cost competitive

I really doubt that. That is a giant structure, which will create a ton of engineering challenges(many that won't be foreseen).

We are talking about something approaching skyscraper height, with over double the width of a football field, and this structure is supposed to be sitting over ocean water.

Because the "shortage" is entirely down to agriculture and it is not cost competitive to grow crops at these prices. Its fairly easy to meet residential water demand.

Hence why you put them in areas with ocean currents. Spend any time scuba diving? There are a LOT of areas that are absolute deserts in the ocean. Sandy and empty. There’s nothing around for miles.

And the currents. Oh my. Does water move. You get caught in one and you are going for a ride. Planning current dives is very popular. Relax in the current, go for a ride. Arrange for a boat to pick you up or sometimes it’s a long wall dive and you end up a long ways out.

The ocean? It’s big. Real big. Insanely big. As long as you have some water movement, you could put a city sized discharge pipe into of these areas and with a 2kph current the brine uptick would be basically undetectable 1km away. The sheer volume of water is nuts.

As long as you locate where water is moving and away from a big habitat area there is ZERO issues.

Then they are taking that water out of its natural cycle in the air - wonder what might happen ?

Are we sure we have a firm understanding of the entirety of our ecosystem to play with it as much as we already do? Doesn’t take much cyanide to kill an entire person, either.

They dump salt All over the roads wbere it freezes too

Let’s not go there

Keep in mind that this $2-$5 per m3 capacity is capital equipment cost (with civil/install/etc ) only. OPEX is an additional 3-5 kwh/m3 produced, which costs can vary whereever you are on the planet.

Seawater desal, specifically reverse osmosis, has a lot of detractors who don't like it because you you're generally getting a recovery of about 40-50%. Which means you're dumping more than half your high salt concentration brine back into the water. This is water that has 2-3x the salinity of the ocean/sea, so there is rightfully a lot of concern about destroying the environment/ecosystem.

There's a push to improve the recoveries in desalination, but the cost is always it requires even greater energy consumption.

Personally, a mix of seawater desal and wastewater reuse would be the best solution for growing water crisis.

The problem is though, its cheaper for salt consumers to buy mined salt than from desalination plants. To concentrate seawater enough to create a viable salt product from the brine would take 4-5x more energy than simply desalinating for potable water use. That is on top of the 2-3x more capital equipment you'll need for this process. It doesn't make it economically feasible to do so (at this time). There's promising technology that's being researched and piloted, but until there is that gap is filled, then desal plants are going to keep dumping concentrate back from where they got their water.

Enough water for 500k people just sounds like a lot to not have it make it wherever it was going.

The oceans are very, very big compared to the amount we use.

The US' entire annual water usage is equal to a square 1500 feet by 1500 feet extending down to the offshore ocean basin. Any removal of anything from anything is going to have repercussions, but this is about as low impact as you can get.

Sounds like a windtrap from the ”Dune” series,

I think they just pump it in a big tank or open field and let it evaporate. Bulldoze it later.

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Most desal plants are producing in the tens of millions of gallons per day range. In order to get a proper evaporation, you're going to need a whole lot of surface area. Just not practical.

Plus, not as simple as concentrating evaporating seawater to get salt. You gotta separate your other type of salts that will form once the brine saturates.

They apparently mine brine for various minerals and trace metals, I was just reading. Rare earth elements and whatnot.

Indeed it does. Now if only we had Spice and Stillsuites and Holtzman engines and all the things in Dune minus the medieval bs they decided to revert back to

In the paper they compare it to the size of an oil rig or cruise ship, and propose a cost of construction of $600 million.

That is an area of 1.65 square inches per person. I hope it scales well...

You know the water still exists on or near the surface of earth after we’re through with it right? We’re not shooting it up into space or shoving it in a wormhole.

No, but we are filling up plastic bottles (sometimes with sugar or minerals added, other times just pure) with water than shoving those bottles into landfills.

So that does fairly permanently remove water from the water cycle.

Edit: Hm. I guess the bottles only take 450 years to decompose in a landfill. That’s a lot less permanent than I expected. It’s still older than the US, but on a geological/size of the ocean scale it doesn’t seem so bad.

The amount of salt produced by desalination plants in staggering

We produced and 290 million metric tons of salt worldwide in 2021: https://www.statista.com/statistics/237162/worldwide-salt-production/

Seawater contains 3.5% salt and has a density of roughly 1020kg/m3, so a cubic meter of seawater has any 35.7kg of salt https://en.m.wikipedia.org/wiki/Seawater

We generate tightly 95 million m3 of water from desalination plants per day globally https://en.m.wikipedia.org/wiki/Desalination_by_country

That's about 3391.5 million kg of salt per day

290 million metric tons= 290,000 million tons

290,000/3391.5 = 85.5 days

If we processed the waste from desalination plants all the way into salt, we would fulfill the world's demand for salt in less than 3 months. That's assuming we don't produce salt from any other sources

We would end up with over 4 times the annual salt production on just the current amount of desalination

Yeah, and demand for fresh potable water is only likely to grow.

However thawing meltwaters from glaciers and icepacks may counter out some of that salinity. I'm not quite up on the ocean science for that though at present.

Tnstaafl!! Haven’t seen a reference like that in a bit

Profitability may depends on demand and the price of the competitions.