Submitted by lughnasadh t3_zx9j0b in Futurology
Reply to comment by Surur in UIUC Researchers propose a new way to get fresh water from seawater, without the disadvantages of traditional desalination. They say that a vertical “capture surface” that is 210 m wide and 100 m tall, could extract enough vapor floating above warm oceans to supply 500,000 people with freshwater by lughnasadh
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.
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.
Have you been to California?
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
Let’s not go there
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.
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.
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/
Yeah I think they brinier the better for those too.
They dump salt All over the roads wbere it freezes too
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.
I think they just pump it in a big tank or open field and let it evaporate. Bulldoze it later.
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.
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.
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.
Like I said, the closely monitored environment in San Diego has not shown any ill effects.
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 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?
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.
> 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.
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.
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.
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.
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