this post was submitted on 28 Sep 2023
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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?
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?
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.
This isn't guesswork.
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
That's what I always thought, but the local effects of hypersalinated water can be terrible for any nearby life
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.
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 cars~~ deicing roads on the east coast.
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.
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.
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.
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.
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.
Salt is an essential nutrient. We already make it from seawater just to get the salt! Now we’ll get some clean water as well.
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.