If people needed as much salt as was contained in the water to begin with, we wouldn’t need to remove it in the first place.

No reason to keep the 1:1 ratio. Use the salt to replace our current salt mines/outtakes and then use the water as an addition to our current freshwater usage.

The waste stream doesn’t contain that much more salt than seawater. Extracting salt from mines is much cheaper than extracting it from slightly brackish wastewater from water treatment plants.

The brine waste from RO is still mostly water. In order to extract the salt you'd need to evaporate the water which still takes a lot more energy. You could use evaporative ponds to let the Sun do the work but that takes a lot of space. In either case you're spending a lot more money per pound than just digging the salt out of a mine.

Is that true when we take into account environmental externalities? I am not an expert in this field; I know that many forms of mining are capital-B Bad for the environment but I don't know how salt mines impact the area around them.

well, mines are bad on the short term. the long term damage is not of the actual digging, but of the separation processes. which all can be done as clean as we wish it just costs more.

Cost more energy

Mining salt costs vastly less energy than using slightly brackish water. Which is why it’s so much cheaper.

> https://www.bbc.com/news/business-61483491

Nuclear desalination like on naval ships is the answer. US and Russian ships already have the technology, it just needs to be scaled for use on land.

Nuclear power in general would be the answer to a lot of energy problems. But the general public in most places doesn't like it.

Is not just a question of preferences, there are risks also.

If the problem is that we need lots of energy to create pressure to separate salt from brine, well... I figure out that there is a lot of free "all that you can eat" pressure in the sea bottom.

The problem would be to calculate if moving all this weight up and down the sea (and in open sea) would be economical or not. Or of would unavoidably lead to people cutting corners and release part of the salt to the deep water ecosystems. Deep water masses are salty yet so a small amount of salt would impact less here than if released on surface, thats for sure.

In any case, physic laws about density and mass are our friend. Things either float or sink without extra energy added.

Having all of this in mind, I would go further and propose to regulate by law changing the material of the deep sea submarine ballasts.

It seems technically doable and would have some benefits

1) Lesser impact on deep sea ecosystems. No human trace left behind.

Disposable loads of iron or concrete will remain forever in the bottom. If we use salt or sand instead the impact on fragile deep sea ecosystems seems reduced. The organisms there are adapted naturally to deal with very salty water. The sand or salt ballast could be released gradually over a bigger surface reducing even more the impact over a particular spot or colony

2) Improved economics?

To dump valuable iron made with valuable energy into the sea seems a suboptimal solution. Substitute it with some common by products that are yet in the area and don't need to be transported from a mine far away could save some money probably. Containers of ballast would be fully recyclable also.

3) Extra safety.

If your load weight gets stuck by a net you are trapped in the bottom forever, With a ballast of sand or salt you have the extra possibility of open a few escape valves and let the concentrated salt go away. You can also release part of the weight much more gradually. After a while the submarine would tend to float and ascend automatically even if the energy supply would have been entirely lost in an accident.

Having the machine on the surface (or closer to the surface) would save millions and would made a big difference on humanitary and economical aspects of the rescue operation. A damaged submarine can be still repaired. Building another would be much more expensive.

Dunno about the possible negative aspects, more volume required for example, but would deserve thinking about it a little more.

> Having all of this in mind, I would go further and propose to regulate by law changing the material of the deep sea submarine ballasts.

Which country's law? There are many of them.

> 1) Lesser impact on deep sea ecosystems. No human trace left behind.

There's barely any submarines around. This is a drop in the bucket.

> 2) Improved economics?

If it improves economics, why do you need to force people with regulation?

If Titan proved something is that economics is not the only factor what matters here.

> I figure out that there is a lot of free "all that you can eat" pressure in the sea bottom.

> Things either float or sink without extra energy added.

That seems intuitively wrong... where is the energy coming from in this scenario? It's like saying we could use the pressure at the bottom of the ocean to spin a turbine and get free electricity.

I guess the obvious problem that sticks out in my mind is that once you've filled this submersible with desalinated water, how do you surface? A typical submarine does that by pumping water out of the ballast tank, but doesn't that require the exact same pressure that you just used to fill the cabin with desalinated water?

Here's an even more interesting physics brain teaser: Imagine you put a reverse osmosis membrane at the bottom of the ocean and connected it to a pipe filled with fresh water leading to the surface. The pressure at the bottom of the pipe would be less than the pressure at the bottom of the ocean, since fresh water weighs less than salt water.

In this setup, would an endless supply of fresh water flow through the membrane and bubble out the top of the pipe? I'm guessing not, but I'm having a hard time understanding why.

Wild guess: maybe only the partial pressure[1] controls whether water will flow through the membrane, and the partial pressure of freshwater in this scenario is identical on both sides?

[1]: https://en.wikipedia.org/wiki/Partial_pressure

> I'm guessing not, but I'm having a hard time understanding why.

Second law of thermodynamics.

Laws of thermodynamics aren't really useful here. They are perfect for explaining universe, and notoriously bad for predicting local events when you zoom and focus at a fine grain level and add time. Life beings are apparently breaking or "delaying" this laws all the f*ng time.

In any case nobody is trying to make a perpetual movement machine.

The goal is to create a cheaper way to extract salt from saltwater, and use the pressure gradient at the sea to put apart brine and water may be a solution waiting for an engineer (in my opinion). It is assumed that will not be free in terms of energy. It doesn't matter as long as is slightly better than the current solution. Would be much faster than waiting for the sun so it does not need to be cheaper than that. It just needs to be able to replace the last energy-expensive phase of our current solution by another process that is cheaper or faster.

A corpse of freshwater immersed in saltwater would experience a force up because its lower density. The weight of the submarine itself cancels this but if we keep adding freshwater at some point we would cross a density threshold. Probably a big volume. Maybe too much to be practical. Dunno.

Even more, ice floats so in a case of live or death if we could freeze with liquid nitrogen or so a big enough volume of cold water while avoiding the effects of the increase in volume, in theory the submarine could emerge automatically. We can't do it in the main submarine (would explode and the non frozen parts would implode immediately), but maybe in an independent storage area attached and able to absorb the extra volume?... dunno

A way to lower the temperature just when the oxygen is about to end would add also some precious extra time. A corpse is dead only when is warm and dead. In any case I'm just digressing wildly about an extreme and hypothetical emergency case. I could be totally wrong or not practical. I prefer not to test it.

> I figure out that there is a lot of free "all that you can eat" pressure in the sea bottom.

Have you heard of the second law of thermodynamics?

There's also lots of all-you-can-eat heat in any piece of matter, eg sea water or rock. But that doesn't mean you can get at it for anything useful, without a heat differential (or a pressure differential).

Hum, I wonder where we could find a heat differential and a pressure differential in this planet... if we except the ocean, and the land, and the atmosphere, and any place with an organism able to fart...

Actually solar powered desalination makes a lot more sence - solar is much cheaper and you don't need 24/7 properties of nuclear. so you are overpaying for no reason.

We cam store huge quantities of water, sometimes a year's worth. So intermittency is not a prohlem.

The idea of floating nuclear reactors used for whatever was floating around for a while, but won't happen with government support. It is really just another approach to modular reactors, not a terrible one, but free market wont do it.

What would make more sence, is making all our large cargo ships nuclear powered, and reducing emissions that way

The problem is that salt brine from seawater contains a lot of side stuff - you still need purification at a scale you don't need mining rock salt.

is this true? I can understand why it would be true, but "sea salt" is a real thing that's been traditionally made in seaside communities through to today, and I find it hard to believe they're cleaning it at anything finer than a gross scale.

https://en.wikipedia.org/wiki/Fleur_de_sel

Microplastics found in 90 percent of table salt

https://www.nationalgeographic.com/environment/article/micro...

The presence of microplastics in commercial salts from different countries

https://www.nature.com/articles/srep46173

thank you for the information, for sure, but i was responding to the claim that sea salt "needs cleaning" to point out that that seasalt isn't being cleaned, so it puts an upper bound on the value of need as it concerns the commercial market including govt regulation. My suspicion was that where would be more to worry about from single-celled life detritus, heavy metals, forever chemicals etc, but the marketplace doesn't seem to be worried about that.

I go about my daily life not worrying about microplastics (I know they are ubiquitous, and I'm not in favor of them, I just don't worry about them) Are microplastics known to cause particular diseases, or just suspected on the grounds that they "couldn't be good"? plastic is pretty inert which is why it remains around for so long, and while it is made from toxic things, it's generally considered safe. I'm just curious about actual microplastic effects rather than the sort of "it's estrogenizing our boys, antivax...er-plastic" suspicions.

Well they carry all sorts of bad stuff, and recently have been found to cross blood brain barrier.

> plastic is pretty inert which is why it remains around for so long, and while it is made from toxic things, it's generally considered safe.

This is very ignorant. plastics release a wide variety of organic compounds.

"Most plastic products, from sippy cups to food wraps, can release chemicals that act like the sex hormone estrogen, according to a study in Environmental Health Perspectives. The study found these chemicals even in products that didn't contain BPA, a compound in certain plastics that's been widely criticized because it mimics estrogen."

Which is why you see plastic change - look at old plastics around you, in shoes, food containers and fabrics - it becomes brittle, changes colour, etc.

really unfortunate how easy it is to channel fud.

for instance, the "can release" weasel words here - technically correct, but also misleading.

it is not the case that all changes you see in plastics are because they're releasing nasty (((chemicals))) into the environment. it is routine to engineer plastics to meet arbitrary emission/contamination standards. different kinds of plastics also require different (or no) such additives. mostly, people are thinking of PVC when they worry about this.

The problem is that if you are a common joe, you cannot know which is which. .So you have to assume that a random product will be leeching

It increasingly has plastic and other crap in it.

Still made all around the south bay.

Not quite that simple. Even isotonic water would probably be too corrosive for existing pipework.

Can't the salt just be dumped in the desert?

The products of desalinization aren’t salt and fresh water. They’re somewhat saltier brine and fresh water.

Sounds like it's time for USA to get another Salton Sea

Just pump it back into the ocean. The little bit of concentrated brine from a desalination plant will be quickly diluted; the ocean contains a LOT of water.

Particularly if they distribute it over a large area, as they do in practice and shown in the vid.

Bury it deep below the surface. In old salt mines, perhaps.

Need for uses other than eating.

Like de-icing roads.

Whoch chews the hell out of cars, requiring additional stock to be made... Salt is hell.

Salt doesn't work below -15C; most snowmelt is actually other solutions these days

The people who need that water tend to shed it after some time.

Discarding waste water into the oceans via rivers is a huge idiocy. You essentially rely on the environment to "magically" sort it all out. Naively so and fraught with huge inefficiencies.

Proper treatment of that waste in the sense of recovering usable matter streams is the logical way to go.

I know that generally speaking, disposing of waste in the ocean and expecting it to disperse enough to be harmless is foolish and wrong. But in the case of salt, It would seem to me that the ocean can handle that amount of salt. Course, I haven't done the math. But it would seem to me that the back in == salt taken out. We'd only be changing the net salinity by the amount of water subtracted. Without having done the math, my gut reaction is to think that's something the ocean can handle.

The problem, as I see it, is localized concentrations. While the ocean at large might be able to absorb it, the localized concentrations can be very problematic.

There are potentially some good reasons to just spray the brine into the air.

Seawater sprayed into the air becomes tiny salt crystals, which in turn help clouds to form, and cause increased rainfall. The rain produced has negligible levels of salt.

In places with dry climates, this often can turn desert land into farmland across an area hundreds of kilometers wide.

Surely the salt falling on the farmland would have some kind of deleterious effects, right? I imagine you’re not trying to grow sea cucumbers in this scenario, and I’m not sure most land plants would be crazy about a ton of salt.

Just ask the Carthaginians…

I believe that when every spec of salt creates a far larger water droplet - and the overall concentration in rain ends up tiny.

If anything, doing lots of this might reduce the salt concentration in soils, due to increased rainfall.

That’s probably what the antediluvian civilization said before they tried it in North Africa! ;)

I guess what I’m forgetting is that the water has a chance to wash salt away back to the ocean. But how much salt does one drip of water absorb? What if the spec of salt that starts in the water droplet is as much as the droplet can wash away?

I suppose it must be slowly becoming clear that I have no idea what I’m talking about (save for a nickel worth of Roman history).

This is what happened with Aral Sea.

It might just cause earlier rainfall, not more of it. There's x amount of water in the atmosphere, and you can't add more by spraying salt crystals.

You can though. The amount of precipitation (averaged over a long enough period of time) is inversely proportional to the amount of evaporation and other water entering the atmosphere (averaged over a long enough period of time). Note that the two things being compared are _rates_ not _masses_. If all you do is cause water to fall sooner then:

1. The humidity in the air drops, increasing evaporation rates because of the lower partial pressure of water vapor in the air.

2. The humidity on the surface increases (dusty areas becoming moist, plant leaves uncurling to expose more surface area for other processes but incidentally increasing evaporation rates, reservoirs having more surface area, ...), increasing the evaporation rate.

There are limits of course, and that back-of-the-napkin analysis ignores 2nd-order changes in temperature and all of the other hairier bits of climate modeling, but it illustrates that things are more complicated than they appear anwyway.

Edit: "inverse" here just meaning a multiplication by -1

Ah yes, that actually makes sense. Making the air drier speeds up the entire water cycle, thus more rainfall.

It would be interesting to have a water cycle simulation with sliders.

Would this be worth doing straight from seawater? I.e. place enormous solar/wind powered rigs in the ocean to spray massive volumes of seawater into the air? What would be the effect (beneficial and otherwise) of that?

The problem with brine from desalination is that it kind of behaves like a heavier liquid, sinking to the bottom. That causes it to stay together, taking longer to mix with the regular ocean; and the coastal seafloor there is a lot of life that doesn't appreciate water with double the salinity of regular ocean.

To solve that you can just dilute it more, either mixing with some other waste water stream or by releasing it over a larger area rather than a single outlet.

Double the salinity? Other comments suggest it’s only slightly more salty than sea water.

Only a very small fraction of water is isolated from a very amount of sea water.

The article states

> Modern desalination plants generally recover about half of the intake flow, which means their brine stream is about twice the concentration of normal seawater.

I imagine this heavily depends on the actual plant design though. Also because of the above mentioned issues you generally don't discharge it like that but blend it with other water.

With enough desalination, the Romans will be able to afford a huge army!