> It takes less energy but produces a concentrated liquid waste stream that must be disposed of.
This implies that creating a concentrated waste stream is a problem unique to reverse osmosis. It isn't. No matter what you do you're going to end up with a bunch of salt that you have to get rid of somehow.
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.
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.
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.
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?
> 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?
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.
Second law of thermodynamics.
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.
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.
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).
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
https://www.nationalgeographic.com/environment/article/micro...
The presence of microplastics in commercial salts from different countries
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.
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.
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.
Like de-icing roads.
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.
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.
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.
Just ask the Carthaginians…
If anything, doing lots of this might reduce the salt concentration in soils, due to increased rainfall.
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).
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
It would be interesting to have a water cycle simulation with sliders.
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.
Only a very small fraction of water is isolated from a very amount of sea water.
> 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.
I've often wondered why dont we have more pure water pumped through the water mains in various countries, and I think after reading about Super K the Japanese Neutrino detector [1] and how the water in the tank was so pure it had dissolved a spanner/wrench that was left in the bottom, years ago, I might have the answer.
Firstly there is health implications for drinking pure water, and whilst it probably wont dissolve your guts [2], it will drastically and quickly alter your chemistry [3] which in moderate doses may be a good way to calm down, I havent tried personally yet, but there is another problem.
The ultra pure water would probably dissolve the older ceramic and metal pipes used to deliver water around the countryside, from the inside out.
In fact I would even go so far to guess that water mains pipes last longer if its delivering hard water compared to soft water, and probably explains the pub culture as the water is standardised in various alcohol brands.
Either way I prefer soft water, its more relaxing and could well help to reduce a certain amount of anxiety in the population along with stress levels, that could be useful for built up cities, but watch the GDP levels of the region go down if that happened and the profile of crimes change [5], not to mention health conditions!
[1] https://www.businessinsider.com/super-kamiokande-neutrino-de...
[2] http://physicsandphysicists.blogspot.com/2018/06/super-kamio...
[3] https://chemistry.stackexchange.com/questions/30754/effect-o...
[4] https://nuscimagazine.com/water-so-pure-it-will-kill-you-261...
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7576670/#:~:tex....
"Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved."
I dunno, I think if you left a wrench soaking in regular water for five years there wouldn't be much left of it after that either.
During WWII Entire tanks drowned in Siberian sumps and were brought back to life with their engines running.
After five years in regular water I bet the wrench would be in working condition.
I'm not feeling particularly convinced by this anecdote. It sounds a bit urban legendy. Still, I won't claim more than a high-school knowledge of Chemistry so I'm eager for someone to correct me and supply an explanation.
I thought salt and impurities in water was the driving factor in rust.
Once it dissolved a tiny bit of the metal it would no longer be so pure. So this sentence makes no sense. It takes just a minuscule amount of mineral to replicate regular well-water.
It has to do with the economics of water treatment. If you supply water you're incentivised to supply it at the lowest acceptable level of treatment. That's because people just want plain old water, and they don't want to pay a lot for it.
> water mains pipes last longer if its delivering hard water compared to soft water
This is the one thing that may actually be true, but it's because the minerals in the hard water build up on the inside of the pipes over time, creating a protective layer. This is especially great for lead pipes, as it can prevent the lead from leeching into the water.
I say this having recently read about the desalination plant in Dubai.
Jericho is the nearest town, 18,000 people, 8” of rain a year, 2 miles from the border. They presumably get their water from that desalination plant. No towns that far south are getting their water from it. The river barely even makes it to the Dead Sea anymore. https://en.wikipedia.org/wiki/Jordan_River#Main_environmenta...
Adding a bit more salt into the famously-salty Dead Sea are the least of their problems in that part of the world. Where else would you put the salt, anyway? Putting it all into the Dead Sea would be even worse —- at least this reduces the amount that makes it back there. Putting it into any other watershed would cause vastly more harm.
It seems like a good enough solution to me. If you think about it, it wouldn’t be in Israel’s interests to inflame tensions with Jordan over this, if it were really an issue.
Ain’t changing anything in the environment.
Come on. They are literally moving salt a few meters.
What do giant piles of salt do aside from melt and "burn" whatever they touch? That's right, they Spread.
JFC that country is fucking evil
I've heard that this brine is toxic. Does this make disposal an issue? Is the toxicity true or hyperbole? I mean, do we know how bad it is, and if we can do anything safely with it? It seems like "salt" is useful in a lot of contexts, including industrial, so can we do something with the brine besides disposing it somewhere?
There is nothing about reverse osmosis that is fundamentally more toxic or harmful than the typical evaporation that takes place naturally in the ocean. And it’s pretty dishonest to claim otherwise. If there’s a problem with too high salinity of discharge, that’s an engineering problem that should be fixed with greater dilution.
I assume that in practice the amount of water taken by a desal plan is tiny and most bays have high tidal inflow and outflow, but it's obvious that more than just dilution should be considered.
But, why not really-long-pipe-with-small-holes-along-the-length? That seems to me like a simple mechanism to send the brine back into the ocean without causing a local disaster on the sea floor. Is there maintenance required that makes it more expensive than I realize?
Have a pump that draws in 10L of ocean water for every 1L of brine you need to dispose of, mix 'em up, and discharge the 11L of only-slightly-saltier water back into the sea.
Not sure when it makes more sense to do that vs. having a leach-field type of brine discharge. They both ultimately do the same thing, but one requires more mechanicals, the other requires more piping and "passive" infrastructure.
The OP mentions that this is common in practice, although it's easier to tell in the video that this is what is being described.
Too much salt can kill stuff (e.g. people, plants), so I suppose that makes it "toxic." Maybe there's a tiny amount old industrial pollution from anywhere an everywhere that concentrated in there, too.
However, if you're desalinating seawater, what's the problem with just dumping the brine back in the sea? Unless you introduced new stuff into it during the desalination process, you wouldn't be making anything worse.
If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump.
Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goes. This is one of the more surprising things I've learned in the past few years, honestly. Your kitchen-scale-based intuition of how long it takes for liquids of different characteristics to blend together turns out to be way off.
Trying to pipe it away to somewhere where it is less of a problem is expensive.
In the long term just dropping it back into the ocean is not a big deal, but that short term is surprisingly destructive. You'd think you could just drop it in and maybe a few hundred feet from the outlet it would be all dissipated and harmless, but unfortunately the physics don't work out that way.
As a visceral example of this in the other direction, the freshwater plume of the Amazon River extends more than 60km into the ocean. [0]
I would love to see these plants placed in areas where there's a nearby dry below-sea-level basin, into which the brine may be discharged. The Salton Sea in CA is one example, there's another similar location in Egypt I'm aware of. The advantage of such locations is they are usually extremely hot and arid, which means there's generally not much of a local ecosystem or human population, and there is ample solar power availability.
[0] https://eos.org/science-updates/the-amazon-rivers-ecosystem-...
The Salton Sea's salinity is already well over that of the ocean (44g per liter compared to 35), and is getting saltier. Considering that the very existence of the Salton Sea is already an ecological disaster, I don't really see dumping salt into it to be another one.
The Salton Sea is 70 miles from the Pacific Ocean. If this were built, it would be only the third longest water tunnel in the world, and second in the US.
It really doesn't, or perhaps only in the most pedantic sense.
That "ocean" is still the mouth of the Amazon itself, and most of it's less than 10 meters deep. It's really the estuary of the river itself. See: https://www.frontiersin.org/articles/10.3389/fmars.2017.0002...
http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_...
This is false and somewhat dishonest. This is simply a choice of not diluting it enough. There is nothing about the discharge from reverse osmosis that is any more fundamentally toxic than the natural process of evaporation.
Proper dilution is essential, and treating the discharge as fundamentally toxic actually undermines the engineering to do this proper dilution because people will figure “oh well, I guess there’s nothing we can do as it’s going to tend to kill no matter what.”
People need to stop misleading about discharge toxicity.
If that choice were up to engineers, it's fine.
In practice that choice is actually made by MBA types, a field where harmful short-termism is almost a religion.
You can't just wave a word at it like dilution and think you're solving an engineering problem.
If you got 1 gallon out of sea water, what do you think you need to dilute it to be safe? Typically, it's 99%∆.
It'll kill however, plenty of things.
What's wrong with pumping 10% CO2 into your office constantly from a compressed gas plant extracting oxygen and argon next door?
How large would those brackish areas near the outlets be? It seems to be that would be a big problem in an enclosed bay, but much less so on a shore facing open ocean.
Could they run pipes out a few kilometers with small, regular holes (maybe some modification of oil pipeline technology) to spread the discharge out and mitigate the concentration problem?
Could they make the waste output less concentrated? Maybe by either running the desalination process less (would that also increase energy efficiency?) or by pre-mixing the waste with some un-desalinated intake water?
“seawater's sodium concentration is above the kidney's maximum concentrating ability. Eventually the blood's sodium concentration rises to toxic levels, removing water from cells and interfering with nerve conduction, ultimately producing a fatal seizure and cardiac arrhythmia.”
1) There's a large difference in energy and entropy between seawater and drinkable "fresh" water. This represents a bare minimum expenditure, below which you can never go, lest you attempt to create a perpetual motion machine.
2) No matter how you do it: Well, now you have a bunch of previously dissolved solids covering everything. How do you get them off of your surfaces and out of your tubes and "away" from everything else?
Once you stare at the first factor, then look at the second factor, then go back and forth, you come to your senses and realize that the dream of a jeroboam of colorless, tasteless water next to a little pile of fine powder is just not going to happen, and that the more sensible thing is to release some extra briny water back to your source and hope it doesn't kill too many fish.
Also, the phase transition for H2O from liquid to gas requires a lot of energy and space (evaporation surface). In other words, it takes ages to evaporate all the water. Also, the larger your pond is, the more expensive it is to scoop up the salt. And then just one rainy afternoon can set you back a lot.
I agree with the entropy part, but isn't the energy practically the same for similar quantities/ temperature?
When you dissolve a "salt" (the whole class of them, rather than just NaCl), there is a lattice energy (you are tearing these crystals apart) and a hydration energy, which are a little give and take from an energy standpoint. Most salts dissolving are slightly exothermic. NaCl dissolving is very slightly endothermic.
Seawater? Well, remember, there's a lot of dissolved solids in there, not just salts. So you have a summation of dissolving a whole menagerie of different things into your water. Last I heard, and it's been many years since I went near anything like that, yes, there's both an entropy and an energy cost, although I would personally dread trying to do calorimeter measurements to verify it experimentally.
The change in entropy between a batch of saline water and a batch of fresh water and enough saline water that its concentration don't change is about the same as letting that same fresh water fall for 200m and converting the resulting energy into heat (at 300K).
What means that desalination will take a lot of energy whatever method you use. There are distillation procedures close to perfect efficiency that wouldn't take much more energy than reverse osmosis; and of course, electrical separation is that one method with lots of promise but that stops due to material related problems every time it's tried. It just so happen that we know how to scale reverse osmosis up cheaply and reliably; but this looks like a feature of our technology and not anything intrinsic.
Distillation and reverse osmosis theoretically use the same amount of energy.
Practically, reverse osmosis tech is far closer to that ideal efficiency level, especially if electricity is your starting energy source.
But it doesn't seem out of the realm of possibility that someone will figure out efficient distillation in the future. distillation has the big benefit that it can make use of low grade heat which is waste from lots of industrial processes.
But we seem to have colossal amounts of essentially free solar energy, and that energy already evaporates large amounts of sea water. We just don't capture it well.
Imagine building a pipe that stands above shallow tropical coastal waters. Make the bottom of it into an almost flat funnel to cover more water surface, using transparent plastic or even glass. Now all the evaporated water and hot air go into the pipe.
Build the pipe a kilometer tall. Humans have adequate technologies already, and the pipe does not need to be bearing much internal load, unlike Burj Khalifa or World Trade 1.
At 1km, the air is cool enough. The hot air will shoot upwards, cooling on its way up and releasing fresh water. Lightweight collector pipes will bring it down into a reservoir. The remaining dampness of the air will help it produce clouds, and thus shadow, over the land.
With a tall enough pipe, we could even generate electricity by putting a turbine inside.
Why are we not building it? It's expensive, and most (sub)tropical countries that lack water are poor. They are also politically unstable, and such an installation would be a high-value military and terrorist target.
Maybe Singapore or Dubai would some day dare and build it. (California, unlikely; it would never pass an environmental review.)
There are no pores, so to speak. Polymer materials form amorphous solids with transient voids which open and close randomly due to thermal motion. They're not "pores" because they aren't permanent over long time scales. Rather, the polymer+water is modeled as a single fluid phase, the same as if you were modeling ethanol+water. The fact that the polymer is a "solid" doesn't affect the fact that it's actually a tangle of vibrating molecules just like any other mixture.
Other materials do have well defined pores, like MOFs and zeolites. In this case, the water does sorb as a liquid in the pore space, but is gated by transport between the pores in a similar manner.
This is made apparent because water does enter into polymers (even those which desalination) freely, with or without the presence of salt. It is not the case that "the pores are too small for water to cross normally". I can take a polymer that will swell with 50% of its own weight in water, and which has no "free" liquid water (as evidenced by the inability of the water in the polymer to form ice), yet make it reject >90% salt at very high pressures (>3000 psi). If you just let salt water sit on one side without pressure, salt and water will make their way through non-selectively. So it can't be that the water is being physically sieved from the ions to enter into the membrane. Rather, the pressure creates a change in the activity of water (due to the mechanical forces acting on the polymer near the low pressure/support material interface). Since the water is more soluble and more mobile in the polymer, it transports at a more rapid rate than the salt, resulting in desalination.
Basically the water can hydrogen bond with the polyamide but the salt can not and is therefore left behind.
>And that’s the problem with desalination. It’s kind of like the nuclear power of water supply. It seems so simple on the surface, but when you add up all the practical costs and complexities, it gets really hard to justify over other alternatives. It’s also harder to compare costs between those alternatives because of desal’s unique problems. It’s just a newer technology, so it’s harder to predict hidden technical, legal, political, and environmental challenges. For example, because of the high energy demands, desalination can strongly couple water costs with electricity costs. During a drought, the cost of hydropower goes up because there’s less water available, increasing overall energy costs and thus making desalination less viable right when you need it most.
You'd then have to compress the water vapor until it condenses barely hotter than the brine, and use both distilled water and residual brine at their approximately equal temperature (water at higher pressure than brine, though) in ofc separate counter-flow heat exchangers to pre-heat the filtered source (sea) water to the column's operating temperature (i.e., where the source water just starts boiling at the column's operating pressure (you want a decent vapor pressure to have a reasonable vapor density and thus feasible power density for capex reasons)).
Thermodynamically this should match a reverse-osmosis process with equal input/output parameters (I left out that you need pumps/turbines to "losslessly" adapt liquid between ambient pressure and internal operating pressure).
One benefit would be that you could directly heat the brine with solar thermal collectors, to get away without having to compress the vapor to condense it, essentially an open-cycle Type-1 absorption heat pump, with solar feed. (Lacking an evaporator, with the condensed output being the desired pure water, and the absorber being fed with source sea water while the return from the generator after the heat exchanger is just warm brine for discharging. If water and brine need to be sub-ambient, you'd evaporate part of the condensed water to chill both the condensate and the brine output streams. That'd be partially-open-cycle.)
And also. None of this is a challenge at all. R.o. water is simple
Different magnetic charge?
Different mass?
Different chemical reactivity?
¯\_(ツ)_/¯
I know the answer must be 'no' since if there were a better answer, none of what I'm thinking of requires more than high-school-level chemistry to discover/exploit.
I am not a physicist but let me give it a stab: except for a few specialized steps like UV or oxidizing heavy metals, most filtration is mechanical. A series of filters with smaller and smaller pores capture more and more of the mess in the water like bacteria and particulates while UV breaks down viruses, the oxidizer precipitates out metals, and so on.
None of those methods work with salt. Salts in general disassociate through ion-dipole interactions - the water dipoles essentially rip the ionic compound apart and surround each ion in what is called a hydration shell. They're bigger than bare water molecules but not much bigger - much too small to target with pore size. This shell also puts them in a thermodynamically stable state and it takes energy to "jostle" the water molecules away from the ions either through evaporation, distillation, or through another chemical reaction that precipitates out the ions.
As it turns out, doing that takes a lot of energy, so we use reverse osmosis as a cheaper alternative: we exploit the hydration shell of the ions by putting them behind a semi-permeable membrane with very small pores, "nanopores" if you will. The pores are too small for water to cross normally, but under high pressures bare water molecules can be forced through the pores while the ions trapped in their shells remain and concentrate into a brine. It takes less energy but produces a concentrated liquid waste stream that must be disposed of.
Someone please correct any mistakes I've made