Why is desalination so difficult?
practical.engineering
practical.engineering
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
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.
> 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.
Ships could be adapted to literally making part the ballast on the open sea while in campaign, instead to need to carry all of it from a port.
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 could 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 [2017]
https://www.nature.com/articles/srep46173
Global Pattern of Microplastics (MPs) in Commercial Food-Grade Salts: Sea Salt as an Indicator of Seawater MP Pollution [2018]
https://pubs.acs.org/doi/10.1021/acs.est.8b04180
Microplastic pollution in commercial salt for human consumption: A review [2019]
https://www.researchgate.net/publication/331006661_Microplas...
"MPs have been found in commercial salts from 128 brands, from 38 different countries spanning over five continents."
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…
Guessing that you know something I don’t here, though.
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?
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.
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.
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.
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?
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 the 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.
“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.”
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.
50 cents per day for a fully desalinated water supply is... incredibly cheap.
If you're interested in water policy and water management / engineering, I cannot recommend enough reading the book "Let There Be Water: Israel's Solution for a Water-Starved World".
Don't forget food, industrial, etc
Adding salt is a great idea, it pushes our collective stupidity to a noteworthy level of nonsensicalness.
It makes me wonder what other hard to remove poisons we could add to challenge ourselves. Perhaps design a new disease?
Clearly, you're not having a rational conversation with comments like this. If there was an abundance of fresh water, the western half of the US would not have been in severe drought conditions for the past however many years. This is where I leave you as you are just making things up like and not even having a good faith conversation
https://ourworldindata.org/grapher/water-withdrawals-per-cap...
So that is around $775 per person per year assuming no net change in water use. In contrast, Germany uses around 410 m^3, France around 475 m^3, and Australia around 724 m^3, so the US is a significant outlier.
Freshwater withdrawals is a very broad category, it also includes water released to turn hydropower turbines. But it's also unfair to compare across countries without taking into account water sent between countries in the form of produce and products.
$0.5 was per household. $2.00 was per capita. So 10x higher.
As you will note, the average German consumes 1,000 liters per day by the same metric which is 2.5 baths per day which is obviously unreasonable if we were only considering direct domestic water consumption.
To be fair, the agriculture is being grown to feed people, so it is fair to include the consumed produce in each person’s water footprint. This is further exacerbated by growing animal feed for animals that are consumed which is even more “water inefficient”. The US is a major food exporter, so it is over-represented in these sorts of numbers, but it is a fair approximation to within a factor of maybe 2-3x of the embodied water consumption of the average American.
But not counting the water used to put food on your table is too small. So this establishes some bounds.
This is an interesting number. Recently, I saw complaints that green hydrogen is impractical because it would use too much water. But if all the per capita energy use in the US went to electrolysis, it would use about 1% of this water per capita (and, of course, green hydrogen would be only a fraction of total energy use, due to all the preferred direct uses of electrical energy.)
There are plenty of valid objections to hydrogen as a fuel, but water use is a total non issue. Not only does it use so little, but when you get energy back out of the hydrogen, the waste product is water again. It’s literally a renewable cycle.
What it does not do is provide freshwater for argibusinesses. As California is also proving in the Central Valley. :(
I wonder if NIMBYism blocked that?
And if an agency wanted to transport water like the USA national oil pipeline system, would they be blocked similarly?
If desalination becomes widespread, I imagine the water not shipped to the coast could remain in the Central Valley. I don’t know one way or another if this would make political or economic sense.
EDIT: Wikipedia has a good overview: https://en.m.wikipedia.org/wiki/Water_in_California
The upfront cost from my understanding is in drilling a deep well. Those wells keep getting deeper and costing more. But, past that, it's just the cost of running the pumps to drain the underground aquifers. IIUC the cost of water is free plus the cost of harvesting it from the commons.
I might be wrong here, but all the billboards that say "is growing food wasting water?" along the interstates in California don't really matter over long time horizons. They're advocating for draining the water tables. You can't do that forever. Doesn't matter if it was a "waste" or not, it'll be gone soon and they'll have to pay to pull water from somewhere else or stop growing crops there (or the state will pay to give them water).
When "free" water runs out, other water sources will suddenly be cost effective. But it's hard to compete with free.
Many of these canals are quite old and while they do require some maintenance, the upfront costs of the dams, reservoirs , and canals are largely paid off. Those maintenance costs and any upgrades are paid by the district customers.
He says it’s viable for many applications.
I assume that's cost to make and not total cost to consumer post treatment plant distribution and maintenance so it would be more expensive than that but still in the ballpark of reasonable.
I assume you meant per year?
https://en.wikipedia.org/wiki/Claude_%22Bud%22_Lewis_Carlsba...
https://www.water-technology.net/projects/sorek-desalination...
In California, where we have persistent water shortages, residential, commercial and industrial water use ( including all landscaping, golf courses, etc) all put together still only amount to 10-20% of overall water use, depending on rainfall
The reason this is there is to downplay the outsized use in agriculture, and also to shift some blame to folks that voted not to allow this water to be used in the first place.
But still, if you want to cut spending and are looking for where your money is spent, you don’t include money you choose not to earn in your list of spending.
What's really interesting and relevant to the topic is that the oyster farm serves as a pre-filter to the desalination plant and there's an symbiotic relationship between the plant and the oyster farm.
> This was the first oyster farm to feature an inventive “depuration and purification” process, which involves immersing the oysters in triple-filtered seawater once they reach full size. This ensures that the oysters are a completely safe, top-quality delicious shellfish product.
https://www.usatoday.com/story/travel/10best/2022/08/04/how-...
https://en.wikipedia.org/wiki/Depuration
TIL.
Anyway, seafood comes from the ocean. I don’t see why they would be worse than other oysters.
It's more than rinsing them off. Oysters are filter feeders. They need to spend enough time in clean water to pump out any contaminants. It's an FDA regulated process:
https://www.fda.gov/food/federalstate-food-programs/national...
> Anyway, seafood comes from the ocean. I don’t see why they would be worse than other oysters.
It depends on the cleanliness of the water. These oysters are raised in a lagoon surrounded by the city of Carlsbad:
https://www.google.com/maps/place/Carlsbad+Aquafarm/@33.1419...
I imagine that lagoon is subject to runoff and not nearly as clean as oysters harvested in open waters.
Israel does this by burning massive quantities of fossil fuels: https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:E...
It's not even remotely economical without huge government subsidies. Completely untenable with current technology for poorer countries, or anyone that cares at all about carbon emissions.
on a serious note, it's a smallish research/etc facility. probably most of things are as deep underground as possible. it's not same thing as full blown nuclear power plant
Same reason it's hard to do anything with solar. Grid scale storage is an unsolved problem.
I wonder if there are more energy-expensive desalinization processes that are better to use with intermittent power sources, like solar.
Israel btw supplies desalinated water to Jordan and PA.
Another consideration is political sovereignty, since solar can’t easily be turned off by a foreign adversary.
But in general in Israel solar has a couple of problems: very dusty (sand storms) and local electrical company which tends to create problems
However the details are important. You'd need to do a deep operations analysis to get an answer. That also would include energy storage as well.
Why shouldn't drinking water of all things receive subsidies? Why must drinking water be a for-profit enterprise?
It's about sustainability, not profit. Of course wealthy nations can (literally) burn enough money turning fossil fuels into water to make their population comfortable and happy. But most can't, and the externalized cost is unimaginable at a global scale.
Easy to say when your government can afford the subsidies. But the vast majority of freshwater-insecure nations will never be able to do this without a 10x technological breakthrough.
Would you tell that to the Israelis if they couldn't afford it?
The point is that yes, the original article is correct. Current desalination tech is woefully inadequate to replace fresh water surface reserves without putting a massive burden on the society using it.
Yes? What else would I tell them, to pray for a miracle? If they don't have enough water, can't get water profitably and cannot even afford to subsidize water, what else is there to do besides find somewhere new to live? What would you tell them?
> without putting a massive burden on the society using it.
Yeah, in some places it will be necessary to subsidize water, placing a burden on society. But considering we're talking about water, that's obviously a burden that needs to be borne. Acquisition of water comes before literally anything else a population might want to spend money on. And if there isn't enough money around to acquire sufficient quantities of water, there isn't enough money to live there at all.
Israel has a strong enough economy, they can afford to make desalination work for them. You objected that they have to subsidize the desalination, but I don't see any sense in that objection. If that's what they need to do, that's what they'll do.
Fresh water, economically speaking, is a classic private good. It gets consumed as someone uses it, and can people can be easily restricted from acess if they dont pay.
https://en.wikipedia.org/wiki/Public_good_(economics)#Defini...
Why not use nuclear power plants to power desalination plants? I even wonder if some of the salt from the brine could be fed into certain types of nuclear reactors (Molten Salt Reactors and the like, possibly) making it an even more symbiotic relationship
https://babel.hathitrust.org/cgi/pt?id=uc1.$b643596&view=1up...
More modern take here: https://www.iaea.org/topics/non-electric-applications/nuclea...
"the country" in this context is Israel, since HN truncates the wiki link right before that.
Maybe it's time to understand that it's not a long term strategy ? That may be they should move to another place where water is naturally more abundant ?
As if immigration isn't a hugely fraught political topic. And you might want to consider how many people moved to Israel and why.
So the old grading system rated the lighter colored plainer sugars and syrups higher than the darker more flavourful varieties. Since less maple flavour made for a better all-purpose sweetener and a more direct competitor to cane sugar.
Nowadays we usually use maple syrup for the flavour, so the grading system is non-judgemental that way. And the darker grades are more likely what you want.
Theoretically, continuous distillation can be extremely efficient, as, you're removing as much heat as you're putting into the system. In reality, you get into diminishing returns fairly quickly, because insulation, pumps, heat exchangers, etc, are all far from free, especially at scale.
Correct for things with that specific label, but other X syrup labels can be fair game:
> In the United States, table syrups can be sold under a name consisting of any word followed by the word syrup with the exception of maple, cane, and sorghum. Commonly used names are table syrup, pancake syrup, waffle syrup, and pancake and waffle syrup.[1]
So, 10,000 sq meter of this baby could pump 150,000 gallons of fresh water over a ten-hour solar shift.
Seems like the secret sauce is 1.2cm (or is that 80mm) separation between diffuser plates thus taking advantage of solar heating/condensation/collection in one area.
Of course, there remains an collection issue of brine discharge which could be removed gradually instead but in same but 3-peat manner (down to 2-3 permille, or 0.2-0.3% salinity level.)
At any rate, this MIT method has leapfrogged the passive solar method ahead of reverse osmosis (RO) method by quite a bit, in terms of energy required to extra fresh water. RO still holds the insurmountable lead in base (non-fluctuating) water output rate.
https://news.mit.edu/2020/passive-solar-powered-water-desali...
https://news.mit.edu/2019/brine-desalianation-waste-sodium-h...
Also - there are lots of un-earthed treasures to be found under the saharan which was once a lush environ and have been covered with sand - so prior to flooding it, we need to lidar and excavate it.
What if we vaccuumed up all the sand and built a new island/continent with the material and just revealed everything underneath - then flooded it. (I believe UAE is in the market for more sand-built-land-masses)
I'm sure someone has done the math to figure out what the proper length is for such a canal, to avoid problems with scaling. And if you've ever been near an ocean for much time, you know the salt tends to get around. So I'm not sure how in a multi-year project you keep that to a minimum.
Some call that par for the course, others unsustainable. Still others don't make a distinction and see them as the same.
It doesn't increase rainfall.
Israel is actually desalinating water and rejuvenating a river, which eventually will reach the dead sea (although that's not why they are doing it, but it makes the point that evaporating water isn't doing much).
Maybe you mean on a far larger scale?
Well - the ocean itself is much larger, and water evaporates from its surface all the time. Humans aren't going to make an evaporation zone larger than the ocean.
Also: Water does not (mainly) evaporate because of heat, but rather because of wind. There's lots of heat in the desert, but not much wind. The ocean has a ton of wind.
That said, none of this contradicts the overall point you were making.
So even if you evaporate a lot of water, it won't fall where you need it or where you can collect it.
Salt was used as money.
EDIT: Only a fn idiot without knowledge of history would downvote a comment... Jimminy Carter, what type of stupid are you trying to promote?
Never heard this saying before. I've heard "worth his weight in gold".
That's not unusual in desalination however, many facilities are combo plants, they're producing power and then using waste heat for desalination.
1) Renewable energy product still has a cost associated with it, even if it is at times, excess.
2) That excess capacity, and the times when there's more energy produced than consumed might not match with water demand.
3) There definitely isn't, and won't be, enough excess renewable capacity to distill even a fraction of the fresh water consumed.
4) This means that you still have to calculate a per kWh cost for the energy consumed to distill salt water to fresh water. The average kWh might not be the same as the market average kWh price, since if you make your distillation plants oversized so you can utilize any spare energy production, but there will still be a price.
5) This price will most likely mean that the per gallon cost of distilled water will be higher than RO, or water pumped through a pipeline.
Desalination is still an extreme measure taken when all other forms of fresh water are cost prohibitive.
This cost is already paid for in the infrastructure. You're not going to tear down extra solar panels when demand is low just to reinstall them an hour later.
> 2) That excess capacity, and the times when there's more energy produced than consumed might not match with water demand.
Water can be stored very easily in large quantities and over long periods of time. Replenishing an aquifer in the summer will still help you even when the dry season is winter.
> 3) There definitely isn't, and won't be, enough excess renewable capacity to distill even a fraction of the fresh water consumed.
You don't need to distill 100% of freshwater, you just need to make up the difference between what is naturally available and what is used. The difference is generally small, especially when combined with water conservation methods. California's water shortfall could be covered by using just 6% of it's current annualized electricity generating capacity for desalination.
> 4) This means that you still have to calculate a per kWh cost for the energy consumed to distill salt water to fresh water. The average kWh might not be the same as the market average kWh price, since if you make your distillation plants oversized so you can utilize any spare energy production, but there will still be a price.
You would presumably locate your desalination plant in an appropriate location and operate it at appropriate times such that your cost per kwh is substantially below normal market rate.
> 5) This price will most likely mean that the per gallon cost of distilled water will be higher than RO, or water pumped through a pipeline.
RO would be desalination. A pipeline is still taking water from somewhere else, the price depending heavily on where you're getting it from and the geography between you and the source. In many cases there isn't a suitable freshwater source to pull from. Certainly there are no fresh water sources so limitless and readily accessible as the world's oceans.
Most raw material processing involves some separation process which requires energy. First, there's gathering something that contains some of what you want. Then there's a phase that often involves breaking big stuff into little stuff and some mechanical separation of easily removed crud. Then there's some chemical step, such as smelting, leaching or distillation, which takes energy and feedstocks to pull the good stuff out of the bad stuff. Then there's getting rid of the bad stuff, which is the source of most industrial pollution. Now you finally have something that's mostly what you want, and go on from there. From desalinization to iron making to fertilizer to oil production, the front end looks like that.
All of those processes are energetically uphill, and all are routinely done on huge scales.
A thousand liters takes about 3kwh. It's not really that expensive. If you run a very inefficient house in the US, that's actually what you'd need per day. You might consider some cost/water saving solutions if that worries you. But, either way, we're talking cents per day per household basically.
Not nothing. But cheap enough that it is a common solution to get water in places that have average incomes far below those common in places like the US where desalination is mostly science fiction.
A large desalination plant means large patches in the sea where life is not sustainable.
BTW, if an average US house really needs 1m^3 per day, that's appalling. These past years, my house has used less than 10m^3 per year and per person. 30× less. I'm afraid most US homes will keep wasting drinkable water and pressure society on building desalination plants, rather than halve (at least!) their water usage and protect the environment.
Molar mass of salt is 58g/mol, and the average sea water salinity is around 3.6%
So a cubic meter of sea water will have 1000*0.036/0.058=620 moles of salt, and it'll require 2.4MJ of energy to remove the salt in a perfect desalinator.
In more common units, 2.4MJ is about 0.75 kWh. Around here electricity is ~10 cents per kWh, so the absolutely lowest price of one cubic meter of desalinated water would be around 8 cents.
> A thousand liters takes about 3kwh.
So, if those numbers are right, desalination is currently at about 25% of theoretical energy efficiency. Is that correct?
But otherwise it's correct, we're at about 20% of the theoretical maximum. The best RO systems are right now working towards 2kWh per cubic meter: https://uh.edu/uh-energy/educational-programs/tieep/content/...
> desalinating 35 g L–1 seawater at 50% water recovery has a theoretical minimum energy requirement of 1.1 kWh m–3 and a practical minimum of 1.6 kWh m–3.
SOTA is apparently ~3.7 kWh m-3. That's not a huge factor
For 90% salt removal with 50% waste-water, they say the limit is 1.09kWh per cubic meter (3.924 MJ)
NB: It is not 100% clear to me if the result is independent of the type of technology, but they do claim:
> We first derive the general expression of the thermodynamic minimum energy of separation determined by the Gibbs free energy, which is independent of the method of desalination
Their result is independent of technology, it's derived from fundamental thermodynamic principles.
Carnot cycle, technically, doesn't apply to all energy sources directly.
For example, solar panels have their "hot side" at around 6000K, so Carnot efficiency would be close to 100%. Real solar panels have other limiting factors, and I believe the absolute achievable theoretical maximum is around 80%.
On the other side of the spectrum, wind turbines have very lousy Carnot efficiency because they're exploiting a temperature difference of just a few degrees. However, the "Carnot tax" is not paid by us directly, so we don't really care about it.
Similarly everyone should know how to rig a basic water purification system using gravel, sand, and charcoal in series.
Even just as applied science experiments to do with kids they’re worthwhile.
Edit: Water based solar power is generally an area I think that deserves more research. While photovoltaics have their advantages, water is cheap, clean, and reliable. Heating water with sun during the day and using it for household heating at night is the simple application that I’m most familiar with, but I wouldn’t be shocked if there’s some scale where an economically interesting Carnot cycle becomes possible.
So many incredible paths to follow: Battery tech. Solar cells. Desalination. Carbon handling. What a time to be alive.
1/ it’s as much an energy and water storage problem as it is a technical problem.
2/ commercially, because of 1/, RO is a municipal sale. It is a civil initiative, rather than a commercial one, which means it gets crowded out by other civil decisions.
Also, the author mentions that people in US use 1100 liters per day (which is too much in my opinion), but not all this water needs to be drinkable, one probably can not drink more than 3-4 liters per day, and the rest of the water can be salty.
I just remember thinking to myself "Bear Grylls drinking his own pee is such a philistine, here is an actual pro using science to remove all the water from that pee instead first." Genuine moment of awe personally.
[1] https://www.powermag.com/statkraft-shelves-osmotic-power-pro...
1. Steam distillation + Product can be perfect DI type 1 water - Expensive: 300+ kJ/L
2. RO membrane + Cheaper - Slow - Wastes more water - Requires regular changing of membranes
The end.
Ocean waves can be used to create electricity and it is also possible to create a dam that uses an artificial river sourced by the ocean and make hydroelectric plants to use that energy. Is it a cost issue in both cases that prevents using electricity generated that way to desalinate?
And now you need to pump the final product up to the land surface, adding cost there as well.
Desalination is verrrrry easy if nature does it for us (sun on the salty sea -> clouds -> precipitation over land). Compared to this, doing it "with a machine" is hard.
You could probably fix the drought situations by reducing consumption.
Put the steam turbines inside the steam room to recover some of the heat as power and you are good to go
The biggest issue is cost for these plants and it isn't worth spending the political capital to build them yet.
Then all I need to do is desalinate drinking water.
“Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.
You at least need special soap: https://en.wikipedia.org/wiki/Saltwater_soap
On top of that all the brine that people produce in their homes would have to be disposed of, and I'm sure many people would just end up flushing it down the drain. So the water treatment plant would have to deal with highly concentrated, contaminated saltwater.
Sewage in particular will create hard deposits in plumbing that needs to be dealt with every few years at a minimum.
Frankly, unless you are in a rather extreme environment, like a desert, or a boat where you have to carry or make all your own fresh water, saving a few gallons on showering and washing is pretty inefficient. You could have a far larger impact by changing habits, and ensuring low flow appliances.
https://www.veoliawatertechnologies.com/en/technologies/mult....
> My garage demo has very little going for it in terms of efficiency. It’s about as basic as distillation gets. There’s lost heat going everywhere. Modern distillation setups are much more efficient at separating liquids, especially because they can take advantage of waste heat. In fact they are often co-located with coal or gas-fired power plants for this exact reason. And there’s a lot of technology just in minimizing the energy consumption of distillation, including reuse of the heat released during condensation, using stages to evaporate liquids more efficiently, and using pumps to lower the pressure and encourage further evaporation through mechanical means.
Less than half a penny per gallon is obviously absurdly cheap."
- Elon Musk, 2023-05-07 https://twitter.com/elonmusk/status/1655262008898383872?ref_...
https://www.youtube.com/watch?v=oO8w6XcXJUs [skip to 14:45]
I don't think he gave any substantiation to the claim then either. (He dismissed delivery of clean water to the world as a problem not interesting enough for him to spend time on.)
Some countries have floods in one part, and drought in the other.
The floods are so bad that large numbers of people die.
Here's a great challenge that should be worked on: how to capture the flood water and use it to mitigate the droughts. Could something like Elon Musk's Boring company concept fix this?