
Hydrophilic disc uses solar power to separate salt from water - HillaryBriss
https://newatlas.com/solar-steam-generator-water-desalination/60726/
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Retric
“This device can produce six to eight liters (1.6 to 2.1 gal) of clean water
per square meter (of surface area) per day”

That’s really bad from a density standpoint. You’re talking ~8,000 gallons per
day per acre of land. Solar powered reverse osmosis is something like 1/500th
the space.

If the can get installed costs below 1$ per square meter it might be
interesting, but even just land costs are likely to be an issue.

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SCAQTony
But what do you do with the salt and brine that is toxic to soil used in the
farming? The wind will scatter the salt in all directions.

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wbl
You dump the brine into well-mixed ocean areas.

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JBReefer
You sell it, salt is required for mammals.

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ryanmarsh
Funny how our bodies need water and salt, both are in such abundance but in a
problematic way.

Max recommended salt intake is less than 1 teaspoon per day. You need 2 liters
of water per day. There's nearly 6 teaspoons of salt in 1 liter of sea water.
That's quite a bit of excess salt. Kind of a bummer really. Wish we had a
gland that got rid of excess salt then we could just drink sea water.

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umvi
> Wish we had a gland that got rid of excess salt then we could just drink sea
> water.

If such a gland existed, it would probably require a lot of energy to work.
Plus, what would the gland do with all of the salt it is filtering just send
it to your kidneys/bladder? I'm imagining kidney-stones formed from all the
excess salt your body is trying to get rid of

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logfromblammo
Halophyte plants use a sacrificial salt leaf. They concentrate excess salt
into a specific leaf, then cut it loose when it reaches capacity.

The mammalian equivalent would likely be salt hairs.

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solstice
Wow interesting. Are there any edible such plants? Then their salt leaves
could be used as natural seasoning

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logfromblammo
_Salicornia bigelovii_ is an amaranth, sometimes known as "sea beans", "sea
asparagus", or "samphire greens". It is edible, and the seeds are an oil crop.
It can grow at 200% the mean salinity of ocean water.

It can grow in seawater, brackish water, or effluent from other agriculture or
aquaculture. We should be growing more of it.

 _Atriplex_ genus are amaranths called "saltbush"; many are edible directly or
usable as livestock forage. _Atriplex hortensis_ is a leaf vegetable, like
spinach, often paired with sorrel.

 _Tetragonia tetragonoides_ is "sea spinach" and has been cultivated as a leaf
vegetable.

 _Attalea speciosa_ is an oil palm tree.

 _Anemopsis californica_ or "yerba mansa" is used as a medicinal herb.

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solstice
Oh wow, of course! I know _salicorne_ from vacations in France. Totally forgot
about it.

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beat
One cool thing about this is that it looks inexpensive and simple, as well as
functional. If a square meter can generate enough clean water for a person per
day, islands of it could support entire cities.

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inflatableDodo
Reminds me of dye chromotography, I wonder if you can get different salts to
turn up at different places on the edge? Might be able to get useful
concentrations of lithium out of it that way.

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jbob2000
This doesn't make for a good drinking water, this creates distilled water that
would drain your body of minerals if you drank it.

You now need to expend energy to gather those minerals from somewhere else and
then put them in the water. Is the energy spent gathering those minerals more
than other desalination processes?

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driverdan
That's an urban legend. We get nutrients and minerals from the food we eat.

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robocat
The first sentence is probably true, the second seems false.

"Results of experiments in human volunteers evaluated by researchers for the
WHO report (3) are in agreement with those in animal experiments and suggest
the basic mechanism of the effects of water low in TDS (e.g. < 100 mg/L) on
water and mineral homeostasis. Low-mineral water markedly: 1.) increased
diuresis (almost by 20%, on average), body water volume, and serum sodium
concentrations, 2.) decreased serum potassium concentration, and 3.) increased
the elimination of sodium, potassium, chloride, calcium and magnesium ions
from the body"

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tom_mellior
Do I understand it correctly that this doesn't actually produce liquid water
but only somewhat more humid air in the general area above the device? I
wonder how much additional effort it takes to actually get the water into a
container.

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carapace
To me it looked like moisture was condensing inside the column and maybe
collecting in the bottom.

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tom_mellior
Yeah, I saw the condensation in the column, but since that's where the salt
water comes in I figured it would be related to that. The article talks about
"steam that builds up on the disc", which I understood to mean its upper
surface.

The university's press release at [https://www.monash.edu/news/articles/water-
solutions-without...](https://www.monash.edu/news/articles/water-solutions-
without-a-grain-of-salt) says: "Researchers created a disc using super-
hydrophilic filter paper with a layer of carbon nanotubes for light
absorption. A cotton thread, with a 1mm diameter, acted as the water transport
channel, pumping saline water to the evaporation disc. The saline water is
carried up by the cotton thread from the bulk solution to the centre of the
evaporation disc. The filter paper traps the pure water and pushes the
remaining salt to the edges of the disc."

My best guess at what this means is that _some_ of the water is turned into
vapor (not really steam at 100 C, I guess?) and that this evaporation drives
the capillary effect that keeps bringing in new water. Some other part of the
water, the part that "the filter paper traps", could then drip out into the
column. Maybe? Or maybe this prototype is really more about just demonstrating
that salt can be collected, and doesn't care about capturing the water.

Here's the original article, paywalled at UKP 42.50:
[https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee0...](https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee00692c/unauth#!divAbstract)

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wollstonecraft
Hydrophilic anything in the environment quickly fouls to hydrophobic.

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ncmncm
Even when supplied via wicking?

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jjtheblunt
[https://en.wikipedia.org/wiki/Solar_still](https://en.wikipedia.org/wiki/Solar_still)

is a lower tech solar solution?

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goda90
One cool application of solar stills is when you can't find any liquid water,
no matter how salty or dirty, but you can cut up parts of plants and seal them
in plastic to collect the moisture from the plants. Obviously not scalable,
but it can be a useful survival technique.

