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Hydrophilic disc uses solar power to separate salt from water (newatlas.com)
126 points by HillaryBriss 61 days ago | hide | past | web | favorite | 59 comments

“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.

The researchers are in Australia, where we have abundant coastal land that is not suitable for agriculture. Indeed there are many salt lake systems already being used for large scale salt production via sea water evaporation (https://www.riotinto.com/australia/dampier-salt-4644.aspx).

Should this type of technology scale out, some of these salt production operations might also be able to produce desalinated water either for domestic or industrial use (in the case it is still too brackish for drinking).

This is research, so the final production will most likely be boosted with refinements.

I feel like there almost needs to be a bot that posts this on everything. So many people comment on things on here saying effectively "in the current state this would not be good enough for practical application", it's like no shit, that's why it's still in the research stage. Explain why you think this can't improve otherwise your comment is worthless.

If you've been around more than 10 minutes, you've seen it a thousand times - some new technology that will save the world, only never to be heard from again. The reason to believe it can't improve is that we've seen it too many times before.

hahaha, yeah, I completely agree with you! I actually think it is kind of sad because this community is all about startups/emerging technology. If you are coming here to read/post then you should know that nothing is perfect in the early stages.

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.

You dump the brine into well-mixed ocean areas.

You sell it, salt is required for mammals.

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.

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

We've got those - they're called kidneys. Unfortunately, they can't get the output dense enough to be useful for drinking saltwater...

(Maximum saltiness of urine is less than that of saltwater, which is why drinking saltwater dehydrates you)

There is a Sci-fi story somewhere in that comment. i.e., Bioengineered kidney solves some globalize freshwater catastrophe; or does it?

Birds have figured it out:

“Animal metabolism produces about 110 grams of water per 100 grams of fat,[1] 42 grams of water per 100 g of protein and 60 grams of water per 100 g of carbohydrate. [...] In mammals, the water produced from metabolism of protein roughly equals the amount needed to excrete the urea which is a byproduct of the metabolism of protein.[6] Birds, however, excrete uric acid and can have a net gain of water from the metabolism of protein.“


> 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

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.

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

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.

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

Sea mammals manage just fine.

Yeah, because they live underwater and can use said water to flush the waste salt. My question is how a non-water mammal gets rid of the waste salt...

A 1 minute web search shows this to be incorrect.

Sea mammals get most of their water from the food they eat (fish, etc.), and don’t drink seawater.

That’s not quite correct, “some marine mammals are known to drink seawater at least on occasion” https://www.scientificamerican.com/article/how-can-sea-mamma...

They do supplement that with water extracted from their food. But unlike humans they are better at expelling salt. “In the seal and sea lion species, for which measurements exist, the animals' urine contains up to two and a half times more salt than seawater does and seven or eight times more salt than their blood.” Human urine on the other hand contains less salt than sea water resulting in dehydration when drinking sea water.

Well then you should be criticizing the person I responded to for suggesting sea mammals have a "gland" that filters salt from water.

> ...for suggesting sea mammals have a "gland" that filters salt from water.

No-one made any such suggestion. One person lamented that such a gland didn't exist; they did not assert its existence. The other person didn't mention glands at all.

The other person responded "sea mammals manage just fine" after I questioned how a salt gland would work in humans.

That infers sea mammals have working salt glands.

Not mammals, but some reptiles and birds do.


You are mixing up the words “infer” and “imply”. But anyhow, no the other commenter did not imply that sea mammals have extra salt glands that humans do not.

> But anyhow, no the other commenter did not imply that sea mammals have extra salt glands that humans do not.

The other commenter clearly implied 2 things:

1. sea mammals have salt glands

2. their bodies have solved the problem of removing waste salt from said glands

There's no way to interpret the commenter's statement otherwise without it being nonsensical. Sea mammals manage (what exactly) just fine?

If you can't see that, then I'm sorry, here's a simpler analogy to illustrate my point:

Me: "Pancakes can't be made without flour"

Commenter: "French chefs manage just fine"

A rational person would deduce that what Person 2 is implying is: "French chefs [are able to make pancakes without flour] just fine", not: "French chefs [are able to make pancakes] just fine"

This begs the question how do fish get water in seawater environments.

By inference something along those lines had to exist somewhere along the ocean food chain...

or let the excess water evaporate and just make a big pile of salt?


pull out the lithium and make batteries?

They "make" energy storage using super heated salt. It's done using mirrors to direct the sun's Ray's to a specific point, creating enough heat to create molten salt. It's kind of a fascinating process and I've done it no justice what so ever. You should look it up, it's pretty cool. It's proposed use is to offset the lack of solar at night.

Hopefully you can fold the surface in 3d space so you don't need a full square meter of 2d space.

Can it be installed at sea?

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.

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.

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?

People pay good money for “sea salt” to use on their food. That’s just the dried residue from this process, assuming clean sea water to begin with.

It’s common to add a bit of salt and Epsom salts to water when brewing - the harder water improves the taste.

You get your minerals from food, not water. I doubt your premise about leaching body minerals by drinking distilled water (or rainwater!).

> People pay good money for “sea salt”

true. and if the salt produced by this process if free of micro plastics, people might pay even more

A very large number of people get their water from captured rain water stored in tanks. I do myself. It's not mineral-free but it's certainly very low in dissolved minerals. I appear to be alive, as do many others.

Does reverse osmosis retain the minerals?

And wouldn't the minerals in food compensate for their lack in water?

No, reverse osmosis filters out most minerals. But reverse osmosis filters aren't always used for drinking water. And yes, minerals in food can compensate.

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

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"

the World Health Organistion seems to think that it's important (but also reasonably easy to fix). https://www.who.int/water_sanitation_health/dwq/nutrientscha...

>You now need to expend energy to gather those minerals from somewhere else and then put them in the water

Did you mean the white stuff coming out :)

Is that just salt? Or a heterogeneous mixture of salt and minerals? You want just the minerals, no salt. How do you separate the salt from the minerals in that "white stuff"?

Most likely the NaCl crystals will have grown larger than the other salts and minerals, so the right progression of sieves will separate it well enough.

Salt is a mineral. You need it.

There are minerals in your food. You don't need to get them all from your water. Anywhere is as good as anywhere else.

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.

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

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... 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...

Hydrophilic anything in the environment quickly fouls to hydrophobic.

Even when supplied via wicking?


is a lower tech solar solution?

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.

Actually the Navy survival kit still seems to even have similar space efficiency if a 1/3m^2 footprint allowed for 2.4L per day. That would translate to 7.2L per M^2 per day which is right around the 6-8L mentioned in the article.

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