Scientists create device that cuts desalination costs by 90% | Hacker News Reader

Scientists create device that cuts desalination costs by 90%

tass.com

146 pointsohjeez72 comments

They seem to be using a fast moving rotor with holes in the backside of the blades that extract the steam from the cavity and then condense it.

--- Links and related articles:

University: http://www.sfu-kras.ru/en/news/22304

Related paper: http://research.sfu-kras.ru/publications/publication/5140807... (doi: 10.1007/s11431-014-5631-0)

List of articles of the mentioned researcher (Kulagin) is at http://research.sfu-kras.ru/publications/author/24184408

(Nothing stands out on arXiv when searching for either desalination, cavitation or Siberian Federal University)

Desalination research isn't pre-published on arXiv. There are ~300 articles on arXiv where desalination is mentioned, and ~18-20k articles in the world. There is even a journal called "Desalination".

I've found 64 articles total that mention "desalination AND cavitation", starting from 2006.

https://sci-hub.tw/https://www.sciencedirect.com/science/art... I think this paper is relevant

So you can suck the gas vapour through the back of the rotor blade, so long as the rotor velocity is not exceeding the sound velocity of the gas?

It seems like you could make one at home or maker workshop with a hollow shaft...

Headline is a lie; it's 90% cheaper only compared to a process that isn't actually used. Flagged.

Could you add some more info on which process isn't actually used, or links to resources that discuss it? I'm not familiar with the state of the art of desalination.

The article is comparing to using atmospheric pressure distillation, which isn't used for commercial scale desalination... reverse osmosis is primarily.

(Where waste heat is available for 'free' flash distillation , which is already a lot more efficient than atmospheric pressure distillation, can be attractive... but if heat isn't available for free, RO uses about 80% less energy than multi-stage flash)

So it sound to me like it may well be in an apples to apples comparison the method discussed in the article may be similar to or less energy efficient than RO. But maybe it could be used to enhance the usefulness of flash distillation for lower levels of waste heat.

>Compared with the methods listed above, our technology allows to reduce the cost of obtaining one cubic meter of fresh water tenfold,” the scientist pointed out.

Who knows what that quote is even referring to... I wouldn't assume that the scientist was able to see the print layout of the article he would be quoted in.

From what I can tell, its a cavitating bubble in a very fast flowing tube. Then water vapor is extracted from inside the bubble (not sure how). Given the energy required to keep the flow going, and the drip of clean water that would result it should be easily calculable what the energy input/volume of water is.

Membrane-based technology has already cut costs significantly over distilling, and it is already commercially mature. It would be more interesting to compare the costs of this to membranes.

Something like this tech would make for a great pre-filter that would greatly extend the life of membrane systems. The last membrane system I saw required extensive rejuvenation of the membranes annually.

It's probably a good idea to develop more than one commercially-viable method regardless.

Israel has been using the membrane process for some time. I think their only issue how is dealing with the brine waste water.

What do they currently do with it?

Dump it in the ocean? It's not like we're extracting water in sufficient quantities to affect the salinity of the Mediterranean.

The issue there is with the mixing rates. While we won't affect the overall average dumping will create local zones of increased salinity, which can be a problem.

I remember reading the problem is that the salinity of the local dumping area rises sharply (maybe killing marine life)

Can you just not let it dry up a little bit more and sell it as sea-salt? I suspect it's not that easy, but on the other hand, the Bay Area has lots of "salt fields" where seawater is dried into useable salt.

The issue is that it's not just salt, but contains many other minerals and contaminants.

Probably better to just dump it on the surface of the desert and let it dry up.

What is the expected timeline for desalination technology? Even with continued investment all efforts have seemed to plateau at some point when costs and feasibility reaches a critical point.

Isn't feasibility a function of the cost of alternative options? If our current methods dry up, what is considered nonviable today suddenly becomes normal.

How would reverse osmosis filtration (the dominant desal method) "dry up"?

He's referring to traditional sources of fresh water like aquifers, rivers, and lakes.

The major issue with desalination as far as I can tell is that it produces toxic brine that proves problematic as far as disposal.

That's a good point. All the salt and other solute needs to go someplace.

As that stuff comes from the ocean one might suggest it goes back into it at a controlled rate.

The biggest challenge I'd read about had been energy costs, so this headline appears to be great news.

If the toxic brine is purely the extracts from the ocean water, you can toss it back into the ocean (with appropriate dilution). If the toxic brine has a bunch of additives that are a byproduct of the desal, then this is indeed problematic. The article mentions that this method eliminates the need for chemical additives so this could be a pretty low-impact method of desal.

> you can toss it back into the ocean (with appropriate dilution)

... what are you going use to dilute the brine? The water you just desalinated? What's the point then?

Seems to me if your input is seawater, and your output is a separated-out set of {fresh water, saltier sea water}, and you put the saltier sea water back in the sea, you're going to create a localized concentration of high salinity, no? Seems kind of unavoidable to me.

Not necessarily. You could mix it in processed sewage. Assuming processed sewage is appropriately disposed off in the sea at limited locations with precautions, this should work. One concern may be the sheer volume from desalination might overburden the sewage disposal.

I've spoken with a few oceanographers about this and the brine can be easily pumped back into the ocean with very minimal impact as long as you are smart about it. The effluent from a normal desal system is only twice the concentration of the source seawater. The key is to place your plant so you can reintroduce the brine into a fast moving and deep waterway.

One interesting ancillary benefit of having a source of brine is that it makes extracting desired minerals and elements from seawater much cheaper and easier. I have personally seen a system that extracts uranium from seawater. Current implementations yield yellow-cake at twice the market rate. There is ongoing work to tie it into a desal plant and bring that cost down. There is also work to combine it with lithium extraction.

This presumably depends on what your water source is. If you are desalinating groundwater, then yes the brine is going to be an issue, for seawater less so

You can dump it on land to evaporate, then sell some and bury the rest.

Israel gets 40% of its fresh water from desalination https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...

Israel went from having severe water shortages if there was no rain (plus environmental damage from overdrawing lakes) to being perfectly fine.

And the costs are not too bad either.

Israel also is the world leaded by far in controlling water leaks, which helps reduce water demand, and they also reuse greywater for farming.

Other places with water shortages could do the same.

There's a good review of existing and novel desalinization technologies, including OP's supercavitation method, here:

https://www.researchgate.net/publication/271673255_Large-sca...

90% compared to heating. But at scale no one desalinates by heating, it's all membrane based.

I'd like to see an energy comparison to that.

exactly this

No citation, but from what I've heard in previous discussions heat and membranes need about the same energy input. With heat you use the steam in heat exchangers so you recover most of your input heat and only need to add more to make up for inefficiencies (the system of course is never 100% efficient). With membranes you need to supply power to the pumps to keep the membranes at the correct pressure differential.

The above assumes engineering went into designing an efficient system. Pumps are easier to make efficient, but at scale they are not necessarily better.

There's already a factor of 10 cost difference between different heating technologies given energy costs and mineral content in the water.

Where does the salt go when you desalinate? At a large enough scale, would we risk salting some area (or body of water) to death?

That's the major issue with desalination. Dumping the brine byproduct back into the ocean is roughly equivalent of dumping other chemicals into the ocean, if not worse.

Why worse? I'd argue that it's less bad, because the salt was already there.

Now, it can still be just as toxic, and that has to be handled. But if properly diluted, then it should be equivalent to the ocean evaporating water, which happens constantly.

Also, the water created through desalination will end up back in the ocean eventually.

> But if properly diluted

That's the key phrase here. Obviously, if you dump it back into the ocean such that it actually does not impact local salinity levels, its fine. But that's also true for essentially anything dumped into the ocean - if you can manage the dumping of a toxic chemical such that it has no impact, wouldn't it also be fine?

No. If I take saltwater from the ocean, and desalinate it, and put the salt back in the ocean, the salt was already there before I started. If I dump a toxic chemical in the ocean, the toxic chemical was not there before I started. Those are not equivalent.

Since we are dumping sewage back into the ocean (after treatment), can't we dilute the salt back into what we are putting back?

Of course if you go down that route much you realize that the output of sewage plants is safe for human consumption there is no technical reason not to put it back into the water supply and greatly reduce the need for makeup water.

This statement is so wrong, brine contains salt that was in the ocean to begin with. As long as it's spread/diluted well, it has no impact.

Are you claiming this is comparable to an oil spill or eutherification?

I think it is a problem:

https://www.ncbi.nlm.nih.gov/pubmed/24241776

Maybe if the plant can spread the salt water further it could be less of an issue?

Typically the waste brine is pumped back out to sea. Its spread over a wide(ish) area to attempt to minimize the environmental impact. There are varying opinions about whether enough is done to avoid damaging the environment.

https://en.wikipedia.org/wiki/Desalination#Environmental

Back into the ocean. If you just dump the saline in one place it's bad, but good practice is to dilute the saline with sea water, after which it's perfectly safe.

The ocean evaporates more fresh water from its surface than humans could ever possibly match by desalination, so that part is perfectly fine.

Just avoid dumping the saline in high concentration (which is easy to do).

The oceans are big. Like... really really really big. According to [1], humanity uses about four trillion cubic meters of water per year. The oceans, per [2], contain about 321,003,271 cubic miles of water. Adjusting units and turning that into a percentage, we would use 4.154*10^-4 percent (0.0004154%) of the ocean’s water per year.

My guess is we can just dump the salt back in. :)

Edit: actually add sources.

[1] https://ourworldindata.org/water-use-stress [2] https://oceanservice.noaa.gov/facts/oceanwater.html

That didn't work for sewage or plastic though. The ocean is huge, which is why if you look at the numbers then you can put all human garbage into it and it won't even take up 0.001% of it.

In reality, the ocean is huge. So all that salt/garbage/whatever is increadibly uneavenly distributed and will naturally collect in certain areas. In the case of extra salt it could easily have an adverse effect on local ecosystems.

The ocean is made of saltwater already, it wasn't made of garbage or plastic.

Also salt dissolves in water which is why desalination is needed in the first place. Really think for a moment about what are saying must be true.

Ocean water has a specific level of salt. Increasing that in specific areas, by even a small amount, could have disastrous consequences. Life has evolved in the ocean at a particular saline level.

The point is not that plastic dissolves I’m water, it’s that the saline concentration won’t be spread evenly throughout the entire expansive ocean without first increasing it locally.

That's not what you said originally, you said it would cluster together like garbage and plastic.

Did I? Or did I say it would be unevenly distributed?

> Really think for a moment about what are saying must be true.

Indeed.

> So all that salt/garbage/whatever is increadibly uneavenly distributed and will naturally collect in certain areas.

You seem to have glossed over his last paragraph. No one's disputing that the ocean can sink the salt if the salt is evenly distributed. Trouble comes if that's not done properly and we get local ecosystems poisened by high salinity. Which if you think about it, is pretty easy to imagine from these plants pumping the salt to the nearest coastline.

This is getting downvoted, but I don't see any problem with it.

Another user, commented that it should be okay to dispose, by releasing it over fast moving currents in deep waters. That makes sense to me. The water we're using will mostly come back to the oceans and we'll have eventual consistency of the water/salt balance (in that process at least). Not sure if I got it right, though.

Either way, I feel that disposal of brine will be a problem if done recklessly, like for example in coastal areas and only on ideal conditions by chance - which is how we dumped most things in the 20th century.

My belief is that we should think about regulation, if we want desalinized water in a industrial scale.

You must be very careful when doing so though; to do so in a haphazard way is dangerous to sea life due to the high salinity of the brine that is the primary byproduct of desalination.

Indeed, local salinity would be higher. I’m not sure how easy it would be to distribute waste salt over a large enough area of water. Alternatively, land-based storage might be an option, not unlike Yucca Mountain.

However the dumping site will quickly become toxic to marine life.

The energy cost of desalination is a function of the salt concentration (saltier water => more power per liter of fresh water).

So when doing commercial desalination you don't want to produce very high salinity output (because it means that at some point in the process you were getting fresh water from very salty water ==> more power).

Of course, this has to offset against the cost of pumping et al, so there's an optimal cost output salinity.

The TL;DR for most modern desalination plants is that the output salinity is not that high. Typically under 7% dissolved solids (versus the ocean at about 3.5%). Meaning that pumping it back into the ocean is fine.

To put it a different way: If the overall salinity of the body of water being desalinated rose appreciably, it would probably render the desalination plant uneconomic.

I dont understand why desalination is an interesting problem given that it can be done whilst wasting minimal heat for processes that already need heat (or cooling due to too much heat). Things like smelting, power plants, nuclear, data centers...

How could this impact political problems?

My understanding of the Golan Heights and Israel vs Palestine is that it's about water. Will this technology help with that problem?

its not really about water. this will help alleviate water problems in coastal areas - israel already desalinates water but making it cheaper is better.

But the issue is far more complex than just water and the scope of this technological fix will not really affect it.

> My understanding of the Golan Heights and Israel vs Palestine is that it's about water.

It's not. Golan Heights has nothing to do with Palestinians, and is about Israel not being shelled from mountains.

Israel vs Palestine is about land, not about water.

> Will this technology help with that problem?

Israel already gets 40% of its water from desalination (see my post elsewhere in this thread). So been there done that :)

Israel also works with Jordan on water issues, so they are using water as a kind of water diplomacy.

it'll definitely help, israel already uses a massive percentage of it's electric generation to desalinate water. (since the country grows quite a bit of its own food)

from wikipedia "By 2014, Israel's desalination programs provided roughly 35% of Israel's drinking water and it is expected to supply 40% by 2015 and 70% by 2050.[18] In recent years, Israel's annual use of water from the Sea of Galilee has shrunk from 513 million cubic meters (in 2001-2) to just 25 million cubic meters (2018–19) as desalinated water has taken its place."

Countries that export food can be seriouslsy affected.

This site should be added to the list of non-trustful sources. TASS is a propaganda agency. Two last "S" are for Soviet Union (Sovetskyi Soyuz in Russian) - this agency was made by communists as a propaganda tool and still plays this role.

This news article, in particular, is a bs without proofs, without scientific magazines citations - they post such bs to create an impression of "positive news".

If requiring scientific magazine citations (which itself seems like a low bar), is our standard for if submissions are accepted, then there ain't going to be much news on Hacker News since most articles here don't meet that threshold.

This article is about scientific research.

Here's the ultimate desalination technology that scientists will end up implementing:

1. Use nano-technology "bots" to attach magnetic particles to the salt in the water.

2. Activate strong magnets to extract the salt.

Among the two byproducts will be the water that will have healing properties.

The day this will hit the news, remember:

You read it here first.

Why would they use nano-bots instead of just ligands ?

Reply on news.ycombinator.com