Desalination Breakthrough Could Lead to Cheaper Water Filtration | Hacker News Reader

Desalination Breakthrough Could Lead to Cheaper Water Filtration

news.utexas.edu

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> The seeds were planted when DuPont researchers found that thicker membranes were actually proving to be more permeable. This came as a surprise because the conventional knowledge was that thickness reduces how much water could flow through the membranes.

It's amazing how often "how it works" is taken for granted. This reminds me of the trend of racing bicycle tires. It used to be "obvious" that you wanted to run a skinny narrow tire at high pressure, for better aerodynamic and rolling efficiency. Even when they started wind tunnel (for tires and wheels) and rolling resistance testing, it was done on steel rollers, not on actual road surfaces. It was assumed that rough roads caused efficiency losses primarily in tire flex (heat), so it made sense to keep pressures high.

In the past decade or so, there's been a radical shift towards wider tires and wheels. There are a lot of people riding/racing on 28-32mm wide tires where you would have been laughed at a decade ago, and told to go back to the "efficient" 23mm wide tires. 10-15 years ago, you'd want to be running 120psi on a 23mm wide tire and today you want to run your tire pressure as LOW as possible, and run a wider tire to compensate, to give more air volume to spread the load and bumps across. The rolling resistance is LOWER, because they've found that the energy losses from rough roads or from bumps is in the tremendous amount of energy expended to move the 150-200lbs of "unsuspended" rider and bicycle up and down rapidly. You're losing single-digit watts in rolling resistance on that lower pressure tire, but saving tens or hundreds of watts in energy that would be lost moving the rider's mass up and down.

I'm not kidding about the "laughed at" part, either. I'm looking up how wide a tire I can fit on my 12 year old road bike, and there are plenty of downright ABUSIVE forum posts from just 6 or 8 years ago, telling people to go buy a mountain bike if they want to run wider than 25mm tires on my particular bicycle, where I'm trying to fit a 28 and would really like to run a 32 if possible.

And a lot of these findings started off as "huh, that's weird" when testing newer wheel shapes in the real world.

https://cyclingtips.com/2016/08/cyclingtips-podcast-episode-...

> there are plenty of downright ABUSIVE forum posts from just 6 or 8 years ago

Reminds me of another post from today:

https://news.ycombinator.com/item?id=25600274

We're now seeing hookless carbon rims that top out at 75psi. The industry has unfortunately taken this trend by the reins and will be shoving substandard wheels down everyone's throat in the name of profit.

Substandard in what way?

They will fail where a stronger rim won't

The botique wheel industry taking advantage of an excuse to cheapen their product? I'm absolutely shocked.

Sounds like the optimum size was a little bit off what was previously thought, but not by much.

28mm is still a very narrow tire, by any other standard than racing bikes. It's narrower than any utility bike and about half than you would run on a mountain bike, and describing the difference as radical seems a bit excessive to an outsider. Those tire pressures also probably excludes anything close to a flat tire.

It's not like anyone thought harder tires were always better. Otherwise they would all be running metal or wooden tires. After all, that was what everyone did before rubber tires were invented, which they were because they were more efficient than bumping around on wood. If someone had guesstimated the optimum at 23mm and 120psi and it was measured at 28mm, was it really that bad?

It’s a huge difference — you’re increasing by 20-40%!

Which means you’re dropping to 75-100 PSI... which is also a big change from 120 PSI.

1.5 the width and 0.65 the pressure is a “big” change for a part like a tire.

That it’s because we assumed something untrue about the mechanics is fascinating.

wow, this is the first time it was pointed out to me that I shouldn't be running my new fat tires at 120 PSI anymore. (face palm).

It's worth giving the podcast I linked a listen. In fact, I just listened to it a 2nd time yesterday after posting this. And it's 4 years old already!

It sounds like the primary reason you need(ed) high pressure, in addition to assumptions about rolling resistance, was to increase air volume to protect the rim. As the tire gets wider, the air volume goes up, so the required pressure to protect the rim goes down. Which is why a narrow road tire can have a rim impact at 40psi where a mountain bike tire would not have a rim impact on the same obstacle at 40psi. So, the wider tire ALLOWS you to run lower pressure and not damage the rim with impacts -- completely leaving rolling resistance aside.

28mm is not the optimum. It's all I can fit on my bike. I'm not sure what the state of the art is -- the podcast mentions testing 50mm and wider tires, and running less than half the pressure of what people used to use. They're talking about, basically, the widest possible tire you can fit, and the lowest pressure you can go (including going tubeless) without the tire coming off the rim in corners or cracking a wheel in an impact.

It's truly a remarkable change in strategy and thinking. As you go wider it's unquestionable that the weight and aerodynamic properties get worse, which means for wider tires to be more efficient, the rolling resistance decrease has to be huge to overcome the aero loss.

There will be an optimum point, where the benefit of the wider tire is balanced out by the extra weight of the rim and extra air resistance. Maybe the rim and tire merge, with spokes or struts connecting directly to a wide rubber rim/tire.

Absolutely true; the only problem is that, quite literally, every road surface is different, so that perfect point changes from second to second, sometimes very subtly, and sometimes in much larger ways.

That's gotta depend on speed and surface type. I know when as a kid I used to purposely run tires half flat just to see (on a loose dirt road) if wider (low pressure) or narrower higher pressure was easier. Higher pressure won over underinflated in pedaling uphill, unless it was powdery dirt where a wider tire didn't bog down as much.

I think the surface is a major factor, but speed not so much. I have no test numbers to prove that, just some practical experience racing MTBs for some years and using various width and pressure combinations based on the surfaces in the race.

I think you've misinterpreted the paper, while the bike conventional wisdom being wrong is interesting, the story about the membranes seems to be that there was an unknown additional difference in the membrane structure between the thinner and thicker membranes that caused the unexpected result. This doesn't mean that the thicker membranes were better due to being thicker, but because they happened to have a better structure. If the thinner membranes can be manufactured with that structure, they will most likely still be better.

Article abstract says exactly this: "They found that variability in local density most affects the performance of the membranes. Better synthesis methods could thus improve performance without affecting selectivity."

If you're not already familiar with bicyclerollingresistance.com (I'm not affiliated, just appreciative), that has been a fantastic resource for understanding what tire, tube, and rim characteristics really mean. There's so much rumor and trend informed butt dynamometer expertise in bicycling and far too little tediously measuring some actual numbers. Even if a rolling drum isn't perfect, it at least correllates to some extent with real world use and is far more consistent than possible by testing on a bike with a human rider.

Anyway, there are a few test series on same make/model/year tires over a range of sizes, which back up your point and add more detail as well:

https://www.bicyclerollingresistance.com/specials/conti-gp40...

https://www.bicyclerollingresistance.com/specials/grand-prix...

https://www.bicyclerollingresistance.com/specials/schwalbe-m...

That's funny. I was just riding my commuter bike yesterday and remarking to my wife how it was funny how much slower I am on it than on my road bike. I assumed it had to do mostly with my aerodynamic profile and to a lesser extent what muscle groups engage when pedaling from a more upright position. The commuter is running Marathons in 32c and my road bike has Continental gp5000s :) likely a 30w difference when multiplied out for 2 tires. At a cruising effort where I'm doing perhaps 120-140w, that's huge! And it reflects where you're doing 12mph instead of 17mph.

This is the actual paper, which is not open access:

https://science.sciencemag.org/content/371/6524/72

I always wondered, so now’s the time to ask I guess, why aren’t these publicly accessible? Aren’t they paid for with government (i.e. public) money?

Not necessarily. I don't have access to the actual article itself, so I can't read the section of the article that indicates who funded the work. But several authors do list corporate affiliation (DuPont and Dow), not that that is itself proof of non-public funding.

Even when you get a government grant for research, sometimes there are open-access requirements for publications, but sometimes not. It varies.

Paper directly written by government employees (like national labs) are usually accessible for free (like on https://www.osti.gov/).

Would it be possible to DPR these publications? I would assume that the funding agency retains a copy of the paper once published.

>Paper directly written by government employees (like national labs) are usually accessible for free

I'm pretty sure all of them are required to be in public domain

Some legislation has been proposed in the US Congress to require access to research paid for with tax money (seems pretty reasonable), but so far I don't think it's been able to get past Dr. No.

Read the article. It says it was funded by DuPont.

That doesn’t answer my question without prior knowledge. Luckily others did manage to provide an insightful answer.

> why aren’t these publicly accessible?

And you say: it’s sponsored by Dupont. So let me rephrase the question incorporating the new bit of information you provided:

Why would a paper be hidden behind a paywall if it’s sponsored by a commercial company?

It would make sense if it was completely off limits. But paying a few hundred dollars (?) means it is still semi public. It’s no secret, but it’s not public either. Why?

To prop up the journal, both financially and from an exclusivity angle. If the editors of the journal happen to be friends of DuPont, and the research is of actually that impactful, than a barrier to access might be beneificial

It's only partially supported by public money, as far as I can tell. Perhaps the industrial sponsors don't want it to be open access?

Luckily, the paper is accessible through SciHub it seems.

From the paper:

Funding: Financial support from The Dow Chemical Company and DuPont is acknowledged. T.E.C. and E.D.G. acknowledge financial support from the National Science Foundation under awards DMR-1609417 and DMR-1905550. K.P.B., A.L.Z., and E.D.G. also acknowledge support from the Center for Membrane Science, Engineering, and Technology (MAST) and the National Science Foundation under award IIP-1841474. M.K. acknowledges support from the National Science Foundation under award CBET-1946392. B.G. and B.K. are funded in part by the National Science Foundation under award CMMI-1906194. B.G. and B.K. also acknowledge computing support from XSEDE TG-CTS110007

The government probably doesn't care enough to bother setting up some sort of repository of papers.

Also, there are some pretty prestigious journals out there. I'm sure there are academics who'd want a whole lot more money if the government asked them to stop publishing in the journals that their peers read.

I believe all publicly funded research is open access after a year. NIH at least.

And for those wondering, you should not go to sci-hub to get the paper, because that would be illegal ;-).

According to the new copyright law in Japan, you could actually be criminally prosecuted for downloading papers from scihub even if you never share them. Starting today.

Bad news for Japanese science, good for their neighbor rivals I suppose. Shooting themselves in their own feet.

Feels like cheap desalination breakthrough every year. I know some middle east petro-states are building out the infrastructure, but it doesn't seem like there's broad adoption. Is it because cheap is still not cheap enough? Granted I don't follow developments closely. I just want better non flush/composting toilets.

I had an uncle who worked in the Middle East. One of the major problems with desalination plants is corrosion of all the pipe work, due to the high salt content. Better membranes will make a difference, but will not solve the corrosion issue that reduces the life time of a desalination plant.

Aren't plastics or polymer inert to salt water?

Yes, but I would guess that at the volumes these pipes will be pushing, the abrasive qualities of a high salt concentrate makes such soft piping material susceptible to being eaten through rather quickly.

So use lower volume across more pipes in parallel? Seems like something to engineer around.

Seems like something where ceramic-like coatings would help.

What about cross linked polyethylene (PEX) ? Why use metal pipes at all?

Just guessing, but probably pressure? PEX has much lower pressure ratings than metal. I plan to use PEX for a water purification system, but it will be sub 100 PSI. Most PEX-A are rated to 200 PSI at room temp and 120-150 PSI at 180 degrees F. They will rupture at 400 to 800 PSI of water depending on the brand. Metal pipes can handle thousands of PSI, required for pushing water through membranes.

If that is the case it still seems like you would just need metal for a section that reduces the size of the pipe down to something smaller to give you the pressure. A larger diameter pex should be able carry the water around with a reducer only where the pressure is needed.

Is Pex used in industry? I’ve only seen it in newish residential construction. Is there such a thing as a 6” diameter pex pipe? And fittings? 12”? 24”?

Where corrosion is a problem i’ve Seen metal pipes coated with epoxies.

I’ve seen big HDPE pipe used for low pressure sections to save cost over metal.

What do you mean by 'in industry'. In what industry? I don't know about anything larger than 3", but the general point was more than it doesn't seem right that corrosion of metal pipes would be a huge barrier to desalination since there are options for non metal pipes. There is also PVC which can be huge in diameter and CPVC which is used in some situations that need pipe that is more inert, but it is very brittle.

“Industry” generally refers to factories or plants as opposed to a commercial or residential setting. Quite often different codes, standards, and construction methods are used in industry than you see elsewhere. But large pex pipes isn’t something that I have seen.

A little digging looks like they at least go up to 120cm OD (almost 4 feet), 1450 psi

http://www.gpsuk.com/catalogue/

https://www.pe100plus.com/PE-Pipes/Technical-guidance/Trench...

Don't you only get differences in pressure due to diameter changes proportional to flow rate? If a membrane requires 400psi to get meaningful flow through it, it doesn't seem like you'd be able to sustain flow with much less than 400 psi of static pressure.

I don't understand what the problem would be. If there is a pressure limit with PEX, use larger diameter PEX, then reduce it where you need the higher pressure. This is the same concept of cleaning something by putting your thumb on the front of a garden hose.

Going from a larger diameter to a smaller diameter only results in a change in pressure if there's flow. In fact, the pressure ends up lower in the smaller diameter section according to wikipedia. Putting your thumb on the front of a garden hose increases pressure inside the entire hose because it reduces the flow rate, not just where your thumb is.

> Going from a larger diameter to a smaller diameter only results in a change in pressure if there's flow

There isn't a question of how much water can flow, the question was only if you need metal to have the high pressure needed for filtering.

> In fact, the pressure ends up lower in the smaller diameter section according to wikipedia.

You are probably seeing the pressure applied to surrounding pipe itself without taking into account the increase in velocity from the conservation of kinetic energy.

> Putting your thumb on the front of a garden hose increases pressure inside the entire hose because it reduces the flow rate, not just where your thumb is.

I think you are missing the point, if you want more focused you can reduce the flow rate since you still have the same kinetic energy of the water.

This is all irrelevant to the main topic though, apparently industrial PEX can go over 1400psi

Israel has led the way here: https://www.scientificamerican.com/article/israel-proves-the...

They've had efficient desalination tech for several years now deployed in the country. My understanding is they use lava stone to make the membranes more efficient. 55 percent of their fresh water now comes from desalinated salt water.

Human civilizations have built population centers close to sources for fresh water for millennia. Cities like Los Angeles that require moving vast amounts of fresh water long distances to be viable are a recent phenomenon - appearing only in the last century or so. So a big reason for the lack of desalination is a lack of demand. Yes, some places are experiencing a lack of water but those are the exception to the norm.

And even if a population center does need more fresh water, desalination is competing against traditional options: digging wells, building aqueducts, and expanding reservoirs. And have lots of experience - again, literally millennia of experience - implementing these pieces of infrastructure.

So in summary, desalination isn't seeing widespread adoption because it's not necessary for most places and we have much more experience with the alternatives. That said, it's great we're still improving desalination and it puts the world in a better place if water scarcity gets to the point that traditional water infrastructure is not sufficient.

> Cities like Los Angeles that require moving vast amounts of fresh water long distances to be viable are a recent phenomenon - appearing only in the last century or so.

That's not exactly true. The Hohokam started building canals in the Sonoran Desert maybe 1500 years ago (some of which form the basis for the modern water supply system of Phoenix!). Somewhat earlier than the Hohokam, the Romans were infamous for their aqueducts, the longest of which stretched over 250 miles. That's longer than the aqueducts that supply New York City or even Los Angeles!

The California aqueduct system has a total length of 444 miles and the main branch is 300 miles [1]. More important is the demographic impact of water management: Rome's largest population center was ~1 million people, the Hohokam ~80,000 as compared to the Los Angeles metro's 18 million. Preindustrial populations had very little capacity to built large infrastructure projects like these. Huge population centers consuming substantially more water than is brought to them naturally is a very recent phenomenon, Roman aqueducts and Hohokam irrigation notwithstanding. In most years Los Angeles imports 80-90% of its water. Situations like these are not possible without industrialized water infrastructure. Los Angeles used to be primarily supplied by the Los Angeles river and its population was correspondingly lower.

Human need water daily to survive, and without pumped plumbing building a population center that isn't near a lake, river, or with access to groundwater is effectively impossible. The Hohokam were no exception. Their aqueduct system did not exist to deliver water to the city center, but to their agricultural settlements. Their main population center was along the Gila river. Preindustrial irrigation systems are impressive when considering they were built without machines, and moreso in hostile terrain like the Sonoran desert or Afghanistan [2] - but it pales in comparison to the demographic impact of water management systems built over the last century.

1. https://en.wikipedia.org/wiki/California_Aqueduct

2. https://en.wikipedia.org/wiki/Qanat

Give global warming more time and see where the need for de-salination is at then. The droughts in SoCal are going to keep making these traditional fresh water sources you mention even more scarce. Less rain means lower lake water levels. Less snow in the winters means less snow pack in the mountains, so less water in the rivers and lakes below. All of this occurring while SoCal has an essentially endless supply of saltwater.

Texas is in a similar situation. The lack of natural lake resevoirs means their manmade lakes are also dependent on rainfall that is very prone to drought conditions as well. Texas also has easy access to saltwater. It's places like Las Vegas, Phoenix, etc that will have a hard time getting saltwater.

The poplulation of all of these areas are only increasing putting that much more strain on these limited fresh water supplies.

>The droughts in SoCal are going to keep making these traditional fresh water sources you mention even more scarce.

What's going on in California is nothing out of the ordinary. California is and always was a desert - and building a city the size of Los Angeles there would never have worked had it not been for importing huge amounts of water from central CA (see: Mona Lake) or the Colorado River.

Actually most of the Colorado river water goes for agriculture at 1930's water rates that are utterly insanely undervalued - but that's a whole other topic :p

> So a big reason for the lack of desalination is a lack of demand. Yes, some places are experiencing a lack of water but those are the exception to the norm.

With yet another year of drought in SoCal and heavy fires as a result of dryer weather in Norcal seem to suggest otherwise: I don't think it's a lack of demand at all.

Carlsbad actually built their desalination (Poseidon) plant when I still lived in CA permanently and the cost was the biggest hurdle, as was waste management, as they sold the water to neighboring areas at a premium in order to recover the costs in a public-private undertaking. Carlsbad is one of the more affluent cities in San Diego County so they had the money during the bubble economy boom before the crash.

Another one is/has been scheduled to be rolled out in Huntington Beach apparently [0].

I definitely think desalination should be explored, tested, and refined especially as the CO river source is/has been closed and CA needs to take advantage of the massive resource it has in addition to reducing consumption while figuring out the waste issue with desalination. And nothing could accelerate it faster than CA's massive need for fresh water. A Day Zero situation is something that should be avoided at all costs and in incredibly myopic in what is essentially the 5th largest economy in the World.

Personally speaking, I always figured it would be perto-states trying to diversify that would be the biggest financial backers of these facilities, as well as massive solar farms, as the automotive World moved further way from fossil fuel and OPEC goes to ever greater money losing schemes to prop up the price of oil. Especially in a World with evermore cheap and hot fiat being thrown at stupid things like Airbnb and Doordash IPOs.

0: https://angeles.sierraclub.org/news/blog/2020/07/stop_the_po...

If we stopped growing Almonds in the CA desert there would be more water for domestic uses.

Agricultural water rates are ridiculously cheap for the value of the water - hence absolutely brain dead schemes such as growing almonds in an otherwise desert!

> If we stopped growing Almonds in the CA desert there would be more water for domestic uses.

Are you seriously advocating that CA, a histrionically Agriculture based State, remove one of its nearly exclusive cash crops to curtail water depletion? Not only is that absurd, but it negates just how quickly that leads to food insecurity. I agree we should divert tax liability for farmers to improve their irrigation systems to reduce consumption and mandate water table depletion instead of letting FAANG and other multinational corps not pay taxes, but this argument doesn't take into account that all the Valley used to be Ag land long before it was ever used planned to be used for every tech corp that wanted to cash-in on a useless app no one cares about.

Ag isn't really the problem, the massive influx of people that came here from somewhere else claiming Agriculture is not a critical part of OUR unique Californian Culture, Cuisine and Identity is the issue, and they often do so in order they can have massive pools and manicured lawns and support other useless and wasteful habits. They're the same imbeciles that claim they can come here and remove access to beaches because they bought beach front property and feel they are entitled to everything that surrounds it, which is entirely against Californian Law (as well as beach/surf culture) as beaches are a public good.

> Agricultural water rates are ridiculously cheap for the value of the water - hence absolutely brain dead schemes such as growing almonds in an otherwise desert!

The central valley remains and has one of the most fertile soils in all of N. America for centuries for a reason, so while almond cultivation in the World certainly suffers from centralization, inefficient pollination irrigation systems, they are correctable with the right incentives and it is most definitely 'worth it' if you understand just how much California feeds not just the US but the rest of the World from that part alone.

And honestly, if you have ever been to massive golf courses and school and University campuses with manicured lawns (Pepperdine in Malibu is insane!) you'll see that excessive water is far more prevalent in areas that don't create any value besides aesthetic landscaping and leisure for the few because they have the fiat to buy what ever it takes to have acres of manicured lawns during fires and droughts and since COVID no one is even on campus to 'appreciate' it all.

You'd have to be an immense fool to think that not addressing those issues is critical before you remove established cash crops that actually feed people in order to curtail water depletion.

Desalination at least solves some issues we could and should address in regards to refilling aquifers and water tables and protect our Cultural heritage, which a big part of it happens to be Agriculture.

If every almond in the entire world disappeared, how much food insecurity would it cause? I've never really considered them a staple

> If every almond in the entire world disappeared, how much food insecurity would it cause? I've never really considered them a staple

Impossible to tell, but what it does do is open the door to the 'well I don't eat it, so it should go away...' narrative that goes hand in hand with things that are far too prevalent in Society today: Cancel culture.

If you were to reduce the water you would essentially decimate the cultivars that have been resilient up until now and destroy the established almond trees in most of the World. This isn't desirable, but merely a consequence of the frankly haphazard centralization of the food supply system, and central points of failure in non-software take far more resources and time to address.

Again, I would like to see more biodiversity in all fruits/veg/grains moving forward and a transition to almond cultivation have a diaspora away from CA is welcomed; but, to seriously consider phasing that out without have the contingencies that are providing viable harvest numbers which will likely take several years to decades.

Interesting thing about LA. I saw a table that showed how much energy was required to deliver water from each source. Some their sources of water require almost as much energy as desalination. Something like 30-50%.

I've wondered about using solar for desalination. Big issue though is desalination plants are capital intensive. So you really want to run them 24/7.

Desalination can be done effectively with thermal cogeneration. It's still inefficient, but since it is using waste heat it's "free" energy so to speak. Saudi Arabia has built such plants. The Soviet Union also built a fast reactor that was cooled with salt water, which was condensed and used as a freshwater supply [1].

Since ~80% of the world population lives on the coast, using seawater as coolant and capturing the condensate could represent a substantial source of freshwater.

1. https://en.wikipedia.org/wiki/BN-350_reactor

> Big issue though is desalination plants are capital intensive.

I thought the main cost was the running cost of replacing the membranes. I saw a video recently of a modular desal plant that was equipment in shipping containers.

I poked around and the Carlsbad Desalination Plant wikipedia page has numbers.

https://en.wikipedia.org/wiki/Claude_%22Bud%22_Lewis_Carlsba...

Cost about $1b to built. Energy costs are $49-5m a year. Total cost $108 million.

That's inline with my rough memory that 45% of the cost is capital, 45% energy, and 10% maintenance. Fudge those numbers as you will.

When I think about the economics it seems complex. Cheap power offsets extra capacity somewhat. Someone that actually manages, designs, plants probably knows real numbers.

There's a physical minimum energy required, but I don't know close things are to this limit.

Found this.

http://www.desware.net/Energy-Requirements-Desalination-Proc...

Seems like reverse osmosis takes 3.5-5.5 kwh/m3. Vs 0.86 theoretical. So 15 to 25% of theoretical efficiency.

Desalination has been inexpensive for 10+ years - ~$0.45/1000 liters (m^3) if you are willing to enter a long term (10+ year) contract. Down in Cabo, Hotels build their own desalination plants.

The reason why you don't see broad adoption is that the competition is free, and often comes with gravity assist. The challenge with desalination isn't so much the cost of the product, but (A) its competition and (B) The ocean (almost) always has to be pumped up to get to its destination, which can be expensive (C) Pollution - you end up with a lot of byproducts that you need to dilute out into the ocean (and you still end up with pretty devastated areas of the ocean floor where it goes out).

Cutting the price of desalination only helps with (A) - Even if desalination were completely free, you would still need to deal with geographic/pumping issues and the pollution.

It's not just used in the middle east.

https://en.wikipedia.org/wiki/Claude_%22Bud%22_Lewis_Carlsba...

Finally you could build them and then just not run them: https://azcapitoltimes.com/news/2018/05/04/yuma-desalination...

There will still be a brine problem though...https://unu.edu/media-relations/releases/un-warns-of-rising-....

As I understand, there are partial solutions to this. Using some of the brine, for one, and combining the brine with treated wastewater for another.

The latter depends a lot on how closed cycle your process is. Most of the water I use to shower or wash my clothes ends up in the sewer. Filling a swimming pool, not so much. Watering my lawn, only what overflows into the storm water system.

It's also distinctly possible we may have to build offshore desal plants to keep the thermohaline cycle running, using the brine as geoengineering.

> Greg Foss of the Texas Advanced Computing Center helped visualize these simulations

Where are those visualizations?

I've often wondered if home water filters, which can filter out lots of things [0] were doing light desalination. A slight amount of salt in water is desirable in specialty water like Vichy, but I'd imagine it would be unhealthy all the time.

0 https://helpatmyhome.com/aquasana-aq-5300-water-filter-revie... filter with the most ANSI/NSF certs that I've seen

I'm sure there are answers in the actual paper behind this press release but I wonder how much more it costs to make the membrane so much more uniform.

Papers don't usually talk about cost, so I wouldn't count on it.

“Desalination Breakthrough Could Lead to Cheaper Water Filtration if we don’t consider costs” sounds like a more honest title

Desalination is a good tech to put some research into now as opposed to when climate change happens too quickly for us to adapt.

Another poster pointed out it’s not popular because it’s not needed right now, which I agree with, but it will probably be a tech our race relies on to survive in the coming centuries. We were too slow to act on climate change.

> it’s not popular because it’s not needed right now

Dubai, a wealthy city of four million on Persian Gulf surrounded by the vast Arabian Desert, sources its water almost exclusively through desalination.

Yes, that’s still not popular by definition though. I understand that non-trivial amounts of water are being provided to major city centers via desalination. I’m saying that there’s a good chance that on century long timelines, we’ll be almost entirely dependent as a species on desalination to provide our fresh water. Even our most aggressive climate models aren’t keeping up with reality. This is a problem where even incremental advancements are important given our current situation.

In my state of Australia someone has built a massive desal plant in the middle of the desert next to a salt water source, the whole thing is powered by an array of mirrors and then the water is used to grow a huge tomato plantation in what would be totally unusable land without having to pipe in water.

The pic is super cool https://en.wikipedia.org/wiki/Sundrop_Farms#/media/File:1604...

Oh man this is super cool! I've never heard of this but this is exactly what I think the future will require. Being able to create your own power and then desalinate it and use it to grow crops in the same space is crazy powerful. I wish them all the best luck.

Can I ask a very naive question? Isn't it viable to use solar energy to make the water evaporate and use the vapor as the desalined water? I'm sure there should be some big issue, otherwise someone would use it. But I'm curious to understand what is wrong with such an approach.

Nothing is wrong with it. Here it is in action here powering a tomato plantation in the middle of the Australian desert https://en.wikipedia.org/wiki/Sundrop_Farms#/media/File:1604...

Interesting fact is these are not PV solar panels but simple mirrors redirecting the suns energy at one point.

down sides beginning you need to keep the mirrors cleaner than you do solar panels. Bird's that fly though the focused beam die. the sun has to be tracked, though I don't know if that's any different from a normal panel farm tracking the sun.

It's the power consumption I guess.

I've membrane filtration at home, it consumes very little power than what you'd need to boil the water and condense it to water again.

I've tried it on my solar panels, getting even 5 liter of water on my 2x350w panel takes 3-4 hours while I get 5 liter water from RO membrane in 1 hour while using 5% of solar panel power.

You could take a long and wide but short pathway of water with a tilted glass top and a black floor. The light is absorbed by the black floor, heating the floor then the water. Water evaporates to a vapor which leaves the salt behind. It then will condense on the tilted class ceiling and run down to a storage tank for consumption (You can also get a warm shower using this lowtech solar method.

Thank you for sharing this.

Will we ever see this technology any time soon or is this like battery tech?

Lithium ion batteries went through an incredible revolution the last 10 years, prices dropped by a factor of ~10.

https://twitter.com/ProfRayWills/status/1342632562477264896

That's ironically why we don't see new battery tech materialize. It has to come out of the gate more cost efficient than Li Ion, which is a tall order now with all the efficiencies of scale the latter enjoys. I believe the term technological lock in is used to describe this problem.

That's not entirely true. The technique to mass-produce Li ion cells (basically: create massive sandwiches and roll them) can probably be applied to most other chemistries.

I think that's mostly only superficially similar, but I'm not an expert in the field.

Chemically it is hard to believe that we can do better than lithium anyway.

I don't know about that, but we could definitely do cheaper though.

I still clearly remember the Nickel-Cadmium days. Kids don't know they're born. ;)

Lithium Iron Phosphate batteries are close to regular lion batteries but don't use manganese or cobalt and are much more durable. They have much higher discharge rates and can undergo around 8x the cycles, making their cost over time significantly better than regular lithium ion.

Lithium Titanate batteries have even more durability.

Both of these are fairly recent to being available commercially.

LiFePO4 batteries have been available for 5+ years. They aren't used in portable devices because they have lower energy density than other lithium batteries. They're great for fixed installations where density isn't an issue.

I think density per volume is similar, but density per weight is a little less from them being heavier. They should work fine in plenty of portable situations, not everything is a drone. Power tools, universal battery packs that offer AC, USB, etc., scooters, motorcycles, and all sorts of other stuff should work very well. Even golf carts and some scooters use lead acid batteries.

LFP batteries were around for close to 15 years.

First BYD EVs came out almost at the same time as Tesla Roadster.

It's like battery tech in that there are a lot of false starts and dead ends. And commercialization tends to play out over 1-2 decades.

That said I think the title using the word break through is clickybait. More honest title would be marginal improvement might lead to low capital costs for desalinated water plants.

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