Graphene-based sieve turns seawater into drinking water (2017) | Hacker News Reader

Graphene-based sieve turns seawater into drinking water (2017)

bbc.com

219 points11thEarlOfMar71 comments

Graphene can do almost anything except exit the lab. I hope to see my grandchildren see its benefits one day.

https://www.reddit.com/r/askscience/comments/6tzy80/graphene...

The sieve is made out of Graphene-oxide, not pure Graphene, so should be easier to produce.

I also have the feeling but people continue to state that it takes 15 years for products to come out in the past. I just don't see how in our day and age we see all the wonders of graphine promises and still sit here waiting for some to start coming to fruition. It holds so much promise.

It's the fusion of material sciences.

One of the key questions for desalination is how good can it get. It turns out that many desalination plants are probably close to the thermodynamic limit [1, 2], which means that even with new technologies it's likely energy costs aren't going to go down by an enormous amount. The Ars review suggests the best we can do is a factor of 3-4x, which is nice, but if we're expecting this to solve all our water needs we may have another thing coming. For reference, the cost of water is as low as $25 per acre-foot [3] in CA, and the most recent desalination plant in San Diego is on the order of $2000 per acre-foot [4]. Even some of the other estimates in [3] suggest that the average cost of water is something like $7-800 per acre-foot, which would put us right around where the thermodynamic limit suggests the floor of desalinated water would be.

Obviously this is great new tech and more water purification technologies are always needed, but given the physical boundaries it's unlikely we'll be able to use desalination as the only solution to water crises. We should still be figuring out ways to be more efficient about water use.

[1] https://arstechnica.com/science/2011/08/desalinization-is-th...

[2] http://science.sciencemag.org/content/333/6043/712

[3] http://www.cpuc.ca.gov/uploadedFiles/CPUC_Public_Website/Con...

[4] https://www.mercurynews.com/2014/05/29/nations-largest-ocean...

You are assuming that electricity is the only cost involved.

Based on the numbers in the article, the plant runs at 38-megawatts, consumes 100,000,000 gallons of sea-water a day, and produces 1 gallon of drinkable water per 2 gallons of sea-water.

Assuming a cost of 15.2 cents/kwh [0] (california seems to be one of the most expensive states), this comes out to an electricity bill of $451.70/acre-foot. A non-trivial portion of the total cost, but there is plenty of room for cost savings without reducing electricity usage.

Its also worth keeping in mind that Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable [1]

[0] https://www.npr.org/sections/money/2011/10/27/141766341/the-...

[1] Although will likely involve less wasteful agricutlure.

> Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable

Israel also has a lot of reclamation systems. Most of their sewage gets filtered and the fresh water reused. In most of North America, we give minimal safe treatment to sewage and then dump it back into our water sources.

That is a very expensive process, but cheaper than desalination usually. We just need to get over the ick factor.

"Gray water" use for irrigation is pretty common in dry areas. I don't know if it used for farms producing food for humans, though.

That is interesting to hear, I grew up in the alps, where water plays an important role in my province (90% of the enery comes from water). You can drink the water from the lakes etc.

The idea not to perfectly clean the sewage water you created, would sound irresponsible to anybody living here, as the water cycle becomes very apparent even to the craziest right wing nut when you live in the mountains.

Political slam unnecessary.

Would it be feasible for a desalination plant to also process and sell sea salt as a byproduct? Alternatively, could the salt be used for molten salt energy storage?

Humans have come up with tons of interesting ways to generate and store energy. I think we'll see some truly innovation solutions combining these methods to solve our biggest problems.

The brine waste from desal is full of nasty stuff you don't want concentrated even further and sold as food. Removing the long list of chemicals and heavy metals is not going to be viable costwise and even the most foolhardy consumer would think twice over regular salt.

A responsible desal plant does studies on how to pump and disperse it in the ocean as best possible. Sadly in the gulf the Saudis aren't doing this and have completely ruined the local ecosystem.

https://www.bloomberg.com/news/articles/2019-01-08/saudi-thi...

Desalination typically only raises the concentration by 2 in the non fresh water output. So it would be another process on top of the desalination.

Doesn't mean it doesn't make economic sense. Just that it's not an easy win.

Your comment sorted below one saying the KSA has ruined the gulf because of intensive hypersaline solutions in the water.

So.. can you help reconcile your optimistic and their pessimistic assumptions? Whats the difference? Gulf doesn't wash out well. Maybe the dumped water doesn't disperse?

There was an article on this not too long ago on HN with a good comments section, you should be able to find it by searching. From what I recall the situation is basically

- Locally it doesn't disperse fast enough, 2x is a lot when talking about sealife.

- They add copper (and maybe some other stuff) to prevent fouling of the pipes, which is bad for you.

If the primary cost is electricity and not equipment this can double as a "battery" by only running when electricity is cheap, lowering the price further.

> Its also worth keeping in mind that Isreal exists, relies heavily on desalination plants, and is an agricultural exporter so we know the situation is solvable

https://www.aljazeera.com/news/2016/06/israel-water-tool-dom...

Fair enough! I didn't know some of those numbers, maybe there's more hope :)

It's worth keeping in mind that residential water use is a tiny number when expressed in acre-foots. The vast majority of drinking water is used by farming.

Desalination, even at today's costs, is not ruinously expensive for drinking water; but it might make farming inefficient crops (i.e., almonds) nonviable in the desert.

Farming might just move geographically, or use water more efficiently. Neither of these are necessarily bad outcomes.

Israel is a leading desalinator and major almond exporter, using less water per bushel than California by a factor of 30.

Their secret? Each tree has a pipe about one meter deep. Water goes into the pipe instead of being sprayed on the ground.

There are huge amounts of low-hanging fruit in California agriculture. Water is priced too low to make it worth taking advantage of.

You’ve touched on another problem:

New/increased usage gets charged the average price.

Meanwhile, new capacity is the most expensive.

So you get subsidized if you switch to a more water-intensive crop.

I think the calculus should get a bit better with cheap renewables - desalinating only when more energy is produced than can be reasonably used.

I think if we can find a bunch of things that can effectively use excess power but aren't time sensitive, it'll also make renewables much more attractive.

The lower the capacity factor of the plant the longer it will take to recover the capital cost of building it. Whether this is economic depends on the ratio of energy cost to capital cost. Do you know what that ratio is?

> only when more energy is produced than can be reasonably used

But when would that ever happen. They'd just get used up in e.g. mining $coins.

Clean energy cost is still going down rapidly and is already cheaper than coal and other fossil fuels. Existing desalination approaches will get progressively cheaper as well simply because of energy price reductions. IMHO, solving cheap, plentiful, clean energy solves a lot of problems as most other problems boil down to being energy problems as well. E.g. food production is bottlenecked on water. Solve cheap energy, you get clean water as well. Solve that, and food production becomes cheaper as well. The water crisis is an energy crisis.

I do agree we need to be smarter how we use the land and water. E.g. California draining its natural resources to provide cheap water in LA is not sustainable. There's no excuse for that city to not have extensive desalination as its primary means of supplying water; other places in the world are managing just fine. That 25$ cost is basically about not factoring in the true cost of destroying natural resources. Also, farming practices in California are kind of wasteful and result in lots of water being wasted.

Great point. Especially given how wasteful we are with drinking water there is far more room for efficiency on the demand side than the supply side.

This source says we use 80-100 gallons (304-380L) per day (in the US) https://water.usgs.gov/edu/qa-home-percapita.html

At $2000 per acre-foot, 100 gallons costs 61 cents.

That's right, $2000 per acre-foot is $0.0061 per gallon.

So even at that cost all you have to worry about is the consequences of using the energy, the cost is no problem.

Wonder if we'll ever run dual source systems...like salt water is just fine for pooing in.

It’s a thing for Hong Kong. Something like 80% of toilets are flushed with sea water.

Chlorination is easy: just electrolyse the water on its way in.

Not sure what impact this has on sewage treatment.

Very interesting concept that I never considered. Shower with salt water and then rinse with regular water. Pay one price for salt, one price for regular water.

The salt water would probably be too corrosive to pipe significant distances, which would make that difficult to get enough scale to make it feasible.

Most of the dual-use water systems I’ve read about were fresh water vs gray water.

Much piping these days (>75% for major distribution pipes, and increasingly common in residential use) is PVC, which doesn't corrode.

Salt and minerals get into fittings, destroy valves, and coat everything when the water evaporates. Probably not a great solution.

You would have to purge your system and shower head with vinegar every day just to keep things clean.

You are assuming that only metal pipes exist. Nowadays most pipes are made by either concrete for the big ones (canal like) or plastic connected with glue that is rated for hot or cold water.

This is assuming the current energy costs though, right? If we can get cheaper energy, say via fusion, it could go down.

For sure! But cheap energy is hard :( I'm cheering for Solar, renewables and Nuclear Fission to become cheaper and more widespread. Fusion... well it would be nice, but given that it's never been demonstrated in a form suitable for commercialization, it's hard to hold out for that.

Anyone know why we don't just use nuclear fission as the heat source in desalination?

I mean, other than the implications of your nuclear purified drinking water.

For the same reason we don’t utilize fission in other areas, people are ignorant and terrified of it, politicians are trying to be re-elected, and as a result real problems such as distributed rather than centralized storage of waste emerge. There are also real issues with processing vast quantities of seawater in a way that doesn’t destroy littoral ecosystems. Then there’s disposal whatever heavy metals and pollutants are concentrated as a byproduct of the process, regardless of your power source.

Still, it’s feasible to overcome the last two issues, but I’m pretty sure that ignorance is going to kill us.

I used to work in the nuclear power industry. When I came on board out of college in my first month or so I was given a bunch of books to read and free time to read the history of the company and industry in the company library. I came across a 1980's feasibility study to use nuclear power for desalinization in a boiling water reactor. The tldr of the report was "not economic" so the project died.

I asked my boss about it since he was around at the time and he hadn't work on the project but did hear about it. He said the study was paid for by Saudi Arabia and that the deal killer wasn't the cost of nuclear heat but fouling of the pipes from mineral deposits in the heat ex-changer and desalination chamber. The coatings killed the thermodynamic efficiencies of the system so there would be really high maintenance costs for continually cleaning and/or replacing the pipes. Like a lot of engineering projects it was a material science problem but nobody wanted to pay for the research to solve.

With renewables due to changing weather and demand, prices for electricity at international markets are falling regularly, sometimes even becoming negative (keeping the frequency is must), only to rise again when there is more demand than supply.

Desalination plants have the advantage that, as long as you have overcapacities compared to the average needs around, they can be turned on when energy is cheap and off when it's expensive. While they are operating, they would fill reservoirs that would provide a continuous supply of water.

There might be a thermodynamic limit onto how much energy you need to desalinate water, but the limits of harvesting renewable energy are far from being reached. We might make the sahara green, in this very century.

"scientists also needed to demonstrate the durability of the membranes under prolonged contact with seawater and ensure the membrane was resistant to "fouling" by salts and biological material (which requires existing barriers to be periodically cleaned or replaced)."

Er, yes. All they have is an experimental membrane that won't pass salt. Lots of those exist. Can you backwash it and get the salt out? It has to handle concentrated brine in reverse. Plus whatever other crud is in the incoming water. Most of the headaches of real desalinization plants revolve around those issues. Fragile membranes are a big issue.

This is in Nature Nanotechnology, not Desalinization, which has a more practical orientation.

Its a matter of degree. If the membranes are cheap enough (the point of the new material in fact) then they don't have to last as long.

Claims of "it's much cheaper" from something that isn't even at pilot plant stage yet are usually suspicious. There are many articles on early-stage desalination membranes.

From 2010: [1] NanoH20. That actually worked. LG Chem bought the company and they sell reverse osmosis cartridges using the technology. In the end, it was about a 20% improvement.[4]

From 2012: [2] Contact membrane. That worked, but doesn't seem to have reached production. Inventor developed other interesting membrane separation systems, mostly for non-seawater applications.

From 2018: [3] Improved membrane production process. No product on the market yet.

Actual progress tends to be in the form of improvements in the 10-20% range. 20% gets you a startup company win.

[1] https://www.greentechmedia.com/articles/read/nanoh2o

[2] https://www.scientificamerican.com/article/desalination-memb...

[3] https://today.uconn.edu/2018/08/new-findings-may-lead-sea-ch...

[4] http://www.lgwatersolutions.com/en/product/seawater-ro

Not to rain on the parade, but is there any example of graphene being used at scale to do anything? I feel like I've heard about graphene for the last 20 years and how it's going to be a miracle material, but we have little to show for it besides some nice lab results

No because that’s exactly what haven’t been solved: mass production / scale.

And it seems that the progress in that area is pretty slow and anemic.

Does graphene coated heatsink count? I don't know, I'm asking.

https://www.pine64.org/?product=rockpro64-slim-profile-graph...

This is a component -- what's the device model? The energy cost of crossing that gradient will continually increase (you could use gravity, but you still have to clean the briny side).

The of course brine disposal is a problem.

Don't get me wrong -- I love this work -- but it's just part of the solution.

For a lot of people in poor, hot regions a simple evaporator of concrete with a glass top is surprisingly effective, both cap ex and op ex (both pretty low, though they assume a tiny cost of labor).

you're the first only commenter to mention the waste products from desalination:

https://news.ycombinator.com/item?id=18911969

https://www.youtube.com/watch?v=qZ5ut_4zKug

What is it about every HYS in the Science section that attracts the population control nutters? We all add one to the total. Those screaming for our numbers to be reduced fail to notice a small part of the solution to the problem every time they look in the mirror.

Does anyone have a solution by now on what to do with the millions of tons of salt which are produced by desalinating water?

I read that right now the salt is just dumped somewhere being a huge burden for flora and fauna.

Store it in salt domes for use on U.S. roads for the inevitable ice age-level snow removal that we will have to contend with. Seriously though, i would guess that this remaining salt is likely not suitable for food preparation...but can't it be used for salting roads in winter? Or, perhaps, maybe in molten salt reactors/energy storage systems?

My guess it is dumped back into the sea which will cause a seriously high salt concentrations close to the dumping site. However it’s net effect on salivation levels in the oceans overall will be neutral since all the fresh water produced will likely end up back in the sea.

Might want to attach the (2017) label, although I hadn’t heard of it until now.

What can't graphene do?

Make it out of the lab.

Salty

i must be missing something. the story says they had to:

1. put epoxy resin on each side of the graphene membrane to prevent swelling when exposed to water (which is important because if the graphene swells, then it allows sodium chloride to pass).

2. "drill" 1 nanometer (or smaller) holes into this membrane

so, what role does the graphene really play here? i mean, as long as you can drill tiny holes into it -- could the filter be made out of other material?

The part about drilling holes was for context, explaining why the alternative (single-layer graphene) was currently impractical. In the case of graphene oxide, which this article is about, the challenge was the swelling, the solution to which seems to be the key discovery in this article.

Graphyne. Cyclohexane rings connected by poly-yne chains of equal length.

Allows for a somewhat tunable pore size, with no "drilling" necessary. Graph-di-yne and graph-tri-yne are nearest the appropriate pore size for water. A series of graphyne filters with larger pore sizes would likely be needed to clear out particulates and larger ions, so that the final purification step proceeds at a reasonable flow rate.

https://arxiv.org/abs/1312.3179

Similar problem as graphene, in that it has not only never been outside of the lab, but also never been outside of the computer model.

right but that's the point - graphene is pretty much the only material so far we've been able to drill holes that size in to

Anything cheap

Osmotic pressure is still a thing and semipermiable membranes already exist. Will be intersting to see what the actual benefits are compared to what already exists.

Good point, these graphene membranes would be useful if they were chemical resistant or stronger. So that the membranes could be backwashed and chemically cleaned more easily.

Graphene is incredibly strong.

I have heard about graphene being some kind of holy water in the last decade quite a few times. Sadly, it seems only possible to recreate amazing results lab wise.

Has there been any progress on it? Seems to be just a lab experiment

This is a comment on graphene as much as it is this particular application!

Seriously this was news 5 years ago.

Taokey?

Excellent news I need a desalinator for my boat and this should bring down there ridiculess costs, can't wait to see the production model. This will revolutionize fresh water production for many dry third world countries and make a lot of revenue for Britain

Reply on news.ycombinator.com