Making Saltwater Drinkable With Graphene 303
An anonymous reader writes "Graphene once again proves that it is quite possibly the most miraculous material known to man, this time by making saltwater drinkable. The process was developed by a group of MIT researchers who realized that graphene allowed for the creation of an incredibly precise sieve. Basically, the regular atomic structure of graphene means that you can create holes of any size, for example the size of a single molecule of water. Using this process scientist can desalinate saltwater 1,000 times faster than the Reverse Osmosis technique."
A foul subject. (Score:5, Interesting)
So how durable is this membrane when it comes to dealing with impurities?
Re:A foul subject. (Score:5, Informative)
Graphene membranes are highly durable. The main problem would be clearing the inlet side of the filter from the buildup of blocked particles.
Prevous Slashdot article here: http://science.slashdot.org/story/12/01/27/1354240/graphene-membranes-superpermeable-to-water
http://www.manchester.ac.uk/research/news/display/?id=7895
http://arxiv.org/ftp/arxiv/papers/1112/1112.3488.pdf
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Well assume they can reverse-flush it on a regular basis and that it won't collapse that way, either.
Don't really need to clean it as much as you think (Score:5, Informative)
RO is not like using a traditional filter. I'll see if I can explain it quickly without the explanation getting too muddy. The last RO project I worked on was in 1990 (and wasn't for salt, but same principles apply), but I doubt the basic structure of the equipment has changed much. Probably more changes are in the actual membranes.
On an industrial scale membranes are placed in canisters and usually in large banks of them. The way the canister is built is usually a couple of sheets of membrane, sandwiching a substrate that allows a reasonable liquid flow rate through it, the whole is then spiral wound (like a roll of paper towel), or better yet, like film on a film winder that goes into a film development tank for those who remember film cameras and how to develop negatives :). The edges of the substrate and membranes are attached to a framework such that the purified liquid can be collected and channelled out either one or both ends of the spiral assembly when the assembly is inserted into a properly designed tube/canister. You put the wound membrane assembly in the tube that has one inlet and two or three outlets (depending on whether you want the purified liquid outlets at either end or just one). So say we have one feed outlet and one purified outlet. On the inlet side you flow your feed liquid at high pressure. One of the two outlets is your "purified" liquid and the other is an outlet for feed liquid.
Because of the pressure differential between the feed side of the membrane and the substrate side of it, the "pure" liquid will be forced through and then flow through the substrate and the pure liquid outlet (at a much, much lower flow rate than the pressurized feed liquid). On the feed side of the membrane, this results in a slightly higher concentration as it passes the membrane and thus, the feed outlet side has a higher concentration of solute than the inlet. But you are always maintaining a flow across the membrane at high pressure and what you end up with is the slightly higher concentration liquid flowing out the far end from the inlet. Note that the downstream line from the canister is still under pressure.
So you don't really need to backflush to clean it, or not as often as you might think. You always have a flow of material over the surface in low enough concentration to keep the salt in solution. Granted that sometimes they will chain membrane canisters, the outlet from one going into the next. Or they may have a feedback loop that keeps a set (higher) concentration on the outlet. This reduces the inlet flow and increases the concentration of the output, but it also increases the pressure required. Regardless, the membrane is usually kept from clogging from the movement of the feed.
FWIW, in some systems you might want a certain concentration on the outlet to use as feed for another process. You might be able to use it to concentrate sugars, or even the salt we're talking about. The more water you squeeze out, the less you need to evaporate. But in the case of desalination, I can think of cheaper ways to get salt (like mining), but this serves as an example of what can be done.
For maintenance in some operations (like for example, in the food industry), once the system is shut down, they will run cleaners through the system and if it needs to stay shut down for a period, they'll fill the system with purified water (if water is the output they can use that). They might add a bacterial inhibitor so that nothing could possibly grow and build up in the system. If they don't keep the canisters full of liquid they will dry out and usually become useless. And they are quite expensive.
Pure water is not always what is sought after. Lower pressure RO, usually called ultra filtration has various uses. For instance, I saw one project using it in making raspberry juice. Don't ask me what they were doing with it, I just saw it in passing at a food research place. I was seconded to a research institute in a past life to study using RO to purify waste
Re:A foul subject. (Score:5, Informative)
But *if* they break... what then?
Let's put this to rest. Graphene is one of the strongest materials ever: http://physicsworld.com/cws/article/news/2008/jul/17/graphene-has-record-breaking-strength [physicsworld.com]
Re:A foul subject. (Score:4, Insightful)
But *if* they break... what then?
Let's put this to rest. Graphene is one of the strongest materials ever:
http://physicsworld.com/cws/article/news/2008/jul/17/graphene-has-record-breaking-strength [physicsworld.com]
Being the strongest material does not mean it is unbreakable.
Re:A foul subject. (Score:5, Informative)
Graphite is a mixture of all kinds of carbon molecules including buckyballs, carbon nanotubes and graphene. You can eat fistfuls of graphite without serious problems. It's not great for your lungs if inhaled, of course, but getting some in your drinking water isn't going to hurt you.
Re:A foul subject. (Score:5, Funny)
Water Filtration (Score:5, Informative)
When thinking of water filtration, a lot of you automatically conjure up a mental picture of a conventional water filter -- ie, dirty water poured from the top, and impurities get trapped in between, and clean clear water drips out from the bottom
In large scale water filtration operation, that traditional top-down model does not work
Instead, raw water is pumped into the inner tube of a double-layered pipe, which is slanted upwards, at a 30-60 degree angle
Sections of wall of the inner tube are made up of filtering membrane - such as Graphene
As the raw water flows upstream , and because of the smaller diameter of the inner tube , pressure building up inside the inner tube of the double layered pipe.
Because of the higher pressure inside the inner tube, molecules of clean water flows out of the inner tube, through Graphene (or other filtration membrane), into the larger pipe on the outer layer of the double-layered pipe
And because the pipe is slanting upward, gravity causes the filtered (clean) water in the outer pipe to flow down and eventually it gathers at a collecting point (usually a tank, or a pool) at the bottom
At the top of the double-layered pipe, there is an opening for the inner-pipe for the impure-water to exit
Because of the outlet, there is no need to do any "back flushing" since impurities, including salt, are continuously being flushed away
Hope this helps
Re:A foul subject. (Score:5, Insightful)
Surely it won't last forever, but the membrane lifetime could be extended by using normal filters to retain impurities, and let the graphene deal with pure saline water. Maybe the graphene filter can be cleaned a couple of times and be reutilized.
Re:A foul subject. (Score:5, Funny)
Surely it won't last forever...
Yes, it will last forever, and don't call me Shirley.
Re:A foul subject. (Score:5, Informative)
http://www.wateronline.com/doc.mvc/nanoporous-graphene-could-outperform-best-commercial-water-desalination-techniques-0001 [wateronline.com]
Article linked from summary links to the above article as a source.
Re:A foul subject. (Score:4, Informative)
Well, TFA brings absolutely no detail. It won't even let you know it it is about something produced in a lab, some theoretical contruction, or even if nobody has no idea how to create such a filter.
Now, graphene is pretty stable. It probably cloges with time, as other athoms get in the place of carbon, but that is an incredibly slow process. A membrane composed of a single graphene sheet should last more than any other component of your plant.
Ok, all the above is great, and etc. But when you get in the real world, membranes get old because of impurities that accumulate on its porous. A single graphene sheet has nowhere for those impurities to accumulate, if you reverse whash it, all impurities are gone (except for the mechanism at the above paragraph). But no practical membrane is composed of a single graphene sheet, thus, durability will be probably all over the scale depending on the quality of the actual membrane, from trash that can't be used on a lab to as good as ceramic filters.
Re:A foul subject. (Score:5, Informative)
According to the other article [wateronline.com] people are posting, this is based on Molecular Dynamics simulations. MD is a theoretical technique that uses time-dependent Newtonian mechanics. It relies heavily on having good-quality data for the interactions between the atoms, but allows relatively large systems to be modelled. The wikipedia article [wikipedia.org] contains a fair bit of information (probably too much).
TLDR: This is just based on computational modelling. The model is fairly crude, but is a standard technique for this scale of system and the results should be taken seriously.
Re:A foul subject. (Score:5, Insightful)
Re:A foul subject. (Score:5, Insightful)
I agree,getting salt out is fine, but, fishy smell, fish pee, industrial pollution (mercury 'n'such ).
Err, no one does that... Seriously. Fishy smell? Fish pee? wtf??
Mercury is not toxic much anyway, unless it is in organic forms.
But then on the plus side, if Uranium cost were > $350/lb, it would be economical to mine Uranium from sea water. It doesn't mean this concentration is toxic for you.
Where I live, most of the water is from a lake, with fish pee and moose pee all mixed in together. haha
Re:A foul subject. (Score:5, Insightful)
A robust and cost effective desalinization system is literally one of the biggest necessities we're going to need in the next century, as average rainfall levels continue to fall all over the U.S.
I know it may be impractical but I see giant desalinization inlets from the ocean leading to a network of irrigation and river systems for the West coast.
Re:A foul subject. (Score:5, Insightful)
It's been pointed out that the most efficient way to do things would be to recycle city waste water for drinking water, since it's more free of some contaminants like mercury, and, more to the point, is already at the point where we'd need it. Piping drinking water from the ocean just to piss it into a river is hugely wasteful.
The biggest impediment to that is the ick factor you just brought up: if the idea of drinking water that had fish urine removed from it, people are going to throw a hissy fit before they'll drink water recycled from their own pee.
Re:A foul subject. (Score:5, Interesting)
Re:A foul subject. (Score:4, Informative)
Pull your head out of your arse and think: water treatment plants of all sorts have been doing that for 120 years using scrapers, settling tanks, sand filters and flocking agents.
Re:A foul subject. (Score:4, Informative)
Salt dissolved in water isn't just a bunch of wet table-salt-shaped crystals. It's a bunch of individual NaCl molecules floating around. And this filter has holes small enough to pass H2O molecules, but not NaCl molecules. Most other molecules, such as those of uric acid, are much larger than NaCl, and therefore this filter will trap them, too.
It isn't breaking anything down. It's not chemically altering the substances in solution. It's simply a filter that has holes so tiny that only molecules that are three atoms or smaller will pass through them.
Re:A foul subject. (Score:5, Informative)
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"scientist" (Score:5, Funny)
Using this process scientist can desalinate saltwater 1,000 times faster than the Reverse Osmosis technique.
Well isn't that swell for 'scientist', but does scientist plan to share?
Re:"scientist" (Score:4, Funny)
Re: (Score:2, Insightful)
Let's break down why you are unfunny.
Holes? (Score:3, Insightful)
what about the holes getting blocked by minerals and impurities? seems high maintenance job.
Re:Holes? (Score:4, Insightful)
Re:Holes? (Score:5, Interesting)
A couple of people have raised this issue, and it relies on a fundamental mis-understanding of how the universe works on a molecular scale.
Suppose that I have my colander and I wash some vegetables in it. Gunk can get stuck in the holes and it has to be washed off, which requires a fair amount of work because I have to break the interaction between the gunk and the surface. That's your macroscopic intuition about how filters and such work.
But your macroscopic intuition will lead you astray in this case. The individual holes in graphene do not work that way; yes, occasionally, molecules of one kind or another will spend some time stuck to the graphene (a useful phenomenon in other circumstances - http://en.wikipedia.org/wiki/High-performance_liquid_chromatography [wikipedia.org]) but, on the scale of atoms, they are effectively in a high-powered washing machine ALL THE TIME.
Can't find quite the movie I want... this'll do:
http://protonsforbreakfast.wordpress.com/2012/04/11/brownian-motion-observed-in-milk/ [wordpress.com]
So you see those oil bubbles wiggling around? Given that amount of constant wiggle, are you worried about having them "stuck" anywhere? That's thermal vibration from being at room temperature. Those milk bubbles are over 1,000 water molecules across, so each of those "wiggles" is 10 or 100 times the size of an individual graphene pore; are you worried about anything another 1000x smaller being "stuck" anywhere? It would be like worrying about gunk stuck in your colander while your colander was sitting in a fire-hose 24/7.
Anyway- to cut to the chase:
obviously you could have you take the graphene and you run the sea water *past* it at high pressure. Occasionally some gunk gets in there but it washes away sooner or later; and nothing spends any appreciable amount of time stuck in an individual graphene hole.
Re:Holes? (Score:5, Funny)
Occasionally some gunk gets in there but it washes away sooner or later; and nothing spends any appreciable amount of time stuck in an individual graphene hole.
She was a real hot-shooter, that bubble. I should have known she'd be trouble from the get go; she was naturally "charged" as they say when they're trying to be polite.
With her bouncing around all over the place even at room temperature, I guess I should have seen it coming. But, as will happen to palookas and wishful thinkers, my hopes and processes got the best of me. I was convinced that any trouble would wash away as soon as it cropped She didn't even say goodbye, just left a note saying she'd thought she had found a solution with me, but couldn't stand the suspension and was afraid of becoming just another precipitate.
That was three years ago. I took the tube directly to this here graphene hole; it was the closest one I could find. I've been stuck here ever since.
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Lol.
I love that video. The music reminds me of The Life Aquatic with Steve Zissou.
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not disagreeing with your assessment, but:
Gunk can get stuck in the holes and it has to be washed off, which requires a fair amount of work because I have to break the interaction between the gunk and the surface. That's your macroscopic intuition about how filters and such work.
I think people may be basing their assumptions on typical RO membranes, which are microscopic in function and do get gunked up and need to be replaced. In fact, that's next on my project list for the kitchen, after I get done wasti
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Disposing of what exactly? Brine? We already to that, with very light effects on the environment. The graphene? It's not toxic, it can be safely handled and stored; burning it will release only CO2 and (a very small amount of) water.
Re:Holes? (Score:5, Insightful)
You sell it as fancy eco-friendly sea salt for $15/lb.
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No, it'll probably drive down the price of sea salt.
BTW, sea salt is great stuff; it tastes much better than table salt (mainly because of the other constituent elements like calcium and magnesium).
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"Normal" sea salt is a commodity. "Fancy" sea salt from specific places (pink salt, fleur de sel, etc.) is expensive. With the right marketing (and with the desalinization plant located in the right place), they could charge "fancy salt" prices.
Re:Holes? (Score:4, Interesting)
Oh please. For one thing, we already have desalination plants in some places dumping brine back into the sea; obviously it's not a big problem. There's a lot of water in the oceans. Secondly, the highly concentrated brine from these graphene filters could potentially be valuable for harvesting sea salt. We already have giant sea salt plants, where basically ocean water is left to dry out so we can take the salt out; between humans taking sea salt and leaving the water, and taking water and leaving the salt, I don't think there's any net effect on the oceans. And these graphene filters could make sea salt harvesting potentially more efficient.
Re:Holes? (Score:5, Informative)
Oh please. For one thing, we already have desalination plants in some places dumping brine back into the sea; obviously it's not a big problem. There's a lot of water in the oceans.
(trying really hard to not be snipe-y or sarcastic here) :)
Actually, dealing with the by-products of plants operations, which are not limited to the 'brine', are a big problem. Older plants create deadzones. Newer plants do better at defusing the saline concentrations, but that's still only one consideration. Check out the Wikipedia page on Desalination to actually learn something.
http://en.wikipedia.org/wiki/Desalination
Also, if you want to convert desalination outflow to usable table salt you have to clean it first. Economically undesirable in most cases. (But not all)
Desalination, as a solution to fresh water needs, is expenSive, complicated and (generally) damaging. It is a "big problem". However, societies generally overlook big problems when they find a way to get things that they want (more). See: fracking.
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Also, if you want to convert desalination outflow to usable table salt you have to clean it first. Economically undesirable in most cases. (But not all)
Why would that be? There's already lots of places where ocean water is evaporated into sea salt, to be used for human consumption. Why not just use desalination outflow for that and kill two birds with one stone?
Desalination, as a solution to fresh water needs, is expenSive, complicated and (generally) damaging. It is a "big problem". However, societies ge
Re:Holes? (Score:4, Interesting)
In that case it is easy. The solution to this pollution is dilution.
I find it so funny how Slashdot seems to be a bastion of anti-tech these days. Many of the issues "Flamable drinking water" actually seem to predate actual fracking. Any contamination of drinking water must be taking place on the down pipe and not the actual fracking zone since natural gas is found below the water table and not above. So the big problem seems to be simple pipe failure which is something that can be fixed. Of course the EPA should regulate the ingredients of the fracking fluid but over all the fear factor on Slashdot is very disappointing. Frankly it almost seems as if coal companies are paying people off for this.
Re:Holes? (Score:5, Insightful)
the highly concentrated brine from these graphene filters could potentially be valuable for harvesting sea salt.
The concentrated brine could also be useful for generating electricity. Demand for desalinated water is highest in warm, arid regions with plenty of sunshine. So here is what you do:
1. Pump seawater through the graphene filter to separate it into fresh water and brine.
2. Move the brine into evaporation ponds, to concentrate it even further.
3. Generate electricity using the electric potential between the brine and regular seawater
4. Use some of the electricity to power step #1, sell the rest.
5. Profit!
Basically, this is a cheap way to collect solar energy (the sunshine falling on the evaporation ponds) while generating fresh water in the process.
Re:Holes? (Score:5, Interesting)
Actually, as with most situations where humans dump heaps of something somewhere without worrying about the consequences too much, the buildup of salt in the ocean potentially can have significant harmful effects on sea life.
This is a major issue near where I live at the moment - we have no water (driest state in the driest continent on Earth) so we are keen on desalination, but the planned desal plant may kill a unique local form of giant cuttlefish because we are going to pump heaps of salt into a gulf that doesn't flush out quickly:
http://www.abc.net.au/news/2007-04-16/cuttlefish-at-risk-from-desalination-plant/2243198 [abc.net.au]
I guess it'd like fish deciding that pumping a few percent of extra CO into the local atmosphere won't be a problem for us because the atmosphere is so big. At a certain point you don't want to be too near the outlet.
Why stop at salt? (Score:5, Interesting)
Re:Why stop at salt? (Score:5, Interesting)
Re:Why stop at salt? (Score:5, Insightful)
Water Molecule: 275 pico-meters
Ecoli Bacteria: 0.6 micro-meters (109,000x larger)
Rhinovirus: 30 nm (110x larger)
Re:Why stop at salt? (Score:5, Funny)
Water Molecule: 275 pico-meters
Ecoli Bacteria: 0.6 micro-meters (109,000x larger)
Rhinovirus: 30 nm (110x larger)
Rhinoceros: 4m (14,545,454,500x larger)
Re:Why stop at salt? (Score:5, Interesting)
The standard of living in the 3rd world would go up dramatically with free access to clean water.
There's a trend towards decreasing access to freshwater in many developed parts of the world as well. Much of the southern United States will be uninhabitable within our lifetimes if they do not secure another source of fresh water. I do not think just the '3rd world' has this problem. We will all be '3rd world' if the trend continues. And then no world... because almost all life on land depends on it.
Re:Why stop at salt? (Score:5, Interesting)
Much of the southern United States will be uninhabitable within our lifetimes if they do not secure another source of fresh water
yet if you mention this to people who live there they go absolutely bonkers denial on you. I guess I'm not speaking about the small minority who will profit from doing the math.
Re:Why stop at salt? (Score:5, Informative)
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The trick seems to be timing. At this point, real estate in Dallas being bought with a 30-year mortgage ought to have water cost factored into the price. AFAICT, it doesn't yet. Maybe 10 years out it will, but that's not usually how property is financed.
I dunno, maybe they'll build an 80' pipeline from the Great Lakes. Probably cheaper than the collective depreciation on all the property in Texas, but
Re:Why stop at salt? (Score:5, Interesting)
Nonsense. Less than 1/4th of all fresh water goes to domestic use. First, other southern states will start adopting some of California's water conservation methods, like low-flow fixtures (toilets, shower-heads, large-drip sprinklers, leech lines), and then it'll escalate to cutting off of ornamental fountains, and disappearing lawns. In the longer-term, grey water systems will be put in-place, and municipalities will be more inclined to supplement groundwater with recycled (sewer) water.
That's just mind-numbing... This is just a method to make desalination CHEAPER. And desalination is just one method of water filtration and reprocessing. My $10/mo water bill going up, even drastically, will have practically no effect on me, while it will make gathering other water sources, and more aggressive processing methods become economical for municipalities... It's good old supply and demand.
Some people pay more per-gallon for water than they do for gasoline, thanks to "bottled water", so we can obviously afford a higher price here in the first-world.
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With pores barely wide enough to allow water molecules through, we're already talking about submicron level filtration.
Again, best practices dictate your filtration membrane is not your only pathogenic barrier. If you had a compromised immune system, and any pathogen in the water could make you exceptionally sick, if not outright kill you, wouldn't you want more than just one step in place? I worked in water filtration for several years. The quality of the feed water would determine which system was best, but even in the best of systems, nothing is 100% (not even ultra-pure, water for injection systems; even then, there's
Re:Why stop at salt? (Score:5, Interesting)
Re:Why stop at salt? (Score:4, Insightful)
Not 'less'. 'fewer'.
Re:Why stop at salt? (Score:5, Interesting)
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i RTFA and this is a membrane replacement only not a complete filtering system. they say the membrane will work much faster than existing membranes becuse most molecules will bounce away. and to be precise the hole size is "This complete salt exclusion was achieved at 23.1 Å2 for hydrogenated pores and 16.3 Å2 for hydroxylated pores."
they don't know how long the membranes last (become damaged by bacteria or molecular wear) none of which is known since this was a computer model not real hardware.
It is a RO membrane, just a really good one (Score:5, Informative)
Basically, the regular atomic structure of graphene means that you can create holes of any size, for example the size of a single molecule of water. Using this process scientist can desalinate saltwater 1,000 times faster than the Reverse Osmosis technique.
It is a RO membrane, just a really good one? They've described exactly how a RO membrane works. Of course this may have more "holes per sq inch" or whatever, maybe even 1000 times as many.
Re:It is a RO membrane, just a really good one (Score:5, Insightful)
This is only a guess by RO filters have two things that take power. They require a high pressure differential across the membrane which makes for expensive pumps, piping and electric bills. Also they have a lot of bypass water which wastes energy by making you bring it up to pressure and then just dump it out.
If this membrane requires less pressure and less bypass it will significantly reduce both the capital costs and operating costs of such a system.
Re:It is a RO membrane, just a really good one (Score:5, Informative)
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From phys.org [phys.org]:
In contrast to RO, which uses high pressure to slowly push water molecules (but not salt ions) through a porous membrane, nanoporous materials work under lower pressures and provide well-defined channels that can filter salt water at a faster rate than RO membranes.
However, this is the first time that scientists have explored the potential role of nanoporous graphene as a filter for water desalination. Single-layer graphene, which is just one carbon atom thick, is the ultimate thin membrane, making it advantageous for water desalination since water flux across a membrane scales inversely with the membrane’s thickness.
[...]
The scientists explain that there are two main challenges facing the use of nanoporous graphene for desalination purposes. One is achieving a narrow pore size distribution, although rapid experimental progress in synthesizing highly ordered porous graphene suggests that this may soon be feasible. The other challenge is mechanical stability under applied pressure, which could be achieved using a thin-film support layer such as that used in RO materials.
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Forget about how long it takes, what's the ENERGY (Score:5, Insightful)
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-------
All notions of cause and effect are merely assertions of faith in statistics.
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Ok, that almost summarizes it.
The only thing missing is that the article implies that nobody have actualy created it. But there aren't enough details to be certain of that. I'd say, "they found, or somebody found, or there are people looking for it, or they think people could look for it".
Re:Forget about how long it takes, what's the ENER (Score:5, Insightful)
Figure 8 on Page 6 of the actual paper [mit.edu] shows what they're measuring. They're comparing filter materials by Salt rejection % vs Water permeability measured in L/cm2/day/MPa. That unit incorporates all the energy-efficeny goodness you want in a filter without looking at what pump technology is actually used to provide the energy input. It says that more filtered water (L) per square centimeter of filter (/cm2) per day (/day) per MegaPascal of pressure (/MPa, the energy input) is more good. Assuming any particular pump technology would give you a number for MPa/MJ that you could apply, but it doesn't help you understadn the performance of the filter itself. The figure for improvement vs existing technology they actually give is 2-3 orders of magnitude (100-1000x) so TFS is taking the optimistic side.
The bottom line is that this has a huge potential but is still a ways from practical application.
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But if this works, it would be nice to have:
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If they've found a way to desalinate water with much less energy, practically, that's huge.
TFA isn't wholly explicit but it actually talks about "efficiency" rather than "faster" as per the submission:
According to researchers at MIT, graphene could also increase the efficicency of desalination by two or three orders of magnitude [...] while you can remove the salt from the water, the current methods of doing so are laborious and expensive. Graphene stands to change all that by essentially serving as the world’s most awesomely efficient filter. If you can increase the efficiency of desalination by two or three orders of magnitude (that is to say, make it 100 to 1,000 times more efficient) desalination suddenly becomes way more attractive as a way to obtain drinking water.
Though following TFA's source link to Water Online [wateronline.com] we come back to "2-3 orders of magnitude faster" and then reference to energy and cost:
In a new study, two materials scientists from MIT have shown in simulations that nanoporous graphene can filter salt from water at a rate that is 2-3 orders of magnitude faster than today’s best commercial desalination technology, reverse osmosis (RO). The researchers predict that graphene’s superior water permeability could lead to desalination techniques that require less energy and use smaller modules than RO technology, at a cost that will depend on future improvements in graphene fabrication methods.
To me that implies subby read that source article, which is a rather better article, leading me to suspect "anonymous reader" subby is from http://www.geekosystem.com/ [geekosystem.com] It does kind of bug me a little when websites find someone else's story, don't contribute anythi
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If others have found a way to abundance of energy, we won't need graphene to desalinate water.
You'd still want both. If you need a given volume of water, you either need a process that's 1000x faster or 1000x the infrastructure. Infrastructure isn't cheap, no matter how much energy you have.
That wouldn't be huge, that would be disruptive.
Perhaps you've noticed the power structure doing less than the minimum it can excuse as valid in this area?
1 - 3 July at College of William & Mary; International Low
Wow! They'd have enough salt to last forever. (Score:4, Funny)
God I loved "Top Secret"
Filtering abilities of graphene membranes (Score:5, Funny)
Just what we need, clean drinking water (Score:2)
This sounds like it could be revolutionary - lack of fresh or clean water is one of the world's biggest problems. I'm assuming pathogens are larger than a molecule of water? Wonder what the cost would be, if it would be cheap enough to just churn out sheets of the stuff, or custom-made filters. The biggest problems aside from production would be clogging/cleaning and accidental contamination of the output stream.
The real link (Score:5, Informative)
The TFA is just a BS article that says nothing.
A better link (and is in the TFA) is Nanoporous Graphene Could Outperform Best Commercial Water Desalination Techniques [wateronline.com]
However that references Nanoporous graphene could outperform best commercial water desalination techniques [phys.org]
Now we finally we get to the actual link Water Desalination across Nanoporous Graphene [acs.org] (which unfortunately you need to have the right credentials to see - which I don't)
How come I can follow those links and the TFS can't?
Re:The real link (Score:5, Informative)
Here's the real article (AFAIK) from The Grossman Group @ MIT, no need for credentials.
Water Desalination across Nanoporous Graphene (Warning PDF Link): http://zeppola.mit.edu/pubs/nl3012853.pdf [mit.edu]
The main site for the Grossman Group is also pretty fascinating: http://zeppola.mit.edu/ [mit.edu]
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You must work for the Department of Redundancy Department, surely?
Don't call me Surely
Um, no. (Score:2)
What they're talking about is reverse osmosis, and there's no way to make it two or three orders of magnitude more efficient. Commercial systems already hit 30% to 60% of the thermodynamic limit for energy efficiency; all graphene offers in this case is a way to increase the speed, decrease the filter size, or reduce the unnecessarily wasted energy. There's sti
Re:Um, no. (Score:4, Informative)
Practical RO systems operate with a pressure drop (and therefore energy consumption per unit volume) that's double or triple the osmotic pressure, in order to achieve useful flow rates across thick membranes with relatively low pore densities. A better filter would allow that excess pressure to be reduced, but can't do anything about the cost of reducing the entropy.
trifecta (Score:5, Funny)
Once we figure out how to make nanobots out of stem cells and graphene, every problem known to humanity will be solved!
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Once we figure out how to make nanobots out of stem cells and graphene, every problem known to humanity will be solved!
What about the as-of-yet unsolved problem of "Where shall we have lunch?"
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Once we figure out how to make nanobots out of stem cells and graphene, every problem known to humanity will be solved!
What about the as-of-yet unsolved problem of "Where shall we have lunch?"
I think you're looking for http://www.wherethefuckshouldigotoeat.com/ [wherethefu...otoeat.com]
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Only if it improved battery life by 10x...
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Only if it improved battery life by 10x...
That would only be possible if it is done in the cloud.
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Incredibly precise sieve? (Score:2)
Of courswe they wouldn't (Score:2, Informative)
These people who didn't discover the Internet till this century...kindly remove yourself from my area of cultivated graminoids.
Other materials (Score:2)
The original paper (Score:5, Informative)
Here's a link to the original paper on Grossman's website. [mit.edu]
Re:The original paper (Score:4, Informative)
Uhmm....I sense a problem with scale. (Score:5, Interesting)
Water molecule size, roughly 0.340 nm
Salt molecule size, roughly 0.500 nm
Graphene molecule size, roughly 0.142 nm
Difference in size between water and salt molecule, roughly 0.160 nm
The difference in size between water and salt is just barely more than the size of a single graphene molecule, so that leaves absolutely *NO* margin for error when designing the graphene sheet with those holes.
This might very well have already been proven to really work... but I expect it would be extremely cost ineffective at larger scales owing to the consistent and extremely accurate precision that would be needed when trying to do this at a macroscopic scale.
Re:Uhmm....I sense a problem with scale. (Score:5, Informative)
Graphene: (Score:4, Funny)
Science reporting (Score:3)
Yeah [discovermagazine.com].
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But they would bury it in chocolate. Delicious, smooth, yummy chocolate.
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Re: (Score:3)
My $30 refrigerator water filter includes a 'block of carbon'. It even says so on the carton, though I sawed one open to see, and yes, a block of carbon.
Anyways, that's still too porous to be very effective compared to RO or the new RO, Graphene.
And virtually NO public water system in the U.S. relys exclusively on gravity. My birthplace pumped water up to on of two standpipes, which then used gravity to supply us water under pressure, but the pumps were needed. Even New York City pumpsm despite their supp
Re:Could you boost durability by stacking several? (Score:5, Informative)
Desalinating is a little more complicated than this. Currently, there are three (fairly simple) methods of desalinating water: reverse osmosis, steam (or vapor compression) distillation, and de-ionization. RO is usually the preferred method, because a commercial RO unit can purify a high volume of sea water at around 70-90% efficiency.
Steam or vapor compression distillation requires a lot of energy, leaves a massive amount of residue, and depending on mineral concentrations of the feed water, requires constant cleaning to prevent the equipment breaking down.
De-ionization requires no energy, but depending on the type of DI resins used, can quickly exhaust the filter bed, requiring regeneration, which again, doesn't require a lot of energy, but it does have a chemical cost to strip and regenerate the Cation/Anion resins.
Regardless of which method of desalination is being used, the feed water should be filtered to remove sediment and volatile organics (or post-filtration, in the case of DI).
The graphene method is essentially creating a thin film membrane like RO. If you jump past the original article, and go to Water Online, the method proposed would be actually be using a thin film scaffolding to support the nano layer of graphene. At that point, you might as well use RO, unless the actual production models (the graphene method proposed is still highly theoretical as the authors admit that consistently producing graphene with a uniform pore diameter is not practical yet) would allow greater pure water production at higher efficiencies than currently available with RO.
If you want to make ultra-pure water (say USP water-for-injection grade) you need to use a combination of all the above. What results you want will determine the method or number of steps required.
Re: (Score:2)
You are the secon one I see here claimming that we can't dump salt on the ocean. WTF? Of course we can dump salt on the ocean. What do you think we'll do with the fresh water after we use it? Those things cancel each other.
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Sell it as sea salt.