
UK researchers create graphene-based sieve that can remove salt from seawater - theklub
http://www.bbc.com/news/science-environment-39482342
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matt4077
Back at university I dreamt of creating bacteria to do desalination, powered
by the sun. All the necessary components exist–in fact, a seemingly endless
number of genes code for channels and transports that selectively target the
charged ions (Na^2+, Cl- mostly, but also Potassium and Magnesium). It's
partially the legacy of life having arisen in saltwater, and many biological
processes are controlled with ion concentration gradients. Signal transmission
along a nerve? -> Ions. Want to get all this water out of here? -> Transport
the salt across the membrane, and the water follows voluntarily.

~~~
pluteoid
This is interesting to think about. As I'm sure you've considered, bacteria
and other living cells exist in a state of highly regulated homeostasis. In
bacteria, things like charged ion concentrations are maintained internally by
various physiological mechanisms (chiefly the membrane-bound transport
channels you describe) at specific concentrations with little variation.
Salinity concentrations are generally the same as the surrounding seawater
(marine bacteria are usually osmoconformers, as opposed to more sophisticated
osmoregulators like fish), and the transport mechanisms exist as adaptations
to maintain this state.

So while some aquatic bacteria can exist at a wide range of external salt
concentrations (they are "euryhaline"), I don't know of any bacteria that have
adaptated to actively concentrate salt internally above the salinity of
typical seawater. Beyond a certain not-very-useful threshold, this would
disrupt too many metabolic pathways and kill the bacterium. So I don't see how
a concentrate-in-the-bacteria-then-filter-them-out approach to industrial
desalination would work.

You might be thinking about brine pool extremophile bacteria / archaea, but
again, they are just well-adapted when it comes to expelling salt or resisting
salt intake, not actively concentrating it internally.

However, if you could embed euryhaline bacteria into some kind of impermeable
membrane in a controlled orientation, and engineer them to express the right
kind of one-way channels on opposite sides of the cell... there are some big
bioengineering obstacles to doing this, but it's an interesting idea. It would
basically be a sped-up version of the double reverse osmosis desalination
approach already widely used, potentially more efficient and available to be
powered more easily by sustainable / free energy sources.

I'm just typing as I think there, so maybe there's been work in this area
already.

------
JoeAltmaier
The layering approach has much potential. In this case, graphene oxide layered
with epoxy resin stabilizes the membrane and lets them control pore size.

The next step, problems with contaminants (seawater) fouling the membrane,
might be mitigated with more layers? Say a Teflon layer to aid in cleaning. Or
an ionized layer to repel many particulates.

I wish they'd said more about how they control pore size. How does the epoxy
layer avoid covering the pores? Is it laid down before pores are etched or
something? Fascinating subject.

~~~
Cogito
The paper is quite short and very readable (especially if you are just
skimming and can skim over some of the details/jargon) but here [0] is a
diagram (from the paper) that perhaps will help you understand what is going
on.

[0] [http://imgur.com/a/LNWUz](http://imgur.com/a/LNWUz)

[edit]

To summarise, they prepared graphene oxide laminates using vacuum filtration,
and then stored them at different relative humidities by changing the salt
concentration of the storage liquid. The different relative humidities cause
different layer spacing, which they measure with X-ray diffraction, and choose
whichever layer spacing they want before adding the epoxy.

The relevant quote from the paper:

 _Thick (≈100 µm) GO laminates were prepared by vacuum filtration of aqueous
GO solutions, as reported previously. The laminates were cut into rectangular
strips (4 mm × 10 mm) and stored for one to two weeks at different relative
humidities (RH), achieved using saturated salt solutions. The resulting
interlayer spacing was measured by X-ray diffraction as shown in Fig. 1e and
varied from ≈ 6.4 to 9.8 Å with RH changing from zero to 100%. GO laminates
soaked in liquid water showed d ≈ 13.7 ± 0.3 Å. All these values agree with
previous reports, where the changes in d were attributed to successive
incorporation of water molecules into various sites between GO sheets.
Individual GO strips with desirable d were then encapsulated and stacked
together using Stycast epoxy as shown in Figs. 1b,c to increase the available
cross-section for filtration to 1 mm (see Methods and supplementary Fig. S1).
The stacked GO laminates, now embedded in the epoxy (Fig. 1c), are referred to
as physically confined GO (PCGO) membranes because the epoxy mechanically
restricts the laminate’s swelling upon exposure to RH or liquid water
(Methods). The stacks were glued into a slot made in either metal or plastic
plate (Fig. 1b). Two sides of these stacked PCGO membranes were then trimmed
off to make sure that all the nanochannels are open (Fig. 1d) before carrying
out permeation experiments, in which ions and water molecules permeates along
the lamination direction as shown in Fig. 1a._

------
mmaunder
Reverse osmosis has been around for a long time and is used on boats
everywhere for desalination. This sounds like a new membrane that requires
less pressure and thus energy? I guess sieve sounded better?

~~~
dreamcompiler
RO membranes are notoriously finicky and non-robust. They require a lot of
maintenance and can be ruined by common chemicals like chlorine. A more robust
desalination membrane would be a very good thing.

~~~
ghaff
When I was involved in RO in the early eighties, that was exactly the issue.
In the context of offshore drilling rigs, we just couldn't get the adherence
to protocol around flushing and filtering that the units needed to work over a
reasonable lifetime.

We eventually gave up and went with an Alfa-Laval heat exchanger based
approach.

~~~
weaksauce
Why wasn't the flushing automated?

edit: I have worked on many RO systems and we always did auto flushing and I
am not sure I ever saw anything other than that. It was pharma though.

~~~
Gibbon1
Likely the issue is, with a large RO plant you hire people for the specific
domain knowledge and develop a work culture around it. For a place like an oil
rig none of this specific domain knowledge is central to the work at hand. So
the technology isn't reliable in that context.

~~~
ghaff
Exactly. It was a small scale system and the rig mechanic or whoever was
supposed to do it as one of their 100 or so responsibilities so it often
wasn't done. It was also pretty much a V1 system so it was just very
sensitive.

To set some context that people here might appreciate, there wasn't a single
computer or data link to offshore drilling rigs at that time. We were just
starting to play with radio modem links.

------
BrendanD
Seeing as we are unable or unwilling to deal with the present micro and nano-
particles resulting from decades of plastic use and disposal, I worry about
the environmental effects of graphene.

~~~
Neliquat
Abspestos 2.0

Funny enough, its not actually banned in the USA, just a liability nightmare.
I ocasionally still see brake pads with the stuff. I suspect graphine, and
other 'nano' materials will be similar in practice.

~~~
BrendanD
That would be _malpractice_.

------
M_Grey
I swear I've heard about this before... is this one of those stories that
emerges about a technology that never seems to enter the market? That "super
slick" coating for condiment container interiors is another that springs to
mind.

~~~
jessriedel
Desalinization is already with about a factor of 2 or 3 of the thermodynamic
optimum, so improvements can't be revolutionary. Desalinization mostly needs
cheap clean energy.

~~~
throwaway91111
Also, waste is a major problem, environmentally.

~~~
jessriedel
Are you talking about the brine? This is trivial if you just put a pipe a few
hundred yards out to sea. The concentration is diluted extremely quickly. (The
only exception is if your desalination plant is _below_ sea level because then
you have to pump the brine up hill, which costs some energy.)

~~~
dredmorbius
I've seen the assumption that the brine dissipates quickly challenged.

Fluids can remain subbornly un-mixed, over large distances and for long times.
Given that brine is heavier than seawater, it will almost certainly tend to
sink and flow along bathymetric contours, perhaps pooling in local low spots.
And sealife can be exceedingly sensitive to changes in temperature, ion
density, salt content, etc.

This reminds me of a book in which an ecologist described a discussion with a
chemist over the concentration of some pollutant in seawater. Roughly,
"Assuming a well-mixed solution..." starts the chemist. "How are you planning
to stir the oceans?" asks the ecologist....

~~~
jessriedel
I've seen data on this and dilution was extremely fast, as expected.

------
desireco42
This is all fine, but if it isn't inert and if it 'leaks' graphene, it can be
super toxic as well. I don't want to pu-pu it, but it is legitimate concern.

~~~
adrianratnapala
I didn't know that graphene was toxic. I should stop licking my pencils.

And from what little chemistry I know, I though graphene oxide was rather
inert.

~~~
krastanov
The naive (very hand-wavy) explanation for the toxicity of graphene (nanotubes
to be specific, not sheets in general) is not chemistry, rather the nanotubes
physically rupturing cell organelles. Same with asbestos: small rigid
particles that cut everything else in pieces.

------
35bge57dtjku
What stops this from getting clogged?

~~~
Neliquat
Standard filters catch most particulate matter, this is able to remove
dissolved impurities afterward.

------
dijit
I hope this isn't Science being taken to a irrational extreme, as tends to
happen with news and science.

This has incredible potential not only for the developing world but also for
sea travel and even the fact that we are running out of drinkable water in the
west.

Only 2.5% of the water on the planet is even potentially drinkable. If we were
able to convert even 1%. Crazy.

~~~
ghaff
Note that reverse osmosis desalination through membranes already exists as the
article notes. (Not sure what the current state of the art is as I haven't
worked in this area for a long time.) The question in whether this has
advantages to the desalination systems used today.

~~~
SEJeff
Generally speaking, the Aussies and Israelis have some of the top of the line
Reverse Osmosis Purification Tech. I saw a ROPU (reverse osmosis purification
unit) truck from the Army Corps of engineers when I was active duty US Army
and that thing was unreal. You could ingest raw sewage into that thing and out
would come drinkable, albeit not wonderful tasting, clean drinking water.

~~~
callalex
That only works when you have the luxury of burning massive quantities of oil
on the taxpayers' dime.

------
sp332
Is there a reason this wouldn't be subject to the same physics that requires a
lot of energy to desalinate water by other means? Thermodynamics puts a limit
on how efficiently you can reduce entropy like that.

~~~
Nomentatus
I wouldn't say "a lot" in economic terms: "The theoretical absolute minimum
amount of energy required by natural osmosis to desalinate average seawater is
approximately 1 kilowatt-hour per cubic meter (kwh/m3) of water produced, or
3.8 kilowatt-hours per thousand gallons (kwh/kgal)."
[https://www.amtaorg.com/wp-
content/uploads/7_MembraneDesalin...](https://www.amtaorg.com/wp-
content/uploads/7_MembraneDesalinationPowerUsagePutInPerspective.pdf)

------
mrcactu5
we have experienced droughts in Puerto Rico. this could likely lower our water
prices as well.

[http://www.noticel.com/noticia/177413/la-sequia-es-para-
larg...](http://www.noticel.com/noticia/177413/la-sequia-es-para-largo-asi-lo-
predice-la-historia.html)

~~~
sirpros
As many drought hot spots around the Globe. I hope this gets the traction it
really deserves

------
Xophmeister
This is somewhat OT, but I've noticed a trend -- although I can't say how
recent -- of headlines of the form "British [X] do [Amazing Thing]",
particularly (but not necessarily) from the BBC. I note that the HN headline
has been changed to "UK researchers" (IIRC, it said "British Scientists"
earlier) and this BBC article doesn't actually use this phrase in their
headline, but it appears prominently in the tagline.

This may be because I'm restricted to English language articles, but I don't
see, for example, "Spanish researchers do [Amazing Thing]". Even in English, I
don't regularly see "US/Australian/NZ/Canadian/South African/etc. [X] do
[Amazing Thing]"; even though I'm sure plenty of amazing things have been done
by these folks.

I understand that the popular press is directed towards the masses, but is the
nationality/allegiance of [X] really so important? More so than their
discovery/invention/whatever? I'm British and, in a time when populist
nationalism is causing all kinds of problems, I'm not sure this rhetoric is
helpful. Just be proud of the achievement.

How about just: "[Amazing Thing]"?

Or, if you want to associate it with people, to make it more personal and less
"stark" (perhaps to sell it better): "Humanity achieves [Amazing Thing]".

~~~
fooballs99
> in a time when populist nationalism is causing all kinds of problems

(I realize this forum will be almost overwhelmingly in favor of the above
statement, but thought I would respond anyway to give an alternative viewpoint
from outside).

What problems? Is it really causing problems, or is it just that you are
politically opposed to it? The _lack_ of nationalism I would say has caused
far more problems over the last few decades (Mass clashing of cultures, rise
of terrorism, global multi-nationals exploiting workers, not paying taxes etc,
moving democracy and accountability further and further away from people).

If a family member achieved something you would naturally feel more "proud"
than if it was a person in the world picked at random.

For some people, their nationality is important to them - an extended family
of shared identity, culture, experiences and values. I would much much rather
use a local taxi company, which will benefit my local community, friends,
family, than use some faceless global thing like Uber, which will benefit some
rich people in another country.

Further, competition is good. It's the way we achieve things. If a team of
scientists in [other_country] see this news, they will likely be spurred on.

This is why things like the space race worked so well.

~~~
chillydawg
Well it's causing the UK to leave the EU which is a disaster by any measure,
not including idiots wanting "control".

~~~
fooballs99
> Well it's causing the UK to leave the EU which is a disaster by any measure,
> not including idiots wanting "control".

So you're just politically opposed to it.

It's not a disaster if you're very much opposed to an EU superstate.

~~~
ppod
This is just a slippery slope fallacy. There was clear opposition to an EU
superstate in many countries, there's no way the UK ever would have ended up
in one. If anything, this makes a (smaller) EU superstate more likely.

