
A way to make water potable using carbon dioxide - spatulan
http://www.economist.com/news/science-and-technology/21722159-lets-hear-it-diffusiophoresis-way-make-water-potable-using-carbon-dioxide
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jessaustin
Cited paper:

[https://www.nature.com/articles/ncomms15181](https://www.nature.com/articles/ncomms15181)

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doorley
Sounds like a promising piece of technology. What I'm more impressed with,
though, is the scientific journalism.

It's balanced, accurate, accessible, representative, and leaves out the
hyperbole. I would pay for science journalism that read like this. Even better
if it came with some biased, inflammatory, hyperbolic editorials on the side.

~~~
PhantomGremlin
_What I 'm more impressed with, though, is the scientific journalism._

Actually I was disappointed with the article.

The image at top shows two output streams: waste, and filtered water. I was
expecting an explanation of this while reading the article. But as I read the
words, the build-up wasn't matching the image.

Finally we come to: _In a working system it would simply be a question of
splitting the water stream into three as it left the processor, with the two
outer branches being recycled and the inner one tapped and piped to
consumers._

So, no, pretty sloppy.

~~~
microcolonel
The sentence before the one you mention explains it; the only problem with the
top diagram in the header image is that it doesn't make it clear that opposite
the CO₂ side of the stream, there is an air side. Seems like the diagram
represents their experimental model (two exit streams), not the practical
application (three exit streams).

> As the team hoped, this arrangement caused suspended particles with positive
> surface charges to concentrate towards the CO₂ side of the water stream, and
> those with negative surface charges to concentrate towards the air side,
> leaving the centre of the stream more or less particle-free.

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mchannon
Is this a breakthrough? Sure. But it's probably not a panacea.

* Getting actual salt particles out of flows of water is not what their experiment accomplished. They got larger particulates out of the water. The latter is quite easy to do, and the former quite difficult.

* Ionic charge is a very powerful driving force when what you're trying to move has a directionality to it, like a magnet picking up iron filings. This would work great for largely insoluble things like bacteria and mineral particles.

* When salts are dissolved, their constituent parts form ionic dipoles that will work far harder to stay together in solution. A little bit of ionic charge bias presents no challenge to a sodium chloride pair.

* CO2 use in this experiment may be close to zero. After CO2 is injected, it can be recovered and reused (at least in part). Finding a use for the petagrams of CO2 we're dumping in the air is a worthwhile goal but no matter how successful this technology may end up, it won't make a dent.

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amelius
> When salts are dissolved, their constituent parts form ionic dipoles that
> will work far harder to stay together in solution. A little bit of ionic
> charge bias presents no challenge to a sodium chloride pair.

An electric field of a few volts over a small channel seems to split this
dipole just fine, [1].

[1] [https://cleantechnica.com/2013/06/30/desalination-with-
small...](https://cleantechnica.com/2013/06/30/desalination-with-small-
electrical-fields-simple-new-method-may-revolutionize-seawater-desalination/)

~~~
xyzzyz
_As of now, the best that the researchers have achieved is 25% desalination_

25% is quite far from "just fine". Has there been any progress on the method
in last 4 years?

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amelius
Repeat the process 10 times, and you're at 95% desalination.

~~~
xyzzyz
It may or may not work, depending on the details of the process. For instance,
the process might only be able to separate the ions if the concentration is
high enough. If it's the case, repeating the process on the result will not
make any difference.

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zackmorris
Maybe this could be combined with electric field desalination to make seawater
potable:

[https://cleantechnica.com/2013/06/30/desalination-with-
small...](https://cleantechnica.com/2013/06/30/desalination-with-small-
electrical-fields-simple-new-method-may-revolutionize-seawater-desalination/)

[http://news.mit.edu/2015/shockwave-process-desalination-
wate...](http://news.mit.edu/2015/shockwave-process-desalination-water-1112)

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ChuckMcM
Nice, other than the necessity of dumping CO2 into the air. I wonder if he
tried creating an electric field across the water as some folks have done for
desalination[1]. Any pollutant with a net positive or negative charge would be
suitably diverted in that way.

[1] [https://cleantechnica.com/2013/06/30/desalination-with-
small...](https://cleantechnica.com/2013/06/30/desalination-with-small-
electrical-fields-simple-new-method-may-revolutionize-seawater-desalination/)

~~~
mhb
_As to the necessary CO2, he imagines this would come from power stations and
other industrial processes, such as cement-making, that produce the gas in
large quantities as exhaust. This would restrict diffusiophoretic water plants
to industrial cities—but, since such cities are huge sources of demand, that
is hardly a problem._

~~~
ChuckMcM
I read that, but noted it suffers from 'scientist' blindness. These industrial
processes, that are producing CO2 in large quantities, don't have an
economical way to capture and cleanse that CO2 to allow for then shipping and
selling it (or giving it) to this guy to clean water with it.

If they could capture the CO2 they could already resell it economically as
there are lots of uses for it. There was some work in 2012 in Canada on that
[1] but it hasn't gone well (here we are 5 years later and there aren't any
products yet). There has been work on recapturing the CO2 in _new_ plants, but
that doesn't help our 'industrial cities' that are sitting on a bunch of
existing infrastructure they cannot afford to refresh given they haven't fully
depreciated the existing infrastructure.

[1] [https://www.scientificamerican.com/article/can-co2-be-
captur...](https://www.scientificamerican.com/article/can-co2-be-captured-and-
sold/)

~~~
ams6110
What is the current process for producing "pure" CO2 gas for sale e.g. as dry
ice, or for use in food/beverage or for other industrial purposes? Unlike e.g.
nitrogen or oxygen, concentrating it out of the atmosphere would seem to be
inefficient as it's only roughly 0.04%.

~~~
URSpider94
It's typically captured either from processes that make ammonia or hydrogen
from methane (with CO2 being the only major byproduct), or by capturing the
output from large-scale fermentation.

Source:
[http://www.uigi.com/carbondioxide.html](http://www.uigi.com/carbondioxide.html)

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haneefmubarak
> he imagines [the necessary CO2] would come from power stations and other
> industrial processes, such as cement-making, that produce the gas in large
> quantities as exhaust.

IANAC, but it seems like that just exchanges one problem for another. I
imagine that most, if not all, of the industrial processes that produce CO2
exhaust gases also result in other gases and particles getting into the
exhaust stream, meaning that you'd have to refine/filter the exhaust from
those processes to get just the CO2.

~~~
allannienhuis
I doubt they're suggesting they use the untreated flue gases as the gas in the
apparatus. I think they're just pointing out that there are industrial sources
of co2, n and that finding a use for the co2 helps with another
pollution/waste issue

~~~
clort
I don't think that this helps really with the pollution issue, since the CO2
is in effect being used as a catalyst and will be emitted afterwards just as
it was before. What the article is saying though, is that a large consumer of
cement (a high CO2 producing process) is also likely to be a large consumer of
clean water.. so that leaves the process of cleaning the water CO2 neutral
except for the small amount of power consumed

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askvictor
Sunlight (specifically, UV radiation) does a pretty good job of killing
pathogens:
[http://www.sodis.ch/methode/index_EN](http://www.sodis.ch/methode/index_EN) .
Though it doesn't remove any non-biological contaminants; this one might be
better at that.

But if it needs an industrial process to do this anyway, is this one
significantly cheaper/easier than what's used in the developed world?

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koolba
This is cool, particularly in the simplicity of the approach. Reminds me of
how a septic tank works but at a much finer scale with the CO2 augmenting
gravity.

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mmjaa
Seems like a highly elegant solution .. one wonders if this could be used to
make better air-breathing rockets ..

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macawfish
This is really cool in its simplicity and sustainability. People get obsessed
with complex tech (e.g. high energy fusion). Sometimes I think that the
ultimate limits of high tech look low tech to the unappreciative.

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wanda
_Potent_ potables?

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sintaxi
You can make virtually any water source potable by boiling it. It so happens
hot water has other useful purposes as well so why are we not showing those
1.8B people how to efficiently boil water? What am I not getting?

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orthecreedence
I did not know you could boil lead out of water.

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sintaxi
1.8B people drink untreated water with feces in it.

