A way to make water potable using carbon dioxide | Hacker News Reader

A way to make water potable using carbon dioxide

economist.com

181 pointsspatulan38 comments

Cited paper:

https://www.nature.com/articles/ncomms15181

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.

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.

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.

I just checked this after reading the article, and that diagram appears as-is in the original paper, per jesseaustin's link to https://www.nature.com/articles/ncomms15181 . So I'm actually going to have to give the journalist a pass; I hardly expect them to produce more accurate diagrams than what is in the original paper.

Was that supposed to be a joke? If not, you can easily pay for journalism like this by subscribing to the Economist.

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.

Could you just use it on your sewer pipe? That would get us to a sustainable water system pretty fast.

Get off the grid: the sewer grid! Drink filtered shitwater, and top it off each week with a gallon of America's Best brand generic Spring Water Plus Shitwater Conditioner. Choose from Mountain Fresh, Country Home, and six other popular flavors!

(product may contain less than 1% of flourine, Nestlé brand product flavors, and other mind controlling food stuffs)

> 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...

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?

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

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.

Desalinating water is a different problem, with a different solution.

Problem this is looking to solve is cleaning up fresh water that is contaminated, which is in itself a large problem in poorer areas.

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

https://cleantechnica.com/2013/06/30/desalination-with-small...

http://news.mit.edu/2015/shockwave-process-desalination-wate...

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...

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.

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...

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%.

Note that the gases coming out of a power plant are mostly nitrogen

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

True, CO2 capture from power plants and cement kilns is not yet reality.

That said, this process should work (if perhaps less efficiently) with less pure streams, since it should just depend on the partial pressure of CO2. Other gases like oxygen and water vapor should just be spectators in the process.

The fun thing is that burning hydrocarbons also itself produce water too!

> 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.

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

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

You would, but more and more, CO2 is being regulated as a pollutant and there is going to have to be recovery from such waste gasses anyway.

IANACE, but there are good reasons to sequester carbon emissions, and this scrubbing can be achieved with renewables (eg. solar thermal) for processes that involve heating the flue gas. The problem of course is that there isn't really an economic case for industry to do it, because the costs of implementing sequestration are quite capital intensive to polluters.

Sunlight (specifically, UV radiation) does a pretty good job of killing pathogens: 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?

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.

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

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.

Potent potables?

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?

Energy cost.

If you're boiling in some sort of still, sure, that will remove impurities, but those aren't common household items. Boiling a pot over a heat source will only kill bacteria; it won't remove impurities.

I would wager everyone out there knows, either explicitly or implicitly, that boiling water is a great way to clean it. People are looking for something better that can scale to give everyone clean drinking water. Boiling water for the length of time needed to render it safe to drink is terribly energy-inefficient, which is why it's not done in water treatment plants anywhere in the developed world.

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

1.8B people drink untreated water with feces in it.

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