New type of Battery takes salt out of Seawater

February 11, 2012 12:14 PM

Nanoscale electrodes separate salt from seawater. It uses special electrodes: ... "It first draws ions from seawater into a pair of electrodes. As the researchers pass current through the electrodes, electrochemical reactions drive chloride ions into a silver electrode and sodium ions to an electrode made from manganese oxide nanorods. Next, the researchers remove the desalinated water and release the trapped ions into a separate stream of waste seawater by reversing the direction of the electrical current." And at this point the salt in the water is only reduced by about 50%.
posted by aleph (29 comments total)

Since "peak water" is is a serious issue, his sounds promising. Of course, they need to figure out:

1. If it works at a usable scale
2. They can make the water drinkable without doing like 6 passes through the cell
3. It can be combined with systems to remove other impurities/pollutants
posted by GenjiandProust at 12:26 PM on February 11

See also.
posted by RoseyD at 12:26 PM on February 11

The last paragraph of the article notes that this a long ways from real use:

John H. Lienhard, of the Massachusetts Institute of Technology, applauds the work but cautions, “There’s still some way to go before this technique could be deployed for large-scale seawater processes.” He says the researchers need to find ways to remove sulfates from seawater, lower the cost of the electrodes, and protect the system from deposits of biofilm and scale that could cripple the device.

Those are some pretty major concerns.
posted by maryr at 12:34 PM on February 11 [4 favorites]

A baby step in the right direction is still a step in the right direction
posted by Renoroc at 12:46 PM on February 11 [4 favorites]

Also, if we as a species ever turn to desalination as a major source of our fresh water (at anything like current consumption levels) I imagine that the environmental effects of dumping all that brine (high-salt water that is left over and which nobody wants, at least not in great quantity) in the ocean would be quite devastating.
posted by Scientist at 12:48 PM on February 11 [3 favorites]

It seams like this would take A LOT more energy per unit of water then this other guys solution. Osmosis can be used in a controlled way to produce clean water much mor effiecently.
posted by KeSetAffinityThread at 12:56 PM on February 11 [2 favorites]

dumping all that brine (high-salt water that is left over and which nobody wants, at least not in great quantity)

Considering that people do rely on salt water evaporation for their salt needs, there might not be as much dumping as you think (if they need water, they also need salt), but, yeah, this is an issue. Getting a handle on population remains pretty critical. Weirdly, raising standards of living seems to reduce birthrates, so maybe we could work on that, too.
posted by GenjiandProust at 12:59 PM on February 11 [1 favorite]

I imagine that the environmental effects of dumping all that brine

would be negligible. It's the ocean. And there's plenty of fresh (rain and river) water being dumped in it every day to counteract adding salt to it.
posted by Critical_Beatdown at 1:10 PM on February 11 [1 favorite]

And there's plenty of fresh (rain and river) water being dumped in it every day to counteract adding salt to it.

Chances are, if you're using this system, your desalinated water will end up right back in the ocean when you're done with it.
posted by Pruitt-Igoe at 1:31 PM on February 11 [4 favorites]

Also, if we as a species ever turn to desalination as a major source of our fresh water (at anything like current consumption levels) I imagine that the environmental effects of dumping all that brine (high-salt water that is left over and which nobody wants, at least not in great quantity) in the ocean would be quite devastating.

Actually this is already true, the vicinity of the brine dump pipes in the Persian gulf are dead zones. Of course, the ocean as a whole isn't a problem.
posted by atrazine at 1:52 PM on February 11 [1 favorite]

would be negligible. It's the ocean.

OK, I don't know anything at all about marine ecosystems, but I imagine that raising the salinity in a local area even a little could cause some effect on the plants and animals nearby, with potentially significant effects, if a desalinization plant was running in the area. I would be OK with being proven wrong, and I assume research has been done on this, but since small changes in chemistry can have pretty large effects, I wouldn't want to be too blase about it....
posted by GenjiandProust at 1:55 PM on February 11 [1 favorite]

Using "Salt domes" for petrochemical storage is already a thing that happens. Cleaning out a salt dome to make room the the oil creates a large amount of waste brine, that then gets dumped in surrounding waters. It s devastating to life, to say the least. And a really stupid thing to be doing with fresh water, in my opinion.

The gulf of mexico is 35ppt salt. These brines are 70ppt and up.
posted by eustatic at 2:13 PM on February 11

"Can you imagine what this will mean for the starving nations of the earth?"

"They'll have enough salt to last forever!"

I'll... just let myself out.
posted by BrashTech at 2:15 PM on February 11 [5 favorites]

Sounds neat. How does the energy use compare with, say, nuclear and nuclear-scale power facilities currently used to drive desalinization plants? How much energy goes into making the electrodes? Is this approach something that can one day scale up industrially while using less energy than current technology, or is it intended for localized, point-of-delivery service?
posted by Blazecock Pileon at 2:21 PM on February 11

as maryr quoted:

the researchers need to find ways to remove sulfates from seawater, lower the cost of the electrodes, and protect the system from deposits of biofilm and scale that could cripple the device.

My ideal solution combines wastewater treatment with desalinification in a microbial fuel cell.

Using those geobacteria to reduce the sulfate might protect the device, but I'm not sure if sulfur should be excluded entirely. A lot of water treatment methods are vulnerable to biofouling, but I think that biotechnology is reaching the point where customized biofilms could be engineered to improve a process. I would assume most of the device cost is in the manganese nanorods, but this paper says that graphite might be useful for sodium adsorption.
As for the leftover salt, it could be useful for heat transfer in a solar thermal plant, or perhaps you could concentrate the halogens into disinfectant for contaminated fresh water.

Hopefully a real chemical engineer will explain why I'm wrong.
posted by MisplaceDisgrace at 2:30 PM on February 11

First Scientist: but how will we separate the desalinated water and dispose of the runoff?

Second Scientist: Hmmm....I've got it! What if we REVERSE THE POLARITY!"
posted by ShutterBun at 3:05 PM on February 11

I wonder why people don't use solar concentrating for desalination. Seems like it would work really well. You only need heat, not electricity - so electrical efficiency wouldn't be an issue. And you don't need to run at night.
posted by delmoi at 3:06 PM on February 11 [2 favorites]

would be negligible. It's the ocean.

You should do some reading about current desalination environmental issues. Obviously, the ocean as a whole is not effected, but at a local level, the release of high quantities of brine is devastating to small coastal environs.
posted by smoke at 3:07 PM on February 11

A Fresnel lens based solar still may be a better solution.
posted by aeschenkarnos at 4:01 PM on February 11

If you're going to desalinate seawater, this strikes me as a pretty good way to go about it.
posted by flabdablet at 4:38 PM on February 11

If we're so worried about peak water, why do we keep shitting and pissing and pouring toxins in it?
posted by Twang at 5:11 PM on February 11

The second law of thermodynamics. Any other questions?
posted by Kid Charlemagne at 5:36 PM on February 11

If we're so worried about peak water, why do we keep shitting and pissing and pouring toxins in it?

If you can figure out a non-megadeath way to stop people from shitting and pissing, I'd love to hear about it.
posted by lumpenprole at 7:12 PM on February 11

Maybe they can pull enough uranium out of the sea water to fuel the nuclear power plant that will be necessary to scale this up.
posted by Crotalus at 7:32 PM on February 11

50% salt removal is a good start for growing salt-tolerant crops. One benefit would be to combat global warming.
posted by Brian B. at 8:42 PM on February 11

"Osmosis can be used in a controlled way to produce clean water much mor effiecently."

That engineered osmosis sounds really interesting! If it works it could be used to clean up any kind of polluted water, as well as desalination.
posted by Kevin Street at 12:14 AM on February 12

Doctor Flamond: A year ago, I was close to perfecting the first magnetic desalinization process so revolutionary, it was capable of removing the salt from over 500 million gallons of seawater a day. Do you realize what that could mean to the starving nations of the earth?

Nick Rivers: Wow! They'd have enough salt to last forever!
posted by Sutekh at 2:23 AM on February 12

Just watched the osmosis video KeSetAffinityThread linked and it is indeed seriously cool. This is actual osmosis, not reverse osmosis; instead of applying hydrostatic pressure to overcome osmotic pressure, this system loads up the output side of an osmotic cell with salts at a higher concentration than that present in the feedstock to draw water through by normal (not reverse) osmosis. The salts used are those produced when ammonia and carbon dioxide meet after being dissolved in water (ammonium carbonate, others) and it takes much less energy to make these dissociate back into the original gases and come out of solution, leaving clean water behind, than it does to run a capacity-equivalent RO or ME desalinator.
posted by flabdablet at 1:13 AM on February 14

John H. Lienhard, of the Massachusetts Institute of Technology...

So not the John H. Lienhard from the University of Houston? And they are both mechanical engineers? That seems like a bit of a coincidence. Must be father and son.
posted by DU at 8:49 AM on February 17