Battery Turns Saltwater Into Drinking Water

An anonymous reader writes "German researchers have developed a battery that can remove sodium and chloride ions from seawater. In theory, their invention could be far more energy efficient than thermal desalination or reverse osmosis. This would cut the cost of using salt water for drinking or irrigation. It could also be used to make compact desalination systems for boats and life rafts, or crops. Each battery is made with manganese oxide nanorod electrodes, which absorb sodium when an electrical current passes through them. When the current is reversed, they dump the sodium ions out into waste water."

Comments

How much energy?

[CapOblivious2010]

Interesting, but how much energy does it take to run this thing? (they call it a 'battery', but I don't think it actually generates electricity). Many of the places that are short on fresh water are also short on electricity (especially "green" energy), so this may not be as helpful as it sounds.

Re:How much energy?

[Smallpond]

They call it a battery because it is a series of electrical cells. The term "battery" means the series arrangement; it comes from a military term for a series of guns. Generating electricity is the best-known use of an electrical battery, but isn't the definition.

Re:How much energy?

[mrmeval]

It's "an electrochemical cell that can desalinate seawater".

You can thank Aaron Rowe for calling it a battery. I'm sure he plays with his food with his feet.

Re:How much energy?

[errandum]

What I'd really want to know is if it is more efficient to use a solar panel to charge the battery to then separate the salt or simply to use the sun to desalinate the water using the tradition process.

Re:How much energy?

[jonadab]

Batteries don't generate energy. They store it, chemically. (Well, the ones we usually think of as "batteries" work chemically.)

Nonetheless, I don't know how they propose to be more energy efficient than a mirror-based distillation rig. Besides keeping the parabola aimed at the sun, which requires negligible energy, the main costs of running such a rig are keeping it supplied with water to distill and flushing it out with solvent once in a while to prevent salt buildup. (You can even use filtered seawater for the solvent.) The latter costs seem unavoidable for electrical-cell-based desalination, and the former is, as I said, negligible.

Of course, it only works in parts of the world that get a lot of sunshine, so for example it would be a non-starter in northern Ohio. (Not that we need desalination in Ohio. Most of our water management issues involve finding ways to get the water to drain away more efficiently so it doesn't flood our basements; that seems likely to be common in places that don't get enough sunshine to boil water with a parabolic mirror... but I suppose there could be exceptions.)

Re:How much energy?

[tqk]

Interesting, but how much energy does it take to run this thing? (they call it a 'battery', but I don't think it actually generates electricity).

Re-read TFA. They came up with this desalination gizmo by reversing another gizmo that does create electrical energy.

I think this's brilliant thinking. They didn't just read the paper. They read it, understood its implications, and extrapolated them in the opposite direction. That's what I expect from scientists. I wish I saw that kind of thinking more often.

As for this gizmo, I'd like to see it built as a group of looping boxes, progressively yielding purer product as it goes through them in sequence. Add other boxes in the chain to filter out other stuff that this gizmo doesn't filter, and you end up with an office water-cooler machine that produces pure water and recyclable sludge. I'd definitely buy one!

Re:How much energy?

[Jack Malmostoso]

Interesting, but how much energy does it take to run this thing?

From the abstract: "Here, we demonstrate an energy consumption of 0.29 Wh lâ"1 for the removal of 25% salt using this novel desalination battery, which is promising when compared to reverse osmosis ( 0.2 Wh lâ"1), the most efficient technique presently available."

Re:How much energy?

[brusewitz]

Of course, it only works in parts of the world that get a lot of sunshine, so for example it would be a non-starter in northern Ohio.

I think the fact that Ohio is not near any source of saltwater would be the real non-starter.

Re:How much energy?

[couchslug]

As with " battery hens", few readers will know what "battery" means in that context.

Cannon artillery analogies are as obsolete as ballista analogies.

Re:How much energy?

[TheLink]

RO water is much purer though. However efficient it gets I doubt this method will remove the other crap from the water, including crap...

Isn't this similar to electrodeionization?

Re:How much energy?

[mosb1000]

Isn't this similar to electrode ionization?

Yes, though the closest analogue is probably electrodialysis reversal. The difference is that no existing technology has been able to economically remove salt in concentrations as high as seawater (though they have been used for brackish water).

Re:How much energy?

[waimate]

Very pure water is bad for you, as it leeches good minerals out of your cells (reverse reverse osmosis, if I'm not mistaken aka osmosis). If your desalination does too good a job, you have to "cut" that water with impure water.

Re:How much energy?

[MagusSlurpy]

Actually, the authors call it a battery in their paper. And it is.

Here's the salient part of the paper:

In this work, we demonstrate a novel electrochemical cell named a “mixing entropy battery”, which extracts energy from the difference in concentration of two solutions and stores it as chemical energy inside the electrode material’s bulk crystal structure. This approach allows us to overcome the challenges of supercapacitor electrodes based on activated carbon. This device consists of a reversible electrochemical system where the salts in the electrolyte are the reactants and the electrode stores ions. We employed two different electrodes: an anionic electrode, which interacts with Cl ions selectively; and a cationic electrode, which interacts with Na+ ions selectively. These electrodes are initially submerged in a low ionic strength solution (river water) in their discharged states, when the electrode materials contain the respective ions incorporated in their structures. In this dilute solution, the battery is charged by removing the Na+ and Cl ions from the respective electrodes (Figure 1a, step 1). Successively, the dilute electrolyte is exchanged for a concentrated solution (seawater), which is accompanied by an increase in the potential difference between the electrodes (Figure 1a, step 2). At this higher potential difference, the battery is discharged, as the anions and cations are reincorporated into their respective electrodes (Figure 1a, step 3). The concentrated solution is then removed and substituted by the dilute electrolyte (river water), which results in a decrease in potential difference between the electrodes (Figure 1a, step 4). We note that the exchange of solution could also be carried out via a flow process, which could be attractive for large scale energy extraction.

Re:How much energy?

[TheLink]

Any scientific study to back that up? e.g. proof that total amount of "good minerals" excreted in urine per day is more when you drink pure water. AFAIK if I drink RO water, I pee more often, but the pee is clearer in colour and if I'm losing more sodium that's a plus not a minus - since I'm a sedentary person who probably consumes more sodium than the RDA, and I'm not an athlete.

Passing pure water through plumbing is a bad idea since it would dissolve all sorts of bad stuff (some places still have lead pipes so they need "hard water") and then you'd drink it... And drinking pure water without taking enough salts and minerals in your diet would cause problems. But that doesn't prove it's bad for you. That's like saying fruits are bad for you because you're not getting enough calcium from them.

And I've had RO and distilled water that wasn't actually pure - some had the taste of acetone, some had some other weird acrid taste. So if the study is not done correctly with actually pure water you might be poisoning the animal/human with the impurities. The problems might not be the pure water.

You want enough minerals, eat more sardines with bones for calcium and a potato/banana for potassium.

Re:How much energy?

[demonlapin]

No, no, no. No. What comes out of you is a function of your kidneys. Drinking distilled water as your only source of water is absolutely harmless. There are limits, of course, to how much your kidneys can concentrate or dilute your urine, but unless you are trying to kill yourself with water intoxication or have a disease, you'll be fine. You do need a certain electrolyte intake, but it's actually quite small. People who have electrolyte disturbances almost always have them because they have no kidney function, or they're taking drugs that alter kidney function, or they're intentionally taking electrolytes, or they're unable to feed themselves and are dehydrated.

Re:How much energy?

[Adriax]

Seriously?
We already do utilize the water that falls from the sky, you know those river things that run into the ocean and most communities were built around?

Water is finite, even that magic skywater. Upstream communities cannot take all the water they want, as downstream communities rely on the same water source. Desalinization technologies not only allow coastal communities to grow where there isn't a major river, but also frees up water for greater upstream use.

Re:How much energy?

[tqk]

Actually, the whole understanding the implications and building something based on [it] isn't science, it's engineering. Science investigated phenomena; Engineering makes use of those phenomena.

Engineering is a superset which includes science. Engineering isn't engineering without the scientific component.

Is the LHC science or engineering, or both? NASA? :-)

Re:How much energy?

[Anonymous Coward]

A report reviewing some of the research as of 1980: Health Risks from Drinking Demineralised Water.

Low-mineral water markedly: 1.) increased diuresis (almost by 20%, on average), body water volume, and serum sodium concentrations, 2.) decreased serum potassium concentration, and 3.) increased the elimination of sodium, potassium, chloride, calcium and magnesium ions from the body.

Re:How much energy?

[FunkDup]

the dude said generate electricity, not energy

Re:How much energy?

[Anonymous Coward]

Sounds like a prima facie case of A Salt and Battery...

Re:How much energy?

[blackicye]

Interesting, but how much energy does it take to run this thing?

From the abstract: "Here, we demonstrate an energy consumption of 0.29 Wh lâ"1 for the removal of 25% salt using this novel desalination battery, which is promising when compared to reverse osmosis ( 0.2 Wh lâ"1), the most efficient technique presently available."

My first impression was that this is was largely just an academic project / exercise, there are other way more interesting applications for these nanorods. 15 times the energy to remove only 25% of the salt? geez, I guess it works, but not to make potable water in any quantity.

Reverse osmosis is already deployed at a comparatively low cost, and scales very well, I don't see this or anything else displacing that as a desalination process any time in the near (or even somewhat further) future.

Almost there!

[cashman73]

The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%.”

Not sure what math they're using when 50% removal of ions is considered "de-salinated". I guess they're getting there, so by publishing this article, maybe they'll be able to snag some venture capital?

Re:Almost there!

[captain_sweatpants]

Indeed. The 'Saltwater to drinking water" headline is a bit misleading, but saltwater to partially desalinated water just doesn't have quite the same ring to it...

Re:Almost there!

[timeOday]

I doesn't put a 50% limit:

"We removed up to 50% of the original salt, but we need to arrive at 98%."

Doing several cycles of ion removal with the battery would further desalinate the water, but those extra cycles cost energy, so La Mantia hopes to improve the efficiency enough so that the battery can remove the salt in a single pass.

If they're really the first to implement a new chemical process here, then the GP implying this is not significant in itself and they just published it so they could get venture capital is pretty sad. There used to be this thing called "research." Most of it went nowhere, yet it created the world we live in.

a total bust, not energy efficient at all

[rubycodez]

requires electricity, unlike thermal desalination which can use free (as in beer) energy, and doesn't produce anything useable. was this summary written to attrack potential investors? it most likely will be a waste of time and money....

Re:a total bust, not energy efficient at all

[rubycodez]

solar ones at municipal scale are being built now in australia, india, spain.

Re:a total bust, not energy efficient at all

[TheRaven64]

I remember in the '90s the Innovations catalogue sold inflatable thermal desalination rafts. You inflated them and they floated on the sea concentrating sunlight on the surface like a greenhouse. The water evaporated and then condensed on the inside of the glass and trickled out into the edges. They produced about 2 pints of water per day and were intended to be kept on life rafts (they couldn't operate on them, but they could float beside them and work, as long as there was sunshine). I presume they haven't stopped existing in the last 15 years...

Re:a total bust, not energy efficient at all

[ras]

http://www.landfallnavigation.com/memss.html

Battery?

[Hentes]

Isn't this called electrolysis?

Hmm

[RenHoek]

Of course, (good) reverse osmosis cleans out a LOT more out of the water then just salt, e.g. bacteria, viruses.

Re:Hmm

[perl6geek]

I'm pretty sure there is room for both techniques. For irrigation you don't need the same quality as for drinking.

Re:Hmm

[Colonel Korn]

Of course, (good) reverse osmosis cleans out a LOT more out of the water then just salt, e.g. bacteria, viruses.

Do you have a sense of how dramatically expensive RO is and how much cheaper it would be if 50% of the salt in seawater could be removed in a relatively low cost preliminary separation? Somehow most of the comments on this story, both positive and negative, seem to assume its main use needs to be as a desalinization gadget where you put the saltwater in one side and delicious drinking water comes out the other. That would be amusing but not particularly useful or realistic. The value of a separation technique is going to come in the form of energy and labor savings. If I talked about this tech at work I'd hear comments like, "imagine the RO fouling reduction!"

Re:Hmm

[Anonymous Coward]

It's electrolytes!! That's what plants crave!

Re:Hmm

[MattskEE]

You might be right that the place for this tech is a pre-treatment for an RO process, but it isn't mentioned in the article and the researchers appear to be looking for a gadget "where you put saltwater in one side and delicious drinking water comes out the other":

The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%.”

Doing several cycles of ion removal with the battery would further desalinate the water, but those extra cycles cost energy, so La Mantia hopes to improve the efficiency enough so that the battery can remove the salt in a single pass.

I'd be dubious about the efficiency of doing this electrochemical desalinization to remove so much of the salt, I would think that the resistance of the water is going to rise substantially as salt leaves so it seems like more and more electrical energy will be required per mole of salt ions as the concentration drops.

So by pre-treating water to remove much of the salt before sending it to RO the membranes will last longer before replacement? How much of the operating cost of an RO plant is determined by this? Would there be an impact on the RO process energy consumption?

Re:Hee'uk

[tqk]

Maganese oxide? I thought [Manganese] was used for Galvanizing metal.

Don't you mean zinc?

Re:Life Rafts

[Anonymous Coward]

I think they already have RO filters with hand pumps that would fit that niche.

A long way from being useful

[Animats]

No, you don't put in salt water and get energy and fresh water out. You put in salt water and energy and get somewhat less salty water out.

As with most desalinization systems, getting rid of the salt and other crud is a big problem. They haven't solved that yet. "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." It took a long time (from 1748 to 1965) before reverse osmosis membranes were developed that could handle that problem. Reverse osmosis systems require an occasional freshwater flush, but this takes far less water than the system produces. It's not clear how the numbers work out on this new approach.

Re:P.S. First! (sorry, I couldn't resist!)

[chromas]

Thanks for making me read that entire paragraph in Christopher Lloyd's dramatically hurried voice.

Late arrivals at the desalination party

[WaffleMonster]

Just the other day it was discovered water magically evaporates thru sheets of graphene about as fast as you can pour.

Kind of makes it difficult to see the point of experiments involving basic chemistry with lousy effeciency falling off a cliff as concentration of salt is reduced.