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?

[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?

[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?

[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?

[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.

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?

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

[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: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