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Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

utexas.edu

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Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#11

Post by fernly »

The paper linked from the article is behind a pay wall but the abstract[1] is very brief: "A simple power supply is used to apply a 3.0 V potential bias across a microelectrochemical cell comprising two microchannels spanned by a single bipolar electrode (BPE) to drive chloride oxidation and water electrolysis at the BPE poles. The resulting ion depletion zone and associated electric field gradient direct ions into a branching microchannel, consequently producing desalted water."

[1] http://onlinelibrary.wiley.com/doi/10.1002/anie.201302577/ab...

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#13

Post by dangrossman »

stephengillie wrote: post #7
zw123456 wrote: post #5

It would be great if a Solar cell or small panel could power it. That could be a life saver in emergency situations.

A solar panel can run this. Or, to be more specific, a small (3" x 3") solar panel could charge a 3v battery which could power this device. I have solar-powered holiday lights which operate on 3v, this application would be simply replacing the lights with this chip. I've actually replaced the charging circuit with a TI MSP-430[1], and powered it directly with solar power. [1]a microcontroller similar to Arduino which…

This thing is producing nanoliters per minute with that power. Sure, you can power this device with a small panel, but you'll die of thirst before it makes enough water to fill one glass.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#14

Post by sbierwagen »

solox3 wrote: post #8
monochromatic wrote: post #3

I'd love to see an energy-conservation analysis of this technique. How many joules per liter does it actually require?

40 nL of desalted water per minute, for a minute, using 3.0V voltage (from article) and 0.7 A current (standard AA, "store-bought battery" from article), yields 3.2 GJ/L. Even if we give it the benefit of the doubt and say we're overestimating the current by a factor of 100, 32 MJ/L still a ridiculous amount of energy, and ~10x more than just distilling water through evaporation, which is 2.23 MJ/L.

The actual paper ( http://libgen.org/scimag5/10.1002/anie.201302577.pdf ) says they manage an efficiency of 25 mWhL^-1 (90 joules per litre)

Where did you get that 0.7A number?

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#15

Post by solox3 »

sbierwagen wrote: post #14
solox3 wrote: post #8

Earlier quoted context omitted.

40 nL of desalted water per minute, for a minute, using 3.0V voltage (from article) and 0.7 A current (standard AA, "store-bought battery" from article), yields 3.2 GJ/L. Even if we give it the benefit of the doubt and say we're overestimating the current by a factor of 100, 32 MJ/L still a ridiculous amount of energy, and ~10x more than just distilling water through evaporation, which is 2.23 MJ/L.

The actual paper ( http://libgen.org/scimag5/10.1002/anie.201302577.pdf ) says they manage an efficiency of 25 mWhL^-1 (90 joules per litre) Where did you get that 0.7A number?

0.7A is the current of the "store bought" (AA) battery, suggested by the article.

To make this technology energetically favourable to boiling, it must not exceed ~700μA in current, and it has to be far less than that to be worth its complexity.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#16

Post by sbierwagen »

solox3 wrote: post #15
sbierwagen wrote: post #14

Earlier quoted context omitted.

The actual paper ( http://libgen.org/scimag5/10.1002/anie.201302577.pdf ) says they manage an efficiency of 25 mWhL^-1 (90 joules per litre) Where did you get that 0.7A number?

0.7A is the current of the "store bought" (AA) battery, suggested by the article. To make this technology energetically favourable to boiling, it must not exceed ~700μA in current, and it has to be far less than that to be worth its complexity.

Uh? No battery[1] delivers a constant amount of current: http://en.wikipedia.org/wiki/Ohm%27s_law

Solving for current, Ohm's law is I = V/R. You only deliver .7 amps of current into a 4.285 ohm load.

If you connect a 3 volt battery to a 1,000 ohm resistor, then only 0.003 amps of current will flow, which is 9 milliwatts.

Connect a 3 volt battery to a .01 ohm load (a dead short, almost) and 300 amps of current will flow, (900 watts!) very briefly, until the battery voltage sags under load.

1: Or any voltage source in general, barring some trickery that you can't do with a simple electrochemical battery.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#17

Post by cmsmith »

hernan604 wrote: post #2

does the ocean still clean these days ? very nice job, expect to see it available soon

This is a great question. Distillation has the side effect of removing all of the microbes from water and sanitizing the output, but if this method only removes the salt will the output water be clean enough to drink?

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#18

Post by cmsmith »

solox3 wrote: post #8
monochromatic wrote: post #3

I'd love to see an energy-conservation analysis of this technique. How many joules per liter does it actually require?

40 nL of desalted water per minute, for a minute, using 3.0V voltage (from article) and 0.7 A current (standard AA, "store-bought battery" from article), yields 3.2 GJ/L. Even if we give it the benefit of the doubt and say we're overestimating the current by a factor of 100, 32 MJ/L still a ridiculous amount of energy, and ~10x more than just distilling water through evaporation, which is 2.23 MJ/L.

This seems somewhat hard to believe. If you were actually pumping that much energy into the chip, wouldn't you end up boiling the water anyways?

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#19

Post by efsavage »

I don't put much stock in those who make claims like "the next world war will be over water", because we have a massive supply of water (the ocean) and a massive supply of energy (the sun) to power whatever we need to do to make it drinkable.

A floating desalination plant powered by an x000-acre floating solar platform, pumping clean water back to shore, and dispersing slightly saltier water across a wide area, doesn't seem like science fiction to me, and doesn't seem very destructive. The process doesn't even have to be super efficient, we may even end up using old-school techniques like distillation or electrolysis to keep the mechanisms simple.

(granted this helps coastal regions more than inland ones, but moving population-heavy coastal areas to this system will preserve more of the natural water supplies for the inland needs).

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#20

Post by djloche »

efsavage wrote: post #19

I don't put much stock in those who make claims like "the next world war will be over water", because we have a massive supply of water (the ocean) and a massive supply of energy (the sun) to power whatever we need to do to make it drinkable. A floating desalination plant powered by an x000-acre floating solar platform, pumping clean water back to shore, and dispersing slightly saltier water across a wide area, doesn…

Water shortages are political in nature. The technical and logistical parts have been solved for a while.
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