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

http://www.utexas.edu/news/2013/06/27/chemists-work-to-desalt-the-ocean-for-drinking-water-one-nanoliter-at-a-time/

by Claudus • 13 years ago

113 60 13 years ago

utexas.edu

hernan604• 13 years ago

does the ocean still clean these days ?

very nice job, expect to see it available soon

voltagex_• 13 years ago

I suspect you got downvoted because English isn't your first language.

Something like: "Is the water from the ocean clean enough to drink? Hope to see this product available to buy soon" might be better

cmsmith2• 13 years ago

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?

ars5• 13 years ago

Do you think they clean your local city water? They don't. They filter it a bit, then add chlorine to deal with biologicals, and that's it.

monochromatic• 13 years ago

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

solox32• 13 years ago

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.

sbierwagen7• 13 years ago

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?

cmsmith2• 13 years ago

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?

bdcs• 13 years ago

I have come back from the land beyond the paywall: Importantly, this device operates with an energy efficiency of 25 mW h L−1 (25±5 % salt rejection, 50 % recovery), which is near the theoretical minimum amount of energy required for this process (ca. 17 mW h L−1).

For that last number, the authors cite ref [1], which does an entropic analysis of unmixing solutions and looks at the minimum (reversible) work required therefore.

[1] Y. A. Cengel, Y. Cerci, B. Wood, Proc. ASME Adv. Energy Syst. Div. 1999, 39, 537–543;

bcks• 13 years ago

The page is returning a database error for me, but the Google cache shows a blog entry describing and linking to the low-power desalination technique announced here: http://www.utexas.edu/news/2013/06/27/chemists-work-to-desal...

andymcsherry• 13 years ago

Yeah, I'd recommend that link. It's slight more technical and written in a neutral voice. The original link feels like more of an excuse for a rant against the IMF.

ParahSailin• 13 years ago

http://libgen.org/scimag5/10.1002/anie.201302577.pdf

zw123456• 13 years ago

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

stephengillie2• 13 years ago

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 operates on 3.3v and was intended to cost $4.30 for the entire development kit. http://www.ti.com/msp430

dangrossman• 13 years ago

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.

ars5• 13 years ago

The absolute minimum energy you need is 2.2kJ per liter. A 4x4 inch solar cell could do that in about 2 hours.

However I suspect that you'll never actually desalinate water for that amount of energy in a portable system.

The very best commercial systems manage to do it with about 3 times the energy of the minimum. More common ones are about 10 times the minimum.

sbierwagen7• 13 years ago

  The absolute minimum energy you need is 2.2kJ per liter.

Where's that number from? For what process?

fernly• 13 years ago

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...

sbierwagen7• 13 years ago

It's already being commercialized: http://www.okeanostech.com/

efsavage2• 13 years ago

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).

djloche• 13 years ago

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

XorNot• 13 years ago

Still doesn't sell massive war - shortages are political in regions where people generally have nothing.

Wars - technological ones of the type major powers would fight - are expensive. Far more expensive then any amount of desalinization we would need to build.

sbierwagen7• 13 years ago

  The process doesn't even have to be super efficient

Economics are important. We didn't go back to the moon because it was too expensive, and we're not going to see massive-scale desalination because it's also too expensive: http://physics.ucsd.edu/do-the-math/2012/10/the-energy-water...

  California uses 46 billion gallons of water per day. 
  Supplying 25% of this via desalination would require 36 GW of 
  thermal-equivalent power. California runs on 30 GW of 
  electricity, and a total energy budget of 262 GW (thermal; 
  from oil, gas, coal, hydro, nuclear, etc.—according to the 
  EIA). That’s a substantial amount for 25% of our water needs.

A "ten dollar glass of water" isn't even the big issue. Agriculture requires water, and expensive water means expensive food. Expensive food means people die, mostly from bullet wounds inflicted by people who are hungry. (I hardly need to provide citations for the number of wars resulting from food shortages)

efsavage2• 13 years ago

A very informative article, thanks for linking.

However, his estimates for the energy required were very conservative, and even if these numbers don't work out with today's water prices, they do make sense at a certain point that is likely lower than one encouraging violence. That effectively provide a cap where we start to go this route if necessary, and the vast supply means that we shouldn't go above that for very long.

adventured• 13 years ago

These types of x-y-z is impossible due to cost assumptions have always been made throughout modern history, and they often end up being wrong. You're judging everything based on today's technology. When in fact technology tends to leap forward massively at times due to necessity, and it's rarely foreseen. The same leaps will happen again and again and again.

gabemart• 13 years ago

Agricultural requires water. But much of the "requirement" is a product of the ready supply and low cost of that water. If fresh water prices rise, the more water-intensive agricultural crops are grown less and become more expensive.

I wonder what the water-used-to-calories-produced ratio is for something like lettuce compared to something like corn or beans. I imagine it's a good number of orders or magnitude higher.

In other words, an increase in the price of fresh water does not necessarily significantly increase the price of feeding yourself, it significantly increases the price of water-intensive crops and likely increases the demand for less water intensive crops.

haldujai2• 13 years ago

Original paper: doi: 10.1002/anie.201302577

From their paper it is mentioned they have a 40 nanolitre/min flow rate (25% desalination rate, 99% is considered safe to drink water).

They use an electric pole to generate an ion depletion zone, their problem right now lies in the severely limited flow rate and desalination rate. From my understanding the 25% desalination rate does not compound linearly and decreases in efficiency as the concentration of salt ions decreases.

Additionally their flow rate is 0.4 microlitres per minute, this would equate to needing 625 000 channels for one pass only to get 250mL / min. Scaling for microfluidics isn't simply using a larger pipe size, microfluidic devices largely operate with minimal forces and a Reynolds number of 1, that doesn't hold as you get larger.

The other big problem here is that this requires pressure driven flow, to do that they made two reservoirs of uneven height on opposite ends to drive flow. Again this is very electrically cheap (picowatts) when dealing with such small and perfect flow conditions.

The biggest problems they need to address are the low filtration rate and the low flow rate, it does not seem like there is a simple answer to the first, they do state that they are conducting a larger scale experiment that they will publish later.

I largely suspect that the larger scale experiment will fail in efficiency as another group (doi:10.1038/nnano.2010.34) who also uses a ion depletion zone (albeit by a different mechanism) found after publishing that they were orders of magnitude (10^3) too low in their predictions.

If anything this will perhaps be better than small, portable RO setups but not replace large factories which are actually pretty efficient.

rflrob• 13 years ago

Additionally their flow rate is 0.4 microlitres per minute, this would equate to needing 625 000 channels for one pass only to get 250mL / min. Scaling for microfluidics isn't simply using a larger pipe size, microfluidic devices largely operate with minimal forces and a Reynolds number of 1, that doesn't hold as you get larger.

What about parallelization? Are there any obvious downsides to simply having lots of the active units, aside from the (what seems to me largely manageable) increase in micro fluidic chip complexity?

sbierwagen7• 13 years ago

Using 625 000 channels is parallelization. Those channels are in parallel.

haldujai2• 13 years ago

Yes, parallelization is actually the currently accepted means of increasing throughput, you'll see diagnostic devices with thousands of channels. The reason it isn't appropriate here is because of the complexity, the design is easy, you make a radial pattern of inlets with the splits towards the middle so you can combine outlets of the same type. Construction is relatively easy as well.

The problem comes from the number of inlets. You can:

a) a common inlet to all of your channels, or b) independent inlet for each channel, or for several channels

a) might seem intuitive, the problem is limitations on channel width, the inlet would have to feed a single channel which would then split (they would split to the inlet channel from the paper), structural limitations of PDMS and manufacturing have maximum widths and heights in millimetres at best. Which would not be enough to achieve the throughput required. The original 'master' inlet would probably have to be at least in the 10-20 cm range to achieve flow rates that could make this a household filter.

Even with another, stronger material, and perhaps manufacturing techniques I'm not aware of you still have limitations of pressure, their channels are very small in the paper (for a reason), pressure becomes a limiting factor to prevent their failure.

The problem with b is sheer complexity, you're talking about 10 000 tubes and connectors and holes punched into a chip if you even do a 1 - 60 split. The chip with just the channels would be about the size of a tissue box, this wouldn't be able to accomodate the channels so now you're talking about something tens of metres x tens of metres. This is hugely cost prohibitive and the channels from connectors would have to be really long, really long channels need more pressure to drive the liquid requiring more energy which reduces the efficiency significantly.

The reason parallelizaton works in pharmaceutical / DNA testing applications is you're going from microlitres of DNA/samples to nano, or picolitres in the channels, a single inlet can sufficiently provide that throughput (you're talking 10 uL / hour perfusion rates)

Edit: TL;DR version: Construction constraints would make this have worse efficiency than reverse osmosis and cost a lot more to manufacture as well.

jyf1987• 13 years ago

its not only make ocean water drinkable, but also make ocean be livable, especially those tropic oceans, they would build solar powered water tower and soilless vegetable/food factories, war might break out between some countries for the ocean

Ellipsis753• 13 years ago

"The new method requires so little energy that it can run on a store-bought battery."

What a silly measurement. I can buy a laptop battery or a car battery at a store. Also it does not give any idea of how much water could be produced from the battery. A teaspoon per battery probably isn't too great. (Although at the moment they get only nanoliters of salty water from it of course).

Luyt• 13 years ago

A similar silly unit is used to measure 'green' energy: "This windmill can power 10.000 households". As if we're too stupid to understand a kWh figure.

aroch• 13 years ago

It's nothing to do with being smart or stupid, 10K homes is a more descriptive number (more easily visualized) than kWh for describing energy production to the general populace.

kunil• 13 years ago

"consumes less energy and is dramatically simpler than conventional techniques."

I remember a video that shows some kind of filter (it looked like a plastic sheet). They were simply pushing water against it and you get clean water from salty water.

I don't think it gets easier than that. However if I remember correctly the filter gets unusable after a while

ars5• 13 years ago

You need energy to "push" the water through the membrane. A LOT of energy.

It's called reverse osmosis if you want to look it up.

pipboy3• 13 years ago

water chip? I need to buy lot of them before World War III starts. I got a feeling I'm gona need one in the vault.

usablebytes• 13 years ago

Why do we usually utilize science to fix the wrong problem?

Shouldn't we be making more efforts on 1) Growing more trees 2) Reducing environmental pollution 3) Controlling human population

???

backprojection• 13 years ago

Because the earth isn't designed to take care of us. If we had stayed a small pre-industrial society, we would still eventually die of something - there are myriad ways species go extinct.

The only way to ensure long-term survival is to develop science and technology quickly enough to solve problems (both natural and artificial) as they come up.

This includes solving problems created by past generations, who necessarily did not have access to the knowledge needed to avoid creating those problems in the first place.

It's certainly not guaranteed that we will do so fast enough.

ajuc2• 13 years ago

There's more than 8 000 000 000 of us, if everybody were just doing the thing with the greatest priority it would be very ineffective division of work. Like digging one hole with 1000 people.

As a humanity we can (and should) multitask, especially when it comes to science and inventions, because you never know which seemingly pointless path can lead you to a great breakthrough.

Imagine everybody since antiquity worked only on the greatest humanity problems as they've seen it at the time. No useless stuff like music, so no irrational numbers for example :)

BillyMaize• 13 years ago

The population of the world is slightly under 7 billion.

andrewflnr• 13 years ago

There is actually a pretty decent amount of work going into better building materials and alternatives to wood-pulp paper. The science involved in growing trees is pretty well established. Since there were trees, in fact. :) Getting more trees is a social problem.

brownbat• 13 years ago

"The new method requires so little energy that it can run on a store-bought battery."

We currently have techniques that require no additional power (just using the sun), but almost every desal operation uses a powered method.

Power consumption isn't the only factor here. A low power technique that has throughput per area equivalent to solar stills is just worse than all available alternatives.

If you made a device that turns the briny sludge byproduct into fuel or some other consumable, that would be amazing.

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

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