Low energy desalination device

[a_majoor]

A small device which can effectively desalinate water on battery power:

http://news.yahoo.com/s/afp/20100322/sc_afp/sciencenanotechnologywaterun

Device to convert seawater offers hope to parched lands
AFP

PARIS (AFP) – Scientists said on Sunday they had made a nanotech device to strip salt from seawater, paving the way to small-scale or even battery-powered desalination for drought-hit regions and disaster zones.

The tiny prototype is reported on the eve of the UN's World Water Day, which aims to highlight the worsening problems of access to clean water.

Conventional desalination works by forcing water through a membrane to remove molecules of salt.

But this process is an energy-gobbler and the membrane is prone to clogging, which means that de-sal plants are inevitably big, expensive, fixed pieces of kit.

The new gadget has been given a proof-of-principle test by Jongyoon Han and colleagues of the Department of Electrical Engineering and Computer Science at Massachusetts Institute of Technology (MIT).

It works through so-called ion concentration polarisation, which occurs when a current of charged ions is passed through an ion-selective membrane.

The idea is to create a force that moves charged ions and particles in the water away from the membrane.

When the water passes through the system, salt ions -- as well as cells, viruses and micro-organisms -- get pushed to the side. This saltier water is then drawn off, leaving only de-salted water to pass through the main microchannel.

The tiny device had a recovery rate of 50 percent, meaning that half of the water used at the start was desalinated. Ninety-nine percent of the salt in this water was removed.

Energy efficiency was similar to or better than state-of-the-art large-scale desalination plants.

"Rather than competing with larger desalination plants, the methods could be used to make small- or medium-scale systems, with the possibility of battery-powered operation," their paper, published by the journal Nature Nanotechnology, suggests.

In an email to AFP, Han said the experiment entailed a tiny microfluidic chip, just a few millimetres (fraction of an inch) square, that desalted just 10 microlitres per minute.

"The idea toward the real-world application is that we would make many of these devices, thousands or tens of thousands of them, on a plate, and operate them in parallel, in the same way semiconductor manufacturers are building many small electronic chips on a single large wafer," explained Han.

"That would bring the flow rate up to around 100 millilitres (three fluid ounces) per minute level, which is comparable to typical household water purifiers and therefore useful in many applications."

A patent has been filed for the device. However, it may be a matter of years before the invention reaches a commercial scale.

At such early days, the costs of the future system are unknown.

But, said Han, overheads may be significantly reduced because gravity can be used to put the water through the device, as opposed to forced it through by pumps, and there is less of a problem of membrane fouling.

The theme of Monday's World Water Day is "Clean Water for a Healthy World," touching on the growing problem of water contamination in countries grappling with water stress and fast-rising populations.

For our purposes, a portable device like this can reduce the need to carry water, and there is no reason it can't be small enough to be carried by a single soldier as part of his kit (notice most of the attention here is to scale it up, a device the size of a canteen would be a wonderful addition for the soldier/camper etc.)

 

[helpup]

Interesting and I can see the usefullness for the civilian as well as Military.  I wonder, thought how it handles highly contaminated sources.  Such as local rivers/ponds used as sewer systems, does it handle man made pollution such as oil, pesticides, and the like. 
I think I would still prefer a larger water purification plant to ensure water safety.  Especially when deployed overseas.

On a larger scale concept.  What happens to the now concentrated water with a high salt content? If this goes large scale with thoughts of solving water problems and turning the desert green ect.  Would that not cause rising salt content of the oceans or other bodies of water to be higher to the point of being toxic?

 

[a_majoor]

I would imagine the water would have to be pre-treated by going through a strainer and a charcoal filter before being fed into the device (with these tiny micro-channels, dirt would become a real problem) so a portable unit would have a funnel top, removable canister and then the actual device.

Since the article states 50% of the flow comes out as clean water, the residue is not highly concentrated and can probably be poured back into the ocean, lake or stream you dipped the water out of.

On a really large scale, concentrated brine is a source of salt, bromine and minerals, so if you have a jumbo unit for desalinating water for a city, then you also create a secondary industry. If this technique can be adapted for sewage wastewater treatment, then the concentrated organic material can be recycled into fertilizer or biomass for biofuels.

To increase the salt content of the ocean to become toxic, you would have to drain off and desalinate 50% or more of the planet's water.

 

[Nfld Sapper]

Interesting numbers there Thucydides considering our ROWPU in Double Pass operation (which is used for CBRN Operations, and can be used for desalination) we produce +/- 2500 L/Hr and requires a source flow rate of appr 12000 l/Hr which results in only about 21% of the water being recovered. The rest is rejected by the machine as not being able to be processed....

 

[helpup]

If this technique can be adapted for sewage wastewater treatment, then the concentrated organic material can be recycled into fertilizer or biomass for biofuels.

I like that idea actually.  Especially since this has the ability to be a small one it should be easier to scale for municipal and industrial uses for cleaning out waste water and sewage prior to releasing it back into river/ocean

To increase the salt content of the ocean to become toxic, you would have to drain off and desalinate 50% or more of the planet's water.

I am leery of that number as due to currents, density varients and natures ability to crop up problems that people overlook.  If this is used in a large scale operations in a few differant spots I can see it being a short time before problems arose.  Yes you would have the ability to recover minerals and salt.  But if the scale is large enough to say feed California/ Nevada's water needs.  I think you would soon have too much of a by product that can be safely dealt with.  Yes the Oceans are vast but so are peoples consumptions and waste.  People once thought the fisheries would be endless. 

I am not saying it can't or shouldnt be done.  Just that it needs to be well thought out or we are working on creating more problems, while sovling one.  ( Oddly enough I am not a tree hugger nor do I follow the Global warming extremism line either.) 

 

[GAP]

Yes you would have the ability to recover minerals and salt.  But if the scale is large enough to say feed California/ Nevada's water needs.  I think you would soon have too much of a by product that can be safely dealt with.  Yes the Oceans are vast but so are peoples consumptions and waste.

You do realize California already has a number of large desalination plants along the coast? In the past 30 years I have not heard any great uproar about the coast becoming saltier.....but maybe that's because global warming is melting so many glaciers that it's diluting the ocean....

Based on your concerns all the salt removal operations throughout the world...for the salt...would have caused the ocean to become less salty....

 

[a_majoor]

Interesting numbers there Thucydides considering our ROWPU in Double Pass operation (which is used for CBRN Operations, and can be used for desalination) we produce +/- 2500 L/Hr and requires a source flow rate of appr 12000 l/Hr which results in only about 21% of the water being recovered. The rest is rejected by the machine as not being able to be processed....

While I am obviously thinking of a small thing you would attach to a canteen, Camelback or maybe a jerrycan, things like this can scale. Interesting how much more efficient this is compared to a ROWPU, I had no idea the efficiency was only 21%.

 

[Nfld Sapper]

While I am obviously thinking of a small thing you would attach to a canteen, Camelback or maybe a jerrycan, things like this can scale. Interesting how much more efficient this is compared to a ROWPU, I had no idea the efficiency was only 21%.

But you got to remember that the water that comes out the other side of the ROWPU is virtually 100% pure, containing nothing more than essential H20 molecules (or so I have been told..)

 

[Kat Stevens]

In double pass mode, the permeate a ROWPU produces is virtually molecularly (is that a word?) pure water.  Mother nature herself can't make it that pure.  Florida has huge desal units that provide a fair percentage of all the fresh water consumed in the state, and the Gulf of Mexico or the Atlantic Ocean aren't going to turn into pickling brine any time soon.