Scientists developing a seawater-desalination chip
Although various alternative technologies are being developed, the large-scale desalination of seawater typically involves forcing it through a membrane that allows the water to pass through, but that traps the salt. These membranes can be costly, they can get fouled, and powerful pumps are required to push the water through. Now, however, scientists from the University of Texas at Austin and Germany’s University of Marburg are taking another approach. They’ve developed a chip that separates salt from water.
The prototype plastic “water chip” contains a microchannel that branches in two, and utilizes a process known as electrochemically mediated seawater desalination.
That process begins with seawater being run into the microchannel, and a 3-volt electrical current being applied. This causes an electrode embedded at the branching point of the channel to neutralize some of the chloride ions in the water, which in turn increases the electrical field at that point in the channel. That area of increased current, called an ion depletion zone, diverts the salt to one branch in the channel while allowing the water to continue down another.
When the electrical current is applied, salt tagged with a fluorescent tracer flows up one branch in the channel (left) – when the current is shut off, the salt flows down both branches
In its present form, the system can run on so little energy that a store-bought battery is all that’s required as a power source. Two challenges still need to be overcome, however.
First of all, the chip currently only removes 25 percent of the salt from the water – 99 percent must be removed in order for seawater to be considered drinkable. Secondly, the system must be scaled up in order to be practical. It presently produces about 40 nanoliters of desalted water per minute. That said, the scientists are confident that with further research, they can rectify both issues.
The system is being developed through spin-off company Okeanos Technologies.
Source: University of Texas at Austin via Treehugger
About the Author
An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.
All articles by Ben Coxworth
Very cool, as an electrical engineer who's about to start work in the water industry this is exciting stuff.
In the mean time it should be noted that there is very little difference in the design of the boiler in a steam cycle power plant and a steam cycle desalination plant.
Perhaps putting several of these in series would get to the 99%. The question would be whether getting 25% is because there is so much salt in solution to remove, or because the process would not get 25% of a more dilute solution.
Bruce H. Anderson
Could this be used in reverse to generate power? Like at the mouth of a river.
Probably not. It uses electricity to push salt from one micro-channel to the other, there does not appear to be an inverse function.
It is Absurdly Simple to desalinate sea water! Just duplicate nature like all the great "Advances" in design and efficiency we have had recently.
You use the Sun.
Pump the sea water through black pipes that have Vacuum tubes sealed around them with this arrangements then has a parabolic mirror channel under it the tubes have one way valves as the salt water will flash boil creating a buzz bomb surging effect and you want to keep it all flowing one direction. Now you need multiple steam beds surging squirting steam so you can bring them together to supply steady pressure to main pipes to power turbines that generate the the plants electrical needs and maybe more for a community.
After the turbines the steam go's to domed cooling chambers chilled with fresh incoming seawater the salt free condensation collects on the dome runs down into channels to be pumped away.
The slurry at the bottom you can pump to drying pools for Food & industrial use or back to the sea.
re; Joseph Mertens
There is a lot more than just salt in the leftover brine. Numerous industrial chemicals including Portland Cement.
Joseph using the sun to evaporate water isn't new, and you make it far to complex and expensive with all your mirrors and vacuum tubes. Large black vessel will get warm enough to produce a vapor pressure that could effectively be condensed. The sun is great for heating water but terrible for producing electricity or in your case desalinating water. There simply is not enough energy to make it useful. There are companies that use the sun to slowly dry out salt water to produce sea salt. then heavy equipment bulldoze the salt. Many companies find that it is far cheaper to simply use electricity or hydrocarbons to evaporate the water in a central area and then process the salt. Most places that need fresh water do not have the money to spend on large complex systems. Additionally large complex plants are not safe from warlords / terrorists. Africa for example is poor and undeveloped because they lack stable governments. For something to be useful it needs to be compact and ideally portable.
@Bruce H. Anderson:
assuming it is as "easy" to remove 25% of the salt every following step as it was in the first one, you would need 16 steps to get 99% of the salt out of the water. But I think it might be more difficult to remove salt out of water with a lower amount of salt in it, meaning: You will not get rid of 25% per step as the percentage might be decreasing.
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