LLNL develops new faster, lower-cost desalination technique using flow-through electrodes

04 August 2012

Lawrence Livermore National Laboratory researchers have developed a new capacitive desalination technique that could lower the cost of and time required for desalinating seawater or brackish water (e.g., effluent from some industrial processes). A paper on their work is published in the RSC journal Energy & Environmental Science.

 Flow-through electrode capacitive desalination uses a new hierarchical porous carbon material to create a new device geometry in which the feed stream passes directly through the electrodes, resulting in significant improvements to salt removal and desalination rate. Source: LLNL. Click to enlarge.

In conventional capacitive desalination (CD), a voltage is applied between two porous electrodes to adsorb ions onto the electrode surface and thus remove them from the feed stream. Traditionally, due to the small pore sizes of the electrodes, the feed stream flows between the electrodes (flow-between CD) and through a dielectric porous separator.

The new technique—called flow-through electrode capacitive desalination (FTE CD)—uses new porous carbon materials with a hierarchical pore structure which allows the saltwater to flow easily through the electrodes themselves. Flowing through the electrode allows for several significant advantages relative to traditional flow between systems, including:

• faster desalination;
• more salt removed for each charge of the capacitor; and
• more energy efficient desalination.

Our cell demonstrates feed concentration reductions of up to 70 mM NaCl per charge and a mean sorption rate of nearly 1 mg NaCl per g aerogel per min, 4 to 10 times higher than that demonstrated by the typical CD cell architecture. We also show that, as predicted by our model, our cell desalinates the feed at the cell’s RC timescale rather than the significantly longer diffusive timescale characteristic of typical CD cells.

—Suss et al.

FTE CD can be used with a thinner separator as the separator is no longer a flow channel, therefore reducing the overall and electrical resistance of the device, which further decreases costs.

By leveraging innovative porous carbon materials recently developed at LLNL, our new method removes the diffusion limitations afflicting traditional CD cells. The desalination process now only takes as long as it takes to charge the electrodes, on the order of minutes or less. The new method currently removes salt five to 10 times faster than previous CD systems, and can be further optimized for increased speed. It also reduces the concentration of the feed up to three times as much per charge.

—Matthew Suss, first author

Capacitive desalination (CD) has advantages over reverse osmosis (RO), the most common way to remove salt from water. With CD, no membrane components are required; it can operate at low pressures and temperatures; and energy recovery is performed with a solid state circuit, which is more scalable and cheaper than the turbines used for energy recovery in RO. However, previous flow-between CD methods were unable easily to desalinate (in a single-charging step) moderate brackish water and took a longer time to desalinate.

FTE CD is capable of desalinating almost all brackish water concentrations in a single step. In some regions around the world, including North America, brackish water is projected to be the main source of water for desalination processes that provide drinking water. Brackish water also is the concentration range of effluent from some industrial processes, such as coal bed methane production—treating this water is essential for proper practical waste reduction. Further, FTE CD performs much better with high salinity streams than regular CD, and lends itself better to energy efficient multi-stage desalination, which allows us to tackle seawater with this method.

Resources

• Matthew E. Suss, Theodore F. Baumann, William L. Bourcier, Christopher M. Spadaccini, Klint A. Rose, Juan G. Santiago and Michael Stadermann (2012) Capacitive desalination with flow-through electrodes. Energy Environ. Sci. doi: 10.1039/C2EE21498A

I know little about desalination, but
".. 4 to 10 times higher than that demonstrated by the typical CD cell architecture..
The new method currently removes salt five to 10 times faster than previous CD systems, and can be further optimized..
reduces the concentration of the feed up to three times as much per charge." sounds like magic - as it's likely intended to sound.

The possibility of deserts to farms, limitless clean water for humanity.

There should be quarterly followup on this and published status, esp. if not commercialized rapidly.

“energy recovery is performed with a solid state circuit ”

Really! The problem with all of these highly efficient methods is that they are not scalable and very expensive.

Currently we have the ability to produce limitless amounts of power and desalinate limitless of water. However, we only need to produce the amount we need. The reason we do not turn deserts into farms is the productivity of American farmers.

This could be a major step forward for both oil production and carbon sequestration.  Oil is associated with saline water (some stripper wells produce 99% water), and deep saline aquifers are among the prospects for disposal of captured CO2.  The water from the former has to be put somewhere, and the available volume in the latter is limited unless water is removed and put elsewhere.

Desalinating these streams of water may be cheaper than other options, and also supply water and possibly useful minerals from the salts.

"Currently we have the ability to produce limitless amounts of power and desalinate limitless of water. However, we only need to produce the amount we need. The reason we do not turn deserts into farms is the productivity of American farmers."

Kip P, you apparently haven't been anywhere near a Midwest American farm this summer and there ain't no "currently..limitless water."

Any system to desalinate water has to respect the law of conservation of energy.

A 100% efficient system still needs to provide the energy to separate the salt from the water. That is described by the Van't Hoff formula : πV = nRT (related to the ideal gas law)

Shortly, you must apply a pressure over the volume to 'push out' the saltions. This pressure for seawater equals about 28 bar. Therefore, the minimal energy you need to desalinate seawater equals what you would need to pump freshwater from a well of 280 meters deep. (however once you have extracted part of the freshwater, the salinity increases, and the energy you need to extract more will increase)
pumping up 1 litre of water over 280 meters costs about 2800 joule.
Thus a wind turbine of 2.8 MW (that's a small one) can pump 1000 liters of water per second.
A 100% efficient desalinater would do the same.
Let's accept a system with a total efficiency of 50%, this could still produce 500 liters per second, or 43000 tons (43000000 liters) per day.

Kelly I grew up in the Midwest and visited there this summer. There is always someplace that has a flood and someplace that has a drought. We do not build desalination plants for infrequent events.

Furthermore we do not grow grow crops with seawater. As Alain points out it takes energy to pump water. I know of semi-arid places that have limitless supplies of fresh water for irrigation. A for a few miles from the river, there is a wide variety of crops then all you see is dryland wheat.

There is not a shortage of electricity either. It is just a case of supply and demand. Farmers have to pay their power bill and buy diesel fuel to get the crops to the river where they are barged to the world market. The reason deserts are not turned into farm land is food is cheap when not grown in the desert.

Kit P, check food prices and think about the 30,000 who starve to death daily. Only 4 % of humans are in US borders.

"There is not a shortage of electricity either.' doesn't agree with http://www.technologyreview.com/news/428685/outage-in-india-could-be-a-harbinger-for-the-rest/ blackouts.

So Kelly what is the root cause of starvation and power shortages? It is not the ability of engineers to produce power or farmers to grow food.

20 billion US gallons (76,000,000 m³) of treated water are evaporated each year.

http://en.wikipedia.org/wiki/Palo_Verde_Nuclear_Generating_Station

This is one power plant, if we can capture the cooling water from other power plants we might have water to irrigate.

nuclear powerplants are always located near abundant fresh water.
I would be surprised if at that location, there would be water shortages.
If they let the water go, it must be because the value of that water is lower than its local comercial value. Any additional 'thing' you do with the water (and it is a lot of water) will cost energy.
I wonder if it is smart to waste energy to produce fresh water at a location where you already have plenty of water.

(if the heat in the steam however could be used in any productive way, that may be beneficial, but I wouldn't care too much about the water)

Sorry,

This one seems to waste a lot of water in a desert region indeed.
Still, the amount of heat-energy they need to get rid of is enormous (about 120% of the generated electricity, or 5GW of thermal energy).
Any alternative to get rid of this heat would probably take so much energy, that it doesn't compare to the "value" of the water.

"So Kelly what is the root cause of starvation and power shortages? It is not the ability of engineers to produce power or farmers to grow food."

Engineers and farmers have made progress everyone can obviously see.

Wizards who state we already have limitless power and water are the problem.

Notice SJC left out the word 'sewage'. You can not use use “The facility evaporates water from the treated sewage of several nearby municipalities to meet its cooling needs.” to grow food. At least not following US regulations.

There are many practical things that can done with sewage and biosolids. I am betting people like SJC would be against it. Not in his backyard.

@Alain

I have worked at two 'dry' site nuke plants where there was not an enormous amount of water. If fact there was very little water at these arid sites in California and Spain. Cooling towers do not use much water compared to the amount of power produced. We used evaporators very several application. The steam is called extraction steam from low pressure turbine stages. Removing low quality steam increases the thermal efficiency of the turbines.

This often referred to as co-generation. If you you have a lot of water that needs treatment, we can treat it economically with nukes.

Let me repeat for the slow learners like Kelly. We can produce a limitless supply of power and water with nukes . However, we only produce what society needs. If there are shortages in the world it is not because we can not meet demand, it is because we were not allowed to build and recover out investment.

There is no magic involved. I am a mechanical engineer and that is what I do. However, while several nuke plants have been proposed to produce water of crop irrigation, none have yet to be built. Society loves innovative ideas until there is a shortage. When there is a shortage, boring ideas work just fine.

The water is treated before using it for cooling. This is enough water for 1000 square miles of land growing miscanthus for fuel.

No sense growing 30 million acres of corn for ethanol when you can make 20% of our gasoline from tall grasses using gasification.

This is water that is just going out the cooling stacks and adding to the humidity, might as well condense it, irrigate land and grow some fuel.

Correction, this one power plant that covers 4000 acres would provide enough water for 100 square miles, or more than 50,000 acres, for one acre foot for each acre per year. You could drip irrigate and save a lot of water, but that costs more.

This is an area 10 miles by 10 miles. 50,000 acres at 4000 gallons of fuel per acre (Cool Planet Fuels) would produce 200 million gallons of synthetic gasoline per year. Enough for about 400,000 cars in the city of Phoenix for a whole year.

Condensing it means extracting the latent heat and putting it somewhere; this is energetically "uphill" because otherwise it would occur spontaneously.  Do you have a recipe for this, SJC?

Good ideas SJC, what is stopping you? There is no shortage of effluent from WWTPs why are you worried about what a nuke plant uses to produce electricity?

If fact I am a big advocate of using nutrients in waste water to grow energy crops. A little advice, avoid California because there are too many people like SJC who spend there time stopping others from getting things done.

In fact SJC send me a check for $5 million and I will stop working on nuke plants and build you a very nice project that combines biomass renewable energy and recycling nutrients from waste water. I had several on the drawing board a few years back. " We can produce a limitless supply of power and water with nukes" - nuts. The world, esp. Japanese, can't afford the nuke costs or radiation already spilled. If earth has limitless power and water, there is no drought or hunger(false). Drop the wild illogical(mechanical?) statements, or is reality to slow.. I am just suggesting an idea, you guys seem to want to say it can never be done, should never be done, but you never do anything yourselves. Have fun. If the Japanese governments were to restart now all of the nuclear power plants that did not fail during the Tsunami, and then offer the use of the homes in the so called radio-active exclusion contaminated area to the original owners or to other displaced persons and families with their electricity at half price and a warning that the area had higher than its usual radioactivity but less than the natural radioactivity of other inhabited parts of the world, the houses would be filled in a week. The contamination is no longer immediately life threatening, and in some of the restricted area never was. A further warning that cancer development theoretically attributable to increased radiation levels, but unprovable, would be less than a tenth of all other cancers of the populations and much less than the cancers caused by smoking or deaths cause by driving automobiles. The Japanese reactors should not have been turned off until all use of cigarettes was banned in Japan to prevent far more life shortening illnesses. Some one could begin to assess how many man-hours, therefore lives, were lost due to the lack of electricity from the operating power plants that were shut down. China now could build many CANDU power plants along the coast(at high elevations or submersible) within the next four or five years and sell the power produced to Japan. The present "waste" fuel from China's and the US light water reactors could power them for centuries or millenia if some thorium were added. Reactors for making pure water out of seawater can use far lower pressures and less costly equipment and can have far larger cheaper tanks of cooling water so that the melting of the fuel cladding (meltdown) is impossible with or without electricity. Such reactor tanks could even be built below sea level with flooding valves to let in sea water with gravity when fresh water from all other reserves ran out. One pound (kilogram) of uranium or thorium or plutonium can supply energy equivalent to three millions pounds (kilograms) of coal or crude oil. The cost of uranium for of making a thousand gallons of fresh water from sea water is less than zero if modified CANDU reactors are used, and a group of many such reactors can be combined with a fuel processing facility that makes the fuel whilst the reactors eliminate all long lived transuranic wastes including all of the several explosive and more nonexplosive isotopes of the inseparable non explosive plutonium isotope mix found in the fuel rods removed from light water reactors as waste during refueling of the reactor. Special reactors can be built to extract at least 50 percent more energy from these unmodified fuel rod assemblies for water desalinization before they are processed to remove the fission products that first slow then stop the chain reaction until removed. Except for the slight additional cost, there is no reason to not build nuclear reactors a hundred or more feet underground. The heat can be sent up as steam and the steam returned as water. Even a Chernobyl type failure would have not disturbed the people on the surface. Until a perfect automobile is built and required, there does not need to be a perfect nuclear power reactor. I will suggest that hundreds of people are dead that would not have been, because working Japanese power reactors were shut off and heat and light were not available at times. Only about 50 workers and no non worker residents of the Chernobyl area were killed by radiation. Every human body, that ever existed, has given off nuclear radiation to other humans that is an easily measurable fraction of that received from space and the earth. You are not nuclear virgins and never were. The bodies of all types of animals know how to repair themselves from nuclear rays as well as they know how to repair the damage caused by oxygen from the air getting into cells or sunlight on the skin. This very second, potassium atoms are exploding in your body cells right next to your DNA or nerve fibre. ..HG.. SJC: I am just suggesting an idea, you guys seem to want to say it can never be done I have an idea: we breed a bunch of unicorns which poop Skittles, dissolve the Skittles in water, ferment them to alcohol, and replace all the world's oil that way. Great idea, huh? Your idea runs afoul of the same laws of physics and thermodynamics. If you don't understand why, education might help you learn the principles and apply them. Until you can do that, you have nothing worthwhile to contribute. Kelly: The world, esp. Japanese, can't afford the nuke costs or radiation already spilled. Hogwash. The tsunami killed tens of thousands; the radiation from Fukushima Dai'ichi killed NOBODY, and is likely to never kill anyone. Furthermore, the paranoia over radiation exposure killed approximately 600 people due to over-zealous evacuation orders; the frail elderly would have been safer to shelter in place than trying to move out under disaster conditions. Most of the Fukushima evacuation area is habitable now, under exposure limits from our best understanding of radiation effects (as opposed to the LNT hypothesis, which is known to be false). Japan can afford another Dai'ichi meltdown, though it's almost certain never to have one (neither Dai'ini nor Onagawa had radiation releases); what Japan cannot afford is another$1 trillion for fossil fuels over the next 20 years.

Kelly correctly points out that the world of full of problems like starvation. I would add that the billions who also do not have access to electricity, also do not have access to clean drinking water.

Kelly incorrectly points out that a rich country like Japan can not afford to recover from a natural disaster. Poor countries that suffer natural disasters have much greater immediate death tolls followed by the death toll caused by water and food borne disease.

I always wonder about folks who worry about low levels of radiation but are not concerned about pathogen bacteria. In Japan, no one was hurt by eating contaminated food.

Countries with good emergency planning avoid the slow accidents.

Engineer-Poet, "The tsunami killed tens of thousands; the radiation from Fukushima Dai'ichi killed NOBODY, and is likely to never kill anyone."

Hogwash. Up to 5% of a small country is irradiated for decades. Don't for a minute pretend lives haven't been shortened in Japan and insurance rates won't gouge this.

Corrupt US medical insurance lumps simple type 2 diabetes with the extreme, often unaffordable, premiums charged AIDs patients - so don't pretend radiation isn't costly, lethal, or in the insurance tables and premiums.

My initial comment on this, yet another 'many fold better' article(now desalination) is that it should be monitored. Every week, there's some breakthrough that, years later, has gone nowhere.

Frankly an app to automatically monitor these 'breakthroughs' would be useful.

Perhaps I'm like JFK, asking '..why not?' A fraction the cost desalination could green parts of the Sahara - and Africans don't have limitless power, water, or food.

I lived through Enron brownouts of Silicon Valley. Why, for God's sake, wasn't just a tenth of a percent of solar electricity distributed at traffic lights to stop HOURS of DAILY 'signals out/traffic jams'?

I mentioned JFK. After a dozen years of S. Vietnam US troop hikes(to 17,000) in Sept. 1963, JFK pulled a 1,000 troops out in Oct.

In Nov, he was then murdered thirty miles from a Texas helicopter factory that suddenly made \$BILLIONS during Nam under the new Texan President.

Now, we've endured one truly despicable track record of decades of Texan President's, yet, like oil, they're seemingly always in the wings.

Others may ask why nuke engineers ALWAYS put redundant water cooling pumps IN the reactor facility, instead of miles away, where they could survive a CATASTROPHE AND ACTUALLY COOL a stricken reactor http://video.pbs.org/video/2202847024?starttime=876001

etc, etc..

EP,

You are why some people don't come here any more. You arrogantly dismiss like the coward bully you are. Grow up or get lost.

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