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A graphene membrane. Credit: The University of Manchester

 

“By 2025 the UN expects that 14% of the world’s population will encounter water scarcity.”

Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.

New research demonstrates the real-world potential of providing for millions of people who struggle to access adequate clean water sources.

The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology. Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.

Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in technologies, which require even smaller sieves.

Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.

The Manchester-based group have now further developed these and found a strategy to avoid the swelling of the membrane when exposed to water. The in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.

As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.

WEF 2017 graphene-water-071115-rtrde3r1-628x330 (2)World Economic Forum: Can Graphene Make the World’s Water Clean?

 

 

 

 

When the common salts are dissolved in water, they always form a ‘shell’ of around the salts molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow anomalously fast which is ideal for application of these membranes for desalination.

Professor Rahul Nair, at The University of Manchester said: “Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination .

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”

Mr. Jijo Abraham and Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper: “The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.” said Mr. Abraham.

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionize water filtration across the world, in particular in countries which cannot afford large scale desalination plants.

It is hoped that graphene-oxide systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh produced.

Explore further: Researchers develop hybrid nuclear desalination technique with improved efficiency

More information: Tunable sieving of ions using graphene oxide membranes, Nature Nanotechnology, nature.com/articles/doi:10.1038/nnano.2017.21

MIT Desal Shock 111315 bt1511_MIT-fracking-pondAs the availability of clean, potable water becomes an increasingly urgent issue in many parts of the world, researchers are searching for new ways to treat salty, brackish or contaminated water to make it usable. Now a team at MIT has come up with an innovative approach that, unlike most traditional desalination systems, does not separate ions or water molecules with filters, which can become clogged, or boiling, which consumes great amounts of energy.

Instead, the system uses an electrically driven shockwave within a stream of flowing water, which pushes salty water to one side of the flow and fresh water to the other, allowing easy separation of the two streams. The new approach is described in the journal Environmental Science and Technology Letters, in a paper by professor of chemical engineering and mathematics Martin Bazant, graduate student Sven Schlumpberger, undergraduate Nancy Lu, and former postdoc Matthew Suss.

This approach is “a fundamentally new and different separation system,” Bazant says. And unlike most other approaches to desalination or water purification, he adds, this one performs a “membrane-less separation” of ions and particles.

Membranes in traditional desalination systems, such as those that use reverse osmosis or electrodialysis, are “selective barriers,” Bazant explains: They allow molecules of water to pass through, but block the larger sodium and chlorine atoms of salt. Compared to conventional electrodialysis, “This process looks similar, but it’s fundamentally different,” he says.

In the new process, called shock electrodialysis, water flows through a porous material —in this case, made of tiny glass particles, called a frit — with membranes or electrodes sandwiching the porous material on each side. When an electric current flows through the system, the salty water divides into regions where the salt concentration is either depleted or enriched. When that current is increased to a certain point, it generates a shockwave between these two zones, sharply dividing the streams and allowing the fresh and salty regions to be separated by a simple physical barrier at the center of the flow.

“It generates a very strong gradient,” Bazant says.

Even though the system can use membranes on each side of the porous material, Bazant explains, the water flows across those membranes, not through them. That means they are not as vulnerable to fouling — a buildup of filtered material — or to degradation due to water pressure, as happens with conventional membrane-based desalination, including conventional electrodialysis. “The salt doesn’t have to push through something,” Bazant says. The charged salt particles, or ions, “just move to one side,” he says.

The underlying phenomenon of generating a shockwave of salt concentration was discovered a few years ago by the group of Juan Santiago at Stanford University. But that finding, which involved experiments with a tiny microfluidic device and no flowing water, was not used to remove salt from the water, says Bazant, who is currently on sabbatical at Stanford.

The new system, by contrast, is a continuous process, using water flowing through cheap porous media, that should be relatively easy to scale up for desalination or water purification. “The breakthrough here is the engineering [of a practical system],” Bazant says.

One possible application would be in cleaning the vast amounts of wastewater generated by hydraulic fracturing, or fracking. This contaminated water tends to be salty, sometimes with trace amounts of toxic ions, so finding a practical and inexpensive way of cleaning it would be highly desirable. This system not only removes salt, but also a wide variety of other contaminants — and because of the electrical current passing through, it may also sterilize the stream. “The electric fields are pretty high, so we may be able to kill the bacteria,” Schlumpberger says.

The research produced both a laboratory demonstration of the process in action and a theoretical analysis that explains why the process works, Bazant says. The next step is to design a scaled-up system that could go through practical testing.

Initially at least, this process would not be competitive with methods such as reverse osmosis for large-scale seawater desalination. But it could find other uses in the cleanup of contaminated water, Schlumpberger says.

Unlike some other approaches to desalination, he adds, this one requires little infrastructure, so it might be useful for portable systems for use in remote locations, or for emergencies where water supplies are disrupted by storms or earthquakes.

Maarten Biesheuvel, a principal scientist at the Netherlands Water Technology Institute who was not involved in this research, says the work “is of very high significance to the field of water desalination. It opens up a whole range of new possibilities for water desalination, both for seawater and brackish water resources, such as groundwater.”

Biesheuvel adds that this team “shows a radically new design where within one and the same channel ions are separated between different regions. … I expect that this discovery will become a big ‘hit’ in the academic field. … It will be interesting to see whether the upscaling of this technology, from a single cell to a stack of thousands of cells, can be achieved without undue problems.”

The research was supported by the MIT Energy Initiative, Weatherford International, the USA-Israel Binational Science Foundation, and the SUTD-MIT Graduate Fellows Program.

Source: Massachusetts Institute of Technology

Nanoposres Seawater id41830University of Illinois engineers have found an energy-efficient material for removing salt from seawater that could provide a rebuttal to poet Samuel Taylor Coleridge’s lament, “Water, water, every where, nor any drop to drink.”

The material, a nanometer-thick sheet of molybdenum disulfide (MoS2) riddled with tiny holes called nanopores, is specially designed to let high volumes of water through but keep salt and other contaminates out, a process called desalination. In a study published in the journal Nature Communications (“Water desalination with a single-layer MoS2 nanopore”), the Illinois team modeled various thin-film membranes and found that MoS2 showed the greatest efficiency, filtering through up to 70 percent more water than graphene membranes.
nanopore water filter
A computer model of a nanopore in a single-layer sheet of MoS2 shows that high volumes of water can pass through the pore using less pressure than standard plastic membranes. Salt water is shown on the left, fresh water on the right. (Image: Mohammad Heiranian)
“Even though we have a lot of water on this planet, there is very little that is drinkable,” said study leader Narayana Aluru, a U. of I. professor of mechanical science and engineering. “If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis.
“Finding materials for efficient desalination has been a big issue, and I think this work lays the foundation for next-generation materials. These materials are efficient in terms of energy usage and fouling, which are issues that have plagued desalination technology for a long time,” said Aluru, who also is affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.
Most available desalination technologies rely on a process called reverse osmosis to push seawater through a thin plastic membrane to make fresh water. The membrane has holes in it small enough to not let salt or dirt through, but large enough to let water through. They are very good at filtering out salt, but yield only a trickle of fresh water. Although thin to the eye, these membranes are still relatively thick for filtering on the molecular level, so a lot of pressure has to be applied to push the water through.
“Reverse osmosis is a very expensive process,” Aluru said. “It’s very energy intensive. A lot of power is required to do this process, and it’s not very efficient. In addition, the membranes fail because of clogging. So we’d like to make it cheaper and make the membranes more efficient so they don’t fail as often. We also don’t want to have to use a lot of pressure to get a high flow rate of water.”
One way to dramatically increase the water flow is to make the membrane thinner, since the required force is proportional to the membrane thickness. Researchers have been looking at nanometer-thin membranes such as graphene. However, graphene presents its own challenges in the way it interacts with water.
Aluru’s group has previously studied MoS2 nanopores as a platform for DNA sequencing and decided to explore its properties for water desalination. Using the Blue Waters supercomputer at the National Center for Supercomputing Applications at the U. of I., they found that a single-layer sheet of MoS2 outperformed its competitors thanks to a combination of thinness, pore geometry and chemical properties.
A MoS2 molecule has one molybdenum atom sandwiched between two sulfur atoms. A sheet of MoS2, then, has sulfur coating either side with the molybdenum in the center. The researchers found that creating a pore in the sheet that left an exposed ring of molybdenum around the center of the pore created a nozzle-like shape that drew water through the pore.
“MoS2 has inherent advantages in that the molybdenum in the center attracts water, then the sulfur on the other side pushes it away, so we have much higher rate of water going through the pore,” said graduate student Mohammad Heiranian, the first author of the study. “It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalize the pore, which is a very complex process with graphene.”
In addition to the chemical properties, the single-layer sheets of MoS2 have the advantages of thinness, requiring much less energy, which in turn dramatically reduces operating costs. MoS2 also is a robust material, so even such a thin sheet is able to withstand the necessary pressures and water volumes.
The Illinois researchers are establishing collaborations to experimentally test MoS2 for water desalination and to test its rate of fouling, or clogging of the pores, a major problem for plastic membranes. MoS2 is a relatively new material, but the researchers believe that manufacturing techniques will improve as its high performance becomes more sought-after for various applications.
“Nanotechnology could play a great role in reducing the cost of desalination plants and making them energy efficient,” said Amir Barati Farimani, who worked on the study as a graduate student at Illinois and is now a postdoctoral fellow at Stanford University. “I’m in California now, and there’s a lot of talk about the drought and how to tackle it. I’m very hopeful that this work can help the designers of desalination plants. This type of thin membrane can increase return on investment because they are much more energy efficient.”
Source: University of Illinois at Urbana-Champaign

GE Desal 111015 greenville5_extra_large-1024x1024The mini desalination system combines 3D printing with GE’s deep reservoir of knowledge of turbo-machinery and fluid dynamics. GE scientists Doug Hofer and Vitali Lissianski used them to shrink a power generation steam turbine that would normally barely fit inside a school gym.

Not too long ago, Lissianski, a chemical engineer in the Energy Systems Lab at GE Global Research, was chatting with his lab manager about new ideas for water desalination. This type of “small talk” happens thousand times a day at the GRC.

Their lab tackles a lot of technical challenges coming from GE’s industrial businesses including Power and Water, Oil and Gas, Aviation and Transportation, and they quickly hit on a possible solution.

It led them to Hofer. As a senior principal engineer for aero systems at GRC and a steam turbine specialist, he was part of another team of GE researchers working on a project for Oil and Gas to improve small scale liquefied natural gas (LNG) production. A key part of the project focused on using 3D printing to miniaturize the turbo expander modeled after a GE steam turbine. (A turbo-expander is a machine that expands pressurized gas so that it could be used for work.)

Hofer was the perfect person in charge. He led the steam turbine aero team at Power and Water before coming to GRC eight years ago. Few people in the world have the kind of expertise and knowledge of steam turbine technology that Doug brings. “In traditional steam turbines, steam condenses and turns to water,” he says. “We thought maybe the same principle could be applied to water desalination.”

The only difference, Hofer explained, would be in using flows through the turbine to freeze the brine, or salt water instead of condensing the steam to water as in a steam turbine. Freezing the brine would naturally separate the salt and water by turning salt into a solid and water to ice.

A 3D printed mini-turbine . Image credit: GE

Lissianski and Hofer compared notes and today they are working on a new project with the US Department of Energy to test their new water desalination concept.

The reality today is that 97.5 percent of the world’s potential clean water drinking supply essentially remains untapped, locked in salty oceans and unsuitable for human consumption. This is in the face of growing global water shortage. According to the United Nations, water scarcity impacts 1.2 billion people, or one fifth of the world’s population.

Not even the United States has been spared. California, which has one of the country’s longest coastlines bordering the ocean, has been suffering through a severe water shortage crisis.

Technology inspired by a miniaturized steam turbine could help change all that. And there’s no reason to believe that it can’t. Advances in miniaturization have proven to have great impact time and time again.

For example, the application of Moore’s Law in the semiconductor world has shrunk the size of computer chips to enable mobile phones that pack more computing power than a roomful of mainframe supercomputers that were state-of-the-art just a few decades ago.

In ultrasound, miniaturization technologies have shrunk consoles to the size of a phone screen and can fit neatly into a doctor’s coat pocket. Doctors today can deliver high quality care in regions where access was previously limited or non-existent.

And steam turbines? They already have proven to be one of the key innovations that spread electricity to virtually every home and business. Miniaturized, they just might hold the key to spreading water desalination around the world.

Top image: Doug Hofer, a GE steam turbine specialist, and Vitali Lissianski, a chemical engineer in GE’s Energy Systems Lab, holding the mini-turbine in front of an actual size power generation steam turbine. Image credit: GE Reports

jeffrey-grossman-mitWith the intensifying drought in California, the state has accelerated the construction of desalination plants. Yet due to high construction and operating costs, as well as environmental concerns, we’re not likely to see reclaimed seawater represent more than a small fraction of America’s clean water reserves for some time to come. Aside from other costs, the immense amounts of energy required to make clean water from seawater continues to make desalination a niche solution in most parts of the world.

When Jeffrey Grossman, a professor at MIT’s Department of Materials Science and Engineering (DMSE), began looking into whether new materials might reduce the cost of desalination, he was surprised to find how little research and development money was being applied to the problem.

“A billion people around the world lack regular access to clean , and that’s expected to more than double in the next 25 years,” Grossman says. “Desalinated water costs five to 10 times more than regular municipal water, yet we’re not investing nearly enough money into research. If we don’t have clean energy we’re in serious trouble, but if we don’t have water we die.”

At the Grossman Group, which explores the development of new materials to address clean energy and water problems, a possible solution may be at hand. Grossman’s lab has demonstrated strong results showing that new made from could greatly improve the energy efficiency of desalination plants while potentially reducing other costs as well.

Graphene, which results from slicing off an atom-thick layer of graphite, is increasingly emerging as something of a wonder material. The Grossman Group, for example, is also looking into using it as a cheaper alternative to silicon for making solar cells.

Graphene Nano Membrane 071615

“It’s never been a more exciting time to be a materials scientist,” says Grossman. “When you look at clean tech or water filtration, you find that the energy conversion bottleneck stems from the material. We can now design materials pretty much all the way down to the scale of the atom in almost any way we want, tailoring materials in ways that were previously impossible. There’s a convergence emerging in which we are facing enormously pressing problems that can only be solved by developing .”

Graphene filters: Up to 50 percent less energy

First isolated in 2003, graphene has different electrical, optical, and mechanical properties than graphite. “It’s stronger than steel, and it has unique sieving properties,” Grossman says. At only an atom thick, there’s far less friction loss when you push seawater through a perforated graphene filter compared with the polyamide plastic filters that have been used for the last 50 years, he says.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

“We have shown that perforated graphene filters can handle the water pressures of desalination plants while offering hundreds of times better permeability,” Grossman explains. “The process of pumping seawater through filters represents about half the operating costs of a desalination plant. With graphene, we could use up to 50 percent less energy.”

Another advantage is that graphene filters don’t become fouled with bio-growth at nearly the rate that occurs with polyamide filters. Desalination plants often run at reduced efficiency due to the need to frequently clean the filters. In addition, the chlorine used to clean the filters reduces the structural integrity of the polyamide, requiring frequent replacement. By comparison, graphene is resistant to the damaging effects of chlorine.

According to Grossman, you could easily replace polyamide filters with graphene filters in existing plants. Like polyamide filters, graphene filters can be mounted on robust polysulfone supports, which have larger holes that sieve out particulates.

Yet, significant challenges remain in bringing down costs. The Grossman Group has made good progress in creating high volumes of graphene at a reasonably low cost. A more serious challenge, however, is cost-effectively poking uniform holes in the graphene in a highly scalable manner.

“A typical plant has tens of thousands of membranes, configured in two-meter long tubes, each of which has 40 square meters of rolled up active membrane,” Grossman says. “We have to match that volume at the same cost, or it’s a nonstarter.”

Making graphene on the cheap

The traditional way to make graphene—since its first isolation in 2003, mind you—is to peel it off with adhesive. “You literally take a piece of Scotch Tape to graphite and you peel,” Grossman explains. “If you keep doing this, you eventually wind up with a single layer. The problem is it would take forever to peel off enough graphene for a desalination plant.”

Another approach is to “grow” graphene by applying super-hot gases to copper foil. “Growing graphene provides the best quality, which is why the semiconductor industry is interested in it,” Grossman says. The process, however, is very expensive and energy-intensive.

Instead, the Grossman Group is using a much more affordable chemical approach, which produces sufficient quality for creating desalination membranes. “Fortunately, our application doesn’t require the best quality,” says Grossman. “With the chemical technique, we put graphite in a solution, and apply low temperature chemistry to break apart the entire chunk of graphite into sheets. We can get lots of graphene very cheaply and quickly.”

Creating pores that block salt but let water molecules pass is a steeper challenge. The reason desalination is possible in the first place is that when diffused in water, salt ions bond with water molecules, thereby creating a larger entity. But the difference in size compared to a free water molecule is still frustratingly small.

“The challenge is to find the sweet spot of about 0.8 nanometers,” Grossman says. “If your pores are at 1.5 nm, then both the water and salt will pass through. If they’re half a nanometer, then nothing gets through.”

A 0.8 nm hole is “smaller than we’ve ever been able to make in a controllable way with any other material,” Grossman says. “And we need to do this over a very large area very consistently and cheaply.”

The Grossman Group is pursuing three techniques to make nanoporous graphene membranes, all of which use chemical and thermal energy rather than mechanical processes. “If you tried to use lithography, it would take years,” Grossman says. “Our first approach involves making the holes too big, and then carefully filling them in. Another tries to make them exactly the right size, and the third involves starting with a material without holes and then carefully ripping it apart.”

The chemical technique for making graphene actually produces graphene oxide, which is considered undesirable for semiconductors, but is fine for filters. As a result, the researchers were able to avoid the difficult step of removing the oxygen from the graphene oxide. In fact, they found a way to use the oxygen to their advantage.

“By controlling the way the oxygen is bonded to the graphene sheet, we can use chemical and thermal energy to drill the holes with the help of the oxygen,” Grossman says.

First target: Brackish water

As the Grossman Group continues to work on the challenge of manufacturing and perforating graphene sheets, Grossman is looking to leverage other benefits of graphene filters to help bring the technology to market.

Although graphene should improve efficiency with seawater and the even saltier, dirtier water used in hydraulic fracturing, it will likely debut in plants that clean brackish water, such as found in estuaries. “It turns out that higher permeability even by a factor of two or three would make a bigger difference with brackish water than with seawater,” Grossman says. “You lower the energy consumption in both cases, but more so for brackish water.”

Graphene filters could also enable the construction of smaller, cheaper plants. “With graphene you have more choices in how you operate the plant,” Grossman says. “You could apply the same pressures but get more water out, or you could operate it at lower pressures and get the same amount of water, but at a lower energy cost.”

Grossman notes that it can take years or even decades to site and permit a plant in heavily populated coastal areas. “A lot of effort goes into how you’re going to build the plant and where you’re going to find enough land,” Grossman says. “Having the option to build a smaller plant would be a big advantage.”

Explore further: Nanoporous graphene could outperform best commercial water desalination techniques

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*** Re-Posted from “One-Green-Planet” ***

All of terrestrial life depends on freshwater. From densely populated cities to rural communities, farmland and forestland, and domestic and wild animals, all are in need of clean water to sustain them. Miraculously, just a small percentage of the water on earth is actually available as freshwater.

According to the U.S. Geological Service, only about 2.5 percent of all the water on planet earth is freshwater. And only 1.2 percent of that is most easily accessible on the earth’s surface in the form of lakes, rivers, swamps, soil moisture, and permafrost. An additional 30.1 percent exists as groundwater while the majority of this freshwater, 68.7 percent to be exact, is locked up as frozen glaciers and ice caps.

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 If you’re reading into the numbers, it would appear that the majority of freshwater is not easily accessible to us for human use. And, unfortunately, many human activities are causing harm to the natural water cycle that’s in place, making freshwater resources even more difficult to access and utilize. Building impervious structures such as buildings and paved roads makes it difficult for precipitation to be absorbed by the land to replenish groundwater resources. We also impact not only the natural flow of water with barriers like dams, but also the composition and safety of water with our pollution. We are often too aggressive in harvesting water from groundwater and surface supplies, depleting underground reserves as well as rivers and lakes.  And our contributions to climate change have impacted precipitation and evaporation rates, making the resource even more unstable and less predictable.

It is in our best interest to treat freshwater supplies with the utmost respect, and yet we’re losing out on this invaluable resource due to our own ignorance and negligence.

So, what can we do to save our water? There are, luckily, a variety of solutions. From education and conservation to emerging technologies, we are hatching up a plethora of solutions to our water woes. One of the strategies that many countries are using is desalination where salt water is essentially converted into freshwater. There’s plenty of salt water on the planet, as we know, so this sounds like a fabulous idea. Or is it?

Getting freshwater From Saltwater – How?

Desalination is a process that converts salt water to freshwater by removing salts and other minerals, leaving behind freshwater, potable water. While there are a variety of methods to accomplish this task, they can be grouped mainly into two types.

The first method, thermal desalination, involves the heating of saline water. Salts are left behind while freshwater is converted to steam and is collected, ultimately to condense back into water that is now saline-free and ready for use in an instance where freshwater is desired.

The second type of desalination involves the use of membranes to separate salt and other minerals from water. Pressure or electric currents may be used to drive saline water through a membrane which acts as a filter. Freshwater ends up on one side of the membrane while saline water stays on the other side as a form of waste.

Of course, these are very, very basic descriptions of some pretty complex and evolving technologies. But they do offer a quick insight into what the process of desalination looks like in most settings around the world. For some individuals, this is the technology used to provide them with clean drinking water.

Where Are Desalination Plants Working Now?

Desalination is a technology that has been around for quite some time and is seeing improved growth around the world in the face of increasing water demands. Since 2003, Saudi Arabia, the United Arab Emirates and Spain have led the world in desalination capacities. As of 2013, there were over 17,000 desalination plants worldwide in roughly 150 countries, providing more than 300 million people with at least some of their daily freshwater needs.

Israel is one successful case-study when it comes to the value of desalination. The nation currently has a quarter of its freshwater needs met through four desalination plants that treat mainly brackish well water (water that is part salt/part fresh). Israel’s desalination plants currently produce 130 million gallons of potable water a year and they are aiming to increase that number to 200 million gallons a year by 2020. While aggressive conservation efforts also helped ease the impact of severe drought, desalination has certainly been an important piece of solving a water crises.

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Singapore is another interesting story when it comes to desalination. The country is currently pushing to improve its desalination capacity in order to gain independence in its freshwater resources. Right now it depends heavily on neighboring Malaysia to import clean water. For Singapore, desalination offers the country the chance to provide citizens freshwater even where saline water sources are much more available, ultimately becoming more independent and self-reliable.

As countries all over the world increase their capacity for desalination plants, drought-stricken areas like the United States southwest are taking note and investing in this technology. In fact, construction on the Western hemisphere’s largest desalination plant is nearly complete in San Diego, California and is expected to open for operation later this year. In the face of severe drought, desalination is becoming a much more appetizing option for this region to put its plentiful access to seawater to good use and to alleviate some of the pressures that developed and agricultural areas are placing on freshwater sources.

Is This The Answer to Water Shortages Worldwide?

Whether or not desalination is the savior for water woes is a complex debate and answers will probably vary depending on who you are asking. You’ll find there are activists, scientists, public agencies, governments, and citizens on both sides of the debate.

Ecological Impact

The first input that comes to mind when you think of desalination is probably the saline water that’s being treated, right? Depending on the source of this saline water, there may be a variety of detrimental impacts to the local ecology to consider when it comes to desalination operations.

Some desalination plants use direct intake methods to gather saline water, meaning they extract water directly from the water column, either from the surface or at greater depths in the ocean. The problem with this extraction method is that, in addition to taking in saltwater that can become a viable freshwater source, a host of marine life is also sucked up in the process. Algae, plankton, jellyfish, fish, and larva of many species can all easily be killed with this direct intake method for harvesting sea water.

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The impact of ocean water extraction on local marine life is not well understood, however, experts will note there are a variety of ways to skate around issues like this. One such method is indirect intake where pipes are buried in the substrate and intake water that is actually filtered down through the sand first. Marine life damage is largely eliminated using this method. Physical barriers to intake pipes may also be utilized where screens or meshes are able to keep smaller marine creatures out of the intake pipes. And behavioral deterrents, like bubble screens and strobe lights, are another option to discourage marine animals from swimming too close to intake systems where they become trapped.

Saline water that is being harvested for desalination projects are not the only issue creating ecological impacts for this water treatment system. The output of wastewater is another issue that critics point out when it comes to desalination. Water discharged from desalination plants has a higher level of saline than the body of water it is entering. While some creatures can tolerate change in salinity, others cannot and may be killed on contact. Discharging water that has been heated in the desalination process can also cause temperature spikes and stress to any aquatic life in a close radius. And, the water discharged from desalination operations may also have an altered chemical composition given the added antifouling agents, heavy metals, chlorine, antiscaling chemicals, and cleaning solutions used in the process. All have a potential to detrimentally impact the local ecology surrounding a desalination operation.

Some solutions for wastewater from desalination operations already exist. Because saline water is more likely to sink and move along the ocean bottom, discharging it upward can help promote mixing of wastewater more quickly to disperse salinity and weaken the impacts that concentrated salt levels can cause. Additionally, plants can invest in technology to lessen the amount of chemicals they use in the treatment process, and even attempt to let wastewater evaporate, leaving behind only solid waste for plant operators to dispose of. These may not be perfect solutions, but they are attempts to make desalination operations more friendly to the local ecology.

Energy Requirements

One major difficulty with fully embracing desalination has to do with the major energy inputs the technology requires. Costs attributed to desalination depend largely on energy costs which can and do fluctuate from year to year. Roughly 60 percent of the cost of operating a thermal desalination plant comes from the energy costs to operate the plant, while 36 percent of the cost to run a reverse osmosis plant comes from the energy it uses.

Greenhouse gas emissions associated with desalination plants depend heavily on the type of energy utilized. In an area where fossil fuels are burned to make electricity, emissions associated with desalination will be higher. Additionally, if a desalination plant relies heavily on hydroelectric power, a drought in the area may increase the cost of energy from the electric plant and thus the cost to run the desalination plant.

Money

As with any new and growing technology, there can be an expected higher cost than the conventional way of doing things. Desalination is no exception. Using San Diego County as an example, we can see just how much more expensive desalination is than other methods of providing freshwater. The cost to save an acre-foot of water through conservation and user education around efficiency may fall anywhere between $150 and $,1000. Importing an acre-foot of water may cost somewhere between $875 and $975. Recycling an acre-foot of potable water has a range in cost between $1,200 and $1,800. And providing an acre-foot of freshwater through seawater desalination would cost between $1,800 and $2,800. As local agencies and governments come up against budget cuts and financing difficulties, it may be impossible to justify this technology in the face of cheaper options that provide the same results.

Citizens will see an increase in their water bill as more of their freshwater is sourced from expensive desalination processes. This rise in basic living costs in the face of economic hardship may be difficult to justify, especially for a resource as important as freshwater. Desalination is certainly not a cost-saving choice.

Is It A Go?

It is certainly important to note the improvements that technology like desalination can provide to society. Especially as we are faced with increased challenges to meet the needs of a growing population, it is important to have a variety of options available to us.

While desalination is certainly an amazing option to convert water that was once too salty for human-use into something that can quench thirsts, maintain sanitation, and irrigate agriculture, one may be left wondering if the cost is really worth it. There are still many improvements left to be made to make this a more environmentally friendly option. As it stands, it is not without some major drawbacks when it comes to local ecology destruction, energy use, and greenhouse gas emissions. And it is certainly a very expensive option when you consider how little money it would take to simply educate the masses on how to conserve water.

Desalination is a wonderful testament to the human mind and inventive capacity, but it may simply be a very advanced and expensive method for maintaining our ignorance to the natural world with exist within. We may be able to provide freshwater in places where it didn’t previously exist, but what’s the point if people continue to remain ignorant to how to better use the water we already have? In the face of a crisis this may certainly be a valuable technology, but we have not even yet begun to address some of the issues that are causing our water shortages in the first place. And that’s an issue we need to work out through education and conversation around sustainability rather than throwing money into more expensive technology.

Lead Image Source: JohnKay/Flickr

KAUST Sunlight Steam untitledChemical tricks improve the efficiency and durability of photothermal membranes that use sunlight to turn water into steam.

A point-of-use solar distillation device that can clean up saltwater and wastewater without producing greenhouse gases has been constructed by a research team from King Abdullah University of Science and Technology (KAUST)1.

The key to the new technology is a floating membrane coated with a special light-absorbing polymer that repairs its hydrophobic “skin” when damaged.

For centuries, attempts have been made to use the sun’s heat to distill clean water from polluted sources. Simple solar stills, such as a glass plate placed over a water-filled box, are inexpensive to operate but are notoriously inefficient. This is because water is a poor light absorber, and any captured heat tends to distribute uniformly through the still instead of localizing at surfaces where evaporation occurs.

To combat these problems, researchers are developing floating “solar generator” materials that heat up quickly in sunlight and then trap heat at air–water interfaces for steam production.

KAUST Sunlight Steam untitled

A polypyrrole (PPy)-coated device that absorbs sunlight and releases it as heat can rapidly purify water through distillation  Reproduced with permission © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

These devices are usually coated with water-repellant waxy molecules, such as fluorinated alkyl chains, for better floating. However, damage from ultraviolet rays and oxidative chemicals can degrade the hydrophobic layers, causing the generator to sink.

Inspired by the lotus flower, a plant that restores damage to its hydrophobic leaves through the migration of waxy molecules, KAUST Associate Professor Peng Wang and colleagues from the University’s Biological and Environmental Science and Engineering Division developed a self-healing solar generator.

The researchers coated a tightly woven stainless steel mesh with polypyrrole (PPy), a light-absorbing polymer with high photothermal conversion efficiency and bumpy surface microstructures. The team modified the PPy film with fluoroalkylsilane chains, enabling it to act as a reservoir that supplies additional hydrophobic chains to damaged regions through biomimetic self-migration.

The new device nearly tripled the output of freshwater from typical solar stills, thanks to a significant jump in temperature at the air–water interface and a conversion efficiency of close to 60 percent. It also exhibited remarkable damage resistance: after the team used a plasma source to oxidize the mesh and make it sink to the bottom of a beaker, they found a simple one-hour treatment in sunlight was sufficient to restore its self-floating capability.

The team’s first prototype — a transparent plastic condensing chamber and solar fan mounted on top of a PPy-coated mesh — floats lightly on the surface of seawater and distills a steady stream of water for more than 100 consecutive hours.

“Careful material selection allowed us to integrate two types of functions into one distillation device,” Wang said. “This has great potential to be employed in point-of-use potable water production.”

Reference

  1. Zhang, L., Tang, B., Wu, J., Li, R. & Wang, P.  Hydrophobic light-to-heat conversion membranes with self-healing ability for interfacial solar heating. Advanced Materials advance online publication, 17 July 2015 doi: 10.1002/adma.201502362 | article

kuwait-desalination_0Funding sponsored through the Kuwait-MIT Center for Natural Resources and the Environment.

A team of MIT researchers, together with a team from Kuwait University, has been awarded a $5.5 million dollar grant for a collaborative research project titled, “Next Generation Brine Desalination and Management for Efficiency, Reliability, and Sustainability”.

The project is being funded through the Signature Research Program of the Kuwait-MIT Center for Natural Resources and the Environment (CNRE) by the Kuwait Foundation for the Advancement of Sciences (KFAS) with a performance period of three years.

The project is designed to address several coupled challenges and to investigate desalination systems from the microfluidic scale up to the system level scale:

  • innovations in electrical desalination technologies combined with high-fidelity modeling, multi-staging and system-wide optimization with detailed techno-economic analysis;
  • innovation in materials and surface coating for increased reliability of operation; and
  • mitigation of negative environmental impacts of brine discharge through innovative coastal discharge configurations, combined with reduction in discharge salinity due to blending of brine with treated waste water effluent, as part of integrated energy recovery schemes.

These core research areas will be investigated in parallel while accounting for coupling between them, adding to the uniqueness of this project.

Jongyoon Han, principal investigator of the project and a professor of both the Department of Electrical Engineering and Computer Science and the Department of Biological Engineering, says, “The issue of proper and efficient brine treatment, both in terms of economic and environmental aspects, is truly an ‘MIT-hard’ challenge, so all of us in the team are motivated by it. Not only will this project have potential impact to Kuwait and other Gulf states, the ideas and concepts developed in this project may have implications to other challenging environmental remediation such as the treatment of produced water from oil and gas industries.”

Bader Al-Anzi, professor at the Department of Environmental Technology Management at Kuwait University and the leading co-principal investigator at Kuwait University was instrumental in the formation of the team and the scope of this collaborative research project during his yearlong appointment at MIT as a visiting scientist.

“Like other GCC countries in the region, Kuwait replenishes its water resources through desalination process, for potable water, and treated wastewater for non-human consumption purposes/applications,” Al-Anzi says. “However, the foregoing processes discharge brine and treated wastewater, respectively, into the Gulf that may pose a serious threat to the marine life if left untreated. The current project addresses such challenges by increasing both energetic and environmental sustainability of Kuwaiti water management by developing / validating novel ideas and interfacing them optimally with existing plant workflow.”

“The ideas in this project build on the unique and synergistic expertise of the MIT and Kuwait University team in desalination and environmental related technologies and sciences,” says Murad Abu-Khalaf, the executive director of CNRE. “The team has the expertise needed to create new innovations in desalination systems from the microfluidic levels up to the system wide level. The project addresses a critical challenge to the sustainable growth of Kuwait, which gets more than 90 percent of its freshwater from desalination, and the Gulf states at large. We are excited by the prospects this collaboration between MIT and Kuwait University brings in addressing challenges of such a global scope. This is the second project to be initiated through CNRE’s Signature Research Program that, collaboratively with researchers in Kuwait, investigates technical challenges that have both regional and global impact.”

The other co-PIs from MIT are Karen Gleason, professor of chemical engineering, John Lienhard, professor of mechanical engineering, Jacob White, professor of electrical engineering and computer science, and Eric Adams, senior research engineer at the Department of Civil and Environmental Engineering.

Directed by Mujid Kazimi alongside associate director Jacopo Buongiorno — both professors in the Department of Nuclear Science and Engineering at MIT — and executive director Murad Abu-Khalaf, CNRE was established at MIT in 2005 to foster collaborations in research and education in areas of energy, water and the environment between MIT and research institutions in Kuwait. The center is funded by the Kuwait Foundation for the Advancement of Sciences.

MIT-natasha-wright-01MIT’s Natasha Wright

MIT: PhD student Natasha Wright makes water safe to drink for rural, off-grid Indian villages. 

When graduate student Natasha Wright began her PhD program in mechanical engineering, she had no idea how to remove salt from groundwater to make it more palatable, nor had she ever been to India, where this is an ongoing need.

Now, three years and six trips to India later, this is the sole focus of her work.

Wright joined the lab of Amos Winter, an assistant professor of mechanical engineering, in 2012. The lab was just getting established, and the aim of Wright’s project was vague at first: Work on water treatment in India, with a possible focus on filtering biological contaminants from groundwater to make it safe to drink.

There are already a number of filters on the market that can do this, and during her second trip to India, Wright interviewed a number of villagers, finding that many of them weren’t using these filters. She became skeptical of how useful it would be to develop yet another device like this.

Although the available filters made water safe to drink, they did nothing to mitigate its saltiness — so the villagers’ drinking water tasted bad and eroded pots and pans, providing little motivation to use these filters. In reviewing the list of questions she had prepared for her interviews with locals, Wright noticed that there were no questions about the water’s salty taste.

“No one had ever asked them about that. And although this might sound obvious, people really don’t like the taste of salt,” Wright says. “So once I started asking, it’s all anyone would talk about.’”

“The biggest surprise of the project so far has been this salt issue, which was the thing that changed the entire purpose of the research,” she adds.

Almost 60 percent of India has groundwater that’s noticeably salty, so later, after returning to MIT, Wright  began designing an electrodialysis desalination system, which uses a difference in electric potential to pull salt out of water.

This type of desalination system has been around since the 1950s, but is typically only used municipally, to justify its costs. Wright’s project aims to build a system that’s scaled for a village of 5,000 people and still cost-effective.

While other companies are already installing desalination systems across India, their designs are intended to be grid-powered. When operating off the grid, these systems are not cost-effective, essentially blocking disconnected, rural villages from using them.

Wright’s solution offers an alternative to grid power: She’s designed a village-scale desalination system that runs on solar power. Since her system is powered by the sun, operational and maintenance costs are fairly minimal: The system requires an occasional cartridge filter change, and that’s it.

The system is also equipped to treat the biological contaminants that Wright initially thought she’d be treating, using ultraviolet light. The end result is safe drinking water that also tastes good.

Earlier this year, Wright’s team won a grant from the United States Agency for International Development (USAID), enabling the researchers to test this system at full scale for the first time in New Mexico two months ago. A second stage of the grant will help bring a pilot to India this summer. Local farmers will use the system and provide feedback at a conference organized by Jain Irrigation, Inc., a company based in Jalgaon, India. Wright’s team is now looking to find out how easy it is for users.

The USAID competition was actually intended for systems built for individual farms, but Wright calculated that the amount of water used by a single farm is similar to the amount of water that a small village needs for its daily drinking water — 6 to 12 cubic meters. 

Although Wright’s work is currently focused on rural villages in India, she sees many uses for the technology in the United States as well. In isolated areas, such as the ranches in New Mexico where she tested her system at full scale, poor access to water pipelines often leads to a heavy reliance on well water. But some ranchers find that even their livestock won’t tolerate the saltiness of this water.

“It’s useful to install a small-scale desalination system where people are so spread out that it’s more costly to pump in water from a municipal plant,” she says. “That’s true in India and that’s also true in the U.S.”

Carbon Nanotube 072515 I Zwitterion-snapshot

Engineered carbon nanotube membranes may help solve our growing demand for desalination.

Of course, you can’t just drink a glass of water straight from the sea. But it is possible to use water from the ocean once the salts are removed. In fact, desalination plants already provide much of the water used by people in many parts of the world, especially in Israel, Saudi Arabia, and Australia.

Climate change is only increasing the demand for desalinated water as greater evaporation and rising seas further limit freshwater supplies for a growing world population. But desalinating water today comes at a very high cost in terms of energy, which means more greenhouse gases and more global warming.

Researchers from the University of Malaya’s Nanotechnology and Catalysis Research Center in Kuala Lumpur in Malaysia say in the journal Desalination that carbon nanotube (CNT) membranes have a bright future in helping the world’s population meet the need for purified water from the sea.

“Currently, about 400 million people are using desalinated water and it has been projected that by 2025, 14 percent of the global population will be forced to use sea water,” said Md. Eaqub Ali, corresponding author of the paper presenting the current problems and future challenges in water treatments.

Existing desalination plants rely on reverse osmosis, vacuum distillation, or a combination of the two, he explained. But those methods are energy intensive, and that’s where the potential for carbon nanotube membranes comes in.

Carbon nanotubes are teeny tiny hexagonal tubes, made by rolling sheets of graphene, said Rasel Das, first author of the paper. They require little energy and can be designed to specifically reject or remove not only salt, but also common pollutants.

“The hollow pores of the CNTs are extremely, extremely tiny,” Ali said. “However, because of their amazing chemical and physical properties, they allow frictionless passes of water through the pores, but reject most salts, ions, and pollutants, giving us purified water, probably in its best form.” An array of carbon nanotubes (red) forming a membrane that is highly permeable to water (blue surface), but not sodium (yellow) and chloride (green) ions.Carbon Nanotube 072515 II Figure_1

That frictionless property is what gives CNTs the potential to purify water with so little energy. And carbon nanotube membranes come with other perks, Das added, including self-cleaning properties.

“What makes CNTs special is that they have cytotoxic properties,” he said. That means that the membranes naturally kill microbes that might otherwise foul up their surfaces. As a result, carbon nanotube membranes have the potential to last longer much longer than those in use today.

There are hurdles yet to overcome, co-author of the paper Sharifah Bee Abd Hamid said. The CNT membranes themselves are now costly to produce, especially for large-scale uses. Research is also needed to produce the membranes with pores of a more uniform distribution and size.

“Most progress in desalination research is focused on demonstrating the capability of CNT membranes at a small scale,” she said.

For larger scale operations, work is needed to produce CNT membranes on thin films or fiber cloth composites. Getting CNT membranes ready for use will require effort on material design, operational requirements, and more.

If someday, these membranes can be put to use in water-filtering pitchers or bottles, “to directly treat salty water at point of use,” Hamid says, “it is a dream come true for many.”

Did you know?

Only 2 percent of the water on Earth comes in the form of freshwater. Of that 2 percent, 70 percent is snow and ice, 30 percent is hidden underground, and less than 0.5 percent is found in surface waters including lakes, ponds and rivers.


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