Based upon an international workshop, this perspective evaluates how nano-scale pore structures and unique properties that emerge at nano- and sub-nano- size domains could improve the energy efficiency and selectivity of electroseparation or electrocatalytic processes for treating potable or waste waters.
An Eisenhower matrix prioritizes the urgency or impact of addressing potential barriers or opportunities. There has been little optimization of electrochemical reactors to increase mass transport rates of pollutants to, from, and within electrode surfaces, which become important as nano-porous structures are engineered into electrodes. A “trap-and-zap” strategy is discussed wherein nanostructures (pores, sieves, and crystal facets) are employed to allow localized concentration of target pollutants relative to background solutes (i.e., localized pollutant trapping).
The trapping is followed by localized production of tailored reactive oxygen species to selectively degrade the target pollutant (i.e., localized zapping). Frequently overlooked in much of the electrode-material development literature, nano-scale structures touted to be highly “reactive” towards target pollutants may also be the most susceptible to material degradation (i.e., aging) or fouling by mineral scales that form due to localized pH changes.
A need exists to study localized pH and electric-field related aging or fouling mechanisms and strategies to limit or reverse adverse outcomes from aging or fouling. This perspective provides examples of the trends and identifies promising directions to advance nano-materials and engineering principles to exploit the growing need for near chemical-free, advanced oxidation/reduction or separation processes enabled through electrochemistry.
CONTRIBUTORS – NEWT (Nano Enabled Water Treatment)
In this special anniversary episode of Stories from the NNI, Dr. Lisa Friedersdorf, Director of NNCO, talks to Prof. Pedro Alvarez, of Rice University. Pedro and Lisa discuss the role nanotechnology plays in water security, exciting research results and applications, and his thoughts on the NNI.
Specks of titanium dioxide adhere to polyvinyl fibers in a mat developed at the Rice University-led NEWT Center to capture and destroy pollutants from wastewater or drinking water. After the mat attracts and binds pollutants, the titanium dioxide photocatalyst releases reactive oxygen species that destroy them. Credit: Rice University/NEWT
A polymer mat developed at Rice University has the ability to fish biologically harmful contaminants from water through a strategy known as “bait, hook and destroy.”
Tests with wastewater showed the mat can efficiently remove targeted pollutants, in this case a pair of biologically harmful endocrine disruptors, using a fraction of the energy required by other technology. The technique can also be used to treat drinking water.
The mat was developed by scientists with the Rice-led Nanotechnology-Enabled Water Treatment (NEWT) Center. The research is available online in the American Chemical Society journal Environmental Science and Technology.
The mat depends on the ability of a common material, titanium dioxide, to capture pollutants and, upon exposure to light, degrade them through oxidation into harmless byproducts.
Titanium dioxide is already used in some wastewater treatment systems. It is usually turned into a slurry, combined with wastewater and exposed to ultraviolet light to destroy contaminants. The slurry must then be filtered from the water.
The NEWT mat simplifies the process. The mat is made of spun polyvinyl fibers. The researchers made it highly porous by adding small plastic beads that were later dissolved with chemicals. The pores offer plenty of surface area for titanium oxide particles to inhabit and await their prey.
The mat’s hydrophobic (water-avoiding) fibers naturally attract hydrophobic contaminants like the endocrine disruptors used in the tests. Once bound to the mat, exposure to light activates the photocatalytic titanium dioxide, which produces reactive oxygen species (ROS) that destroy the contaminants.
Established by the National Science Foundation in 2015, NEWT is a national research center that aims to develop compact, mobile, off-grid water-treatment systems that can provide clean water to millions of people who lack it and make U.S. energy production more sustainable and cost-effective.
NEWT researchers said their mat can be cleaned and reused, scaled to any size, and its chemistry can be tuned for various pollutants.
“Current photocatalytic treatment suffers from two limitations,” said Rice environmental engineer and NEWT Center Director Pedro Alvarez. “One is inefficiency because the oxidants produced are scavenged by things that are much more abundant than the target pollutant, so they don’t destroy the pollutant.
The Rice University-led NEWT Center created a nanoparticle-infused polymer mat that both attracts and destroys pollutants in wastewater or drinking water. A mat, top left, is immersed in water with methylene blue as a contaminant. The contaminant is then absorbed at top right by the mat and, in the bottom images, destroyed by exposure to light. The mat is then ready for reuse. Credit: Rice University/NEWT
“Second, it costs a lot of money to retain and separate slurry photocatalysts and prevent them from leaking into the treated water,” he said. “In some cases, the energy cost of filtering that slurry is more than what’s needed to power the UV lights.
“We solved both limitations by immobilizing the catalyst to make it very easy to reuse and retain,” Alvarez said. “We don’t allow it to leach out of the mat and impact the water.”
Alvarez said the porous polymer mat plays an important role because it attracts the target pollutants. “That’s the bait and hook,” he said. “Then the photocatalyst destroys the pollutant by producing hydroxyl radicals.”
“The nanoscale pores are introduced by dissolving a sacrificial polymer on the electrospun fibers,” lead author and former Rice postdoctoral researcher Chang-Gu Lee said. “The pores enhance the contaminants’ access to titanium dioxide.”
The experiments showed dramatic energy reduction compared to wastewater treatment using slurry.
“Not only do we destroy the pollutants faster, but we also significantly decrease our electrical energy per order of reaction,” Alvarez said. “This is a measure of how much energy you need to remove one order of magnitude of the pollutant, how many kilowatt hours you need to remove 90 percent or 99 percent or 99.9 percent.
“We show that for the slurry, as you move from treating distilled water to wastewater treatment plant effluent, the amount of energy required increases 11-fold. But when you do this with our immobilized bait-and-hook photocatalyst, the comparable increase is only two-fold. It’s a significant savings.”
The mat also would allow treatment plants to perform pollutant removal and destruction in two discrete steps, which isn’t possible with the slurry, Alvarez said. “It can be desirable to do that if the water is murky and light penetration is a challenge. You can fish out the contaminants adsorbed by the mat and transfer it to another reactor with clearer water. There, you can destroy the pollutants, clean out the mat and then return it so it can fish for more.”
Tuning the mat would involve changing its hydrophobic or hydrophilic properties to match target pollutants. “That way you could treat more water with a smaller reactor that is more selective, and therefore miniaturize these reactors and reduce their carbon footprints,” he said. “It’s an opportunity not only to reduce energy requirements, but also space requirements for photocatalytic water treatment.”
Alvarez said collaboration by NEWT’s research partners helped the project come together in a matter of months. “NEWT allowed us to do something that separately would have been very difficult to accomplish in this short amount of time,” he said.
“I think the mat will significantly enhance the menu from which we select solutions to our water purification challenges,” Alvarez said.
More information: Chang-Gu Lee et al, Porous electrospun fibers embedding TiO2 for adsorption and photocatalytic degradation of water pollutants, Environmental Science & Technology (2018). DOI: 10.1021/acs.est.7b06508
Rice University’s indium-palladium nanoparticle catalysts clean nitrates from drinking water by converting the toxic molecules into air and water. Credit Jeff Fitlow/Rice University
A simple, one-step catalyst could help yield cleaner drinking water with less nitrates.
A team from Rice University’s Nanotechnology Enabled Water Treatment (NEWT) Center have discovered that a catalyst made from indium and palladium can clean toxic nitrates from drinking water by converting them into air and water.
“Indium likes to be oxidized,” co-author Kim Heck, a research scientist at Rice, said in a statement. “From our in situ studies, we found that exposing the catalysts to solutions containing nitrate caused the indium to become oxidized.
“But when we added hydrogen-saturated water, the palladium prompted some of that oxygen to bond with the hydrogen and form water, and that resulted in the indium remaining in a reduced state where it’s free to break apart more nitrates,” she added.
In previous research, the researchers discovered that gold-palladium nanoparticles were not good catalysts for breaking apart nitrates. This led to the discovery of indium and palladium as a suitable catalyst.
“Nitrates are molecules that have one nitrogen atom and three oxygen atoms,” Rice chemical engineer Michael Wong, the lead scientist on the study, said in a statement. “Nitrates turn into nitrites if they lose an oxygen, but nitrites are even more toxic than nitrates, so you don’t want to stop with nitrites. Moreover, nitrates are the more prevalent problem.
“Ultimately, the best way to remove nitrates is a catalytic process that breaks them completely apart into nitrogen and oxygen or in our case, nitrogen and water because we add a little hydrogen,” he added. “More than 75 percent of Earth’s atmosphere is gaseous nitrogen, so we’re really turning nitrates into air and water.”
Nitrates, which could also be a carcinogenic, are considered toxic to both infants and pregnant women.
Nitrate pollution is common in agricultural communities, especially in the U.S. Corn Belt and California’s Central Valley, where fertilizers are heavily used. Studies have shown that nitrate pollution is on the rise because of changing land-use patterns.
The Environmental Protection Agency regulates allowable limits both nitrates and nitrites for safe drinking water. In communities with polluted wells and lakes, that typically means pretreating drinking water with ion-exchange resins that trap and remove nitrates and nitrites without destroying them.
“Nitrates come mainly from agricultural runoff, which affects farming communities all over the world,” Wong said. “Nitrates are both an environmental problem and health problem because they’re toxic.
“There are ion-exchange filters that can remove them from water, but these need to be flushed every few months to reuse them, and when that happens, the flushed water just returns a concentrated dose of nitrates right back into the water supply.”
The researchers will now try to develop a commercially viable water-treatment system.
“That’s where NEWT comes in,” Wong said. “NEWT is all about taking basic science discoveries and getting them deployed in real-world conditions.
“This is going to be an example within NEWT where we have the chemistry figured out, and the next step is to create a flow system to show proof of concept that the technology can be used in the field,” he added.
Clusters of nanoparticles with phage viruses attached find and kill Escherichia coli bacteria in a lab test at Rice University.
Abstract:
Magnetic nanoparticle clusters have the power to punch through biofilms to reach bacteria that can foul water treatment systems, according to scientists at Rice University and the University of Science and Technology of China.
Magnetized viruses attack harmful bacteria: Rice, China team uses phage-enhanced nanoparticles to kill bacteria that foul water treatment systems.
Researchers at Rice and the University of Science and Technology of China have developed a combination of antibacterial phages and magnetic nanoparticle clusters that infect and destroy bacteria that are usually protected by biofilms in water treatment systems. (Credit: Alvarez Group/Rice University)
The nanoclusters developed through Rice’s Nanotechnology-Enabled Water Treatment (NEWT) Engineering Research Center carry bacteriophages – viruses that infect and propagate in bacteria – and deliver them to targets that generally resist chemical disinfection.
Without the pull of a magnetic host, these “phages” disperse in solution, largely fail to penetrate biofilms and allow bacteria to grow in solution and even corrode metal, a costly problem for water distribution systems.
The Rice lab of environmental engineer Pedro Alvarez and colleagues in China developed and tested clusters that immobilize the phages. A weak magnetic field draws them into biofilms to their targets.
The research is detailed in the Royal Society of Chemistry’s Environmental Science: Nano.
“This novel approach, which arises from the convergence of nanotechnology and virology, has a great potential to treat difficult-to-eradicate biofilms in an effective manner that does not generate harmful disinfection byproducts,” Alvarez said.
Biofilms can be beneficial in some wastewater treatment or industrial fermentation reactors owing to their enhanced reaction rates and resistance to exogenous stresses, said Rice graduate student and co-lead author Pingfeng Yu. “However, biofilms can be very harmful in water distribution and storage systems since they can shelter pathogenic microorganisms that pose significant public health concerns and may also contribute to corrosion and associated economic losses,” he said.
The lab used phages that are polyvalent – able to attack more than one type of bacteria – to target lab-grown films that contained strains of Escherichia coli associated with infectious diseases and Pseudomonas aeruginosa, which is prone to antibiotic resistance.
The phages were combined with nanoclusters of carbon, sulfur and iron oxide that were further modified with amino groups. The amino coating prompted the phages to bond with the clusters head-first, which left their infectious tails exposed and able to infect bacteria.
The researchers used a relatively weak magnetic field to push the nanoclusters into the film and disrupt it. Images showed they effectively killed E. coli and P. aeruginosa over around 90 percent of the film in a test 96-well plate versus less than 40 percent in a plate with phages alone.
The researchers noted bacteria may still develop resistance to phages, but the ability to quickly disrupt biofilms would make that more difficult. Alvarez said the lab is working on phage “cocktails” that would combine multiple types of phages and/or antibiotics with the particles to inhibit resistance.
Graduate student Ling-Li Li of the University of Science and Technology of China, Hefei, is co-lead author of the paper. Co-authors are graduate student Sheng-Song Yu and Han-Qing Yu, a professor at the University of Science and Technology of China, and graduate student Xifan Wang and temporary research scientist Jacques Mathieu of Rice.
The National Science Foundation and its Rice-based NEWT Engineering Research Center supported the research.
ERCs produce both transformational technology and innovative-minded engineering graduates. Credit and Larger Version
NSF-funded Nanosystems Engineering Research Center to enable deployment of mobile, efficient water treatment and desalination systems
** NEWT is a joint designated collaboration between Rice University, ASU, UTEP and Yale University
Water, water is everywhere, but we need more drops to drink.
The primary mission of the recently founded Nanotechnology Enabled Water Treatment (NEWT) Center, a consortium based at Rice University and led by environmental engineer Pedro Alvarez, is to produce more drinkable drops where they’re needed the most.
According to Alvarez, treated water is too often unavailable in parts of the world that cannot afford large treatment plants or miles of pipes to deliver it. Moreover, large-scale treatment and distribution uses a great deal of energy. “About 25 percent of the energy bill for a typical city is associated with the cost of moving water,” he said.
The center, funded by a five-year, $18.5 million National Science Foundation (NSF) award was founded to transform the economics of water treatment by using nanotechnology to develop compact, mobile, off-grid systems to provide clean water to millions of people around the world. A second goal is to make U.S. energy production more sustainable and cost-effective in regards to its water use.
NEWT is the first NSF Engineering Research Center (ERC) based in Houston. ERCs are interdisciplinary, multi-institutional centers that join academia, industry and government in partnership to produce both transformational technology and innovative-minded engineering graduates primed to lead the global economy. ERCs often become self-sustaining and typically leverage more than $40 million in federal and industry research funding during their first decade.
Water has long been a passion for Alvarez, who studies treatment and reuse, remediation strategies for contaminated aquifers and the water footprints of biofuels. His work also covers the environmental implications of using nanotechnology, and the transport — and eventual fate of — toxic chemicals in the environment. As NEWT director, he partners with researchers at Arizona State University (ASU), Yale University and the University of Texas at El Paso.
The consortium set as its first goal the development of modular water treatment systems that can deploy almost anywhere in the world. But Alvarez said the potential to make a significant impact is already expanding, with opportunities to address wastewater treatment at oil and gas drilling sites, nano-infused desalination in urban environments, and improved water treatment through more efficient filtration at existing plants.
Alvarez paused between classes recently to talk about the center’s plans.
Q. Where do you think NEWT’s greatest impact will be in 10 years?
A. It will be in drinking water, providing cleaner water to millions of people who now lack it. I think it’s going to be in developing small, portable units that will not only provide humanitarian water but also emergency response.
There will be other Flints. There will be other Elk River spills that will impact municipalities and water. I think we will be able to respond to those things.
We will probably have tremendous impact on desalination. Low-energy desalination will be one of our hallmarks, I believe. Of course, we will be very good also at treating some of the oil-and-gas water issues, but that’s a more difficult problem.
I expect we’ll also have high institutional impact because people may be more ready to consider unconventional water sources using portable systems that are easier to deploy. People are going to start considering more and more decentralized water-treatment approaches, especially as new cities and neighborhoods and developments evolve.
Q. What kind of sources will your technology be able to treat?
A. Briny ground water, for example, could be a source of drinking water in areas experiencing drought. Or in coastal areas. I think we will see more of that. We’ll see more harvesting of storm water, certainly, and for some uses, even greywater.
Those are the kinds of things our technologies will enable, but it’s not just about technology. It’s about the philosophy of changing to more sustainable, integratable water management, where we reuse more water, where we tap water that we thought was of too low quality but, as it turns out, is perfectly fine and safe and more economical for a sole intended use.
Q. In what directions are the initial projects headed?
A. I think the first thing we’re going to have out there is an adsorbent filter being developed by [NEWT deputy director] Paul Westerhoff at ASU. It’s a block of carbon with embedded nanoparticles. These particles adsorb — that is, they grab onto and hold — oxyanion contaminants like nitrate, arsenic and chromate, and effectively remove them from the water supply. [Oxyanions are negatively charged ions that contain oxygen.] It will be part of a drinking-water treatment unit.
Q. Would the technology apply to large water treatment plants?
A. Yes. Though we originally intended to carve a niche in the decentralized water treatment market, we do aspire to bigger things as our products, materials and processes gain momentum.
I am sure there will be a lot that can be used by the municipal water treatment community. It’s a more difficult industry to penetrate because it’s very conservative. You have to convince them that a technology is going to save them a lot of money and that they don’t have to change too much of the infrastructure or the configuration of the plant.
We have some very good ideas of things that will fit them. If they’re already using membranes for filtration, for example, our membranes may offer better rejection of contaminants and perhaps less susceptibility to being fouled, so they will last longer without having to be replaced. They won’t clog up as easily. They will not use as much energy.
Q. Why did you pursue hosting this NSF center?
A. I think that we as scientists and as engineers, especially in developed countries, have a social debt toward many poor people who lack access to clean water because they are denied the right to a life consistent with their inalienable dignity.
The lack of clean water is a major hindrance to human capacity. It goes beyond public health: It’s directly tied to the need for economic development.
That is certainly one important factor in my passion to provide water to many. It’s related to the concept of world affirmation, the idea that the world can be a better place and we can do something about it. Providing clean water is one way to do it.
The other big incentive was to try to move towards energy self-sufficiency in the United States in a manner that is more cost-effective and more sustainable with regards to the water footprint.
A major challenge for our energy industry is that they need to operate and extract oil and gas in areas that are relatively dry and semi-arid, where water is scarce. And they need relatively large quantities of water to obtain this energy. To get a barrel of oil in Texas, you need about 10 barrels of water. To frack a well to get shale gas or shale oil, you may need up to 6 million gallons of water, again in areas where water is scarce.
Once it’s used, disposal of that water becomes a major challenge and a potentially serious source of pollution. So the solution to both scarcity and minimizing impact is to reuse this water. That’s one of the things we’re trying to do: develop systems that are small and easily deployed that can enable industrial wastewater reuse in remote areas.
Q. What can you do with nanoparticles that you couldn’t have done before?
A. We need to recognize that at the nanoscale, the properties of matter change. Some elements, such as gold, that are very inert can become hypercatalytic at that scale, and materials that are good insulators like carbon can become superconductors.
When you exploit these extraordinary size-dependent properties, it allows you to introduce multifunctionality at both the reactor and materials level. This combination of multifunctionality — for example, membranes that have self-cleaning and self-healing properties — with the nanotechnology-enabled ability to selectively remove pollutants allows you to have smaller reactors. These can treat even unconventional sources of water, difficult sources, that currently would require huge reactors and very large and complex treatment trains that are impossible to take to remote locations.
Making them smaller, multifunctional and modular brings you tremendous versatility to handle a wide variety of challenges in water purification. Nanotechnology allows us to do that. It’s essential to our vision of decentralized water treatment systems.
Q. You’re an environmental engineer who knows aquatic chemistry, and you rely on other kinds of engineers and scientists for different parts of the water systems.
A. Absolutely. This has to be a multidisciplinary collaborative effort to build this innovation ecosystem. We need people who know how to make materials and people who know how to characterize them, how to immobilize them, how to manipulate them — how to assess their reactivity and bioavailability and mobility, and eventually scale them up.
We want people who are good at designing and building reactors all the way to systems to think about the whole lifecycle, the techno-economic implications of these materials, to make sure they’re feasible and improve on current practices.
They have to do it in a way that’s sustainable and avoids unintended, undesirable consequences as well.
Alvarez is the George R. Brown Professor of Environmental Engineering in the Department of Civil and Environmental Engineering at Rice University.
Investigators
Pedro Alvarez
Menachem Elimelech
Naomi Halas
Qilin Li
Paul Westerhoff
Related Institutions/Organizations William Marsh Rice University
Arizona State University
University of Texas-El Paso
Yale University
Some of the world’s most important farming regions rely on freshwater from large underground aquifers that have filled up slowly over thousands of years. Think of the Central Valley aquifer system in California. Or the Indus basin in Pakistan and India. This groundwater is particularly valuable when rain is scarce or during droughts.
But that groundwater may not last forever. Data from NASA’s Grace satellites suggests that 13 of the world’s 37 biggest aquifers are being seriously depleted by irrigation and other uses much faster than they can be recharged by rain or runoff. And, disturbingly, we don’t even know how much water is left in these basins. That’s according to a 2015 paper in Water Resources Research.
The map below gives an overview. There were 21 major groundwater basins — in red, orange, and yellow — that lost water faster than they could be recharged between 2003 and 2013. The 16 major aquifers in blue, by contrast, gained water during that period. Click to enlarge:
The researchers found that 13 basins around the world — fully one-third of the total — appeared to be in serious trouble.
Eight aquifer systems could be categorized as “overstressed”: that is, there’s hardly any natural recharge to offset the water being consumed. In the direst state was the Arabian aquifer system beneath Saudi Arabia and Yemen, which provides water for 60 million people and is being depleted by irrigation for agriculture. Also in bad shape were the Indus Basin that straddles India and Pakistan and the Murzuq-Djado Basin in Africa.
Another five aquifer systems were categorized as “extremely” or “highly” stressed — they’re being replenished by some rainwater, but not nearly enough to offset withdrawals. That list includes the aquifers underneath California’s Central Valley. During California’s recent brutal, five-year drought, many farmers compensated for the lack of surface water by pumping groundwater at increasing rates. (There are few regulations around this, though California’s legislature recently passed laws that will gradually regulate groundwater withdrawals.)
The result? The basins beneath the Central Valley are being depleted, and the ground is actually sinking, which in turn means these aquifers will be able to store less water in the future. Farmers are losing a crucial buffer against both this drought, if it persists, and future droughts.
The big question: How soon until these aquifers run dry?
Here’s the other troubling bit: It’s unclear exactly when some of these stressed aquifers might be completely depleted — no one knows for sure how much water they actually contain.
In a companion paper in Water Resources Research, the researchers took stock of how little we know about these basins. In the highly stressed Northwest Sahara Aquifer System, for instance, estimates of when the system will be fully drained run anywhere from 10 years to 21,000 years. In order to get better measurements, researchers would have to drill down through many rock layers to measure how much water is there — a difficult task, but not impossible.
“We don’t actually know how much is stored in each of these aquifers. Estimates of remaining storage might vary from decades to millennia,” said Alexandra Richey, a graduate student at UC Irvine and lead author on both papers, in a press release. “In a water-scarce society, we can no longer tolerate this level of uncertainty, especially since groundwater is disappearing so rapidly.”
The researchers note that we should figure this out if we want to manage these aquifers properly — and make sure they last for many years to come. Hundreds of millions of people now rely on aquifers that are rapidly being depleted. And once they’re gone, they can’t easily be refilled.
*** Note to Readers: We at Team GNT™ believe very strongly that “Water Solutions for a thirsty Planet” can be and will be enabled by Nanotechnology. Whether those solutions come in the form of Nano Enabled Membrane Technology, Catalyst-Thermal Technology or (Yet To Be Discovered-Developed Technology) … we expect “Great Things from Small Things”! As such we always appreciate “perspective articles” such has been offered here.
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.
Rice University’s indium-palladium nanoparticle catalysts clean nitrates from drinking water by converting the toxic molecules into air and water. Credit Jeff Fitlow/Rice University
Water, water is everywhere, but we need more drops to drink.
Genesis Nanotechnologyo and l o 
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