Tag Archives: desalinization

US and Chinese researchers develop cheap solar still to produce drinking water

A team of researchers from the US and China has developed a passive, solar-powered desalinization system that could quench the thirst of remote, arid coastal areas on the cheap.

Image credits Zhenyuan Xu et al., (2020), Energy Environ. Sci.

The system employs several layers of solar evaporators and condensers stacked on top of each other in a vertical array, topped off with an insulating layer of (transparent) aerogel.

Salt-B-gone

“When you condense water, you release energy as heat,” says corresponding author Evelyn Wang, professor of mechanical engineering and head of the Department of Mechanical Engineering at MIT. “If you have more than one stage, you can take advantage of that heat.”

The system uses heat released by each layer to take salt out of seawater, eventually yielding drinkable water. Essentially, it’s a series of solar-powered liquor stills all working in tandem — the energy released by each layer (or ‘stage’) is captured by the next one and re-used. The team showed that their rig can achieve a very impressive 385% conversion rate of sunlight into energy used to evaporate water.

The flat panels absorb heat from sunlight and transfer it to the water, making it evaporate. As the vapor rises, it encounters the next stage, where it condenses on the surface of a new panel. This also helps to transfer heat from the vapor to the receiving panel. Turning water vapor into liquid is as simple as cooling it down; in a traditional still, waste heat from the vapor is released into the environment. The team designed their multi-layered evaporator specifically to retain and reuse this energy, boosting its overall efficiency and speed.

In theory, extra layers can be added to make the system even more efficient at churning our drinkable water, but each layer means more cost and weight. They settled on a 10-stage evaporator as an acceptable compromise between cost and efficiency and installed it on an MIT building rooftop.

They report that the device yielded 5.78 liters per square meter of solar collecting area (1.52 gallons per 11 square feet) per hour, or about twice as much as any other passive solar-powered desalinization system, according to Wang. The still showed no signs of salt accumulation and didn’t produce any brines that needed to be disposed of, the team adds, meaning that the still can be set out in “a free-floating configuration” during the day

The device is still at a proof-of-concept stage, and the team plans to further refine it — they plan to double its efficiency. It’s also built from inexpensive materials, such as a commercial black solar absorber and paper towels. The aerogen layer on top is the single most expensive component, but the team says less expensive insulators could be used as an alternative.

Ultimately, the team plans to scale-up their device and tailor it for commercial use. They hope the still — which they call a thermally localized multistage desalination system — will help provide drinking water for developing areas that lack reliable electricity but have ample seawater and sun.

The paper “Ultrahigh-efficiency desalination via a thermally-localized multistage solar still” has been published in the journal Energy & Environmental Science.

Scientists find new way of desalinating water

The challenge of guaranteeing a regular supply of freshwater has led to many cities across the world to turn to desalination, taking mineral components from saline water. But the process can be expensive and complex. Now, scientists at Berkeley Lab might have found a way around it.

Credit: Flickr

Researchers have investigated how to make desalination less expensive and discovered promising design rules for making so-called “thermally responsive” ionic liquids to separate water from salt. The work was published in the journal Nature Communications Chemistry.

Useful in forward osmosis to separate contaminants from water, ionic liquids are a liquid salt that binds to water. Even better are thermally responsive ionic liquids as they use thermal energy rather than electricity, which is required by conventional reverse osmosis (RO) desalination for the separation.

The new Berkeley Lab study studied the chemical structures of several types of ionic liquid/water to determine what “recipe” would work best.

“Our study shows that the use of low-cost “free” heat—such as geothermal or solar heat or industrial waste heat generated by machines—combined with thermally responsive ionic liquids could offset a large fraction of costs that go into current RO desalination technologies that solely rely on electricity,” said Robert Kostecki, co-author of the study.

Kostecki partnered with co-corresponding author Jeff Urban to investigate the behavior of ionic liquids in the water at the molecular level. Using nuclear magnetic resonance spectroscopy, dynamic light scattering, and molecular dynamics simulation techniques, the team made an unexpected finding.

According to Urban, it was long thought that an effective ionic liquid separation relied on the overall ratio between organic components (parts of the liquid neither positively nor negatively charged) and its positively charged ions. But, as part of their research, the team at Berkeley discovered that the number of water molecules an ionic liquid can separate from seawater depends on the proximity of its organic components to its positively charged ions.

“This result was completely unexpected,” Urban said. “With it, we now have rules of design for which atoms in ionic liquids are doing the hard work in desalination.”

Thanks to the investigation, a decades-old membrane-based reverse osmosis technology is now experiencing a resurgence. There are 11 desalination plants in California, and more have been proposed. Berkeley Lab scientists are pursuing a range of technologies for improving the reliability of the U.S. water system.

“Our study is an important step toward lowering the cost of desalination,” said Kostecki. “It’s also a great example of what’s possible in the national lab system, where interdisciplinary collaborations between the basic sciences and applied sciences can lead to creative solutions to hard problems benefiting generations to come.”

As the climate crisis continues to take its toll, water availability is becoming a severe issue in many parts of the world. Technologies like this offer new hope to address those issues.

Credit: Max Pixel.

New desalinization technique separates seawater into freshwater and lithium

A new desalinization technique can not only turn seawater into delicious freshwater but also recover lithium ion for use in batteries.

Credit: Max Pixel.

Credit: Max Pixel.

You might have come across the viral story that follows Cape Town’s impending water crisis, which threatens millions. The South African city isn’t alone — it’s a heartbreaking story, but it’s just one of many other cases happening due to poor water management and unsustainable usage.

Earth, the pale blue dot, looks like a watery paradise from outer space. It sounds ludicrous that there isn’t enough water to go around but, despite covering about 70% of the Earth’s surface, water — particularly, drinking water — is not as plentiful as you might think. Only 3% of it is fresh.

Due to population growth, climate change, and human action, global demand for fresh water is expected to exceed supply by 40% in 2030, according to a UN report. Already, over one billion people lack access to drinkable water and another 2.7 billion find it scarce for at least one month of the year.

Bearing all of this in mind, it’s no wonder that many institutions and companies have been wildly experimenting with desalinization farms all over the world, particularly in countries vulnerable to droughts. Some of these projects cross the boundaries between reality and science fiction, such as The Pipe — a solar-powered offshore desalination plant that could serve pure drinkable water directly into a Californian city’s primary water piping.

https://www.youtube.com/watch?time_continue=49&v=vLgmFRceoVE

Typical desalination plant process. 

From salty to fresh in one pass

Researchers at Monash University, the CSIRO, and the University of Texas at Austin think they have a more efficient solution. Instead of relying on external power to drive reverse osmosis pumps, the team is experimenting with a more passive desalinization technique.

A scanning electron microscope image of metal-organic frameworks used to seaparate seawater into freshwater and lithium. Credit: CSIRO.

A scanning electron microscope image of metal-organic frameworks used to separate seawater into freshwater and lithium. Credit: CSIRO.

They developed a membrane based on metal-organic frameworks (MOFs), inspired by the “ion selectivity” of biological cell membranes. The scientists designed their membrane such that the MOFs only dehydrate specific ions that pass through passively, without having the water forced into the membrane, thus saving energy.

“We can use our findings to address the challenges of water desalination. Instead of relying on the current costly and energy-intensive processes, this research opens up the potential for removing salt ions from water in a far more energy efficient and environmentally sustainable way,” Huanting Wang, a professor at Monash, said in a statement.

Not only does the MOF membrane output clean, drinkable water, but it also filters out lithium from the seawater. The lithium stays embedded within the membrane’s spongy structure, ready to be collected. Lithium is in high demand by the electronics industry which requires it for lithium-ion batteries, the kind that power everything from smartphones to Tesla roadsters.

“Also, this is just the start of the potential for this phenomenon. We’ll continue researching how the lithium ion selectivity of these membranes can be further applied. Lithium ions are abundant in seawater, so this has implications for the mining industry who current use inefficient chemical treatments to extract lithium from rocks and brines,” Wang added.

MOFs have a huge internal surface area — the largest of any known material. If you’d unfold a single gram of the material, you could cover an entire football field. Previously, researchers have exploited MOFs’ intricate structure in carbon emission sponges, high-precision sensors, microbial water filters, and even artificial photosynthesis reactors that produce liquid fuels literally out of thin air. 

The same technique could also be employed in other applications, particularly in waste management. The mining industry, for instance, relies on reverse osmosis membranes to reduce water pollution and recover valuable minerals. Likewise, reverse osmosis is used by the industry to filter wastewater in processes like fracking.

“Produced water from shale gas fields in Texas is rich in lithium,” says Benny Freeman, co-author of the study. “Advanced separation materials concepts such as ours could potentially turn this waste stream into a resource recovery opportunity.”

The findings have been published in  Science Advances.

Researchers describe improved technique to extract water from brine

Engineers working in the US have found a way to extract almost 100% of the water from brine, up from 6%. This innovation can alleviate water shortages in parts of the world where water is scarce, but it can also reduce the high salinity of disposable waste (ie in hydraulic fracking).

Hot brines used in traditional membrane distillation systems are highly corrosive, making the heat exchangers and other system elements expensive, and limiting water recovery. Now, researchers have developed a new mechanism which is not only cheaper but also more efficient than previously existing options. Image credits: UC Riverside.

Water shortage is no joke. As the world population continues to grow, more and more areas use water unsustainably and are almost certainly set for a future water crisis. In these conditions, desalination becomes more and more a tempting option, as Israel has been demonstrating for a few years already. Still, the process can be significantly improved, as a team from University of California, Riverside, has proven.

The team has developed a carbon nanotube heating element, vastly improving the recovery of fresh water during membrane distillation processes. Describing the new approach in the journal Nature Nanotechnology. David Jassby, an assistant professor of chemical and environmental engineering in UCR’s Bourns College of Engineering explains that previously, the recovery rate was capped at a much lower figure.

“In an ideal scenario, thermal desalination would allow the recovery of all the water from brine, leaving behind a tiny amount of a solid, crystalline salt that could be used or disposed of,” Jassby said. “Unfortunately, current membrane distillation processes rely on a constant feed of hot brine over the membrane, which limits water recovery across the membrane to about 6 percent.”

Most desalinization facilities use reverse osmosis, but the more salt you have in the water, the less efficient this process becomes. When dealing with brines, reverse osmosis becomes highly inefficient.

While such brines are rarely prevalent naturally, they are often produced as waste and must be disposed of to prevent environmental damage. What Jassby and his collaborators did not only ensure that all the water is desalinized, but it also reduces the necessary heat for the process, and thus saves a lot of energy.

The study has another interesting outcome — hot, briny water is a highly corrosive environment, and in order to develop this device, they also had to make sure that the parts can survive and operate properly for a longer period of time. Specifically, a threshold frequency was identified where electrochemical oxidation of the nanotubes was prevented.

Journal Reference: Alexander V. Dudchenko, Chuxiao Chen, Alexis Cardenas, Julianne Rolf & David Jassby — Frequency-dependent stability of CNT Joule heaters in ionizable media and desalination processes.  doi:10.1038/nnano.2017.102

Credit: Land Art Generator Initiative

Meet the Pipe: a beautiful desalinization plant that might one day serve 1.5 billion gallons of water to California

Credit: Land Art Generator

Credit: Land Art Generator Initiative

Khalili Engineers from Canada came up with an innovative solution — and a strikingly beautiful one to boot — to California’s growing water shortage problem. Their solution is “The Pipe” — a solar-powered offshore desalination plant that could serve pure drinkable water into the city’s primary water piping.

The company that designed the Pipe say the huge structure would employ electromagnetic desalination, which is a cheaper, simpler method than those currently used in mainstream engineering. The technology, which is only three years old, involves running a voltage through a chip filled with seawater, which then neutralizes chloride ions in the seawater creating “ion depletion zones”. This change in the electric field is sufficient to redirect salts into one branch, allowing desalinated water to pass through the other branch.

The Pipe

Credit: Land Art Generator Initiative

To power this process, Khalili engineers claim all the required energy would be supplied by solar panels that can generate 10,000 MWh each year. In turn, the Pipe uses this energy to produce 4.5 billion liters (1.5 billion gallons) of drinking water from the sea, as well as clear water with twelve percent salinity.

“The drinking water is piped to shore, while the salt water supplies the thermal baths before it is redirected back to the ocean through a smart release system, mitigating most of the usual problems associated with returning brine water to the sea,” Khalili Engineers said.

The project is a finalist for this year’s Land Art Generator Initiative, an annual design competition that challenges  artists, architects, scientists, landscape architects, engineers, and others to design sustainable solutions to leading environmental problems. The artistic component has to be there too because the organizers believe problem solving can be enhanced with aesthetics.

Credit: Land Art Generator Initiative

Credit: Land Art Generator Initiative

“The sustainable infrastructure that is required to meet California’s development goals and growing population will have a profound influence on the landscape, ” say Rob Ferry and Elizabeth Monoian, co-founders of the Land Art Generator Initiative, in a press release. “The Paris Climate Accord from COP 21 has united the world around a goal … which will require a massive investment in clean energy infrastructure.”

For now, this project is just a pipe dream, but if there’s interest — and by interest I mean cash — this innovative solution to a very complex problem might one day dock off the shore of some important Californian city.