Tag Archives: seawater

Scientists develop battery that taps into ‘blue energy’ formed when freshwater meets seawater

Deer Island wastewater treatment plant. Credit: Wikimedia Commons.

In coastal regions where freshwater mixes with seawater, a salt gradient is formed. Scientists at Stanford University have now found a way to tap into the energy of this gradient, which is sometimes called “blue energy”. The authors envision a future where their technology could be used to make waste-water treatment facilities energy independent.

Energy from moving salt

For every cubic meter of freshwater that mixes with seawater, about .65 kilowatt-hours of energy is produced — just about enough to power the average American home for 30 minutes. All around the world, coastal wastewater treatment plants have access to about 18 gigawatts of blue energy, or the equivalent of powering 1,700 U.S. homes for an entire year.

Other groups have previously succeeded in harnessing blue energy but the Stanford group is the first to employ an electrochemical battery rather than pressure or membranes.

“Blue energy is an immense and untapped source of renewable energy,” said study coauthor Kristian Dubrawski, a postdoctoral scholar in civil and environmental engineering at Stanford. “Our battery is a major step toward practically capturing that energy without membranes, moving parts or energy input.”

The group was led by Craig Criddle, a professor of civil and environmental engineering, who has a lifetime of experience developing technologies for wastewater treatment. The battery developed by Criddle and colleagues first releases sodium and chloride ions from the device’s electrodes into a solution, making a current flow between the electrodes. When wastewater effluent and seawater are combined, the electrodes reincorporate sodium and chloride ions, reversing the current flow. According to the researchers, energy is recovered during both freshwater and seawater flushes. There is no initial energy investment required, nor is there any need for charging. In other words, this is a passive energy system that doesn’t require any input of energy.

The power output is relatively low per electrode area, but the authors highlight the fact that their technology’s strong point lies in its simplicity. The blue energy capturing device doesn’t have any moving parts and passively generates energy without the need for any external instruments to control voltage or charge. The electrodes are manufactured from Prussian Blue, a material widely used in medicine, which costs less than a $1 per kilogram, as well as polypyrrole, which costs less than $3 a kilogram.

If the technology is scaled, it should prove robust enough to provide energy for any coastal treatment plant in the world. Any surplus production could then be diverted to other nearby applications, such as desalination plants. A scaled version that could someday be used in a municipal wastewater plant is currently being designed by the Stanford researchers.

“It is a scientifically elegant solution to a complex problem,” Dubrawski said. “It needs to be tested at scale, and it doesn’t address the challenge of tapping blue energy at the global scale – rivers running into the ocean – but it is a good starting point that could spur these advances.”

The findings appeared in the American Chemical Society’s ACS Omega.

Alan Turing. Credit: Public Domain.

Alan Turing’s final paper inspires new way to desalinate water

Alan Turing. Credit: Public Domain.

Alan Turing. Credit: Public Domain.

Alan Turing is famous as the father of computer science and artificial intelligence, as well as a WWII code breaker. However, Turing was also heavily involved in what was, at the time, an obscure field of science: mathematical biology. In 1952, just two years before his death, the brilliant British scientist published a paper in which he proposed a mathematical model that finally described how embryonic cells turn into complex structures like organs or bones. Now, Chinese researchers have built a unique nanostructure of tubular strands inspired by Turing’s work in mathematical biology. They’ve incorporated the structure into a filter that removes salt from water three times faster than some conventional filters.

Dot-based and tube-based Turing-type membranes (imaged with electron microcope). Credit: Z. Tan et al./Science

Dot-based and tube-based Turing-type membranes (imaged with electron microcope). Credit: Z. Tan et al./Science

Turing structures arise when imbalances in diffusion rates make a stable steady-state system sensitive to small heterogeneous perturbations. For example, Turing patterns occur in chemical reactions when a fast-moving inhibitor controls the motion of a slower-moving activator. The motion causes the inhibitor to push back the activator, causing a pattern of spots or stripes to appear on the product. It’s not clear whether this reaction-diffusion process does indeed take place at the cellular level, but previously scientists have used it to explain zebra stripes, sand ripples, and the movements of financial markets.

Attempts to synthesize such structures have so far been confined to 2D patterns. Now, thanks to the marvels of 3D printing, a team of researchers at Zhejiang University in Hangzhou, China have created a 3D Turing structure out of a polyamid (a material similar to nylon). The substance is the result of the reaction between piperazine and trimesoyl chloride. In typical conditions, trimesoyl chloride diffuses faster than piperazine but not fast enough to result in a Turing structure. The researchers, led by material scientist Lin Zhang, used a nifty trick: they added polyvinyl alcohol to the piperazine, further lowering its diffusion rate and allowing it to act as the activator to the trimesoyl chloride’s inhibitor.

The resulting material is a rough, porous mesh with a nanostructure resembling a Turing pattern. The Chinese researchers were even able to print two variants: dots and tubes. These are the two types of self-organizing structure predicted by Turing’s model.

The primary objective of the new study was to produce 3D Turing structures. However, the researchers were amazed to learn that membranes fashioned this way were incredibly efficient water filters. Due to the filter’s tubular structure, water can pass through a much larger surface area compared to conventional filters. In experiments, the amount of table-salt inside a slightly saline solution passing through the Turing filter was reduced by half. The Turing filter proved much more efficient with other salts: magnesium chloride was reduced by more than 90%, and magnesium sulfate (aka Epsom salt) was reduced by more than 99%, as reported in the journal  Science.

The membranes may be impractical on their own for desalinating seawater due to the rather low effectiveness for this purpose. Zhang, however, says it could be used to pretreat the seawater before eliminating the rest of the salt via reverse osmosis, which would make the overall process much more efficient. The tubular Turin filter could also be useful for purifying brackish water and industrial wastewater. And perhaps, in the future, the tubular Turing structures could be used to fashion artificial veins or bones. Turing would have been so proud!

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.


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.

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.