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MAY 2, 2016 by JOSH RICHARDSON
Global Looming Water Crises Solved With One Simple Invention


It's not rocket science. It's practically elementary for the world's scientists and engineers, but we refuse to adopt a fundamental technology that could transform the world's drinkable water supply. One simple invention when applied to any coastal geographical region will make fresh water scarcity and thing of the past.


When an artificial global crisis is masked by seemingly unconnected regional problems, it's even harder to muster a coordinated global response. Stand next to a river and it seems very much like a local resource. But transnational rivers blur the boundaries and global supply chains complicate them even further.

Less than 1 percent of the Earth's water is drinkable, so do you ever wonder how we have made it this far? Why do we make fresh water such a problem? Freshwater appears to becoming the new oil of the 21st century -- scarce, expensive and fought over. By 2025, the UN expects 14% of the world's population to be encountering water scarcity. Artificial scarcity that is.

Unless you are located in the regions surrounding the great lakes of North America, a large portion of fresh water accessibility use is located outside the borders of most countries worldwide. Half of this externalized water footprint is in countries where water is already scarce. Rivers in southern Europe, Africa and the U.S are slowly drying. Global manufacturing and trade are ravenous drinking straws, sucking at reservoirs, rivers and aquifers wherever they may be.

So What's The Solution?

This appears like a "duh" moment in history and it will likely be seen as such when our successors view our absolute ignorance over fresh water supplies in favor of oil. After all, we can create transport pipeline networks spanning hundreds of miles for oil but can't do the same for water?

Technological advances have made desalination and demineralization feasible solutions for increasing the world's supply of freshwater.

Current desalination plants consume a tremendous amount of electricity many using more than 200-300 million kilowatt-hours each day. Because of their gluttonous energy consumption, desalination plants are nearly always collocated with electrical power generating stations. Most of these archaic plants are based on old technology using outdated vacuum distillation--essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal.

The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology. Membrane processes use semipermeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation.

However, none of these methods will make it out of the next decade, especially with the invention of nanotechnology desalination units. These units will be a fraction of the size of outdated systems and will produce far more drinkable water than all other methods combined.

The Future of Desalination

A team of experimentalists led by the Department of Energy's Oak Ridge National Laboratory has demonstrated an energy-efficient desalination technology that uses a porous membrane made of strong, slim graphene--a carbon honeycomb one atom thick. The results were published in Nature Nanotechnology.

"Our work is a proof of principle that demonstrates how you can desalinate saltwater using free-standing, porous graphene," said Shannon Mark Mahurin of ORNL's Chemical Sciences Division, who co-led the study with Ivan Vlassiouk in ORNL's Energy and Transportation Science Division.

"It's a huge advance," said Vlassiouk, pointing out a wealth of water travels through the porous graphene membrane. "The flux through the current graphene membranes was at least an order of magnitude higher than [that through] state-of-the-art reverse osmosis polymeric membranes."

Making pores in the graphene is key. Without these holes, water cannot travel from one side of the membrane to the other. The water molecules are simply too big to fit through graphene's fine mesh. But poke holes in the mesh that are just the right size, and water molecules can penetrate. Salt ions, in contrast, are larger than water molecules and cannot cross the membrane.

The porous membrane allows osmosis, or passage of a fluid through a semipermeable membrane into a solution in which the solvent is more concentrated. "If you have saltwater on one side of a porous membrane and freshwater on the other, an osmotic pressure tends to bring the water back to the saltwater side. But if you overcome that, and you reverse that, and you push the water from the saltwater side to the freshwater side--that's the reverse osmosis process," Mahurin explained.

Graphene to the rescue. Graphene is only one-atom thick, yet flexible and strong. Its mechanical and chemical stabilities make it promising in membranes for separations. A porous graphene membrane could be more permeable than a polymer membrane, so separated water would drive faster through the membrane under the same conditions, the scientists reasoned. "If we can use this single layer of graphene, we could then increase the flux and reduce the membrane area to accomplish that same purification process," Mahurin said.


Other methods involve efficient and fouling-free desalination process based on the ion concentration polarization (ICP) phenomenon -- a fundamental electrochemical transport phenomenon that occurs when an ion current is passed through ion-selective membranes -- for direct desalination of sea water.

"Our work brings to the field of desalination a novel mechanism for removing salts, which is different from more conventional reverse osmosis or electrodialysis," Jongyoon Han tells Nanowerk. "This new mechanism removes not only salts but also any charged colloids in the source water, such as cells or bacteria, thereby fundamentally eliminating the potential for membrane fouling and clogging. This can significantly reduce the complexity and cost of direct seawater desalination."

Han, an associate professor of Biological Engineering at MIT, explains that this new process has several unique and attractive features for water desalination applications: "It has a power efficiency that more or less matches that of current state-of-the-art reverse osmosis plants. In a single-step operation, 99% of the salt contained in the sea water is removed, with 50% of the incoming sea water being recouped as desalted water.

"Reporting their findings in Nature Nanotechnology ("Direct seawater desalination by ion concentration polarization"), Han's team has demonstrated that an ion concentration polarization zone (ion depletion zone) generated in a microfluidic channel can be used to remove salts from seawater in an energy efficient manner.

"While additional engineering work needs to be done, we think this method eventually can be made into a small scale, portable desalination system," says Han. "Current desalination technology can be quite efficient as well, but only at a large, plant scale operation. Resource-limited areas or disaster-striken areas that are suffering from the shortage of water often do not have necessary desalination plant and electricity / water delivery infrastructure. In those places, and for diverse humanitarian / military applications, such a small scale, portable system could make a difference."

The team's next target is to build a scaled-up version of the current unit device. Instead of making the same device larger, they will duplicate the unit microfluidic device on a wafer scale in order to reach meaningful flow rate (~100mL/min).

Water and civil engineer Christoff Serafino said current technology is all leading to smaller scaled systems which in part will produce medicinal water. "Russian scientists have shown that water can be made into a medicinal fluid by magnetizing it. Downsized desalination systems of the future will embrace nanotechnology once they realize that magnetic nanobots which attach themselves to salts will produce not only drinking water but medicinal water once it passed through the filtration systems," stated Serafino. This could revolutionize water filtration around the world.

Sources:
nature.com
greenprophet.com
phys.org
nanowerk.com

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