Lockheed Martin has found a way to slash the amount of energy needed to remove salt from seawater, potentially making it vastly cheaper to produce clean water at a time when scarcity has become a global security issue. Because the sheets of graphene are so thin – just 1 atom in thickness – it takes much less energy to push the seawater through the filter with the force required to separate the salt from the water.

The material is called Perforene and is mostly vaporware as of 2018:

The potential of graphene to serve as a key material for advanced membranes comes from 1 major possible advantages of this atomically thin 2D material: permeability and selectivity. Graphene-based membranes are also hypothetically attractive based on concentration polarization and fouling, and graphene’s chemical and physical stability. Further research is needed to fully achieve these theoretical benefits, however. In addition, improvement in the design and manufacturing processes, so to produce performance and cost-effective graphene-based desalination devices, is still an open question. Finally, membranes are only one part of desalination systems, and current processes are not optimized to take full advantage of the higher selectivity and permeability of graphene. New desalination processes are, therefore, needed to unlock the full benefits of graphene.

2014-03-04: Graphene membranes

The researchers have now found a strategy to avoid the swelling of the membrane when exposed to water by building smaller sieves. When the common salts are dissolved in water, they form a “shell” of water molecules around the salt molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow faster, which is ideal for application of these membranes for desalination. “Realization 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 technology”

These graphene sheet water filters are a huge deal for desalination and safe drinking water.

Researchers have devised a way of making tiny holes of controllable size in sheets of graphene, a development that could lead to ultrathin filters for improved desalination or water purification. A big limitation in existing nanofiltration and reverse-osmosis desalination plants, which use filters to separate salt from seawater, is their low permeability: Water flows very slowly through them. The graphene filters, being much thinner, yet very strong, can sustain a much higher flow.

2016-08-01: Israel desalination

Amazingly, Israel has more water than it needs. The turnaround started in 2007, when low-flow toilets and showerheads were installed nationwide and the national water authority built innovative water treatment systems that recapture 86% of the water that goes down the drain and use it for irrigation — vastly more than the second-most-efficient country in the world, Spain, which recycles 19%.

But even with those measures, Israel still needed ~1.9b cubic meters of freshwater per year and was getting just 1.4B cubic meters from natural sources. That shortfall was why the Sea of Galilee was draining like an unplugged tub and why the country was about to lose its farms.

The country faces a previously unfathomable question: What to do with its extra water? Enter desalination. Desalination plants can provide some 600m cubic meters of water a year, and more are on the way.

2022-02-28: Salt fouling

“There have been a lot of demonstrations of really high-performing, salt-rejecting, solar-based evaporation designs of various devices. The challenge has been the salt fouling issue, that people haven’t really addressed. So, we see these very attractive performance numbers, but they’re often limited because of longevity. Over time, things will foul.”

Many attempts at solar desalination systems rely on some kind of wick to draw the saline water through the device, but these wicks are vulnerable to salt accumulation and relatively difficult to clean. The team focused on developing a wick-free system instead. The result is a layered system, with dark material at the top to absorb the sun’s heat, then a thin layer of water above a perforated layer of material, sitting atop a deep reservoir of the salty water such as a tank or a pond. A system with just 1m2 of collecting area should be sufficient to provide a family’s daily needs for drinking water, and would cost $4.

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