Transcript
Two-thirds of the Earth’s surface is covered with water. Yet, clean and drinkable water is largely inaccessible to billions of people. Fortunately, that may soon change. A breakthrough purification solution developed by researchers at the Beckman Institute for Advanced Science and Technology was described recently in the journal ACS Energy Letters. It uses an electrified version of dialysis to separate salt and other extraneous particles from the potable product.
The method has been successfully applied to wastewater with planned expansion into rivers and seas. Best of all, it uses 90% less energy than its counterparts. De-salting water usually requires filtration or evaporation to separate out undesirable elements like sodium, chloride, organic matter, and assorted atomic stowaways. Heat, for example, does this trick well — a simple kitchen experiment shows that boiling salted water causes the liquid to evaporate and the salt to abide as a solid, briny crust.
The Beckman team took a different approach: electrodialysis. Just like dialysis of the blood, which, kidney-like, flushes salt and other toxins from our veins, electrodialysis salts and organic matter from wastewater to produce a clean, drinkable product. Electrodialysis is an effective desalination tool, but often comes at a high energy cost. Furthermore, it normally requires charged ion-exchange membranes, so named because only ions (atoms with a positive or negative electric charge) can pass through.
Ion-exchange membranes are one of the costliest components of electrodialysis because they require diligent upkeep and frequent replacement. The researchers sought to purify water without the usual energy toll of electrodialysis or the financial strain of ion-exchange membranes. So, they modified the traditional approach in two major ways.
First, to save energy, the researchers streamlined the salt separation process with a chemical phenomenon called a redox reaction. Physically, triggering a redox reaction involves adding a special polymer-based material to the wastewater before it’s filtered and purified. Chemically, the results are transformative. Instead of splitting water molecules into positively and negatively charged slices to coax out the salt, the redox reaction changes the charge of the entire water molecule in one fell swoop, achieving the same degree of salty separation with about 90% less energy than traditional water-splitting.
Second, to add economic savings beyond energy efficiency, the researchers swapped conventional ion-exchange membranes for nanofiltration membranes, a more robust and less expensive option. Experiments at a regional water treatment plant demonstrated that the researchers’ method can successfully purify wastewater; future plans include expanding into saltwater and brackish water sources like groundwater and rivers.
Due to its low energy requirement, redox-inspired electrodialysis will pair well with solar panels. And it’s positive performance in hot climates makes it useful in many regions where low-cost, low-energy desalination is very much needed. According to the team members, “We have the right polymer, we have the right membrane, and we have the right conditions. The next step is paving a way for deploying these devices for real-world water treatment.”
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