Suramya's Blog : Welcome to my crazy life…

August 7, 2019

Using a slice of wood to make saltwater drinkable

Filed under: My Thoughts,Techie Stuff — Suramya @ 5:45 PM

“Water water everywhere, not a drop to drink” This is an often quoted line from The Rime of the Ancient Mariner by Samuel Taylor Coleridge and is something that is becoming more and more true every day. 71% of earth is covered by Oceans but we still have 2.8 billion people around the world who face water scarcity at least one month out of every year. Earlier this year city officials in Chennai, India declared that “Day Zero” (the day when almost no water is left in the city) had been reached in Chennai, as all the four main reservoirs supplying water to the city had run dry due to deficient monsoon rainfall in the previous years. Due to this finding more ways of generating drinking water a high priority for the Human race. Without water life as we know it can’t exist and our civilization can and will collapse.

One of the ways to solve this issue is to convert sea water to drinkable water by filtering the salt out and there are existing solutions which do this (check out the Saudi water desalination) but they require a lot of energy and/or specialized engineering. But this is about to change thanks to the effort of Jason Ren and his colleagues from Princeton University in New Jersey. They have developed a method that uses a new kind of membrane made of American basswood instead of plastic that enables filtration without requiring high pressure pumping of salt water. Basically they took a thin slice of American basswood and treated it with a chemical bath to remove extra fibers from the wood and make its surface slippery to water molecules. Once the wood is treated water flows down one side of the membrane and is heated to the point that it vaporizes. The vapor then travels through the pores in the membrane toward its colder side leaving the salt behind, condensing as fresh, cool water.

This process takes less energy than simply boiling all of the saltwater because there’s no need to maintain a high temperature for more than a thin layer of water at a time as per Jason Ren. In the initial testing using this method the team was able to filter about 20 kilograms of water per square metre of membrane per hour, which is not quite as quick as polymer membranes but this can improve if the membrane is made thinner.

This is quite a breakthrough and when I first read the article I was not clear why we need to use wood for the process. I mean we can use a polymer membrane and still achieve the same effect by heating only a thin layer of water at a time. But then I spent some time reading the actual research paper and that’s when I realized what a massive breakthrough this was. Basically the current commercial MD membranes have porosity lower than 0.80, thermal conductivity higher than 0.050 W m−1 K−1, and thermal efficiency up to 60% where as the new membrane has a porosity of ~90%, low thermal conductivity (~0.04 W m−1 K−1) and a thermal efficiency of ~71%. These factors combined reduce the energy requirements for desalination by a significant amount.

Now that we have a Proof of Concept that this works, we need to be able to scale this up on a massive scale and work for this is currently ongoing.

Thanks to Newscientist.com for the original link.
Research Paper: Hydrophobic nanostructured wood membrane for thermally efficient distillation

Well this is all for now. Will post more later.

– Suramya

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