Desalinating seawater can require a lot of energy or specialized engineering. A thin membrane made of porous wood may be able to simplify the process.
In membrane desalination, the salt water is pumped through a film, usually made of some type of polymer with very narrow pores that filter out the salt and only allow water molecules to pass through. Jason Ren of Princeton University in New Jersey and his colleagues developed a new type of membrane made from natural wood instead of plastic.
If you think about traditional water filtration, it takes very high pressure pumping to squeeze the water out, so it is very energy consuming. This is more energy efficient and does not use fossil fuel based materials like many other membranes for water filtration.
The membrane of your equipment is made from a fine piece of basswood, which undergoes chemical treatment to remove extra fibers from the wood and make its surface slippery for water molecules. One side of the membrane is heated so that when water flows through that side it vaporizes.
The water vapor then travels through the pores of the membrane to its cooler side and leaves the salt behind, condensing as fresh water. This requires much less energy than simply boiling all of the salt water because there is no need to maintain a high temperature for more than a thin layer of water at a time, Ren says.
This system filters about 20 kg of water per square meter of membrane per hour, which is not as fast as polymeric membranes. The researchers think this may be because they did not have the equipment to make their membrane so thin – it is 500 microns thick, whereas polymer membranes are generally closer to 130 microns thick.
Making wood membranes thinner shouldn’t be too difficult with the right equipment, says Ren. ” The functional part of the membrane is one micrometer thick, ” he says. “ The rest is just a support structure to make it harder to break. “
More information: advances.sciencemag.org