Sometimes low-tech solutions make the most sense, particularly in developing countries with limited access to affordable technology. It often happens these same countries experience chronic water shortages, so MIT researchers designed a brilliant solution that relies on nature to clean up after itself. It turns out certain kinds of tree branches, when peeled, rival cilantro’s ability to scrub contaminated water clean of harmful bacteria. In an experiment, they found sapwood is capable of eliminating 99 percent of E.coli bacteria. The same properties that allow xylem tissue to transport sap from a tree’s roots to its crown traps bacteria and other particles over 20 nanometers in size.
“Today’s filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily,” says Rohit Karnik, associate professor of mechanical engineering at MIT. “The idea here is that we don’t need to fabricate a membrane, because it’s easily available. You can just take a piece of wood and make a filter out of it.”
In order to test their theory, MIT researchers first used 1-inch by 1/2-inch bits of white pine xylem tissue inside a plastic tube held together with clamps and epoxy to trap red dye, which has large particles. The bark collected the dye particles, but allowed clean water to trickle through like a cheesecloth. With that success the researchers moved onto bacteria, a more challenging conquest. Once again it was successful. Coniferous sapwood prevents 99 percent of E.coli bacteria from passing through its bark, offering hope for a low-cost water filtration system attainable to people in the developing world.
While this filter is effective with most kinds of bacteria, Karnik says it probably won’t work with viruses, which are significantly smaller. That being said, there are several different kinds of trees which can be used effectively, broadening its usefulness in places where more expensive technologies are not readily available.
“There’s huge variation between plants,” Karnik says. “There could be much better plants out there that are suitable for this process. Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost. It’s orders of magnitude cheaper than the high-end membranes on the market today.”
Images via MIT, Shutterstock