A new report by MIT researchers suggests that if you run out of drinking water in the woods, all you need to do is to break off a branch from the nearest pine tree. Next pour lake water through the branch and this low-tech filtration system can produce up to four liters of drinking water a day. A small piece of sapwood is reportedly able to filter out more than 99% of the bacteria E. coli due to the size of the pores in the xylem tissue.
Co-author Rohit Karnik, an associate professor of mechanical engineering at MIT, says that “sapwood is a promising, low-cost, and efficient material for water filtration, particularly for rural communities where more advanced filtration systems are not readily accessible.”
“Today’s filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily,” Karnik says. “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.”
While there are plenty of water purification technologies on the market today, most rely on chlorine treatment, which works well but is expensive. Boiling water requires fuel, which may not be available in an emergency. Man-made membrane-based filters are expensive and can become easily clogged.
The amazing thing about sapwood is its porous xylem tissue, which conducts sap from a tree’s roots to its crown. This system of vessels and pores contains pit membranes small enough to trap bacteria and keep it from spreading throughout the wood.
“Plants have had to figure out how to filter out bubbles but allow easy flow of sap,” Karnik observes. “It’s the same problem with water filtration where we want to filter out microbes but maintain a high flow rate. So it’s a nice coincidence that the problems are similar.”
Images: James P. Mann/MIT