Researchers from MIT have created a water filter fashioned from a small piece of sapwood, an inexpensive and disposable technology that could help millions of people in the developing world who don’t have access to safe drinking water.
The key ingredient is plant xylem — a tissue in plants made up of vessels and tiny pores. The vessel pathways allow sap to travel up from the tree’s roots to the shoots, while the pores trap air bubbles so they don’t spread into the wood and kill the tree.
“It’s the same problem with water filtration where we want to filter out microbes but maintain a high flow rate,” Rohit Karnik, co-author of the study and an associate professor of mechanical engineering at MIT, said in a media release.
It’s also a coincidence that the size of these xylem pores, anywhere from a few nanometers to 500 nanometers depending on the plant, are the perfect size for blocking out pathogens, researchers said in a study published Wednesday in the journal PLoS One.
For this study, researchers used plant xylem from the branch of white pine trees. The device was made by simply peeling the bark from the branch, cutting it up into inch-long pieces, and shoving it into a plastic tube. They used a simple tube fastener to provide a tight seal.
In the lab, the MIT team found that the tree branch filtered out 99% of E. coli bacteria from water. In an interview with Popular Mechanics, Rick Andrews, global business development director of water systems at the National Sanitation Foundation International, cautioned that the results might be slightly different if conducted in a real-world setting. It’s possible that very polluted water could clog the pores of the tree branch making it less effective.
But the design is still a positive step forward. Because xylem filters are low-tech and made from wood, an easily available material, they could be produced on a small-scale at a much lower cost than current water-disinfecting technologies, such as boiling (which requires lots of fuel), expensive chlorine treatments, and UV lamps, according to the study.
The xylem filters aren’t only applicable in the developing world. Researchers think that sapwood could also be used as a makeshift filter on a camping trip.
“Break off a branch from the nearest pine tree, peel away the bark, and slowly pour lake water through the stick,” they said.
The MIT team is now looking at the xylem tissue of other plants, particularly from locally available sources, to see how well they filter out bacteria and other pathogens.
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