Researchers have created a simple and more cost effective way to filter water that could revolutionize the way people access clean water around the world.
At a conference, Rohit Karnik found himself fascinated by a scientist’s description of how sap flows through trees. He realized that the way that trees have evolved to prevent air bubbles from forming and blocking their circulatory system might be an effective way of filtering out microscopic pathogens from drinking water.
Karnik and a team that includes a high school teacher and a high school student reported the details last week in the journal PLoS ONE of a water filter that might be effective, cheap, and biodegradable.
“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.”
“There is a community of people who do look at sap flow and drying in plants because it’s obviously important, but that community doesn’t intersect with the water purification community,” Karnik, an associate professor of mechanical engineering at the Massachusetts Institute of Technology told Boston in an interview. “They are thinking about how plants work and not how we can use plants to accomplish something else.”
Trees have a tissue inside called xylem that transports sap. The hardwood at the center of the tree is old, dried xylem that has filled in with resins. But in the outer layer of the tree and in new growth is the xylem that transports sap.
Trees use a structure of channels similar to pipes, connected by a membrane that allows fluid through but blocks out small particles or air bubbles.
“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.”
To see if it really worked the way he thought, he created a simple setup using sapwood from pine trees on private land in Massachusetts. He peeled the bark off a pine branch and took the sapwood underneath containing the xylem into a tube. He then sent a stream of water containing tiny particles through the tube and showed that the wood filter removed them.
“We also flowed in bacteria and showed we could filter out bacteria using the xylem,” he says. Karnik estimates the xylem removed 99.9 percent of the bacteria.
“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.”
The wood filter they tested would be able to cleanse about four liters of water a day.
“We would like to see this developed further, so we are seeking funding to develop this into filtration devices,” Karnik said. “We did not file for a patent. I just felt one shouldn’t patent something that’s so universal, but I think that how do we process xylem or how do we make filters out of it—that’s where I think there’s a lot of potential to develop this technology.”
Scientists Find Natural Water Filter in Tree Branches
Researchers from the Massachusetts Institute of Technology have discovered a natural water filtration system inside the branches of a sapwood white pine tree.