Sapwood could filter out 99 percent of E. coli bacteria.
The natural filtration system could produce up to four liters of water a day, which is enough to sustain the average person, an MIT news release reported.
The pores in sapwood contain xylem tissue, which transports sap "up the length of a tree," the news release reported. The tissue allows water through but captures most particles and bacteria.
"Today's filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily," Co-author Rohit Karnik, an associate professor of mechanical engineering at MIT, said in the news release. "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."
The team attached plastic tubing to stripped white pine branches. The researchers poured water enhanced with red ink particles that were between 70 to 500 nanometers in size through the wood. The team cut the branch in half length-wise and found the red dye was mostly contained in the upper levels of the wood, leaving the filtered water clear. The wood proved to be unable to capture particles that were below 20 nanometers.
The wood can filter out most bacteria, but viruses are usually too small to be caught by the pores. The water filters could be used in regions where surface water, which often contains debris, is collected for consumption. It is important to keep the wood damp when using it as a filter.
"The xylem tissue acts as a natural filter, similar to a manmade membrane," says Prakash, who was not involved in the research. "The study by the Karnik group shows that use of abundant, naturally occurring materials could pave the way for a new generation of water filters that are potentially low-cost enough to be disposable."
