MIT scientists turned tree branches into water filters that remove more than 99% of bacteria and viruses |
Tree branches could provide a simple way to filter drinking water. MIT engineers have developed water filters made from sapwood, the living wood found beneath the bark of trees such as pine and ginkgo. The material contains tiny channels called xylem that normally carry water through a tree. Thin membranes between these channels act like natural sieves, allowing water to pass while trapping contaminants. In laboratory tests, treated xylem filters removed more than 99% of E. coli and rotavirus. The researchers also tested filters made from native trees in India and worked with local communities to develop a simple filtration system.
How can tree branches be turned into water filters
MIT engineers turned tree branches into filters by using the structure of sapwood. In nonflowering trees such as pine and ginkgo, sapwood contains xylem, a network of straw-like conduits that carries water through the trunk and branches. These conduits are linked by thin membranes that work as sieves. The team had previously shown that peeled sapwood could filter bacteria, but the work addressed problems that appeared when the wood dried and became less permeable. Researchers treated sections in hot water for an hour, then dipped them in ethanol and dried them.
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How well did the tree-based filters remove bacteria and viruses
The treated xylem filters were tested against two contaminants, E. coli and rotavirus. In laboratory experiments, the filters removed more than 99% of both. The researchers tested water from contaminated spring, tap, and groundwater sources and found that the filters could remove bacteria. The treatment was important because untreated wood could lose its filtering performance as it dried. Hot-water and ethanol treatment helped prevent the membranes from sticking to conduit walls. Filter thickness could also be adjusted according to tree type. White pine filters retained water flow similar to commercial filters after being stored dry for two years.
Researchers used community feedback to improve the water filter design
The researchers then took the technology to India to see how it performed outside the laboratory. Over two years, the team worked in mountain and urban areas with organisations and tested filters made from native pine trees. They also tested filters made from ginkgo trees in the United States. The filters removed bacteria found in local drinking water sources. The team conducted interviews, focus groups, and design workshops to understand how communities treated water and what they wanted from a filtration system. Feedback from more than 1,000 users helped shape the design, including preferences for natural materials and frequent payments.
How could the new filter make water treatment more affordable
The India fieldwork led to a prototype designed for use. Users fill a receptacle at the top, allowing water to flow down a one-metre-long tube and through a xylem filter before leaving through a valve-controlled spout. The filter can be replaced daily or weekly, depending on household needs. The prototype purified water at a rate of one litre per hour. The researchers are exploring large-scale production using available resources. One idea is to sell replacement filters in affordable, pay-as-you-go packets. This approach is intended to avoid the larger upfront cost associated with filter cartridges and make water treatment easier.
How could researchers expand the use of xylem water filters
The researchers say xylem filters have potential for community use because their raw materials are inexpensive and available, while fabrication is relatively simple. MIT’s team is exploring how the technology could be produced and distributed more widely, in places where contaminated drinking water contributes to disease and death. However, the researchers have not established that the filters remove every type of contaminant. The team specifically noted that it does not yet know how the filters affect chemical contaminants such as arsenic and fluoride.
