MIT engineers demonstrate low-tech tree branch filters to purify water

Engineers affiliated with the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) at MIT have recently developed a new filter from tree branches that has the potential to provide an effective, cheap and low-tech solution for water purification. Designed by Rohit Karnik, J-WAFS principal investigator and Seed Grant recipient (2015-2023), the filter takes advantage of xylem, which are thin membranes of interconnected conduits found in the non-flowering trees such as pine and ginkgo. These thin membranes act as natural sieves, filtering out bubbles from water and sap. Rohit and his co-researchers have developed filters from white pine branches which have been found to effectively remove E. coli and rotavirus, two common waterborne disease-causing pathogens.

In order to ensure that the filter works effectively, the researchers improved its permeance by soaking the wood in hot water and then dipping it in ethanol to let it dry.

Satisfied that the filter worked in a lab, they took the xylem filters to India in order to understand how it performed in a real-world setting. They designed the filter to meet the ‘two-star comprehensive protection’ criteria set by the World Health Organisation, and found that it removed more than 99% of both the E. coli and rotavirus bacteria.

Rohit and his team are now exploring ways to make xylem filters available at large scale and at an accessible price, observing that users in low-income households preferred paying for their filters in small amounts frequently than an upfront cost. They’ve also launched an open-source website which provides guidelines for designing and fabricating xylem filters from various tree types.