MIT engineers have been investigating sapwood’s natural filtering ability, and have previously fabricated simple filters from peeled cross-sections of sapwood branches, demonstrating that the low-tech design effectively filters bacteria. Now, the same team has advanced the technology and shown that it works in real-world situations. Source: Timberbiz
They have fabricated new xylem filters that can filter out pathogens such as E.coli and rotavirus in lab tests, and have shown that the filter can remove bacteria from contaminated spring, tap, and groundwater.
They also developed simple techniques to extend the filters’ shelf-life, enabling the woody disks to purify water after being stored in a dry form for at least two years.
The researchers took their techniques to India, where they made xylem filters from native trees and tested the filters with local users. Based on their feedback, the team developed a prototype of a simple filtration system, fitted with replaceable xylem filters that purified water at a rate of one litre per hour.
Their results show that xylem filters have potential for use in community settings to remove bacteria and viruses from contaminated drinking water.
The researchers are exploring options to make xylem filters available at large scale, particularly in areas where contaminated drinking water is a major cause of disease and death.
The team has launched an open-source website with guidelines for designing and fabricating xylem filters from various tree types. The website is intended to support entrepreneurs, organizations, and leaders to introduce the technology to broader communities, and inspire students to perform their own science experiments with xylem filters.
Karnik’s study co-authors are lead author Krithika Ramchander and Luda Wang of MIT’sDepartment of Mechanical Engineering, and Megha Hegde, Anish Antony, Kendra Leith,and Amy Smith of MIT D-Lab.In their prior studies of xylem, Karnik and his colleagues found that the woody material’s natural filtering ability also came with some natural limitations.
As the wood dried, the branches’ sieve-like membranes began to stick to the walls, reducing the filter’s permeance, or ability to allow water to flow through. The filters also appeared to “self-block” over time, building up woody matter that clogged the conduits.
Surprisingly, two simple treatments overcame both limitations. By soaking small cross-sections of sapwood in hot water for an hour, then dipping them in ethanol and letting them dry, Ramchander found that the material retained its permeance, efficiently filtering water without clogging up. Its filtering could also be improved by tailoring a filter’s thickness according to its tree type.
The researchers sliced and treated small cross-sections of white pine from branches around the MIT campus and showed that the resulting filters maintained a permeance comparable to commercial filters, even after being stored for up to two years, significantly extending the filters’ shelf life.
The researchers also tested the filters’ ability to remove contaminants such as E. coli and rotavirus — the most common cause of diarrheal disease. The treated filters removed more than 99% of both contaminants.
With information from more than 1,000 potential users across India, they designed a prototype of a simple filtration system, fitted with a receptacle at the top that users can fill with water. The water flows down a 1-meter-long tube, through a xylem filter, and out through a valve-controlled spout. The xylem filter can be swapped out either daily or weekly, depending on a household’s needs.
The team is exploring ways to produce xylem filters at larger scales, with locally available resources and in a way that would encourage people to practice water purification as part of their daily lives — for instance, by providing replacement filters in affordable, pay-as-you-go packets.
This research was supported, in part, by the Abdul Latif Jameel Water and Food SystemsLab (J-WAFS) at MIT and the MIT Tata Center for Technology and Design.
