In India, more than one in ten households still lack sufficient drinking water, according to the 69th round of the National Sample Survey.
While expensive alternatives to filter water exist, the search for a simple, cost-effective technique continues. And scientists believe that they might have unearthed one such option.
According to a paper published in PLoS ONE, researchers from MIT have been able to filter water using plant xylem. In tests conducted with deionised water in which bacteria and dye were introduced, the xylem filter effectively removed both when subjected to pressure.
“I was at a conference in Israel and happened to listen to a talk about how sap moves in the xylem of plants. That is when we started exploring the possibility that plant xylem could be used for low-cost water filtration,” Rahul Karnik, Associate Professor of Mechanical Engineering at MIT and a coauthor of this study, said in an email to this Correspondent.
Xylem is a transport tissue in vascular plants that conducts water and dissolved nutrients upwards from the roots. Tracheids, which are cells in the xylem, are shorter and have smaller diameters in conifers, thereby offering higher resistance to flow but a greater cross-sectional area of the stem to conducting xylem tissue. This likely makes it the most suitable xylem tissues for filtration at the micron or larger scale.
While these initial results are cause for optimism, the fact remains that these tests were conducted under laboratory conditions. “This filter should work with real-world water samples as long as it is not highly turbid. Turbidity tends to clog filters, and this one is not an exception,” Karnik said.
The researchers prepared the xylem filter by removing the bark of pine tree branches and then inserting it into a tube. The pressure that was used for this study suggests that it is easily achievable using a gravitational pressure head. The device construction therefore seems to be simple, considering that the wood might have to be replaced often. “The idea is that these filters should be inexpensive enough to dispose off rather than attempt to clean them,” Karnik added.
A cheap disposable xylem filter might just be the solution to availability of safe drinking water.
It is important to note that these filters are still in their nascent stages. Identifying locally available sources of xylem, testing the flow through xylem of different plants, improving the rejection of viruses up to nanoparticles are some of the challenges that lay ahead.
“This is a very new technology with lot of work to be done. Our eventual goal is to enable practical implementation of xylem-based filters,” Karnik noted. “It may take 2-3 years to develop the first prototype.”