MIT scientists show tree branch to be effective water purifier

A suitable water filter is already growing in most forests.

By Brooks Hays
MIT scientists show tree branch to be effective water purifier
Sapwood filter (MIT)

BOSTON, Feb. 27 (UPI) -- Dirty, contaminated water is a problem for many developing nations. But water filters are relatively expensive and not something easily assembled in the shed, garage or backyard -- unless, of course, the water filter is already assembled and growing in the backyard.

New research by scientists at MIT proves that a water filter made out of a small piece of sapwood from a white pine tree can rid contaminated water of 99 percent of the bacteria E. coli, producing up to four liters of clean, potable water a day.


They say the small pores of a sapwood branch or section of trunk -- tissue that's designed to transport sap throughout the tree -- works to trap and block most types of bacteria as water filters through.

The details of the researchers' discovery was recently published in Plos One.

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“Today’s filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily,” explained Rohit Karnik, co-author of the new study and associate professor of mechanical engineering at MIT. “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 tree technology isn't perfect, researchers acknowledged. The sapwood was only able to filter out particles 70 nanometers and larger. That works fine for stopping bacteria, the vast majority of which are no smaller than 200 nanometers. Viruses, on the other hand, are much, much smaller, Karnik said, and would likely be able to bypass the wood filter.

Still other trees and plants out in the forest might work even better than the branch of pine tree.

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“There’s huge variation between plants,” Karnik says. “There could be much better plants out there that are suitable for this process. Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost. It’s orders of magnitude cheaper than the high-end membranes on the market today.”

[Plos One] [MIT]

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