A simple solution to dirty water: tree branches

MIT researchers find that sapwood can filter 99 percent of the E. coli bacteria. The finding could usher in a new generation of low-cost, low-tech water filters.
Written by Tyler Falk, Contributor
Forget biomimicry. When it comes to clean water, the answer might be the humble tree branch. 

Researchers at MIT have discovered that sapwood can be used as an effective water filtration device. In a study published in Plos One, the researchers demonstrated that, using a simple sapwood filtration device, they could filter 99 percent of the E. coli bacteria from water and 99 percent of particles over 150 nanometers. 

The steps taken to make the filter were simple: cut a branch of sapwood (like a pine tree), peel off the bark, fasten a rubber tube to the branch and seal it with epoxy. The key element in sapwood is the xylem tissue used which moves sap. It can also allow for the flow of water and capture bacteria. The researchers say the system was able to produce four liters of drinking water in a day.
There are 783 million people in the world without access to clean water and while filtration systems are available, they aren't always practical in communities where cost is an issue. That makes the development of wood filtration even more important to providing clean water across the globe. 

"Today’s filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily," said co-author of the study, Rohit Karnik, a professor of mechanical engineering at MIT, in a press release. "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."

Saurya Prakash, a professor of mechanical engineering at Ohio State University, put the discovery into perspective in a statement to MIT News: "The study ... shows that use of abundant, naturally occurring materials could pave the way for a new generation of water filters that are potentially low-cost enough to be disposable."

But there are a few caveats about the filtration system, according to MIT:

  •  Future product designers will need to find ways to keep the wood damp or dry while maintaining the functionality of the xylem tissue.
  • The wood probably can't filter most viruses because they are too small for the pores to capture. 
  • Pores in the wood are also too big to filter out salt.

But, with this discovery, the researchers say they plan to search for other natural filtration systems that could be even more effective.  

Update: Added the amount of drinking water the system produces in a day.

Photo: Flickr/The Nick Page

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