Engineers at MIT have developed a water filter made from cross-sections of tree branches that can filter bacteria from contaminated water.

The filter takes advantage of the natural sieving abilities of xylem -- thin, interconnected membranes found in the sapwood branches of pine, ginkgo and other nonflowering trees.

Researchers previously demonstrated the the filtering capabilities of xylem cross-sections in the lab, but the for the latest study, the team of engineers wanted to test the technology in real-world situations.

After traveling to India to make and test filters using local trees, engineers created a prototype filtration system with replaceable xylem filters.

They described their technology Thursday in the journal Nature Communications.

But the science journal isn't the only place readers can learn more about the tree-based water filter.

Researchers also created a website and published instructions for developing xylem filters using the cross-sections of different types of trees.

"Because the raw materials are widely available and the fabrication processes are simple, one could imagine involving communities in procuring, fabricating, and distributing xylem filters," Rohit Karnik told MIT News.

"For places where the only option has been to drink unfiltered water, we expect xylem filters would improve health, and make water drinkable," said Karnik, a professor of mechanical engineering at MIT.

While developing their prototype, researchers ran into two problems.

The xylem sieves dry out easily in storage, sticking to the walls of the filter and slowing water filtration. The sieves also gum up after being used multiple times.

Researchers were able to solve the problem by soaking the sapwood cross-sections in warm water and then dipping them in ethanol. After being allowed to dry, the filters proved much more durable.

In real-world tests around the MIT campus, the filters removed 99 percent of bacteria contaminants such as E. coli and rotavirus, matching the performance of commercial filters.

"We think these filters can reasonably address bacterial contaminants," said mechanical engineer Krithika Ramchander. "But there are chemical contaminants like arsenic and fluoride where we don't know the effect yet."

The filters performed equally well in field tests in India, where many rural communities are without access to clean drinking water.

Researchers gathered feedback from locals in order to better understand their current water filtration methods -- tweaking the design and materials to accommodate the preferences of early adopters.

The resulting prototype features a meter-long tube that sends water through a replaceable sapwood filter and out a spout. The filter can be swapped out daily or weekly.

"One of the things that scored very high with people was the fact that this filter is a natural material that everyone recognizes," said researcher Megha Hegde.

"We also found that people in low-income households prefer to pay a smaller amount on a daily basis, versus a larger amount less frequently. That was a barrier to using existing filters, because replacement costs were too much," said Hegde.

The research team is currently working on ways to economically scale production of the xylem filters, so that users in India can receive a steady supply.

"Xylem filters are made from inexpensive and abundantly available materials, which could be made available at local shops, where people can buy what they need, without requiring an upfront investment as is typical for other water filter cartridges," Karnik said. "For now, we've shown that xylem filters provide performance that's realistic."

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