From: Yao-Hua Law, SciDevNet, More from this Affiliate
Published March 18, 2014 01:21 PM

Scientists develop system to filter water using plant sticks

Scientists from the Massachusetts Institute of Technology (MIT) in the United States are working with their counterparts in developing countries to produce an "economical and efficient" means of filtering out bacteria from water using plant xylem that normally transports water and nutrients from the soil.

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The novel technology could provide a solution to the burden of water-borne diseases in East Asia and the Pacific where about 180 million people lack access to safe water supply, according to the UNICEF (UN Children's Fund).

Rohit Karnik, an associate professor of mechanical engineering at MIT where he heads the Microfluidics and Nanofluidics Research Laboratory, says his team is interacting with water treatment experts in developing countries to produce a prototype of the xylem filter in the next 2-3 years.

"Low cost, easy-to-use and effective methods of water purification are needed to provide clean drinking water to a significant fraction of the global population," says Karnik. "Our eventual goal is to enable practical implementation of xylem-based filters."

In a recent study published in PLOS One (26 February), Karnik's team demonstrated that the xylem of certain plants can effectively filter bacteria from water. Xylem tissue works like pipes in which water and minerals move from the roots to the leaves.

Using the sapwood of coniferous trees stripped of their bark, the team fitted pine branch cuttings into one end of a plastic tube. They then used this simple setup to filter a solution containing a high concentration of the E. coli bacteria.

They found that the xylem filter removed "at least 99 per cent" of the bacteria. A small stick around three centimetres long is sufficient to filter several litres of water a day — "sufficient to meet the clean drinking water needs of one person" the study says.

While acknowledging the potential of xylem filters, Daniele Lantagne, assistant professor at the Tufts University Department of Civil and Environmental Engineering in the United States, emphasises that prototypes must first be "tested according to the WHO guidelines for evaluation of household water treatment products".

Lantagne, who has worked with water treatment programmes in more than 40 countries, says the current xylem filter fails the WHO standards for drinking water, which must contain "no detectable E. coli in every 100 millilitre sample".

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