Simple water filter can nail arsenic

From Montreal, at a joint meeting of the American and Canadian Geophysical Unions

BED OF NAILS. Up to 96 percent of the arsenic in tainted groundwater can be removed by this filter made of iron nails. Murcott

Field tests in Nepal suggest that people who live in areas with arsenic-tainted aquifers may be able to purify their drinking water by passing it through a low-cost, low-tech filter with a simple active ingredient—a few handfuls of iron nails.

Groundwater in many areas of the world contains arsenic (SN: 11/15/03, p. 315: Attack of the Rock-Eating Microbes!). In the Terai region of southern Nepal, about 90 percent of the residents get their drinking water from wells, says Susan Murcott of the Massachusetts Institute of Technology. More than 500,000 of the region’s inhabitants consume water with arsenic concentrations that exceed the World Health Organization’s recommended threshold of 10 micrograms per liter, she notes.

Many previous arsenic-removal projects in the Terai region have failed because of equipment costs, maintenance issues, the need for materials that aren’t readily available in remote areas, and slow filtering rates. The device that Murcott and her colleagues designed has none of these drawbacks.

The two-stage filter is made of concrete molded around a simple rectangular form. Water poured into the top of the filter passes through a tray that contains a few kilograms of iron nails—whose chemical action scours the arsenic from the fluid—and then collects in a sand-filled bottom compartment. When the water is drawn out of the sand, sediment particles and many microbes are left behind, says Murcott.

Data gathered during field tests of 250 such filters indicate that they remove more than 96 percent of the arsenic from tainted water when flow rates don’t exceed 30 liters of water per hour, which is plenty for a typical household. Built strictly with locally available materials and labor, each filter costs only $25. That’s still a sizeable investment in a region where workers earn $1 a day, Murcott notes. She and her coworkers have made similar devices within large plastic garbage cans for just $15.

Murcott’s team is now monitoring the water quality in more than 800 filter-equipped households in the Terai region. By year’s end, they hope to have built and installed another 1,700 of the devices.

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