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MIT Grant Funds a Water Filter

High-school students design $150 system
September 8, 2006

Ten girls from an all-female high school in Webster Groves, MO, have invented a device that could benefit women throughout the developing world: a pushcart-mounted barrel that filters and carries water.

Nerinx Hall students demo their filter at MIT. (Courtesy of the Lemelson-MIT Program)

The project’s inspiration came from La Chinantla, a rural Mexican town that lacks running water. In a ritual repeated worldwide, Chinantecan women and children lug unclean water from faraway wells. The task can take hours and keeps children out of school. In March 2005, on an annual service trip to the site, two Nerinx Hall High School students learned about the problem firsthand. “We carried water in five-gallon buckets,” says Katie Kollef, who recently graduated. The water was contaminated with farm waste, and samples from rivers, springs, and wells all tested positive for E. coli.

Last October, Nerinx students won a $7,800 grant from Lemelson-MIT InvenTeams, a national program to help high-school inventors develop their ideas.

Their invention–a plastic barrel in a rolling steel cart–is simple. The barrel holds nine cylindrical filters, each containing sand, activated carbon (charcoal), and a ceramic cup. The sand removes organic debris; the carbon filters out color, odor, and taste; and the cup removes pathogens. The water is filtered before reaching a spigot at the barrel’s bottom.

Made from easily found materials, the device costs about $150 to produce. The cart is made of welded scrap metal and rolls on bicycle wheels. Barrels are “everywhere” in La Chinantla, says Kollef. The sand comes from the ground;
the carbon could come from charred nutshells. The ceramic cup is a mixture of clay, water, and coffee grounds poured into a mold–half a coconut shell will do–and fired in a pit. The coffee grounds burn away, leaving holes in the clay that catch bacteria but let water through. “It’s nothing fancy,” says project mentor Julie Sutfin. “Just dirt and used coffee.”

Yet it’s an elegant solution. It beats camp filters that provide little water, large filters that aren’t portable, and chlorine tablets that give water a bad taste. It takes weight off the bodies of water carriers. A barrel can hold 75 liters of water and filter it at about 40 liters an hour, removing 95 percent of E. coli. The average person in the developing world uses only 10 liters daily, so one barrel could supply the daily needs of up to seven people.

The final design took about 10 months to develop, with help from Peace Corps volunteers, waste­water treatment managers, and structural and environmental engineers. In March, the students tested a prototype in La Chinantla. “People … were very impressed and were ready to use it,” says Sutfin.

To boost E. coli filtration rates to closer to 100 percent, the students could add colloidal silver to the filter. But the aim is to design a device that could be locally made and sold. “The goal is for women to make a profit from a job they’ve been struggling with forever,” says recent graduate Lydia Caldwell, who helped test the prototype in La Chinantla.

This year, 45 students plan to look for natural materials that improve the bacterial removal rate, says Sutfin.

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