Silver is known for its antibacterial qualities, and has thus found its way into water filters created at institutions such as Stanford and McGill universities. Given that these filters are often used in developing nations, however, it would be nice if they could also contribute to the local economy – instead of being just one more thing that’s brought in from outside. Well, that’s just the idea behind the University of Virginia’s PureMadi filters and MadiDrops.

The two devices were created as part of the university’s PureMadi program, for use in South African communities that have little if any access to clean water – the Tshivenda South African word for water is “madi.” Leading the program is civil/environmental engineer James Smith, and Dr. Rebecca Dillingham.

The filter resembles a flower pot, and is used to both mechanically remove particulate matter from the water, and to kill microbes within it. The devices are made by the villagers, starting with a mixture of locally-sourced clay, sawdust and water. That mix is pressed into a mold, then fired in a kiln.

The firing process burns up the sawdust, leaving fine pores within the ceramic material – those pores are large enough to allow water molecules to soak through at a rate of three liters (0.8 US gallons) per hour, but small enough to trap most particles. A coating of silver (or copper) nanoparticles is then painted onto the surface of the filter, to kill bacteria.

In use, one of the flowerpot filters is simply placed over a 5-gallon (19-liter) bucket, then untreated water is poured into the filter. By the time it has trickled through into the bucket, a reported 99.9 percent of all the pathogens within it have been either trapped or killed. Trace amounts of the nanoparticles make it into the treated water, that are reportedly “within the safe water standards of the developed world.”

The more recently-developed MadiDrop is composed of the same materials as the filters, but takes the form of a tablet that is simply dropped into a bucket of untreated water. Its silver nanoparticles then go to work killing microbes in the water. Although the tablet does nothing in the way of filtration, it should be cheaper, easier to manufacture and use, and less awkward to transport than the filters. This, in turn, means that it should find use with a larger number of people.

One filter should remain effective for two to five years, while the MadiDrops last for about six months.

Local workers are currently employed at a factory in Limpopo province, making the filters. “Eventually that factory will be capable of producing about 500 to 1,000 filters per month, and our 10-year plan is to build 10 to 12 factories in South Africa and other countries,” said Smith. “We plan to eventually serve at least 500,000 people per year with new filters.”

The filters and tablets could also find use in first world nations, in rural areas where municipally-treated water is scarce.

More information on the PureMadi program is available in the video below.

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