Locally Made Clay Tablet Helps Purify Water In South Africa

A ceramic tablet infused with silver or copper nanoparticles can disinfect water for up to six months.

Called MadiDrop, the tablets are being developed for use in communities in South Africa that have little to no access to water.

PureMadi, a nonprofit University of Virginia organization, invented the tablet and has established a water filter factory in Limpopo province, South Africa, employing local workers. The factory has produced several hundred flowerpot-like water filters that utilize the same technology as the tablets to purify water.

The MadiDrop tablet is a small ceramic disk impregnated with silver or copper nanoparticles. It can repeatedly disinfect water for up to six months simply by resting in a vessel where water is poured. (image credit: Rachel Schmidt/Futurity)

The MadiDrop tablet is a small ceramic disk impregnated with silver or copper nanoparticles. It can repeatedly disinfect water for up to six months simply by resting in a vessel where water is poured. (image credit: Rachel Schmidt/Futurity)

“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,” says James Smith, a University of Virginia civil and environmental engineer who co-leads the project with Rebecca Dillingham, director of the university’s Center for Global Health.

“Each filter can serve a family of five or six for two to five years, so we plan to eventually serve at least 500,000 people per year with new filters,” adds Smith.

The idea is to create sustainable businesses that serve their communities and employ localworkers. A small percentage of the profits go back to PureMadi and will be used to help establish more factories.

The filters are made of local clay, sawdust, and water. Those materials are mixed and pressed into a mold. The result is a flowerpot-shaped filter, which is then fired in a kiln.

The firing burns off the sawdust, leaving a ceramic with very fine pores. The filter is then painted with a thin solution of silver or copper nanoparticles that serve as a highly effective disinfectant for waterborne pathogens, the type of which can cause severe diarrhea, vomiting and dehydration.

The design allows a user to pour water from an untreated source, such as a river or well, into the pot and allow it to filter through into a five-gallon bucket underneath.

The pot has a flow rate of one to three liters per hour, enough for drinking and cooking. The filtered water is accessed through a spigot in the bucket.

A worker at the factory molds a filter from local clay, sawdust, and water. (image credit: Rachel Schmidt/Futurity)

A worker at the factory molds a filter from local clay, sawdust, and water. (image credit: Rachel Schmidt/Futurity)

Smith says testing has shown that 99.9 percent of the pathogens in water can be removed or killed by the filter.

MadiDrop is an alternative to the flowerpot filter, but ideally would be used in conjunction with it. The plan is to mass-produce the product at the same factories where the PureMadi filters are produced.

“MadiDrop is cheaper, easier to use, and is easier to transport than the PureMadi filter, but because it is placed into the water, rather than having the water filter through it, the MadiDrop is not effective for removing sediment in water that causes discoloration or flavor impairment,” Smith says.

“But its ease of use, cost-effectiveness and simple manufacturing process should allow us to make it readily available to a substantial population of users, more so than the more expensive PureMadi filter.”

Testing shows that the filters are safe to use and release only trace amounts of silver or copper particles, well within the safe water standards of the developed world. The filters also would be useful in rural areas of developed countries such as the United States where people rely on untreated well water.

The National Science Foundation, the National Institutes of Health, and the University of Virginia support PureMadi. Partners include the University of Venda in South Africa; Potters for Peace, a nonprofit organization committed to providing safe drinking water in the developing world; and local communities in Limpopo province in South Africa.

Source: University of Virginia

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