Leaving bottles of water in the sun kills pathogens--but only if the
water is transparent. Michigan Tech's Joshua Pearce has devised a
simple way to clarify water, so even muddy water could be made safe for
drinking. (Credit: SODIS Eawag photo)
Nearly 80 percent of disease in developing countries is linked to bad
water and sanitation. Now a scientist at Michigan Technological
University has developed a simple, cheap way to make water safe to
drink, even if it's muddy.
It's easy enough to purify clear water. The solar water disinfection
method, or SODIS, calls for leaving a transparent plastic bottle of
clear water out in the sun for six hours. That allows heat and
ultraviolet radiation to wipe out most pathogens that cause diarrhea, a
malady that kills 4,000 children a day in Africa.
It's a different story if the water is murky, as it often is where
people must fetch water from rivers, streams and boreholes. "In the
developing world, many people don't have access to clear water, and it's
very hard to get rid of the suspended clay particles," says Joshua
Pearce, an associate professor of materials science and engineering.
"But if you don't, SODIS doesn't work. The microorganisms hide under the
clay and avoid the UV."
Thus, to purify your water, you first have to get the clay to settle
out, a process called flocculation. Working with student Brittney Dawney
of Queen's University in Ontario, Pearce discovered that one of the
most abundant minerals on Earth does this job very well: sodium
chloride, or simple table salt.
Salt is inexpensive and available almost everywhere. And it doesn't take very much to make muddy water clear again.
"The water has a lower sodium concentration than Gatorade," Pearce
says. This would still be too much salt to pass muster as American tap
water, but American tap water is not the alternative.
"I've drunk this water myself. If I were somewhere with no clean
water and had kids with diarrhea, and this could save their lives, I'd
use this, no question," he says.
Salt works best when the suspended particles are a type of clay
called bentonite. The technique doesn't work as well with other kinds of
clay. However, by adding a little bentonite with the salt to water
containing these different clays, most of the particles glom together
and settle out, creating water clear enough for SODIS treatment.
Pearce and Dawney are running more tests on water containing various
types of clays, and they are also investigating different soil types
across Africa to see where their methods might work the best.
With UV light from the sun, microbes can be killed by direct sunlight exposure.
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