There is something new under the sun: an easy, inexpensive way to disinfect water using nothing but sunlight.
The development could provide a nifty way to treat foul water in disaster areas, as well as help the 800 million people in the world who consistently lack safe drinking water.
The system uses the sun’s ultraviolet radiation to destroy waterborne pathogens. Sunlight is captured by a parabolic reflector and focused onto a UV-transparent pipe though which water is pumped. (Another emergency water decon method was reported in this space recently, but that one was designed to remove radioactive contaminants.)
“This process works by focusing solar UV radiation to deactivate pathogens,” said Purdue University engineer Ernest Blatchley.
This is done using a device called a compound parabolic collector. It may sound complicated, but it’s really not much more than a light foil-covered frame shaped like folded wings, which reflect sunlight to a focal point.
“We used aluminum foil as a reflective material for the collector, but there are other materials that will also work,” Blatchley said.
Water is pumped through a UV-transparent pipe placed in the unit’s focal area. As water-borne microbes, such as E. coli, are carried through the pipe, they are exposed to concentrated solar UVB radiation. The radiation damages the microbes’ genetic material, preventing reproduction.
While the system was built for applications in developing countries, Blatchley said the technology could certainly be used in any disaster response/recovery situation where drinking water supplies might be bio-contaminated.
Much of the world routinely lives with contaminated water, where drinking water is not treated to remove pathogenic microorganisms. As a result, hundreds of children die daily from diarrhea and its dehydrating consequences.
People in the developed world, who take clean water for granted, nevertheless live with a lurking fear that terrorists might find a way to contaminate water reservoirs.
“Half of the world’s hospital beds are occupied by people who are sickened by the water they drink,” Blatchley said.
As it turns out, a large fraction of the world’s population who lack access to safe drinking water live near the equator, where solar UV radiation is intense and consistently available.
Equatorial proximity is not required, however, for Blatchley’s device to work.
Most of the United States receives enough solar radiation to deactivate waterborne microorganisms with this type of system most of the year. Blatchley tested his system on the roof of Purdue’s Civil Engineering Building in Lafayette, Ind., latitude 40° N.
Moreover, Blatchley said, this technology is inexpensive. His prototype was built with less than $100 of materials.