Whether turning on a tap to fill a container or drinking from a fountain, people in developed countries normally have readily available and inexpensive access to a clean, safe water supply.
That is not the case for more than 800 million people in developing countries, according to Ernest "Chip" R. Blatchley III, professor of civil engineering and environmental and ecological engineering at Purdue Univ. Blatchley and other researchers are working to provide safe water supplies for these people by using ultraviolet (UV) radiation from the sun to purify water.
"Millions of people in developing countries do not have readily available water, or they become sick because of the water they drink," he said. "People in these countries may not have the infrastructure or financial resources to clean the water, deliver it and keep it clean until it's used. Common problems include microbial pathogens, which are largely associated with human and animal waste."
Blatchley and Bruce Applegate, associate professor of food science and biological sciences at Purdue, have developed prototypes of a water disinfection system to take advantage of UV radiation from the sun, which is plentiful in many areas where clean water is lacking.
"If you take a global view of people who have little or no access to safe water, you'll see that most live close to the equator," Blatchley said. "Bruce, student researchers and I have created prototypes that disinfect water by amplifying and concentrating solar UV radiation, which is abundant in equatorial and near-equatorial nations."
Applegate said the Purdue water disinfection system pumps water through a UV-transparent pipe placed on a parabolic reflector.
"The shape of the reflective mirror concentrates the sun's UV rays so the radiation inside the pipe is more intense than outside," he said. "The radiation damages the DNA in microorganisms. When this is done, the microbes can no longer grow and the water is safe."
Solar UV systems have been developed by other groups. The Purdue system, however, uses different materials than others.
"We are using the range of solar UV wavelengths that are most effective for damaging microorganisms' DNA. Using material that is transparent to these wavelengths of radiation allows us to disinfect water a lot faster," Blatchley said. "We can pump water continuously through the system and produce water in a larger quantity."
Blatchley and Applegate have conducted experiments in West Lafayette using non-pathogenic bacteria that are very closely related to those that cause cholera and typhoid. Blatchley said the results from the experiments could translate to the field where disease-causing microorganisms and higher levels of UV radiation exist.
"We have information about how UV irradiance in West Lafayette compares to cities around the world including Port-au-Prince, Haiti, and the Kenyan cities of Eldoret and Mombasa," he said. "The maximum solar irradiance that occurs in West Lafayette is similar to the minimum values observed in these near-equatorial cities. The experiments we conduct here, where we have had success, should be at least as successful if they were conducted in Port-au-Prince, Eldoret and Mombasa, and probably quite a bit more."
Having proven the concept of concentrating UV rays to disinfect water, the researchers now are determining how to scale up production in the system. The prototypes currently produce water at a rate of about 10-20 milliliters per minute.
"The original prototypes were intentionally built on a small scale so we could conduct experiments using a relatively modest amount of time and resources," Blatchley said. "We have ideas on how we expect it to scale up, and we plan to demonstrate those."