SUNLIGHT CAN CLEAN WATER FOR DRINKING

Sunlight can clean water for drinking

In an effort to eliminate the drinking water problem in developing countries a US professor has invented a solar-based UV filtration system that can kill waterborne pathogens

A team of Purdue University researchers has invented a prototype water disinfection system that could help the world’s 800 million people who lack safe drinking water. The system uses the sun’s ultraviolet radiation to inactivate waterborne pathogens. Sunlight is captured by a parabolic reflector and focused onto a UV-transparent pipe though which water flows continuously. “We’ve been working on UV disinfection for about 20 years,” said Ernest Blatchley, a professor. “All of our work up until a couple years ago dealt with UV systems based on an artificial UV source. What we are working on more recently is using ultraviolet radiation from the sun.” Motivating the research is the need to develop practical, inexpensive water-treatment technologies for developing nations. “The water available for people to drink in many developing countries hasn’t been treated to remove contaminants, including pathogenic microorganisms. As a result, thousands of children die daily from diarrhea and its consequences, including dehydration. Half of the world’s hospital beds are occupied by people who are sickened by the water,” Blatchley said. Blatchley built the parabolic reflector in his garage. The team finished the prototype in the lab, lining it with aluminum foil. The system was then tested on the roof of a building. “We demonstrated that we can disinfect water using sunlight. The reactor was very inexpensive to build, less than $100,” he said The natural UV system inactivated E coli bacteria. However, the system must be able to kill dangerous pathogens such as Vibrio cholerae, which causes cholera and Salmonella typhi, which causes typhoid. “In the future we want to prove that our solar-UV system is going work against these other pathogens,” said Blatchley. “We also want to automate it and build sensors for it so that we know how fast the water should be pumped through the system, depending on how sunny it is at any particular time.” The parabolic reflector is made out of a wood called paulownia. “That material was selected because the tree grows very rapidly in regions near the equator, where many people lack safe drinking water,” Blatchley said. “It is very light, strong and stable, so it’s not going to twist or warp or bend or crack.” Natural UV has a longer wavelength than most artificial UV sources, which means it has less energy. Blatchley’s hypothesis, however, is that UV from sunlight will inactivate pathogens via the same mechanism as artificial UV: The radiation damages the genetic material of microbes, preventing them from reproducing. “We are looking at other inexpensive reflecting materials, for example metallised plastic,” Blatchley said. “It’s similar to the material that’s used to make potato chip bags.” Improving water quality in developing countries has been named a “millennium development goal” by the United Nations.
(MM 4O1011)