Solar UV disinfects drinking water
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 NSF funded Vadheim’s work through its Research Experiences for Undergraduates program.
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 in a climate that’s alternating between humid and dry.”
The release notes that 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 metalized plastic,” Blatchley said. “It’s similar to the material that’s used to make potato chip bags. We’ve done measurements, and some of these materials are about twice as reflective as aluminum foil.”
Improving water quality in developing countries is one of fourteen “grand challenges” established by the National Academy of Engineering and also has been named a “millennium development goal” by the United Nations.
Blatchley also is working on an inexpensive filtration system that uses layers of sand and gravel to clean water.
The filters were developed by Aqua Clara International, a Michigan-based nonprofit corporation. Purdue and Aqua Clara are teaming up with Moi University in Kenya on that project. Purdue students tested the behavior of the filters in a Global Design Team project in Africa through Purdue’s Global Engineering Program.
Water flows slowly through the filter, allowing a bacterial film to establish near the top of the filter to remove organic contaminants while certain pathogens also are removed by attachment to the sand.
The water, however, may still require disinfection to kill remaining pathogens, and it might be possible to use the slow-sand filters in combination with a water-disinfection system like the new solar UV approach.
“We want to develop drinking water treatment systems that improve water quality for people in developing countries, using Kenya as an example,” Blatchley said.
Aqua Clara has developed a business model for the filtration system.
“This provides business opportunities for local entrepreneurs who are trained how to make these filters out of locally available materials,” he said. “You can build one of these things for $10, and it’s capable of producing something like 40 liters of water a day. It’s intended to produce enough water for a family of four.”
The use of the filters is becoming more widespread. “About 1,900 of the sand filters have been installed in villages throughout Kenya,” said William Anderson, director of the Global Engineering Program. “More and more, Purdue’s faculty and students are extending our land-grant tradition for the benefit of people throughout the world.”
