Technology▼Solutions Low-tech solution for pasteurizing water water is safe. Metcalf makes the thermometers himself, and while they may appear to be simplistic, he says they took years of labor to devise. “I wanted a reusable indicator so that when you get to 65 °C, you can reuse it again and again,” he says. To build a thermometer, he seals a small ball of wax into a glass tube. This tube is then attached to a piece of fishing line along with a common washer to weight the thermometer down to the pot’s bottom. The wax is blended to melt at 65 °C, so once it liquefies the user knows the water is pathogen-free. The weight keeps the device at the bottom of the pot. Metcalf has found that solar heating creates a thermal cline in the water, meaning that the temperature along the bottom can sometimes be 5 °C lower than at the top. It is critical for pasteurization, he says, that all the water reach the proper temperature. In environments like western Kenya that are hot, dry, and sparsely vegetated, solar radiation is arguably the most effective means to disinfect water. “People would have to spend a quarter of their meager income on wood instead of buying food,” Metcalf says. “The amount of wood need-
BOB METCALF
Approximately 2.5 billion people do not have access to safe drinking water, a crisis that leads to about 1.58 million deaths every year, according to the World Health Organization. Bob Metcalf, a professor of biology at California State University in Sacramento, is teaching villagers in rural Kenya how to pasteurize water with a solar radiation kit. Surprisingly, the tools he uses are cardboard, aluminum foil, a handmade thermometer, and sunshine. “I’ve been in Tanzania and Kenya, and local water supplies are often highly contaminated with bacteria,” Metcalf says. Metcalf has been studying solar pasteurization since the early nineties, and his research has found that water does not need to be boiled to kill bacteria; it just needs to be heated to 65 °C. But in many parts of the globe, there is little fuel wood, so he designed a solar reflector made of cardboard covered with aluminum foil. This reflector concentrates solar radiation onto a black, water-filled pot. After about three hours in the sun, the water should have reached the correct temperature, but Metcalf’s cleverly designed thermometer ensures that the
ed for one day would cost about 30 [Kenyan] shillings. You could buy a pound and a half of beans or rice with that money.” Over the past year, Metcalf tested his technology at 40 different water sources in Kenya’s Nyanza province, where the incidence of typhoid fever and bacterial and amoebic dysentery is among the country’s highest. Most of the wells, rivers, and ponds were contaminated with coliform bacteria, but heating the water to 65 °C killed off the pathogens. With the success of this demonstration project, Metcalf has now begun talks with Kenya’s Ministry of Water about expanding into other regions of the country. A similar project using discarded water bottles made from PET plastic is being carried out by the Swiss Federal Institute for Environmental Science and Technology (EAWAG). This process also utilizes sunlight, but instead of heat sterilization it uses UV radiation to kill pathogens. Martin Wegelin, the Program Director at EAWAG’s Department of Water and Sanitation, says they have ongoing projects in 20 different countries that provide safe drinking water to half a million people. “The science behind this technology is good,” says Metcalf. “It just needs to become common knowledge worldwide.” —PAUL D. THACKER
American scientists are teaching villagers in developing countries how to pasteurize water with sunshine, using nothing more than aluminum foil and a wax-filled vial. Disinfection of drinking water could save over 700,000 lives every year. © 2004 American Chemical Society
SEPTEMBER 1, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 327A
