UD's patented technology, developed jointly by researchers in the College of Agriculture and Natural Resources and the College of Engineering, incorporates highly reactive iron in the filtering process to deliver a chemical "knock-out punch" to a host of notorious pathogens, from E. coli to rotavirus.
The new technology could dramatically improve the safety of drinking water around the globe, particularly in developing countries. According to the World Health Organization (WHO), over a billion people--one-sixth of the world's population--lack access to safe water supplies.
Four billion cases of diarrheal disease occur worldwide every year, resulting in 1.8 million deaths, primarily infants and children in developing countries. Eighty-eight percent of this disease is attributed to unsafe water supplies, inadequate sanitation and hygiene.
In the United States, viruses are the target pathogenic microorganisms in the new Ground Water Rule under the Environmental Protection Agency's Safe Drinking Water Act, which took effect on Jan. 8.
"What is unique about our technology is its ability to remove viruses--the smallest of the pathogens--from water supplies," Pei Chiu, an associate professor in UD's Department of Civil and Environmental Engineering, said.
Chiu collaborated with Yan Jin, a professor of environmental soil physics in UD's plant and soil science department, to develop the technology. They then sought the expertise of virologist Kali Kniel, an assistant professor in the animal and food sciences department, who has provided critical assistance with the testing phase.
"A serious challenge facing the water treatment industry is how to simultaneously control microbial pathogens, disinfectants such as chlorine, and toxic disinfection byproducts in our drinking water, and at an acceptable cost," Chiu noted.
Viruses are difficult to eliminate in drinking water using current methods because they are far smaller than bacteria, highly mobile, and resistant to chlorination, which is the dominant disinfection method used in the United States, according to the researchers.
Of all the inhabitants of the microbial world, viruses are the smallest--as tiny as 10 nanometers. According to the American Society for Microbiology, if a virus could be enlarged to the size of a baseball, the average bacterium would be the size of the pitcher's mound, and a single cell in your body would be the size of a ballpark.
"By using elemental iron in the filtration process, we were able to remove viral agents from drinking water at very high efficiencies. Of a quarter of a million particles going in, only a few were going out," Chiu noted.
The elemental or "zero-valent" iron (Fe) used in the technology is widely available as a byproduct of iron and steel production, and it is inexpensive, currently costing less than 40 cents a pound (~$750/ton). Viruses are either chemically inactivated by or irreversibly adsorbed to the iron, according to the scientists.
Technology removes 99.999 percent of viruses
The idea for the UD research sprang up when Jin and Chiu were discussing their respective projects over lunch one day.
Since joining UD in 1995, Jin's primary research area has been investigating the survival, attachment and transport behavior of viruses in soil and groundwater aquifers. One of the projects, which was sponsored by the American Water Works Association Research Foundation, involved testing virus transport potential in soils collected from different regions across the United States. Jin's group found that the soils high in iron and aluminum oxides removed viruses much more efficiently than those that didn't contain metal oxides.
"We knew that iron had been used to treat a variety of pollutants in groundwater, but no one had tested iron against biological agents," Chiu said. So the two researchers decided to pursue some experiments.
With partial support from the U.S. Department of Agriculture and the Delaware Water Resources Center, through its graduate fellowship program, the scientists and their students began evaluating the effectiveness of iron granules in removing viruses from water under continuous flow conditions and over extended periods. Two bacteriophages--viruses that infect bacteria--were used in the initial lab studies.
Since then, Kniel has been documenting the technology's effectiveness against human pathogens including E. coli 0157:H7, hepatitis A, norovirus and rotavirus. Rotavirus is the number-one cause of diarrhea in children, according to Kniel.
"In 20 minutes, we found 99.99 percent removal of the viruses," Chiu said. "And we found that removal of the viruses got even better than that with time, to more than 99.999 percent."
The elemental iron also removed organic material, such as humic acid, that naturally occurs in groundwater and other sources of drinking water. During the disinfection process, this natural organic material can react with chlorine to produce a variety of toxic chemicals called disinfection byproducts.
"Our iron-based technology can help ensure drinking-water safety by reducing microbial pathogens and disinfection byproducts simultaneously," Chiu noted.
Applications in agriculture and food safety
Besides helping to safeguard drinking water, the UD technology may have applications in agriculture.
Integrated into the wash-water system at a produce-packing house, it could help clean and safeguard fresh and "ready to eat" vegetables, particularly leafy greens like lettuce and spinach, as well as fruit, according to Kniel.
"Sometimes on farms, wash-water is recirculated, so this technology could help prevent plant pathogens from spreading to other plants," she said.
This UD research underscores the importance of interdisciplinary study in solving problems.
"There are lots of exciting things you can discover working together," Jin said, smiling. "In this project, we all need each other. Pei is the engineer and knows where we should put this step and how to scale it up. I study how viruses and other types of colloidal particles are transported in water, and Kali knows all about waterborne pathogens.
"Our hope is that the technology we've developed will help people in our country and around the world, especially in developing countries," Jin noted.