New Ultraviolet Light Technique Developed To Clean Tap Water
A new way of measuring microbes’ exposure to ultraviolet light could strengthen efforts to use UV light to improve the quality and safety of tap water in the United States.
The novel “microsphere dosimeter” technique developed by researchers at Duke University’s Pratt School of Engineering is the first direct test of how much UV light microorganisms in fluids have been exposed to, said the researchers.
The technique allows scientists to complete a critical step in validating the use of UV light treatment for preventing the spread of infection through drinking water. The technique was reported in the November 15 issue of “Environmental Science and Technology” by Professor Karl Linden and colleagues.
Professor Linden, Ph.D., teaches classes on physical and chemical treatment processes, and chemistry and microbiology for environmental engineers.
Linden’s technique uses fluorescent microspheres, which become bleached with exposure to UV light, to mimic pathogenic microbes in water flowing through a UV reactor.
By measuring the bleaching of the microspheres, the researchers can obtain precise measures of the full distribution of UV doses that a pathogen may experience – information critical for gauging the treatment’s capacity to kill disease-causing bacteria or parasites before they reach the public.
Funded by the American Water Works Association Research Foundation, the new technique is timely. The U.S. Environmental Protection Agency (EPA) is set to introduce regulations in December requiring water treatment plants at risk of infection to add UV reactors as an additional line of defense against pathogenic contaminants in the water supply, Linden said.
“The use of UV will certainly lower the public’s risk of microbial pollution because it offers a second barrier of defense,” Linden said. UV treatment will also reduce the need for chemical disinfection, he added.
In the U.S., chemical treatment with chlorine remains the primary method for disinfecting drinking water, he said. However, chlorine can produce chemical byproducts that have been linked to cancer. Such byproducts are also coming under stricter regulations in the new EPA rules for drinking water, Linden said.
Chlorine also fails to kill some infectious microbes, such as the protozoan parasite Cryptosporidium. Known as “Crypto,” the parasite is a common cause of waterborne disease in the United States. In 1998, water quality researchers, including Linden, discovered that UV is very effective in killing Crypto, a finding that subsequently became a fundamental basis for the new EPA regulations.
In addition to improvements in the fight against waterborne illness, UV offers a more environmentally friendly water treatment method, Linden said. Its implementation will allow a reduction in chlorine use, which will lower the concentration of chemical byproducts found in the water supply and help to meet the new byproduct standards, in addition to the Crypto regulations.
Similar to the more familiar Giardia parasite, which often infects hikers who drink untreated water, Crypto can be transmitted through ingestion of drinking water, person-to-person contact, or other exposure routes, Linden said. Symptoms of the condition include acute diarrhea, abdominal pain, vomiting and fever that can last up to two weeks in healthy adults, but may be chronic or fatal in those with a compromised immune system.
In 1993, a massive outbreak of Crypto transmitted through the public water supply infected an estimated 400,000 people in Milwaukee and led to more than 100 deaths, Linden said.
In the last two decades, Crypto has become recognized as one of the most common causes of waterborne disease among people in the U.S., according to the Centers for Disease Control and Prevention. The parasite can be found in drinking water and recreational water worldwide.
Provided by the Environmental News Service.