Safe water

Researchers at Duke’s Pratt School of Engineering have developed a new way to measure microbes’ exposure to ultraviolet light. The tool could bolster efforts to use UV light to improve the quality and safety of tap water.

The novel “microsphere dosimeter” technique is the first direct test of how much UV light microorganisms in fluids have been exposed to, said the researchers - a critical step in validating the use of UV light treatment for preventing the spread of infection through drinking water.

Researcher Karl 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,  precise measures of the full distribution of UV doses that a pathogen may experience can be obtained. And this information is critical for gauging the treatment’s capacity to kill disease-causing bacteria or parasites before they reach the public.

“The use of UV will certainly lower the public’s risk of microbial pollution because it offers a second barrier of defence,” Linden said. UV treatment will also reduce the need for chemical disinfection, he added.

In the US, 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 new EPA rules for drinking water.

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 US. 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.

“While chlorine attacks the cell membrane, UV attacks organisms by breaking down their genetic material,” Linden said. “Combining the two disinfection methods will better protect against known threats like Crypto and against the next ‘bug of the month.’

“The microsphere dosimeter tool we’ve developed is an important step in advancing our understanding of how UV treatment works to disinfect drinking water,” he said.

In addition to improvements in the fight against waterborne illness, UV also offers a more environmentally-friendly water treatment method, Linden added. Its implementation will allow a reduction in chlorine use, which will lower the concentration of chemical byproducts found in the water supply.