WaterUV offers hope for safer drinking water

Published 26 December 2012

Recent changes in the Environmental Protection Agency’s (EPA) surface water treatment rules mandate, among other things, more aggressive monitoring and control of various pathogens, notably including Cryptosporidium; this microbe, which can cause severe illness or death, is highly resistant to chlorine-based disinfection practices; as one means to reducing the threat, the EPA has called for treating water with ultraviolet (UV) radiation, which also serves as a “secondary barrier” to inactivate (prevent reproduction of) other key pathogens such as adenovirus and other viruses, as well as bacteria and parasites such as Giardia

A group of researchers from PML’s Sensor Science Division is part of a project that will have a direct effect on improved safety of the nation’s drinking water.

Recent changes in the Environmental Protection Agency’s (EPA) surface water treatment rules mandate, among other things, more aggressive monitoring and control of various pathogens, notably including Cryptosporidium. This microbe, which can cause severe illness or death, is highly resistant to chlorine-based disinfection practices. As one means to reducing the threat, the EPA has called for treating water with ultraviolet (UV) radiation, which also serves as a “secondary barrier” to inactivate (prevent reproduction of) other key pathogens such as adenovirus and other viruses, as well as bacteria and parasites such as Giardia.

The water is treated by cylindrical UV lamps suspended in pipes, and the illumination is monitored by adjacent sensor units. Each pathogen has a different inactivation response to different wavelengths, and it now appears that certain pathogens are most susceptible to wavelengths shorter than the shortest in the spectrum produced by conventional lamps. Recent advances in medium-pressure (MP) UV lamp technology, however, have led to increased UV light output at wavelengths less than 240 nm, prompting researchers to address numerous unresolved questions.

A NIST release reports that these questions include: Which wavelengths or combinations of wavelengths (termed “action spectra”) are most effective on which pathogens? How much irradiation is required to achieve a “4-log” (99.99 percent) inactivation for different microbes? How can a new generation of UV sources and sensors be reliably calibrated and validated in water facilities of all sizes across America? And how accurately do benign microbes, used as pathogen surrogates by testing facilities, represent inactivation performance in target microorganisms at different wavelengths?

All these questions and more are under investigation by a multi-organization collaborative project, headed by Karl Linden at the University of Colorado and funded by the Water Research Foundation (the Water Research Foundation is funded by more than 950 subscribing water utilities in the United States, Canada, Europe, Australia, and northern Asia) with the goal of eventually developing guidelines for testing future systems using MP mercury vapor lamps as UV sources.

“Most of the spectral response data for different pathogens was set up for low-pressure (LP) mercury-vapor lamps as UV sources inside water pipes,” says Thomas Larason of NIST’s Optical Radiation Group, who leads the PML contribution to the water project. “Those lamps produce a relatively narrow UV spectrum

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