A method of ultraviolet germicidal irradiation (UVGI) for water pathogen inactivation effectiveness using tunable, narrowband laser light is described. A transportable tunable UV (TTUV) laser system for providing a known irradiance (μW/cm2) or dose (mJ/cm2) suitable for irradiating water samples in Petri dishes over the wavelength range of 210 nm–300 nm was developed by the National Institute of Standards and Technology. The TTUV facility, consisting of a 1 kHz pulsed UV laser and light-tight enclosure containing the optics necessary to uniformly irradiate a water sample, was used in a microbiology laboratory to dose drinking water pathogens and surrogates as part of a Water Research Foundation study in the summer and fall of 2012. The approach demonstrated improved accuracy and simplified spectral analysis over conventional pathogen inactivation sources consisting of broadband UV sources and bandpass filters. In this work, the TTUV facility design and key components are described, including modifications in the field to provide the required irradiance levels. The irradiance and dose levels produced by the tunable UV laser during the project are also presented. The transportability of the TTUV system enabled it to be brought to a microbiology facility allowing the water samples (microbial suspensions) to be irradiated in a location with experienced staff and facilities for preparing, handling, analyzing, storing, and shipping the many samples studied. These results, published elsewhere, established that the tunable UV laser system provides unique UVGI capabilities for use with water pathogens and has applications for other pathogen experiments, for example, air-purification studies.

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Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

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