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Wavelength-Specific UV Inactivation, Molecular Mechanisms, and Potential Synergies
Citation:
Beck, S., K. Linden, H. Ryu, L. Boczek, J. Cashdollar, K. Jeanis, O. Lawal, P. Suwan, AND T. Koottatep. Wavelength-Specific UV Inactivation, Molecular Mechanisms, and Potential Synergies. Presented at UV LED Technologies & Applications International Conference, Berlin, GERMANY, April 22 - 25, 2018.
Impact/Purpose:
This research assessed the wavelength-specific effects of germicidal ultraviolet (UV) irradiation on microorganisms including bacteria, viruses, and helminth eggs. Every organism has a unique spectral sensitivity to UV irradiation. In many cases, the sensitivity of bacteria strongly correlates with their DNA or RNA absorbance. For many viruses, however, the sensitivity deviates from the UV absorbance of their DNA or RNA because mechanisms other than nucleic acid damage are contributing to their UV inactivation. This is especially important for disinfection with UV light emitting diodes (LEDs), which emit across the germicidal wavelength range depending on their substrates and coatings.
Description:
This work evaluated UV LEDs emitting at 260 nm, 280 nm, and the combination of 260|280 nm together for their efficacy in inactivating a common fecal indicator, E. coli, as well as human enteric viruses on the United States Environmental Protection Agency’s contaminant candidate list (adenovirus 2 and four enteroviruses such as coxsackievirus A10, echovirus 30, enterovirus 70, and poliovirus 1), and surrogate microorganisms used for validating UV reactors, MS2 coliphage and Bacillus pumilus spores. When possible, inactivation by LEDs was compared with the efficacy of another common polychromatic UV source, the medium-pressure (MP) UV lamp as well as with low-pressure (LP) UV irradiation emitted at 254 nm. For some microorganisms, exposure to two UV LED wavelengths simultaneously was evaluated for potential synergistic effects. No dual-wavelength synergy was detected for bacterial and viral inactivation nor for DNA and RNA damage. Some scenarios were compared for electrical energy per order of log reduction. For UV-C LEDs to match the electrical efficiency per order of log reduction of conventional LP UV sources, they must reach efficiencies of 25-39% or be improved by smart reactor design. Follow-on research evaluated UV LEDs emitting at 280 nm and LP UV for their efficacy at inactivating Ascaris lumbricoides, an intestinal parasite common in low- to middle-income countries, responsible for roundworm infections in 1.4 billion people worldwide. Both UV sources were effective at very high doses with sufficient mixing: approximately 100 mJ/cm2 of LP UV irradiation and 250 mJ/cm2 of irradiation from a 280 nm UV LED were required for 1-log reduction of Ascaris lumbricoides.This wavelength-specific research will be discussed within the broader context of UV LED disinfection.