Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Karl G. Linden

Second Advisor

Roberto A. Rodriguez

Third Advisor

Mark Hernandez

Fourth Advisor

JoAnn Silverstein

Fifth Advisor

James P. Malley, Jr.

Abstract

This research assessed the wavelength-specific effects of germicidal ultraviolet (UV) irradiation on viruses and microorganisms. Every organism has a unique spectral sensitivity to UV irradiation, called its action spectrum. In many cases, the action spectra of bacteria strongly correlate with their DNA or RNA absorbance. For many viruses, however, the action spectra deviate from the UV absorbance of their DNA or RNA, suggesting that mechanisms other than nucleic acid damage are contributing to their UV inactivation.

This research determined the UV spectral sensitivity of Cryptosporidium parvum, adenovirus 2 and coliphage MS2, T1UV, Q Beta, T7, and T7m. Two viruses, MS2 coliphage and adenovirus, were studied more thoroughly to investigate whether UV damage to their genomes contributed alone to virus inactivation or whether UV damage to other viral components was also a contributing factor. The results indicated that polychromatic UV inactivation of MS2 coliphage is dominated by damage to its viral RNA across the germicidal wavelength range. However, for adenovirus, UV-induced damage to viral proteins also contributed to loss of infectivity, primarily at wavelengths below 240 nm. This finding provides insight into why UV irradiation from polychromatic, medium-pressure UV sources has been shown to be more effective than monochromatic (254 nm), low-pressure UV irradiation at inactivating adenovirus.

The research informed the design of a tailored, multiple-wavelength UVC LED unit that combines LEDs emitting at 260 nm and 280 nm with the goal of optimizing pathogen inactivation at a lower energy cost. The unit was tested with E. coli, MS2 coliphage, adenovirus 2, and Bacillus pumilus spores. Although the UVC LEDs are competitive with LPUV and MPUV lamps for water disinfection, they currently require more energy per log reduction of MS2, adenovirus 2, and B. pumilus spores. The 280 nm UV LED was more efficient (per log reduction) for inactivating E. coli. The UVC LED unit was also evaluated for potential synergistic effects. No dual-wavelength synergy was detected in bacterial or viral inactivation or in damage to the DNA or RNA.

Ultimately, the research adds fundamental insight into the mechanisms of inactivation of polychromatic germicidal UV irradiation for improving ultraviolet water disinfection.

Comments

Sixth advisor: Oliver R. Lawal.

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