Date of Award
Spring 2022
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil, Construction, and Environmental Engineering
First Advisor
Mayer, Brooke
Second Advisor
McNamara, Patrick
Third Advisor
Starke, Jeffrey
Abstract
The presence of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in the environment is a growing issue, which been exacerbated by the overuse and misuse of antibiotics in various healthcare and agricultural systems. One possible means of antibiotic resistance mitigation is through drinking water and wastewater treatment, specifically disinfection processes. Ultraviolet light emitting diodes (UV-LEDs) are an emerging disinfection technology that utilize LEDs that emit at varying peak wavelengths in the UV light spectrum. This study analyzed the effect of UV-LED on ARB and ARGs compared to conventional low-pressure UV (LP-UV) treatment and calculated electrical energy efficiencies for each system. Three peak polychromatic UV-LED wavelengths were utilized: 255 nm, 265 nm, and 285 nm; LP-UV emits a monochromatic wavelength at 254 nm. The ARB used here was TOP10 E. coli containing the pUC19 plasmid which carries resistance to ampicillin via the blaTEM gene. Two forms of ARGs were used: intracellular (blaTEM incorporated in the cell’s DNA in intact cells) and extracellular (free floating blaTEM plasmids). Increasing UV fluence increased log inactivation for both bacteria and genes. ARB tests indicated that damage to DNA (255 nm, 265 nm, LP-UV wavelengths) was more effective for inactivation than damage to cell proteins (285 nm wavelength) due to higher kinetic rate constants. Overall, the ARGs were less effectively damaged compared to bacteria. Furthermore, intracellular DNA was less effectively damaged than extracellular DNA, possibly because of the protective structures that encompass intracellular DNA. The UV-LEDs exerted larger energy demands compared to LP-UV treatment. This difference can be attributed to the low wall plug efficiencies for the LED wavelengths compared to LP-UV treatment. Energy efficiency was in the order of ARB < extracellular DNA < intracellular DNA, whereas the relative order was reversed considering first order rate constants for inactivation. Overall, UV-LEDs can successfully inactivate ARB and ARGs; however, for LEDs to become more competitive with LP-UV systems, energy efficiencies will have to improve greatly.