Dose–Response Behavior of Pathogens and Surrogate Microorganisms across the Ultraviolet-C Spectrum: Inactivation Efficiencies, Action Spectra, and Mechanisms

The dose-response behavior of pathogens and inactivation mechanisms by UV-LEDs and excimer lamps remains unclear. This study used low-pressure (LP) UV lamps, UV-LEDs with different peak wavelengths, and a 222 nm krypton chlorine (KrCl) excimer lamp to inactivate six microorganisms and to investigate their UV sensitivities and electrical energy efficiencies. The 265 nm UV-LED had the highest inactivation rates (0.47-0.61 cm²/mJ) for all tested bacteria. The bacterial sensitivity strongly fitted the absorption curve of nucleic acids at wavelengths of 200-300 nm; however, indirect damage induced by reactive oxygen species (ROS) was the leading cause of bacterial inactivation under 222 nm UV irradiation. In addition, the guanine and cytosine (GC) content and cell wall constituents of bacteria affect inactivation efficiency. The inactivation rate constant of Phi6 (0.13 ± 0.002 cm²/mJ) at 222 nm due to lipid envelope damage was significantly higher than other UVC (0.006-0.035 cm²/mJ). To achieve 2log reduction, the LP UV lamp had the best electrical energy efficiency (required less energy, average 0.02 kWh/m³) followed by 222 nm KrCl excimer lamp (0.14 kWh/m³) and 285 nm UV-LED (0.49 kWh/m³).