Comparing the efficacy of UVC-LED and low-pressure mercury lamps upper-room UVGI systems for air disinfection

In this study, we compared the performance of a novel UVC light-emitting-diode and the conventional mercury lamp UV systems, hereafter named LED- and mercury-type UR-UVGI systems, respectively, in a room-type air disinfection scheme to inactivate bacteria aerosols. Under constant environmental and well-mixed conditions, Escherichia coli and S. epidermidis were aerosolized and subjected to endogenous or natural decay. They were also exposed to each of the two UR-UVGI systems, independently. For the natural decay experiments, the k_n values were 0.0022±0.0005 s^-1, and 0.0007±0.0003 s^-1 for E. coli and S. epidermidis, respectively. The estimated decay rates, k, improved with the application of either the LED- or mercury-type UVGI system but varied between the two bacteria species. There was no significant difference (p = 0.3) between the inactivation of E. coli under the mercury-type (kUV-MV = 0.0045 ± 0.002 s^-1) and the LED-type UV irradiations (kUV-LED = 0.0031±0.001 s^-1). Likewise, the inactivation of S. epidermidis with LED-type (kUV-LED = 0.0019±0.0003 s^-1) and mercury-type (kUV-MV = 0.0022±0.0005 s^-1) UV irradiations were similar. However, S. epidermidis was more resistant to UV light than E. coli. These results showed that the LED-type UR-UVGI system can effectively inactivate microorganisms with equal performance as the conventional mercury lamp UR-UVGI system. This suggests that the LED-type UR-UVGI system can be used as a safe UV irradiation source to replace the conventional mercury vapor-filled UV lamps. Nevertheless, improvements in the UV-LED technology are necessary to enhance its performance for the disinfection of indoor bioaerosols, irrespective of species typology.