Characterization of a robot-assisted UV-C disinfection for the inactivation of surface-associated microorganisms and viruses.

Microorganisms pose a serious threat for us humans, which is exemplified by the recent emergence of pathogens such as SARS-CoV-2 or the increasing number of multi-resistant pathogens such as MRSA. To control surface microorganisms and viruses, we investigated the disinfection properties of an AI-controlled robot, HERO21, equipped with eight 130-W low pressure UV-C mercury vapor discharge lamps emitting at a wavelength of 254 nm, which is strongly absorbed by DNA and RNA, thus inactivating illuminated microorganisms. Emissivity and spatial irradiance distribution of a single UV-C lamp unit was determined using a calibrated spectrometer and numerical simulation, respectively. The disinfection efficiency of single lamps is determined by microbiological tests using B. subtilis spores, which are known to be UV-C resistant. The required time for D99 disinfection and the corresponding UV-C irradiance dose amount to 60 s and 37.3 mJ•cm-2 at a distance of 1 m to the Hg-lamp, respectively. Spatially resolved irradiance produced by a disinfection unit consisting of eight lamps is calculated using results of one UV-C lamp characterization. This calculation shows that the UV-C robot HERO21 equipped with the mentioned UV-C unit causes an irradiance at λ=254 nm of 2.67 mJ•cm-2•s-1 at 1 m and 0.29 mJ•cm-2•s-1 at 3 m distances. These values result in D99 disinfection times of 14 s and 129 s for B. subtilis spores, respectively. Similarly, human coronavirus 229E, structurally very similar to SARS-CoV-2, could be efficiently inactivated by 3-5 orders of magnitude within 10 - 30 s exposure time or doses of 2 - 6 mJ•cm-2, respectively. In conclusion, with the development of the HERO21 disinfection robot, we were able to determine the inactivation efficiency of bacteria and viruses on surfaces under laboratory conditions.