Effectiveness Evaluation for Bacteria and Fungi Disinfections of Developed Ozone Machine

A low-cost ozone machine was developed to generate gaseous ozone for decontaminating the non-ventilated and unoccupied room within a 50-minute ozonation duration. This ozone machine, equipped with a centrifugal blower, could assist in thoroughly dispersing ozone gas throughout an enclosed area, as a result this ozone machine could raise the ozone concentration up to 2.4 ppm inside a 50 square-meter classroom after the ozonation period. Performances of this ozone machine were experimentally evaluated inside both non-ventilated and ventilated classrooms. First, an average total ozone dose of 58 ppmmin, which was close to an upper limit for the >90% viral disinfection, demonstrated the machine effectiveness in the viral inactivation. Second, a waiting period for ozone decomposition and removal using a ceiling ventilated fan could be predicted from an exponential decay rate of ozone concentration to be about 1.5 hour before the decontaminated room could be re-entered safely. Third, the disinfection of bacteria and fungi, which are tougher than most viruses, were validated by the cultural tests using standard plate count agars after the 50-minute ozone exposure. Results of the colony count and microorganism identification using the MALDI-TOF MS and the fungi slide culture technique revealed that 11 species of bacteria and 5 species of fungi could be inactivated by ozone gas after the specified ozonation period.