Development and testing of a real-time sterilization unit using in ventilation duct

Recent study results in Taiwan have shown high concentration of microorganisms that sampled from the hospital HVAC (heating, ventilating, and air conditioning) system. As it is hard to empty the whole hospital patients and then sterilize the ventilation ducts, a real-time sterilization unit that located in the ventilation duct is a useful method to control the bioaerosol-transmitted infections in hospitals. The objective of this research was to develop a real-time sterilization unit and evaluate the unit under wind tunnel system and in field study. The real-time sterilization unit consists of Nickel-based filters and UVGI (ultraviolet germicidal irradiation) modules. In the experiment, a Collison nebulizer was used to generate Bacillus subtilis spores and Escherichia coli as challenge aerosols. Two Andersen 6-stage samplers were used to sample bacteria concentration upstream and downstream of the real-time sterilization unit. Moreover, two hospital wards and one nurse station located in central Taiwan were recruited in the field study. The results showed the real-time sterilization unit could be used to reduce the bacteria concentration under wind tunnel conditions. In field study, the real-time sterilization unit that coating with silicone oil revealed less large size bioaerosol bounce during velocity between 1.8 to 2.5 m/s in the ventilation duct. The average bacteria disinfection rate of ward 1, ward 2 and nurse station was 88.6 %, 92.5 % and 88.8 % by using six-stage Andersen impactor, respectively. The conclusions recommended that the Nickel-filter-based real-time sterilization unit should coat with silicone oil to avoid the large bioaerosol bounce effect, and was better to use the unit in main duct under high face velocity.