Experimental evaluation of positive and negative air ions disinfection efficacy under different ventilation duct conditions

This study investigated the effectiveness of different polarities of ionizers in inactivating bioaerosols in a duct flow condition. Three bacteria species—Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium), and Staphylococcus epidermidis (S. epidermidis) —were aerosolized into the duct under three airstream velocities, ranging from 3.0 to 6.5 m/s. The positive ionizer showed better disinfection performance than the negative ionizer by 29%–41%. Our results showed an inverse correlation between air velocity and the disinfection efficiencies. As the velocity was increased from 3.0 to 6.5 m/s, the corresponding disinfection efficiencies of positive ionizer decreased from 88.5% to 44.0%, 49.0% to 38.7%, and 35.1% to 19.8% for E. coli, S. typhimurium, and S. epidermidis, respectively. For the negative ionizer, the corresponding disinfection efficiencies decreased from 62.9% to 35.4%, 54.2% to 30.0%, and 42.9% to 30.2% for E. coli, S. typhimurium, and S. epidermidis, respectively. The positive ionizer was further tested at three relative humidity levels (50%, 70%, and 90%)and three temperature (17.5 °C, 21.0 °C, and 25.0 °C)levels. From 50% to 90% relative humidity, the disinfection efficiencies decreased from 46.0% to 23.6%, 35.2% to 22.5%, and 24.8% to 20.7%, for E. coli, S. typhimurium, and S. epidermidis, respectively. At the same time, the efficacy of the ionizer increased as temperature decreased. Therefore, from a temperature of 17.5 °C to 25.0 °C, our results show that the disinfection efficiencies decreased from 56.0% to 32%, 38.8% to 22.6%, and 24.8% to 21.5%, for E.coli, S. typhimurium, and S. epidermidis, respectively. The ozone emission rates of both ionizers were measured and found to be very small.