Evaluation of cold plasma inactivation efficacy against different airborne bacteria in ventilation duct flow

A full-size, experimental, ventilation ductwork was designed and set up to measure one-pass inactivation efficacies of a cold plasma installation under various practical environmental conditions. Five types of microorganisms, which are commonly associated with nosocomial infection, including Escherichia coli, Pseudomonas alcaligenes, Staphylococcus epidermidis, Micrococcus luteus and Serratia marcescens, were chosen and tests were conducted at four airstream velocities, ranging from 2 to 7 m/s, and two different relative humidity (R.H.) levels. The inactivation efficacies for the first three types of bacteria varied from 20% to 70%. It is interesting to note that the inactivation efficacy increased with velocity. No detectable inactivation effect was found for M. luteus and S. marcescens. The inactivation efficacy at 90% R.H. dropped to 10% of the value measured at 55% R.H. The negative ion intensities measured near the plasma installation were correlated with the airstream velocities. When compared with data from systems using conventional fibrous filters, the pressure drop measured across the plasma unit was very small. Our experiments showed that cold plasma technology has high potential to be used as an energy-efficient method for disinfection. Limitations of application are also discussed.