Inactivation of Bacteria in Flight by Direct Exposure to Nonthermal Plasma

Plasma treatment is a promising technology for fast and effective sterilization of surfaces, waterflow, and airflow. The treatment of airflow is an important area of healthcare and biodefense that has recently gained the interest of many scientists. In this paper, we describe a dielectric barrier grating discharge (DBGD) which is used to study the inactivation of airborne Escherichia coli inside a closed air circulation system. Earlier published results indicate approximately 5-log reduction (99.999%) in the concentration of the airborne bacteria after single DBGD exposure of 10-s duration. This paper investigates plasma species influencing the inactivation. The two major factors that are studied are the effect of charged and short-lived species (direct exposure to plasma) and the effect of ozone. It is shown that for a 25% reduction in direct exposure, the inactivation falls from 97% to 29% in a single pass through the grating. The influence of ozone was studied by producing ozone remotely with an ozone generator and injecting the same concentration into the system, as that produced by the DBGD plasma. The results show a 10% reduction in the bacterial load after 10-s exposure to ozone; thus, ozone alone may not be one of the major inactivating factors in the plasma.