Non-thermal plasma applications in air sterilization

Abstract

In recent years, non-thermal atmospheric pressure plasma has been the focus of research as an improved method for the sterilization of air from biological contaminates. Although non-thermal plasma has been proven to inactivate and, in some cases, destroy many different types of biomaterials, such as viruses and bacteria, the primary mechanism by which this occurs is not completely understood. Some researchers speculate that electrostatic forces within the plasma can overcome the tensile strength of bacterial membranes and literally rip them apart. Many others believe that the sterilization mechanism is a result of a combination of factors including the interaction of ultraviolet radiation and active chemical species, such as ozone and hydroxyl radicals, that chemically alter and destroy the complex molecular structures that comprise the outer membranes of biomaterials. Furthermore, the plasma treatment times required to destroy different classes of bacteria and viruses have been shown to vary significantly, thus indicating that the chemical composition of each class of biomaterial is an important factor to consider when designing a plasma sterilization device. In our present study, we are constructing a physiochemical model of the oxidizing effects of the active chemical species generated by nonthermal atmospheric pressure plasma on the influenza A virus. The results of our model will provide us with an estimate of the optimal dose of active species required to destroy varying concentrations of airborne influenza viruses. We are specifically investigating the sterilizing effects of hydroxyl radicals (OH) because they are the most aggressive of the active chemical species created by non-thermal plasma and have a much shorter lifetime than ozone (O3). Ozone is a proven sterilizing agent, but it is known to have negative health effects and its longer lifetime can potentially lead to human exposure in shorter ventilation systems. Additionally, in order to achieve complete air sterilization, that is the complete oxidation of all organic matter including DNA, we will experiment with plasmas that have a relatively high temperature and large power density that can work at atmospheric pressure, but are still as efficient as cold plasma in providing active species. An example of such transitional non-thermal plasma is Gliding Arc in Tornado (GAT), which uses a reverse vortex flow to provide high velocity to a gliding arc discharge resulting in rapid convective cooling of the arc, recirculation of active species, and longer residence time of the organic matter in the plasma discharge zone. Based on the results of this study, a commercial system can be developed that will have low power consumption requirements, the capability to be retrofit into existing HVAC systems, and the highest efficiency at eliminating hazardous biomaterials as compared with modem decontamination systems today.