Air and Water Sterilization using Non-Thermal Plasma

Abstract

Summary form only given. Various investigations have proven the effectiveness of nonthermal plasma against microorganisms. This sterilization effect is of great importance in countering the threat of bioterrorism. So far, most of sterilization studies have been in the direction of surface sterilization. The sterilization effect of plasma on air and water were investigated in this study. For air sterilization, a small scale model of HVAC was designed and dielectric barrier discharge plasma source was used for treatment of air. This PDRF (Pathogen Detection and Remediation Facility) consisted of a circulatory airflow system, a plasma chamber and a sampling system. The airflow was set to mimic actual air flow in an HVAC system (25 L/sec). The bacterium E coli have been used as a prototype bacterium in these experiments. It is a gram negative non-spore forming bacteria. E coli bacteria were cultured in liquid broth media and grown overnight. The bacterial containing aerosol was introduced into the system using a collision nebulizer. Air sampling system consisted of AGI Air Samplers. The plasma discharge was then ignited. This created a "screen" of plasma across the chamber and the entire contaminated air stream was treated. Air samples taken from the system were analyzed using the plate count method and flow cytometry. The first pass through this screen of plasma produced greater than 1 log reduction and by the time of the second treatment with plasma, the 5 log reduction had been achieved. The present study provides data on the effectiveness of the sterilization action of pulsed spark discharge in water containing Escherichia coli (E. coli). Potable water containing E.coli was treated with a pulsed spark discharge system. The other discharge systems used for water sterilization: pulsed corona, gliding arc and DC discharge over the water were also investigated for comparison. The present study demonstrated that a rather low energy input of 400-600 J/ml of water was required to obtain a one-log reduction in E. coli concentration. The energy consumption for other plasma sources used for water sterilization (corona, gliding arc and DC discharge) to obtain the same sterilization effect was much higher.