Killing of bacterial spores contained in a paper envelope by a microwave plasma torch

The air plasma effluent of an arc-seed microwave torch is used to kill bacterial spores contained inside an envelope. The torch is operated at a 60-Hz periodic mode (with about 40% duty cycle) and runs stably at a low airflow rate (e.g., 0.393 l/s). The images of plasma torch plumes show that the arc loop of the discharge prolongs from the electrodes by nearly 3 cm and microwave energizes the charge particles along the arc loop considerably. The emission spectroscopy of the torch indicates that the plasma effluent contains an abundance of reactive atomic oxygen. Bacillus cereus is chosen for the biological agent in the decontamination experiment. The experiment and the decontamination efficacy of this torch are presented. The averaged temperature inside the envelope is measured to be less than 40 °C, thus ruling out the thermal decontamination mechanism.