Bio-decontamination by DC discharges at atmospheric pressure: various methods for identification of microbial inactivation mechanisms

摘要

Bio-decontamination of water contaminated by bacteria or yeasts and of surfaces contaminated by spores is investigated by using three types of DC discharges in atmospheric pressure air. The discharges are operated in point-to-plane geometry or with one electrode submerged in water and diagnosed by electrical measurements, temporally-resolved optical emission spectroscopy, and fast ICCD imaging. The streamer corona with small current pulses (approx10 mA) with a 10-30 kHz repetitive frequency generates very cold non-equilibrium plasma (300-350 K). With increasing applied voltage, the streamers transit to the transient spark: the spark with very short (<100 ns) high current pulses (approx1 A) of 0.5-5 kHz repetitive frequency and very limited energy. Thanks to the very short spark pulse duration given by the small internal capacity of the discharge system and the limiting series resistor, the plasma cannot reach LTE conditions (500-1000 K). With an appropriate ballast resistor, this transient regime evolves into a pulse-less discharge with properties of a typical glow discharge. The three DC discharges generate non-thermal plasmas with various gas temperatures and properties and different effects on tested microorganisms.