Inactwation of bacillus subtilis spores in water by a cold, atmospheric-pressure air plasma microjet

Summary form only given. Recently, a few attempts have been reported to inactivate bacteria in aqueous environments. Although effective inactivation of bacteria in their vegetative state (suspended in water) by non-thermal plasmas in or near the water has been reported, few studies have observed effective inactivation of bacterial spores. In this study, a direct-current, cold plasma microjet (PMJ) with atmospheric air as the working gas, sustained in a quasi-steady gas cavity in water, was used to inactivate Bacillus subtilis spores (suspended in water). The PMJ was operated at an air at a flow rate of ~5 slm and a current of 30 mA. The overall pH and temperature of the liquid were observed to change from 7.5 to a steady-state value of 3.4 and from 25° C to 40° C, respectively. The concentrations of NO₂^-, NO₃^- and H₂O₂ were observed to change from 0 to tens of ppm after a 20 min PMJ treatment. Water (without spore suspension) treated with plasma for 20 min was immediately applied to B. subtilis spores to evaluate the effect of long-lived reactive species in water (such as O3) on the inactivation. Other reactive oxygen species and reactive nitrogen species (ROS/RNS), such as OH, O₂^- and ONOO^- were detected by Electron Spin Resonance spectroscopy.