Influence of the Air Humidity on the Reduction of Bacillus Spores in a Defined Environment at Atmospheric Pressure Using a Dielectric Barrier Surface Discharge

From literature different plasma species are known for their possibility to inactivate microorganisms. Most studies report on the inactivation of germs by UV light emitted from rare gas discharges like plasma-jets or low pressure discharges or disruption of cell membranes due to charging effects. Our aim was to show the influence of air humidity and active plasma power in a simple atmospheric pressure dielectric barrier surface discharge on the reduction of Bacillus atrophaeus spores within a few minutes of treatment time. The plasma treatment time was varied at humidity levels between 0 and 70% relative moisture with a distance of 0.6 mm between the dielectric barrier and test strip. The obtained results have shown an influence of the air humidity on the spore inactivation rate which has been reached by plasma treatment. The plasma does not emit a significant amount of UV light below 320 nm. From these results the role of reactive species, especially the effect of hydroxyl radicals, is discussed.