Inactivation of bacteria using dc corona discharge: role of ions and humidity

Here we present the results of an experimental study of the effect of ions produced in a dc corona discharge on inactivation of bacteria on the surface of agarose gel. Both positive and negative corona discharges in various gases at different humidities were studied. The measurements in air, O-2, N-2, Ar and He mixtures show that there is no inactivation in pure N-2, pure O-2 and an N-2-H2O mixture. The best results were achieved in the case of direct treatment, when discharge was ignited in oxygen and water-containing mixtures. We show that neither UV radiation, ozone or H2O2 nor other neutral active species alone produced by corona have an effect on bacteria viability. It is shown that the main role of charged particles may be related to the faster transport of active peroxide species-cluster ions OH-(H2O)(n) and H3O+(H2O)(n). The efficiency of these radicals is much higher than that of the oxygen radicals and ions (including O-2(-), O-4(+) and O-3) and that of nitrogen and argon ions.