Oxidation and bio-decontamination effects of impulsive discharges in atmospheric air

Chemical oxidation and the bactericidal capabilities of non-thermal plasma discharges can be used in different practical applications such as bio-decontamination, sterilisation of medical equipment, waste water treatment, syn-gas treatment and others. In this paper, the oxidation and bio-decontamination effects of impulsive plasma discharges which propagate across a liquid sample/air interface (surface discharges), and through the bulk of a liquid sample (direct discharges), have been investigated. The oxidising capability was analysed by measuring the degree of decolourisation of indigo carmine dye in water solutions. Gram-negative and Gram-positive bacteria, E. coli and S. aureus, respectively, were used as model microorganisms in the investigation of the biocidal effects of plasma discharges. Surface and direct plasma discharges were generated by high-voltage impulses of both polarities, with magnitudes of 20 kV, 24 kV and 28 kV, the chemical oxidation and bio-decontamination capabilities of such discharges have been obtained and analysed. It has been established that the defining factor in the chemical and biological effects of plasma discharges is the normalised delivered charge (dose). The results obtained in this study show that surface discharges have greater bio-decontamination capability as compared with direct transient plasma discharges. Also, it was shown that the decontamination rate of E.coli is more than double than that of S. aureus.