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Chemical oxidation and the bactericidal capabilities of nonthermal plasma discharges can be used in different practical applications, such as biodecontamination, sterilisation of medical equipment, waste water treatment, syn-gas treatment, and others. In this paper, the oxidation and biodecontamination effects of impulsive plasma discharge, which propagate across a liquid sample/air interface (surface discharges), and through the bulk of a liquid sample (direct discharges), have been investigated. The oxidizing capability was analyzed by measuring the degree of decolorization of indigo carmine dye in water solutions. Gram-negative and gram-positive bacterias, 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 the magnitudes of 20, 24, and 28 kV, and the chemical oxidation and biodecontamination capabilities of such discharges have been obtained and analyzed. It has been established that the defining factor in the chemical and biological effects of plasma discharges is the normalized delivered charge (dose). The results obtained in this paper show that surface discharges have greater biodecontamination 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. [ABSTRACT FROM AUTHOR]

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method. [ABSTRACT FROM AUTHOR]