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This paper presents an experimental study of the inactivation in water of two representative classes of bacteria, Gram-negative Escherichia coli and Gram-positive Bacillus subtilis, using pulsed dielectric barrier discharges (PDBDs) in a coaxial arrangement. To this purpose, an adjustable plasma source supplies 25-kV/500-Hz pulses, 30 \mu\s long, at atmospheric pressure, with total energy consumption estimated at about 100 mJ/pulse. The inactivation effect of a PDBD on these types of microorganisms has been previously studied in dependence on an oxygen gas flow mode (null, continuous, and modulate). The results have shown a significant bacterial reduction rate from 10^8 to 10^3\ \cells/mL with E. coli and from 10^7 to 10^3\ \cells/mL with B. subtilis. The inactivation effectiveness is substantially similar in both kinds of bacteria, although some data suggest a greater susceptibility of the Gram-negative E. coli to plasma exposure. Plasma diagnostics was carried out using optical emission spectroscopy whereby the OH radical and reactive oxygen species formation rates in solution were found and the level of ozone produced by the discharge was monitored. Finally, a kinetics model was developed to characterize the chemical species taking place in nonthermal plasma inactivation processes in water. [ABSTRACT FROM PUBLISHER]

The design and construction of a 13.56-MHz RF power amplifier has been carried out on the basis of a modified resonant LC circuit in parallel regarding to the classic E-class amplifier LC series resonant circuit; this was done in order to take advantage of the operation characteristics of the resonant capacitor as a bidirectional voltage source. Therefore, the parallel LC circuit amplifies the voltage signals which can be applied to resistive or capacitive–resistive loads without the need for an impedance matching network, conventionally used with plasma generators. The main achievement of the described instrumentation lays in its constant response under a wide interval of load impedance. This facility has been applied to the generation of steady discharges in plasma needle appliances and both parallel plate and coaxial dielectric barrier discharge (DBD) reactors. Some relevant results of the DBD sterilization of four different kinds of microorganisms are included, showing the feasibility of the technique within reduced processing times, under 80 s in all the cases. [ABSTRACT FROM PUBLISHER]