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Study of the Characteristics of DC Multineedle-to-Water Plasma-Activated Water and Its Germination Inhibition Efficiency: The Effect of Discharge Mode and Gas Flow

In this article, a negative dc multineedle-to-water discharge device was designed to generate plasma-activated water (PAW) with a total volume of 580 mL. The physicochemical properties of PAW were investigated. The results showed that the products concentration of PAW and its acidity were not continuously increased by adding the applied voltage. When it turned from pulse corona discharge to DC glow-like discharge (−19.5 to −20.5 kV), the corresponding value decreased with the increase of the applied voltage. This decrease was attributed to the fact that the differences in the discharge figure had an effect on the reactions of transient species with NxOy in different discharge modes. In addition, by comparing the product concentrations of PAW in different gas conditions, we discovered that the gas flow would lead to a decrease of active species in PAW and its inactivation. Although the gas flow took away the NxOy diffused in the discharge chamber and formed microbubbles in the gas-washing bottle, which benefitted for increasing the absorption area with water, this process also took away NO out of the discharge area, which decreased its reaction with transient species such as OH, O2−, and O to form HNO2 and HNO3 directly. Finally, the germination inhibition rate (GIR) of penicillium spores was calculated to estimate the inactivation efficiency of PAW. The maximum GIR was 71.5% when the applied voltage was −19.5 kV (corona discharge) and the gas flow rate was 0 L/h.