Inactivation of Bacteria in an Aqueous Environment by a Direct-Current, Cold- Atmospheric-Pressure Air Plasma Microjet

摘要

A direct-current, cold-atmospheric-pressure air plasma microjet (PMJ) sustained in a quasi-steady gas cavity in a liquid medium is used to inactivate Staphylococcus aureus (S. aureus) suspended in the liquid. The temperature and the pH value of the liquid change to steady-state rnvalues of about 40 ℃ and 3.0-4.5, respectively, after 10 min of plasma treatment. The decrease in the pH is attributed to the reaction of NO_x produced in the air plasma with water at the gas-liquid interface. The concentrations of NO_3~- and NO_2~- are measured to be 37 mg?L~(-1) and 21 mg ? L~(-1), respectively, after a 20 min of plasma treatment. Effective inactivation of S. aureus is found to start after the pH values decreases to about 4.5. This is attributed to the high oxidizing potential of the perhydroxyl radical (HOC) on the fatty acid in the cell membranes of the microorganisms in the liquid.