The Role of Acidification for Antimicrobial Activity of Atmospheric Pressure Plasma in Liquids

TLDR

The study investigated indirect plasma disinfection of water using a surface dielectric barrier discharge. The liquid was neither part of the discharge electrode configuration nor stirred during plasma treatment. Plasma treatment completely inactivated high concentrations of *E. coli* and *S.

Abstract

Abstract Water disinfection by indirect plasma treatment was investigated using a surface dielectric barrier discharge (DBD). Liquid was neither part of the discharge electrode configuration nor stirred during plasma treatment. High concentrations (10 6 –10 8 cfu·mL −1 ) of Escherichia coli and Staphylococcus aureus have been completely inactivated within 5–15 min, depending on liquid sample volume. Inactivation occurred in non‐buffered liquids, only, where pH decrease was found. Measurements of pH, nitrate, and nitrite concentrations after DBD plasma or NO gas treatment lead to the conclusion that nitric acid formation from plasma‐generated reactive nitrogen species are the main source of liquid acidification. Incubation of bacteria in nitric acid alone did not result in comparable inactivation effects. Increase of H 2 O 2 concentration was found as a result of plasma treatment of liquids but not after treatment by NO gas. Therefore, synergistic action of both reactive oxygen and nitrogen species are discussed to be responsible for antimicrobial plasma effects. magnified image