Comparison of direct DBD treatment and DBD exhaust gas treatment of liquids

Summary form only given. The treatment of liquid with a surface dielectric barrier discharge (DBD) under atmospheric pressure in air results in pH decrease and generation of nitrate (NO₃^-), nitrite (NO₂^-) and hydrogen peroxide (H₂O₂) in water. Even, after plasma treatment antimicrobial effects on suspended microorganisms were investigated [1] [2]. To investigate the effect of stable DBD generated reactive species, these experiments now were performed with the exhaust gas of the DBD. Therefore, the DBD arrangement for direct treatment [2] was flushed with an air flow of 0.5 slm and the exhaust gas of the device was blown through a long tube into another chamber with the liquid sample. In the DBD exhaust treated water were found nearly the same pH, nitrate and nitrite concentration, but no hydrogen peroxide. These results suggest that the acidification is initiated by reactive nitrogen species (RNS) mainly. To confirm the results, experiments with argon instead of air were performed. By direct DBD treatment in argon pH decrease and H₂O₂, but no nitrate and nitrite were detected. The treatment with exhaust gas from the DBD in argon resulted in no acidification and formation of hydrogen peroxide. The antimicrobial effects of E. coli were reduced in case of all experiments with DBD exhaust gases. Therefore, H₂O₂ formation of liquids by means of direct plasma treatment in argon and air is a result of short lived plasma species and maybe radiation. In case of direct argon DBD treatment acidification is not due to RNS but might be from short lived species like OH radicals.