Avaly Doubla

Evidence of Temporal Postdischarge Decontamination of Bacteria by Gliding Electric Discharges: Application to Hafnia alvei

ABSTRACT This study aimed to characterize the bacterium-destroying properties of a gliding arc plasma device during electric discharges and also under temporal postdischarge conditions (i.e., when the discharge was switched off). This phenomenon was reported for the first time in the literature in the case of the plasma destruction of microorganisms. When cells of a model bacterium, Hafnia alvei, were exposed to electric discharges, followed or not followed by temporal postdischarges, the survival curves exhibited a shoulder and then log-linear decay. These destruction kinetics were modeled using GinaFiT, a freeware tool to assess microbial survival curves, and adjustment parameters were determined. The efficiency of postdischarge treatments was clearly affected by the discharge time (t*); both the shoulder length and the inactivation rate kmax were linearly modified as a function of t*. Nevertheless, all conditions tested (t* ranging from 2 to 5 min) made it possible to achieve an abatement of at least 7 decimal logarithm units. Postdischarge treatment was also efficient against bacteria not subjected to direct discharge, and the disinfecting properties of “plasma-activated water” were dependent on the treatment time for the solution. Water treated with plasma for 2 min achieved a 3.7-decimal-logarithm-unit reduction in 20 min after application to cells, and abatement greater than 7 decimal logarithm units resulted from the same contact time with water activated with plasma for 10 min. These disinfecting properties were maintained during storage of activated water for 30 min. After that, they declined as the storage time increased.

Postdischarge Long Life Reactive Intermediates Involved in the Plasma Chemical Degradation of an Azoic Dye

The gliding electric discharge is a source of nonthermal plasma at atmospheric pressure efficient for pollutant abatement. It was used with a wet airflow to determine the kinetics of the postdischarge oxidation process of methyl orange dye in acidic solution (i.e., an oxidation reaction occurring after switching off the discharge). A strong postdischarge degradation of the dye giving N.N dimethyl-4-nitroaniline, as the major yellow intermediate product with a relevant overall first-order kinetics, was observed. Effects of both discharge exposure time and wet airflow were studied, showing linear correlations between these parameters and the overall rate constant. Such results combined with the studies of nitrous acid occurrence and oxidation of the dye by HNO2 and H2O2 suggest that nitrous and peroxonitrous acids are the main oxidizing species involved in the phenomenon