Acidity control of plasma-chemical oxidation: applications to dye removal, urban waste abatement and microbial inactivation

Electric discharges burning in humid air at atmospheric pressure over aqueous solutions induce acid effects in the liquid phase resulting from the formation of nitric acid and peroxynitrous acid as transient precursor. These acid effects affect the degradation mechanisms of organic wastes and the relevant kinetic rates; therefore they thus must be controlled (e.g. using buffers). Nitrogen reactive species such as peroxynitrous acid or its salt are directly concerned with both acid effects as precursor to nitric acid, and strong oxidizing properties E degrees (ONO2H/NO2) = 2.02 V/SHE. Illustrating examples are given in the case of an organic dye (Alizarin S) removal and the gliding discharge treatment of urban wastewaters. Additional arguments are presented to explain the biocidal effect of humid air discharges.