David Moussa

Disposal of spent tributylphosphate by gliding arc plasma.

The gliding arc in humid air is a relevant source of free radicals and strongly oxidising species such as HO* (shown by emission spectroscopy), which are able to degrade organic wastes. This feature was used in a new process for mineralising spent tributylphosphate (TBP) which is an important waste from nuclear industry. The degradation kinetics is examined by monitoring the conversion of TBP into phosphoric acid in a batch reactor. The kinetics exhibits three steps and especially an overall zero-order linear step with a rate of 10 mmol h(-1) at the beginning of the treatment. This zero-order step agrees with a surface oxidation process. After a 13.7h treatment, about 45% of the TBP is converted into inorganic phosphorus compounds, with phosphoric acid as the major product (63% of inorganic phosphorus compounds), and at least 19.5% is not degraded. Dibutylphosphoric acid (HDBP) was identified as the main by-product by a nuclear magnetic resonance technique, infrared spectroscopy and gas chromatography.

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?(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.

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

Gliding discharge-induced oxidation of a toxic alkaloid

The gliding discharge is a quenched plasma source suitable for the plasma treatments of liquids since it is operated in quasi-normal T and P conditions. Discharges in wet air provide a flow of strongly oxidizing radicals, e.g., NO and HO, able to oxidize and mineralize many organic pollutants in aqueous solution. The present paper reports on the destruction of nicotine, a toxic alkaloid from tobacco used as insecticide. Mineralization was monitored by total organic carbon (TOC) analysis and obeyed an overall first order kinetics mechanism. Carbon dioxide formation was followed by specific reactive Dräger tubes. The influence of the airflow rate was considered.

Reactions induced by electrical discharges in pollutant abatement and bacterial inactivation

Non-thermal plasmas generated by electrical discharges burning in natural air at atmospheric pressure involve gaseous active species which present particular chemical properties and may thus be later used for various environmental applications. This paper is devoted to identifying the relevant species and their specific chemical properties. The main species able to react at the surface of an aqueous solution of organic waste solutes derive from the parent species N2, O2 and H2O forming the atmosphere around the discharge. Most of the reactions induced at the surface or in the liquid phase i.e., oxidation and acid formation, are related with the occurrence of NO and OH and their derivatives such as hydrogen peroxide and nitric acid. Reacting intermediates (e.g., peroxynitrite and the matching acid) also form and participate in the overall reactive capacity of the plasma such as the degradation of organic solutes.