This article reports on experiments in a nonequilibrium plasma produced by nanosecond repetitively pulsed (NRP) spark discharges in water vapor at 450 K and atmospheric pressure. The objective is to determine the electron number density in the post-discharge, with spatial and temporal resolution, to gain a better understanding of the discharge development and chemical kinetics. Electron number densities were measured in water vapor from the broadenings and shifts of the H _α and H _β lines of the hydrogen Balmer series and of the atomic oxygen triplet at 777 nm. For an average reduced electric field of about 150 Td, high electron densities up to 3 × 10¹⁸ cm⁻³ are measured at the cathode, up to 5 × 10¹⁷ cm⁻³ at the anode, and up to 4 × 10¹⁶ cm⁻³ in the interelectrode gap. The high density near the electrodes is attributed to ionization enhancement and secondary electron emission due to the high electric field in the plasma sheath. In the middle of the inter-electrode gap, we show that the electron density mainly decays by electron attachment reactions. The dissociation fraction of water vapor is estimated to be around 2% in the middle of the gap.

Bacterial resistance to antibiotics has become a major public health problem in recent years. The occurrence of antibiotics in the environment, especially in wastewater treatment plants, has contributed to the development of antibiotic-resistant bacteria (ARB) and the spread of antibiotic resistance genes (ARGs). Despite the potential of some conventional processes used in wastewater treatment plants, the removal of ARB and ARGs remains a challenge that requires further research and development of new technologies to avoid the release of emerging contaminants into aquatic environments. Non-thermal atmospheric pressure plasmas (NTAPPs) have gained a significant amount of interest for wastewater treatment due to their oxidizing potential. They have shown their effectiveness in the inactivation of a wide range of bacteria in several fields. In this review, we discuss the application of NTAPPs for the degradation of antibiotic resistance genes in wastewater treatment.

The spatially-resolved electron temperature, rotational temperature, and number density of the two metastable Ar $1s$ levels were investigated in a miniature RF Ar glow discharge jet at atmospheric pressure. The $1s$ level population densities were determined from optical absorption spectroscopy (OAS) measurements assuming a Voigt profile for the plasma emission and a Gaussian profile for the lamp emission. As for the electron temperature, it was deduced from the comparison of the measured Ar $2p_i\to 1s_j$ emission lines with those simulated using a collisional-radiative model. The Ar $1s$ level population higher than 10 ${}^{18}$ m ${}^{-3}$ and electron temperature around 2.5 eV were obtained close to the nozzle exit. In addition, both values decreased steadily along the discharge axis. Rotational temperatures determined from OH(A) and N ${}_2$ (C) optical emission featured a large difference with the gas temperature found from a thermocouple; a feature ascribed to the population of emitting OH and N ${}_2$ states by energy transfer reactions involving the Ar $1s$ levels.

This work presents spatial variations of the helium He(2 ³ S ₁ ) metastable atom absolute densities in a plasma jet at atmospheric pressure in He + 0.2% O ₂ gas mixture impinging on a liquid target. The plasma jet is ignited with 6 kV pulses of 2.5 μ s duration and 8 ns rise and fall times at 20 kHz repetition rate. Streamers are created in both rising and falling fronts of the high voltage (HV). From Abel inversion of the line averaged absorbance of 1083 nm helium line, measured by laser absorption spectroscopy, the radial profiles of He(2 ³ S ₁ ) density along the plasma jet are deduced in two sources with different residence time of the gas within the discharge volume, having three different outlet tube diameters and with two gas flow rates. The metastable densities up to ∼3 × 10 ¹³ cm ⁻³ have been measured. The radial profile remained always axially centered for the 1.5 mm outlet tube and with 0.5 slm for the larger diameter tubes. But in this later tubes and with 2 slm gas flow rate, the profile changed from a ring shape at the tube exit to axially centered when increasing the distance from the tube edge. In the rising front of the HV, the ring profile of He(2 ³ S ₁ ) density in the tube exit is attributed to the shape of the electric field, produced by the applied HV to the electrode wrapped around the dielectric tube. In the falling front of the HV, the electric field results from electrons deposited on the inner surface of the dielectric tube and positive ions accumulated on the surface of liquid during the 2.5 μ s duration of the HV pulse. The influence of oxygen by-products formed in the plasma volume (O, O ₂ (Δ), O ₃ , positive and negative oxygen ions) on the dynamic of the plasma jet are analyzed.

Les décharges plasma dans la vapeur d’eau sont d’un grand intérêt pour de nombreuses applications potentielles, telles que le traitement biomédical, la production d’hydrogène ou la combustion assistée par plasma. Cette thèse propose une caractérisation expérimentale détaillée de l’effet thermique et chimique des décharges non-thermique nanosecondes répétitives pulsées (NRP) à la pression atmosphérique dans la vapeur d’eau pure. Un réacteur a été conçu pour fonctionner avec la vapeur d’eau préchauffée à 400-500 K. Les conditions opératoires retenues sont un débit de 300 g/h à 500 K et une décharge avec une énergie moyenne de 20 à 100 W, en régime Spark. Différents diagnostics ont été développés afin de déterminer les produits de cette décharge en termes d’espèces intermédiaires, de densité électronique et des produits stables. La concentration des produits de réaction stables (H2 et O2) et leurs débits respectifs ont été mesurés par chromatographie en phase gazeuse. Une valeur maximale de 0,85 g-H2/kWh a été obtenue. La densité électronique a été mesurée par spectroscopie d’émission optique (OES) résolue en temps grâce à l’élargissement par effet Stark des raies (H, H et O). La densité électronique maximale mesurée est 2X1018 cm-3 pendant l’impulsion. La température du gaz a été mesurée lors de la décharge de 20 ns par OES ainsi que entre deux décharges (100 us) par fluorescence induite par laser du radical OH (OH-PLIF) à deux couleurs. L’élévation maximale de la température est de 950 K après l’impulsion, et la température décroît ensuite de façon exponentielle avec un temps de décroissance caractéristique de 5 us. La densité relative du radical OH a été mesurée par OH-PLIF, révélant la durée de vie relativement longue de OH avec un temps de décroissance d’environ 50 us. En utilisant un modèle cinétique 0-D, la densité absolue OH à la fin de l’impulsion a été estimée à 400 plus ou moins 200 ppm. Les résultats obtenus ont permis d’éclairer les mécanismes sous-jacents à la génération de décharges NRP en régime Spark dans la vapeur d’eau pure à basse température.