Aim: To evaluate the microbial disinfection efficacy of a plasmachemical solution obtained by the activation of water with gliding electric discharges.
Methods and Results: Distilled water was ...activated for 5 min by a nonthermal quenched plasma of the glidarc type operating in humid air and at atmospheric pressure. The plasma‐activated water (PAW) was then used to treat planktonic and adherent cells of Staphylococcus epidermidis, Leuconostoc mesenteroides (as models of Gram‐positive bacteria), Hafnia alvei (a Gram‐negative bacteria) and Saccharomyces cerevisiae (as a yeast model). The treatments were less efficient on adherent cells than on planktonic cells in the case of bacteria, but not of S. cerevisiae. Inactivation was more effective for bacteria than for the yeast.
Conclusions: Significant reductions in microbial populations were achieved in all cases, demonstrating the effectiveness of this new approach to treat contaminated media.
Significance and Impact of the Study: PAW is a promising solution with potential application to the decontamination of equipment and surfaces.
Manganese (IV) oxide (MnO
2
) nanoparticles were synthesized, via a plasma-chemical route by using a gliding arc discharge at atmospheric pressure. α-MnO
2
nanorods were obtained from the chemical ...reduction of KMnO
4
. The synthesis yield was 96.8% after 4.5 min of exposure of the solution to the plasma. Further increase of the exposure time induced a decrease of MnO
2
yield because of its reductive transformation into Mn
2+
ions. Particles were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier Transform Infrared spectroscopy, and nitrogen physisorption. The plasma-catalytic properties of the synthesized material were tested in the bleaching of amaranth red (AR). AR bleaching efficiencies of 17 and 44% were respectively obtained when the plasma and plasma-catalyst processes were applied for 30 min with initial pH 10. The influence of the initial pH, and catalyst concentration were investigated: the AR bleaching efficiency increased linearly with the catalyst concentration and increased markedly when the pH of the solution decreased.
This study investigates the ability of spatial post-discharge mode functionalized kaolin to remove textile dye Reactive Red 2 from aqueous solution compared to that of the raw kaolinite. To fulfill ...the aim, the removal conditions, including plasma exposure time, processed mode (direct and post-discharge), pH of the aqueous dye solution, initial dye concentration and adsorbent dosage, were investigated. The changes that occur on clay surfaces before and after gliding arc plasma treatment were followed by Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen physisorption. The point of zero charge and the changes of the textural properties after gliding arc plasma treatment were also examined. The experimental data were analyzed using pseudo-first-order, pseudo-second-order and empirical Elovich models. The diffusion phenomenon was also studied. The results obtained indicate that spatial post-discharge pre-treatment of kaolin deeply influences the functional groups of some of its minerals as well as the morphology and texture of its particles. Consequently, at room temperature (∼30 °C), the maximum adsorption capacities of natural raw kaolin clay were tripled after treatment with gliding arc plasma in spatial post-discharge mode and were almost doubled after the direct treatment mode.
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 HNO 2 and H 2 O 2 suggest that nitrous and peroxonitrous acids are the main oxidizing species involved in the phenomenon
Kaolin samples obtained from Cameroon were used to produce geopolymer binders. Prior to its application, the raw kaolin samples were activated through the gliding arc plasma treatment using both ...spatial post-discharge and direct mode. A mixture of sodium hydroxide and silicate was used as the alkaline solution. In order to study the influence of the modifications generated by the gliding arc plasma treatment on the geopolymerization process, X-ray diffraction, thermogravimetric analysis, differential scanning calorimeter and Fourier transform infrared spectroscopy were carried out. In addition, scanning electron microscopy, nitrogen physisorption and compression tests analysis were also carried out on the resulting geopolymer samples to access their mechanical performance. The results showed that the geopolymerization process was not completed at the curing temperature of 90 °C. Plasma spatial post-discharge mode treated kaolin led to 20.48% increase in compressive strength when compared with the geopolymer prepared from raw kaolin.
A Cameroonian kaolinite powder was treated with gliding arc plasma in order to increase the amount of hydroxyl functional groups present on its external surfaces. The functional changes that occurred ...were monitored by Fourier transform infrared spectroscopy. The crystalline changes were followed by the X-ray diffraction. The ionisation effect, acid effect, and water solubility of the treated samples were also evaluated. Results showed that there is breaking of the bonds in the Si–O–Si and Si–O–Al groups, followed by the formation of new aluminol (Al–OH) and silanol (Si–OH) groups at the external surface of kaolinite after exposing the clay to the gliding arc plasma. The increase in hydroxyl groups on the surface of kaolinite leads to the increase of its hydrophilicity. Moreover, new charges appear on its surfaces and no significant change in crystallinity has occurred. This study shows that clays in powder form being can effectively be functionalised by gliding arc plasma in spatial post discharge processing mode. Knowing that the treatment in spatial post discharge offers the possibility to process large amounts of clay, this work is of great interest to the industry.
The performance of a plasma reactor for the degradation of chlorinated hydrocarbon waste is reported. Chloroform was used as a target for a recently patented destruction process based using an ...inductive plasma torch. Liquid waste was directly injected axially into the argon plasma with a supplied power of ∼4 kW in the presence of oxygen as oxidant and carrier gas. Decomposition was performed at CHCl3 feed rates up to 400 g·h−1 with different oxygen/waste molar ratios, chloroform destruction was obtained with at least 99% efficiency and the energy efficiency reached 100 g·kWh−1. The conversion end products were identified and assayed by online FTIR spectroscopy (CO2, HCl and H2O) and redox titration (Cl2). Considering phosgene as representative of toxic compounds, only very small quantities of toxics were released (< 1 g·h−1) even with high waste feed rates. The experimental results were very close to the equilibrium composition predicted by thermodynamic calculations. At the bottom of the reactor, the chlorinated acids were successfully trapped in a scrubber and transformed into mineral salts, hence, only CO2 and H2O have been found in the final off-gases composition.
The gliding arc discharge, which is a source of nonthermal plasma, was used to enhance the biodegradation of crystal violet (CV), a triphenylmethane non-biodegradable organic dye. The determination ...of the biodegradability index, i.e., biochemical oxygen demand (BOD
5
)/chemical oxygen demand (COD) ratio, and the total organic carbon measurement were used to assess the biodegradability. For the biological treatment alone, a bacterial strain of
Aeromonas hydrophila
(8 × 10
8
CFU mL
−1
) bleached 42 % of CV solution (50 mg L
−1
) after 12-h incubation. The bleaching rate was enhanced by increasing the initial bacterial concentration; however, a drop in the bleaching rate was noted when CV concentration was increased. For the plasma process alone, a 15-min treatment resulted in a color removal of 49.7 %, at a mineralization rate of 12.2 %, thereby increasing the BOD
5
/COD ratio from 0.11 to 0.23. There was an increase in the bleaching rate in temporal post-discharge conditions (i.e., self-continuity of reaction after the discharge was switched off): For 2 h of temporal post-discharge reaction, the color removal of the 15-min plasma-pre-treated CV increased to 55 %. The disappearance of color during each treatment method followed the first-order kinetics. With regard to the combined plasma/biological treatment process, the 15-min plasma-pre-treated sample was bleached at 92 % by
A. hydrophila
after 2-h incubation and completely bleached for 6 h. Therefore, there is a positive synergism of bacterial and plasma treatments. This combined treatment is useful in reducing the energy involved in complete mineralization of wastewater containing non-biodegradable dyes.
Discharges in humid air are valuable tools for producing active species which react both at the liquid surface of the targets and in the solution. These species are responsible for a noticeable ...abatement of the pollutant concentration, even of recalcitrant compounds. The relevant kinetics are examined with special emphasis on Temporal Post Discharges Reactions which develop in the solution after the discharge is switched off and without supplying extra energy. The moieties responsible for this feature are discussed and arguments favour H 2 O 2 and peroxynitrous acid. ONO 2 H, which degrades lipoproteins is probably involved in the attacks at the bacterial membranes causing the death of the microorganisms. TPDR are also identified in case of bacterial inactivation. Plasma activated water induces inactivation of bacterial colonies even 24 h after the plasma treatment. Developments to improve the efficacy of the discharges and reduce the running costs are presented.
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