Download or read book Nanosecond-pulsed Pin-to-liquid Discharges for the Degradation of Recalcitrant Aqueous Organic Pollutants written by Maria Elena Corella Puertas and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "In this PhD thesis, a plasma-based reactor was developed for treating water contaminated with persistent organic pollutants. Specifically, the chosen configuration was a pin-to-liquid discharge reactor (gas discharge contacting the liquid surface), powered by repetitively pulsed nanosecond discharges. The initial proof-of-concept was achieved with a preliminary pin-to-liquid discharge configuration by testing the degradation of the methylene blue dye. In the present work, 84 % removal of methylene blue (7 mg/L nominal initial concentration, 1 ml) was achieved after 11 min of treatment without stirring the solution, which is improved until almost complete removal by introducing mixing. The preliminary configuration allowed to study and optimize operating parameters (stirring, voltage, pulse frequency, electrode polarity). Stirring the solution and increasing the voltage and pulse frequency led to more effective dye removal, whereas switching electrode polarity had little effect. Regarding transport of species within not-stirred solutions, an area of convective transport linked to Marangoni flow was observed close to the liquid surface, whereas in the bulk of the liquid mass transport was limited by diffusion. The knowledge gained through the preliminary configuration helped to design and construct a compact, nanosecond-pulsed pin-to-liquid discharge reactor (7.5 ml sample volume), which was used in the remaining part of the present work.In the process of choosing a suitable material for the high-voltage pin electrode, an extensive literature review revealed that various electrode materials erode in in-liquid discharge configurations, but there was no data available on the erosion of gas-side, high-voltage pin electrodes with above-liquid discharges. Therefore, the compact pin-to-liquid discharge reactor was used to study the erosion of high-voltage pin electrodes, using three different electrode materials (stainless steel, copper and hafnium) with two plasma gases (air, oxygen). Electrode erosion was observed for all studied cases, producing crater-like morphologies on the pin electrode tips and releasing metals in ionic and particle form into the plasma-treated water. The electrode material did not influence the energy deposited per pulse. Based on the results of this study, the preferred material was stainless steel for its low erosion rate in both plasma gases and its inexpensiveness. Furthermore, the effect of metals introduced through electrode erosion on reactive species in plasma-treated water was investigated over four weeks post-plasma exposure. Three long-lived reactive oxygen and nitrogen species (H2O2, NO2- and NO3-) were detected in plasma-treated water, and their concentration and lifetime were not affected by the electrode material.The ultimate application of the plasma-based reactor was the degradation of a particularly persistent aqueous pollutant, the pharmaceutical diatrizoate (DTZ). Conventional wastewater treatment plants are not able to remove DTZ, which has been detected in various aqueous environments such as surface waters, groundwaters and wastewater treatment effluents in numerous countries, with concentrations ranging from ng/L to μg/L. Oxygen and air plasmas were used for DTZ removal, with oxygen plasma performing better (e.g. after 20 min treatment of 200 μg/L DTZ in pure water, oxygen led to 90% degradation whereas air achieved 20% degradation). Transformation products (TPs) of DTZ were identified: m/z 486A, 504A, 504B, 628, 630A, 630B (previously described in literature) and m/z 486B, 550, 555, 565, 578 (novel). The residual, acute toxicity of TPs was tested on Aliivibrio fischeri. No acute toxicity of TPs was observed. Since DTZ is a particularly recalcitrant aqueous organic pollutant, its successful removal and the lack of formation of toxic TPs indicates that the developed plasma-based technology is promising for treating challenging wastewaters, such as hospital wastewaters"--