Hydrogen peroxide generation by DC and pulsed underwater discharge in air bubbles

The generation of H(2)O(2) in underwater discharge in air bubbles is studied with consideration of the influence of electrodes polarity, input power, solution conductivity and the inter-electrode distance. The efficiency of hydrogen peroxide generation strongly depends on the polarity, input power and the inter-electrode distance. Discharges in air bubbles with water as a cathode have significantly higher energy yield of hydrogen peroxide in comparison with negative DC or pulsed discharges. The generation of hydrogen peroxide by DC discharge increases with decrease in the inter-electrode distance, but it is opposite for pulsed discharges. Different efficiency of H(2)O(2) production is explained based on physical processes which result to formation of OH radicals

Under water discharge in bubbles in very low conductive solutions

This contribution presents experimental results obtained with underwater electric discharge created in rising gas bubbles. This discharge configuration is relatively new, and combines both gas and liquid phase discharges. The properties and mechanism of bubble discharge generation were investigated using a single pulsed high voltage. The electric discharge was generated in a pin-to-plate electrode configuration submerged in deionized water with conductivity of 2.0–5.0 μS/m. The gas bubbles were formed by injecting the gas through a glass filter disc at the bottom of the water tank. Air and helium were used as inlet gas. A spark gap pulse generator triggered the single negative high voltage pulses with rise times below 10 ns and peak voltages of 15–20 kV. The bubble position at the moment of high voltage application was accidental. The measured spectra were qualitatively reproducible, but significant quantitative differences were observed. We observed two types of discharge inside the bubble: delayed and direct spark discharge. The emission spectra of these two discharge kinds were qualitatively very similar

Electrical and spectroscopical characterization of pulsed single bubble discharge in water with a pin-to-plate electrode configuration

Plasma discharges inside gas or vapour bubbles in water have been proposed in the last decade as a new and effective method of water treatment. However, the fundamental nature of bubble discharge is still poorly understood. In the present paper, the mechanism and properties of bubble discharge are investigated by application of a high voltage pulse to a single free gas bubble in between a pin-to-plate electrode configuration submerged in de-ionised water. A spark gap pulse generator is used to create triggered negative voltage pulses with rise times below 10 ns. The peak voltage is varied from 12 kV up to 18 kV. In the present research, the metal pin electrode is consequently chosen as the cathode. The low conductivity of the de-ionised water is maintained on the order of 10 µS/m for all experiments. The gas bubbles are formed on the tip of a capillary positioned underneath the electrodes such that every bubble passes in between the pin and plate electrode. The He gas flow rate through the capillary is kept as low as 30 sccm in order to avoid discharge in successive bubbles by a single voltage pulse. In our first setup, voltage pulses are not triggered according to the bubble flow rate. Therefore, vertical bubble position at the moment of discharge is not made reproducible in successive measurements. The bubbles are estimated to be slightly smaller than the distance between the electrodes, i.e. 2 mm. Time dependence of voltage and current during discharge are measured in both cases with and without gas bubbling. Comparison shows that two types of bubble discharge are observed. One is spark discharge in a bubble and the other one is a delayed bubble discharge that starts the same way as discharge without bubbles. Spectra of the different types of discharge are measured in a wavelength range from 200 nm up to 900 nm. Electron temperature and density are determined from emission lines. Plasma parameters are determined for peak voltages of -12 kV, -15 kV and -18 kV respectively. Influence of the bubbling gas is discussed by comparison of measurements with helium and argon

Applications of plasma-liquid systems : a review

Plasma-liquid systems have attracted increasing attention in recent years, owing to their high potential in material processing and nanoscience, environmental remediation, sterilization, biomedicine, and food applications. Due to the multidisciplinary character of this scientific field and due to its broad range of established and promising applications, an updated overview is required, addressing the various applications of plasma-liquid systems till now. In the present review, after a brief historical introduction on this important research field, the authors aimed to bring together a wide range of applications of plasma-liquid systems, including nanomaterial processing, water analytical chemistry, water purification, plasma sterilization, plasma medicine, food preservation and agricultural processing, power transformers for high voltage switching, and polymer solution treatment. Although the general understanding of plasma-liquid interactions and their applications has grown significantly in recent decades, it is aimed here to give an updated overview on the possible applications of plasma-liquid systems. This review can be used as a guide for researchers from different fields to gain insight in the history and state-of-the-art of plasma-liquid interactions and to obtain an overview on the acquired knowledge in this field up to now

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of similar to 1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to similar to 4mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O-2 caused by the increasing electrical field, when the discharge is operated in ambient air

Electrical Discharge in Water Treatment Technology for Micropollutant Decomposition

Hazardous micropollutants are increasingly detected worldwide in wastewater treatment plant effluent. As this indicates, their removal is insufficient by means of conventional modern water treatment techniques. In the search for a cost-effective solution, advanced oxidation processes have recently gained more attention since they are the most effective available techniques to decompose biorecalcitrant organics. As a main drawback, however, their energy costs are high up to now, preventing their implementation on large scale. For the specific case of water treatment by means of electrical discharge, further optimization is a complex task due to the wide variety in reactor design and materials, discharge types, and operational parameters. In this chapter, an extended overview is given on plasma reactor types, based on their design and materials. Influence of design and materials on energy efficiency is investigated, as well as the influence of operational parameters. The collected data can be used for the optimization of existing reactor types and for development of novel reactors