Corona Discharge In Water Research Articles

Acoustic Effects of Underwater Plasma Pulsed Sound Source under Different Electrical Parameters

Methods of pulse discharge in water were studied under different voltage and conductivity parameters. The voltage and current data in the experiment were collected and analyzed. Then the mechanism of the two discharge modes was briefly discussed (the initial mechanism of the corona mode is still unclear compared to the thermal process mechanism of the arc mode). Finally, two kinds of discharge methods were compared and analyzed from the aspects of experimental phenomena, production mechanism and application prospects. The experiment found that the acoustic effect of corona discharge in water under large solution conductivity is obvious, which provides a new idea for the design of underwater plasma sound source.

Effect of pulse width on streamer propagation of underwater corona discharge

The propagation of pulsed negative corona discharges in water as a function of electrical pulse width ranging from 100 ns to 100 μs has been studied experimentally. Using point‐to‐plane electrodes, it is demonstrated that the propagation of streamers exhibits different behavior under excitations with different pulse width. For pulses with width shorter than 1 µs, the average velocity stays relatively constant at about 1000 m s−1. For pulses with width longer than 1 µs, the average velocity decreases dramatically with increasing pulse width. Numerical fitting shows that the relationship between the velocity and pulse width follows u ∝ τ−0.72. Two different mechanisms are proposed to explain the different discharge characteristics observed at different time scales. At the initial stage before the generation of any significant heat, we show that the electrostatic force may play a major role in supplying the driving force. As the pulse width increases, the gas temperature rises, and the pressure caused by evaporation may become the dominant force to push the head of the filament to propagate. The transition time between two modes was estimated to be in the order of microseconds. Our quantitative predictions are in reasonable agreement with experimental results.

Fenton chemistry promoted by sub-microsecond pulsed corona plasmas for organic micropollutant degradation in water

Differences in the liquid chemistry due to different ground electrode materials (titanium, stainless steel) were compared for corona discharges in water. The plasma was generated by applying positive high voltage pulses that are characterized by short rise times of about 20 ns, a peak voltage of 80kV and pulse lengths of about 150–160ns (FWHM). Phenol was admixed to the water for quantification of the bulk reaction chemistry, such as phenol decomposition and H2O2-formation. Optical emission spectroscopy was conducted to relate chemistry to plasma processes. Possible electrode corrosion was determined by atomic absorption spectroscopy (AAS).The post-discharge chemistry strongly depends on ground electrode material. With stainless steel electrodes, decomposition efficiency of phenol increased by about three quarters (74.9 %) when compared with titanium electrodes. This result can be explained by dissolved metal ions corroded from the ground electrode, which catalytically decomposed the H2O2 that had been formed into hydroxyl radicals again. Ground electrodes were corroded due to electrochemical processes. Corrosion rates and overall reaction chemistries cannot readily be described similar to conventional DC electrochemical processes at low voltages. The repetitive application of sub-microsecond high voltage pulses has to be taken into account explicitly. Altogether, electrode materials, ground electrode corrosion and associated catalytic processes are more important for plasma processes in aqueous solutions than was recognized so far. Therefore, the effects need to be taken into account in the analysis of laboratory results as well as the development of respective novel water treatment technologies.

A comparative summary on streamers of positive corona discharges in water and atmospheric pressure gases

From an intention of summarizing present understandings of positive corona discharges in water and atmospheric pressure gases, we tried to observe streamers in those media by reproducing and complementing previously reported results under a common experimental setup. We used a point-to-plane electrode configuration with different combinations of electrode gap (7 and 19 mm length) and pulsed power sources (0.25 and 2.5 e s duration). The general features of streamers were similar and the streamer-to-spark transition was also observed in both the media. However, in the details large differences were observed due to inherent nature of the media. The measured propagation speed of streamers in water of 0.035 × 10 6 ms −1 was much smaller than the speed in gases (air, N 2 and Ar) from 0.4 to 1.1 × 10 6 ms −1 depending on species. In He the discharge looked glow-like and no streamer was observed. The other characteristics of streamers in gases, such as inception voltage, number of branches and thickness did also depend on the species. The thickness and the length of streamers in water were smaller than those in gases. From the volumetric expansion of a streamer in water after the discharge, the molecular density within the streamer medium was estimated to be rarefied from the density of water by about an order of magnitude in the active discharge phase. We derived also the electron density from the analysis of Stark broadened spectral lines of H and O atoms on the order of 10 25 m −3 at the earlier time of the streamer propagation. The analyzed background blackbody radiation, rotational temperature of OH band emission and population density of Cu atomic lines yielded a consistent temperature of the streamer medium between 7000 and 10 000 K. Using the present data with a combination of the analysis of static electric field and previously reported results, we discuss the reason for the relatively low streamer inception voltage in water as compared to the large difference in the medium density between water and gases.

Decomposition of Pharmaceuticals by Pulsed Corona Discharges in Water Depending on Streamer Length

Pulsed corona discharges generated in water provide a possibility for the abatement of even stable organic compounds. Decomposition efficacy correlates with the length of streamers, which in turn depends on water conductivity and applied voltage. We investigated the relation between conductivities from 25 to 500 μS/cm, pulse duration, and visible streamer length for applied peak voltages of 70 and 82 kV. Streamer development for an initially applied peak voltage of 70 kV was related to the decomposition rates of the pharmaceutical carbamazepine that was dissolved in solutions with conductivities in the same range.

Inactivation of Bacillus subtilis var. niger of both spore and vegetative forms by means of corona discharges applied in water

Spores are dormant units of bacteria resistant to numerous disinfection methods. Additionally, the effects on bacteria of repetitive electrical discharges in water by used of the so-called “corona discharges” or streamer are poorly described. In this study vegetative and spore forms of Bacillus subtilis var. niger were subjected to these discharges. To generate corona discharges in water, a Marx generator capable of delivering 60–90 kV was used with a coaxial chamber of treatment. Vegetative and spore form reductions were defined using colony-forming unit counting. Proteins extracts were separated by two-dimensional electrophoresis and spots of interest were characterized by mass spectrometry. Shock waves were assessed by the diminution of liposome size and OD400 nm. The results show a decrease in bacteria viability of 2 log10 after 1000 discharges on the vegetative form and 4 log10 after 10,000 discharges on the spores. Two-dimensional electrophoresis showed that the streamers impact the regulation of several proteins in the vegetative forms with UniProt ID: P80861, Q06797, P80244, C0ZI91, respectively. The reduction appears to be due, in part, to hydrogen peroxide (H2O2) generated by the corona discharges while spore deactivation remained insensitive to these chemicals. The spore eradication was associated to shock waves induced by the discharges but not H2O2. Corona discharges appear as a prospective method for eradication of spores in water. The corona discharges can be an efficient method for decontamination processes of waste water.

The catalytic role of tungsten electrode material in the plasmachemical activity of a pulsed corona discharge in water

The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle–plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H2O2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50–70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H2O2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H2O2, which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H2O2, in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H2O2 and DMSO.

Inactivation of MS2 bacteriophage by streamer corona discharge in water

Electrical discharge processes are emerging as water treatment technologies applicable to both the degradation of organic contaminants as well as inactivation of pathogens. Particularly as a disinfection technology, electrical discharge processes do not produce toxic byproducts, and effectively inactivate a wide spectrum of microorganisms by multiple lethal actions generated by the formation of plasma channels. This study demonstrates the inactivation of a virus using the streamer corona discharge process (SCDP) with MS2 phage as a surrogate. A rapid inactivation of MS2 phage (i.e., approximately 4 log inactivation in 5 min) was observed in all experimental runs conducted. Discharge conditions such as applied voltage and storage capacitance significantly affected the inactivation efficiency of MS2 phage, whereas the influence of water quality parameters was minor. In order to elucidate the mechanism of MS2 phage inactivation, potentially lethal factors that can be generated by the SCDP were selected, and their roles in the inactivation of MS2 phage were examined. As a result, effects of UV radiation, chemical oxidants, and pulsed electric fields were found to be insignificant. The shockwave generated upon plasma channel formation appears to be the most important factor responsible for MS2 phage inactivation.

Streamer Propagation in a Large-Volume Underwater Corona Discharge Reactor

The underwater electrical discharges have received extensive attention in water or wastewater treatment. It is important to generate a large-volume underwater corona discharge at a relatively low voltage for its practical applications in water and wastewater treatment. A coaxial rod-cylinder electrode configuration has been developed for generating a large-volume corona discharge in water. The electrical characteristics of the corona discharges in water were investigated. The temporal evolution images of the streamer propagation were observed by an ultrahigh-speed frame camera system. The effect of water conductivity on the corona discharges was studied. The results show that the maximum of the measured current and the dissipated energy per pulse increase as the water conductivity increases while the maximum streamer length and the number of ignition seams per centimeter of the anode during one pulse duration decrease with increasing water conductivity. It was found that the propagation velocity of the streamer is ~30 km/s, and the water conductivity has no significant influence on it.

The Role of Surface Chemistry at Ceramic/Electrolyte Interfaces in the Generation of Pulsed Corona Discharges in Water Using Porous Ceramic‐Coated Rod Electrodes

AbstractEffects associated with the electrical breakdown of water using porous ceramic‐coated rod electrodes were investigated for two types of ceramics, oxide (corundum) and silicates (almandine). Properties of the ceramic layer and its interaction with the electrolyte were found as important factors in the generation of electrical discharges in water. Initiation of the discharge depended not only on the permittivity and porosity of the ceramic, but also the surface charge formed on the ceramic, which was determined by the polarity of the applied voltage, and the pH and chemical composition of aqueous solution. An electrical double layer associated with the buildup of surface charge at ceramic/electrolyte interface affected the electric field distribution on the ceramic electrode. Using monopolar high voltage pulses, this layer became polarized, which, under certain experimental conditions, eventually quenched the electrical discharge in water. Applying bipolar pulses eliminated these effects.magnified image

Large Area Pulsed Corona Discharge in Water for Disinfection and Pollution Control

To investigate the efficiency of submerged pulse corona (SPC) discharges in water we built a laboratory scale, parallel-plate reactor that is part of a closed loop water circulation system. A pulsed voltage is applied across the electrodes. One of the electrodes is coated with a porous ceramic layer to create local field enhancements to initiate corona discharges. For energization of the SPC reactor a pulse generator was developed which is based on a capacitor discharge initiated by a semiconductor switch. A pulse transformer, followed by two magnetic pulse compression stages, produces voltage pulses with amplitudes of up to 30 kV at a pulse width of 0.3 ?s. Simulation of the circuit behavior leads to good agreement with voltage and current measurements. Details of the pulse generator and first experimental results concerning the efficiency of radical production are presented. Depending on the conductivity of the water to be treated, pulse currents of > 600 A at a voltage of 20 kV to > 30 kV are obtained for electrode sizes of around 50 cm2. The efficiency of the radical production is measured in terms of the hydrogen peroxide (H2O2) concentration, which is formed by recombination of hydroxyl radicals (OH.) at sufficiently high concentrations downstream of the plasma reactor. At pulse repetition rates of 20 to 100 Hz, H2O2 concentrations of several mg/l are produced, at efficiencies in the range of up to ?1 g/kWh.

Ultraviolet radiation from the pulsed corona discharge in water

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (∼1–3 J pulse−1) was performed using the potassium ferrioxalate actinometry. Photon flux J190–280 and radiant energy Q190–280 of the UV light emitted from the discharge at spectral region 190–280 nm was determined in dependence on the applied voltage (17–29 kV, positive polarity) and the solution conductivity (100–500 µS cm−1). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders of magnitude within the range of solution conductivities 100–500 µS cm−1. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190–280 = 44.33 (quanta pulse−1). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

Characteristics of atomic oxygen produced by a pulsed streamer corona discharge

Various active species can be formed by a pulsed discharge in water, and these active species may play an important role in killing bacteria and degrading organic compounds. In recent years, interest in the formation of OH, O3 and H2O2 has grown enormously. The O is also a very powerful oxidant, but little research has been done on the oxygen radical. In this paper, production of atomic oxygen by the pulsed streamer corona discharge in water has been identified. The effects of applied voltage polarity, peak voltage, oxygen and inert gases bubbling on radical formation have been investigated.

Erosion of needle electrodes in pulsed corona discharge in water

Erosion of needle electrodes in the pulsed corona discharge in water with a pulse energy of ∼ 2÷; 3 J was investigated in dependence on the electrode material (platinum, tungsten and stainless-steel) and the solution conductivity (100 and 500 µS/cm). Erosion of electrodes remarkable increased with the higher solution conductivity for all three tested metals. The highest erosion rates were determined for tungsten while platinum was the least eroded material. In addition to the dominant melting effect, release of anode material by the electrolysis significantly contributed to the total erosion of needle electrodes. The highest contribution of electrolysis was determined for stainless-steel electrodes that released up to 40–50% of eroded metal in the form of iron ions. Peculiar protrusions were observed on the surface of eroded tungsten electrodes.

Synthesis of superabsorbent copolymers by pulsed corona discharges in water

Pulsed corona discharges have been utilized for plasma polymerization in aqueous solution for the first time. Superabsorbent copolymers, i.e., poly(acrylamide-co-acrylic acid) hydrogels, were synthesized by aqueous solution polymerization using free radicals produced by pulsed corona discharges as initiator and N,N-methylene-bis-acrylamide as cross-linking agent. Acrylic acid contents in the monomers varied from 0% to 50%. The copolymers thus formed adsorbed 30–1100 g H2O/g of copolymer. The FTIR spectra of the copolymers are comparable with the published FTIR spectra of the corresponding copolymers synthesized by a conventional chemical method and by γ-ray technique.

Synergistic effect of pulsed corona discharges and ozonation on decolourization of methylene blue in water

The effect of O2 and O3 bubbling on decolourization of methylene blue by pulsed corona discharges in water was studied. The pulsed corona discharges were produced by charging an 80 pF capacitor with a 40 kV DC source, through a 100 MΩ resistor, and discharging it into a needle-plate type reactor at 60 Hz through a rotating spark gap switch. A 20 ml sample of 13.25 mg l-1 methylene blue in distilled water was decolourized in 120 min. Bubbling O2 at 10 ml min-1 through the discharge region reduced the decolourization time to 25 min. Bubbling O2 containing 1500 µmol O3 l-1 at 10 ml min-1 reduced the decolourization time to 8 min. The O3 was produced by fractionating input energy between a water treatment reactor and a O3 generator, i.e. no additional energy was consumed for O3 production. Under the same experimental conditions methylene blue solution in tap water was decolourized in >210 min by corona discharge in solution, in 30 min by corona discharge with O2 bubbling, and in 11 min by corona discharge with bubbling of O2 containing 1500 µmol O3 l-1.

Advanced oxidation processes using pulsed streamer corona discharge in water

Degradation of complex organic dyes by pulsed streamer corona discharge in water has been investigated using a ring-to-cylinder electrode geometry system. The obtained result shows that the efficiency of the decoloration depended on the initial pH of solution and the decoloration rate was higher at lower initial pH value. In the case of hydrogen peroxide addition, the decoloration rate increased due to the reactions of dye with hydroxyl radicals formed by photo-dissociation of hydrogen peroxide in the plasma discharge channels. However, the reactor with two rings was more effective than that of one ring for the decoloration due to a larger volume occupied by the streamer plasma channels in water.

Characteristics of Ring-to-Cylinder Type Electrode System on Pulsed Discharge in Water

AbstractThe pulsed streamer corona discharge in water has been investigated for oxidation of organic contaminants in water solution. The reactor with ring-to-cylinder electrode system has been designed and tested in this investigation. It was found that the insulation method of the ring electrode was the most important factor to lower streamer initiation voltage. A large volume of streamer corona discharge was generated around the ring electrode and the streamer corona discharge formations are greatly dependent on the electrode geometry, polarity and the water conductivity. The degradation of phenol was also tested by this electrode system. It was found that the degradation rate of phenol was higher for the positive pulse than that of negative pulse, and the intermediate products were removed when the treatment time increased.

Wastewater treatment

Differences in the liquid chemistry due to different ground electrode materials (titanium, stainless steel) were compared for corona discharges in water. The plasma was generated by applying positive high voltage pulses that are characterized by short rise times of about 20 ns, a peak voltage of 80 kV and pulse lengths of about 150–160 ns (FWHM). Phenol was admixed to the water for quantification of the bulk reaction chemistry, such as phenol decomposition and H2O2-formation. Optical emission spectroscopy was conducted to relate chemistry to plasma processes. Possible electrode corrosion was determined by atomic absorption spectroscopy (AAS).The post-discharge chemistry strongly depends on ground electrode material. With stainless steel electrodes, decomposition efficiency of phenol increased by about three quarters (74.9 %) when compared with titanium electrodes. This result can be explained by dissolved metal ions corroded from the ground electrode, which catalytically decomposed the H2O2 that had been formed into hydroxyl radicals again. Ground electrodes were corroded due to electrochemical processes. Corrosion rates and overall reaction chemistries cannot readily be described similar to conventional DC electrochemical processes at low voltages. The repetitive application of sub-microsecond high voltage pulses has to be taken into account explicitly. Altogether, electrode materials, ground electrode corrosion and associated catalytic processes are more important for plasma processes in aqueous solutions than was recognized so far. Therefore, the effects need to be taken into account in the analysis of laboratory results as well as the development of respective novel water treatment technologies.

Degradation of Acetophenone in Water by Pulsed Corona Discharges

Degradation of acetophenone in dilute aqueous solution has been studied using pulsed corona discharges in water. Higher conversions of acetophenone were obtained with the addition of oxygen or ozone than with the addition of nitrogen and without the addition of any gas. Intermediates of acetophenone degradation, as determined by gas chromatography–mass spectroscopies (GC–MS), were phenethyl alcohol, toluene, and 2-acetylphenol. In addition, the degradation reaction pathways of acetophenone in water are discussed.