Gas-phase Pulsed Corona Discharge Research Articles

Oxidation of aqueous p-Nitroaniline by pulsed corona discharge

Toxic and potentially carcinogenic aromatic amines widely used in industry find their way to the aquatic environment. Gas-phase pulsed corona discharge (PCD) treatment of recalcitrant organic pollutants is a promising energy-efficient advanced oxidation process. The study assessed the energy efficiency of PCD in oxidation of p-nitroaniline (PNA), a persistent and ubiquitous pollutant of the aquatic environment. The effect of process control parameters on the energy efficiency of PNA degradation was studied including pH, gas–liquid contact surface and applied pulse repetition frequency. The results showed that PCD surpasses the commercially available competitor, Fenton reagent, for about three times. The reaction intermediates were analysed by HPLC-MS(ESI ± ) resulting in proposal of two transformation products. The PNA oxidation process followed the second-order kinetics showing the reaction rate coefficient moderately increasing with the contact surface and decreasing with the pulse repetition frequency. The acute toxicity of PNA solutions decreased substantially on the course of PCD treatment.

Degradation of anti-inflammatory drug dexamethasone by pulsed corona discharge: The effect of peroxycompounds addition

The oxidation of anti-inflammatory dexamethasone (DXM) in water was experimentally studied using a gas-phase pulsed corona discharge (PCD) with the addition of extrinsic oxidants: peroxydisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2), aiming the increased energy and overall treatment efficiency. The effects of pH, the dose of supplementary oxidant, and the composition of real water matrix on the efficiency of DXM oxidation were established. For PCD and the PCD/oxidant combinations, a faster and more complete degradation of DXM was observed in acidic media. In neutral media, the PCD/PDS process showed the highest TOC removal and energy efficiency of DXM oxidation. Overall, the carefully optimized dose of extrinsic oxidant resulted in a perceptible improvement of oxidation efficiency in PCD/PDS and PCD/H2O2 combinations compared to PCD under similar treatment conditions. In the groundwater matrix, the use of PCD/PDS and PCD/H2O2 combinations demonstrated considerably faster DXM degradation and mineralization at higher efficiency. The results of this study contribute to the possible application of combined PCD/oxidant processes for efficient removal of DXM from polluted water matrices.

Oxidation of aqueous bisphenols A and S by pulsed corona discharge: Impacts of process control parameters and oxidation products identification

Widespread usage of bisphenol A (BPA) and its potential replacement bisphenol S (BPS) has led to their presence in natural waterbodies. The experimental research into degradation of both aqueous pollutants by application of gas-phase pulsed corona discharge (PCD) was undertaken with variation of process control parameters, pulse repetition frequency, gas–liquid contact surface and addition of surfactant OH-radical scavenger sodium dodecyl sulphate (SDS). Although the contact surface variation had only a moderate impact on bisphenols degradation, its effect was stronger in total organic carbon removal. The addition of SDS showed a moderately negative impact on energy efficiency at all studied conditions. The obtained results showed energy efficiency surpassing the closest competitors, ozonation and other electric discharge processes. The detected major oxidation intermediates were mainly formed through hydroxylation and cracking of benzene rings, followed by further degradation into short chained aliphatic acids. The oxidation end-products were quantified as acetate, formate and oxalate.

Oxidation of Aqueous Dexamethasone Solution by Gas-Phase Pulsed Corona Discharge

The most widely used anti-inflammatory corticosteroid dexamethasone (DXM), frequently detected in waterbodies due to its massive consumption and incomplete removal in wastewater treatment processes, was experimentally studied for oxidation with gas-phase pulsed corona discharge (PCD) varied in pulse repetition frequency, pH, DXM initial concentration and additions of surfactant sodium dodecyl sulphate (SDS) and tert-butyl alcohol (TBA). The experimental study also included ozonation as compared to PCD in energy efficiency. The advantageous energy efficiency of PCD was observed in wide spans of pH and DXM initial concentrations surpassing ozonation by about 2.4 times. Identified transformation by- and end-products (fluoride and acetate), as well as the impact of radical scavengers, point to the prevalent radical oxidation of DXM. Somewhat increased toxicity observed on the course of PCD-treatment of high DXM concentrations presents a subject for further studies.

Oxidation of Aqueous Toluene by Gas-Phase Pulsed Corona Discharge in Air-Water Mixtures Followed by Photocatalytic Exhaust Air Cleaning

The treatment of wastewaters containing hazardous volatile organic compounds (VOCs) requires the simultaneous treatment of both water and air. Refractory toluene, extensively studied for its removal, provides a basis for the comparison of its abatement methods. The oxidation of aqueous toluene by gas-phase pulsed corona discharge (PCD) in combination with the subsequent photocatalytic treatment of exhaust air was studied. The PCD treatment showed unequalled energy efficiencies in aqueous and gaseous toluene oxidation, reaching, respectively, up to 10.5 and 29.6 g·kW−1·h−1. The PCD exhaust air contained toluene residues and ozone in concentrations not exceeding 0.1 and 0.6 mg·L−1, respectively. As a result of the subsequent photocatalytic treatment, both airborne residues were eliminated within a contact time with TiO2 as short as 12 s. The results contribute to the possible application of the studied approach in closed-loop energy-saving ventilation systems.

Oxidation of aqueous organic molecules in gas-phase pulsed corona discharge affected by sodium dodecyl sulphate: Explanation of variability

Oxidation of waterborne organic compounds by gas-phase pulsed corona discharge (PCD) provides substantial energy efficiency benefits. Surfactant sodium dodecyl sulphate (SDS) alters the energy efficiency of oxidation providing decelerating, neutral or accelerating effect. Determining the causal connection between the pollutant's molecular structure and the effect of SDS addition presents the research objective. Computational chemistry Spartan 14 1.1.4 software was used for modelling of SDS molecule interaction with selected textile dyes and pharmaceuticals with subsequent verification in PCD treatment experiments. Effects of SDS addition were predicted for acid orange 7, indigotetrasulfonate, paracetamol and indomethacin and confirmed experimentally.

Oxidation of ubiquitous aqueous pharmaceuticals with pulsed corona discharge

Aqueous pharmaceuticals present an emerging environmental problem for their potent character. Advanced oxidation processes (AOPs) present efficacious abatement strategy, being, however, unaffordable in mass application. Energy efficient gas-phase pulsed corona discharge was experimentally studied for oxidation of aqueous ibuprofen, diclofenac, metformin and tramadol showing the energy yields of 53, 21, 15 and 89 g kW-1 h-1, respectively, at 10 mg L-1 initial concentrations, surpassing other AOPs. Impacts of alkaline pH and starting concentrations on oxidation energy efficiency are beneficial to various extents to all considered pharmaceuticals. The removal efficiency was found to correlate with molecular structure and hydrophobicity of medications.

Effects of persulfate and hydrogen peroxide on oxidation of oxalate by pulsed corona discharge

Application of gas-phase pulsed corona discharge (PCD) to oxidation of aqueous pollutants shows unequalled energy efficiency among advanced oxidation processes (AOPs). Improved AOPs often activate extrinsic oxidants. Experimental research was undertaken into sodium persulfate and hydrogen peroxide activation by PCD in oxidation of 1.11 mM oxalate. Oxidant and target compound concentration ratios, pH, gas-liquid contact surface and pulse repetition frequency were studied as control parameters. Results implicated a beneficial effect at oxalate/persulfate molar ratios from 1:0.1 to 1:1 in acidic medium with the optimum at 1:0.5, moderate contact surface and lower frequency. However, the observed synergism of PCD/PS combination decreased with increasing the initial pH of the treated solution. Hydrogen peroxide exhibited negative or neutral impact in all media. Non-assisted PCD proved the most energy efficient approach towards water treatment at neutral and alkaline conditions.

Degradation of aqueous alachlor in pulsed corona discharge

Gas-phase pulsed corona discharge (PCD) gained attention due to its energy-efficient oxidation of waterborne organic pollutants and simplicity in use and maintenance. Experimental study in PCD oxidation of aqueous herbicide alachlor was undertaken for its energy efficiency and degradation products. Plasma oxidation efficiency exceeds the one of ozonation by at least two times. Electric conductivity up to 10 mS cm−1 demonstrated negligible impact. Bicarbonates reduced the oxidation efficiency scavenging hydroxyl radicals. Identification of degradation intermediates proposed the rationale of predominant OH-radical reactions including dehalogenation, electrophilic attack of aromatic ring, ether bond cleavage, and cyclisation.

Oxidation energy efficiency in water treatment with gas-phase pulsed corona discharge as a function of spray density

Gas-phase pulsed corona discharge (PCD) shows promising energy efficiency in oxidation of aqueous pollutants. Further progress requires knowledge in efficiency dependent on the contact surface of treated water sprinkled to the discharge zone. Experimental studies focused on the dependency used phenol and oxalate solutions at various pH for variable oxidation kinetics. For slow reactions within the experimental limits, oxidation rate was growing substantially with the spray density. Rapid oxidation showed an optimum spray density determined by discharge power at sufficiently developed interface. The oxidation kinetics fits to description of a pseudo-second order process predicting optimum choice of sprinkling rate.

Surfactant and non-surfactant radical scavengers in aqueous reactions induced by pulsed corona discharge treatment

The choice of energy input rate in treatment of aqueous media with gas-phase pulsed corona discharge (PCD) requires quantification of reactive oxygen species (ROS) reactions dependent on oxidation kinetics. The role of surfactant and non-surfactant OH-radical scavengers in PCD was studied in respect of oxidation of phenol, oxalic and humic acid. Phenol reacts fast, whereas oxalate is known to selectively react with OH-radicals. Humic acid oxidation is slow. Rapid energy intake is advised for oxidation induced exclusively by radical reactions, such as humics, whereas abatement of admixtures reacting with both surface-borne and long-living oxidants benefits from reduced pulse repetition frequency.

Behaviour of aqueous sulfamethizole solution and temperature effects in cold plasma oxidation treatment

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k1) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k2). At elevated temperature of 50 °C, the k1, k2 values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

Hospital wastewater treatment with pilot-scale pulsed corona discharge for removal of pharmaceutical residues

In recent years, accumulation of pharmaceutical compounds in the environment has been an issue of growing concern. Conventional wastewater treatment has limited effectiveness with many pharmaceuticals at concentrations of ppb or ppt scale. An intuitive solution would be to treat the pharmaceuticals-contaminated wastewaters at the source sites before dilution in sewer networks. Health institutions with concentrated drug consumption provide logical point sources for pharmaceuticals entering the sewage. This paper describes the pilot-scale removal of a wide range of pharmaceuticals from real wastewaters via gas-phase pulsed corona discharge oxidation. The process was studied for raw sewage from a public hospital and for biologically treated wastewater of a health-care institute. The non-selective oxidation of the observed pharmaceuticals (32 compounds) was effective at reasonable energy cost: 87-% reduction in residual pharmaceuticals (excluding biodegradable caffeine) from raw sewage was attained with 1 kWh m−3 from the raw sewage and 100% removal was achieved for biologically treated wastewater at only 0.5 kWh m−3. The impact for affected aquatic environments upon the present solution would be a dramatically reduced load of pharmaceutical accumulation.

Effect of recycling overhead gases on pollutants degradation efficiency in gas-phase pulsed corona discharge treatment

In the present study, pollutant degradation efficiency was investigated by recycling of overhead gases from gaseous phase to aqueous phase in gas-liquid interface pulsed corona discharge reactor. Methylene blue (MB) was used as a model pollutant and its degradation was compared by recycling and non-recycling of oxygen, air and argon gases. The degradation rate constants of MB were 0.28 and 0.23 min−1 in recycled condition which was decreased to 0.22 and 0.21 min−1 in non-recycled condition in oxygen and argon gas, respectively. On contrary, in air medium, comparatively higher MB degradation rate (0.21 min−1) was achieved in non-recycled condition compared to recycled condition (0.11 min−1). The long-lived reactive oxygen species (ROS) such as hydrogen peroxide and ozone were quantified in both conditions. We observed that the concentration of ozone present in the aqueous solution was slightly higher in recycling conditions as compared to that of non-recycled condition in all the gases. Moreover, higher hydrogen peroxide concentration was detected in recycled condition (185 and 168 mg/L) compared to non-recycled condition (112 and 40 mg/L) in the presence of oxygen and argon, respectively, and vice-versa in air medium. The economic comparison revealed that up to 33% of electrical energy could be saved by recycling overhead oxygen gas.

Pulsed Corona Discharge Induced Hydroxyl Radical Transfer Through the Gas-Liquid Interface

The highly energetic electrons in non-thermal plasma generated by gas phase pulsed corona discharge (PCD) produce hydroxyl (OH) radicals via collision reactions with water molecules. Previous work has established that OH radicals are formed at the plasma-liquid interface, making it an important location for the oxidation of aqueous pollutants. Here, by contacting water as aerosol with PCD plasma, it is shown that OH radicals are produced on the gas side of the interface, and not in the liquid phase. It is also demonstrated that the gas-liquid interfacial boundary poses a barrier for the OH radicals, one they need to cross for reactive affinity with dissolved components, and that this process requires a gaseous atomic H scavenger. For gaseous oxidation, a scavenger, oxygen in common cases, is an advantage but not a requirement. OH radical efficiency in liquid phase reactions is strongly temperature dependent as radical termination reaction rates increase with temperature.

Abatement of amoxicillin and doxycycline in binary and ternary aqueous solutions by gas-phase pulsed corona discharge oxidation

The presence of pharmaceutical compound residues in water bodies is becoming an increasingly serious problem. Various pharmaceuticals have been detected in raw municipal wastewaters, after wastewater treatment plant processes, and even in drinking water. Many common pharmaceuticals are bio-accumulating and they can have a harmful impact on aquatic and terrestrial organisms.In this work, pulsed corona discharge technology (PCD) is studied as a potential method for antibiotic compounds abatement. Two antibiotics, amoxicillin and doxycycline, were chosen as test pharmaceutical compounds. The aim of the study was to investigate the transformation kinetics of binary solutions (water – single antibiotic compound) and ternary solutions (water – two antibiotic compounds) of the compounds and to optimize operational parameters for improved oxidation performance. Ternary solutions were investigated to obtain data on transformation kinetics when two competing pharmaceutical molecules are present in the solution. The experiments showed that reactions of doxycycline oxidation are always first order reactions. Reaction of amoxicillin oxidation has second order in the case of experiments with binary solution in alkaline medium. In other cases, it has first order. The transformation products formed were identified and monitored based on liquid chromatography mass spectrometer analysis. OH-amoxicillin, amoxicillin pencilloic acid, OH-doxycycline and 2-OH-doxycycline had the largest peaks areas. All studied compounds and all transformation products can be easily oxidized by PCD. Approximately 1 kWh/m3 and 0.5 kWh/m3 delivered energy is enough for oxidation of great part of amoxicillin and doxycycline respectively. Low frequency, 50 pps, and high (pH = 12) are preferable for oxidation of both antibiotics from the energy consumption point of view.

Pulsed corona discharge for improving treatability of coking wastewater

Coking wastewater (CW) contains toxic and macromolecular substances that inhibit biological treatment. The refractory compounds remaining in biologically treated coking wastewater (BTCW) provide chemical oxygen demand (COD) and color levels that make it unacceptable for reuse or disposal. Gas-phase pulsed corona discharge (PCD) utilizing mostly hydroxyl radicals and ozone as oxidants was applied to both raw coking wastewater (RCW) and BTCW wastewater as a supplemental treatment. The energy efficiency of COD, phenol, thiocyanate and cyanide degradation by PCD was the subject of the research. The cost-effective removal of intermediate oxidation products with addition of lime was also studied. The energy efficiency of oxidation was inversely proportional to the pulse repetition frequency: lower frequency allows more effective utilization of ozone at longer treatment times. Oxidative treatment of RCW showed the removal of phenol and thiocyanate at 800 pulses per second from 611 to 227mg/L and from 348 to 86mg/L, respectively, at 42kWh/m3 delivered energy, with substantial improvement in the BOD5/COD ratio (from 0.14 to 0.43). The COD and color of BTCW were removed by 30% and 93%, respectively, at 20kWh/m3, showing energy efficiency for the PCD treatment exceeding that of conventional ozonation by a factor of 3–4. Application of lime appeared to be an effective supplement to the PCD treatment of RCW, degrading COD by about 28% at an energy input of 28kWh/m3 and the lime dose of 3.0kg/m3. The improvement of RCW treatability is attributed to the degradation of toxic substances and fragmentation of macromolecular compounds.

Pulsed corona discharge oxidation of aqueous carbamazepine micropollutant

ABSTRACTThe anti-epileptic drug carbamazepine (CBZ) receives growing attention due to slow biodegradation and inherent accumulation in the aquatic environment. The application of a gas-phase pulsed corona discharge (PCD) was investigated to remove CBZ from synthetic solutions and spiked wastewater effluent from a municipal wastewater treatment facility. The treated water was showered between high voltage (HV) wires and grounded plate electrodes, to which ultra-short HV pulses were applied. CBZ was readily oxidized and 1-(2-benzaldehyde)-4-hydroquinazoline-2-one (BQM) and 1-(2-benzaldehyde)-4-hydro-quinazoline-2,4-dione (BQD) were identified as the most abundant primary transformation products, which, contrary to CBZ ozonation data available in the literature, were further easily oxidized with PCD: BQM and BQD attributed to only a minor portion of the target compound oxidized. In concentrations commonly found in wastewater treatment plant effluents (around 5 µg L−1), up to 97% reduction in CBZ concentration was achieved at mere 0.3 kW h m−3 energy consumption, and over 99.9% was removed at 1 kW h m−3. The PCD application proved to be efficient in the removal of both the parent substance and its known transformation products, even with the competing reactions in the complex composition of wastewater.

Aqueous Benzene Oxidation in Low-Temperature Plasma of Pulsed Corona Discharge

AbstractWastewaters polluted with non-biodegradable volatile organic compounds (VOCs), such as aromatic substances, present a growing problem meeting no adequately affordable technological response. Low-temperature plasma generated in the gas-phase pulsed corona discharge (PCD) presents competitive advanced oxidation technology in abatement of various classes of pollutants, although the process parameters, the pulse repetition frequency and the liquid spray rate, require optimization. The experimental research into aqueous benzene oxidation with PCD was undertaken to establish the impact of the parameters to the energy efficiency. The oxidation reaction was found under the experimental conditions to mostly proceed in the gas phase showing little influence of the pulse repetition frequency and the gas-liquid contact surface. Oxidation of benzene and, presumably, other volatile pollutants in the volume of PCD reactor compartment presents an effective strategy of aqueous VOCs abatement.

Pulsed Corona Discharge in Water Treatment: The Effect of Hydrodynamic Conditions on Oxidation Energy Efficiency

Water treatment by gas-phase pulsed corona discharge (PCD) relies mainly on utilization of ozone and OH radicals as oxidizing agents. In a configuration where the treated solution is showered through the plasma zone, the gas–liquid contact surface is the primary OH-radical formation site and the interface in the mass transfer of ozone. Its significance to overall process efficiency is therefore notable. In this study, the effect of varying contact surface area at different discharge powers was investigated from the perspective of efficient utilization of the two prime oxidants in slow reaction with oxalate. It is seen that increasing the area of the contact surface improves OH-radical utilization up to the point where the pollutant oxidation efficiency abruptly decreases presumably because of unfavorable pulse energy distribution in the gas–liquid mixture. The existence of an optimal area for a given power has implications for future studies in the design of pulsed plasma applications for water treatment.