Double Dielectric Barrier Discharge Reactor Research Articles

Development of pilot-scale plasma bubble reactors for efficient antibiotics removal in wastewater

Plasma bubble (PB) is a promising technology to control antibiotic wastewater pollution. However, the practical implementation of PB technology at the industrial-scale is still underdeveloped. In addition, the influence of different discharge modes for PB on wastewater treatment is largely unknown. This study designed pilot-scale PB reactors with different discharge modes to investigate the degradation effect of norfloxacin (NOR) and tetracycline (TC) in bulk tap water. Results indicate that the dielectric barrier discharge (DBD) mode with low average discharge power demonstrates superior degradation ability and higher production of O3(g) and .O2−(aq) compared to the spark mode which exhibits the high-intensity spark discharge in the tip area of the tube. After 40 min of treatment in a Double DBD reactor, 97.4% and 100% of NOR and TC are removed from 2 L tap water, attributed to the accumulation of antibiotic molecules by PBs and the in-situ generation of O3(g) and .O2−(aq) produced by plasma. Furthermore, a larger-scale PB reactor is developed by creating an array of four DBD reactors, effectively degrading 8 L mixed antibiotics solution. This study provides valuable insights for PB reactor design and the degradation performance of antibiotic wastewater, which will contribute to the further development of synergistic systems for plasma degradation.

Degradation of methylene blue using a novel gas-liquid hybrid DDBD reactor: Performance and pathways

A novel gas-liquid hybrid double dielectric barrier discharge (DDBD) reactor with coaxial cylinder configuration was developed for the degradation of methylene blue (MB) in this study. In this DDBD reactor, the reactive species generation occurred in the gas-phase discharge, directly in the liquid, and in the mixture of the working gas bubbles and the liquid, which could effectively increase the contact area between the active substance and MB molecules/intermediates, resulting in an excellent MB degradation efficiency and mineralization (COD and TOC). The electrostatic field simulation analysis by Comsol was carried out to determine the appropriate structural parameters of the DDBD reactor. The effect of discharge voltage, air flow rate, pH, and initial concentration on MB degradation was evaluated. Besides, major oxide species, ·OH, the dissolved O3 and H2O2 generated in this DDBD reactor were determined. Moreover, major MB degradation intermediates were identified by LC-MS, based on which, possible degradation pathways of MB were proposed.

Experimental analysis of gas- and particle-phase organic byproducts formed by plasma-induced toluene destruction processes

• Organic byproducts were evaluated by NTP degradation of toluene at ambient temperature and atmospheric pressure. • PTR-TOFMS measurement showed that toluene degradation resulted in dozens of organic by-products. • Size distribution and number concentration of particles formed during toluene degradation were measured by SMPS. • NTP-induced polymerization and oxidation contribute to particle formation with diameters in the range of 10 and 100 nm. Non-thermal plasma (NTP) technology has great potential to treat volatile organic compounds (VOCs) at low concentrations and large volumes. In this work, toluene, one of the most stable VOCs, was employed as a model pollutant to study its degradation by double dielectric barrier discharge (DDBD) at ambient temperature and atmospheric pressure. The performance of the DDBD reactor was evaluated in terms of discharge power, removal efficiency, CO x selectivity, and byproduct formation. Online and continuous measurements by PTR-TOFMS showed that toluene degradation resulted in the formation of 12 major volatile organic byproducts as well as 7 minor ones with concentrations ranging from ppbv to ppmv. Moreover, the particle size distribution and number concentration of particles formed during toluene degradation were measured using a scanning mobility particle sizer, and the effects of discharge power, initial toluene concentration, gas flow rate and O 2 content on particle formation were systematically investigated. The results show that both NTP-induced polymerization and oxidation contribute to aerosol formation, and the total concentration of organic byproducts in the aerosol phase is about 10 7 cm −3 with diameters in the range of 10 and 100 nm. This pioneered investigation on gas- and particle-phase organic byproducts from toluene degradation by NTP would deepen the understanding of plasma degradation of VOCs and accelerate the practical application of NTP for VOCs treatment.

A novel double dielectric barrier discharge reactor for toluene abatement: Role of different discharge zones and reactive species

A coaxial cylindrical double dielectric barrier discharge (DDBD) reactor with two separate discharge zone was designed and the role of its different discharge zones and reactive species were explored in toluene degradation. The inner tube (the space between the high voltage electrode and the inner barrier) had a higher gas temperature and reactive species concentration due to its stronger discharge intensity compared with the outer tube (the space between the inner and outer barriers). The two discharge zones exhibited similar toluene removal efficiency, whereas the mineralization rate of the inner tube exceeded that of the outer tube under 18–22 kV, and the result was opposite under 24–28 kV. The gas-flow direction had no significant effect on the toluene removal efficiency, but the mineralization rate of the down-flow reactor (23.7%–54.4%) exceeded that of the reverse-flow reactor (20.7%–45.5%). The inner and outer tubes mainly responsible for the initial degradation and further oxidation of toluene, respectively. The role of long-lived (N2(A3∑u+) and metastable O2 (a1Δg and b1Σg+)) and short-lived (N2(C3∏u), N2(B3∏g), and atomic O (1D and 3P)) reactive species on toluene degradation and oxidation was analyzed. The plausible toluene degradation mechanism in the DDBD reactor was proposed based on the role of different discharge zones and reactive species. The finding herein is significant in the design, optimization and application of DBD reactors.

Double dielectric barrier discharge incorporated with CeO2-Co3O4/γ-Al2O3 catalyst for toluene abatement by a sequential adsorption–discharge plasma catalytic process

As a promising technique to remove volatile organic compounds (VOCs), non-thermal plasma (NTP) has been paid much attention recently. However, the practical implementation of NTP is limited owing to its disadvantages such as low mineralization rate, unsatisfactory energy efficiency and the generation of multiple byproducts. Reactor configuration optimization and plasma coupled catalysis are the two alternatives to improve the efficiency of NTP. A packed bed double dielectric barrier discharge (DDBD) system was established and the performance of CeO2-Co3O4 catalysts for toluene abatement was evaluated in a sequential process. It was found that complete toluene removal could be achieved in the DDBD reactor packed with different catalysts. Among them, CeO2-Co3O4 binary catalysts showed higher toluene degradation performance than monometallic samples and Ce1Co3 had the best mineralization rate (89.68%) and energy yield (3.04 g/kWh). The effects of Ce/Co ratio on the structural and redox characteristics of the samples were analyzed by BET, XRD, TEM, XPS and H2-TPR. The superior catalytic activity was attributed to the interplay between Ce and Co species, which created abundant defects and oxygen vacancies and improved the concentration of surface adsorbed oxygen and the reducibility of catalyst. The effects of the relative parameters, such as applied voltage, toluene adsorbed amount and discharge time on the toluene degradation efficiency were also explored. Finally, the toluene decomposition mechanism in the DDBD catalytic system was speculated according to the detected organic products. The findings in this work can provide vital insight in plasma catalytic degradation of VOCs by sequential process.

Degradation of benzene, toluene, and xylene with high gaseous hourly space velocity by double dielectric barrier discharge combined with Mn3O4/activated carbon fibers

A novel strategy for the degradation of high gaseous hourly space velocity benzene, toluene, and xylene (BTX) by double dielectric barrier discharge (DDBD) coupled with Mn3O4/ activated carbon fiber (ACF) catalysts was proposed in this work. A series of Mn3O4/ACF catalysts were synthesized using the hydrothermal method and characterized. The results showed that all the prepared catalysts could improve the degradation of BTX in the DDBD system and inhibit the production of ozone. Among the catalysts with different Mn loading, the 5.6%Mn3O4/ACF, with the highest Mn(+3) content (43.2%) and the highest absorbed oxygen content (38.5%), presented the best catalytic performance. In the 5.6% Mn3O4/ACF + DDBD system, the degradation efficiency of benzene, toluene and xylene could reach 49.9%, 79.7% and 97.1%, respectively, with a specific input energy of 400 J l−1. The carbon balance and CO2 selectivity, meanwhile, were 83.3% and 51.1%, respectively. It seemed that Mn(+3) and absorbed oxygen content could be a reference for the catalytic performance of Mn3O4/ACF catalysts. The higher the Mn (III) and absorbed oxygen, the better the catalytic performance of the Mn3O4/ACF catalysts. The organic by-products were identified by chromatography-mass spectrometry, and a possible reaction mechanism of BTX in the DDBD reactor and catalyst surface was proposed based on the composition of organic by-products.

A novel double dielectric barrier discharge reactor with high field emission and secondary electron emission for toluene abatement

Dielectric barrier discharge (DBD) has been extensively investigated in the fields of environment and energy, whereas its practical implementation is still limited due to its unsatisfactory energy efficiency. In order to improve the energy efficiency of DBD, a novel double dielectric barrier discharge (NDDBD) reactor with high field emission and secondary electron emission was developed and compared with traditional DDBD (TDDBD) configuration. Firstly, the discharge characteristics of the two DDBD reactors were analyzed. Compared to TDDBD, the NDDBD reactor exhibited much stronger discharge intensity, higher transferred charge, dissipated power and gas temperature due to the effective utilization of cathode field emission and secondary electron emission. Subsequently, toluene abatement performance of the two reactors was evaluated. The toluene decomposition efficiency and mineralization rate of NDDBD were much higher than that of TDDBD, which were 86.44%–100% versus 28.17%–80.48% and 17.16%–43.42% versus 7.17%–16.44% at 2.17–15.12 W and 1.24–4.90 W respectively. NDDBD also exhibited higher energy yield than TDDBD, whereas the overall energy constant of the two reactors were similar. Finally, plausible toluene decomposition pathway in TDDBD and NDDBD was suggested based on organic intermediates that generated from toluene degradation. The finding of this study is expected to provide reference for the design and optimization of DBD reactor for volatile organic compounds control and other applications.

Real-time analysis of intermediate products from non-thermal plasma degradation of ethyl acetate in air using PTR-MS: Performance evaluation and mechanism study

Non-thermal plasma (NTP) has developed into an emerging end-of-pipe technology for treating volatile organic compounds (VOCs) present in unhygienic point source of air streams. In this work, NTP oxidation of low-concentration ethyl acetate was performed in a coaxial double dielectric barrier discharge reactor. The effects of initial ethyl acetate concentration, gas flow rate, and external electrode length on ethyl acetate degradation were systematically investigated as a function of discharge power. In addition, detailed real-time and online proton transfer reaction mass spectrometry analysis was used to identify the transient species formation and transition in the various NTP oxidation periods of ethyl acetate. Based on the analysis of organic by-products, the degradation mechanism was speculated and the major reaction channels were presented. This study would deepen the understanding of plasma degradation of VOCs and reveal the plasma-chemical mechanism.

High energy efficient degradation of toluene using a novel double dielectric barrier discharge reactor

A double dielectric barrier discharge (DDBD) reactor was established to decompose toluene with high energy efficiency. Differences in discharge characteristics including visual images, voltage-current waveforms, Lissajous figures, and temperature variation, were determined between the DDBD and SDBD reactors. Removal efficiency, mineralization rate, CO2 selectivity, and energy yield were used to evaluate the toluene abatement performance of the two reactors. Compared to the SDBD reactor, the DDBD reactor exhibited more uniform and stable discharges due to a change in discharge mode. In addition, the DDBD reactor’s dissipated power and reactor temperature (including the gas, barrier and ground electrode) were significantly lower than those in the SDBD reactor. At 22−24 kV, the DDBD reactor showed a higher toluene removal efficiency and mineralization rate, while at 14−16 kV, the SDBD reactor exhibited higher respective value. The energy efficiency of the DDBD was 2.5–3 times that of the SDBD reactor, and the overall energy constant koverall of the DDBD reactor (1.47 mL/J) was significantly higher than that of the SDBD reactor (0.367 mL/J) as revealed by the kinetics study. Lastly, a plausible toluene degradation mechanism in the DDBD and SDBD reactors was proposed based on organic intermediates that formed during toluene decomposition.

Abatement of Toluene by Reverse-Flow Nonthermal Plasma Reactor Coupled with Catalyst

In order to make full use of the heat in nonthermal plasma systems and decrease the generation of by-products, a reverse-flow nonthermal plasma reactor coupled with catalyst was used for the abatement of toluene. In this study, the toluene degradation performance of different reactors was compared under the same conditions. The mechanism of toluene abatement by nonthermal plasma coupled with catalyst was explored, combined with the generation of ozone (O3), NO2, and organic by-products during the reaction process. It was found that a long reverse cycle time of the reactor and a short residence time of toluene decreased the internal reactor temperature, which was not beneficial for the degradation of toluene. Compared with the dielectric barrier discharge (DBD) reactor, toluene degradation efficiency in the double dielectric barrier discharge (DDBD) reactor was improved at the same discharge energy level, but the concentrations of NO2 and O3 in the effluent were relatively high; this was improved after the introduction of a catalyst. In the reverse-flow nonthermal plasma reactor coupled with catalyst, the CO2 selectivity was the highest, while the selectivity and amount of NO2 was the lowest and aromatics, acids, and ketones were the main gaseous organic by-products in the effluent. The reverse-flow DBD-catalyst reactor was successful in decreasing organic by-products, while the types of organic by-products in the DDBD reactor were much more than those in the DBD reactor.

Remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil with double dielectric barrier discharge plasma technology: Influencing parameters

A double dielectric barrier discharge (DDBD) plasma reactor was used for the remediation of simulated contaminated soil by a mixture of two, three and four rings PAHs i.e. naphthalene (Nap), phenanthrene (Phe) and pyrene (Pyr). Various influencing parameters such as peak-to-peak applied voltage, soil moisture, oxygen to nitrogen ratio (O2:N2) of carrier gas and soil depth in the reactor were investigated. The results illustrate that with an initial PAH concentration of 100 mgkg−1 the remediation efficiency increased by 27–30% when the applied voltage was increased from 28 to 40 kV. When the moisture content had been raised from 1.7% to 4% the remediation efficiency of Nap, Phe and Pyr increased from 89.55, 84.51 and 83.36% to 96.32, 89.08 and 88.59% respectively. However, further increase in moisture content decreased the PAHs remediation efficiency. With increasing oxygen to nitrogen ratio, the remediation efficiency of PAHs increased up to 20%. Higher oxygen concentrations in DDBD reactor has beneficial effect due to the generation of increased oxygenated species such as ozone, atomic oxygen and nitrogen oxides in discharge zone. When the soil thickness in the reactor was increased from 1 mm to 3 mm – due to decreased penetration of active species into the deeper zone of the soil – the remediation efficiencies decreased by 10%. Compared to ozonation the treatment of PAHs in the DDBD reactor resulted in higher remediation efficiencies. This is due to the generation of more active species in case of DDBD plasma treatment. The study demonstrates that DDBD plasma is a promising technology for remediation of heavily contaminated sites of PAHs due to its high remediation efficiency and robustness.

Remediation of pyrene contaminated soil by double dielectric barrier discharge plasma technology: Performance optimization and evaluation

Polycyclic aromatic hydrocarbons (PAHs) in soil are not only detrimental to environment but also to human health. Double dielectric barrier discharge (DDBD) plasma reactor used for the remediation of pyrene contaminated soil was studied. The performance of DDBD reactor was optimized with influential parameters including applied voltage, type of carrier gas, air feeding rate as well as pyrene initial concentration. The analysis of variance (ANOVA) results showed that input energy had a great effect on pyrene remediation efficiency followed by pyrene initial concentration, while, the effect of air feeding rate was insignificant. More specifically, the remediation efficiency of pyrene under air, nitrogen and argon as carrier gas were approximately 79.7, 40.7 and 38.2% respectively. Pyrene remediation efficiency is favored at high level of applied voltages and low level of pyrene initial concentration (10 mgkg−1) and air feeding rate (0.85 L/min). Moreover, computation of the energy efficiency of the DDBD system disclosed that an optimal applied voltage (35.8 kV) and higher initial pyrene concentration (200 mgkg−1) favored the high energy efficiency. A regression model predicting pyrene remediation under DDBD plasma condition was developed using the data from a face-centered central composite design (FCCD) experiment. Finally, the residual toxicity analysis depicted that the respiratory activity increased more than 21 times (from 0.04 to 0.849 mg O2 g−1) with a pyrene remediation efficiency of 81.1%. The study demonstrated the DDBD plasma technology is a promising method not only for high efficiency of pyrene remediation, but also recovering biological function without changing the physical-chemical properties of soil.

Time-resolved characterization of non-thermal plasma-assisted photocatalytic removal of nitric oxide

We performed time-resolved characterization of plasma-photocatalytic removal of nitric oxide (NO) in a ceramic foam packing double dielectric barrier discharge reactor using mid-infrared laser absorption spectroscopy. Non-thermal plasma (NTP) was generated in the porous ceramic foam coated with mesoporous TiO2 thin film. Real-time NO monitoring was performed using a quantum cascade laser at 5.26 µm combined with a custom-designed multipass gas cell, leading to a sub-ppm detection limit at 0.1 s measurement time. By analyzing the feed gas of 90 ppm NO/1% O2 balanced in N2, the plasma treatment without TiO2 photocatalyst had no effect on NO removal when the discharge power was below 45 W. In comparison, the NTP-TiO2 system achieved an efficiency of 49% for NO removal even at the relatively low discharge power of 18 W. The synergy between NTP and TiO2 photocatalyst effectively promotes the NO removal at low plasma discharge powers. However, we also observed a negative effect of TiO2 photocatalyst on NO removal at a relatively high discharge power of 135 W.

Using non-thermal plasma for decomposition of toluene adsorbed on γ-Al2O3 and ZSM-5: Configuration and optimization of a double dielectric barrier discharge reactor

A novel hybrid system was established to degrade adsorbed toluene efficiently. A double dielectric barrier discharge (DDBD) reactor was filled with two common adsorbents, γ-Al2O3 and ZSM-5, in various combinations. Packing material, high-voltage electrode structure, and gas-flow mode were investigated to optimize this reactor. The reactor packed with a mixture of γ-Al2O3 and ZSM-5 provided a mineralization rate 6.1% to –14.1% greater than one using a single material. Specifically, the highest mineralization rate was obtained in a DDBD reactor packed with γ-Al2O3 in the inner tube and ZSM-5 in the outer tube. Using the optimal combination of packing material, two high-voltage electrodes were compared. A higher mineralization rate was observed in the reactor with a rod electrode (63.3%) than in one equipped with a coil electrode (53.7%), The total amounts of O3 and N2O generated were much less in the reactor with a rod electrode. The effect of gas-flow mode on toluene decomposition was investigated and the result showed that mode 1 (with the gas flowing from the inner tube into the outer tube during both adsorption and discharge phases) could not only improve the degradation of toluene, but could also suppress the generation of O3 and N2O. A possible mechanism for toluene decomposition in the packed-bed DDBD reactor was proposed based on the analysis of organic intermediates remaining in the adsorbents.

DDBD ozone plasma reactor generation: the proper dose for medical applications

Double Dielectric Barrier Discharge (DDBD) ozone plasma reactor generation are presented in this paper. The generation of this reactor generates ozone concentration which can be arranged upon the proper dose for medical applications. AC high voltage is applied to the range of 0-3 kV and the frequency of 50 Hz. Pure oxygen gas was piped into the DDBD reactor with flow rate variations of 2, 4 and 6 L/min. The results showed that current as a function of voltage where the current is increased with the increasing of voltage. Ozone productivity is shown by the significant increase of current. Ozone concentration is increasing as the increase of the voltage provided, but rather the concentration of ozone is decreasing as the increasing of flow rate. The Ozone capacity is affected by ozone concentration and flow rate, and can be used to determine the ozone dose. The proper dose of ozone can be ozone therapy for various kinds of diseases.

Ar plasma jet generation and its application for water and surface sterilization

Microorganisms are widely distributed in the living environment of human, animals and plants. Some of the microorganisms are harmful for their pathogenic effects. Non-thermal plasma technology, especially, the atmospheric pressure plasma jet, is considered to be one of the promising technologies for sterilization. This work proposes a double-dielectric barrier discharge reactor for Ar plasma jet generation. Charteristics of discharge and temperature thermogram of plasma jet are investigated by the means of U-P curve and infrared image, respectively. Performance of the plasma jet is evaluated by surface and water sterilization. The results show that, Ar plasma jet is generated stable with double-dielectric barrier discharge. The length of plasma jet increases as the applied voltage, frequency or gas flow increased, but the plasma jet generation can be restricted in high frequency or gas flow. For E. coli in the water and surface, high sterilization efficiency is observed for a short time treatment by Ar plasma jet.

Process for Chloroform Decomposition: Nonthermal Plasma Polymerization with Methane and Hydrogen

This paper describes an alternative process for chloroform decomposition via nonthermal plasma polymerization at atmospheric pressure and investigates the effect of methane and hydrogen addition on the process. The effect of both additives was assessed separately, where experiments were conducted in a double dielectric barrier discharge reactor under nonoxidative conditions. The most profound impact of the additives was a significant increase in the yield of non-cross-linked polymer produced compared to that in their absence. The addition of methane resulted in a 120% increase in polymer yield, while in hydrogen the increase was 31%. Critical parameters such as effect of the methane and hydrogen concentration on the conversion of chloroform at various applied voltages, the product distribution, mass balance, and polymer characterization are elucidated in this paper. Single pass conversions of 61% and 68% (with corresponding mass balances of 98% and 95%, respectively) were achieved for CHCl3 + CH4 and CHCl3 + H2 feed scenarios, respectively. Furthermore, a polymerization mechanism which explains the formation of major chain structures as well as structural defects in the polymer is expounded upon in the paper.

Effects of Reduced Electric Field on Sulfur Hexafluoride Removal for a Double Dielectric Barrier Discharge Reactor

Sulfur hexafluoride (SF6) is a greenhouse gas with very high global warming potential. This paper investigated the effects of reduced electric field, E/N, on SF6 abatement by using a coaxial double-layer dielectric barrier discharge (DBD) reactor. The concentration of SF6 was 2%, and the remaining 98% of the feed gas is He/water vapor. The reduced electric field of the discharge region was calculated. The effects of different reduced electric fields on SF6 removal and the mechanisms were studied in terms of the removal efficiency and energy yield (EY). The experimental results showed that higher removal efficiency was achieved when the reduced electric field was higher than 126 Td and as the E/N increased; the time for removing SF6 completely was shortened. However, the EY at different reduced electric fields did not change much. SO2F2, SOF4, SOF2, and SO2 were the main products after the plasma removal process.

Volatile organic compounds (VOCs) removal in non-thermal plasma double dielectric barrier discharge reactor

Non-thermal plasma (NTP) an emerging technology to treat volatile organic compounds (VOCs) present in unhygienic point source air streams. In present study, double dielectric barrier discharge (DDBD) reactors were used for the first time to evaluate the removal efficiency of VOCs mixture of different nature at constant experimental conditions (input power 16–65.8 W, VOCs mixture feeding rate 1–6 L/min, 100–101 ppm inlet concentration of individual VOC). Reactor A and B with discharge gap at 6 mm and 3 mm respectively, were used in current study. When treated at an input power of 53.7 W with gas feeding rate of 1 L/min in DDBD reactor A, removal efficiency of the VOCs were: tetrachloroethylene (100%), toluene (100%), trichloroethylene (100%), benzene (100%), ethyl acetate (100%) and carbon disulfide (88.30%); whereas in reactor B, the removal efficiency of all VOCs were 100%. Plasma-catalyst (Pt-Sn/Al2O3, BaTiO3 and HZSM-5) synergistic effect on VOCs removal efficiency was also investigated. Highest removal efficiency i.e 100% was observed for each compound with BaTiO3 and HZSM-5 at an input power 65.8 W. However, integrating NTP with BaTiO3 and HZSM-5 leads to enhanced removal performance of VOCs mixture with high activity, increase in energy efficiency and suppression of unwanted byproducts.

Tailoring the wettability of glass using a double-dielectric barrier discharge reactor

A double dielectric barrier discharge reactor operated at a low power frequency of 400 Hz and atmospheric pressure was utilized for regulating the wettability of glass surface. The hydrophobic treatment was performed by plasma polymerization of tetramethylsilane (TMS, in argon gas). The obtained results showed that the TMS coatings formed on the glass substrates without oxygen addition were smooth, uniform films with the maximum water contact angle (WCA) of about 106°, which were similar to those obtained by low pressure, high power frequency plasmas reported in the literature. The addition of oxygen into TMS/Ar plasma gas decreased the WCA and induced the formation of SiOSi and/or SiOC linkages, which dominated the existence of Si(CH2)nSi network formed in TMS/Ar (without oxygen) plasma.