Dielectric barrier discharge plasma as excellent method for Perchloroethylene removal from aqueous environments: Degradation kinetic and parameters modeling

Efficient degradation and mineralization of aniline in aqueous solution by new dielectric barrier discharge non-thermal plasma

Aniline is a priority pollutant that is unfavorable to the environment and human health due to its carcinogenic and mutagenic nature. The performance of the dielectric barrier discharge reactor was examined based on the aniline degradation efficiency. Different parameters were studied and optimized to treat various wastewater conditions. Role of active species for aniline degradation was investigated by the addition of inhibitors and promoters. The optimum conditions were 20 mg/L initial concentration, 1.8 kV applied voltage, 4 L/min gas flow rate and a pH of 8.82. It was observed that 87% of aniline was degraded in 60 min of dielectric barrier discharge treatment at optimum conditions. UV-Vis spectra showed gradual increase in the treatment efficiency of aniline with the propagation of treatment time. Mineralization of AN was confirmed by TOC measurement and a decrease in pH during the process. To elicit the aniline degradation route, HPLC and LC-MS techniques were used to detect the intermediates and byproducts. It was identified that aniline degraded into different organic byproducts and was dissociated into carbon dioxide and water. Comparison of the current system with existing advanced oxidation processes showed that DBD has a remarkable potential for the elimination of organic pollutants.

Dielectric barrier discharge plasma coupled with WO3 for bisphenol A degradation

Based on the difficulty of the refractory organic compounds degradation in water by the traditional wastewater treatment methods, the research relies on the technology of the dielectric barrier discharge plasma (DBDP) and the catalysis of the nano WO₃, investigating the bisphenol A (BPA) degradation in the synergistic system of DBDP/WO₃. The coupled degradation percentage of the BPA under different amounts of WO₃ addition, different initial solution pH and carrier gas were investigated to confirm the catalysis of the WO₃ in the DBDP system. It was obtained from the experimental results that the optimal additive amount of the WO₃ was 175 mg L^-1 and change of the solution pH value and the carrier gas variety could not change the catalysis of the WO₃. The BPA degradation percentage could reach 100% after treating 30 min in the DBDP/WO₃ system with 0.5 L min^-1 O₂ as the carrier gas. The WO₃ still had a better catalysis after four times usage and the discharge had little effect on the microstructure of the WO₃. The existence of the WO₃ in the DBDP system could result in the reduction of the O₃ concentration and the enhancement of the H₂O₂ concentration, which improve the catalysis of the WO₃ in the DBDP system, while the experiments on the scavengers' addition verified the major role of the OH on the BPA degradation. The catalytic mechanism of the WO₃ as well as the BPA degradation pathway was also speculated in the research.

Dielectric barrier discharge plasma with photocatalysts as a hybrid emerging technology for degradation of synthetic organic compounds in aqueous environments: A critical review

Dielectric barrier discharge (DBD) plasma has been recently used for removal of synthetic organic compounds (SOCs) from aqueous environments. The removal of SOCs by alone DBD is significantly limited by its high electricity needs and inefficient mineralization, which affects the further application of DBD for SOCs. The combined application of DBD with other technologies and the addition of a supplementary substance for energy-saving were proposed to resolve these problems. The addition of catalysts is considered to be a promising and innovative approach to increase the energy yield of DBD, improve the environment friendly of DBD, develop the variety of goal SOCs, and improve the removal efficiency of DBD system. Despite the increasing use of the coupling form of DBD and catalysts, as catalytic dielectric barrier discharge (CDBD), but it still requires a comprehensive review to summarize the last studies and highlight the future perspectives in this area. Therefore, this work is the first literature review aimed to critically assess the latest developments of catalysts coupling with DBD employed in aqueous environments. Moreover, performance evaluation, energy yield, toxicity, eco-friendly, and future perspectives of the CDBD systems for SOCs removal were discussed and overviewed. The results showed that the coupling of catalysts with DBD presents synergistic effects and had excellent removal performance for aqueous SOCs. Overall, it can be concluded that the essential principles of environmental and economic sustainability have been addressed for the removal of persistent pollutants from aqueous environments in the CDBD systems.

Evaluating the Performance of a Lab-Scale Water Treatment Plant Using Non-Thermal Plasma Technology

In this study, a lab-scale plant was designed to treat water in continuous flow condition using non-thermal plasma technology. The core was an electrode system with connected high-voltage (HV) pulse generator. Its potentials and limitations were investigated in different experimental series with regard to the high-voltage settings, additions of oxygen-based species, different volume flow rates, and various physical-chemical properties of the process water such as conductivity, pH value, and temperature. Indigo carmine, para-Chlorobenzoic acid, and phenol were chosen as reference substances. The best HV settings was found for the voltage amplitude Û = 30 kV, the pulse repetition rate f = 0.4–0.6 kHz, and the pulse duration tb = 500 ns with an energy yield for 50% degradation G50, which is of 41.8 g∙kWh−1 for indigo carmine, 0.32 g∙kWh−1 for para-Chlorobenzoic acid, and 1.04 g∙kWh−1 for phenol. By adding 1 × 10−3 mol∙L−1 of oxygen, a 50% increase in degradation was achieved for para-Chlorobenzoic acid. Conductivity is the key parameter for degradation efficiency with a negative exponential dependence. The most important species for degradation are hydroxyl radicals (c ≈ 1.4 × 10−8 mol∙L−1) and solvated electrons (c ≈ 1.4 × 10−8 mol∙L−1). The results show that the technology could be upgraded from the small-scale experiments described in the literature to a pilot plant level and has the potential to be used on a large scale for different applications.

Electro-Absorbers: A Comparison on Their Performance with Jet-Absorbers and Absorption Columns

This work focuses on the removal of perchloroethylene (PCE) from gaseous streams using absorbers connected with electrolyzers. Two types of absorption devices (jet absorber and absorption column) were compared. In addition, it has been evaluated the different by-products generated when a simultaneous electrolysis with diamond anodes is carried out. PCE was not mineralized, but it was transformed into phosgene that mainly derivates into carbon tetrachloride. Trichloroacetic acid was also formed, but in much lower amounts. Results showed a more efficient absorption of PCE in the packed column, which it is associated to the higher gas–liquid contact surface. Jet absorber seems to favor the production of carbon tetrachloride in gaseous phase, whereas the packed column promotes a higher concentration of trichloroacetic acid in liquid. It was also evaluated the scale up of the electrolytic stage of these electro-absorption devices by using a stack with five perforated electrode packages instead of a single cell. Clarification of the effect of the applied current density on the speciation attained after the electrolysis of the absorbent has been attempted. Experiments reveal similar results in terms of PCE removal and a reduced generation of gaseous intermediates at lower current densities.

Degradation of 4-chlorophenol in aqueous solution by dielectric barrier discharge system: effect of fed gases

A dielectric barrier discharge system with a discharging zone where degradation processes happen is designed to remove 4-chlorophenol from water. The removal of 4-chlorophenol was influenced by the processing parameters such as gas flow rate, flow ratio of oxygen and argon, applied voltage and total applied power. Increasing the power or gas flow rates within a certain range enhanced the removal efficiency. 99% of 4-chlorophenol was removed in 6.5 min at reactor's efficient point which is set by adjusting the flow ratio of introduced gases and voltage. The removal percent was about 95% at 5 min of non-thermal plasma treatment with peak voltage of 10 kV and oxygen and argon flow rate of 20 SCCM and 200 SCCM respectively. Then by adjusting the flow ratios in order to find the optimum point. At this point the efficiency reached its peak due to excessive introduction oxygen gas which results in production of more oxidative agents. HPLC and GC-MS analysis have been carried out in order to investigate the by-products of degradation process. After 6.5 min of treatment at efficient point of degradation reactor, a 64% decrease in COD index has been indicated.

Photochemical degradation of toluene in gas-phase under UV/visible light graphene oxide-TiO2 nanocomposite: influential operating factors, optimization, and modeling

The current study aimed to investigate the removal efficiency of toluene using synthesized titanium dioxide-graphene oxide composites under visible light and UV irradiation. The characterization of synthesized composites was examined by field emission scanning electron microscope equipped with energy dispersive, X-ray diffraction and fourier transforms infrared. In order to find the optimum of the main experimental parameters affecting the removal efficiency of toluene including the length of the reactor, initial concentration, and flow rates, central composite design together with response surface methodology with R software was used. The initial concentration of toluene in the inlet of the reactor as well as its concentration in the outlet was measured using gas chromatography with the flame ionization detector. Analysis of variance results for the quadratic model showed that the highly significant and simple linear regression was established as a predicting model. Multiple and adjusted R² were 0.965 and 0.974 for UV irradiation GO-TiO₂ model and 0.951 and 0.959 for visible light GO-TiO₂ model, respectively. As such, the differences less than 0.2 between multiple and adjusted R² in two models indicate that two examined models were fitted well. The highest removal efficiency of toluene using UV irradiation GO-TiO₂ and visible light GO-TiO₂ was obtained at optimum condition; length of reactor 40 cm, initial concentration of 0.1 ppm, and flow rate equal to 1 l min^-1, with 97.7 and 77.2%, respectively. The results indicated that the removal efficiency of toluene increased considerably with rising the length of the reactor, decreasing flow rates, and initial concentration.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

A comparison of the electrolysis of soil washing wastes with active and non-active electrodes

A comparison between the performance of electrolysis of three different soil-washing wastes with platinum and boron doped diamond (BDD) anodes is carried out in this work. Results demonstrate that the treatment is more efficient with BDD for perchloroethylene and clopyralid but not for the case of lindane, because in this case there is a competitive oxidation between lindane and Sodium Dodecyl Sulfate used to extract this pollutant from soil. First order kinetics are observed in each compound with higher removal at the early stages and generally better results are obtained when using BDD as anode. The evolution of pH and a voltammetry study indicate a higher direct oxidation rate in the case of platinum and more importance of hydroxyl radical mediated processes with diamond anodes. Similar speciation is obtained during the electro-oxidation using BDD and platinum electrodes although the concentration of intermediates vary significantly.

Electrochemical hydrodechlorination of perchloroethylene in groundwater on a Ni-doped graphene composite cathode driven by a microbial fuel cell

Enhancing the activity of the cathode and reducing the voltage for electrochemical hydrodechlorination of chlorohydrocarbon were always the challenges in the area of electrochemical remediation. In this study, a novel cathode material of Ni-doped graphene generated by Ni nanoparticles dispersed evenly on graphene was prepared to electrochemically dechlorinate PCE in groundwater. The reduction potential of Ni-doped graphene for PCE electrochemical hydrodechlorination was −0.24 V (vs. Ag/AgCl) determined by cyclic voltammetry. A single MFC with a voltage of 0.389–0.460 V and a current of 0.221–0.257 mA could drive electrochemical hydrodechlorination of PCE effectively with Ni-doped graphene as the cathode catalyst, and the removal rate of PCE was significantly higher than that with single Ni or graphene as the cathode catalyst. Moreover, neutral conditions were more suitable for Ni-doped graphene to electrochemically hydrodechlorinate PCE in groundwater and no byproduct was accumulated.

Ni-doped graphene was prepared to electrochemically dechlorinate PCE driven by a microbial fuel cell. Dechlorination efficiency and reduction potential were significantly higher than for bare Ni or graphene.