Study on purification technology of polyacrylamide wastewater by non-thermal plasma

In this work, non-thermal plasma has been applied to treat polyacrylamide (PAM) wastewater. We have investigated the influence of the rule of PAM wastewater initial pH, solution concentration and discharge time, discharge voltage on chemical oxygen demand (COD) degradation rate. At the same time, the effect of pH and discharge time on the viscosity removal rate of PAM solution was also studied. Then, the effect of pH on the viscosity removal rate of 1.0 gl ⁻¹ PAM solution was studied separately. Through orthogonal test, the factors affecting the COD degradation rate of PAM wastewater were determined as follows: discharge time>discharge voltage>solution concentration>wastewater initial pH. The COD highest removal rate of PAM wastewater reached 85.74%, when the optimal conditions are as follows: discharge voltage 40 kV, discharge time 5 h, solution concentration 1.0 gl ⁻¹, pH 1.5. This research provides some basic data and new theoretical basis for PAM wastewater purification.     

Advanced oxidation technology for H2S odor gas using non-thermal plasma

Non-thermal plasma technology is a new type of odor treatment processing. We deal with H2S from waste gas emission using non-thermal plasma generated by dielectric barrier discharge. On the basis of two criteria, removal efficiency and absolute removal amount, we deeply investigate the changes in electrical parameters and process parameters, and the reaction process of the influence of ozone on H2S gas removal. The experimental results show that H2S removal efficiency is proportional to the voltage, frequency, power, residence time and energy efficiency,while it is inversely proportional to the initial concentration of H2S gas, and ozone concentration. This study lays the foundations of non-thermal plasma technology for further commercial application.     

Applying chemical engineering concepts to non-thermal plasma reactors

Process scale-up remains a considerable challenge for environmental applications of non-thermal plasmas.Undersanding the impact of reactor hydrodynamics in the performance of the process is a key step to overcome this challenge.In this work,we apply chemical engineering concepts to analyse the impact that different non-thermal plasma reactor configurations and regimes,such as laminar or plug flow,may have on the reactor performance.We do this in the particular context of the removal of pollutants by non-thermal plasmas,for which a simplified model is available.We generalise this model to different reactor configurations and,under certain hypotheses,we show that a reactor in the laminar regime may have a behaviour significantly different from one in the plug flow regime,often assumed in the non-thermal plasma literature.On the other hand,we show that a packed-bed reactor behaves very similarly to one in the plug flow regime.Beyond those results,the reader will find in this work a quick introduction to chemical reaction engineering concepts.     

Recent progress on non-thermal plasma technology for high barrier layer fabrication

This review describes the application of non-thermal plasma (NTP) technology for high barrier layer fabrication in packaging area.NTP technology is considered to be the most prospective approaches for the barrier layer fabrication over the past decades due to unpollution,high speed,low-costing.The applications of NTP technology have achieved numerous exciting results in high barrier packaging area.Now it seemly demands a detailed review to summarize the past works and direct the future developments.This review focuses on the different NTP resources applied in the high barrier area,the role of plasma surface modification on packaging film surface properties,and the deposition of different barrier coatings based on NTP technology.In particular,this review emphasizes the cutting-edge technologies of NTP on interlayer deposition with organic,inorganic for multilayer barriers fabrication.The future prospects of NTP technology in high barrier film areas are also described.     

Enhanced CO2 decomposition via metallic foamed electrode packed in self-cooling DBD plasma device

A self-cooling dielectric barrier discharge reactor, packed with foamed Cu and Ni mesh and operated at ambient conditions, was used for the composition of CO₂ into CO and O₂. The influences of power, frequency, and other discharge characteristics were investigated in order to have a better understanding of the effect of the packing materials on CO₂ decomposition. It is found that porous foamed Cu and Ni not only played a role as the carrier of energy transformation and electrode distributed in discharge gaps but also promoted the equilibrium shifting toward the product side to yield more CO by consuming some part of O₂ and O radicals generated from the decomposition of CO₂. The maximum CO₂ decomposition rates of 48.6% and 49.2% and the maximum energy efficiency of 9.71% and 10.18% were obtained in the foamed Ni and Cu mesh, respectively.     

Effect of the amount of trapped particulate matter on diesel particulate filter regeneration performance using non-thermal plasma assisted by exhaust waste heat

An experimental system of diesel particulate filter(DPF) regeneration using non-thermal plasma(NTP) technology assisted by exhaust waste heat was conducted and regeneration experiments of DPFs with different amounts of trapped particulate matter(PM) were conducted. The concentrations of the PM decomposition products(COx) and the internal temperature of the DPF were monitored to determine the performance of DPF regeneration and thermal safety of the NTP technology. The results showed that the concentrations of CO and CO_2 and the mass of PM decomposition increased with the increase in the amount of captured PM, whereas the concentration of the NTP active substance(O_3) escaping from the DPF decreased under the same working conditions of the NTP injection system. A higher amount of captured PM promoted the oxidative decomposition reaction between NTP and PM and improved the utilization rate of the NTP active substances. The peak temperature at the same measuring point inside the DPF generally increased and the phases of the peak temperature were delayed as the amount of captured PM increased. The temperature peaks and temperature gradients during the DPF regeneration process were far lower than the failure limit value, which indicates that NTP regeneration technology has good thermal durability and increases the service life of the DPF.     

Numerical analysis of thermal plasma scrubber for CF4 decomposition

CF₄ gas emitted in the semiconductor and display manufacturing process is a very harmful greenhouse gas. It must be removed or converted safely due to its extreme toxicity. Although a CF₄ decomposition system using a thermal plasma scrubber was commercialized, its removal efficiency is limited. In this work, a numerical analysis of CF₄ decomposition in the thermal plasma scrubber was carried out in order to propose an efficient decomposition environment. The decomposition and recombination temperatures of CF₄ were analyzed using thermodynamic equilibrium calculations. The chemical reaction of CF₄ decomposition into carbon and fluorine gas was considered in this numerical analysis. The injection position and angle of the CF₄ were controlled in order to enhance the decomposition rate. The vertical injection of CF₄ near the torch exit improved the mixing of the CF₄ with the thermal plasma flame. In addition, it was confirmed that the high temperature region expanded due to a vortex generated by strong turbulence in the bottleneck-shaped reactor. As a result, it is revealed that the CF₄ injection location and the reactor configuration are the most important factors in improving the decomposition rate.     

Strengthening decomposition of oxytetracycline in DBD plasma coupling with Fe-Mn oxide-loaded granular activated carbon

A catalytic approach using a synthesized iron and manganese oxide-supported granular activated carbon (Fe-Mn GAC) under a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of oxytetracycline (OTC) in water. The prepared Fe-Mn GAC was characterized by x-ray diffraction and scanning electron microscopy, and the results showed that the bimetallic oxides had been successfully spread on the GAC surface. The experimental results showed that the DBD + Fe-Mn GAC exhibited better OTC removal efficiency than the sole DBD and DBD + virgin GAC systems. Increasing the fabricated catalyst and discharge voltage was favorable to the antibiotic elimination and energy yield in the hybrid process. The coupling process could be elucidated by the ozone decomposition after Fe-Mn GAC addition, and highly hydroxyl and superoxide radicals both play significant roles in the decontamination. The main intermediate products were identified by HPLC-MS to study the mechanism in the collaborative system.     

Enhancing toluene removal in a plasma photocatalytic system through a black TiO_2 photocatalyst

An efficient toluene removal in air using a plasma photocatalytic system(PPS) not only needs favorable surface reactions over photocatalysts under the action of plasma,but also requires the photocatalysts to efficiently absorb light emitted from the discharge for driving the photocatalytic reactions. We report here that the PPS constructed by integrating a black titania(B-TiO_2)photocatalyst with a dielectric barrier discharge(DBD) can effectively remove toluene with above 70% CO_2 selectivity and remarkably reduced the concentration of secondary pollutants of ozone and nitrogen oxides at a specific energy input of 1500 J·l~(-1),while exhibiting good stability. Photocatalyst characterizations suggest that the B-TiO_2 provides a high concentration of oxygen vacancies for the surface oxidation of toluene in DBD,and efficiently absorbs ultraviolet–visible light emitted from the discharge to induce plasma photocatalytic oxidation of toluene. The presence of B-TiO_2 in the plasma region also results in a high discharge efficiency,facilitating the generation of large numbers of reactive species and thus the oxidation of toluene towards CO_2. The greatly enhanced performance of the PPS integrated with B-TiO_2 in toluene removal offers a promising approach to efficiently remove refractory volatile organic compounds from air at low temperatures.     

Degradation of phenol using a combination of granular activated carbon adsorption and bipolar pulse dielectric barrier discharge plasma regeneration

A combined method of granular activated carbon (GAC) adsorption and bipolar pulse dielectric barrier discharge (DBD) plasma regeneration was employed to degrade phenol in water. After being saturated with phenol, the GAC was filled into the DBD reactor driven by bipolar pulse power for regeneration under various operating parameters. The results showed that different peak voltages, air flow rates, and GAC content can affect phenol decomposition and its major degradation intermediates, such as catechol, hydroquinone, and benzoquinone. The higher voltage and air support were conducive to the removal of phenol, and the proper water moisture of the GAC was 20％. The amount of H2O2 on the GAC was quantitatively determined, and its laws of production were similar to phenol elimination. Under the optimized conditions, the elimination of phenol on the GAC was confirmed by Fourier transform infrared spectroscopy,and the total removal of organic carbons achieved 50.4％. Also, a possible degradation mechanism was proposed based on the HPLC analysis. Meanwhile, the regeneration efficiency of the GAC was improved with the discharge treatment time, which attained 88.5％ after 100 min of DBD processing.     

NO_x storage and reduction assisted by non-thermal plasma over Co/Pt/Ba/γ-Al_2O_3 catalyst using CH_4 as reductant

N_Ox storage and reduction(NSR) technology has been regarded as one of the most promising strategies for the removal of nitric oxides(NO_x) from lean-burn engines, and the potential of the plasma catalysis method for NO_x reduction has been confirmed in the past few decades. This work reports the NSR of nitric oxide(NO) by combining non-thermal plasma(NTP) and Co/Pt/Ba/γ-Al_2O_3(Co/PBA) catalyst using methane as a reductant. The experimental results reveal that the NO_x conversion of NSR assisted by NTP is notably enhanced compared to the catalytic efficiency obtained from NSR in the range of 150 °C–350 °C, and NO_x conversion of the 8% Co/PBA catalyst reaches 96.8% at 350°C. Oxygen(O_2) has a significant effect on the removal of NO_x, and the NO_x conversion increases firstly and then decreases when the O_2 concentration ranges from 2% to 10%. Water vapor reduces the NO_x storage capacity of Co/PBA catalysts on account of the competition for adsorption sites on the surface of Co/PBA catalysts. There is a negative correlation between sulfur dioxide(SO_2) and NO_x conversion in the NTP system, and the 8% Co/PBA catalyst exhibits higher NO_x conversion compared to other catalysts, which shows that Co has a certain SO_2 resistance.     

Influence of water content on the inactivation of P. digitatum spores using an air–water plasma jet

In order to investigate whether an air–water plasma jet is beneficial to improve the efficiency of inactivation, a series of experiments were done using a ring-needle plasma jet. The water content in the working gas(air) was accurately measured based on the Karl Fischer method. The effects of water on the production of OH(A~2Σ~+–X~2Π_i) and O(3p~5P–3s~5S) were also studied by optical emission spectroscopy. The results show that the water content is in the range of 2.53–9.58 mg l~(-1), depending on the gas/water mixture ratio. The production of OH(A~2Σ~+–X~2Π_i) rises with the increase of water content, whereas the O(3p~5P–3s~5S) shows a declining tendency with higher water content. The sterilization experiments indicate that this air–water plasma jet inactivates the P. digitatum spores very effectively and its efficiency rises with the increase of the water content. It is possible that OH(A~2Σ~+–X~2Π_i) is a more effective species in inactivation than O(3p~5P–3s~5S) and the water content benefit the spore germination inhibition through rising the OH(A~2Σ~+–X~2Π_i) production. The maximum of the inactivation efficacy is up to 93% when the applied voltage is -6.75 kV and the water content is 9.58 mg l~(-1).