Synergistic degradation performance and mechanism of 17β-estradiol by dielectric barrier discharge non-thermal plasma combined with Pt–TiO2

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.

Removal of Pharmaceutical Residues from Water and Wastewater Using Dielectric Barrier Discharge Methods-A Review

Persistent pharmaceutical pollutants (PPPs) have been identified as potential endocrine disruptors that mimic growth hormones when consumed at nanogram per litre to microgram per litre concentrations. Their occurrence in potable water remains a great threat to human health. Different conventional technologies developed for their removal from wastewater have failed to achieve complete mineralisation. Advanced oxidation technologies such as dielectric barrier discharges (DBDs) based on free radical mechanisms have been identified to completely decompose PPPs. Due to the existence of pharmaceuticals as mixtures in wastewater and the recalcitrance of their degradation intermediate by-products, no single advanced oxidation technology has been able to eliminate pharmaceutical xenobiotics. This review paper provides an update on the sources, occurrence, and types of pharmaceuticals in wastewater by emphasising different DBD configurations previously and currently utilised for pharmaceuticals degradation under different experimental conditions. The performance of the DBD geometries was evaluated considering various factors including treatment time, initial concentration, half-life time, degradation efficiency and the energy yield (G50) required to degrade half of the pollutant concentration. The review showed that the efficacy of the DBD systems on the removal of pharmaceutical compounds depends not only on these parameters but also on the nature/type of the pollutant.

Review on the treatment of organic wastewater by discharge plasma combined with oxidants and catalysts

Discharge plasma technology is a new advanced oxidation technology for water treatment, which includes the effects of free radical oxidation, high energy electron radiation, ultraviolet light hydrolysis, and pyrolysis. In order to improve the energy efficiency in the plasma discharge processes, many efforts have been made to combine catalysts with discharge plasma technology. Some heterogeneous catalysts (e.g., activated carbon, zeolite, TiO₂) and homogeneous catalysts (e.g., Fe²⁺/Fe³⁺, etc.) have been used to enhance the removal of pollutants by discharge plasma. In addition, some reagents of in situ chemical oxidation (ISCO) such as persulfate and percarbonate are also discussed. This article introduces the research progress of the combined systems of discharge plasma and catalysts/oxidants, and explains the different reaction mechanisms. In addition, physical and chemical changes in the plasma catalytic oxidation system, such as the effect of the discharge process on the catalyst, and the changes in the discharge state and solution conditions caused by the catalysts/oxidants, were also investigated. At the same time, the potential advantages of this system in the treatment of different organic wastewater were briefly reviewed, covering the degradation of phenolic pollutants, dyes, and pharmaceuticals and personal care products. Finally, some suggestions for future water treatment technology of discharge plasma are put forward. This review aims to provide researchers with a deeper understanding of plasma catalytic oxidation system and looks forward to further development of its application in water treatment.

Comparative endocrine disrupting compound removal from real wastewater by UV/Cl and UV/H2O2: Effect of pH, estrogenic activity, transformation products and toxicity

Extensive use of endocrine disruptor compounds (EDCs) and their release through various pathways into the environment are emerging environmental concerns. In this context, H₂O₂ and chlorine UV-based treatments were carried out to evaluate their efficiency in the removal of the bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) at 100 μg L^-1 from ultrapure water and from wastewater treatment plants (WWTP). Photolysis was performed under different irradiation sources, i.e. UVC and UVA. The effect of H₂O₂ (3 and 30 mg·L^-1), free chlorine concentrations (1 and 2 mg·L^-1) and pH (5, 7 and 9) were also investigated. Toxicity (Raphidocelis subcapitata) and estrogenic activity (yeast estrogen screen - YES assay) were assessed during the processes. Compound removal at optimal operating parameters reached 100% after 15 and 2 min for UVC/H₂O₂ (pH 9 and 3 mg L^-1 of H₂O₂), and UVC/Cl (pH 9 and 2 mg L^-1 of chlorine), respectively. Total organic carbon (TOC) removal achieved 37% and 45% for the H₂O₂ and Cl-UV based process, respectively. The in vitro YES assay indicated that the formed by-products were non-estrogenic compounds, while the toxicity evaluation revealed high cell growth inhibition due to UVC/Cl byproducts. During the UV-based processes, 30 transformation products (TPs) were identified, in which three new chlorinated TPs from E2 and EE2 may be responsible for toxicity effects. EDC degradation by UV/Cl is faster than by UV/H₂O₂, although chlorinated toxic byproducts were also formed during the UV/Cl process.

Catalytic degradation of clothianidin with graphene/TiO2 using a dielectric barrier discharge (DBD) plasma system

Clothianidin served as the model pollutant to investigate the performance and mechanism of pollutant removal by dielectric barrier discharge plasma (DBD) combined with the titanium dioxide-reduced graphene oxide (rGO-TiO₂) composite catalyst. In this study, different ratios of titanium dioxide-graphene catalysts were loaded onto honeycomb ceramic plates via the sol-gel method, and the modified catalytic ceramic plates were characterized by XRD, SEM, FTIR, DRS, and energy dispersive X-ray. The results suggested that the rGO-TiO₂ was well loaded on the surface of the honeycomb ceramic plates. According to the results of the characterization experiments and the degradation of the clothianidin solution with different proportions of the catalyst, 8 wt% rGO-TiO₂ was selected as the optimum ratio for degradation. Clothianidin degradation efficiency was significantly influenced by input power, clothianidin concentration, pH value, liquid conductivity, free radical quencher. Finally, six degradation products of clothianidin were identified by HPLC-MS, and the possible transformation pathways of clothianidin degradation were identified. Graphical abstract.

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.

Study on the Preparation of Plasma-Modified Fly Ash Catalyst and Its De⁻NOX Mechanism

Fly ash and bentonite were mixed in a certain proportion as raw materials to prepare a denitration catalyst. In previous studies, it has been concluded that fly ash-type catalysts can provide significant catalytic activity for denitrification after being modified with oxygen. In this study, the effect of plasma conditions on the denitration performance of the catalyst was investigated from the aspects of plasma modification power, modification time, and the flow rate of the gas. Boehm titration and infrared analysis systems were used to characterize the performance of the catalyst. The experimental results show that the optimal modification power is 60 W, the optimal modification time is 20 min, and the optimal gas flow rate is 40 mL/min.

Enhanced degradation of perfluorooctanoic acid using dielectric barrier discharge with La/Ce-doped TiO2

A synergistic system of dielectric barrier discharge (DBD) combined with La/Ce-TiO₂ was developed to investigate the decomposition performance of the environmentally persistent perfluorooctanoic acid (PFOA). The La/Ce-TiO₂ was modified by sol-gel method and characterized by XRD, SEM, and energy dispersive X-ray. The effects of PFOA concentration, applied voltage, initial pH, liquid conductivity, and additives on the removal rate of PFOA were explored. The results showed that the La/Ce-TiO₂ exhibited excellent catalytic effects on PFOA degradation in DBD system. When the applied voltage, PFOA concentration, pH value, and solution volume were 75 V, 100 mg/L, 3.63, and 1000 mL, respectively, the removal efficiency of PFOA was up to 97.5% by adding La₄Ce₁-TiO₂ in DBD. The corresponding defluorination ratio, TOC removal, and decomposition yield were 62.2%, 57.3%, and 37 g/kWh, respectively. Furthermore, five main intermediates including CF₃(CF₂)₆H, CF₃(CF₂)₅COOH, CF₃(CF₂)₅COH, CF₃(CF₂)₄COOH, and CF₃CF₂CF₃ were identified with LC-MS, and the degradation pathways of PFOA were proposed. The degradation mechanisms revealed that hydroxyl radicals play a significant role in the degradation of PFOA in the synergistic system.