Effect of peroxydisulfate on the degradation of phenol under dielectric barrier discharge plasma treatment

Response surface optimisation for corona discharge treatment of nicosulfuron in water

Sulfonylurea herbicides are the most widely used herbicides in the world, which are widely used in the prevention and control of weeds in rice, wheat, soybean and other fields. Long-term application will cause environmental pollution, and the use of plasma technology to degrade herbicides in water is expected to be an effective method to restore pollution. In this experiment, corona discharge plasma was used to treat nicosulfuron in water, and the response surface method was used to optimise the operating conditions of the single system of corona discharge treatment of nicosulfuron and the synergistic system of corona discharge treatment of nicosulfuron with the addition of persulfate. The results showed that the degradation rate of nicosulfuron was 75.08% after 10 min under the optimum operating condition of single system. Under the optimum operating conditions, the degradation rate of nicosulfuron after 10 min was 100%. The R2 and P values of the two system models were both greater than 9.3 and less than 0.01, and the reliability of the simulated degradation rate data was verified by experiments, which provided basic data for the future research on the use of low temperature plasma to degrade herbicides.

Plasma-microbubble treatment and sustainable agriculture application of diclofenac-contaminated wastewater

The demand for efficient wastewater treatment is becoming increasingly urgent due to the rising threat of pharmaceutical residues in water. As a sustainable advanced oxidation process, cold plasma technology is a promising approach for water treatment. However, the adoption of the technology encounters several challenges, including the low treatment efficiency and the potentially unknown environmental impact. Here, microbubble generation was integrated with cold plasma system to enhance treatment of wastewater contaminated with diclofenac (DCF). The degradation efficiency depended on the discharge voltage, gas flow, initial concentration, and pH value. The best degradation efficiency was 90.9% after 45 min plasma-bubble treatment under the optimum process parameters. The hybrid plasma-bubble system exhibited strongly synergistic performance heralded by up to seven-times higher DCF removal rates than the two systems operated separately. The plasma-bubble treatment remains effective even after addition of SO₄^2-, Cl^-, CO₃^2-, HCO₃^-, and humic acid (HA) as interfering background substances. The contributions of •O₂^-, O₃, •OH, and H₂O₂ reactive species to the DCF degradation process were specified. The synergistic mechanisms for DCF degradation were deduced through the analysis of the degradation intermediates. Further, the plasma-bubble treated water was proven safe and effective to stimulate seed germination and plant growth for sustainable agriculture applications. Overall, these findings provide new insights and a feasible approach with a highly synergistic removal effect for the plasma-enhanced microbubble wastewater treatment, without generating secondary contaminants.

Volatile organic compounds degradation by nonthermal plasma: a review

Volatile organic compounds (VOCs) have posed a severe threat on both ecosystem and human health which thus have gained much attention in recent years. Nonthermal plasma (NTP) as an alternative to traditional methods has been employed to degrade VOC in the atmosphere and wastewater for its high removal efficiency (up to 100%), mild operating conditions, and environmental friendliness. This review outlined the principles of NTP production and the applications on VOC removal in different kinds of reactors, like single/double dielectric barrier discharge, surface discharge, and gliding arc discharge reactors. The combination of NTP with catalysts/oxidants was also applied for VOC degradation to further promote the energy efficiency. Further, detailed explanations were given of the effect of various important factors including input/reactor/external conditions on VOC degradation performance. The reactive species (e.g., high-energy electrons, HO·, O·, N₂⁺, Ar⁺, O₃, H₂O₂) generated in NTP discharge process have played crucial roles in decomposing VOC molecules; therefore, their variation under different parameter conditions along with the reaction mechanisms involved in these NTP technologies was emphatically explained. Finally, a conclusion of the NTP technologies was presented, and special attention was paid to future challenges for NTP technologies in VOC treatment to stimulate the advances in this topic.

Effect of dielectric barrier discharge plasma on persulfate activation for rapid degradation of atrazine: Optimization, mechanism and energy consumption

Dielectric barrier discharge plasma (DBDP) is an emerging and promising advanced oxidation process (AOP) for wastewater treatment. After investigating the effect of input voltage, O₃ (generated by dielectric barrier discharge), and peroxydisulfate (PDS) dosage, the DBDP_O3/PDS system was established. With the assistance of PDS, the atrazine (ATZ) removal efficiency increased from 69.67% to 82.46% within 25 min. Synergistic effect calculation suggests that there were markedly synergies between DBDP, O_3, and PDS. Under the effect of SO₄^-•, the total organic carbon (TOC) removal and dechlorination efficiency were significantly improved. In addition, the DBDP_O3/PDS system maintained the ATZ removal efficiency at a high level over a wide range of initial pH values. According to quenching experiments and electron paramagnetic resonance (EPR) detection, the dominant radical for ATZ degradation in the DBDP_O3/PDS system was HO^•. A possible degradation pathway of ATZ was proposed based on density functional theory (DFT) analysis, quadrupole-time of flight-liquid chromatography/mass spectrometry (Q-TOF-LC/MS) results, and related literature. The acute toxicity to aquatic minnows and the developmental toxicity of intermediate products prediction confirmed that the DBDP_O3/PDS system could effectively reduce ATZ toxicity. The electrical energy per order (E_EO) was 7.10 kWh m^-3 order^-1 illustrating that the DBDP_O3/PDS was a more energy-economic system than other energy-intensive processing technologies.

Activation of persulfate for degradation of sodium dodecyl sulfate by a hybrid catalyst hematite/cuprous sulfide with enhanced FeIII/FeII redox cycling

Surfactants are recalcitrant compounds that require advanced treatment for their degradation. Heterogeneous advanced oxidation processes (AOPs) using iron-based catalysts can be a promising method for surfactant degradation. The acceleration of the Fe^III/Fe^II redox cycling is the key to enhance the catalytic degradation. Herein, a hybrid catalyst composed of α-Fe₂O₃ and Cu₂S was synthesized to improve the reduction of Fe^III in a heterogeneous persulfate-AOP system. The results of XRD, Raman and TEM demonstrated the successful preparation of the hybrid catalyst. Because of the optimized Fe^II regeneration, the AOP containing the catalyst FC₇₅ achieved 100.0% removal of sodium dodecyl sulfate (SDS) in a neutral aquatic environment, significantly higher than 22.9 ± 2.4% with pure α-Fe₂O₃ or 39.6 ± 2.5% with pure Cu₂S. The catalyst FC₇₅ demonstrated effective SDS removal in the recycling test (82.7 ± 7.0% after six recycling test) and in actual wastewater (84.4 ± 4.5%). The regeneration of Fe^II was confirmed by the increased proportion of Fe^II from 39.5% in the fresh catalyst to 42.6% in the used catalyst. The main active species was revealed to be sulfate radicals under an acidic condition and shifted to hydroxyl radicals under a basic condition. In the hybrid catalyst, α-Fe₂O₃ provided Fe^II to activate persulfate to radicals, with an oxidation product of Fe^III, which was then reduced to Fe^II by Cu^I provided by Cu₂S, coupling with the oxidation of Cu^I to Cu^II. The S element in Cu₂S could directly or indirectly facilitate the Fe^III/Fe^II redox cycling as an electron donor. Those results have demonstrated that the developed hybrid catalyst is able to promote Fe^II regeneration for effective SDS removal.

Phenol removal kinetics from synthetic wastewater by activation of persulfate using a catalyst generated from shipping ports sludge

Disposal sludges from shipping docks contain elements that have the potential to catalyze the desired treatment process. The current work was designed to decompose phenol from wastewater by activation peroxymonosulfate (PMS) using a catalyst made from sea sediments (at 400 °C for 3 h). The catalyst had a crystalline form and contained metal oxides. The parameters of pH (3-9), catalyst dose (0-80 mg/L), phenol concentration (50-250 mg/L), and PMS dose (0-250 mg/L) were tested to specify the favorable phenol removal. The phenol removal of 99% in the waste sludge catalyst/PMS system was achieved at pH 5, catalyst quantity of 30 mg/L, phenol content of 50 mg/L, PMS dose of 150 mg/L, and reaction time of 150 min. From the results, it was implied that the pH factor was more important in removing phenol with the studied system than other factors. By-products and phenol decomposition pathways were also provided. The results showed that the sea sediment catalyst/PMS system is a vital alternative for removing phenol from wastewater medium.

Degradation of aqueous atrazine using persulfate activated by electrochemical plasma coupling with microbubbles: removal mechanisms and potential applications

Persulfate (PS) activated by dielectric barrier discharge (DBD) integrated with microbubbles (MBs) was designed to decompose atrazine (ATZ) from aqueous solutions. The degradation efficiency reached 89% at a discharge power of 85W, a PS concentration of 1mM, and a air flow rate of 30mL/min after 75min treatment. Heat caused by DBD favoured ATZ removal. Besides, the effect of PS dosage, discharge power and initial pH values on ATZ removal was evaluated. The calculated energy yield revealed that it was economical and promising to treat 1L of ATZ-wastewaters. The existence of SO₄^2-, Cl^-, CO₃^2- and HCO₃^- lead to negative effects, while positive effect was observed when the presence of MBs and humic acid. The identification results of radicals and degradation intermediates suggested that multiple synergistic effects (such as heat, e_aq^- and H•) activated PS, and ¹O₂/reactive nitrogen species, •OH and SO₄^-• with contributions of 18%, 26%, and 29%, were main species attacking ATZ. ATZ degradation pathways including olefination, alkylic-oxidation, dealkylation, and dechlorination were proposed. An environment-friendly and a novel method for enhancing the PS-activation and ATZ-decomposition was provided, which fully utilised the electric-chemical conversion of DBD and high mass transfer efficiency of MBs.

Degradation of trimethoprim in aqueous by persulfate activated with nanosecond pulsed gas-liquid discharge plasma

The persulfate activation by nanosecond pulsed gas-liquid discharge (NPG-LD) is employed to degrade the trimethoprim (TMP) in water. The results show that persulfate addition enhances the degradation of TMP by NPG-LD through an obvious synergetic effect. With treatment time of 50 min, the high removal efficiency and energy yield reach 94.6% and 0.57 gkWh^-1 in air NPG-LD with the addition of persulfate, respectively, which is 13.5% and 0.09 gkWh^-1 higher than that in solo air NPG-LD, respectively. Correspondingly, the calculated synergetic factor achieves 1.62, indicating the synergetic effect is established. The activation mechanism of persulfate by NPG-LD is analyzed by the measurement of reactive species and the effects of radical scavenger addition on TMP removal. It is found that the synergetic effect between NPG-LD and persulfate is attributed to the increased production of OH, H₂O₂, and . Besides, the TMP degradation by NPG-LD and persulfate synergetic system is influenced by discharge working gas, pulse voltage, addition dosage of persulfate, initial TMP concentration, and initial pH value. Subsequently, the degradation pathway of TMP is analyzed using LC-MS/MS.

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.