Analysis on the removal of ammonia nitrogen using peroxymonosulfate activated by nanoparticulate zero-valent iron

Efficient removal of 3,6-dichlorocarbazole with Fe0-activated peroxymonosulfate: performance, intermediates and mechanism

Nowadays, polyhalogenated carbazoles (PHCZs) are a major pollutant that has recently sparked widespread concern. In this work, peroxymonosulfate (PMS) was activated by zero valent iron (Fe⁰) to remove 3,6-dichlorocarbazole (3,6-CCZ). First, the key parameters influencing 3,6-CCZ degradation (PMS dosage, Fe⁰ dosage, initial pH, temperature and co-existing ions) were determined. Under the determined optimum conditions, the removal rate of 3,6-CCZ reached 100% within 1.5 h. Sulfate radicals (SO₄·^-), hydroxyl radicals (OH·), and singlet oxygen (¹O₂) generated in the reaction were directly identified with 0.1 M 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) by in-situ electron paramagnetic resonance (EPR) and indirectly identified by radical quenching experiments. The main reactive oxygen species (ROS) were different from most reported hydroxyl radicals (OH·) and sulfate radicals (SO₄·^-). In this study, it was found that OH· and ¹O₂ play a major role. Then, fresh and reacted Fe⁰ were characterized by XRD, SEM, and XPS. Iron corrosion products such as Fe₂O₃, Fe₃O₄, and FeOOH were generated. Finally, 3,6-CCZ degradation intermediates were identified by GC-MS and its degradation pathway was speculated. The intermediate pathway confirmed the combined action of (OH·) and (¹O₂) in 3,6-CCZ removal. This study provides new insight into the activation mechanism of Fe⁰-activated PMS and the removal mechanism of 3,6-CCZ.Highlights Fe⁰ is a long-lasting and efficient catalyst of PMS for the degradation of 3,6-CCZ.The key parameters influencing 3,6-CCZ degradation were determined.The degradation pathways of 3,6-CCZ were inferred.OH· and ¹O₂ were the main ROS in Fe⁰-activated PMS system.

Degradation of methylene blue by an E-Fenton process coupled with peroxymonosulfate via free radical and non-radical oxidation pathways

This paper reports a combined advanced oxidation process to degrade methylene blue and investigates its oxidation mechanism and degradation pathway.

Landfill leachate treatment by persulphate related advanced oxidation technologies

Landfill leachate is produced from garbage decomposition with highly toxic and bio-refractory compounds, which poses serious harm to environmental security and human health. Thus, it is urgent to treat landfill leachate properly. Persulfate (PS) oxidation has attracted extensive attentions in terms of fast reaction speed, non-selectivity to target pollutants and thorough oxidation. In recent years, PS oxidation has been widely adopted for landfill leachate purification. However, the related results have been rarely summarized. In this review, the treatment of landfill leachate by PS oxidation system is discussed systematically including oxidants, activation modes and oxidation mechanisms. In addition, the current situation of PS oxidation system and other coupled systems for landfill leachate treatment is also summarized. Finally, the challenges and future research directions of landfill leachate treatment based on PS oxidation process are proposed. Meaningfully, this review will provide valuable references for the development of landfill leachate treatment process, promoting the application of advanced oxidation technology in landfill leachate treatment.

Enhanced kinetic performance of peroxymonosulfate/ZVI system with the addition of copper ions: Reactivity, mechanism, and degradation pathways

Advanced oxidation processes (AOPs) based on the bimetallic system has been demonstrated as a promising way to enhance the degradation of pollutants in the water. In this study, the degradation of Rhodamine B (RhB) in a zero-valent iron (ZVI)/ peroxymonosulfate system with Cu²⁺ was thoroughly investigated. RhB could be efficiently removed (99.3 %) in the optimal ZVI/PMS/Cu²⁺ system, while only 58.2 % of RhB could be degraded in the ZVI/PMS system. The influence of reaction parameters on the degradation of RhB was further investigated. Quenching experiments and electron paramagnetic resonance (EPR) tests revealed that various reactive oxygen species could be generated in the ternary system, of which, ¹O₂ and O₂^- were identified for the first time. The effect of various anions, NOM and different water matrix were also considered at different concentrations. A variety of byproducts and degradation pathways were identified using HPLC/MS/MS. Finally, the Quantitative Structure Activity Relationship (QSAR) method of Toxicity Estimation Software Tool (TEST) was applied to estimate the toxicity of the byproducts and the results indicated that the overall toxicity of the target was relatively reduced. This study demonstrated the potential for the removal of environmental reluctant pollutants in water via the combined radical and non-radical pathways.

Enhanced heterogeneous Fenton-like degradation of nuclear-grade cationic exchange resin by nanoscale zero-valent iron: experiments and DFT calculations

Nanoscale zero-valent iron (nZVI) was prepared and used as a heterogeneous Fenton-like catalyst for the degradation of nuclear-grade cationic exchange resin. The properties of nZVI before and after reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analysis. The results showed that nZVI-H₂O₂ system exhibited the enhanced degradation of cationic resins, compared with Fe²⁺-H₂O₂, Cu⁰-H₂O₂, and Fe⁰/Cu⁰-H₂O₂ systems. The effects of initial temperature, nZVI dose, and H₂O₂ concentration were studied, and the higher temperature and nZVI dose with relatively low H₂O₂ concentration brought faster degradation rate. The degradation of cationic resins followed the pseudo-first-order kinetics with the apparent activation energy of 53.29 kJ/mol. According to the experimental and calculated infrared and UV-visible spectra, the carbon skeleton of cationic resins was broken with the detachment of benzene ring and the desulfonation of resin polymer by hydroxyl radicals (•OH), generating long-chain alkenes. These intermediates were further oxidized through the hydroxyl substitution, hydrogen abstraction, ring cleavage, or carbonylation reactions, finally forming carboxylic acids remained in solution.

Coupled heat-activated persulfate - Electrolysis for the abatement of organic matter and total nitrogen from landfill leachate

This work analyzes the viability of a coupled heat-activated persulfate (PS) and electro-oxidation treatment toabatetheorganic matter and nitrogen from ahigh polluted landfill leachate (5500 mg L^-1 TOC; 5849 mg L^-1 TN, pH: 8.4). These characteristics makes PS as a suitable oxidant to deal with the recalcitrant organic matter. Under the optimal conditions (70 °C and 60% of the stoichiometric amount of PS), around 60% of the initial organic load was mineralized. On the contrary, the nitrogen removal was below 20%. A subsequent electrolytic stage using Ti/IrO₂-TaO₂ anode at 175 mA cm^-2 and 0.42 M NaCl during 60 min, led to overall organic matter and nitrogen removal above 85% and 90%, respectively, with energy requirement of 38 kWh per kg of nitrogen removed. In this sense, the combined process achieves a significant reduction in terms of energy consumption, up to one fifth in relation to sole electrolysis. These results confirm the feasibility of this combined process to treat landfill leachate.

Enhanced degradation performance of bisphenol M using peroxymonosulfate activated by zero-valent iron in aqueous solution: Kinetic study and product identification

In the present work, we first examined the performance of zero-valent iron (Fe⁰) activated peroxymonosulfate (PMS) for the removal of that bisphenol M (BPM). In 90 min, 95.9 ± 1.0% of BPM (initial concentration of 10 μM) could be removed in the optimal reaction conditions: [BPM]₀:[PMS]₀ = 1:40 (molar ratio), [PMS]₀:[Fe⁰]₀ = 1:3 (molar ratio), pH = 8.0 (maintained by 0.1 M phosphate buffer solution), T = 35 °C. Common environmental ions like HCO₃^-, Cl^-, NO₃^- accelerated BPM degradation while NH₄⁺ hindered it. In radical quenching tests, sulfate radicals (SO₄^-) were found to play a dominant role in BPM degradation, while hydroxyl radicals (OH) were also detected. By high-performance liquid chromatography-tandem mass spectrometry analysis, 13 products of BPM including small molecules, oligomers and hydroxylated derivatives were identified, and five possible degradation pathways were then proposed. The predicted acute toxicity of the reaction products was reduced after BPM was treated by Fe⁰/PMS. All these results prove that Fe⁰/PMS is an efficient, convenient, and environmentally friendly treatment method for the removal of BPM.