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The investigation into the degradation of metronidazole (MNZ), a frequently employed antibiotic, through the electrochemical activation of peroxymonosulfate (PMS) utilizing either boron-doped diamond (BDD) or dimensional stable anode (DSA) as the anode, was conducted in a systematic manner. The enhancement of MNZ removal was observed with increasing current density, PMS dosage, and initial pH. Response surface methodology (RSM), based on a Box–Benken design, was utilized to evaluate the efficiency of MNZ elimination concerning current density (ranging from 11.1 to 33.3 mA/cm2), initial pH (ranging from 3 to 9), PMS dosage (ranging from 1 to 5 mmol·L−1), and reaction time (ranging from 25 to 45 min). The optimal operational conditions for MNZ removal were determined as follows: a current density of 13.3 mA/cm2, a pH of 3.7, a PMS dosage of 2.4 mmol·L−1, and a reaction time of 40 min. Electron paramagnetic resonance (EPR), quenching experiments, and chemical probe experiments confirmed the involvement of •OH, SO4•− and 1O2 radicals as the primary reactive species in MNZ degradation. The presence of HCO3− and H2PO4− hindered MNZ removal, whereas the presence of Cl− accelerated it. The degradation pathways of MNZ were elucidated by identifying intermediates and assessing their toxicity. Additionally, the removal efficiencies of other organic pollutants, such as sulfamethoxazole (SMX), carbamazepine (CBZ), and nitrobenzene (NB), were compared. This study contributes to a comprehensive understanding of MNZ degradation efficiency, mechanisms, and pathways through electrochemical activation of PMS employing BDD or DSA anodes, thereby offering valuable insights for the selection of wastewater treatment systems. [ABSTRACT FROM AUTHOR]

The ethylenediamine-N,N′-disuccinic acid (EDDS) was utilized to form Fe-EDDS complex to activate peroxymonosulfate (PMS) in the electrochemical (EC) co-catalytic system for effective oxidation of naphthenic acids (NAs) under neutral pH conditions. 1-adamantanecarboxylic acid (ACA) was used as a model compound to represent NAs, which are persistent pollutants that are abundantly present in oil and gas field wastewater. The ACA degradation rate was significantly enhanced in the EC/PMS/Fe(III)-EDDS system (96.6%) compared to that of the EC/PMS/Fe(III) system (65.4%). The addition of EDDS led to the formation of a stable complex of Fe-EDDS under neutral pH conditions, which effectively promoted the redox cycle of Fe(III)-EDDS/Fe(II)-EDDS to activate PMS to generate oxidative species for ACA degradation. The results of quenching and chemical probe experiments, as well as electron paramagnetic resonance (EPR) analysis, identified significant contributions of •OH, 1O2, and SO4•− in the removal of ACA. The ACA degradation pathways were revealed based on the results of high resolution mass spectrometry analysis and calculation of the Fukui index. The presence of anions, such as NO3−, Cl−, and HCO3−, as well as humic acids, induced nonsignificant influence on the ACA degradation, indicating the robustness of the current system for applications in authentic scenarios. Overall results indicated the EC/PMS/Fe(III)-EDDS system is a promising strategy for the practical treatment of NAs in oil and gas field wastewater. [ABSTRACT FROM AUTHOR]

In this study, molybdenum disulfide (MoS 2) has been investigated as a catalyst to boost the redox cycle of Fe(III)/Fe(II) to activate peroxymonosulfate (PMS) to effectively break down cyclohexanecarboxylic acid (CHA), which is a model naphthenic acid (NA) pollutant. The optimum conditions of pH 3, MoS 2 concentration of 0.4 g/L, Fe(III) concentration of 0.3 mmol/L, and PMS concentration of 2 mmol/L has been applied for complete degradation of 0.1 mmol/L CHA in 10 minutes reaction time. Based on results of electron paramagnetic resonance analysis, chemical probe and quenching experiment, it was found that all of •OH, SO 4 •−, 1O 2 , and Fe(IV) contributed to the MoS 2 /Fe(III)/PMS oxidation system. Eighteen CHA byproducts and three primary CHA degradation pathways were revealed according to the results of UHPLC-QTOF-MS analysis. By using XPS, SEM, and XRD to characterize the MoS 2 powders before and after the reaction, MoS 2 was found with high stability and the oxidation of Mo(IV) on the surface was negligible. The impacts of background anions on CHA degradation were found to be nonimportant, and commercial NAs mixture were verified to be efficiently degraded in current system. Overall results indicate the capacity and potential of MoS 2 /Fe(III)/PMS system to be utilized for future treatment of authentic oil and gas field wastewater. [Display omitted] • Both Mo(IV) and S2- of MoS 2 can activate PMS to generate ROS to degrade CHA. • The main reactive species are 1O 2 , •OH, SO 4 •−and Fe(IV) in the system. • Chain scission, hydrogen extraction and decarboxylation are main reaction pathways. • No Mo(V) oxidation was found on the surface of MoS 2 powder after the reaction. • The commercial NAs mixture was examined for efficient degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • BDD/PMS/Fe(III) process is dominated by radical oxidation. • DSA/PMS/Fe(III) process is dominated by nonradical oxidation. • BDD/PMS/Fe(III) system is inclined to oxidize electron-rich contaminants. • DSA/PMS/Fe(III) system is apt to oxidize electron-deficient contaminants. • Degradation pathways of sulfamethoxazole were systematically revealed. Herein, peroxymonosulfate (PMS) activation via electro-cocatalytic system with circulated Fe(III)/Fe(II) was investigated with boron-doped diamond (BDD) anode and dimensionally stable anode (DSA) for degradation of sulfamethoxazole (SMX). Radicals of OH and SO 4 − as well as non-radicals of 1O 2 and Fe(IV) were all present in BDD/PMS/Fe(III) and DSA/PMS/Fe(III) systems, according to the results of scavenging experiment and electron paramagnetic resonance (EPR) analysis. Interestingly based on the results of chemical probe experiments, the ratio of OH, SO 4 −, and 1O 2 were 9% (7.19 μmol/L), 76% (58.39 μmol/L), and 15% (11.45 μmol/L) in BDD/PMS/Fe(III) system, and were 28% (5.81 μmol/L), 18% (3.76 μmol/L), and 54% (10.93 μmol/L) in DSA/PMS/Fe(III) system. The yield of Fe(IV) in DSA/PMS/Fe(III) process was relatively higher than that in BDD/PMS/Fe(III) process. These results indicated that BDD/PMS/Fe(III) is a radical oxidation system while DSA/PMS/Fe(III) system is mainly non-radical system. Due to the high electrochemical activity of BDD anode, the one-electron transfer reaction might occur to produce more SO 4 −. The co-existing ions including Cl−, H 2 PO 4 −, and NO 3 − showed significant effects on the degradation efficiency of BDD/PMS/Fe(III) and nonsignificant impacts on DSA/PMS/Fe(III) process, indicating that DSA/PMS/Fe(III) process could be less affected by complex water matrix. BDD/PMS/Fe(III) is inclined to oxidize electron-rich contaminants, while DSA/PMS/Fe(III) is apt to oxidize electron-deficient contaminants. The degradation routes of SMX and its toxicity evolution were systematically studied with the analysis of byproducts. Overall results compared the oxidation mechanisms and primary oxidation pathways of electro-cocatalytic systems with BDD versus DSA anodes, and revealed the merits of each system for future selection and system optimization of treatment processes regarding targeted contaminants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient degradation of NAs was achieved by EC/PMS/Fe(III) system. • The redox cycle of Fe(III)/Fe(II) was triggered on the cathode. • The chemical structures of NA molecules affect their reactivity. • •OH, SO 4 •− and 1O 2 are the main reactive species in EC/PMS/Fe(III) system. • CHA degradation pathways and byproducts were revealed. In this study, an electrochemical/peroxymonosulfate/Fe(III) (EC/PMS/Fe(III)) system was established for efficient degradation of four naphthenic acids (NAs) compounds including cyclohexanecarboxylic (CHA), heptanoic (HPA), benzoic (BA) and 2-methylhexanoic acids (2-MHA). The introduction of electric field enhances the redox cycle of Fe(III)/Fe(II) to activate PMS for degredation of NAs. Complete degradation of NAs compounds (5 mg/L) has been achieved within 30 min in the EC/PMS/Fe(III) system. The results of electron paramagnetic resonance (EPR) analysis, scavenging experiment, and chemical probe experiments indicated hydroxyl radical (•OH), sulfate radical (SO 4 •−) and singlet oxygen (1O 2) are primary reactive oxygen species (ROS) in the EC/PMS/Fe(III) system. NAs compounds with different structures exhibit inconsistent degradation efficiency in current system (k CHA > k BA > k HPA > k 2-MHA), depending on the selectivity of the different ROS and stability of respective intermediate organic radicals. Besides, multiple degradation pathways of CHA, mainly including hydroxylation and carbonylation, were proposed by combining the results of mass spectrometry analysis with the calculated Fukui index based on density functional theory (DFT) calculation. In addition, the EC/PMS/Fe(III) system exhibited robust performance with the addition of co-existing ions. This work provides a novel strategy for efficient degradation of NAs for future remediation of petroleum wastewater. [ABSTRACT FROM AUTHOR]

Herein, an electrochemical (EC) system was applied as "co-catalyst" to enhance the activation of peroxymonosulfate (EC/Fe(III)/PMS) for efficient Sulfamethoxazole (SMX) degradation. The cathodic reduction reaction can facilitate electron transfer to Fe(III) and trigger the sustainable Fe(III)/Fe(II) redox cycle. Unexpectedly, in addition to hydroxyl radical (•OH) and sulfate radical (SO 4 •−), non-radicals mechanism including singlet oxygen (1O 2) and Fe(IV) were also found involved in EC/Fe(III)/PMS system. The degradation of SMX in EC/Fe(III)/PMS system was accomplished by the collaboration of radicals and non-radicals oxidation. The generation routes and mechanisms of involved reactive oxygen species (ROS) were explored. The relative contributions of •OH, SO 4 •−, and nonradical species for the degradation of SMX were calculated to 4.75 %, 25.31 %, and 69.94 %, respectively. Besides, multiple degradation pathways of SMX were proposed by identifying the formed byproducts. The EC/Fe(III)/PMS process could efficiently degrade SMX under the influence of co-existing ions and inactivate pathogens in the wastewater. [Display omitted] • Electrochemical system was used as a "co-catalyst" to promote the Fe(III)/Fe(II) redox cycle. • SMX is effectively degraded with a weak electrical current consumption in EC/Fe(III)/PMS system. • EC/Fe(III)/PMS system is mainly a non-radical pathway dominated by 1O 2 and Fe(IV). • EC/Fe(III)/PMS system demonstrated the ability to simultaneously eliminate contaminants and pathogens. [ABSTRACT FROM AUTHOR]

• The EC/PMS/Fe(III)-EDTA system was tested under a pH range of 3–9. • Fe(II)-EDTA complex maintains high reaction rates to degrade ACA at neutral pH. • •OH, 1O 2 , SO 4 •− and Fe(IV) are the dominant reactive species in the system. • The addition of EDTA established a new pathway for producing 1O 2 in the system. • ACA degradation pathways and byproducts were revealed based on mass spectra. In this work, ethylene diamine tetraacetic acid (EDTA) was applied as a chelating agent to stabilize Fe(III)/Fe(II) cycle to effectively activate peroxymonosulfate (PMS) in an electrochemical (EC) co-catalytic system for elimination of naphthenic acids (NAs) under neutral pH condition. 1-Adamantanecarboxylic acid (ACA) was applied as the model compound for NAs that are persistent contaminants in petroleum industrial wastewater. In the PMS/EC/Fe(III)-EDTA system, complete removal of ACA has been achieved in 20-min reaction under neutral pH condition. Degradation mechanisms were investigated via electron paramagnetic resonance (EPR) analysis, probe experiments and quenching experiments to reveal the reactive species •OH, SO 4 •− and 1O 2 for ACA removal, the production of which have been significantly facilitated by the introduction of EDTA complex. A new pathway has been found for the production of 1O 2 via several intermediates including hydrogen peroxide and superoxide radicals. Density functional theory (DFT) calculations and mass spectrometry analysis were applied to predict ACA degradation pathways and byproducts. Decarboxylation, hydroxyl substitution and carbonyl substitution byproducts of ACA were detected. The PMS/EC/Fe(III)-EDTA system suffered nonimportant influence at the presence of humic acid, H 2 PO 4 -, HCO 3 –, NO 3 – and Cl- for ACA removal. Overall results demonstrate the effectiveness and reliability of the PMS/EC/Fe(III)-EDTA system for efficient removal of NAs in petroleum wastewater in natural environment under neutral pH condition. [ABSTRACT FROM AUTHOR]

In this work, the pulsed electrochemical (PE) system was investigated to activate peroxymonosulfate (PMS) with the addition of Fe(III) to achieve efficient degradation of sulfamethoxazole (SMX) with reduced energy consumption, in comparison with the direct current (DC) electrochemical system. The operational conditions of PE/PMS/Fe(III) system were optimized as 4 kHz pulse frequency, 50% duty cycle, and pH 3, at which 67.6% reduction of energy consumption and enhanced degradation performance were achieved compared to the DC/PMS/Fe(III) system. Results of electron paramagnetic resonance spectroscopy analysis and quenching and chemical probe experiment revealed the presence of •OH, SO 4 •−, and 1O 2 in the system, with •OH being the dominant role. The concentrations of these active species were averagely 15 ± 1% higher in the PE/PMS/Fe(III) system than those of the DC/PMS/Fe(III) system. Identification of SMX byproducts was achieved based on high resolution mass spectrometry analysis to predict the degradation pathways. The SMX byproducts could eventually be eliminated by the PE/PMS/Fe(III) system with extended treatment time. Overall, the PE/PMS/Fe(III) system was demonstrated with high energy and degradation performance, and is appear to be an robust strategy for practical treatment of wastewater. [Display omitted] ● The PE system are more energy-efficient and effective than DC system. ● PE/PMS/Fe(III) system can improve the utilization of iron ions. ● •OH is the dominant active species in PE/PMS/Fe(III) system. ● The degradation pathways and byproducts toxicity of SMX were further evaluated. [ABSTRACT FROM AUTHOR]

This work investigated the activation of peroxymonosulfate by electrochemical (EC) system assisted with Fe(III)-nitrilotriacetic acid (NTA) complex for degradation of persistent naphthenic acids (NAs) under neutral initial pH conditions. As NAs are a complicated mixture, 1-adamantanecarboxylic acid (ACA) was selected as the model NA compound for degradation experiment. The addition of NTA is to chelate with Fe(III), gaining stability under neutral pH condition to facilitate the circulation of Fe(II)/Fe(III) by the electrochemical process to activate PMS. The EC/Fe(III)-NTA/PMS system was explored with applicable pH range of 3–9 and an optimized molar ratio 1: 2 for Fe: NTA. Results of quenching and chemical probe experiment together with results of electron paramagnetic resonance (EPR) analysis revealed the main reactive species of the system, including •OH, SO 4 •−, 1O 2 and possibly Fe(IV). With the addition of NTA, the yields of •OH, SO 4 •−, 1O 2 were enhanced. Results of mass spectrometry analysis and DFT calculations indicated the formation of 9 degradation byproducts of ACA via three primary degradation pathways such as hydroxyl substitution, carbonyl substitution, and decarboxylation. Furthermore, the EC/Fe(III)-NTA/PMS system could achieve excellent removal efficiency of ACA with different anions such as Cl-, HCO 3 -, NO 3 - and H 2 PO 4 - in the background. The practical applicability of the system was also verified with the high removal of commercial NAs mixture standard. Overall results have indicated the EC/Fe(III)-NTA/PMS system could be utilized for efficient reclamation of authentic oil and gas industrial wastewater under natural pH conditions. [Display omitted] • The EC/Fe(III)-NTA/PMS system was explored with applicable pH range 3–9. • The redox cycle of Fe(III)-NTA/Fe(II)-NTA was boosted to activate PMS. • Fe(II)-NTA complex maintains high reaction rates to activate PMS at neutral pH. • •OH, SO 4 •−, 1O 2 and Fe(IV) are the main reactive species in the system. • ACA degradation pathways and byproducts were revealed based on mass spectra. [ABSTRACT FROM AUTHOR]

[Display omitted] • The combination technology of SR-AOPs and membrane filtration (MF) was summarized. • The current scenario of various integrated catalytic filtration membranes methods was centralized. • SR-AOPs/MF was used to remove pollutants and reduce membrane fouling. • The future opportunities and challenges of this technology are discussed. Integration of membrane filtration (MF) and sulfate radical-advanced oxidation processes (SR-AOPs) has progressively attracted extensive attention for environmental remediation because of simultaneous degradation and filtration of pollutants in wastewater. Current development of the integration of MF and SR-AOPs can be divided into three main categories: (1) peroxymonosulfate (PMS)/peroxydisulfate (PDS) are activated by membrane materials to achieve the purpose of synergistic oxidation-filtration process; (2) removal of contaminants was achieved by filtering through the membrane, and then adding PMS/PDS to regenerate the membrane; (3) the membrane can be directly used as an oxidant-catalyst/water contactor to promote SR-AOPs. On this basis, this review comprehensively summarizes the classification, preparation methods and properties of different types of membrane-based materials and filtration devices. In addition, the antifouling effect and self-purification regeneration ability of different SR-AOPs systems on the membrane are highlighted. Moreover, the main mechanisms including the analysis of active sites, the generation of free radicals, and the theoretical calculations in integration of MF and SR-AOPs are defragmented and discussed. Finally, the technical challenges of coupling technology in wastewater treatment are discussed, and the development and application prospects of the collaborative mixing process are prospected. [ABSTRACT FROM AUTHOR]