The electrochemical advanced oxidation processes coupling of oxidants for organic pollutants degradation: A mini-review

Enhanced Treatment of Antimony Mine Wastewater by Sulfidated Micro Zerovalent Iron (S-mZVI)

Commercial micron zerovalent iron (mZVI) and sulfur were used to prepare sulfidated micro zerovalent iron (S-mZVI) through ball milling. The corrosion potentials of mZVI and S-mZVI were -0.01 and -0.37 V, respectively, indicating S-mZVI possessed a stronger electron-donating ability. The practical antimony mine wastewater (C0(Sb(V)) = 3.8296 mg/L, pH = 8.29) was treated. If meeting the national discharge standard of 5 μg/L, 2.0 g/L mZVI and 1.6 g/L S-mZVI were required within 120 min. Passing N2 or reducing wastewater pH enhanced the treatment of Sb(V) by S-mZVI, in which the wastewater acidification was more effective. Once the wastewater pH was adjusted to 3.00, only 0.7 g/L S-mZVI and 40 min long time were needed to achieve the emission below 5 μg/L. Even S-mZVI underwent four cycles, and the final concentration of Sb(V) was as low as 4.67 μg/L. As the pHzpc value was 4.09 and the corrosion potential was -0.56 V at pH 3.0, the electron-donating ability of S-mZVI as well as the electrostatic attraction between the surface of S-mZVI and Sb(V) increased. Sulfidation of mZVI and then application under the acid condition significantly improved the treatment efficiency of Sb(V).

Pomelo peel biomass derived highly active advanced-oxidation-process catalyst: Complete elimination of organic pollutants

The advanced oxidation process (AOPs) is playing an important role in the elimination of hazardous organic pollutants, but the development of inexpensive and highly active advanced catalysts is facing challenges. In this study, a low-cost and readily available agricultural waste resource pomelo peel-flesh (PPF) biomass was used as the basic raw material, and the uniformly dispersed small cobalt nanoparticles were effectively anchored in the biochar derived from pomelo peel-flesh (BDPPF) by impregnation adsorption/complexation combined with heat treatment. Co/BDPPF (BDPPF embedded with Co) can effectively activate peroxymonosulfate (PMS) to SO4·-, ·OH and 1O2 reactive oxygen species, and achieve nearly 100% degradation of tetracycline persistent organic pollutant. Co/BDPPF can not only degrade tetracycline efficiently in complex water environment, but also degrade most organic pollutants universally, and has long-term stability, which solves the problem of poor universality and stability of heterogeneous catalysts to a certain extent. Importantly, Co/BDPPF derived from waste biomass was also innovatively designed as the core of an integrated continuous purification device to achieve continuous purification of organic wastewater. In this study, agricultural waste resources were selected as biomass raw materials to achieve efficient capture of Co2+, and finally developed advanced AOPs catalyst with excellent performance to achieve the purification of organic wastewater. It also provides a promising solution for the preparation of simple, low-cost, large-scale production of AOPs catalysts that can be put into actual production.

Selective oxidation behavior based on iron-doped MOF derived carbon-based catalysts: Active site regulation and degradation mechanism analysis

Selective removal of target organic pollutants in complex water quality of municipal sewage is extremely important for the deep treatment of water quality. Here, energetic MOF and Fe-MOF are doped in electrostatic spinning process to adjust the structure and composition of the catalysts, active oxygen species (ROSs), realizing the selective removal of organic pollutants. Non-azo and azo pollutants are selected as target pollutants. Catalysts PCFe-8 with Fe nanoclusters, EPCFe-8 with Fe-Nx, and EPC-8 without Fe doping are used to activate peroxymonosulfate (PMS) for degrading pollutants. The results show that the PCFe-8/PMS system can produce the most SO4- and exhibit superior removal of azo pollutants, whereas the degradation behavior of non-azo pollutants is more inclined to occur in the EPCFe-8/PMS system and the EPC-8/PMS system. This work provides a reference for elucidating the relationship between catalyst structure and components, types of ROSs, and selective degradation of pollutants.

A critical review of ozone-based electrochemical advanced oxidation processes for water treatment: Fundamentals, stability evaluation, and application

In recent years, electrochemical advanced oxidation processes (EAOPs) combined with ozonation have been widely utilized in water/wastewater treatment due to their excellent synergistic effect, high treatment efficiency, and low energy consumption. A comprehensive summary of these ozone-based EAOPs is still insufficient, though some reviews have covered these topics but either focused on a specific integrated process or provided synopses of EAOPs or ozone-based AOPs. This review presents an overview of the fundamentals of several ozone-based EAOPs, focusing on process optimization, electrode selection, and typical reactor designs. Additionally, the service life of electrodes and improvement strategies for the stability of ozone-based EAOPs that are ignored by previous reviews are discussed. Furthermore, four main application fields are summarized, including disinfection, emerging contaminants treatment, industrial wastewater treatment, and resource recovery. Finally, the summary and perspective on ozone-based EAOPs are proposed. This review provides an overall summary that would help to gain insight into the ozone-based EAOPs to improve their environmental applications.

Remediation of soils contaminated with methomyl using electrochemically produced gaseous oxidants

This prospective work focuses on the use of two different gaseous oxidants (chlorine dioxide and ozone) to remediate soil polluted with methomyl in two different applications: ex-situ and in-situ. In the first, the soil washing is integrated with the bubbling of the oxidant, while in the second, the gas was introduced by a perforated pipe located sub-superficially. Regarding the soil washing treatment, results demonstrate that direct use of ozone is not very efficient, although an important improvement is obtained following activation with hydrogen peroxide or UV light. In contrast, chlorine dioxide exhibited complete methomyl depletion from the soil, although with higher energy consumption and technical complexity compared to ozone. The direct dosing of the gaseous oxidants in perforated pipes is effective, achieving methomyl removals of 7.8 % and 9.2 % using ozone and chlorine dioxide, respectively. In these cases, soil conditions are not significantly modified, which becomes an important advantage of the technology as compared with other electrochemically assisted soil remediation process, in which large regions of the treated soil are affected by important changes in the pH or by depletion of ions. This lower impact makes these novel technologies more promising for further evaluations.

Effective peroxymonosulfate activation by lithium cobaltite recovered from spent lithium-ion batteries for enhanced carbamazepine degradation in a wide pH range

Considering the high cost and complicated recycling process of spent lithium-ion batteries (SLIBs), transforming SLIBs into environment functional materials may be a wise approach. Herein, lithium cobaltite (LCO) cathode powders recovered from SLIBs were used to activate peroxymonosulfate (PMS) for removing carbamazepine (CBZ). The recovered LCO enables a 98.2% removal efficiency of CBZ (2.5 mg/L) within 10 min, which was effective at a broader pH range (pH = 5.0-11.0). The influence of key factors (initial pH, PMS, and catalyst dosage) and coexisting substances (SO42-, H2PO4-, NO3-, Cl-, HCO3-, and HA) on CBZ degradation were examined in detail. The primary radical species during the degradation of CBZ were proved to be 1O2, SO4-, and.OH that generated from PMS activation initiated by the valence change of Co in recovered LCO. The recovered LCO displayed excellent reusability with about 80.0% removal of CBZ after six cycles. Homogeneous activation of PMS mainly contributed to CBZ degradation in the first run, but the recovered LCO catalyst dominated the heterogeneous activation of PMS for the degradation of CBZ in the second to sixth run. Finally, the CBZ degradation pathways were presented based on the identified intermediates. This research has offered a new strategy of "treating wastes with wastes" to maximize the recycling of electronic wastes to remove emerging pollutants.

Sulfate-reducing bacteria decreases fractional pressure of H2 to accelerate short-chain fatty acids production from waste activated sludge fermentation assisted with zero-valent iron activated sulfite pretreatment

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H2-consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO4- and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation.

Were Persulfate-Based Advanced Oxidation Processes Really Understood? Basic Concepts, Cognitive Biases, and Experimental Details

Persulfate (PS)-based advanced oxidation processes (AOPs) for pollutant removal have attracted extensive interest, but some controversies about the identification of reactive species were usually observed. This critical review aims to comprehensively introduce basic concepts and rectify cognitive biases and appeals to pay more attention to experimental details in PS-AOPs, so as to accurately explore reaction mechanisms. The review scientifically summarizes the character, generation, and identification of different reactive species. It then highlights the complexities about the analysis of electron paramagnetic resonance, the uncertainties about the use of probes and scavengers, and the necessities about the determination of scavenger concentration. The importance of the choice of buffer solution, operating mode, terminator, and filter membrane is also emphasized. Finally, we discuss current challenges and future perspectives to alleviate the misinterpretations toward reactive species and reaction mechanisms in PS-AOPs.

Tungsten-based nanocatalysts with different structures for visible light responsive photocatalytic degradation of bisphenol A

Environmental pollution, such as water contamination, is a critical issue that must be absolutely addressed. Here, three different morphologies of tungsten-based photocatalysts (WO3 nanorods, WO3/WS2 nanobricks, WO3/WS2 nanorods) are made using a simple hydrothermal method by changing the solvents (H2O, DMF, aqueous HCl solution). The as-prepared nanocatalysts have excellent thermal stability, large porosity, and high hydrophilicity. The results show all materials have good photocatalytic activity in aqueous media, with WO3/WS2 nanorods (NRs) having the best activity in the photodegradation of bisphenol A (BPA) under visible-light irradiation. This may originate from increased migration of charge carriers and effective prevention of electron‒hole recombination in WO3/WS2 NRs, whereby this photocatalyst is able to generate more reactive •OH and •O2- species, leading to greater photocatalytic activity. About 99.6% of BPA is photodegraded within 60 min when using 1.5 g/L WO3/WS2 NRs and 5.0 mg/L BPA at pH 7.0. Additionally, the optimal conditions (pH, catalyst dosage, initial BPA concentration) for WO3/WS2 NRs are also elaborately investigated. These rod-like heterostructures are expressed as potential catalysts with excellent photostability, efficient reusability, and highly active effectivity in different types of water. In particular, the removal efficiency of BPA by WO3/WS2 NRs reduces by only 1.5% after five recycling runs and even reaches 89.1% in contaminated lake water. This study provides promising insights for the nearly complete removal of BPA from wastewater or different water resources, which is advantageous to various applications in environmental remediation.

Treatment of Organics in Wastewater Using Electrogenerated Gaseous Oxidants

This work focuses on the comparison of the performance of direct electrochemical oxidation with indirect electrolysis mediated by gaseous oxidants in the treatment of diluted wastewater. To do this, energy consumptions of the electrolysis using mixed metal oxide (MMO) electrodes are compared with those required for the production and use of chlorine dioxide in the degradation of methomyl contained in aqueous solutions. Results demonstrate the feasibility of the mediated oxidation process and that this process is competitive with direct oxidation. The oxidants are produced under optimized conditions using the same anodic material applied for the direct degradation of organics, thus avoiding efficiency losses associated with mass transfer limitations in the degradation of dilute organic solutions. Thus, using the ClO2 gaseous oxidant, a concentration of 0.1 mM of methomyl from a solution containing 500 mL is completely removed with an energy consumption as low as 50 Wh. The application of the same energy to a direct electrolytic process for treating the same wastewater can only reach less than half of this removal. These findings may have a very important application in the use of electrochemical technology to achieve the remediation of persistent pollutants in wastewater, where their low concentrations typically make direct processes very inefficient.

Sample preparation, analytical characterization, monitoring, risk assessment and treatment of naphthenic acids in industrial wastewater and surrounding water impacted by unconventional petroleum production

Industrial extraction of unconventional petroleum results in notable volumes of oil sands process water (OSPW), containing elevated concentrations of naphthenic acids (NAs). The presence of NAs represents an intricate amalgamation of dissolved organic constituents, thereby presenting a notable hurdle for the domain of environmental analytical chemistry. There is growing concern about monitoring the potential seepage of OSPW NAs into nearby groundwater and river water. This review summarizes recent studies on sample preparation, characterization, monitoring, risk assessment, and treatment of NAs in industrial wastewater and surrounding water. Sample preparation approaches, such as liquid-liquid extraction, solid phase microextraction, and solid phase extraction, are crucial in isolating chemical standards, performing molecular level analysis, assessing aquatic toxicity, monitoring, and treating OSPW. Instrument techniques for NAs analysis were reviewed to cover different injection modes, ionization sources, and mass analyzers. Recent studies of transfer and transformation of NAs provide insights to differentiate between anthropogenic and natural bitumen-derived sources of NAs. In addition, related risk assessment and treatment studies were also present for elucidation of environmental implication and reclamation strategies. The synthesis of the current state of scientific knowledge presented in this review targets government regulators, academic researchers, and industrial scientists with interests spanning analytical chemistry, toxicology, and wastewater management.

Development of an environmentally sustainable technique to minimize the sludge production in the textile effluent sector through an electrokinetic (EK) coupled with electrooxidation (EO) approach

This study presents an environmentally sustainable method for minimizing sludge production in the textile effluent sector through the combined application of electrokinetic (EK) and electrooxidation (EO) processes. AAS and XRF analyses reveal that utilizing acidic electrolytes in the EK method successfully eliminates heavy metals (Cu, Mn, Zn, and Cr) from sludge, demonstrating superior efficiency compared to alkaline conditions. In addition, the total removal efficiency of COD contents was calculated following the order of EK-3 (60%), EK-1 (51%) and EK-2 (34%). Notably, EK-3, leveraging pH gradient fluctuations induced by anolyte in the catholyte reservoir, outperforms other EK systems in removing COD from sludge. The EK process is complemented by the EO process, leading to further degradation of dye and other organic components through the electrochemical generation of hypochlorite (940 ppm). At an alkaline pH of 10.0, the color and COD removal were effectively achieved at 98 and 70% in EO treatment, compared to other mediums. In addition, GC-MS identified N-derivative residues at the end of the EO. This study demonstrates an integrated approach that effectively eliminates heavy metals and COD from textile sludge, combining EK with EO techniques.

Mechanistic investigation of the electricity and gallic acid synergistically accelerated Fe(III)/Fe(II) cycle for the degradation of carbamazepine

This study investigated the application of a natural plant polyphenol, gallic acid (GA) to form complex with iron to promote the redox cycle of Fe(III)/Fe(II) under neutral initial pH conditions in the electrochemical (EC) system for activation of peroxymonosulfate (PMS) to efficiently degrade carbamazepine (CBZ). Results demonstrated that the synergistic effects of GA and EC significantly improved the removal efficiency, and the EC/GA/Fe(III)/PMS system effectively removed 100% of CBZ within a wide initial pH range of 3.0-7.0. The optimum stoichiometric ratio of GA to Fe(III) was found as 2:1. Investigations including quenching experiment, chemical probe analysis, and electron paramagnetic resonance (EPR) analysis were conducted to identify the primary reaction radicals as •OH, SO4•-, along with the 1O2 and Fe(IV). In the EC/GA/Fe(III)/PMS system, the synergistic effect of GA and electrochemistry led to a remarkable enhancement in the generation of •OH. Furthermore, the complexation reduction mechanism of GA and Fe(III) was proposed based on experimental and instrumental analyses, which demonstrated that the semi-quinone products of GA were the main substances promoting the Fe(III)/Fe(II) cycle. Mass spectrometry results showed that CBZ generated 27 byproducts during degradation, with formic acid as the main product of GA. The degradation efficiency of the EC/GA/Fe(III)/PMS system remained stable and excellent, exhibiting remarkable performance in the presence of various inorganic anions, including Cl- and NO3-, as well as naturally occurring organic compounds such as fulvic acid (FA). Overall results indicated that the EC/GA/Fe(III)/PMS system can be applied to effectively treat practical wastewater treatment without requirement of pH adjustment.

Application of advanced oxidation processes for the removal of micro/nanoplastics from water: A review

Micro/nanoplastics (MNPs) have been increasingly found in environments, food, and organisms, arousing wide public concerns. MNPs may enter food chains through water, posing a threat to human health. Therefore, efficient and environmentally friendly technologies are needed to remove MNPs from contaminated aqueous environments. Advanced oxidation processes (AOPs) produce a vast amount of active species, such as hydroxyl radicals (·OH), known for their strong oxidation capacity. As a result, an increasing number of researchers have focused on using AOPs to decompose and remove MNPs from water. This review summarizes the progress in researches on the removal of MNPs from water by AOPs, including ultraviolet photolysis, ozone oxidation, photocatalysis, Fenton oxidation, electrocatalysis, persulfate oxidation, and plasma oxidation, etc. The removal efficiencies of these AOPs for MNPs in water and the influencing factors are comprehensively analyzed, meanwhile, the oxidation mechanisms and reaction pathways are also discussed in detail. Most AOPs can achieve the degradation of MNPs, mainly manifest as the decrease of particle size and the increase of mass loss, but the mineralization rate is low, thus requiring further optimization for improved performance. Investigating various AOPs is crucial for achieving the complete decomposition of MNPs in water. AOPs will undoubtedly play a vital role in the future for the removal of MNPs from water.

The magic of algae-based biochar: advantages, preparation, and applications

Compared with other biomass sources, the use of algae as a raw material to prepare biochar (BC) has important advantages including safety, high yield and economy. The protein content of algae cells is as high as 3.2 mg DCW/L, and the graphitic-N and N-O functional groups generated by the pyrolysis of proteins could effectively activate free radicals. Combined with the generated pore structure, the electron transfer/exchange capability was enhanced, which is conducive to improving its catalytic performance. Algae as a natural N source, the manuscript analyzed the surface properties and physicochemical properties of algae-based BC, and investigated its degradation effect on organic/inorganic pollutants in wastewater. Subsequently, the effect of nitrogen-doped BC on the adsorption/catalysis capacity was discussed. Finally, the directed preparation of algae-based BC applied in different scenarios was summarized. Algae-based BC has the property of N doping, which broadens its application efficiency in the environmental field. Overall, this manuscript reviews how to achieve efficient utilization of algae-based BC in wastewater.

Real-time in situ monitoring using visible spectrophotometry as a tool for probing electrochemical advanced oxidation processes for dye decolorisation

An apparatus for real-time in situ monitoring of electrochemical processes using UV-visible spectrophotometry has been used to optimise the electrochemically-activated persulfate decolorisation of Acid Orange 7. The impacts of varying electrode composition, current density, persulfate loading, and stirring speed on the rate of decolorisation have been probed. Decolorisation through this activated persulfate approach was compared to that using anodic oxidation for nine dyes; three from each of the azo, triarylmethane, and xanthene families. The core structure and presence of functional groups have a significant impact on the rate of decolorisation. Azo and xanthene dyes decolorise faster than triarylmethane dyes, while electron-withdrawing groups and halogens are especially detrimental to the rate of decolorisation. Electrochemically-activated persulfate resulted in faster decolorization than anodic oxidation for almost every dye, an effect that was enhanced with the electron-deficient substrates. This type of systematic structural comparison study is essential for designing electrochemical degradation procedures for the remediation of real wastewater.

Potential Environmental Contaminants: Exploring Hydrolyzed Dyes in Household Washing Sources and Electrochemical Degradation

Reactive dyes are often released into the environment during the washing process due to their susceptibility to hydrolysis. The hydrolysis experiment of a pure reactive dye, red 195 (RR 195), and the washing experiment of RR 195-colored fabrics (CFSCs) were carried out successively to explore the sources of hydrolyzed dyes in the washing microenvironment. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used for the analysis of hydrolysis intermediates and final products of reactive red 195. The experimental results indicated that the structure of the dye washing shed is consistent with the final hydrolysate of reactive red 195, which is the main colored contaminant in washing wastewater. To eliminate the hydrolyzed dyes from the source, an electrochemical degradation device was designed. The degradation parameters, including voltage, electrolyte concentration, and dye shedding concentration are discussed in the electrochemical degradation experiment. The electrochemical degradation device was also successfully implemented and verified in a home washing machine.

Theoretical study of Ponceau S oxidation using the electro-Fenton process under optimal operational conditions

Electrochemical methods as one of the Advanced Oxidation Processes (AOPs) have been applied effectively to the degradation of recalcitrant organic molecules in aqueous solutions. In the present study, the performance of the electro-Fenton (EF) process on the oxidation of Ponceau S(PS) dye was studied. The experimental study performed at the optimal factors like the solution pH, the PS concentration and the ferrous ions dose provided 74.35% of PS degradation. The results, however, showed a decreased removal efficiency of PS when using sodium sulphate as the supporting electrolyte. From a theoretical point of view, the hydroxyl radical being an electron acceptor and the PS dye an electron donor, from a theoretical point of view, the hydroxyl radical being an electron acceptor and the PS dye an electron donor, furthermore, the nitrogen atom 2N being the most nucleophilic site of the PS dye with the most electrophilic site of the hydroxyl radical being the oxygen atom, the first stage of the reaction between PS and the hydroxyl radical was suggested.

One-step electrodeposition preparation of boron nitride and samarium co-modified Ti/PbO2 anode with ultra-long lifetime: highly efficient degradation of lincomycin wastewater

Lincomycin (LC) is an extensively applied broad-spectrum antibiotic, and its considerable residues in wastewater have caused a series of environmental problems, which makes degradation of LC wastewater extremely urgent. In this work, we have constructed a novel boron nitride (BN) and samarium (Sm) co-modified Ti/PbO2 as anode for high-performance degradation of LC wastewater. Compared with Ti/PbO2, Ti/PbO2-Sm, and Ti/PbO2-BN electrodes, Ti/PbO2-BN-Sm electrode with smaller pyramidal particles possesses higher oxygen evolution potential (2.32 V), excellent accelerated service life (103 h), and outstanding electrocatalytic activity. The single-factor experiments demonstrate that under optimized conditions (current density of 20 mA.cm-2, 6.0 g L-1 Na2SO4, pH 9, and temperature of 30°C), removal rate and COD degradation rate of LC at 3 h have reached 92.85% and 89.11%, respectively. At the same time, degradation of LC is in accordance with the primary kinetic model. Based on the analysis of high-performance liquid chromatography-mass spectrometry (HPLC-MS), four possible degradation pathways are hypothesized. Therefore, efficient electrochemical degradation of LC by using an extremely long-life Ti/PbO2 electrode with high catalytic activity may be a promising method.

Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes

Urbanization and industrialization have exerted significant adverse effects on water quality, resulting in a growing need for reliable and eco-friendly treatment technologies. Persulfate (PS)-based advanced oxidation processes (AOPs) are emerging as viable technologies to treat challenging industrial wastewaters or remediate groundwater impacted by hazardous wastes. While the generated reactive species can degrade a variety of priority organic contaminants through radical and nonradical pathways, there is a lack of systematic and in-depth comparison of these pathways for practical implementation in different treatment scenarios. Our comparative analysis of reaction rate constants for radical vs. nonradical species indicates that radical-based AOPs may achieve high removal efficiency of organic contaminants with relatively short contact time. Nonradical AOPs feature advantages with minimal water matrix interference for complex wastewater treatments. Nonradical species (e.g., singlet oxygen, high-valent metals, and surface activated PS) preferentially react with contaminants bearing electron-donating groups, allowing enhancement of degradation efficiency of known target contaminants. For byproduct formation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimated electrical energy per order of reaction (EE/O) parameter and show significantly higher energy requirements for the nonradical pathways. Overall, these critical comparisons help prioritize basic research on PS-based AOPs and inform the merits and limitations of system-specific applications.

Pulsed versus direct current electrochemical co-catalytic peroxymonosulfate-based system: Elevated degradation and energy efficiency with enhanced oxidation mechanisms

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, SO₄^•-, and ¹O₂ 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.

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.

Application of Electrochemical Oxidation for Water and Wastewater Treatment: An Overview

In recent years, the discharge of various emerging pollutants, chemicals, and dyes in water and wastewater has represented one of the prominent human problems. Since water pollution is directly related to human health, highly resistant and emerging compounds in aquatic environments will pose many potential risks to the health of all living beings. Therefore, water pollution is a very acute problem that has constantly increased in recent years with the expansion of various industries. Consequently, choosing efficient and innovative wastewater treatment methods to remove contaminants is crucial. Among advanced oxidation processes, electrochemical oxidation (EO) is the most common and effective method for removing persistent pollutants from municipal and industrial wastewater. However, despite the great progress in using EO to treat real wastewater, there are still many gaps. This is due to the lack of comprehensive information on the operating parameters which affect the process and its operating costs. In this paper, among various scientific articles, the impact of operational parameters on the EO performances, a comparison between different electrochemical reactor configurations, and a report on general mechanisms of electrochemical oxidation of organic pollutants have been reported. Moreover, an evaluation of cost analysis and energy consumption requirements have also been discussed. Finally, the combination process between EO and photocatalysis (PC), called photoelectrocatalysis (PEC), has been discussed and reviewed briefly. This article shows that there is a direct relationship between important operating parameters with the amount of costs and the final removal efficiency of emerging pollutants. Optimal operating conditions can be achieved by paying special attention to reactor design, which can lead to higher efficiency and more efficient treatment. The rapid development of EO for removing emerging pollutants from impacted water and its combination with other green methods can result in more efficient approaches to face the pressing water pollution challenge. PEC proved to be a promising pollutants degradation technology, in which renewable energy sources can be adopted as a primer to perform an environmentally friendly water treatment.

Treatment of gaseous streams polluted with H2S: Comparison of electrolytic and electro-Fenton assisted absorption processes

H₂S is a gaseous compound that contributes to air pollution. In this work, the electrochemical oxidation treatment of gaseous streams polluted with H₂S is evaluated using a jet mixer and electrochemical cell device, in which the performance of electrolytic and electro-Fenton assisted absorption processes are compared. Results demonstrate the feasibility of both processes to remove H₂S, reaching coulombic efficiencies of nearly 100% in the electrolytic assisted absorption, and 70-80% in the electro-Fenton assisted absorption. Aqueous solutions containing phosphate salts as electrolyte were found to be suitable as absorbents for the process. Efficiency in the cathodic production of H₂O₂ in these solutions using the experimental device was found to be as high as 32.8% (1.184 mgH₂O₂/min) at 12 °C and atmospheric pressure. Sequential formation of SO₂ and SO₃ is obtained by the oxidation of H₂S contained in the gas. These species are hydrolysed, and a part remained in the absorbent as SO₃^2- and SO₄^2-, while the rest is dragged in the outlet gas. SO₃ production is promoted by electrolytic assisted absorption and polysulphides by the electro-Fenton technology. Low concentrations of elemental sulphur are detected in the solid suspensions formed during the process.

Peracetic acid activation via the synergic effect of Co and Fe in CoFe-LDH for efficient degradation of pharmaceuticals in hospital wastewater

As an oxidant, peracetic acid (PAA) is gradually applied in advanced oxidation processes (AOPs) for pollutants degradation due to its high oxidation and low toxicity. In this study, the prepared Co₂Fe₁-LDH showed excellent PAA activation ability for efficient degradation of various pharmaceuticals with a removal efficiency ranging from 82.3% to 100%. Taking sulfamethoxazole (SMX) as a model pharmaceutical, it's found that organic radical (R-O^•) with high concentration of 5.27 × 10^-13 M is the dominant ROS responsible for contaminants degradation. Further analysis demonstrated that bimetallic synergistic effect between Co and Fe can improve electron transfer ability of Co₂Fe₁-LDH, resulting in the accelerated conversion of Co from +3 to +2 valence state with a high reaction rate (4.3 × 10¹-1.483 × 10² M^-1 s^-1) in this system. Density functional theory (DFT) reveals that C1, C3, C5 and N11 with higher ƒ⁰ and ƒ^-values concentrated on aniline group of SMX are the main attack sites, which is consistent with the results of degradation products. Besides, Co₂Fe₁-LDH/PAA system can effectively reduce biological toxicity after reaction, due to lower biotoxicity of degradation products and the carbon sources provided by PAA. In application, Co₂Fe₁-LDH/PAA system was capable of resisting the influence of water matrix and effectively removing pollutants in actual hospital wastewater. Importantly, this study comprehensively evaluated the ability of Co₂Fe₁-LDH/PAA system to remove organics and improve the biodegradability of actual hospital wastewater, providing guidance for application of PAA activation system.

Facile fabrication of mesoporous carbon-anchored cobalt ferrite nanoparticles as a heterogeneous activator of peroxymonosulfate for efficient degradation of Congo red

Herein, mesoporous carbon-anchored cobalt ferrite nanocomposites (nano-CoFe₂O₄@MC) were fabricated using a hydrothermal method for application as heterogeneous catalysts to activate peroxymonosulfate (PMS), in order to solve the problems of low activation performance and secondary pollution caused by the inter-particle agglomeration, metal ion leaching, and difficult recovery of nano metal catalysts. Analysis techniques such as SEM, TEM, XRD, BET, FTIR, VSM, TGA, and Raman spectroscopy indicated that the prepared nanocomposites have excellent surface properties, structural stability, and magnetic properties. The performance of nano-CoFe₂O₄@MC for Congo red (CR) degradation was evaluated by comparison with other treatment systems and study of the influence of experimental parameters, including the anchoring ratios, catalyst dosage, PMS concentration, initial pH, CR concentration, coexisting anions, and humic acid. Both radical and nonradical pathways were observed in the activation process of PMS by nano-CoFe₂O₄@MC. The analysis results of the element composition and ionic state of the catalyst show that the redox cycle of two ion pairs, Co³⁺/Co²⁺ and Fe²⁺/Fe³⁺, could enhance the multipath electron transfer on the catalyst surface to promote the generation of reactive oxygen species. Identification of the intermediate products revealed CR was transformed into 12 intermediates through two branch pathways in the nano-CoFe₂O₄@MC/PMS system. After five cycles of use, the catalytic efficiency of the catalyst did not decrease significantly. Nanocomposites with high catalytic performance, stability, recyclability, and a low ion leaching rate have broad application prospects in the treatment of antibiotic wastewater.

Singlet oxygen generation in light-assisted peroxymonosulfate activation by carbon nitride: Role of elevated crystallinity

Carbon nitride (CN) is an emerging 2D non-metal semiconductor material that could be used in photocatalysis and advanced oxidation processes (AOPs) for pollutants degradation. The radical-induced degradation by CN in photocatalysis or photo-assisted AOPs was widely reported in previous studies. Nevertheless, how the non-radical degradation by CN materials could be achieved under irradiation is neither well understood nor controlled. In this work, crystalline carbon nitride (CCN) was synthesized via a facile molten-salt method, and used to activate peroxymonosulfate (PMS) under visible light (>420 nm) to selectively and efficiently degrade tetracycline (TC). Compared to the traditional polymeric carbon nitride (PCN), CCN was found to be a superior PMS activator with the assistance of visible light, which was ascribed to the increased crystallinity of CN tri-s-triazine units and the increased number of catalytic sites, thereby optimizing the photoelectric properties. The activation performance could be further improved by copper loading, with TC degradation rate nearly six times more than that of PCN. EPR trapping and quenching tests showed that singlet oxygen (¹O₂) was the dominant reactive oxygen species in the CCN/PMS/visible light system, attributing to the increased graphitic N sites and formation of electron-deficient C in C-N bonding between neighboring tri-s-triazine units upon crystallinity elevation in CCN. In contrast to the conventional radical-based photocatalysis and AOP processes, the visible light-assisted non-radical AOP degradation was highlighted for the selectivity and the remarkable resistance to the impacts of background inorganic anions or natural organic matter (up to 10 mg/L) in the actual water matrix. This work revealed the ¹O₂ generation mechanism by CN-based materials under the joint assistance of visible light illumination and crystallinity elevation, and its excellent removal performance demonstrates the great potential of CCN-based materials in the practical wastewater treatment.

Organics abatement and recovery from wastewater by a polymerization-based electrochemically assisted persulfate process: Promotion effect of chloride ion and its mechanism

Ubiquitous chloride ion (Cl^-) in wastewaters usually inhibits the degradation of organic contaminants and generates numerous toxic chlorinated products in conventional degradation-based advanced oxidation processes (AOPs). Herein, a more Cl^- tolerant polymerization-based electrochemical AOP for organic contaminants abatement and simultaneous organic resource recovery was demonstrated with eight typical organic contaminants and two real industrial wastewaters for the first time. This process can significantly promote dissolved organic carbon (DOC) abatement in the presence of Cl^-, differing greatly from conventional degradation-based processes. Compared to sulfate radical (SO₄^•-) (or hydroxyl radical (HO^•)), dichloride radical (Cl₂^•-) derived from Cl^- has moderate reactivity towards most contaminants, which facilitates the organics polymerization as it ensures the formation of polymerizable organic radicals while inhibiting their excessive degradation. Thus, high DOC abatement (over 75 %) and high organic resource recovery ratio (48-79 % separable organic-polymer yield) can be achieved for most contaminants. Both soluble chlorinated compounds and solid chlorinated polymers are formed in the presence of Cl^-. The chlorinated products (e.g. chlorophenols) can be polymerized as new monomers, thus the concentration of dissolved organic chlorinated products is much lower than that in conventional degradation-based process. The tolerance of the present process to Cl^- is tested in real coking wastewaters, and exceeding 60 % of the abated chemical oxygen demand (COD) is obtained in the form of recoverable organic-polymers.

A non-steroidal drug "diclofenac" is a substrate for electrochemical degradation process using graphite anode

In the electrochemical degradation process, the elimination of organic pollutants could be enhanced using supporting electrolyte and applied voltage. After degradation of the target organic compound, some by-products are formed. Chlorinated by-products are the main products formed in the presence of sodium chloride. In the present study, an electrochemical oxidation process has been applied to diclofenac (DCF) using graphite as an anode and sodium chloride (NaCl) as a supporting electrolyte. Monitoring the removal of the by-products and elucidating them were provided using HPLC and LC-TOF/MS, respectively. A high removal% of 94% DCF was observed under the conditions: 0.5 g NaCl, 5 V, and 80 min of electrolysis, while the removal% of chemical oxygen demand (COD) was 88% under the same conditions, but 360 min of electrolysis was required. The pseudo-first-order rate constant values were quite varied based on the selected experimental conditions; the rate constants were between 0.0062 and 0.054 min^-1, between 0.0024 and 0.0326 min^-1 under the influence of applied voltage and sodium chloride, respectively. The maximum values of energy consumption were 0.93 and 0.55 Wh/mg using 0.1 g NaCl and 7 V, respectively. Some chlorinated by-products, C₁₃H₁₈Cl₂NO₅, C₁₁H₁₀Cl₃NO₄, and C₁₃H₁₃Cl₅NO₅, were selected and elucidated using LC-TOF/MS.

Identifying the evolution of primary oxidation mechanisms and pollutant degradation routes in the electro-cocatalytic Fenton-like systems

Herein, electro-catalysis (EC) as the electron donor to accelerate the continuable Fe(III)/Fe(II) cycles in different inorganic peroxides (i.e., peroxymonosulfate (PMS), peroxydisulfate (PDS) and hydrogen peroxide (HP)) activation systems were established. These electro-cocatalytic Fenton-like systems exhibited an excellent degradation efficiency of sulfamethoxazole (SMX). A series of analytical and characterization methods including quenching experiments, probe experiments, and electron paramagnetic resonance spectrometry (EPR) were implemented to systematically sort out the source and yield of reactive oxygen species (ROS). A wide kind of ROS including hydroxyl radical (^•OH), singlet oxygen (¹O₂), and sulfate radical (SO₄^•-), which contributed 38%, 37%, and 24% were produced in EC/Fe(III)/PMS system, respectively. ^•OH was the dominant ROS in both EC/Fe(III)/PDS and EC/Fe(III)/HP processes. According to the analysis of SMX degradation routes and biotoxicity, abundant degradation pathways were identified in EC/Fe(III)/PMS process and lower environmental impact was achieved in EC/Fe(III)/HP process. The diversiform ROS of EC/Fe(III)/PMS system makes it exhibit greater environmental adaptability in complex water matrixes and excellent low-energy consumption performance in many organic pollutants degradation. Continuous flow treatment experiments proved that the three systems have great sustainability and practical application prospect. This work provides a strong basis for constructing suitable systems to achieve different treatment requirements.

Controlling waste by waste: a modified landfill leachate coagulation sludge activated peroxymonosulfate process achieves complete BPA degradation

In this study, a modified coagulation sludge (MCS) from a real landfill leachate coagulation pretreatment was first prepared with polymerized ferric sulfate (PFS) as the activator for PMS to degrade bisphenol A (BPA). The results showed that 43.34% of BPA was adsorbed by MCS when [BPA]₀ = 20 mg/L, [MCS]₀ = 0.8 g/L, and time = 80 min. Thereafter, by adding 3000 mg/L PMS to initiate the oxidation process, complete BPA removal, i.e. 100%, was achieved in 60 min. In addition, in tap water and municipal wastewater scenarios, 100% and 90.07% removal of BPA were obtained, respectively, and MCS exhibited outstanding performance after repeated use. MCS displayed an excellent adsorption capacity in which chemical adsorption was the main effect, and hydroxyl radicals were the major contributor to BPA degradation. Characterizations of fresh and reacted MCS were conducted, and the results showed that the MCS structure was stable after repeated use, and the surface functional groups, surface defect sites, and iron oxides participated in PMS activation. Overall, this study demonstrated successful recycling of coagulation sludge from landfill leachate pretreatment to activate PMS for environmental pollution control, which is in accordance with the goal of using waste to control waste.

Enhanced energy recovery from landfill leachate by linking light and dark bio-reactions: Underlying synergistic effects of dual microalgal interaction

Bioconversion of nutrients and energy from landfill leachate (LL) to biohydrogen and volatile fatty acids (VFAs) using dark fermentation (DF) is a promising technique for developing a sustainable ecosystem. However, poor performance of DF caused by vulnerable fermentative bacteria vitality and strong LL toxicity significantly hinder its commercialization. Herein, an integrated technique linking microalgae photosynthesis and DF was proposed, in which mixed microalgae were applied to robustly reclaim nutrients and chemical oxygen demand (COD) from LL. Then, microalgae biomass was fermented into biohydrogen and VFAs using the DF process. Underlying synergistic mechanisms of the interaction of Scenedesmus obliquus and Chlorella vulgaris resulting from the functioning of extracellular polymeric substances (EPS) were discussed in detail. For better absorption of nutrients from LL, the mixed microalgae secreted obviously more EPS than pure microalgae, which played vital roles in the assimilation of cellular nutrients by forming more negative zeta potential and secreting more tyrosine-/tryptophan-family proteins in EPS. Besides, mixed microalgae produced more intracellular proteins and carbohydrates than the pure microalgae, thereby providing more feedstock for DF and achieving higher energy yield of 10.80 kJ/L than 6.64 kJ/L that was obtained when pure microalgae were used. Moreover, the energy conversion efficiency of 7.75% was higher for mixed microalgae than 4.77% that was obtained for pure microalgae. This work may inspire efficient disposal of LL and production of bioenergy, together with filling the knowledge gaps of synergistic mechanisms of dual microalgal interactions.

Theoretical exploration of the structural, electronic and optical properties of g-C3N4/C3N heterostructures

Integration of graphene-like carbon nitride materials is essential for nanoelectronic applications. Using density-functional theory (DFT), we systematically investigate the structural, electronic and optical properties of a s-triazine-based g-C₃N₄/C₃N heterostructure under different modified conditions. The g-C₃N₄/C₃N van der Waals heterostructure (vdWH) formed has an indirect bandgap with type-II band alignment and the band structures can be tuned from type-II band alignment to type-I band alignment by applying biaxial strains and external electric fields (E_field). Compared to single transition metal (TM) atoms at g-C₃N₄/C₃N surfaces, the TM atoms anchored in the interlayer region exhibit more stability, and the corresponding bandgaps are changed from 0.19 eV to 0.61 eV. In addition, the g-C₃N₄/C₃N heterostructure has a strong absorption coefficient in the ultraviolet-visible light region along the x direction. It is found that compressive strain has a large influence on the absorption coefficient of the g-C₃N₄/C₃N system. With the increased compressive strain, the absorption spectra in the visible light region disappeared. Tensile strain has a slight effect on the absorption range, but causes a red shift of the absorption spectrum. In comparison, the light absorption coefficient of the g-C₃N₄/C₃N system remains almost unchanged under the E_field conditions. In summary, the formation of a s-triazine-based g-C₃N₄/C₃N heterostructure has shown potential for applications in nanoelectronic and optoelectronic devices.

Ferrous-Iron-Activated Sulfite-Accelerated Short-Chain Fatty Acid Production from Waste-Activated Sludge Fermentation: Process Assessment and Underlying Mechanism

To break the bottlenecks of slow hydrolysis and low acid production efficiency of waste-activated sludge (WAS) in the traditional anaerobic fermentation process, this study investigated the employment of ferrous-iron (Fe(II))-activated sulfite to produce hydroxyl, sulfate, and other highly oxidizing radicals on WAS floc cracking and short-chain fatty acid (SCFAs) production during anaerobic fermentation. The effect of the dosage ratio of Fe(II)/S(IV) was also studied. Results showed that the combined pretreatment of Fe(II)-activated sulfite significantly promoted the exfoliation of extracellular polymers and the subsequent SCFAs production. The highest concentration of SCFAs reached 7326.5 mg COD/L under the optimal dosage of 1:2 for Fe(II)/S(IV), which was 1.1~2.1 times higher than that of other research groups. Meanwhile, the analysis by 3D fluorescence spectroscopy and EPR (electron paramagnetic resonance) showed that Fe(II)-activated sulfite had a synergistic effect on the rupture of sludge cells and the stripping of extracellular polymers, with SO4− and OH as the key radicals generated and being much stronger in the 1:1 and 1:2 groups. High-throughput sequencing showed that the Fe(II)-activated sulfite system significantly changed the functional microbial diversity. The anaerobic fermentation bacteria and sulfate-reducing bacteria were significantly enriched. The underlying mechanism of Fe(II)-activated sulfite oxidation and molecular ecological network of key microbiomes were unveiled.

Synergistic mechanism of supported Mn-Ce oxide in catalytic ozonation of nitrofurazone wastewater

In this study, the catalytic materials of MnO_x/γ-Al₂O₃, CeO₂/γ-Al₂O₃, and Mn_xCe_1-xO₂/γ-Al₂O₃ for catalytic ozonation were synthesized. The catalysts were used in heterogeneous catalytic ozonation of the wastewater containing ntrofurazone (NFZ). The effects of the catalytic ozonation operational factors were systematically evaluated in terms of ozone dosing, catalyst dosing, initial NFZ concentration, and pH. The results showed that the catalytic activity of the Mn_xCe_1-xO₂/γ-Al₂O₃ was higher than that of the MnO_x/γ-Al₂O₃ and CeO₂/γ-Al₂O₃. The kinetics analysis revealed that bimetallic loading has a synergistic effect and the mechanism of this effect was investigated in the catalytic ozonation system. The catalysts were characterized by FESEM, EDS, XRD, XPS, IR, and BET. The characteristics of the catalysts revealed that Mn could alter the oxide species on the metal surface and interfere with the formation of CeO₂ crystals, which led to smaller grains, enhanced adsorption oxygen, and greater specific surface area. The Mn_xCe_1-xO₂/γ-Al₂O₃ crystals could form a solid solution, which helps higher catalytic activity. This study adds to the understanding of the synergistic mechanism of the loaded Ce-Mn oxide catalysts in the heterogeneous catalytic ozonation system and provides a feasible method for degrading pharmaceutical wastewater.

Direct photolysis of diclofenac under simulated sunlight: Transformation pathway and biological concerns

Topical diclofenac gels are frequently applied on human skin and, consequently are exposed to sunlight during outdoor activities. The degradation of diclofenac (DCF) with sunlight exposure is known to occur but the detailed transformation characteristics and biological concerns have not been comprehensively investigated. In the present work, the transformation products during diclofenac photolysis were identified with the aid of ultra-performance liquid chromatography coupled with triple time-of-flight mass spectrometry (UPLC-TripleTOF). Biological concerns, including microtoxicity, genotoxicity, cytotoxicity and antiestrogenicity were examined with multiple in-vitro bioassays. Spearman correlation analysis was conducted to obtain further insight into the contributions of photolysis products to overall biological concerns. The results demonstrated that diclofenac was readily degraded under sunlight to form five main photolysis products via substitution, dechlorination, dehydroxylation, homodimerization and heterodimerization. Products P1, P2 and P5 were reported previously, while two dimer products (P3 and P4) are innovative products and have not been found in prior studies. A significant elevation in the microtoxicity was found during the photolysis of diclofenac, resulting mainly from the carbazole-containing photolysis products P2, P3, P4 and P5. Genotoxicity and antiestrogenicity declined along with the reduction of diclofenac, indicating that no photolysis products were genotoxic or anti-estrogenic. Modest cytotoxicity to the human skin epidermis cell line was observed and attributed to the formation of intermediate species. This outcome highlighted the biological concerns of diclofenac to human health when exposed to sunlight.

Electrified ceramic membrane actuates non-radical mediated peroxymonosulfate activation for highly efficient water decontamination

Electrified ceramic membranes (ECMs) achieve high water decontamination efficiency mainly through implementing in situ radical-mediated oxidation in membrane filtration, whereas ECMs leveraging non-radical pathways are rarely explored. Herein, we demonstrated a Janus ECM realizing ultra-efficient micropollutant (MP) removal via electro-activating peroxymonosulfate (PMS) in a fast, flow-through single-pass electro-filtration. The Janus ECM features two separate palladium (Pd) functionalized electrocatalytic reaction zones engineered on its two sides. We confirmed that the PMS/electro-filtration system induced non-radical pathways for MP degradation, including singlet oxygenation and mediating direct electron transfer (DET) from MP to PMS. Under the design of the ECM featuring dual electrocatalytic reaction zones in the ceramic membrane intrapores, the Janus ECM showed over one-fold increase in micropollutant removal rate as 94.5% and lower electric energy consumption as 1.78 Wh g^-1 MP in the PMS electro-activation process, as compared with the conventional ECM assembly implementing only half-cell reaction. This finding manifested the Janus ECM configuration advantage for maximizing the PMS electro-activation efficiency via singlet oxygenation intensification and direct usage of cathode for DET mediation. The Janus ECM boosted the PMS electro-activation and water decontamination efficiency by enhancing the convective mass transfer and the spatial confinement effect. Our work demonstrated a high-efficiency PMS electro-activation method based on electro-filtration and maximized the non-radical mediated PMS oxidation for MP removal, expanding the ECM filtration strategies for water decontamination.

Fast peroxydisulfate oxidation of the antibiotic norfloxacin catalyzed by cyanobacterial biochar

Peroxydisulfate (PDS) is a common oxidant for organic contaminant remediation. PDS is typically activated by metal catalysts to generate reactive radicals. Unfortunately, as radicals are non-selective and metal catalysts may cause secondary contamination, alternative selective non-radical pathways and non-metal catalysts need attention. Here we investigated PDS oxidation of commonly detected antibiotic Norfloxacin (NOR) using cyanobacterial nitrogen rich biochars (CBs) as catalysts. NOR was fully degraded by CB pyrolysed at 950 °C (CB950) within 120 min. CB950 caused threefold faster degradation than low pyrolysis temperature (PT) CBs and achieved a maximum surface area normalized rate constant of 4.38 × 10^-2 min^-1 m^-2 L compared to widely used metal catalysts. CB950 maintained full reactivity after four repeated uses. High defluorination (82%) and mineralization (>82%) were observed for CB950/PDS. CBs were active over a broad pH range (3-10), but with twice as high rates under alkaline compared with neutral conditions. NOR is degraded by organic, ^•OH and SO₄^•- radicals in low PT CBs/PDS systems, where the presence of Mn^II promotes radical generation. Electron transfer reactions with radicals supplemented dominate high PT CBs/PDS systems. This study demonstrates high PT biochars from algal bloom biomass may find use as catalysts for organic contaminant oxidation.

Synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater by electro-peroxone process

Herein, a highly efficient electro-peroxone (E-peroxone) process with graphite felt as ozone diffusion electrode (ODE) was developed for the synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater. Under optimal conditions, the total organic carbon (TOC) removal rate of real hospital wastewater could reach 93.9%. Importantly, 126 pharmaceutical compounds (antibiotics, antivirals, analgesics, antiepileptics, hormones, and others) were determined in hospital wastewater by using ultra performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS). 110 pharmaceutical compounds could be efficiently degraded in E-peroxone system. Concurrently, the microbial community analysis through high-throughput sequencing showed that E-peroxone process exhibited an excellent disinfection effect in real hospital wastewater. Escherichia coli as a bacterial indicator could be completely inactivated in E-peroxone process·H2O2 and hydroxyl radical (OH) were found in E-peroxone system based on the results of chemical probe experiments and electron paramagnetic resonance (EPR) analysis. The in-situ generation of H2O2 from cathodic oxygen reduction in ODE can react with ozone to produce OH, and realize high efficiencies for the elimination of pharmaceutical and sterilization. This work established a green and effective way without extra addition of chemical reagents for high-efficiency treatment of real hospital wastewater.

Effective peroxymonosulfate activation by natural molybdenite for enhanced atrazine degradation: Role of sulfur vacancy, degradation pathways and mechanism

In this study, natural molybdenite (MoS₂) was applied to activate peroxymonosulfate (PMS) for the removal of atrazine (ATZ) and its degradation mechanism was investigated. Molybdenite exhibits superior catalytic performance. The best condition for atrazine degradation efficiency (>99%) was obtained with molybdenite concentration of 0.4 g/L, PMS concentration of 0.1 mM, and ATZ concentration of 12 μM within 10 min under experimental conditions. Electron paramagnetic resonance (EPR) test and chemical probe test further proved that HO^• and SO₄^•- played important roles in the molybdenite/PMS system, and SO₄^•- was dominant. Meanwhile, Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) tests showed that sulfur vacancies and edge sulfur played important roles in the system. Edge sulfur was conducive to Mo⁴⁺ exposure, while sulfur vacancy facilitated electron transfer and reduced Mo⁶⁺ back to Mo⁴⁺. Combined with DFT calculation, the role of sulfur in the degradation process was verified. Besides, five ATZ degradation pathways were proposed. Finally, the degradation ability of the molybdenite/PMS system for different pollutants and in actual water bodies was also explored. This work provided ideas for exploring the degradation of organic contaminants by natural minerals.

Single-Atom Iron Anchored Tubular g-C3 N4 Catalysts for Ultrafast Fenton-Like Reaction: Roles of High-Valency Iron-Oxo Species and Organic Radicals

Single-atom catalysts have emerged as an efficient oxidant activator for eliminating organic pollutants in Fenton-like systems. However, the complex preparation, single active site, lack of understanding of the fundamental mechanism, and harsh pH conditions currently limit their practical applications. In this work, single-atom iron anchored nitrogen-rich g-C₃ N₄ nanotubes (FeCNs) are designed and synthesized by a facile approach, and eco-friendly peracetic acid (PAA) is selected as the oxidant for Fenton-like reactions. The constructed heterogenous system achieves an enhanced degradation of various organic contaminants over a wide pH range of 3.0-9.0, exhibiting an ultrahigh and stable catalytic activity, outperforming equivalent quantities of pristine g-C₃ N₄ by 75 times. The ¹⁸ O isotope-labeling technique, probe method, and theoretical calculations demonstrate that the efficient catalytic activity relies on the high-valency iron-oxo species coupled with organic radicals generated by PAA. An increase in electron transport from the contaminant to the formed "metastable PAA/FeCN catalyst surface complex" is detected. A double driving mechanism for the tubular g-C₃ N₄ regulated by a single Fe site and PAA activation is proposed. This work opens an avenue for developing novel catalysts with the coexistence of multiple active units and providing opportunities for significantly improving catalytic efficiency.

Performance of a Three-Dimensional Electrochemical Reactor (3DER) on Bisphenol A Degradation

This study constructed a three-dimensional electrochemical reactor (3DER) using meshed stainless steel sheets and titanic magnetite particles (TMP) to investigate bisphenol A (BPA) degradation through the synergistic action of electrical current and TMP. We examined some TMP characteristics, such as particle size, specific surface areas, X-ray diffraction, surface imaging, elemental constituents, and electrical resistivity. It was found that TMP was a micron-level material with excellent electrical conductivity, and it could be regarded as a magnetite-based material comprising Fe(II) and Fe(III). The single-factor experiment determined the optimal conditions for BPA removal in 3DER, specifically by introducing 200 ml of BPA-simulated wastewater (10 mg L⁻¹) into 3DER. At the initial pH of 9.00, current and electrodes gap of 300 mA and 15 mm, respectively, and adding 1 ml of 0.5 M potassium peroxymonosulfate and 1 g TMP, > 98% of BPA was removed after 55 min of electrochemical reaction. In addition, liquid chromatography–mass spectrometry identified the intermediates formed during the BPA treatment, showing two possible pathways for BPA degradation. The final degradation intermediates were chain organics with simple molecular structures. This research provided an understanding of the potential application of 3DER for BPA removal in water.