Electro-Fenton removal of Orange II in a divided cell: Reaction mechanism, degradation pathway and toxicity evolution

Efficient degradation of 2,4-dichlorophenol in water by sequential electrocatalytic reduction and oxidation with a Pd-MWCNTs/Ni-foam electrode

Our previous study indicated excellent dechlorination efficiency and phenol conversion rate in the electrocatalytic reduction of 2,4-dichlorophenol (2,4-DCP) with a Pd-MWCNTs/Ni-foam electrode; it is deserved to investigate whether this electrode can efficiently degrade phenol in electro-Fenton oxidation (EFO) process and realize the effective mineralization of 2,4-DCP in aqueous solution. In this work, the sequential electrocatalytic reduction and oxidation of 2,4-DCP were studied after examining phenol degradation in the EFO process. The results showed that the removal efficiency of 0.31 mM phenol could reach 96.76% after 90-min degradation with the rate constant of 0.0367 min^-1, and hydroxy radicals (·OH) were the main active species in the EFO process. In the sequential electrocatalytic reduction and oxidation processes, the removal efficiencies of 2,4-DCP, phenol, and total organic carbon (TOC) reached 99.72%, 97.07%, and 61.45%, respectively. The possible degradation mechanism of 2,4-DCP was proposed through monitoring the reaction products, and the stability and reusability of the electrode were also examined. This study suggested that 2,4-DCP in wastewater can be effectively mineralized to realize its efficient degradation through the sequential electrocatalytic reduction and oxidation.

Degradation of Ibuprofen in flow-through system by the Electro-Fenton Process activated by two iron sources

The electrochemical degradation of ibuprofen (IBP) by electro-Fenton process has been studied in a flow-through system by evaluating the performance of two different iron sources, sacrificial cast iron anode and FeSO4 salt. The effect of operating conditions, including initial IBP concentration, cast iron anode location, initial FeSO4 concentration, applied current, the split current on the iron anode, solution pH, and flow rate on the efficacy of the process was evaluated. The sequence of the electrodes significantly influences ibuprofen removal. When using cast iron anode as iron source, placing the iron anode upstream achieved the best IBP removal rate. Split current of 3 mA applied on the iron anode out of 120 mA total current is the optimum current for remove 1 mg/L of IBP under a flow rate of 3 mL/min. There is a linear correlation between the applied current and the Fe2+ concentration in the FeSO4-system. The initial IBP concentration does not influence the rate of Fenton reaction. Flow rate influences the degradation efficiency as high flow rate dilutes the concentration of OH radicals in the electrolyte. FeSO4-system was less affected by the flow rate compared to the iron anode-system as the concentration of the Fe2+ was steady and not diluted by the flow rate. Both systems prefer acidic operation conditions than neutral and alkaline conditions. Iron-anode can be used as an external Fe2+ supply for the treatment for iron-free. These findings contribute in several ways to our understanding of the electro-Fenton process under flow conditions and provide a basis for how to design the reactor for the water treatment.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

Heterogeneous Fenton catalysts: A review of recent advances

Heterogeneous Fenton catalysts are emerging as excellent materials for applications related to water purification. In this review, recent trends in the synthesis and application of heterogeneous Fenton catalysts for the abatement of organic pollutants and disinfection of microorganisms are discussed. It is noted that as the complexity of cell wall increases, the resistance level towards various disinfectants increases and it requires either harsh conditions or longer exposure time for the complete disinfection. In case of viruses, enveloped viruses (e.g. SARS-CoV-2) are found to be more susceptible to disinfectants than the non-enveloped viruses. The introduction of plasmonic materials with the Fenton catalysts broadens the visible light absorption efficiency of the hybrid material, and incorporation of semiconductor material improves the rate of regeneration of Fe(II) from Fe(III). A special emphasis is given to the use of Fenton catalysts for antibacterial applications. Composite materials of magnetite and ferrites remain a champion in this area because of their easy separation and reuse, owing to their magnetic properties. Iron minerals supported on clay materials, perovskites, carbon materials, zeolites and metal-organic frameworks (MOFs) dramatically increase the catalytic degradation rate of contaminants by providing high surface area, good mechanical stability, and improved electron transfer. Moreover, insights to the zero-valent iron and its capacity to remove a wide range of organic pollutants, heavy metals and bacterial contamination are also discussed. Real world applications and the role of natural organic matter are summarised. Parameter optimisation (e.g. light source, dosage of catalyst, concentration of H2O2 etc.), sustainable models for the reusability or recyclability of the catalyst and the theoretical understanding and mechanistic aspects of the photo-Fenton process are also explained. Additionally, this review summarises the opportunities and future directions of research in the heterogeneous Fenton catalysis.

Biological treatment of non-biodegradable azo-dye enhanced by zero-valent iron (ZVI) pre-treatment

Zero-valent iron (ZVI) pre-treatment in sequential strategy for removal of non-biodegradable azo-dye Orange II by activated-sludge was quantitatively examined. The decolorization and TOC (total organic carbon) removal of Orange II by ZVI pre-treatment were examined in the ranges of pH from 3 to 11 and ZVI dosage from 500 to 2000 mgL^-1. While the decolorization was enhanced with decreasing pH and the optimal pH for decolorization was found at pH 3, the TOC removal rate at pH 3 remained at 22.2% and the maximum TOC removal rate of 78.2% was obtained at pH 4. The decolorization and TOC removal of Orange II were monotonously increased with increasing ZVI dosage. To quantify the ZVI pre-treatment, the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by ZVI were defined. Novel kinetic models for the ZVI pre-treatment and activated-sludge post-treatment were developed. The proposed kinetic models satisfactorily predicted the transitional behaviors of the ZVI pre-treatment and activated-sludge post-treatment and the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by the ZVI pre-treatment. The complete removal of non-biodegradable azo-dye Orange II of 300 mgL^-1 was accomplished by 78.2% removal after 360 min ZVI pre-treatment with the ZVI dosage of 1000 mgL^-1 at pH 4 and subsequently 21.8% removal after 480 min activated-sludge post-treatment. The ZVI pre-treatment integrated with activated-sludge post-treatment was proved to be an effective strategy for treating non-biodegradable pollutants.

The practical utility of the synthesis FeNi3@SiO2@TiO2 magnetic nanoparticles as an efficient photocatalyst for the humic acid degradation

Humic acid (HA) compounds in drinking water and wastewater disinfection processes are viewed as precursors of highly toxic, carcinogenic, and mutagenic disinfection by-product chemicals. In recent times, these compounds have gained considerable attention of scientists for their successful removal from aqueous solutions to permissible limits. To achieve this aim, the present study investigated, for the first time, the photocatalytical performance of the synthesis FeNi₃@SiO₂@TiO₂ nanoparticles for the HA degradation under different environmental conditions. The photocatalytic reactions were performed using ultraviolet (UV) radiation, whose intensity was fixed at 2500 μW/cm² throughout the experimental study. The characterization study performed, using specific diagnostic techniques, revealed the presence of several good morphological, magnetic, and catalytic specifications of the synthesized nanoparticles. The use of the simplified form of the Langmuir-Hinshelwood equation sufficiently describes the experimental data of the HA kinetic degradation, as it shows a high coefficient of regression values. Furthermore, the complete HA degradation was reached under conditions of pH = 3; initial HA concentration = 10 mg/L; FeNi₃@SiO₂@TiO₂ nanoparticles dosage = 0.01 g/L; and reaction time >30 min. Thus, the results obtained from this research suggested that the catalyst of FeNi₃@SiO₂@TiO₂ nanoparticles was an attractive, novel, and effective agent, which could be used for the degradation of HA in the photocatalytic processes.

Wood-based biochar as an excellent activator of peroxydisulfate for Acid Orange 7 decolorization

Wood-based biochar, as a metal-free heterogeneous activator of peroxydisulfate (PDS), was successfully prepared by pyrolysis of polar sawdust for efficient removal of Acid Orange 7 (AO7). The results demonstrate PDS could be effectively activated by wood-based biochar, and AO7 was rapidly eliminated in a wide range of pH value (3.0-10.0) with AO7 removal achieved ≥ 99.3% after 14 min reaction. The dominant reactive species in the biochar/PDS system were verified via radical quenching tests and electron paramagnetic resonance (EPR) technique. It is speculated that sulfate radicals (SO₄^•-) and hydroxyl radicals (^•OH) were formed on the surface of biochar. Based on the results of X-ray photoelectron spectroscopy (XPS), π-electron density and oxygen-containing functional groups (especially C-OH) on biochar surface were active centers for the catalytic reaction. Recycle experiments of biochar for 4 runs were carried out and the regeneration method of the catalyst was also studied.

Transformation products and degradation pathway of textile industry wastewater pollutants in Electro-Fenton process

In this study, pollutants from textile industry wastewater were transformed/oxidized using Ti/RuO₂ electrode by Electro-Fenton (EF) method in a continuous reactor. The performance was evaluated in terms of % COD removal, % color removal and energy consumed. Electrolysis time, retention time, current, and ferrous sulphate concentration as Fenton catalyst were selected as EF process parameters. To determine the optimum operating conditions multiple response optimization with desirability approach based on central composite design under response surface methodology was used. Spectrophotometric and GC-MS analysis were performed to identify the degraded/transformation compounds, and on this basis degradation mechanism during EF process as well as disposability of treated wastewater was analyzed. Further, bioassay test of treated textile wastewater was conducted for toxicity analysis in view of its disposal quality. Results showed that all the components of textile wastewater were totally eliminated/transformed in lower molecular weight compounds after EF treatment of textile effluent. Further, bioassay test analysis confirmed the nontoxic nature of treated wastewater.

Removal of lindane wastes by advanced electrochemical oxidation

The effective removal of recalcitrant organochlorine pesticides including hexachlorocyclohexane (HCH) present in a real groundwater coming from a landfill of an old lindane (γ-HCH) factory was performed by electrochemical oxidation using a BDD anode and a carbon felt cathode. Groundwater (ΣHCHs = 0.42 mg L^-1, TOC₀ = 9 mg L^-1, pH₀ = 7, conductivity = 3.7 mS cm^-1) was treated as received, achieving the complete depletion of the HCH isomers and a mineralization degree of 90% at 4 h electrolysis at constant current of 400 mA. Initial groundwater contains high chloride concentration (Cl₀^- = 630 mg L^-1) that is progressively decreased due to its oxidation to different oxychlorine species: Cl₂, HClO, ClO^-, ClO₂^- ClO₃^- and ClO₄^- some of them (Cl₂, HClO, ClO^-) playing an important role in the oxidation of organic pollutants. The oxidation rate of chloride (and its oxidized intermediates) depends on the applied current value. Although some of the species generated from them are active oxidants, the presence of inorganic salts is detrimental to the efficiency of the electrochemical process when working at current densities above 100 mA due to the high consumption of hydroxyl radicals in wasting reactions. The initial organic carbon content is not crucial for the extension of the process but high organic loads are more profitable for cost effectiveness. The addition of a supporting electrolyte to the solution could be interesting since it increases the conductivity, reducing the cell potential and therefore, decreasing the energy consumption.

Horseradish peroxidase-mediated decolourization of Orange II: modelling hydrogen peroxide utilization efficiency at different pH values

Enzymatic decolourization of azo-dyes could be a cost-competitive alternative compared to physicochemical or microbiological methods. Stoichiometric and kinetic features of peroxidase-mediated decolourization of azo-dyes by hydrogen peroxide (P) are central for designing purposes. In this work, a modified version of the Dunford mechanism of peroxidases was developed. The proposed model takes into account the inhibition of peroxidases by high concentrations of P, the substrate-dependant catalatic activity of peroxidases (e.g. the decomposition of P to water and oxygen), the generation of oxidation products (OP) and the effect of pH on the decolourization kinetics of the azo-dye Orange II (OII). To obtain the parameters of the proposed model, two series of experiments were performed. In the first set, the effects of initial P concentration (0.01-0.12 mM) and pH (5-10) on the decolourization degree were studied at a constant initial OII concentration (0.045 mM). Obtained results showed that at pH 9-10 and low initial P concentrations, the consumption of P was mainly to oxidize OII. From the proposed model, an expression for the decolourization degree was obtained. In the second set of experiments, the effect of the initial concentrations of OII (0.023-0.090 mM), P (0.02-4.7 mM), HRP (34-136 mg/L) and pH (5-10) on the initial specific decolourization rate (q₀) was studied. As a general rule, a noticeable increase in q₀ was observed for pHs higher than 7. For a given pH, q₀ increased as a function of the initial OII concentration. Besides, there was an inhibitory effect of high P concentrations on q₀. To asses the possibility of reusing the enzyme, repeated additions of OII and P were performed. Results showed that the enzyme remained active after six reuse cycles. A satisfactory accordance between the change of the absorbance during these experiments and absorbances calculated using the proposed model was obtained. Considering that this set of data was not used during the fitting procedure of the model, the agreement between predicted and experimental absorbances provides a powerful validation of the model developed in the present work.

An overview on the removal of synthetic dyes from water by electrochemical advanced oxidation processes

Wastewater containing dyes are one of the major threats to our environment. Conventional methods are insufficient for the removal of these persistent organic pollutants. Recently much attention has been received for the oxidative removal of various organic pollutants by electrochemically generated hydroxyl radical. This review article aims to provide the recent trends in the field of various Electrochemical Advanced Oxidation Processes (EAOPs) used for removing dyes from water medium. The characteristics, fundamentals and recent advances in each processes namely anodic oxidation, electro-Fenton, peroxicoagulation, fered Fenton, anodic Fenton, photoelectro-Fenton, sonoelectro-Fenton, bioelectro-Fenton etc. have been examined in detail. These processes have great potential to destroy persistent organic pollutants in aqueous medium and most of the studies reported complete removal of dyes from water. The great capacity of these processes indicates that EAOPs constitute a promising technology for the treatment of the dye contaminated effluents.

Electrolysis assisted persulfate with annular iron sheet as anode for the enhanced degradation of 2, 4-dinitrophenol in aqueous solution

Annular iron sheet (AIS), playing a dual role of anode electrode and source of activator, was combined with electrolysis technology for the activation of persulfate to improve the degradation of 2, 4-dinitrophenol (DNP) in aqueous solution. In this study, effects of current density (0-10.0mA/cm²), persulfate (PS) dosage (0-8.0mM), initial pH (3.0-11.0), reaction temperature (25-60°C) and reaction time (0-30min) on COD removal of DNP in aqueous solution were investigated, respectively. COD removal reached its maximal value (63.4%) after 15min treatment due to the synergistic effect in electro/AIS/PS system under the optimal conditions. Furthermore, comparative studies of 7 different experimental processes were setup. In addition, the reasonable DNP degradation pathway was proposed based on intermediates detected by HPLC. According to characterization analysis of SEM-EDS, XRD and XPS of the generated flocculation in electro/AIS/PS system, the possible reaction mechanism was proposed in detail. In a word, the electrolysis process coupled with annular iron sheet as anode activating persulfate technology shows a significant synergetic effect in enhancing degradation of DNP in aqueous solution.

Novel magnetic g-C3N4/α-Fe2O3/Fe3O4 composite for the very effective visible-light-Fenton degradation of Orange II

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was successfully synthesized through a simple hydrothermal method. The structure, morphology, and optical properties of the catalyst were characterized. The photocatalytic activity of the heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst for the photo-Fenton degradation of Orange II in the presence of H₂O₂ irradiated with visible light (λ > 420 nm) at neutral pH was evaluated. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ photocatalyst was found to be an excellent catalyst for the degradation of Orange II and offers great advantages over the traditional Fenton system (Fe(ii/iii)/H₂O₂). The results indicated that successfully combining monodispersed Fe₃O₄ nanoparticles and g-C₃N₄/α-Fe₂O₃ enhanced light harvesting, retarded photogenerated electron–hole recombination, and significantly enhanced the photocatalytic activity of the system. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ (30%) sample gave the highest degradation rate constant, 0.091 min⁻¹, which was almost 4.01 times higher than the degradation rate constant for α-Fe₂O₃ and 2.65 times higher than the degradation rate constant for g-C₃N₄/α-Fe₂O₃ under the same conditions. A reasonable mechanism for catalysis by the g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was developed. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was found to be stable and recyclable, meaning it has great potential for use as a photo-Fenton catalyst for effectively degrading organic pollutants in wastewater.

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was firstly synthesized and exhibited very effective visible-light-Fenton degradation of Orange II at neutral pH.

Catalytic degradation of Orange II in aqueous solution using diatomite-supported bimetallic Fe/Ni nanoparticles

A functional diatomite-supported Fe/Ni nanocomposite successfully remediated Orange II contaminant in aqueous solution. The hypothesis was that diatomite-supported Fe/Ni would not only be more effective than Fe/Ni but also require less metallic loading to effect the catalytic reaction. Batch experiments indicate that 99.00% of Orange II was removed using diatomite-supported Fe/Ni, while only 86.64 and 3.59% of Orange II were removed using bimetallic Fe/Ni nanoparticles and diatomite, after 6 h of reaction, respectively. Characterisation by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) indicates that the use of diatomite as a support material reduced the aggregation of bimetallic Fe/Ni nanoparticles, thereby resulting in an enhancement in the reactivity. A synergistic mechanism for the removal of Orange II by diatomite-supported Fe/Ni was proposed which involves adsorption, followed by catalytic reduction. This study has demonstrated that diatomite may be a suitable support material for stabilizing and dispersing bimetallic Fe/Ni nanoparticles and the resulting diatomite-supported Fe/Ni composite could be a promising catalyst for the remediation of dye-contaminated wastewater.

A functional diatomite-supported Fe/Ni nanocomposite successfully remediated Orange II contaminant in aqueous solution.

Removal of polyvinylamine sulfonate anthrapyridone dye by application of heterogeneous electro-Fenton process

Diversity and rapidly multiplication of the pollutants incite as to improve the conventional treatments wastewater methods. One of the bottlenecks often faced is the presence into wastewater of organic pollutants with complex structures that requests the design of efficient processes. Thus, this work investigates the removal of polyvinylamine sulfonate anthrapyridone (PSA) dye which complex structure makes difficult its degradation by conventional technologies. For that, a heterogeneous oxidative process using pyrite as sustainable catalyst was designed. Initially, the performance of the system BBD-carbon felt as anode and cathode, respectively for the production of H₂O₂ was determined in comparison with system boron-doped diamond nickel foam. The carbon felt electrode provided the highest oxidant production, and it was selected for the treatment of the polymeric dye. Several oxidative processes were evaluated, and the best degradation levels were obtained by application of electro-Fenton-pyrite process. In addition, it was determined that dye removal followed a kinetic model of pseudo-first-order achieving the highest efficiency by operation at optimum dosage of pyrite 2 g/L and 200 mA of current intensity. Depending on the optimal experimental conditions, these values lead to a nearly complete mineralization (total organic carbon removal of 95%) after 6 h. Furthermore, the reusability of pyrite was evaluated, by removal of PSA in four cycles.

Hydroxyl radical generation in electro-Fenton process with a gas-diffusion electrode: Linkages with electro-chemical generation of hydrogen peroxide and iron redox cycle

The hydroxyl radical generation in an electro-Fenton process with a gas-diffusion electrode which is strongly linked with electro-chemical generation of hydrogen peroxide and iron redox cycle was studied. The OH radical generation subsequent to electro-chemical generations of H₂O₂ was examined under the constant potential in the range of Fe²⁺ dosage from 0 to 1.0 mM. The amount of generated OH radical initially increased and gradually decreased after the maximum was reached. The initial rate of OH radical generation increased for the Fe²⁺ dosage <0.25 mM and at higher Fe²⁺ dosages remained constant. At higher Fe²⁺ dosages the precipitation of Fe might inhibit the enhancement of OH radical generation. The experiments for decolorization and total organic carbon (TOC) removal of azo-dye Orange II by the electro-Fenton process were conducted and the quick decolorization and slow TOC removal of Orange II were found. To quantify the linkages of OH radical generation with dynamic behaviors of electro-chemically generated H₂O₂ and iron redox cycle and to investigate effects of OH radical generation on the decolorization and TOC removal of Orange II, novel reaction kinetic models were developed. The proposed models could satisfactory clarify the linkages of OH radical generation with electro-chemically generated H₂O₂ and iron redox cycle and simulate the decolorization and TOC removal of Orange II by the electro-Fenton process.

Removal of artificial sweetener aspartame from aqueous media by electrochemical advanced oxidation processes

The degradation and mineralization of aspartame (ASP) in aqueous solution were investigated, for the first time, by electrochemical advanced oxidation processes (EAOPs) in which hydroxyl radicals were formed concomitantly in the bulk from Fenton reaction via in situ electrogenerated Fenton's reagent and at the anode surface from the water oxidation. Experiments were performed in an undivided cylindrical glass cell with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. The effect of Fe²⁺ concentration and applied current on the degradation and mineralization kinetics of ASP was evaluated. The absolute rate constant for the reaction between ASP and OH was determined as (5.23 ± 0.02) × 10⁹ M^-1 s^-1 by using the competition kinetic method. Almost complete mineralization of ASP was achieved with BDD anode at 200 mA constant current electrolysis. The formation and generation of the formed carboxylic acids (as ultimate end products before complete mineralization) and released inorganic ion were monitored by ion-exclusion high performance liquid chromatography (HPLC) and ion chromatography techniques, respectively. The global toxicity of the treated ASP solution during treatment was assessed by the Microtox^® method using V. fischeri bacteria luminescence inhibition.

Effect of a solar Fered-Fenton system using a recirculation reactor on biologically treated landfill leachate

The effects of electrochemical oxidation (EO), Fered-Fenton and solar Fered-Fenton processes using a recirculation flow system containing an electrochemical cell and a solar photo-reactor on biochemically treated landfill leachate were investigated. The most successful method was solar Fered-Fenton which achieved 66.5% COD removal after 120min treatment utilizing the optimum operating conditions of 47mM H2O2, 0.29mM Fe(2+), pH0 of 3.0 and a current density of 60mA/cm(2). The generation of hydroxyl radicals (OH) are mainly from Fered-Fenton process, which is enhanced by the introduction of renewable solar energy. Moreover, Fe(2+)/chlorine and UV/chlorine processes taking place in this system also result in additional production of OH due to the relatively high concentration of chloride ions contained in the leachate. The energy consumption was 74.5kWh/kg COD and the current efficiency was 36.4% for 2h treatment. In addition, the molecular weight (MW) distribution analysis and PARAFAC analysis of excitation emission matrix (EEM) fluorescence spectroscopy for different leachate samples indicated that the organics in the leachate were significantly degraded into either small molecular weight species or inorganics.

Bioelectro-Fenton: A sustainable integrated process for removal of organic pollutants from water: Application to mineralization of metoprolol

The relevant environmental hazard related to the presence of pharmaceuticals in water sources requires the development of high effective and suitable wastewater treatment technologies. In the present work, a hybrid process coupling electro-Fenton (EF) process and aerobic biological treatment (Bio-EF process) was implemented for the efficient and cost-effective mineralization of beta-blocker metoprolol (MPTL) aqueous solutions. Firstly, operating factors influencing EF process were assessed. MTPL solutions were completely mineralized after 4h-electrolysis under optimal operating conditions and BDD anode demonstrated its oxidation superiority. The absolute rate constant of MTPL oxidation byOH (kMTPL) was determined by the competition kinetics method and found to be (1.72±0.04)×10(9)M(-1)s(-1). A reaction pathway for the mineralization of the drug was proposed based on the identification of oxidation by-products. Secondly, EF process was used as pre-treatment. An increase of BOD5/COD ratio from 0.012 to 0.44 was obtained after 1h EF treatment, along with 47% TOC removal and a significant decrease of toxicity, demonstrating the feasibility of a post-biological treatment. Finally, biological treatment successfully oxidized 43% of the total TOC content. An overall 90% mineralization of MPTL solutions was achieved by the Bio-EF process, demonstrating its potentiality for treating wastewater containing pharmaceutical residues.

Electro-assisted heterogeneous activation of persulfate by Fe/SBA-15 for the degradation of Orange II

The removal of Orange II by activation of persulfate (S2O8(2-), PS) using synthesized Fe/SBA-15 in the electrochemical (EC) enhanced process was reported in this study. The reaction rate constants, degradation mechanism, catalyst stability, and evolution of mineralization and toxicity were detailed investigated. On the basis of radical scavenger results, both the sulfate radicals (SO4(-)) and hydroxyl radicals (OH) were responsible for the degradation of Orange II. A possible pathway is suggested to describe the degradation of Orange II according to the degradation intermediates identified. The results showed that the Fe/SBA-15 catalyst maintained strong reusability and stability with a low level of iron leaching. In addition, favorable mineralization efficiency in terms of COD removal efficiency (75.4%) and TOC removal efficiency (46.3%) was obtained when the reaction time was prolonged to 24h. The toxicity experiments implied that the toxicity of the treated solution ascended at the first 30min but then dropped to almost zero eventually. This study provides a proof-of-concept that can be applied widely for the PS remediation of contaminated water.

A coupled Bio-EF process for mineralization of the pharmaceuticals furosemide and ranitidine: Feasibility assessment

A coupled Bio-EF treatment has been applied as a reliable process for the degradation of the pharmaceuticals furosemide (FRSM) and ranitidine (RNTD) in aqueous medium, in order to reduce the high energy consumption related to electrochemical technology. In the first stage of this study, electrochemical degradation of the drugs was assessed by the electro-Fenton process (EF) using a BDD/carbon-felt cell. Biodegradability of the drugs solutions was enhanced reaching BOD5/COD ratios close to the biodegradability threshold of 0.4, evidencing the formation of bio-compatible by-products (mainly short-chain carboxylic acids) which are suitable for biological post-treatment. Moreover, toxicity evaluation by the Microtox(®) method revealed that EF pre-treatment was able of detoxifying both, FRSM and RNTD solutions, constituting another indicator of biodegradability of EF treated solutions. In the second stage, electrolyzed solutions were treated by means of an aerobic biological process. A significant part of the short-chain carboxylic acids formed during the electrochemical phase was satisfactorily removed by the used selected microorganisms. The results obtained demonstrate the efficiency and feasibility of the integrated Bio-EF process.

Degradation of artificial sweetener saccharin in aqueous medium by electrochemically generated hydroxyl radicals

The removal of artificial sweetener saccharin (SAC) in aqueous solution by electrochemical advanced oxidation using electro-Fenton process was performed. Experiments were carried out in an undivided cylindrical glass cell with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. The removal of SAC by electrochemically generated hydroxyl radicals followed pseudo-first-order kinetics with both Pt and BDD anode. The absolute rate constant of the SAC hydroxylation reaction was determined for the first time using the competition kinetic method and found to be (1.85 ± 0.01) × 10(9) M(-1) s(-1). The comparative study of TOC removal efficiency during electro-Fenton treatment indicated a higher mineralization rate with BDD than Pt anode. The identification and evolution of short-chain carboxylic acids and inorganic ions formed during oxidation process were monitored by ion-exchange chromatography and ion chromatography, respectively. The assessment of toxicity of SAC and/or its reaction by-products during treatment was performed using Microtox® method based on the Vibrio fischeri bacteria luminescence inhibition. Results showed that the process was able to efficiently detoxify the treated solution.

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres: the effect of Fe/Cu ratio on heterogeneous Fenton degradation of a dye

A series of iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres with different Fe/Cu ratios were prepared using a simple post-impregnation and sodium borohydride reduction strategy.

Heterogeneous activation of hydrogen peroxide using γ-Al2O3 supported bimetallic Fe, Mn for the degradation of reactive black 5

A Fe–Mn/γ-Al₂O₃ catalyst was prepared via a wet impregnation method and used for the degradation of reactive black 5 (RB5) as an activator of hydrogen peroxide (H₂O₂).

Complete removal of AHPS synthetic dye from water using new electro-fenton oxidation catalyzed by natural pyrite as heterogeneous catalyst

The mineralization of a new azo dye - the (4-amino-3-hydroxy-2-p-tolylazo-naphthalene-1-sulfonic acid) (AHPS) - has been studied by a novel electrochemical advanced oxidation process (EAOP), consisting in electro-Fenton (EF) oxidation, catalyzed by pyrite as the heterogeneous catalyst - the so-called 'pyrite-EF'. This solid pyrite used as heterogeneous catalyst instead of a soluble iron salt, is the catalyst the system needs for production of hydroxyl radicals. Experiments were performed in an undivided cell equipped with a BDD anode and a commercial carbon felt cathode to electrogenerate in situ H2O2 and regenerate ferrous ions as catalyst. The effects on operating parameters, such as applied current, pyrite concentration and initial dye content, were investigated. AHPS decay and mineralization efficiencies were monitored by HPLC analyses and TOC measurements, respectively. Experimental results showed that AHPS was quickly oxidized by hydroxyl radicals (OH) produced simultaneously both on BDD surface by water discharge and in solution bulk from electrochemically assisted Fenton's reaction with a pseudo-first-order reaction. AHPS solutions with 175 mg L(-1) (100 mg L(-1) initial TOC) content were then almost completely mineralized in 8h. Moreover, the results demonstrated that, under the same conditions, AHPS degradation by pyrite electro-Fenton process was more powerful than the conventional electro-Fenton process.

Heterogeneous photo-Fenton decolorization of Orange II over Al-pillared Fe-smectite: response surface approach, degradation pathway, and toxicity evaluation

A ferric smectite clay material was synthesized and further intercalated with Al2O3 pillars for the first time with the aim of evaluating its ability to be used as heterogeneous catalyst for the photo-Fenton decolorization of azo dye Orange II. UV irradiation was found to enhance the activity of the catalyst in the heterogeneous photo-Fenton process. Catalyst loading of 0.5g/L and hydrogen peroxide concentration of 13.5mM yielded a remarkable color removal, accompanied by excellent catalyst stability. The decolorization of Orange II followed the pseudo-first-order kinetics for initial dye concentrations from 20 to 160mg/L. The central composite design (CCD) based on the response surface methodology (RSM) was applied to evaluate the effects of several operating parameters, namely initial pH, catalyst loading and hydrogen peroxide concentration, on the decolorization efficiency. The RSM model was derived and the response surface plots were developed based on the results. Moreover, the main intermediate products were separated and identified using gas chromatography-mass spectrometry (GC-MS) and a possible degradation pathway was proposed accordingly. The acute toxicity experiments illustrated that the Daphniamagna immobilization rate continuously decreased during 150min reaction, indicating that the effluent was suitable for sequential biological treatment.

Template-free synthesis of Fe3O4 nanorod bundles and their highly efficient peroxidase mimetic activity for the degradation of organic dye pollutants with H2O2

The high surface to volume ratio of Fe₃O₄ nanorods facilitates the excellent activation of H₂O₂ for the photo-Fenton-like degradation of crystal violet dye under solar light.