electro-Fenton Oxidation Process Research Articles

In-situ interconnected 1D/2D/3D architectures of CNT/MoS2/Fe3O4 membranes for increasing degradation efficiency of penetrative electro-Fenton under low energy consumption

The electro-Fenton oxidation process for the degradation of organic pollutants in recalcitrant wastewater has garnered significant attention and research efforts in the field of advanced water treatment. This is primarily due to its highly effective degradation capabilities and the advantages it offers, including the avoidance of unsafe transportation and storage of hydrogen peroxide (H2O2). However, challenges such as relatively high energy consumption, complex operational requirements, and limited operational stability continue to pose significant economic constraints on the widespread application of electro-Fenton technology in water purification. In this study, we employed a secondary hydrothermal method to construct a multi-layered CNT/MoS2/Fe3O4 composite heterostructure in situ. Leveraging the synergistic effects of the introduced variable valence elements, Fe and Mo, and the interconnected multi-layered membrane structure, the CNT/MoS2/Fe3O4 electro-Fenton membrane holds promise in a permeable filtration system. Under the conditions of a current density of 1.50 mA/cm² and an electrolyte concentration of 0.50 mol/L, the CNT/MoS2/Fe3O4 composite membrane exhibited a degradation efficiency of over 90.00 % for 100.00 mg/L RhB within 10 minutes, and the degradation rate approached nearly 99.00 % at 60 minutes. Furthermore, the degradation efficiency for various recalcitrant organic dye wastewaters, including phenol, methyl orange, and methylene blue, could be maintained at levels ranging from 80.00 % to 97.00 %. Particularly, under optimized operating conditions, the specific energy consumption (EC) for the CNT/MoS2/Fe3O4 membrane process was measured at 0.60±0.01 kWh/m³, showcasing exceptionally low energy consumption characteristics. In conclusion, it is expected to contribute to the reduction of the overall consumption of heterogeneous electro-Fenton oxidation systems and enhance their operational efficiency. This innovative approach represents a significant advancement in the field, offering the potential to address the economic limitations associated with electro-Fenton technology in water quality purification.

PbO2 /graphite and graphene/carbon fiber as an electrochemical cell for oxidation of organic contaminants in refinery wastewater by electrofenton process; electrodes preparation, characterization and performance

The electro-Fenton oxidation process was used to treat organic pollutants in industrial wastewater as it is one of the most efficient advanced oxidation processes. The novel cell in this process consists of a prepared PbO2 electrode by electrodeposition on graphite substrate and carbon fiber modified with graphene as a cathode. X-ray diffraction, fluorescence, analysis system, atomic force microscopy, and scan electron microscopy were used to characterize the prepared anode and cathode. XRD patterns clearly show the characteristic reflection of the mixture of  - and β phases of PbO2 on graphite and carbon fiber, and AFM results for cathode and anode present that PbO2 on graphite substrate and graphene on carbon fiber surface are on a nanoscale. Contact angle measurement was determined for the carbon fiber cathode before and after modification. The anodic polarization curve showed a higher anodic current when utilizing the PbO2 anode than the graphite anode. Phenol in simulated wastewater was removed by electro-Fenton oxidation at 8 mA/cm2 current density, 0.4 mM of ferrous ion concentration at 35 °C up to 6 h of electrolysis. Chemical oxygen demand for the treated solution was removed by 94.02 % using the cell consisting of modified anode and cathode compared with 81.23% using modified anode and unmodified cathode and 79.87 % when using unmodified anode and modified cathode.

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.

Preparation of lotus-leaf-like carbon cathode for the electro-Fenton oxidation process: Hydrogen peroxide production, various organics degradation and printing wastewater treatment

To develop an electro-Fenton (EF) oxidation process for highly efficient organics degradation, a carbon cathode with lotus-leaf-like super-hydrophobic surface was prepared using ordinary graphite powder as an electro-catalyst material, polytetrafluoroethylene (PTFE) as an adhesive agent, boric acid (H3BO3) as a pore-forming agent, and using copper wire meshes to shape the surface morphology. The obtained results show that the carbon cathode with a lotus-leaf-like morphology led to an evident increase in hydrophobicity, which greatly enhanced hydrogen peroxide (H2O2) production performance. In the air-aerated Na2SO4 solution (pH = 2.8), the cathode prepared under optimized conditions yielded 527.5 mg L−1 H2O2 within 60 min with an observed current efficiency (CE) of 35.1 %. The developed EF oxidation process exhibited the strong oxidation ability for the degradation of several organics including rhodamine B (RhB), methylene blue trihydrate (MBT), p-nitrophenol (p-NP) and tetracycline (TC). What's more, the treatment of one real printing wastewater by this EF system presented the chemical oxygen demand (COD) removal of 76.8 % and the total organic carbon (TOC) removal of 73.5 %, and concurrently enhanced the biodegradability evidently. In addition, it was found that chloride ion (Cl−) might have an adverse effect on organics degradation due to the meaningless H2O2 consumption caused by HClO and ClO−. The results of this study indicate that the developed EF process can be used not only for the efficient removal of organic pollutants, but also as a pre-treatment before biological treatment for the enhancement of biodegradability.

The Taguchi Approach in Studying and Optimizing the Electro-Fenton Oxidation to Reduce Organic Contaminants in Refinery Wastewater Using Novel Electrodes

This study investigated the degradation of organic pollutants using an advanced electrochemical oxidation technique in a batch reactor cell consisting of a graphite anode, modified by electrodeposition of PbO2, and a graphene-modified carbon fiber cathode. The experiment was designed by the Taguchi design approach with an orthogonal array of L18 to study and optimize the degradation of Chemical Oxygen Demand (COD) by the electro-Fenton oxidation process. Four process parameters, Current Density (CD), Temperature, Fe2+ concentration, and time were measured at different levels. The impact of each factor was analyzed by analysis of variance (ANOVA). Furthermore, a linear model analysis was applied for the Signal-to-Noise (S/N) ratio and mean values, obtaining the optimal conditions. The most significant parameter of the COD removal efficiency was time, and the least one was temperature.

Kinetics and Energetic Parameters Study of Phenol Removal from Aqueous Solution by Electro-Fenton Advanced Oxidation Using Modified Electrodes with PbO2 and Graphene

The Electro-Fenton oxidation process is one of the essential advanced electrochemical oxidation processes used to treat Phenol and its derivatives in wastewater. The Electro-Fenton oxidation process was carried out at an ambient temperature at different current density (2, 4, 6, 8 mA/cm2) for up to 6 h. Sodium Sulfate at a concentration of 0.05M was used as a supporting electrolyte, and 0.4 mM of Ferrous ion concentration (Fe2+) was used as a catalyst. The electrolyte cell consists of graphite modified by an electrodepositing layer of PbO2 on its surface as anode and carbon fiber modified with Graphene as a cathode. The results indicated that Phenol concentration decreases with an increase in current density, and the minimum Phenol concentration obtained after 6 h of electrolysis at 8 mA/cm2 is equal to 7.82 ppm starting from an initial concentration about 155 ppm. The results obtained from the kinetic study of Phenol oxidation at different current density showed that the reaction followed pseudo first-order kinetics regarding current density. Energetic parameters like specific power consumption and current efficiency were also estimated at different current density. The results showed that an increase in current density caused an increase in the specific power consumption of the process and decreased current efficiency.

Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 °C, using 150 mM H2O2 and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H2O2 concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of performance as well as energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.

Study of Electro-Fenton Oxidation for the Removal of oil content in refinery wastewater

In this study, refinery wastewater treatment scheme, the electro-Fenton oxidation process is obtainable. Through Fenton oxidation treatment, numerous working limits remained examined, for instance hydrogen peroxide, electrolysis time and pH. The effects of the working variables including the pH (2-9), hydrogen peroxide concentration (20-60 mg/L) and the reaction time (10-30 minutes) and remained thoughtful through means of answer surface methodology and Minitab-17. The current, agitation speed and sodium chloride of the aqueous solution consumed remained engaged as 1 Amps, 200 rpm and 0.2 g congruently. Beneath the finest standards of the employed variables extra than 98% oil removal in refinery wastewater.

Evaluation of Using Photovoltaic Cell in the Electro-Fenton Oxidation for the Removal of Oil Content in Refinery Wastewater

In this study, the refinery wastewater treatment system by the photovoltaic electro-Fenton oxidation process was presented, which integrates the environmentally friendly photovoltaic and autonomous solar energy along with the capability of electro for oil content removing in the refinery wastewater. The direct connection between the photovoltaic panel and the electro-oxidation reactor can be accomplished without using batteries. This connection increases the sustainability of the system and eliminates the environment hazard resulted from the inappropriate disposal of the batteries. The photovoltaic electro-oxidation system is commonly made for multipurpose usage depending on the instantaneous solar irradiation by setting the volume of the wastewater to the supplied current intensity that provided by the photovoltaic array. The effect of several parameters that have critical impacts on the system efficiency of the presented process has studied by the Minitab-17 and the response surface methodology. Speed of agitation, solution electrolysis time, and the temperature have been presented and the optimal levels that corresponds to the optimal conditions were investigated and presented as well. Results of the experimental work showed that the working conditions of the agitation speed was 175 rpm, temperature was 70 oC and 15 min-reaction time, the concentration of oil in the treated refinery wastewater (RWW) was significantly decreased from 96.5 ppm (initial value) to specific values less than 2 ppm (the permissible limit), a removal percentage with an amount more that 98% and 20.4 kWh/m3 for the energy consumption were obtained. The suggested process is suitable for refinery wastewater remediation, especially for small amounts of oil content in RWW.

Catalytic activity comparison of typical iron-bearing particle electrodes in heterogeneous electro-Fenton oxidation processes

Four kinds of iron-bearing materials including chalcopyrite, pyrite, sponge iron and iron–carbon composite were exploited as catalysts and 3D electrodes (particle electrode) for heterogeneous electro-Fenton oxidation processes. Their catalytic activities were compared according to decolorization (i.e. 1−C∕C 0) and COD removal efficacies, using Reactive Red X-3B as a model organic pollutant in dyeing wastewater. The iron–carbon composite was found to be the most effective catalyst, and 99.63 ± 1 % of decolorization and 79.86 ± 2 % of COD removal can be achieved. The addition of sodium chloride reduced catalytic efficacies of sponge iron and iron–carbon composite slightly, but promoted those of chalcopyrite and pyrite. Furthermore, the stability and reusability of catalysts were examined and insignificant reduction on catalytic activity was observed for 5 cycles of electro-Fenton processes.

Highly stable binder free CNTs/rGO aerogel electrode for decolouration of methylene blue & palm oil mill effluent via electro-Fenton oxidation process.

In this study, single wall carbon nanotubes (CNTs)/reduced graphene oxides (rGO) aerogels were prepared by a one-pot hydrothermal process without using a binder. The produced CNTs/rGO aerogel was used as cathode in electro-Fenton system for the decolouration of methylene blue (MB) and palm oil mill effluent (POME). The addition of CNTs increased the surface area, pore volume and conductivity of the rGO aerogel, which further enhanced their performance as cathode towards the decolouration of MB and POME via electro-Fenton reaction. Complete decolouration of MB using rGO aerogel without CNTs could not be achieved. The effect of electro-Fenton reaction parameters conducted using the aerogel samples including, current, electrolyte concentrations and pH, were investigated accordingly. The CNTs/rGO aerogel electrode also showed high stability and reusability for up to six consecutive treatment cycles for MB. Besides, the CNTs/rGO aerogel also showed good performance in treating POME with 69.8%, 47.6% and 58.1% of reduction in true colour, total organic carbon (TOC) and chemical oxygen demand (COD), respectively, via 60 minutes electro-Fenton reaction. This study showed that CNTs/rGO aerogels with high porosity and stability can be prepared using simple procedure without adding binder. This fully carbon-based aerogel can serve as effective cathode for decolouration of organic dye and effluent.

Treatment of landfill leachate with combined biological and chemical processes: changes in the dissolved organic matter and functional groups

ABSTRACTLeachates contain complicated and hazardous substances that need multiple treatment processes to meet the discharge standards. Few studies have considered the changes in different fractions, based on their molecular weight (MW), of dissolved organic matter, during the different treatment processes. In this study, we investigated the application of a biological method, using sequencing batch reactors, and a chemical method, using the electro-Fenton oxidation process, in combination. The combined treatment, and the electro-Fenton process alone, was applied to a landfill leachate. Samples taken at various points during the treatment processes were fractionated according to their MW using ultra-membranes; this divided the samples into their less biodegradable constituents (0.45 μm: >10 kDa MW), their bio-refractory constituents (10–1 kDa MW) and their biodegradable constituents (<1 kDa MW). The dominant contributors to the chemical oxygen demand (COD) in the raw leachate comprised the biodegradable constituents (79% of total COD). The COD was reduced to 33.6% and 18.5% of its original levels, by the electro-Fenton process alone and the combined treatment, respectively. Based on the absorption intensities in the Fourier transform infrared (FTIR) spectra, the functional groups in the raw leachate were reduced by the biological treatment, but changed by the electro-Fenton process.

Efficient removal of dimethyl phthalate with activated iron-doped carbon aerogel through an integrated adsorption and electro-Fenton oxidation process

A promising activated iron-doped carbon aerogel (AFeC) possessing high adsorption capacity and “self-cleaning” ability via generated OH radicals was fabricated and applied to remove dimethyl phthalate (DMP). Around 90% of the DMP (50 ppm) was first adsorbed on the surface of a DMP-imprinted AFeC electrode and then further catalytically oxidized by surface OH produced via an electro-Fenton reaction. DMP removal of 98% can be achieved in 150 min in the heterogeneous electro-Fenton process. The addition of Fe0 favoured the generation of graphene sheets of amorphous carbon and then provided strong π-π interaction with aromatic pollutants. In addition to iron, a DMP molecular template was also introduced to AFeC to create special molecular imprinting affinity for DMP. The CO2-N2 activation treatment increased the porosity and enriched the hydroxyl and quinone groups (C-O and C=O). The high DMP adsorption capacity of the DMP-imprinted AFeC electrode can be ascribed to the following mechanism: (i) electrostatic interaction; (ii) hydrophobic interaction; (iii) π-π electron-donor-acceptor interactions; (iv) molecular imprinting affinity between template molecules and imprinted sites. Thus, this carbon-based material is promising to be potentially applied in the removal of DMP containing wastewater through integrated adsorption and degradation.

A quantitative toxicogenomics assay reveals the evolution and nature of toxicity during the transformation of environmental pollutants.

The incomplete mineralization of contaminants of emerging concern (CECs) during the advanced oxidation processes can generate transformation products that exhibit toxicity comparable to or greater than that of the original contaminant. In this study, we demonstrated the application of a novel, fast, and cost-effective quantitative toxicogenomics-based approach for the evaluation of the evolution and nature of toxicity along the electro-Fenton oxidative degradation of three representative CECs whose oxidative degradation pathways have been relatively well studied, bisphenol A, triclosan, and ibuprofen. The evolution of toxicity as a result of the transformation of parent chemicals and production of intermediates during the course of degradation are monitored, and the quantitative toxicogenomics assay results revealed the dynamic toxicity changes and mechanisms, as well as their association with identified intermediates during the electro-Fenton oxidation process of the selected CECs. Although for the three CECs, a majority (>75%) of the parent compounds disappeared at the 15 min reaction time, the nearly complete elimination of toxicity required a minimal 30 min reaction time, and they seem to correspond to the disappearance of identified aromatic intermediates. Bisphenol A led to a wide range of stress responses, and some identified transformation products containing phenolic or quinone group, such as 1,4-benzoquinone and hydroquinone, likely contributed to the transit toxicity exhibited as DNA stress (genotoxicity) and membrane stress during the degradation. Triclosan is known to cause severe oxidative stress, and although the oxidative damage potential decreased concomitantly with the disappearance of triclosan after a 15 min reaction, the sustained toxicity associated with both membrane and protein stress was likely attributed at least partially to the production of 2,4-dichlorophenol that is known to cause the production of abnormal proteins and affect the cell membrane. Ibuprofen affects the cell transporter function and exhibited significantly high membrane stress related to both membrane structure and function. Oxidative degradation of ibuprofen led to a shift in its toxicity profile from mainly membrane stress to one that exhibited not only sustained membrane stress but also protein stress and DNA stress. The information-rich and high-resolution toxicogenomics results served as “fingerprints” that discerned and revealed the toxicity mechanism at the molecular level among the CECs and their oxidation transformation products. This study demonstrated that the quantitative toxicogenomics assay can serve as a useful tool for remediation technology efficacy assessment and provide guidance about process design and optimization for desired toxicity elimination and risk reduction.

MBR excess sludge reduction by combination of electrocoagulation and Fenton oxidation processes

This study investigates the disintegration of excess sludge produced in a membrane bioreactor (MBR) with electrocoagulation, electrofenton and electrofenton–Fenton processes. The optimum reaction times for electrocoagulation, electrofenton and electrofenton–Fenton processes were 120, 90 and 70min, respectively. Technical and economical investigations showed that electrofenton–Fenton system was the best one. It was found that 15min electrofenton oxidation process was enough to trigger Fenton oxidation process and 55min remaining reaction time could be operated without electrolysis combination. This process had low energy consumption, and the total cost was 2.02€/m3. After optimization, two MBRs were operated in parallel with and without the batch sludge electrofenton–Fenton oxidation process. The application of electrofenton–Fenton oxidation process to MBR was effective in terms of minimizing production of excess sludge and reducing membrane fouling. The sludge yield constant (Yobs) of the control run was approximately 0.10g MLSS/g COD, while in MBR with the sludge oxidation process, MLSS was kept nearly stable and excess sludge production was negligible. Moreover, effluents from both systems were maintained at an acceptable level. Operation of the MBR system with sludge disintegration process led to a better total nitrogen removal than the control run.

Degradation of organic pollutants by visible light synergistic electro-Fenton oxidation process

Visible light irradiation combined with homogeneous iron and/or hydrogen peroxide to degrade organic dye rhodamine B (RhB) and small molecular compound 2,4-dichlorophenol (2,4-DCP) in a home-made bottle reactor was assessed. The concentration of oxidize species, Fe3+ and Fe2+ were determined during the degradation process. The results demonstrated that visible light irradiation combined with electro-Fenton improved the degradation efficiency. Moreover, both RhB and 2,4-DCP were mineralized during visible light synergistic electro-Fenton oxidation process. 95.0% TOC (total organic carbon) removal rate of RhB occurred after 90 min and 96.7% of COD (chemical oxygen demand) removal rate after 65 min of irradiation. 91.3% TOC removal rate of 2,4-DCP occurred after 16 h of irradiation and 99.9% COD removal rate occurred after 12 h of illumination. The degradation and oxidation process was dominated by the hydroxyl radical (·OH) generated in the system. Both the impressed electricity and dye sensitization by visible light facilitated the conversion between Fe3+ and Fe2+, thus, improving Fenton reaction efficiency.

A comparative study for treatment of white liquor by different applications of Fenton process

In this paper, the treatability of white liquor by conventional (CFP), modified (MFP) and electro-Fenton oxidation processes (EFP) was investigated depending on the COD parameter. Based on the experimental results, up to 62.4%, 58.4% and 54.9% COD removals by the CFP, MFP and EFP were achieved, respectively. It was observed that adjustment of initial pH to acidic values is not required in the CFP. The optimal operational conditions were found to be [Fe2+]=500mg/L, [H2O2]=1000mg/L at pH 7.3 (original pH) in the CFP, [Fe0]=1250mg/L, [H2O2]=1000mg/L at pH 3 in the MFP, and I=1.0A, [H2O2]=1500mg/L at pH 3 in the EFP, respectively. As a result, the CFP has been determined as a more efficient alternative treatment method.

COD and color removal from synthetic textile wastewater by ultrasound assisted electro-Fenton oxidation process

Combination of electro-Fenton (EF) oxidation process with sonication for both the degradation of C.I. Reactive Black 5 (RB 5) and removal of chemical oxygen demand (COD) from synthetic textile wastewater was investigated under different operating conditions. Optimal conditions were found as the initial pH of 3, DC current of 0.25A, H2O2 dosage of 800mg/L and electrode distance of 2.5cm for both EF and ultrasound assisted electro-Fenton (sono-EF) processes. However, the combination of EF with sonication was negligibly improved in terms of COD and color removals, compared to EF process.

Biodegradability enhancement of wastewater containing cefalexin by means of the electro-Fenton oxidation process

The comparative degradation behavior of cefalexin (CLX) using advanced oxidation processes (AOPs) with the aim of improving CLX biodegradability was studied. Among the AOPs used, RuO2/Ti anodic oxidation (AO), AO in the presence of electro-generated H2O2 (AO-H2O2), and the electro-Fenton (EF) process, the EF process was the most effective. In the EF process an activated carbon fiber (ACF) was used as a cathode. Different input variables, including catalyst concentration, pH, and current density were evaluated to find the optimum conditions for the EF. The most suitable operational conditions were as follows: a current density of 6.66mA/cm2, a pH of 3, and a concentration of 1mM of Fe2+ as the catalyst. Different CLX concentrations were analyzed as well of different reaction times to assess the degree of mineralization. The change in biodegradability was evaluated by the BOD5/COD and the BOD14/COD ratios. The EF did not effectively remove the COD, but removed enough to achieve suitable biodegradability for a further biological process.

Rapid Mineralization of Azo-Dye Wastewater by Microwave Synergistic Electro-Fenton Oxidation Process

A method for in situ improvement of the electro-Fenton (EF) oxidation process using microwave radiation was proposed. The microwave enhanced electro-Fenton (MW-EF) degradation of azo dye wastewater with boron-doped diamond (BDD) anode was carried out in a continuous flow system under atmospheric pressure. The activation effects of microwave were studied through determining the accumulated hydroxyl radicals, electrogenerated H2O2, and the evolution of iron ions and intermediates. The results showed that, under microwave irradiation, both cathode and anode surfaces were activated efficiently. For cathode, the presence of microwave in electro-Fenton oxidation process accelerated the Fe(III)/Fe(II) redox cycles, leading to relatively steady Fe(II) recovery. Moreover, the transduction of electrons was promoted and the electrosynthesis of H2O2 from O2 was greatly accelerated on the cathode. For BDD anode, under microwave, the blocking of electrode surface by intermediates was enormously alleviated and more acti...