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The presence of refractory micropollutants in natural waters poses significant environmental and health risks. Preferably, advanced oxidation techniques like electro-Fenton (EF) and bio-electro-Fenton (BEF) are used to mitigate micropollutants; nevertheless, their field-scale implementation is limited by prohibitive catalyst cost. As an alternative, waste-iron electrocoagulated algal biomass (A-BC/Fe) was explored as a heterogeneous Fenton catalyst to eliminate dimethyl phthalate (DMP) from wastewater. The Fenton-conducive morphological, chemical, and electrochemical properties of the A-BC/Fe catalyst were revealed by detailed characterisation. In EF treatment, 10 mg/L of DMP was completely degraded within 15 min at pH of 7.0, 50 mM Na2SO4, and cathode potential of − 1.4 V vs. Ag/AgCl. Moreover, the EF system achieved 87.80 ± 2.10% and 96.14 ± 1.10% of DMP removal from secondary and tertiary treated municipal sewage, respectively. The A-BC/Fe catalyst-driven EF process disintegrated DMP into benign non-toxic by-products and showed stable performance over eight batch cycles with only a 1.71% decline in DMP removal efficiency. Further, the A-BC/Fe-catalysed BEF system eliminated 94.81 ± 1.90% of DMP in 4 h while achieving a maximum power density of 124.03 ± 5.64 mW/m2. This investigation underscores the potential of repurposing electrocoagulated algal biomass as a sustainable heterogenous catalyst for micropollutant remediation. [ABSTRACT FROM AUTHOR]

Erythrosine B (EB) is a dye widely used in the food and textile industries. Despite many studies that have been proposed in the literature about the electrochemical oxidation of dyes, few studies considered such recalcitrant xanthene compound, although it has been recognized as a threat to health and the environment. Then, this study investigates the oxidation of EB by a homogeneous electro-Fenton process using iron (II) sulfate heptahydrate as a catalyst, carbon felt cathode, and Ti/RuO2 anode. The treated synthetic wastewater contains 100 mg L−1 of EB and has a pH = 3. The effects of three independent variables have been considered for process optimization, such as applied current intensity (0.1–0.5 A), iron concentration (1–10 mM), and stirring rate (100–1000 rpm). Their interactions were investigated considering response surface methodology (RSM) based on Doehlert design as optimization method. EB removal efficiency and energy consumption were considered as model responses after 30 min of electrolysis. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.9819), adj-R2 (0.9276), and low Fisher probability (< 0.0181) for the EB removal model, and R2 (0.9968), adj-R2 (0.9872) and low Fisher probability (< 0.0014) relative to the energy consumption model, suggesting a robust statistical significance. The energy consumption model significantly depends on current density, as expected. The foregoing results obtained by RSM led to the following optimal conditions for EB degradation: current intensity of 0.2 A, iron concentration of 9.397 mM, and stirring rate of 500 rpm, which gave a maximum decolorization rate of 98.15% with a minimum energy consumption of 0.74 kWh m−3 after 30 min of electrolysis. The competitiveness of the electro-Fenton process has been confirmed by the literature analysis proposed as well as by the preliminary economic analysis proposed in the second section of the study. [ABSTRACT FROM AUTHOR]

Dyes are common pollutants that are found in industrial wastewater including food, pharmaceutical, and cosmetic industries. This study aimed to degrade Ponceau 4R (P4R) by the electro-Fenton (EF) process based on iron electrodes in the aqueous solutions. For the EF process, a 900 mL glass reactor containing two iron electrodes which connected to a power supply was used. The effects of five experimental variables namely applied voltage (5–20 V), electrolyte concentration (0–0.2 mol L−1 Na2SO4), initial P4R concentration (50–250 mg L−1), pH of the solution (2–6), and H2O2 content (0.033–0.100 %v/v) were investigated in four levels and optimized by Taguchi method (OA16). The residual concentrations of P4R after the EF process were spectrophotometrically determined at 505 nm in the time range of 0–90 min with time intervals of 10 min and the removal efficiencies were obtained. Based on the results, the optimum conditions were obtained as pH = 3, voltage = 20 V, H2O2 = 0.033 % v/v, C Na2SO4 = 0.1 M and the CP4R = 50 mg L−1. Under the optimum conditions, about 100% of P4R was removed during 10 min. The energy consumed in the EF process was calculated as 19.82 KWh/m3 during 10 min. The results obtained good removal efficiencies for the degradation of P4R in the real aqueous solutions introducing it as an efficient decolorization method for treatment of P4R polluted waters. [ABSTRACT FROM AUTHOR]

A study of the degradation of diclofenac (DCF) in an electrochemical reactor equipped with two carbon cloth (CC) electrodes operating in recirculation mode, is presented. The analysis of the effects of the operating variables on the degradation of the DCF showed that, as expected, the applied voltage has a direct influence on the reactions that take place at the anode and cathode. In fact, the addition of O2 and Fe(II) to the medium demonstrated that the electro-Fenton (EF) process was taking place and that under the following conditions, 4 V, 0.05 M Na2SO4, 50 mg/L DCF, 0.25 g Fe(II)-loaded resin, and 50 mL/min, 79.8% of DCF mineralization was obtained in a process described by a pseudo-first order kinetics (k = 0.0184 min−1). Using a simulated domestic wastewater effluent, the EF reactor under study not only showed a similar DCF mineralization value (81.8%), but also reasonable energy consumption (2.16 kWh/m3) as well as CC electrode stability upon several treatment cycles. These results suggest that an EF approach using low-cost CC electrodes and neutral pH conditions, constitute a technically and economically viable option for DCF wastewater treatment. [ABSTRACT FROM AUTHOR]

The inertness of carbon felt as cathode is still one of the challenges encountered in the degradation of pollutants by electro-Fenton. In this study, we used a simple ultrasonic oxidation method to introduce oxygen-containing groups and defect carbons on carbon felt surface to improve the electro-Fenton performance. The modified carbon felts were prepared by ultrasonic treatment in three dilute solutions of HNO3, H2SO4, and HNO3–H2SO4. Ultrasound can provide an extra energetic environment to accelerate the oxidation process, while NO3− has stronger oxidation properties in the presence of excess H+, greatly increasing the amounts of C–O–C/C=O and C–C active sites on carbon felt surface. And an electro-Fenton system with modified CF as the cathode was used to degrade rhodamine B, and the factors affecting the degradation were discussed. The results showed that the modified cathode material was significantly more efficient in degrading rhodamine B, under the conditions of O2 flow rate of 0.3 L min−1, pH = 3, voltage of − 0.7 V, and addition of 0.2-mM Fe2+, HNO3–H2SO4 solution modified CF with 37% higher than that of the raw CF, and the decolorization rate reached 96% after 120 min. Modified carbon felt still has good degradation properties after 5 cycles. The CF was modified by ultrasonic oxidation technique to introduce oxygen-containing functional groups and C-sp3 on the surface of the carbon felt.Using this CF as a cathode for the degradation of RhB in an electro-Fenton system. [ABSTRACT FROM AUTHOR]

Coal gasification technology is essential for realizing clean and efficient conversion of coal, as well as for reducing carbon emissions. However, coal gasification technology is accompanied by a large amount of coal gasification wastewater that is biodegradable. In this work, tourmaline was applied as a catalyst in electro-Fenton like process for treating coal gasification wastewater. The optimal applied parameters of coal gasification wastewater were investigated as follows: current density of 90 mA cm−2, tourmaline dosage of 8 g L−1, electrode gap of 1 cm, and temperature at 25 °C; the COD removal ratio reached 91.24% after 240-min treatment. In addition, the current density and tourmaline dosage were further optimized by response surface method. The result was about current density with 82.4 mA cm−2 and catalyst with 7.57 g L−1; the predicted COD removal efficiency was 86.91%. Under the optimal parameters the actual COD removal efficiency was 88.25% a little high than the predicted value. To explore the reusability of tourmaline as Fenton reaction catalyst, five cycles of experiments were carried out. The result demonstrated that tourmaline could be used as catalyst for treating coal gasification wastewater by electro-Fenton like process. [ABSTRACT FROM AUTHOR]

In this study, cobalt etched graphite felt electrodes were produced using a simple etching technique. It was used in combination with a solid polymer electrolyte (SPE) for the degradation of the target contaminant Orange II by Electro-Fenton (EF) technique in low conductivity water. In this method, 94% of Orange II in low conductivity water was removed in 90 min. The characterization analysis substantiates the hypothesis that the electrodes produced exhibit a three-dimensional porous structure, augmented defect concentration, and enhanced electron transfer capability. In addition, the potential reaction mechanism was inferred from the radical quenching experiments, and hydroxyl radicals (·OH) were deemed the main reactive substances. The combination of cobalt etched graphite felt electrodes with SPE demonstrates remarkable efficacy in the treatment of organic wastewater characterized by low electrical conductivity. [ABSTRACT FROM AUTHOR]

Wastewater containing reactive textile dyes constitutes a crucial environmental problem as they are permanent and dangerous. The electro-Fenton (EF) method is promising as an effective technique for degrading organic materials such as dyestuffs. In this study, the optimization of influential variables in removing reactive yellow 145 azo textile dye by EF was investigated using response surface methodology (RSM). Central composite design was used to study the combined effects of critical parameters such as voltage (2.5–12.5 V), H2O2 addition (0.1–1.3 mL), pH (1.75–4.75), electrode spacing (0.25–3.25 cm), and treatment time (25–85 min). The optimum values of the variables to ensure the highest dye removal efficiency (approx. 93%) with the lowest energy consumption (approx. 3.4 Wh/L) were approximately 9.4 V voltage, pH 3.7, 2.5 cm electrode spacing, 1 mL H2O2 addition, and a 40-min treatment time. ANOVA analysis of the predicted quadratic polynomial model showed a regression coefficient value of approximately 0.97 for both objective functions; this highlights the model's applicability for navigating the design space. Simultaneous optimization of process parameters using RSM was achieved with a few experiments. [ABSTRACT FROM AUTHOR]

The dairy industry is among the most contaminated of the food industries. Dairy industry wastewater contains a high organic load and chemical oxygen demand (COD). In recent years, due to the development of the dairy industry, the administration of dairy effluents has become the main problem since dairy effluents can be a dangerous and significant threat, especially to the aqueous environment. Therefore, there is an important need to improve the management and remediation of dairy effluents in order to ensure the economic viability of this major agricultural industry and to decrease environmental problems. Several works focused on the remediation of dairy wastewater. In this study, the effect of the electro-Fenton process on COD and turbidity removal from dairy wastewater was studied. The electro-Fenton process was optimized for four independent variables (pH, reaction time, volume of H2O2, and H2O2/Fe2+ (the molar ratio)). Moreover, the response surface methodology was utilized to design experiments and determine optimum operating conditions. Under optimal conditions (pH = 5.95, reaction time = 60 min, volume of H2O2 = 1.5 ml and the molar ratio of H2O2/Fe2+ = 1.8), the removal efficiency of COD was 95.8%. Also under optimal conditions (pH = 6.37, reaction time = 60 min, volume of H2O2 = 1.5 ml and the molar ratio of H2O2/Fe2+ = 2.09), the removal efficiency of turbidity was 97.2%. [ABSTRACT FROM AUTHOR]

Pharmaceutical wastewater containing contaminants like aspirin, ofloxacin, and amoxicillin are emerging as a worldwide issue due to its significant effects on the ecosystem and public health. In this study, wastewater containing aspirin was treated by using Mn3O4 etched graphite felt (EGF) as a cathode in an MFC-powered electro-Fenton system. The electrochemical characterization of etched electrodes revealed that etching at 400 °C for 1.5 h showed the highest electrochemical activity and rapid electron transfer with a peak current of − 0.058A. The physicochemical characterization exhibited a porous morphology with high defect concentration (ID/IG ratio of 1.56) and increased specific surface area and superhydrophilicity, proving its ability to regenerate Fe2+ on the cathodic surface and promote H2O2 generation. MFC exhibits a maximum power density of 0.053 W/m2 and a current density of 0.516 A/ m 2 . Under optimized conditions of 0.7 mM iron concentration, pH 3, and 100 Ω resistance, the MFC-powered electro-Fenton system showed a maximum of 95.85% aspirin degradation in 30 h with a highest H2O2 generation of 11.84 mg/l. The results highlight the potential of EGF electrodes as efficient cathodes in MFC-powered electro-Fenton systems and suggest that this technology can be opted as an energy-saving system for degrading pharmaceuticals such as aspirin from wastewater. [ABSTRACT FROM AUTHOR]

In this study, efficiency and cost of the Fenton, electro-Fenton, and biosorption processes for treatment of ariazol brown GR and indigo carmine dye mixture were compared. The Box-Behnken experimental design and response surface methodology (RSM) were used to optimize the process variables such as pH, [Fe2+], [H2O2], voltage, biosorbent dose, and time. Finally, the costs of 1 m3 wastewater treatment were calculated in optimal conditions. The operating costs for classical Fenton, electro-Fenton, and biosorption processes were 0.92, 0.48, and 0.13 US$ per 1 m3 wastewater, respectively. The efficiency of the Fenton and electro-Fenton processes for dye removal was similar, but the cost of the electro-Fenton method was half of the Fenton. Furthermore, the electro-Fenton was nine times faster than the Fenton. Efficiency of electro-Fenton was better than the biosorption process even if it is repeated four times with fresh biosorbent (total cost is the same as electro-Fenton). As a general conclusion, the electro-Fenton process is an appropriate choice based on speed and cost in wastewater treatment with respect to Fenton and biosorption processes. [ABSTRACT FROM AUTHOR]

Wastewater containing high concentrations of polyvinyl alcohol (PVA) resists conventional methods such as biological oxidation and requires high doses of chemicals in the case of chemical processes such as coagulation and adsorption. Due to these features, a comparative study has been conducted for the treatment of PVA in textile industrial wastewater by classic Fenton (CF) and electro-Fenton (EF). According to the results of CF, the optimum removal efficiency of the total organic carbon was obtained as 81% at pH 3.0, 43.5 g/L of H2O2 dose, 2.5 g/L of FeSO4·7H2O during 24 h and it reached 85.5% at 120 min in EF at the optimum values (pH 3, H2O2 dose = 43.5 g/L and 0.58 A of the current). When the cost of treatment by the CF method was found as 78.206 €/m3, it was 78.046 €/m3 by the EF process. For the first time in the literature, a comparative study of EF and CF in treatment of the PVA-containing wastewater was presented and high treatment efficiency was achieved. In this study, pH change in the EF process and its negative effects on the treatment efficiency were observed. Determining the need for constant pH adjustment to eliminate these negative effects is one of the most important outputs of this study. In addition, higher treatment efficiencies by EF have been obtained compared to CF. [ABSTRACT FROM AUTHOR]

Wastewater pollution is a worldwide concern, and wastewater treatment is gaining growing global attention. Electro-Fenton is a promising method for the treatment of wastewater containing organic pollutants. This work offers an overview and bibliometric analysis of research on electro-Fenton treatment of wastewater. The literatures, consisting of 1898 documents from 2000 to 2021 collected from the Web of Science database, were analyzed using bibliometric tools such as Bibliometrix package, CiteSpace, and VOSviewer. Document types, publication trends, subject categories, journals, institutions, countries, authors, keywords, and highly cited papers were analyzed. Research in this field has undergone three stages with the rapid development in the past 5 years. Environmental Sciences (24.42%) is the leading Web of Science category, and Engineering (48.37%) is the leading research area. China (38.46%) is the most productive country, followed by Spain (8.59%), Iran (8.11%), France (6.27%), and India (5.80%), while University of Barcelona (7.38%) is the most productive institute. Enric Brillas is the leading author and has the most publications (120 papers) and the highest h-index (58). The top five clusters include "landfill leachate", "heterogeneous electro-Fenton", "electrochemical oxidation", "photoelectro-Fenton", and "photocatalytic degradation". With the rapidly growing number of electro-Fenton related studies, novel research interests and feasible large-scale applications, various techniques are proposed. [ABSTRACT FROM AUTHOR]

A magnetorheological electro-Fenton composite polishing technology was proposed that enables chemical and mechanical "double enhancement" of the machining process to improve processing efficiency. In this process, a novel high-efficiency catalytic oxidation magnetorheological chemical polishing slurry is configured. Frictional wear experiments are carried out in a magnetorheological electro-Fenton environment to study the corrosion mechanism and material removal behavior of electro-Fenton chemical reactions during magnetorheological electro-Fenton compound polishing. Finally, cluster magnetorheological electro-Fenton compound polishing tests are carried out using the optimized parameters. The results show that the •OH generated by the reaction in the friction and wear of the magnetorheological electro-Fenton composite can effectively oxidize GaN in the friction and wear trajectory to produce a loose cracked Ga2O3 corrosion layer. The corrosion effect increases and then decreases as the current increases from 20 to 60 mA; the corrosion effect also shows a trend of increasing and then decreasing when the rate of H2O2 supplementation increases from 0.30 to 0.60 g/min. The best corrosion effect was achieved when the current was 20 mA, and the H2O2 was replenished at a rate of 0.30 g/min, with a mass fraction of 58.6% of the element O on the sample surface. Using silica sol to polish the GaN for 1 h under the same process, magnetorheological electro-Fenton compound polishing can reduce the surface roughness from Ra 2 to 0.8 nm, while ordinary magnetorheological polishing roughness is only reduced to Ra 1.86 nm. A magnetorheological basis combined with electrochemical means to control and enhance the chemical effect can significantly improve the polishing efficiency. [ABSTRACT FROM AUTHOR]

Diazinon (DZ), an organophosphorus pesticide, has a large consumption for agricultural activities, which its discharge into groundwater and surface is associated with serious concerns for the animal and plants. Thus, the degradation of the mentioned pesticide from an aqueous environment was examined in the electro-Fenton (EF) and sono-electro-Fenton process (SEF) process using SS316/β-PbO2 anode. To characterize the synthesized anode, the analyses, e.g., XRD, SEM, and EDX, were used. The central composite design (CCD) was the method used to assess the effect of selected parameters (DZ concentration = 25–75 mg/L, voltage = 5–15 V, pH = 3–9, and electrolysis time = 20–80 min) and their interactions on the DZ degradation in the evaluated system. Detecting the intermediates of DZ degradation was carried out by LC–MS analysis, and its degradation pathways were proposed. To conduct the toxicity tests for inlet and outlet, the growth inhibition percentage of Pseudomonas aeruginosa and Staphylococcus aureus was estimated. SEF process could represent the DZ degradation, COD, and TOC removal efficiencies of 92.2%, 73.2%, and 67.4%, respectively. According to kinetic studies, the pseudo-first-order kinetic (R2 > 0.99) was detected to be an adequate model for the enlightenment of data of the degradation of DZ by the evaluated system. Finally, DZ is converted into carbon dioxide (CO2(and water (H2O). The results of this study showed that the degradation and mineralization of DZ using the SEF process were successfully carried out. [ABSTRACT FROM AUTHOR]

Petrochemical alcoholic wastewater is one of the most pollutant and toxic wastewaters and its treatment has always been associated with a lot of problems for the petrochemical industry. Electro-Fenton process as an efficient technique can be applied to reduce the chemical oxygen demand of an alcoholic effluent prepared by 2-Ethylhexanol (2EH) unit. The Box-Behnken module was used to design the experiments and then evaluate the effect of various parameters during the treatment. The optimum conditions (81.70% for COD removal) were experimentally found at pH of 4.62, reaction time of 61.81 (min), volume ratio of H2O2 to wastewater of 1.52 (ml/l), H2O2/Fe2+ molar ratio of 3.17 and current density 68.17 (mA/cm2). [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) such as Fenton's reagent, which generates highly reactive oxygen species, are efficient in removing biorefractory organic pollutants from wastewater. However, Fenton's reagent has drawbacks such as the generation of iron sludge, high consumption of H2O2, and the need for pH control. To address these issues, Electro-Fenton (EF) and heterogeneous Electro-Fenton (HEF) have been developed. HEF, which uses solid catalysts, has gained increasing attention, and this review focuses on the use of mineral catalysts in HEF and derived processes. The reviewed studies highlight the advantages of using mineral catalysts, such as efficiency, stability, affordability, and environmental friendliness. However, obstacles to overcome include the agglomeration of unsupported nanoparticles and the complex preparation techniques and poor stability of some catalyst-containing cathodes. The review also discusses the optimal pH range and dosage of the heterogeneous catalysts and compares the performance of iron sulfides versus iron oxides. Although natural minerals appear to be the best choice for effluents at pH>4, no scale-up reports have been found. The need for further development in this field and the importance of considering the environmental impact of trace toxic metals or catalytic nanoparticles in the treated water on the receiving ecosystem is emphasized. Finally, the article acknowledges the high energy consumption of HEF processes at the lab scale and calls for their performance development to achieve environmentally friendly and cost-effective results using real wastewaters on a pilot scale. [ABSTRACT FROM AUTHOR]

Synthetic organic dyes contaminate the aquatic environment. A fast and efficient preparation of catalysts plays a vital role in wastewater treatment to reduce costs and increase its market. In this study, we prepared different Si-rich ZSM-5 catalysts (Si/Al = 200) through the one-pot synthesis and impregnation technique that include Fe species. The catalysts were applied in heterogeneous electro-Fenton (HEF) to remove methylene blue (MB), an organic dye which is a model compound for water contaminants. The parent and modified catalysts were characterized by XRD, FT-IR, FE-SEM, NH3-TPD, and N2 adsorption–desorption methods. The results showed the well crystalline framework (89%), high surface area (359 m2 g−1), mesopore structure (0.05 cm3 g−1), and uniform distribution of the Fe species. The optimum operating conditions for the [Fe]-ZSM-5 catalyst were pH = 4, applied current of 100 mA, and catalyst concentration of 0.1 g L−1, which resulted in the highest MB removal (98%) in 15 min through the HEF process. The results confirm the applicability of the one-pot synthesis of the [Fe]-ZSM-5 catalyst. [ABSTRACT FROM AUTHOR]

In this study, the efficacy of electrocoagulation (EC), electro-Fenton (EF), and a combined EC/EF approach—in treating real chemical industrial wastewater—was investigated. Optimal conditions for the EC process were identified at an applied current density of 480 mA/cm2 and a duration of 13 min. In contrast, the EF process demonstrated peak performance at a current density of 350 mA/cm2 and a duration of 147 min. Importantly, a consistent supporting electrolyte concentration of NaCl at 3.3 g/L was maintained for both EC and EF treatments. Under these optimized conditions, the EC process showcased superior efficiency in total suspended solids (TSS) removal, achieving an impressive 82.87% removal rate, whereas the EF process yielded a moderate 41.41%. Conversely, the EF process outperformed in organic removal, registering an exceptional 96.83% removal rate compared to the 53.21% achieved by the EC treatment. Remarkably, the sequential application of both EC and EF processes led to the complete removal of TSS and organics, resulting in a CI reduction to zero. Biological testing corroborated the effectiveness of the combined treatment, confirming the water to be 100% sterilized and thereby suitable for both irrigation and potable use. The novelty of this study lies in the sequential application of electrocoagulation (EC) and electro-Fenton (EF) processes, which, for the first time, achieved complete removal of total suspended solids (TSS) and organics from real chemical industrial wastewater, while also sterilizing the water, rendering it suitable for irrigation and potable use. [ABSTRACT FROM AUTHOR]

A columnar N-doped graphene aerogel (NGA) was successfully fabricated by one-step hydrothermal synthesis using L-hydroxyproline as reductant, N-doping, and swelling agent, and it was used as the cathode with internal aeration mode for the electro-Fenton degradation of p-nitrophenol. Owing to the stable solid–liquid–gas three-phase interface, more active defects, and modulated nitrogen dopants, the NGA cathode exhibited enhanced electrocatalytic activity. H2O2 could be continuously electro-generated via a two-electron oxygen reduction, and the yield of H2O2 was 153.3 mg·L−1·h−1 with the low electric energy consumption of 15.3 kWh kg−1. Simultaneously, the NGA cathode had better charge transfer capability with N-doping, which was conducive to the conversion of Fe3+/Fe2+. Under the optimal condition, nearly 100% removal of p-nitrophenol and 84% removal of TOC were obtained within 60 and 120 min, respectively. The NGA cathode also presented good stability and versatile applicability in different water matrices. Therefore, the NGA is a cost-effective cathode material in electro-Fenton system with adequate activity and reuse stabilization. [ABSTRACT FROM AUTHOR]

Redwater is a highly toxic waste generated during the purification of 2,4,6-trinitrotoluene (TNT), one of the most widely used military explosives. Redwater treatment is difficult because of its high chemical oxygen demand (COD) and strong red color. In this study, we present a comprehensive study on the treatment of the actual TNT redwater by a combination of chemical coagulation and electro-Fenton process. The pretreatment by traditional coagulation using poly-aluminum chloride (PAC) was investigated at different operation conditions of solution pH (4–11), PAC concentration (500–3500 mg/L), flocculant concentration (0–3.5 mg/L), times for coagulation (0–7 min) and flocculation (0–4 min), and stirring speed (100–700 rpm). This pretreatment could removal 52.84% of COD, 53.22% of color, 36.76% of TSS, and 25.88% of total nitrogen under optimal conditions (i.e., pH 7.0, PAC dosage of 2500 mg/L, anion flocculant dosage of 1.25 mg/L, coagulation time of 4 min, flocculation time of 1 min, and stirring speed of 500 rpm). The pretreated redwater was then subjected to an electro-Fenton process using Pt/Ti as anode and carbon felt as the cathode. The effects of solution pH (2–6), iron content (0.05–1 mM), current intensity (8.33–33.33 mA/cm2) and reaction times (0–200 min) on the electro-Fenton treatment were investigated. Under optimal condition (i.e., pH 3.0, Fe(II) concentration of 0.1 mM, current intensity of 16.67 mA/cm2, and reaction time of 120 min), the removal efficiency reached 87.07, 96.2, 72.94, and 50.26% for COD, color, TSS, and total nitrogen, respectively. UV-Vis spectroscopy results confirmed the role of electro-Fenton for the effective removal of aromatic nitro compounds in the redwater. These results suggest that the combination of coagulation and electro-Fenton process could be a promising technology for treating TNT redwater. [ABSTRACT FROM AUTHOR]

Anionic surfactant wastewater has an irreversible effect on aquatic animals and plants. In this paper, the oxidation of sodium dodecylbenzene sulfonate (SDBS) by electro-Fenton system was researched. The results demonstrated that HO2· had a weak ability to oxidize SDBS; ·OH was the primary active substance for oxidizing SDBS. The broken bond sites of SDBS molecules oxidized by the active substances were analyzed by using the concept density functional theory. The calculation results indicated that ·OH initially attacked the C3-C11 bond in the SDBS molecule, and then ·OH underwent addition reactions, forming two typical structures: aromatic sodium p-hydroxybenzene sulfonate and aliphatic linear alkanes. Phenol and sodium dodecyl sulfate (SDS) were selected to study their oxidation behaviors in the electro-Fenton system. It can reflect the oxidation process of the products after the SDBS molecule was broken. The main active substance for oxidizing phenol in the electro-Fenton cathode chamber was ·OH, but the main active substance for oxidizing SDS was HO2·. Unlike the ·OH produced by the cathode, the Pt(·OH) produced by the anode had no effect on the removal of SDBS. Nevertheless, Pt(·OH) exhibited an excellent oxidation effect on SDBS bond-breaking products. The research results clarified the mechanisms of SDBS oxidation in electro-Fenton system and the direction of regulation for the reaction path. It is believed that promoting the ·OH generated at the cathode makes SDBS bond breakage a key step in the electro-Fenton oxidation of SDBS. It provided a theoretical basis for enhancing the current efficiency of the system. [ABSTRACT FROM AUTHOR]

The challenges associated with electro-Fenton during water treatment involve changing the traditional cathode to one showing high efficiency, low cost, and easy preparation. H2O2 electrogeneration in the electro-Fenton process can be promoted by a transition metal-doped cathode. Therefore, an iron-doped cathode can greatly enhance H2O2 production and promote the Fenton reaction to lend efficient pollutant degradation ability. This study proposes a low-cost and easy-prepared iron-deposited graphite cloth cathode (G-Fe). The presence of iron renders G-Fe conductive and supports the active sites for H2O2 production. Aeration was a critical factor for H2O2 electrogeneration. A total of 17.126 and 8.345 mg/L H2O2 was produced from the G-Fe surface, with and without the aeration condition (current density of 100 mA/m2 in 60 min with a neutral pH), respectively. The degradation rate of methyl orange with a cathode of G-Fe with aeration at 100 mA/m2 was 97.5%, which was higher than the value obtained with graphite cloth as the cathode in an aeration environment or in G-Fe without aeration. [ABSTRACT FROM AUTHOR]

The highest total organic carbon (TOC) and color removal efficiency of Acid Orange 7 (0.1 mM initial concentration) on graphite carbon/carbon nanotubes electrodes (KS44/CNT) reached more than 98% in three hours of Electro-Fenton (EF) treatment under optimal conditions (pH=3 and I=20 mA), compared to carbon graphite electrode developed without carbon nanotubes (KS44-0). The apparent kinetic constants of degradation were 0.17 and 0.12 min−1 for the KS44-(20)/CNT and KS44-0, respectively. The long-term stability and system durability were attributed to the graphite carbon/CNT electrodes due to continuous operating treatment that allowed processing efficiency and reusability without any decrease of the catalytic activity in time after five cycles of use. Regardless of the medium, superior decolorization and TOC removal efficiency were obtained for electrodes (KS44-(20)/CNT) containing 20 wt% of ferrocene powder as catalyst for CNTs' growth and iron nanoparticle establishment. Furthermore, the presence of CNTs and iron particles as precursors enhanced drastically the electrochemical and physical properties of the electrode synthesized in a one-step process. The results confirmed that carbon electrodes behave as multifunctional materials acting both as adsorbent and active cathode in the electro-Fenton process for the destruction and total mineralization of Acid Orange 7 (AO7) as a model for organic contaminated wastewater. [ABSTRACT FROM AUTHOR]

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H2O2 and the energetic consumption by means of a factorial design methodology using a 24 factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H2O2 production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500 mL min−1 (with an average residence time of 1.09 min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H2O2 concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H2O2 produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88 µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11 µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5 min of electrolysis. [ABSTRACT FROM AUTHOR]

Leachate landfills contain significant amounts of heavy metals, organic pollutants, inorganic salts, ammonia nitrogen, and chlorinated organics, which negatively influence the environment. Therefore, it is a must to treat them before being released into the environment efficiently. This study investigated the effectiveness of batch Electrocoagulation (EC) and Electro-Fenton (EF) processes to treat the high-strength landfill leachate. The effect of operating parameters, including initial pH of the leachate, contact time, and a mass ratio of COD: H2O2, was investigated on the removal efficiencies of chemical oxygen demand (COD) and color from leachate. The result shows that, under the optimal pH 6 and reaction time of 17.5 min, EC achieved COD and color removal of 66.2% and 94.4%, respectively. However, EF obtained a higher COD removal of 69.8% and 88.1% of color removal at pH of 9 and COD: H2O2 Ratio of 9.5 within 6.7 min. The result revealed that both processes are reported to remove more than 80% color. However, EF obtained a higher degradation rate than EC. Besides, the EF process also generated 47.4% less sludge than the EC process under the optimal conditions. Cost estimation indicates that EF is less expensive (0.48 USD) than electrocoagulation (0.75 USD). In summary, Electro-Fenton is a more reliable, cost-effective, and energy-efficient method of removing landfill leachate than electrocoagulation, requiring less treatment time and producing less sludge. [ABSTRACT FROM AUTHOR]

This study investigates the decolorization of two widely used textile dyes (Acid Black 172 (AB172) and Disperse Blue 56 (DB56) by using a combined sono-photo-electro-Fenton (SPEF) process. The effects of dye structure and processing factors on dye degradation from contaminated water and COD removal efficiency were determined by adopting response surface methodology. The results confirmed that current density, irradiation time, pH, H 2 O 2 C 0 , and AB172 concentration had the most impacts on COD removal, respectively, whereas DB56 removal efficiency was highly dependent on the initial dye concentration and H 2 O 2 C 0 , compared to other processing factors. The dye degradation efficiency of 95.5% and COD removal efficiency of 91.6% for DB56 were obtained at optimum conditions of pH = 3, current density = 2 mA.cm−2, dye concentration = 200 ppm, H 2 O 2 C 0 of 0.78 and irradiation time of 30 min. In the case of AB172, the same optimum conditions were found unlike reaction time of 50 min and H 2 O 2 C 0 of 0.33, which resulted in the optimal dye degradation efficiency and COD removal of 97.4% 94.5%, respectively. These results verified that the type of dye and its structure can be a key factor in the Fenton-based degradation process. The comparison of the performance of different Fenton-based processes confirmed that the removal efficiency of electro-Fenton, sono-electro-Fenton, photo-electro-Fenton, and SPEF was 82–88%, 89.5–91%, 91.5–92.3% and 95.5–97.4%, respectively. The Fenton-based processes are highly effective methods that can be applied for water and wastewater treatment. [ABSTRACT FROM AUTHOR]

Dairy wastewater contains high levels of organic matter that would be a serious threat if being discharged to the environment without any treatment. This study investigated the influence of various parameters including the concentration of poly aluminum chloride (PAC) on the chemical coagulation process and the concentration of H2O2, pH of the solution, reaction time, voltage and distance of electrodes in the electro-Fenton (EF) process. The optimum conditions obtained in this study included PAC concentration of 100 mg/L, pH of 3, reaction time of 60 min, voltage of 20 V, H2O2 concentration of 1.5 g/L and electrode distance of 2 cm. This resulted in the removal efficiency of 90.3%, 87.25%, and 87% for chemical oxygen demand (COD), biochemical oxygen demand (BOD5), and total suspended solids, respectively. The estimated cost of the process in terms of 1 kg COD removal was about $1.16. Two experimental models, called the feed-forward artificial neural network (FF-ANN) and partial least squares (PLS), were developed to predict the behavior of the process in COD removal. The results confirmed that both FF-ANN and PLS were powerful tools in predicting COD removal in the EF process, as the correlation coefficients between the predicted COD and the actual COD for the PLS and FF-ANN models were 0.854 and 0.971, respectively. Sensitivity analysis of both models showed that the reaction time and electrode distance had the most influence on the output of PLS and FF-ANN, respectively. Therefore, this combined process can be regarded as a thought-provoking one for dairy wastewater treatment, and the FF-ANN model was a more powerful tool than the PLS one. [ABSTRACT FROM AUTHOR]

Fenton-based processes, chemical and electrochemical, have attracted the interest of industrial and academic researchers for wastewater treatment. However, the deficiency of rigorous comparison between different methods, including assessment of their impact on the environment, has hindered their large-scale application. This study reports for the first time on the sustainability of raw textile wastewater treatment through two sequential processes, Coagulation-Flocculation-Fenton-Neutralization (CF-F-N) and Coagulation-Flocculation-Electro-Fenton-Neutralization (CF-EF-N), based on Life Cycle Assessment (LCA) approach. The CF-F-N and CF-EF-N were optimized at laboratory scale and compared through LCA, using the IPCC-2013 and ReCiPe-2016 midpoint and endpoint methods. The highest CO2 emissions relied on the wastewater primary treatment by CF. This due to the high amount of hazardous sludge generated and the technology necessary for its disposal (i.e., 16.89 kg CO2-Eq/FU for underground deposit in security cells or 47.52 kg CO2-Eq/FU for incineration) as well as the consumption of reagents required for the treatment (alum, 7.72 kg CO2-Eq/FU; and slaked lime, 5.56 kg CO2-Eq/FU). Regarding the sequential processes, the EF-N presented lower carbon footprint (CFP) than the F-N (14.74 kg CO2-Eq/FU vs. 20.74 kg CO2-Eq/FU). Electricity (87.02% of the total CFP) and reagents (88.63% of the total CFP) denoted the main environmental hotspot during the EF-N and F-N, respectively. The EF-N, compared to the F-N, had an inferior incidence in 14 of the 18 impact categories analyzed using the ReCiPe-2016 method at the midpoint level. This is the result of low consumption of reagents and auxiliary chemicals. The electricity was also found as main environmental hotspot of the EF-N. The ReCiPe-2016 method at the endpoint level showed that the EF-N resulted in lower environmental load in all impact categories. The economic performance (11.91 USD/m3 for CF-EF-N vs. 13.66 USD/m3 for CF-F-N) and LCA demonstrated the competitiveness of the electrochemical sequential process compared to the chemical one. The CF-EF-N can be considered more environmentally sustainable technology. [ABSTRACT FROM AUTHOR]

Most of the current researches still stay at attaching the catalyst to the sheet electrode through an additional binder, which is an inefficient and complicated process that also affects the stability of the electrode. In this study, porous graphite particles (GP) were used as the carrier, and in situ growth method was used to prepare PANI-GP electrodes which was carbonized to prepare a nitrogen-doped modified cPANI-GP electrode with a large specific surface area. Then controlling the carbonization temperature, 700cPANI-GP with high content of pyridinic N is prepared. GP, PANI-GP and cPANI-GP were characterized by scanning electron microscope, Raman spectroscopy, X-ray electron energy spectroscopy and nitrogen desorption adsorption. The existence of hydroxyl radical (·OH) was identified by electron spin resonance technique. And, the phenacetin (PNT) was used as the target pollutant to confirm the electrocatalytic performance of the particle electrode. The results show that in the electro-Fenton system with a 700cPANI-GP cathode, the degradation rate of PNT and the removal rate of COD reach 92.1% and 83.3% in 2 h, respectively, when the pH is 3 and the current density is 7 mA cm−2. And, in the reaction system using 700cPANI-GP electrode as the cathode, the concentration of ·OH is largest that confirm pyridinic N is the active site that activates H2O2 into ·OH. [ABSTRACT FROM AUTHOR]

A porous carbon cathode was prepared using graphite, polytetrafluoroethylene (PTFE), and degreasing cotton (DC) through sintering treatment. The carbonization of DC by heat treatment played an ideal role in pore-creating, which weakened the mass transfer resistance of O2, and as a result, the adoption of degreasing cotton significantly improved the performance of H2O2 electro-generation. The optimized cathode was able to generate 567 mg L−1 H2O2 with a current efficiency (CE) of 86.7% by the electrochemical reaction of 60 min in a divided reactor. Furthermore, the degradation of rhodamine B (RhB) was carried out by an electro-Fenton system using the optimal cathode selected. The developed electro-Fenton system exhibited an excellent RhB degradation performance. The RhB solution of 50 mg L−1 was decolorized completely by the treatment of 10 min. Moreover, the degradation of 50~90 mg L−1 RhB solution presented over 90% TOC removal by the treatment of 120 min, indicating the ideal mineralization of organic pollutants. In addition, it was found that •OH was the major oxidizing specie responsible for the organics degradation. Finally, the possible pathway of RhB degradation in the electro-Fenton system was proposed by GC-MS analysis. The adoption of natural fibers for pore-creating provides an innovative and low-cost method to prepare porous cathode, which may promote the application of electro-Fenton oxidation in wastewater treatment. [ABSTRACT FROM AUTHOR]

Vinasse wastewater from tequila industry that has been conventionally treated is usually characterized by a chemical oxygen demand (COD) above 150 mg L−1, which is the maximum content permitted for discharge by Mexican Regulation. In order to increase the wastewater quality, different processes were applied, and from the experimental results, the advantages and limitations were analyzed. In this way, although Fenton experiments showed acceptable COD removal efficiencies (79–90%), operation as well as cost limit its adoption as a viable technology. Therefore, additional experiments explored electro-Fenton (EF) as well as adsorption coupled to EF in a tubular reactor. The corresponding data revealed that there was no additional increase in COD removal performance probably due to the low oxygen solubility in the electrolytic solution and the high pH that prevents the existence of Fe2+ ions necessary for the Fenton mixture. In view of these results, when an activated carbon (AC) filter was coupled to polarization at current densities between 0.5 and 2 mA cm−2, removal efficiencies from 71 to 81%, corresponding to final COD of 78 to 33 mg L−1, were achieved. Also, the adsorbent surface was continuously regenerated, promoting a more efficient adsorption and a longer service life for the AC filter. In this case, by using a current density of 0.5 mA cm−2, COD was reduced to sufficiently small values for discharge into natural water bodies, maintaining low energy consumption and therefore acceptable operation costs. [ABSTRACT FROM AUTHOR]

Imidacloprid (IMI) is a widely used systemic pesticide that acts on the central nervous system of insects. In Vietnam, IMI was imported and manufactured in large quantities for agriculture activities. The presence of high IMI levels in IMI manufacturing wastewater is an environmental concern as this chemical is highly toxic and difficult to remove by traditional methods. In this study, IMI degradation by electro-Fenton process using Fe3O4–Mn3O4 nanoparticle composite catalyst was investigated over ranges of pH, current density, reaction duration, Mn3O4/Fe3O4 ratio, catalyst dosage, and initial IMI concentration. Three kinds of electrodes (graphite-, platinum-, and boron-doped diamond) were also employed to compare their application potential. With BDD electrodes, experiment results showed that at a current density of 15.0 mA/cm2, a Mn3O4/Fe3O4 ratio of 1:3 (w/w), and a catalyst dosage of 2.5 g/l, 60.0 mg/l IMI was reduced to 0.9 mg/l after 180 min reaction at pH 4.0. Outputs of TOC and BOD5 were 0.8 ± 0.5 mg/l and 2.6 ± 0.3 mg/l, respectively, which reflects that nearly all organic compounds were mineralized in the experiment. BDD electrode also shows the best performance. In addition, it was found that catalyst dosage should be increased with the growth of IMI concentration. The limitation for this correlation was at IMI concentration of 60.0 mg/l, which corresponded to a catalyst dosage of 2.5 g/l. Some other conditions provided good performance with economic potential also found for external desire. [ABSTRACT FROM AUTHOR]

In the present study, heterogeneous electro-Fenton (EF) treatment using a sepiolite/pyrite (Sep/FeS2) nanocomposite was employed to degrade methylene blue (MB) dye. The morphology and structure properties of the prepared catalyst were thoroughly studied by field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and elemental mapping analysis. The EF studies were carried out in an undivided electrochemical cell equipped with a platinum (Pt) sheet as anode and graphite plate as cathode. Effects of initial pH, applied current intensity, catalyst dose and initial dye concentration on the mineralization of MB were examined, and their values were determined as 3.0, 1.0 g L−1, 50 mg L−1 and 150 mA, respectively. An almost total mineralization was acquired for a 50 mg L−1 MB solution in 75 min reaction time. The degradation mechanism using the Sep/FeS2-EF treatment was suggested with the analysis of intermediate products by liquid chromatography–mass spectrometry. Accounting for the high catalytic capability, chemical constancy and inexpensive cost, the Sep/FeS2 nanocomposite has great potential working as an EF catalyst for industrial applications. [ABSTRACT FROM AUTHOR]

Current work deals with the treatment of leachate nanofiltration concentrate which was exposed to ultrafiltration membrane treatment following anaerobic biological process and nitrification–dentrification process before. Advanced electrocoagulation processes [electro-Fenton (EF) and electro-persulfate (EF)] were applied to the wastewater characterized by high inert COD content arising from resistant organic matter. Response surface methodology and central composite design were employed for modeling and optimizing the processes. Adequacy of the model was examined by application of variance analysis that verified the conformity of experimental and predicted data. Under statistically obtained optimized conditions for COD removal (H2O2/COD ratio 1.42, current 2.27 A, pH 2.9, and reaction time 30.3 min for EF; and S2O8−2/COD ratio 1.72, current 1.26 A, pH 5.0 and reaction time 34.8 min for EP processes), predicted COD removal efficiencies were determined to be 67.1% and 72.6% for EF and EP treatments, respectively. By performing experimental sets for validation, 60.8% and 71.4% COD removals through EF and EP processes were obtained under these conditions. NF concentrate COD fractions were also determined before and after treatment processes. Soluble COD fraction increased from 71.4 to 83.2% and 87.7% whereas biodegradable COD fraction increased from 12.2 to 19.2% and 32.5% after EF and EP processes, respectively. Results of the study showed that both EF and EP processes were efficient alternatives for leachate NF concentrate treatment but EP process can be preferred due to lower energy consumption. Article Highlights: Electro-Fenton and Electro-Persulfate processes were applied for inert COD removal from leachate nanofiltration concentrate. Response surface methodology approach using Central Composite Design was employed for modelling. Under statistically optimized conditions 60.8% and 71.4% COD removals through EF and EP processes were obtained. Biodegradable COD fraction increased and insoluble COD fraction was significantly converted to soluble fraction. Total cost of EF process (5.0 €/ m3) was found to be higher than that of and EP process (2.8 €/ m3). [ABSTRACT FROM AUTHOR]

Electro-Fenton (EF) and alkaline/persulfate systems are two important systems capable of producing ·OH and SO4−· for environmental remediation. However, the major drawbacks of these two processes are the necessity of operating in low pH (2.0–4.0) or high pH environments, where the acidification/alkalization steps and subsequent neutralization processes significantly increase the operation cost and limit their applicability. In this work, we propose a system that can simultaneously electrochemically develop acidic and alkaline environments in two divided compartments to solve this problem. pH values of 2.9–3.2 and 10.9–11.9 in two separated compartments were obtained, and the results show that the electrochemically developed acidic environment (pH of 3 and 4) enhances the EF process by facilitating H2O2 electrogeneration and Fe2+ regeneration. The alkaline environment (11 and 12) that was also developed electrochemically is effective for persulfate activation. Finally, the system was found to be effective for Rhodamine B removal using an acidic pH-enhanced EF process and an alkaline pH-supported persulfate process. [ABSTRACT FROM AUTHOR]

The 'water reuse' option is increasingly becoming crucial in the context of global warming and water scarcity. Water reuse consists in the recycling of water toward sectors requiring different water qualities, such as industry, agriculture and human consumption. Water treatment by biological methods is cheap, yet they do not to remove completely recalcitrant pollutants. Alternatively, advanced oxidation processes (AOP) for wastewater treatment are more efficient because a strong oxidizing agent such as the hydroxyl radical (•OH) is generated under mild conditions. In particular, processes of electrochemical advanced oxidation have recently attracted attention because they allow continuous and in situ electrocatalytic generation of strong oxidizing species under mild conditions, with the advantage of avoiding external addition of chemicals. In addition, energy can be provided by solar light in photochemical electrolysis systems. Here we review photoelectrochemical reactors. We present reactions and synergetic mechanisms. Under optimal conditions, eight •OH production sites are identified in photoelectro-Fenton combined with photoanodic oxidation and photocatalysis or photoelectrocatalysis. Reactions are controlled by pH, applied wavelength, and competition between reactions requiring the same reagent. Then we discuss reactor design and catalysis. Various reactor configurations are presented: sequential and hybrid reactors, divided and undivided cells, flow cell and stirred tank reactor; and light source positioning can be external, immersed, vertical, horizontal, at the top, at the bottom, or on the side of the reactor. The distance between the light source and the electrode should be minimized to obtain maximal synergy and maximum quantum yields. Hybrid reactors in undivided flow cells are best for the lower footprint, the possibility to regenerate iron catalysts, and the enhancement of mass transfer, compared with stirred tank reactors. Moreover, the interelectrode gap can be easily controlled in flow cell, which allows the optimization of the penetration depth when the light is applied through the reactor. [ABSTRACT FROM AUTHOR]

A combined process comprised of electro-Fenton and bioslurry (EF–bioslurry) was developed at lab scale for remediating a real coking plant soil with an initial polycyclic aromatic hydrocarbons (PAHs) content of 3605 mg/kg. Sodium citrate was used as a complexant to keep the iron in solution at near-neutral pH conditions for increasing the reaction rate. The appropriate order of application was to perform EF process followed by bioslurry, which was evaluated through analysis of degradation characteristics of individual processes. The optimum EF duration was assessed through an analysis of the induced changes in PAHs degradation and bacterial counts. The optimum application time of EF process was determined to be 24 h. The removal of PAHs was 95.2% for EF–bioslurry after 40 days, and the efficiency was increased by almost 150%, compared with the individual bioslurry treatment. The EF reaction caused significant cell death and high inhibition to polyphenol oxidase (PPO) activity of soil. The bacterial activity and counts in the slurry recovered rapidly after EF oxidation through the addition of raw soil (2%, w/w). Therefore, the combined process of EF–bioslurry process may be an efficient and promising approach for the remediation of highly organic-contaminated soil. [ABSTRACT FROM AUTHOR]

Treatments of simulated effluent solutions containing the Reactive Black 5 (RB5) were carried out by electrochemical, photoelectrochemical, electro-Fenton and photoelectro-Fenton methods using a one-compartment cell with a boron-doped diamond anode and a 3% of manganese dioxide nanoflowers supported on a carbon Vulcan XC72 gas diffusion electrode cathode. In the photo-assisted processes, the solution was irradiated using a 40-W UVC lamp immersed in the treated solution. For Fenton-based processes, only 5 min was required to attain 95% (photoelectro-Fenton) and 93% (electro-Fenton) RB5 dye degradation. When conversion to CO2 is taken into account after 6-h treatment, electrochemical method mineralized ~ 13% of the organic load whereas removals greater than 90% were attained using the Fenton-based processes. These completely different results can be explained by the distinct spatial availability of the generated hydroxyl radical: only near the anode surface as in electrochemical-based processes or added to those distributed across the solution bulk as in Fenton-based processes. [ABSTRACT FROM AUTHOR]

The paper reports the oxidative decolorization of the direct blue 14 (DB-14) dye in an aqueous phase via an ecologically friendly electrochemical advanced oxidation process. The investigation of several experimental conditions such as the solution pH, initial concentrations of the oxidant, the dye, and current density was carried out in a single-compartment electrolytic cell with the use of an iron sheet as anodic material, the graphite plate being the cathodic material. The optimal operating conditions were found to be as follows: (DB-14)0—500 mg/L; (H2O2)0—35 mM concentration; pH 3 using 0.1 M Na2SO4 salt as supportive electrolyte at room temperature. It has been observed that the dissolved iron (Fe2+) content from the anode was continuously increasing in aqueous media on passing a constant current to it. Initially, it was 1.58 mM, then 4.46 mM (after 30 min of reaction time), and 5.35 mM of dissolved Fe2+ for 60 min of the reaction time. The study of kinetics for the decolorization of DB-14 shows that the degradation kinetics follows the second order, with the reaction rate being constant: k2—0.5 × 10–4 mgL–1 min–1. Electrochemical oxidation of DB-14 reduces the chemical oxygen demand of the colored solution. The unit energy demand, expressed in kWh/kg of the chemical oxygen demand reduced, for optimum experimental parameters have also been determined. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) electrogenerated via two-electron oxygen reduction reaction at cathode plays an important role in electrochemical advanced oxidation processes for organic pollutants removal from wastewater. Herein, multi-walled carbon nanotubes and carbon black co-modified graphite felt electrode (MWCNTs-CB/GF) was prepared as an efficient cathode for H2O2 electrogeneration and amoxicillin removal by anodic oxidation with hydrogen peroxide (AO-H2O2) and electro-Fenton (EF) under mild pH condition. Besides, the physicochemical and electrochemical properties of MWCNTs-CB/GF were characterized by scanning electron microscopy, N2 adsorption and desorption experiment, contact angle measurement, X-ray photoelectron spectroscopy, and linear sweep voltammetry. Compared with GF, MWCNTs-CB/GF showed a higher H2O2 generation of 309.0 mg L−1 with a current efficiency of 60.9% (after 120 min) and more effective amoxicillin removal efficiencies of 97.5% (after 120 min) and 98.7% (after 30 min) in AO-H2O2 and EF (with 0.5 mM Fe2+) processes, under the condition of current density 12 mA cm−2 and initial pH 5.5. Meanwhile, the TOC removal efficiency was 45.2% during EF process after 120 min. Anodic oxidation, H2O2 oxidation, and methanol capture indicated that ∙OH generated via electro-activation reaction at MWCNTs-CB/GF and Fenton reaction in solution played the dominant role in amoxicillin removal. Moreover, the TOC removal was associated with ∙OH generated during Fenton reaction in the solution. The major intermediates of AMX degradation by EF process were identified using LC-MS and the possible degradation pathways were proposed containing of β-lactam ring opening, hydroxylation reaction, decarboxylation reaction, methyl groups in the thiazolidine ring oxidation reaction, bond cleavage, and rearrangement processes. All of the above results proved that MWCNTs-CB/GF was an excellent cathode for AMX degradation under mild pH condition. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the degradation and mineralization of Malachite Green (MG) in an electro-Fenton process (EFP). We studied the influence of several important parameters including solution pH (2–11), current density (0–20 mA/cm2), H2O2 concentration (0–200 mg/L) and MG concentrations (200, 600, 1000, 1500, 2000, 3000 mg/L) at different reaction time (2.5–30 min). The intermediates produced during the degradation were determined by GC–MS. The optimum pH, current density and H2O2 concentration were found to be approximately 3, 10 mA/cm2 and 50 mg/L, respectively. It was concluded that acidic pH was required to increase the efficiency of the EFP. At optimum conditions and a reaction time of 15 min, MG was completely removed without any significant variation in the corresponding maximum wavelengths or new absorption bands. Due to formation of intermediates, almost all the organic compounds were completely mineralized (95.3%) to CO2 and water at reaction time of 30 min. Results indicated the effect of hydroxyl radical (·OH) on MG degradation is greater than that of superoxide radical scavenger ( O 2 · - ). The results showed that the degradation process of MG followed pseudo-first-order kinetic model and the treatment time required in EFP was 4.6 times lower than ECP. Furthermore, the results showed that EFP was an extremely efficient process for degradation and mineralization of a high concentration of MG (1000 mg/L) at a short reaction time (30 min). [ABSTRACT FROM AUTHOR]

To achieve superior advanced oxidation processes (AOPs), transitional state activators are of great significance for the production of active radicals by H2O2, while instability limits their activation efficiency. In this study, density functional theory calculation (DFT) results showed that Cu+ exhibits excellent H2O2 activation performance, with Gibbs free energy change (ΔG) of 33.66 kcal/mol, two times less than that of Cu2+ (77.83 kcal/mol). Meanwhile, an electro-Fenton system using Cu plate as an anode was proposed for in situ generation of Cu+. The released Cu with low-valence state can be well-confined on the surface of the exciting electrode, which was confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis spectroscopy. The hydroxyl radicals in this Cu-based electro-Fenton system were determined by the electron spin resonance (ESR). The nitrobenzene degradation ratio was greatly increased by 43.90% with the introduction of the proposed in situ electrochemical Cu+ generation process. Various characterization results indicated that the production of Cu+ was the key factor in the highly efficient Cu-based electro-Fenton reaction. [ABSTRACT FROM AUTHOR]

This study investigates the degradation and mineralization of BTEX by heterogeneous electro-Fenton process using GO/MWCNT/Fe3O4 as a catalyst and MWCNT-Ce/WO3/GF as an electrode. The nanoscale MWCNT-Ce/WO3 composite catalyst was distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. After optimization of pH and time variables, the Box–Behnken experimental design (BBD) and response surface methodology (RSM) were used to design and optimize the performance of proposed system and energy consumption. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.98) and adj-R2 (0.97). The significance levels of linear and interaction effects of the reaction parameters on process efficiency were obtained. Then, the optimization of the working conditions for the design of a sustainable treatment system with optimum efficiency was carried out using a response surface methodology. The experiment carried out in the calculated optimal conditions for the electro-Fenton degradation process (current intensity 300 mA, catalyst dosage of 0.6 g, initial BTEX concentration of 100 ppm, and electrode distance of 1 cm) showed a BTEX removal of 73.2% and energy consumption of 12.3 (kWh/m3) close to the theoretical value predicted by the model 73. 2% and 11.8 (kWh/m3), respectively. Furthermore, the reusability test of GO/MWCNT/Fe3O4 nanocomposite after several cycles confirmed the high catalytic activities of adsorbent. Comparing the proposed system with conventional GF electrode and Fe2+ catalyst showed that modification of cathode and catalyst led to increasing COD removal efficiency by around 36.6 and 31.6%, respectively. The findings of present study revealed that the proposed heterogeneous electro-Fenton process can be utilized as pre-treatment technology to improve the biodegradability and reduce the organic load of wastewater by combine oxidation and coagulation. [ABSTRACT FROM AUTHOR]

The magnetite (Fe3O4) nanoparticles were synthesized and supported on the reduced graphene oxide. The characterization of the catalyst was performed by FT-IR, VSM, SEM, XRD, and BET techniques. The obtained results indicated that the in situ synthesis of Fe3O4 using coprecipitation method caused the homogenous formation of magnetite nanoparticles on the surface of reduced graphene oxide (average particle size ~ 71.032 nm) with high stability and catalytic activity toward electro-Fenton removal of Reactive Red 195. The effect of various factors (current intensity, initial pollutant concentration, catalyst weight, and pH) was evaluated by response surface methodology using central composite design. The analysis of variance exhibited that the experimental data are in accordance with the quadratic model. At the optimized operation condition (current intensity of 194.96 mA, initial RR195 concentration of 168.43 mg L−1, 2.0 mg catalyst at pH 3.04), the RR195 and COD removals reached 93.34% and 75.27% in 60 min, respectively. The DFT simulation was performed at B3LYP level of theory. The HOMO–LUMO energy gap was reduced from 2.536 to 2.514 eV after supporting of Fe3O4 on the reduced graphene oxide, which demonstrated the higher electrical conductivity. The RR195 removal followed pseudo-first-order kinetics model (k = 0.044 min−1, R2 = 0.9938). The stability of the catalyst against leaching was evaluated, and only 2.4% of iron was leached. The catalyst almost remained efficient after six cycles. [ABSTRACT FROM AUTHOR]

This paper describes the removal of methylene blue (MB) dye using [Fe(II)]-based gas diffusion electrodes (GDEs). GDEs were developed by rolling carbon black and polytetrafluoroethylene as a conductive layer for efficient oxygen reduction reaction, with an [Fe(II)] ink layer ( 5 mg cm - 2 loading) to conduct Fenton chemistry. The GDEs demonstrated the ability to remove the colour and mineralize MB dye in an undivided, three-electrode cell. Colour removal achieved 99% in a 150 cm 3 solution containing 100 ppm of MB dye at constant potential of - 1.0 V vs. Hg/HgSO 4 in 240 min. The kinetics of the MB decolouration showed pseudo-first-order batch kinetics. The results demonstrated that a GDE containing immobilized Fe(II) ions appears to be a viable option for the environmental remediation of organic dyes in wastewater by an anodic Fenton oxidation. [ABSTRACT FROM AUTHOR]

In this study, we report an effective degradation method for trace level beta-blockers (propranolol and acebutolol) in hospital wastewater using a new droplet flow-assisted heterogeneous electro-Fenton reactor (DFEF) system. Biogenic iron–carbon nanocomposites (RHS/C-x% Fe) as eco-friendly and low-cost heterogeneous Fenton catalysts were synthesized from rice husk via hydrolytic sol–gel routes. Here, we demonstrate the use of natural air as a nebulizing agent for fast and continuous catholyte air saturation and Fenton catalyst transfer to the cathode electrode. The effects of key operational parameters were evaluated and optimized using central composite design. Results clearly indicated that enhanced beta-blocker degradation was mainly dependent on the interactive effects of electrolysis time, current density, and catalyst dosage. Fast degradation efficiencies (≥ 99.9%) was recorded at neutral pH conditions. The decay followed pseudo-first-order kinetics with degradation rates of up to 2.72 × 10−2 and 2.54 × 10−2 min−1 for acebutolol and propranolol, respectively. The synergistic contribution of •OHbulk attributable to DFEF process and •OHadsorbed for anodic oxidation (AO) at the anode electrode significantly enhanced the degradation process. Compared to AO, the conventional flow-assisted electro-Fenton (FEF), and the batch electro-Fenton (BEF), DFEF degradation efficiency followed a decreasing order: DFEF ˃ FEF ˃ BEF˃ AO. This trend in performance was mainly due to the fast and continuous cathodic electro-generation of H2O2 and Fe2+ regeneration. Additionally, in order to elucidate degradation mechanism, we used a combination of DFEF approach with liquid chromatography-tandem mass spectrometry analysis. This approach demonstrates a simple, cleaner, and highly efficient degradation approach for trace level recalcitrant pollutants in a complex aquatic matrix, without the need for external chemical addition and pH adjustment. [ABSTRACT FROM AUTHOR]

Background: Composting plant leachate is considered as one of the highly polluted wastewaters which is necessary to be treated by simple, economic, fast and environmentally compatible methods. In this study, treatment of fresh composting plant leachate by electro-Fenton (EF) process was investigated. Methods: The effect of various input variables like pH (2–7), DC currents (1.5–3 A), H2O2 concentrations (theoretical ratio H2O2/COD: 0.1–0.6), TDS changes (4–6%), feeding mode, and BOD/COD ratio at the optimal point were studied. The settling characteristics of the waste sludge produced by the treatment (sludge volumes after 30-min sedimentation: V30) were also determined. Artificial neural network (ANN) approach was used for modeling the experimental data. Results: Based on the results, the best removal rate of COD was obtained at pH: 3, 3 A constant DC current value, 0.6 theoretical ratio H2O2/COD and the feeding mode at four step injection. BOD/COD ratio at the optimal point was 0.535 and the maximum COD removal was achieved at TDS = 4%. In the optimal conditions, 85% of COD was removed and BOD/COD ratio was increased from 0.270 to 0.535. The data follow the second-order kinetic (R2 > 0.9) and neural network modeling also provided the accurate prediction for testing data. Conclusion: Results showed that EF process can be used efficiently for treatment of composting plant leachate using the proper operating conditions. [ABSTRACT FROM AUTHOR]

The first application of a novel electro-Fenton (EF) for coking wastewater (CW) treatment at the original pH (6.80) by using tripolyphosphate (TPP) ligand was proposed. Total organic carbon (TOC) decay of CW followed a pseudo-first kinetic rate constant with an apparent rate constant (kapp) of 1.07 × 10−2 min−1 for the EF in the presence of TPP (EF/TPP), which was 2.10 times higher than that of conventional EF (kapp = 5.10 × 10−3 min−1) working at pH 3. The high efficiency of EF/TPP at neutral pH was mainly attributed to the newly formed Fe-O-P coordination in the iron-ligand compound (Fe2+-TPP) supported by UV-absorption spectra results, activating oxygen to produce •OH and hence enhancing the oxidation capacity. Key operating parameters of CW mineralization by EF/TPP including Fe2+ concentration and pH value were systematically investigated. Excitation-emission matrix (EEM) spectra technique was used to assess the variance of dissolved organic matters during the EF/TPP process. Results showed an 81% mineralization of CW after 3 h electrolysis coupled with a low energy consumption (0.129 kWh g−1 TOC) which were obtained by the EF/TPP process. Microtox toxicity demonstrated that TPP could reduce the toxicity of raw CW and importantly, it showed that EF/TPP was effective for detoxification. Mechanism study via simulated matrix with similar components as CW revealed that •OH produced both from Fenton and Fe2+-TPP activation together with the generated active chlorine was responsible for CW mineralization. In summary, the TPP-assisted EF process was presented as a promising technique for extending coking wastewater treatment at near-neutral pH with a high mineralization. [ABSTRACT FROM AUTHOR]

In this work photo-electro-Fenton (PEF) processes using a dimensionally stable anode-gas diffusion electrode (DSA-GDE) system under light emission diodes (LED)-type radiation were used in the degradation of the angiotensin-II-receptor antagonists (ARA II), valsartan (VAL), and losartan (LOS), which are used in the treatment of hypertension diseases, and are considered among the emerging contaminants (ECs). Organic acids as citric, tartaric, and oxalic acids were used as complexing agents of iron ions in order to maintain the performance of the Fenton reaction at near-neutral pH value. The results show that at 3.42 mA/cm2 after 90 min of electro-Fenton (EF) treatment, degradation of 70% of VAL and 100% of LOS were observed. Total degradation of VAL and LOS was reached with a PEF process at the same time with mineralization of 30%. When citric and tartaric acids were used instead of oxalic acid, similar results were obtained, i.e., total degradation of both compounds, LOS and VAL, after 90 min of treatment. The degradation performance can be attributed to the increase of the initial dissolved iron in the system, facilitating the Fe3+/Fe2+ turnover in the catalytic photo-Fenton reaction and consequently, hydroxyl radical (•OH) production. In addition, the increased photo-activity of the complexes can be associated with their high capability to complex Fe3+ and to promote ligand-to-metal charge transfer, which is of key importance to feed Fe2+ to the Fenton process. The results show that the system evaluated was more efficient to eliminate sartan family compounds using LED lighting in comparison with traditional UV-A lamps used in this kind of work. Moreover, three transformation products of VAL degradation and two transformation products of LOS degradation were identified by high-resolution mass spectrometry (HRMS) using hybrid quadrupole-time-of-flight (QTOF) MS and, at the end of the PEF system, the several organic compounds accumulated and no mineralized were effectively treated in a subsequent aerobic biological system. [ABSTRACT FROM AUTHOR]