The “In-cell” and “Ex-cell” Fenton treatment of phenol, 4-chlorophenol and aniline

A comparative study of phenol, 4-chlorophenol and aniline degradation with the electro-generation of H₂O₂ at gas-diffusion electrodes was carried out under three different conditions: electro-Fenton^® treatment in an undivided cell; electro-Fenton treatment in the catholyte of a membrane cell divided by a proton-exchange membrane (in-cell electro-Fenton membrane process); and a treatment of polluted solution in the cathode space of a membrane cell with the generation of H₂O₂, followed by the addition of Fe(II) salt in the other reactor (ex-cell electro-Fenton process).An optimized cell design with no gap between the membrane and the anode, along with the appropriate choice of supporting electrolytes, ensured a voltage reduction with a membrane cell in comparison with that of an undivided cell. The accumulation of hydrogen peroxide in concentrations sufficient for the almost complete destruction (90–98%) of aromatic organic pollutants was achieved in all cases but the ex-cell process with the preparative electrolysis in the pilot scale membrane reactor separated by the proton-exchange membrane MK-40 showed higher treatment efficiency and lower specific energy consumption in comparison with known technologies. Damage of the gas-diffusion layer was observed in some tests which could be caused by alkaline conditions in the pores of the gas-diffusion cathode (GDE). The pH indicator paper showed a color specific for alkaline media in contact with the GDE treated in the solution with pH 3 in the bulk. A possible explanation could be that even in acid media, hydrogen peroxide generation in pores of the gas diffusion layer proceeds with formation of HO ₂ ^? which is common for alkaline media and consecutive protonation occurs at the interface with the acid solution.     

Comparative study of hydrogen peroxide electro-generation on gas-diffusion electrodes in undivided and membrane cells

The generation of hydrogen peroxide by means of the cathodic reduction of oxygen at gas-diffusion electrodes with a near 100% current efficiency was achieved in concentrations sufficient for the mineralization of refractory organics in Fenton treatment. A decrease in current efficiency over time at high temperatures and high current densities was observed. The polarization study carried out in potentiostatic, potentiodynamic and galvanostatic modes in 0.5 M Na₂SO₄ solution at pH 3 showed that the destruction of hydrogen peroxide at the cathode of the electrochemical reactor, as well as its chemical decomposition in the bulk solution, takes place at a significantly lower rate than the oxidation of H₂O₂ at the Ti–IrO₂ anode. Preparative electrolysis in the membrane reactor showed much higher current efficiencies for H₂O₂ electro-generation in comparison with tests carried out in an undivided cell. The performance of different proton-exchange membrane in this process was studied and a membrane cell with a heterogeneous MK-40 type PEM was found to be suitable. An optimized cell design, the appropriate selection of electrodes, supporting electrolytes, and a membrane resulted in a lower voltage in the membrane cell in comparison with the undivided cell.     

Degradation of pentachlorophenol by an electroenzymatic method using immobilized peroxidase enzyme

In this study, pentachlorophenol (PCP) was degraded by the electroenzymatic method, which combines the enzymatic catalysis and the electrogeneration of hydrogen peroxide (H₂O₂). The experiments were conducted in a two-compartment packed-bed reactor using horseradish peroxidase (HRP) immobilized electrode. The highest production of H₂O₂ and the current efficiency were observed at −0.4 V vs. Ag/AgCl and a flow rate of 1 mL/min. The highest initial degradation rate and degradation efficiency of PCP were achieved at pH 5 and 25 °C. Under the conditions, the electrolysis was compared with an electrochemical method. The presence of chloride ion indicates that PCP was dechlorinated at the initial period of degradation. According to the proposed breakdown pathway and the intermediates, the electroenzymatic method showed an improved degradation ability compared to an electrochemical method.     

Electro-Fenton degradation of azo dye using polypyrrole/anthraquinonedisulphonate composite film modified graphite cathode in acidic aqueous solutions

Amaranth azo dye has been degraded by electro-Fenton method using an undivided cell containing the polypyrrole (PPy)/anthraquinonedisulphonate (AQDS) composite film modified graphite cathode and Pt anode. In acidic media, the PPy/AQDS composite film exhibits the characteristic of gas diffusion cathode and is highly efficient for hydrogen peroxide electrogeneration with high generation rate and current efficiency. This new electro-Fenton system can degrade amaranth azo dye efficiently in various acidic solutions. The amaranth decay and total organic carbon (TOC) removal were determined as a function of pH, cathode potential, Fe²⁺ and doping AQDS concentrations. Total dye decay and 80.3% mineralization were achieved at the optimum conditions (pH 3.0, E_cath = −0.65 V vs. SCE, 2.0 mM Fe²⁺ concentration). The electrochemical stability and electrocatalytic activity of the composite film after use in electro-Fenton process were also investigated using cyclic voltammetry (CV) and Fourier transfer infrared (FTIR) spectroscopy technologies.     

Electrogeneration of hydrogen peroxide on a novel highly effective acetylene black-PTFE cathode with PTFE film

A novel acetylene black-PTFE cathode for electrogeneration of hydrogen peroxide (H₂O₂) was fabricated using acetylene black powder (ABP) as catalyst, PTFE as binder. The effect of mass ratio of ABP to PTFE, solution pH (3–11), applied current density (5–20 mA cm⁻²) and surface hydrophobic property on the activity and useful life of cathode was investigated using a two-electrode undivided cell fed with air at 2 L min⁻¹ in Na₂SO₄ solution of 0.05 M, and the characteristics of cathode were examined by FTIR spectra, BET measurement, SEM image and CV study. The experimental results showed that: (1) so far the activity of cathode is the highest for the electrogeneration of H₂O₂ with air feed, at pH 3 and the current density of 20 mA cm⁻² the average H₂O₂ generation rate reaching 58.9 mg L⁻¹ h⁻¹ cm⁻² during 150 min of electrolysis and the current efficiency being 92.7%; (2) a proper and stable surface hydrophobic property could significantly increase the useful life of cathode; (3) the cathode had a remarkable restoration and regeneration performance.     

Mineralization of an azo dye Acid Red 14 by photoelectro-Fenton process using an activated carbon fiber cathode

The mineralization of an azo dye Acid Red 14 (AR14) by the photoelectro-Fenton (PEF) process was studied in an undivided electrochemical reactor with a RuO₂/Ti anode and an activated carbon fiber (ACF) cathode able to electrochemically generate H₂O₂. Anodic oxidation and UV irradiation of AR14 were also examined as comparative experiments. Results indicate that the electro-Fenton process yielded about 60–70% mineralization of AR14, while the photoelectro-Fenton could mineralize AR14 more effectively (more than 94% total organic carbon (TOC) removal) even at low current densities assisted with UV irradiation after 6 h electrolysis. The mineralization current efficiency (MCE) of the PEF process increased with the increasing AR14 concentrations. In addition, the initial solution pH ranging from 1.49 to 6.72 had little influence on the TOC removal probably due to the formation of organic carboxylic acids which balanced the pH increase caused by the cathodic generation of hydrogen gas. The ACF cathode showed a long-term stability during multiple experimental runs for degradation of AR14, indicating its good potential for practical application in treating refractory organic pollutants in aqueous solutions.     

Advanced oxidation of cork‐processing wastewater using Fenton's reagent: kinetics and stoichiometry

This work evaluates Fenton oxidation for the removal of organic matter (COD) from cork‐processing wastewater. The experimental variables studied were the dosages of iron salts and hydrogen peroxide. The COD removal ranged from 17% to 79%, depending on the reagent dose, and the stoichiometric reaction coefficient varied from 0.08 to 0.43 g COD (g H₂O₂)^?1 (which implies an efficiency in the use of hydrogen peroxide varying from 17% to 92%). In a study of the process kinetics, based on the initial rates method, the COD elimination rate was maximum when the molar ratio [H₂O₂]_o:[Fe²⁺]_o was equal to 10. Under these experimental conditions, the initial oxidation rate was 50.5 mg COD dm^?3 s^?1 with a rate of consumption of hydrogen peroxide of 140 mg H₂O₂ dm^?3 s^?1, implying an efficiency in the use of the hydrogen peroxide at the initial time of 77%. The total amount of organic matter removed by Fenton oxidation was increased by spreading the H₂O₂ and ferrous salt reagent over several fractions by 15% for two‐fractions and by 21% for three‐fractions. Copyright © 2004 Society of Chemical Industry     

The sonochemical decolorisation of textile azo dye CI Reactive Orange 127

In the present study, Fenton and sono‐Fenton processes were applied to the oxidative decolorisation of synthetic textile wastewater including CI Reactive Orange 127 and polyvinyl alcohol. Process optimisation [pH, ferrous ion (Fe²⁺) and hydrogen peroxide (H₂O₂)], kinetic studies and their comparison were carried out for both of the processes. The sono‐Fenton process was performed by indirect sonication in an ultrasonic water bath, which was operated at a fixed 35‐kHz frequency and 80 W power. The optimum conditions were determined as [Fe²⁺] = 20 mg l^?1, [H₂O₂] = 15 mg l^?1 and pH = 3 for the Fenton process and [Fe²⁺] = 25 mg l^?1, [H₂O₂] = 5 mg l^?1 and pH = 3 for the sono‐Fenton process. The colour removals were 89.9% and 91.8% by the Fenton and sono‐Fenton processes, respectively. The highest decolorisation was achieved by the sono‐Fenton process because of the production of some oxidising agents as a result of sonication. Consequently, ultrasonic irradiation in the sono‐Fenton process slightly increased the colour removal to 91.8%, while decreasing the hydrogen peroxide dosage to one‐third of that of the Fenton process.     

Post-Treatment of Pulp and Paper Industry Wastewater by Advanced Oxidation Processes

The aim of this study was to investigate the effectiveness of chemical oxidation by applying ozonation, combination of ozone and hydrogen peroxide and Fenton's processes for decolorization and residual chemical oxygen demand (COD) removal of biologically pretreated pulp and paper industry effluents. The batch tests were performed to determine the optimum operating conditions including pH, O₃, H₂O_2, and Fe²⁺ dosages. H₂O₂ addition reduced the reaction times for the same ozone dosages; however combinations of ozone/hydrogen peroxide were only faintly more effective than ozone alone for COD and color removals. In the Fenton‘s oxidation studies, the removal efficiencies of COD, color and ultraviolet absorbance at 254 nm (UV₂₅₄) for biologically treated pulp and paper industry effluents were found to be about 83, 95, and 89%, respectively. Experimental studies indicated that Fenton oxidation was a more effective process for the reduction of COD, color, and UV₂₅₄when compared to ozonation and ozone/hydrogen peroxide combination. Fenton oxidation was found to have less operating cost for color removal from wastewater per cubic meter than the cost for ozone and ozone/hydrogen peroxide applications.     

Bio-electro-Fenton systems for sustainable wastewater treatment: mechanisms,novel configurations,recent advances,LCA and challenges. An updated review

Bio-electro-Fenton processes use biological electrons produced from bioelectrochemical systems to treat wastewater. The most significant advantages of bio-electro-Fenton systems are high effectiveness, low toxicity, gentle operation conditions, environmentally friendly treatment without sludge accumulation and energy conservation. Though promising, bio-electro-Fenton systems still face several challenges, such as high power density, H₂O₂ concentration, cathode materials, Fe²⁺ concentration and pH. This review comprehensively discusses the mechanisms of bio-electro-Fenton systems. Then, structural configurations are critically reviewed, including microbial fuel cells coupled with electro-Fenton systems, microbial electrolysis cells coupled with electro-Fenton systems and other bioelectrochemical systems coupled with electro-Fenton systems. Furthermore, recent advances in bio-electro-Fenton systems for wastewater treatment are introduced, including dye solution, pharmaceuticals and personal care products, oily wastewater, landfill leachate and other pollutants. In addition, the current challenges and specific future prospects of bio-electro-Fenton, such as possible mechanisms for improving the power output, electrode materials that are potentially useful, self-designed electrodes and methods of maintaining circumneutral pH values, are also explored. Heretofore, great progress in bio-electro-Fenton has been made, but further improvements are still needed in order to make this system more economical and practical. © 2020 Society of Chemical Industry     

Treatment of paper and pulp wastewater and removal of odorous compounds by a Fenton‐like process at the pilot scale

A Fenton‐like process, involving oxidation and coagulation, was evaluated for the removal of odorous compounds and treatment of a pulp and paper wastewater. The main parameters that govern the complex reactive system [pH and Fe(III) and hydrogen peroxide concentrations] were studied. Concentrations of Fe(III) between 100 and 1000 mg L^?1 and of H₂O₂ between 0 and 2000 mg L^?1 were chosen. The main mechanism for color removal was coagulation. The maximum COD, color and aromatic compound removals were 75, 98 and 95%, respectively, under optimal operating conditions ([Fe(III)] = 400 mg L^?1; [H₂O₂] = 500–1000 mg L^?1; pH = 2.5; followed by coagulation at pH 5.0). The biodegradability of the wastewater treated increased from 0.4 to 0.7 under optimal conditions and no residual hydrogen peroxide was found after treatment. However, partially or non‐oxidized compounds present in the treated wastewater presented higher acute toxicity to Artemia salina than the untreated wastewater. Based on the optimum conditions, pilot‐scale experiments were conducted and revealed a high efficiency in relation to the mineralization of organic compounds. Terpenes [(1S)‐α‐pinene, β‐pinene, (1R)‐α‐pinene and limonene] were identified in the wastewater and were completely eliminated by the Fenton‐like treatment. Copyright © 2006 Society of Chemical Industry     

Monitoring the Physicochemical and Chemical Treatment of Textile Wastewater using GC/MS,LC/MS and ‐MS/MS Techniques

Abstract

Conventional biological wastewater treatment processes often fail in the elimination of finishing agents contained in textile wastewater such as dyes, surfactants, and softeners. Therefore, discharges from the textile industry are known as a major source of water pollution reaching groundwater and even drinking water treatment. Physicochemical treatment and advanced treatment processes (AOP) were applied to eliminate the pollutants prior to discharge. Ozone (O₃), O₃/UV, hydrogen peroxide/UV (H₂O₂/UV), Fenton's reagent (Fe²⁺/H₂O₂) were applied to eliminate by oxidation while ultrasonication (US) alone, US/UV or powdered activated carbon (PAC) were used for the physicochemical treatment. Elimination was monitored by a conventional sum parameter analyses (COD, BOD, DOC) while gas chromatography/mass spectrometry (GC/MS) and liquid chromatography coupled with MS and tandem mass spectrometry (LC/MS and ‐MS/MS) was applied for follow‐up of pollutants and their degradation products. The application of PAC, Fenton, and O₃/UV resulted in the highest dissolved organic carbon elimination. A complete or partial elimination and/or degradation of non‐polar or polar pollutants was observed by GC/MS or flow injection analysis/MS (FIA/MS) respectively. LC/MS and MS/MS analyses confirmed that ethoxylated surfactants (AEO) present in the original wastewater could be oxidized or destroyed resulting in carboxylated AEO and polyethylene glycol (PEG) or even carboxylated PEG.     

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H₂O₂ electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O₂ reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H₂O₂ is also reported. Experiments were performed in 0.3 M K₂SO₄ at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L⁻¹ of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10⁻⁵ to 10⁻⁴ s⁻¹. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.     

Treatment of a mixture of three pesticides by photo- and electro-Fenton processes

In the present work, a comparative study of a mixture of three pesticides (chlortoluron, carbofuran and bentazon) has been investigated by advanced oxidation processes such as photo-Fenton and electro-Fenton. These processes are based on the in situ production of hydroxyl radical, a highly strong oxidant, which allows the degradation of organic pollutants until their mineralization into CO₂ and H₂O. For the photo-Fenton process, the effect of key parameters such as initial catalyst (Fe³⁺) concentration and hydrogen peroxide (H₂O₂) dosage were studied. Under optimal operating conditions, the evolution of total organic carbon (TOC) has been investigated for the two processes. Obtained results showed that more than 90% of TOC removal was obtained after only 2 h of photo-Fenton treatment whereas the electro-Fenton process needed 8 h of treatment. Nevertheless, the comparison of cost treatment shows that the photo-Fenton process is more expensive than electro-Fenton. The evolution of pesticide's concentration during treatment was determined by high performance liquid chromatography (HPLC). Inorganic ions released such as chloride, nitrate, sulphate and ammonium ions are identified and their kinetic evolution was measured by ion chromatographic analyses.     

Advanced Oxidation Processes for the Elimination of Drugs Resisting Biological Membrane Treatment

The recalcitrant pharmaceutical compounds carbamazepine, clofibric acid, diazepam, and diclofenac were monitored in municipal wastewater by ESI-LC-MS and -MS-MS in positive and negative mode. Although biological treatment by conventional and membrane bioreactor failed, the advanced oxidation methods using ozone (O₃), O₃/UV or hydrogen peroxide in combination with UV (H₂O₂/UV), successfully achieved their complete elimination. Target compounds could be confirmed as permanently present pollutants in Aachen-Soers wastewater in concentrations between 0.006 and 1.9 μg L^?1 prior to AOP treatment resulting in a complete elimination.     

Electrochemical oxidation of Crystal Violet in the presence of hydrogen peroxide

BACKGROUND: The combination of electrochemical oxidation using a Ti/RuO₂? IrO₂ anode with hydrogen peroxide has been used for the degradation of Crystal Violet. The effect of major parameters such as initial pH, hydrogen peroxide concentration, current density, electrolyte concentration and hydroxyl radical scavenger on the decolorisation was investigated. RESULTS: The decolorisation rate increased with initial pH and hydrogen peroxide concentration, but decreased with electrolyte and radical scavenger concentration. The decolorisation rate increased with current density, but the increase became insignificant after current density exceeded 47.6 mA cm^?2. On the other hand, hydrogen peroxide decomposition rate increased with initial pH and current density, but decreased with electrolyte and radical scavenger concentration. The amount of hydrogen peroxide decomposed during 30 min reaction increased linearly with hydrogen peroxide dosage. The main intermediates were separated and identified by gas chromatography–mass spectrometry (GC–MS) technique and a plausible degradation pathway of Crystal Violet was proposed. At neutral pH, the electrochemical process in the presence of hydrogen peroxide was more efficient than that in the presence of Fenton's reagent (electro‐Fenton process). CONCLUSION: The anodic oxidation process could decolorise Crystal Violet effectively when hydrogen peroxide was present. Almost complete decolorisation was achieved after 30 min reaction under the conditions 2.43 mmol L^?1 hydrogen peroxide, 47.6 mA cm^?2 current density and pH₀ 7, while 62% COD removal efficiency was obtained when the reaction time was prolonged to 90 min. Copyright © 2010 Society of Chemical Industry     

A new reactor coupling heterogeneous Fenton‐like catalytic oxidation with membrane separation for degradation of organic pollutants

BACKGROUND: There is growing interest in employing heterogeneous Fenton‐like catalysts in slurry to obtain higher activity. However, fine size particles create problems associated with recovery from the treated water. Therefore, it is highly desirable to develop a novel Fenton‐like process that not only has high degradation efficiency of organic pollutants, but also allows for easily reusing the catalysts. RESULT: A new reactor was investigated by coupling the heterogeneous Fenton‐like oxidation with membrane separation. Results showed that the FeY catalyst could be almost filtrated by a submerged micro‐filtration membrane in the reactor to continuously activate H₂O₂. For a FeY dose of 1 g L^?1 and a residence time of 120 min, the degradation efficiency of AO II reached 97%. CONCLUSIONS: In the new reactor, degradation of AO II occurred continuously and efficiently without an additional FeY separation process. The treatment capacity of this FeY catalyst for wastewater containing 100 mg L^?1 AO II in the reactor was estimated to be 82 times that of a reactor in which the catalyst could not be reused. The distinguishing technical feature of this reactor was the reuse of the Fenton‐like catalyst. Copyright © 2011 Society of Chemical Industry     

Multi‐phase electro‐chemical catalytic oxidation of wastewater

The removal of organic pollutants from synthetic wash wastewater by a combined multi‐phase electro‐catalytic oxidation method was evaluated using porous graphite as anode and cathode, and CuO–Co₂O₃–PO₄^3? modified kaolin as catalyst. The synergic effect on COD removal was studied when integrating the electro‐chemical reactor with the effective modified kaolin in a single undivided cell; the results showed that higher COD removal efficiency was obtained than those obtained using the individual processes. Under optimal conditions of pH 3, 30 mA cm^?2 current density, very effective reduction of organic pollutants was achieved with this combined electro‐chemical method. High removal efficiency (90%) of the chemical oxygen demand (COD) was obtained in 60 min in the treatment of simulated wash wastewater (anionic surfactant, sodium dodecyl benzene sulfonate [DBS]). This method was also applied to treat wastewater form paper‐making and resulted in a COD reduction of 84%. Based on the investigation, a possible mechanism of this combined electro‐chemical process was proposed. The pollutants in wastewater could be decreased by the high reactive OH? that were produced via the decomposition of electro‐generated H₂O₂ activated by the synergic effect of electro‐field and catalyst. The results indicate that the multi‐phase catalytic electro‐chemical oxidation process is a promising technique for wastewater treatment. Copyright © 2006 Society of Chemical Industry     

The addition of hydrogen peroxide in the electrocoagulation treatment for improving toxic organic matters removal: A comparative study

The role of hydrogen peroxide (H₂O₂) in the electrocoagulation (EC) treatment for removing toxic organic matters in wet-spun acrylic fibers (WAFs) manufacturing effluents was investigated. The addition of H₂O₂ in the EC resulted in electro-Fenton (EF) treatment, which improved the removal of organic pollutants. Biodegradability of the EF-treated effluents was significantly improved over the EF treatment and reached 0.18. In addition, evaluation of the toxicity of the treated effluents using luminous bacteria revealed that the EF treatment resulted in the greater removal of toxic compounds than the EC treatment, with 80.9% decline in the EC₅₀.     

Indirect Electrochemical Oxidation of Phenol in the Presence of Chloride for Wastewater Treatment

Electrochemical oxidation of phenol using a Ti/TiO₂‐RuO₂‐IrO₂ anode in the presence of chloride as the supporting electrolyte was investigated. The experiments were performed in an undivided batch reactor. Preliminary investigations showed that only a small fraction of phenol was oxidized by direct electrolysis, while complete degradation of phenol was achieved by indirect electrochemical oxidation using chloride as a supporting electrolyte. The effect of operating parameters such as initial pH, supporting electrolyte concentration, phenol concentration, and charge input was studied using Box‐Behnken second order composite experimental design. The effect of current density on COD removal was studied separately. TOC removal and AOX formation were studied for selected conditions. It was found that the formation of chlorinated organic compounds was pronounced at the beginning of electrolysis, but it was reduced to lower levels by extended electrolysis.