Comparative Study of Electrocoagulation and Electrooxidation Processes for the Degradation of Ellagic Acid From Aqueous Solution

A comparative study of electrocoagulation and electrooxidation processes for the degradation of ellagic acid from aqueous solution was carried out. For the electrocoagulation process, metallic iron was used as electrodes whereas graphite and RuO₂/IrO₂/TaO₂ coated titanium electrodes were used for the electrooxidation processes. The effect of the process variables such as initial pH, concentration of the supporting electrolyte, applied current density, electrolysis time, and anode materials on COD removal were systematically examined and discussed. Maximum COD removal of 93% was obtained at optimum conditions by electrocoagultion using an iron electrode. The ellagic acid was degraded completely by electrooxidation using graphite electrodes under the optimum conditions. During electrooxidation, the chloride ion concentration was estimated and the effect of the Cl^? ion was discussed. The finding of this study shows that an increase in the applied current density, NaCl concentration, and electrolysis time enhanced the COD removal efficiency. The UV–Vis spectra analysis confirms the degradation of ellagic acid from aqueous solution.     

Treatment of textile dye wastewater by using an electrochemical bipolar disc stack reactor

Textile dye house wastewater from a reactive dye processing unit was treated by using an electrochemical oxidation technique. The experiments were carried out in an electrochemical bipolar disc reactor using RuO₂ coated on titanium as anode and titanium as cathode. The sodium chloride present in the effluent was used as supporting electrolyte. Operating parameters such as current density, reservoir hold‐up and electrolysis time were studied for maximum Chemical Oxygen Demand (COD) reduction and other relevant parameters such as current efficiency and power consumption per kg of COD removal were calculated. The higher flow rate and lower reservoir hold‐up resulted in improved COD removal. The applied current density was also found to significantly influence the reduction of COD. A suitable mathematical model is also proposed to illustrate the relationship between the basic parameters. Pseudo mass transfer coefficients were also evaluated for different experimental conditions. Copyright © 2004 Society of Chemical Industry     

电催化处理含酚废水实验研究

通过静态实验对比研究了模拟含酚废水在二维电解槽和三维电解槽中的电化学氧化过程,考察了支持电解质浓度、电解电压以及初始pH值对对苯二酚去除效果的影响,比较了两种电解系统对含酚废水的处理效果。结果表明:对苯二酚去除率随电解质浓度增大而先增大后减小;随施加电压的增加,对苯二酚的去除率有所提高;接近中性的条件下有利于对苯二酚的去除。三维电极系统可在较低的支持电解质浓度条件下操作,更有利于含酚废水的有效处理。在pH=7的条件下,对苯二酚去除率可达90%以上。     

Study of electrochemical bleaching of <Emphasis Type="Italic">p</Emphasis>-nitrosodimethylaniline and its role as hydroxyl radical probe compound

In the present paper, research on the electrochemical bleaching of p-nitrosodimethylaniline (RNO) in different electrolyte systems is presented with special attention to the role of RNO as a selective hydroxyl radical probe compound. At a Ti/Pt₉₀–Ir₁₀ anode, RNO was found to be bleached in 0.050 M sodium sulphate electrolyte due to lattice active oxygen without hydroxyl radicals being intermediately present. In 0.050 M sodium chloride, the bleaching rate was greatly enhanced due to indirect bulk oxidation by active chlorine species, again without the presence of hydroxyl radicals in the oxidation mechanisms. Under galvanostatic electrolysis, a linear relationship was found between the concentration of added chloride to a supporting sodium sulphate electrolyte and the first order rate constant of the bleaching reaction, showing the importance of the indirect bulk chlorine bleaching in chloride electrolyte systems. In this fashion both the chemically bonded active oxygen and the chemical bulk oxidation by active chlorine species proved to be valid bleaching pathways of RNO that according to these findings cannot be regarded as a fully selective hydroxyl radical probe compound. In addition, the difference in the mechanisms of chloride electrolysis at Ti/Pt₉₀–Ir₁₀ and Si–BDD anodes was clearly demonstrated using t-BuOH as hydroxyl radical scavenger.     

几种电化学法处理苯酚废水对比试验研究

以苯酚模拟废水为研究对象,对几种电化学法处理苯酚废水的效果进行对比研究,采用正交试验对pH值、电解电压、电解质浓度,电解时间等4个因素对苯酚去除率的影响进行分析,并确定最佳反应条件。试验结果表明,电催化氧化法处理苯酚废水的最佳反应条件为:pH值为6,电解电压为9 V,电解质的质量浓度为20 g/L,电解时间为120 min;电-Fenton法处理苯酚废水的最佳反应条件为:pH值为3,电解电压为9 V,电解质的质量浓度为20 g/L,电解时间为120 min;在此基础上,三维电极法最佳活性炭投加量为150 g/L。4种电化学法处理苯酚废水效果的优劣顺序依次为:三维电极与电-Fenton耦合法三维电极法电-Fenton法电催化氧化法。     

Effects of Cl-based chemical coagulants on electrochemical oxidation of textile wastewater

As a supporting electrolyte and the source of chloride reactant, NaCl is generally added for the electrochemical oxidation process. In this study, Cl-based chemical coagulation was employed as the pretreatment step for the preremoval of suspended and colloidal solids which impede electrochemical oxidation. It was adopted for the purpose of providing the source of the chloride reactant for the electrochemical oxidation. It was ultimately intended to omit the artificial addition of electrolyte solution and to decrease the pollutant loading efficiently on the post electrochemical oxidation process in order to improve the performance of organics removal. PAC and FeCl₃, Cl-based chemical coagulants, were successfully employed as the pretreatment step of electrochemical oxidation. PAC and FeCl₃, were able to achieve sufficient removal efficiency of organics as well as to exclude the artificial addition of a supporting electrolyte and the source of a chloride reactant.     

Electrochemical oxidation of 1,3,5-trimethoxybenzene in aqueous solutions at gold oxide and lead dioxide electrodes

A kinetic study of the electrochemical oxidation of 1,3,5-trimethoxybenzene (TMB) by direct electron transfer at treated gold disk was combined with results of electrolysis in order to produce total degradation into CO₂ and H₂O at Ta/PbO₂ anode. The oxidation of TMB at gold electrode was studied by cyclic voltammetry. The cyclic voltammogram shows one irreversible anodic peak (I) corresponding to the oxidation of adsorbed TMB molecules. The proposed mechanism is based on the hypothesis of two-electron oxidation of TMB molecule leading, via intermediate of a radical cation, to the formation of the 2,4,6-trimethoxyphenol (TMP) and an adsorbed polymeric film. The TMP molecule undergoes a rapid oxidation leading to the formation of 2,6-dimethoxy-p-benzoquinone (DMBQ) as a major product. Degradation of TMB was studied by galvanostatic electrolysis using Ta/PbO₂ anode. The influence of initial TMB concentration and applied current density was investigated. Measurement of total organic carbon (TOC) and analysis by HPLC were used to follow this degradation. The experimental data indicated that the removal of TMB follows a pseudo first-order kinetic. The efficiency of the electrochemical process increases at lower current density and higher TMB initial concentration while it decreases with the TOC removal progress.     

Electrooxidation of glyphosate herbicide at different DSA compositions: pH, concentration and supporting electrolyte effect

This paper has investigated the electrochemical oxidation of glyphosate herbicide (GH) on RuO₂ and IrO₂ dimensionally stable anode (DSA^®) electrodes. Electrolysis was achieved under galvanostatic control as a function of pH, GH concentration, supporting electrolyte, and current density. The influence of the oxide composition on GH degradation seems to be significant in the absence of chloride; Ti/Ir_0.30Sn_0.70O₂ is the best electrode material to oxidize GH. GH oxidation is favored at low pH values. The use of chloride medium increases the oxidizing power and the influence of the oxide composition is meaningless. At 30 mA cm⁻² and 4 h of electrolysis, complete GH removal from the electrolyzed solution has been obtained. In chloride medium, application of 50 mA cm⁻² leads to virtually total mineralization (release of phosphate ions = 91%) for all the evaluated oxide materials.     

苯酚废水的铈掺杂钛基电极处理工艺

采用热分解方法制备了铈掺杂钛基电极,并以铈掺杂钛基电极为阳极,纯钛板为阴极组成电解池,以苯酚为目标有机污染物进行降解,采用高效液相色谱法检测苯酚的含量。讨论了Ce的掺杂量、电解池中电极间距、电解电压、电解质溶液的pH、电解质浓度、目标物的浓度以及电解时间对苯酚去除率的影响。结果表明该电解池降解苯酚废水的最佳条件：SnCl4·5Hz0、SbCl3、Ce（NO3）,物质的量比为100：10：1、电极间距为4．0cm、电解电压为9V、pH为6．55、电解质NaSO。浓度为10g／L、苯酚浓度为100mg／L、电解时间为6h。在最佳试验条件下苯酚去除率达到100％,完全符合排污标准GB8978--1996,该电极持续使用10d,对苯酚的去除率仍然可以达到85％,降解苯酚的机理趋于直接燃烧。     

Highly stable Fe/γ‐Al2O3 catalyst for catalytic wet peroxide oxidation

BACKGROUND: A highly stable Fe/γ‐Al₂O₃ catalyst for catalytic wet peroxide oxidation has been studied using phenol as target pollutant. The catalyst was prepared by incipient wetness impregnation of γ‐Al₂O₃ with an aqueous solution of Fe(NO₃)₃· 9H₂O. The influence of pH, temperature, catalyst and H₂O₂ doses, as well as the initial phenol concentration has been analyzed. RESULTS: The reaction temperature and initial pH significantly affect both phenol conversion and total organic carbon removal. Working at 50 °C, an initial pH of 3, 100 mg L^?1 of phenol, a dose of H₂O₂ corresponding to the stoichiometric amount and 1250 mg L^?1 of catalyst, complete phenol conversion and a total organic carbon removal efficiency close to 80% were achieved. When the initial phenol concentration was increased to 1500 mg L^?1, a decreased efficiency in total organic carbon removal was observed with increased leaching of iron that can be related to a higher concentration of oxalic acid, as by‐product from catalytic wet peroxide oxidation of phenol. CONCLUSION: A laboratory synthesized γ‐Al₂O₃ supported Fe has shown potential application in catalytic wet peroxide oxidation of phenolic wastewaters. The catalyst showed remarkable stability in long‐term continuous experiments with limited Fe leaching, < 3% of the initial loading. Copyright © 2010 Society of Chemical Industry     

Effect of chloride concentration on the electrochemical treatment of a synthetic tannery wastewater

The electrochemical treatment of a synthetic tannery wastewater prepared with 30 compounds used in animal skin processing was studied. Electrolyses were performed in a one-compartment flow cell at a current density of 20 mA cm⁻², using a dimensionally stable anode (DSA^®) of composition Ti/Ir_0.10Sn_0.90O₂ as the working electrode. Effects of chloride concentration and presence of sulfate were evaluated. Variation in the concentration of phenolic compounds as a function of electrolysis time revealed a first-order exponential decay; faster phenol removals were obtained with increasing chloride concentration in the wastewater. Lower phenol removals were obtained in the presence of sulfate. Higher chloride concentrations led to a faster decrease in total organic carbon (TOC), chemical oxygen demand (COD), and absorbance values at 228 nm. Faster wastewater color removal, higher current efficiency and lower energy consumption were also obtained. This electrochemical treatment was also able to reduce the wastewater toxicity for Daphnia similis.     

Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Direct synthesis of diphenyl carbonate by mediated electrocarbonylation of phenol at Pd-supported activated carbon anode

Mediated electrocarbonylation of phenol to diphenyl carbonate (DPC) at a PdCl₂-supported activated carbon anode in 1 atm CO at 298 K was studied. A dry CH₂Cl₂ or CH₃CN solvent and a galvanostatic electrolysis of 1 mA were necessary for formation of DPC, while the addition of a base and a supporting electrolyte was also essential. A combination of triethylamine (Et₃N) and tetrabutylammonium perchlorate (Bu₄NClO₄) was suitable in various combinations. The addition of 2 equiv. of Et₃N to the electrolyte (C₆H₅OH/Bu₄NClO₄/CH₂Cl₂) at 1-h intervals was more efficient in the formation of DPC than a single initial addition of the same amount of Et₃N. The yield of DPC was 130% based on Pd and its current efficiency (CE) was 42% for 6 h. The CE of the CO₂ formation was only 3%. Sodium phenoxide (PhONa) showed dual functionality as a base and supporting electrolyte. When the mediated electrocarbonylation was conducted in a C₆H₅OH/PhONa/CH₃CN electrolyte, DPC was produced in 172% yield and 40% CE for 6 h. The CE of the CO₂ formation was 10%. DPC formed continuously after a single initial addition of 4 equiv. of PhONa. Li or K phenoxide also worked as promoters for the mediated electrocarbonylation of phenol to DPC.     

Influence of Experimental Parameters in the Treatment of Distillery Effluent by Electrochemical Oxidation

The electrochemical oxidation of distillery effluent was studied in a batch reactor in the presence of supporting electrolyte NaCl using Mixed Metal Oxide (MMO) electrode. The effect of operating parameters such as current density, initial pH, and initial electrolyte concentration on the percentage of Chemical Oxygen Demand (COD) removal, power consumption, and current efficiency were studied. The maximum percentage removal of COD was observed to be 84% at a current density of 3 A/dm²at an electrolyte concentration of 10 g/l with an effluent COD concentration of 1000 ppm and at an initial pH of 6. The operating parameters for the treatment of distillery effluent by electrochemical process were optimized using response surface methodology by CCD. The quadratic regression models with estimated coefficients were developed for the percentage removal of COD and power consumption. It was observed that the model predictions matched with experimental values with an R² value of 0.9504 and 0.9083 for COD removal and power consumption respectively. The extent of color removal and oxidation of organic compounds were analyzed using UV spectrophotometer and HPLC.     

An optimization study on microwave irradiated decomposition of phenol in the presence of H2O2

BACKGROUND Removal of phenol from industrial waste waters involves basic techniques namely extraction, biodegradation, photocatalytic degradation, etc. Among the available processes, the oxidation of phenols using H₂O₂ is a suitable alternative because of low cost and high oxidizing power. The application of an oxidation process for the decomposition of stable organic compounds in waste water leads to the total degradation of the compounds rather than transferring from one form to another. Since oxidation using Fenton's reagent is more dependent on pH, in this present work it was proposed to use H₂O₂ coupled with microwave irradiation. The effects of initial phenol concentration, microwave power and the irradiation time on the amount of decomposition were studied. RESULTS: In the present work experiments were conducted to estimate the percentage degradation of phenol for different initial concentrations of phenol (100, 200, 300, 400 and 500 mg L^?1), microwave power input (180, 360, 540, 720 and 900 W) for different irradiation times. The kinetics of the degradation process were examined through experimental data and the decomposition rate follows first‐order kinetics. Response surface methodology (RSM) was employed to optimize the design parameters for the present process. The interaction effect between the variables and the effect of interaction on to the responses (percentage decomposition of phenol) of the process was analysed and discussed in detail. The optimum values for the design parameters of the process were evaluated (initial phenol concentration 300 mg L^?1, microwave power output 668 W, and microwave irradiation time 60 s, giving phenol degradation 82.39%) through RSM by differential approximation, and were confirmed by experiment. CONCLUSION: The decomposition of phenol was carried out using H₂O₂ coupled with microwave irradiation for different initial phenol concentrations, microwave power input and irradiation times. The phenol degradation process follows first‐order kinetics. Optimization of the process was carried out through RSM by forming a design matrix using CCD. The optimized conditions were validated using experiments. The information is of value for the scale up of the oxidation process for the removal of phenol from wastewater. Copyright © 2008 Society of Chemical Industry     

Electrochemical treatment of olive mill wastewater

Background Olive mill wastewater (OMW) constitutes a very strong agro‐industrial wastewater posing severe environmental threats in olive oil producing countries. The main objective of this study was to treat olive mill wastewater by electrochemical oxidation. The variables studied included the type and concentration of electrolyte solutions, voltage and time applied. Results: The electrolyte type and concentration significantly affected the degradation efficiency of the electrochemical oxidation. Optimal conditions for NaCl concentration were 3% (w/v) and 16 V. At these conditions chemical oxygen demand (COD) removal reached 70.8% after 8 h of electrochemical treatment, while color and turbidity were completely removed after short periods of treatment. However, bio‐assays indicated that the ecotoxicity of the treated wastewater remained unchanged, possibly due to the formation of chlorinated by‐products. Na₂SO₄ did not demonstrate sufficient efficiency. The simultaneous use of FeCl₃ and NaCl contributed to electro‐coagulation of OMW. After settlement, two separate phases were formed: the supernatant phase and the settled solids. Under optimal conditions (2% Na₂SO₄ + 1% FeCl₃; 24 V), the removal efficiency of COD reached 85.5% at the supernatant phase. Conclusion: NaCl was an effective electrolyte for OMW treatment. The electro‐coagulation process was also a successful process, but as in the case of NaCl the remaining acute toxicity of treated OMW was high. Copyright © 2007 Society of Chemical Industry     

Phenol Removal through Chemical Oxidation using Fenton Reagent

In this study, phenol, aromatic, and non‐biodegradable organic matter were investigated and found to be removed from the model solution through chemical oxidation using Fenton reagent. The effects of the initial phenol concentration, hydrogen peroxide, and ferrous sulfate concentrations on the removal efficiency were investigated. Performance of the chemical oxidation process was monitored with phenol and COD (Chemical Oxygen Demand) analyses. In the experimental studies, phenol removal of over 98 % and COD removal of nearly 70 % were achieved. The optimum conditions for Fenton reaction both for initial phenol concentrations of 200 and 500 mg/L were found at a ratio [Fe²⁺]/[H₂O₂] (mol/mol) equal to 0.11. According to the results, chemical oxidation using Fenton reagent was found to be too effective, especially for phenol removal. However, this method has limited removal efficiency for COD.     

Electrochemical treatment of wastewaters containing 4‐chlororesorcinol using boron doped diamond anodes

The electrochemical oxidation of aqueous wastes polluted with 4‐chlororesorcinol has been studied on boron‐doped diamond electrodes on acidic medium. The voltammetric results showed that in the potential region where the supporting electrolyte is stable, reactions occur, resulting in the loss of activity due to electrode fouling. Galvanostatic electrolysis study showed that the oxidation of these wastes in single‐compartment electrochemical flow cell with boron doped diamond anodes deal to the complete mineralization of the organics but is no indication of electrode fouling. Resorcinol, 1,2,4‐trihydroxybenzene, benzoquinone, maleic, fumaric, and oxalic acids have been detected as soluble organics and chlorides (Cl^?) and hypochlorites (ClO^?) as mineral products during the electrolysis of 4‐chlororesorcinol. The electrochemical oxidation of 4‐chlororesorcinol consists of a sequence of steps: Release of Cl and/or hydroxylation of the aromatic ring; formation of quinonic compounds; oxidative opening of aromatic ring to form carboxylic acids; and oxidation of carboxylic acids to carbon dioxide. Both, direct oxidation at boron doped diamond surface and mediated oxidation by powerful oxidants electrogenerated from electrolyte oxidation at anode surface are involved in these stages.     

Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment applications was investigated on lead dioxide packed-bed anodes. Cells were operated in both batch and continuous modes with feed streams up to 1100 nig/1 phenol dissolved in aqueous solutions of Na₂SO₄ and H₂SO₄ or NaOH. All the phenol in solution could be readily oxidized but complete total organic carbon (T.O.C.) removal was more difficult. The percent phenol oxidized increased with increasing current density, and decreased as initial phenol concentration, electrolyte flow rate, pH and anode particle size were increased. Results are compared to simple mathematical models.     

Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment applications was investigated on lead dioxide packedbed anodes. Cells were operated in both batch and continuous modes with feed streams up to 1100 mg/l phenol dissolved in aqueous solutions of Na₂SO₄ and H₂SO₄ or NaOH. All the phenol in solution could be readily oxidized but complete total organic carbon (T.O.C.) removal was more difficult. The percent phenol oxidized increased with increasing current density, and decreased as initial phenol concentration, electrolyte flow rate, pH and anode particle size were increased. Results are compared to simple mathematical models.