Electrochemical oxidation of Basic Blue 3 dye using a diamond anode: evaluation of colour,COD and toxicity removal

BACKGROUND: Textile industries generate considerable amounts of waste‐water, which may contain strong colour, suspended particles, salts, high pH and high chemical oxygen demand (COD) concentration. The disposal of these coloured wastewaters poses a major problem for the industry as well as a threat to the environment. In this study, electrochemical oxidation of Basic Blue 3 (BB3) dye was studied in a bipolar trickle tower (BTT) reactor using Raschig ring shaped boron‐doped diamond (BDD) electrodes in recirculated batch mode. The effects of current density, temperature, flow rate, sodium sulfate concentration (Na₂SO₄) as supporting electrolyte, and initial dye concentration were investigated. RESULTS: The best experimental conditions obtained were as follows: current density 0.875 mA cm^?2, temperature 30 °C, flow rate 109.5 mL min^?1, Na₂SO₄ concentration 0.01 mol L^?1. Under these conditions, 99% colour and 86.7% COD removal were achieved. Toxicity tests were also performed on BB3 solutions under the best experimental conditions. CONCLUSION: Based on these results, the BDD anode was found to be very successful for the simultaneous degradation of BB3 and removal of COD. Additional toxicity test results also showed that electrochemical treatment using a BDD Raschig ring anode in a BTT reactor is an effective way of reducing toxicity as well as removing colour and COD. Copyright © 2010 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     

Copper recovery and simultaneous COD removal from copper phthalocyanine dye effluent using bipolar disc reactor

Electrochemical treatment of real acidic effluent of copper phthalocyanine dye manufacturing plant with a view to explore the feasibility of the simultaneous removal of copper and phthalocyanine using a bipolar disc electrochemical reactor has been investigated. Experiments were conducted in a bipolar capillary gap disc stack electrochemical reactor under batch recirculation mode. Electrodes were RuO₂ and IrO₂ coated on titanium as anode and titanium as cathode. Effects of current density, electrolysis time and effluent flow rate on copper recovery and simultaneous COD removal and energy consumption were critically examined. The current density of 2.5 A dm⁻² and flow rate of 20 L h⁻¹ achieved 91.1% COD removal and 90.1% copper recovery with the energy consumption of 50.86 kWh kg⁻¹ for COD removal and simultaneous recovery of copper in a bipolar disc stack reactor.     

Hypochlorite production on Ru-Sn binary oxide electrode and its application in treatment of dye wastewater

Ruthenium-tin binary oxides [(Ru+Sn)O₂] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviours were characterized by cyclic voltammetry and linear-scan voltammetry (LSV) methods. The effects of electrolysis condition for the current efficiency (CE) of hypochlorite production on binary (Ru+Sn)O₂ electrodes and the treatment of a high salt-containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production exists on an RS3 (40 to 80 mol% Sn in coating solution) electrode. The major factors influencing CE for hypochlorite production are the electrolyte flow rate, current density, and chloride (Cl-) concentration. Major factors affecting energy yield are current density, Cl- concentration, and electrode distance. For low current density (300 mA.cm^?2), high Cl- concentration (1 mol.L^?1), and 0.45 cm electrode separation, a high specific energy is obtained. The RS3 electrode exhibits the best removal of organics and chromophor groups in the dye wastewater. On this electrode, better removal of organics and chromophor groups is obtained at 300 mA.cm^?2. The colour of black-red dye wastewater becomes light yellow when a charge of 792 A·min was passed, while the chemical oxygen demand (COD) of this wastewater is decreased from 10500 mg.L^?1 to 1250 mg.L^?1.     

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.     

Hypochlorite generation on Ru–Pt binary oxide for treatment of dye wastewater

Ruthenium–platinum binary oxides [(Ru + Pt)O _x ] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviour was characterized by cyclic voltammetry (CV) and linear scanning voltammetry (LSV). The effects of electrolyte conditions on the current efficiency (CE) of hypochlorite production on binary (Ru + Pt)O _x electrodes and the treatment of a high salt-containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production occurred on the RP1 (20 mol% Pt in precursor) electrode. The major factors influencing CE for hypochlorite production were the electrolyte flow rate, current density and chloride ion (C1^–) concentration. The RP1 electrode exhibited the best removal of organics and chromophoric groups in the dye wastewater. On this electrode, better removal of organics and chromophoric groups was obtained at 300 mA cm^–2. The colour of black–red dye wastewater became light yellow when a charge of 13.2 A h was passed while the COD of the wastewater decreased from 10 500 to 1250 mg L^–1.     

Treatment of dairy industry wastewater by EC and EF processes using hybrid Fe?Al plate electrodes

BACKGROUND: In this study electrochemical treatment of dairy industry wastewater (DW) was investigated using a combined electrode system consisting of iron and aluminum as sacrificial electrodes. The dairy industry generates strong wastewaters characterized by high biological oxygen demand and chemical oxygen demand concentrations. Dairy industry waste effluents are concentrated in nature, and the main contributors of organic load to these effluents are carbohydrates, proteins and fats originating from the milk. Since dairy waste streams contain high concentrations of organic matter, these effluents may cause serious environmental problems. RESULTS: A pole changer device was employed to change polarization in given time intervals to generate iron and aluminum based coagulants respectively. The effects of current density, initial pH, sodium sulfate (Na₂SO₄) and H₂O₂ concentrations on the removal efficiency were investigated. The best experimental conditions obtained in electrochemical studies were as follows: current density = 15 mA cm^?2, natural pH, without supporting electrolyte addition, H₂O₂ concentration = 3 × 1000 mg L^?1. Under these conditions, 79.2% COD removal from DW was achieved. CONCLUSION: According to the results, 20 min electrolysis is enough, since insignificant variations in COD removal were observed after this time. These methods were found to be successful for the treatment of DW. Copyright © 2011 Society of Chemical Industry     

Electrochemical oxidation of textile dye indigo

Electrochemical methods are being used increasingly as an alternative treatment process for the remediation of textile wastewaters. This study focused mainly on the colour removal and chemical oxygen demand (COD) reduction of vat textile dye (CI Vat Blue 1: indigo) from its aqueous solution by electrochemical oxidation. The process was carried out in a batch‐type divided electrolytic cell under constant potential using a Pt cage as anode and Pt foil as cathode. Operating variables such as supporting electrolyte, pH, ultrasonification and treatment time were investigated to probe their effects on the efficiency of the electrochemical treatment. Colour removal was estimated by monitoring the disappearance of the absorbance peak at 681.5 nm. It was found that in acidic conditions the electrolysis was more efficient. At pH 1, an NaCl concentration of 0.24 mol dm^?3, a dyeing solution concentration of 0.1% (w/v) and a period of 90 min of electrolysis, there was almost 100% colour removal and 60% reduction in COD. Voltammetric and IR investigations demonstrated that partial degradation of dye was achieved. The experimental results indicate that this electrochemical method could effectively be used as a pretreatment stage before conventional treatment. Copyright © 2005 Society of Chemical Industry     

Electrochemical incineration of dyes using a boron‐doped diamond anode

The electrochemical oxidation of a synthetic wastewater containing the model dyes alizarin red (an anthraquinone) and Eriochrome black T (an azoic compound) has been studied on a boron‐doped diamond electrode (BDD) by both cyclic voltammetry and bulk electrolysis. The influence of the current density and dye concentration were investigated. The results obtained show that complete chemical oxygen demand (COD) and colour removal was obtained for both wastewaters. However, the nature of the pollutant, and specially the presence of functional groups (such as the azoic group) seems to strongly influence the performance and efficiency of the electrochemical process. The electro‐oxidation of alizarin red behaves as a mass‐transfer‐controlled process. In such a system, an increase in the current density leads to a decrease in the current efficiency. This can be explained by direct or hydroxyl radical mediated oxidation. The contrary tendency has been observed in Eriochrome black T electro‐oxidation. In this case, higher efficiencies were obtained working at high current densities. This may indicate that the mediated oxidation by electrogenerated reagent (such as peroxodisulphate) is the main oxidation mechanism involved in Eriochrome black T treatment. These compounds have a longer average lifetime than hydroxyl radicals, and it allows the reaction to be extended to the whole wastewater volume. This study has shown the suitability of the electrochemical process for completely removing the COD and total organic carbon and effectively decolourising of wastewaters containing synthetic dyes. Copyright © 2007 Society of Chemical Industry     

Effect of stream segregation on ozonation for the removal of significant COD fractions from textile wastewater

Ozonation was tested on selected streams of cotton finishing textile plant wastewater for optimizing chemical oxygen demand (COD) removal. For this purpose, significant COD fractions in the wastewater were experimentally identified and the effect of ozone on these fractions was investigated. Ozonation experiments were performed with a 1 dm³ sample volume. Ozone treatment of batches of raw wastewater provided, at a rate of 62 mg min^?1 and a gas feeding time of 15 min, achieved complete colour removal but only 21% COD reduction. Increasing the feeding time to 30 min slightly increased the COD removal to 32%. At this feeding time, removal of the readily biodegradable COD was 60%, but soluble inert COD reduction remained at 16%, indicating selective preference of ozone for simpler compounds. At low concentrations, ozone was mainly influential on soluble COD compounds. Longer feeding times also affected particulate compounds, resulting in the solubilization of the COD fractions. Pre‐ozonation of the dye‐house wastewater, as a segregated stream, proved much more effective in the breakdown of refractory organic compounds, rendering the overall plant effluent more amenable to biological treatment. © 2002 Society of Chemical Industry     

Improvement of dye electrochemical treatment by combination with ultrasound technique

BACKGROUND: Currently, the combination of conventional physicochemical techniques appears to be an attractive option to apply to wastewater treatment. In this work, a hybrid technique, called sonoelectrochemistry as a result of the combination of electrochemical and ultrasound technology, was undertaken in order to increase the efficiency of textile wastewater remediation. RESULTS: Results have demonstrated the superiority of the sonoelectrochemical process over each treatment alone. Although in the sonoelectrochemical treatment, the decolourisation rate of di‐azo dyes was lower than mono‐azo or diphenylnaphthylmethane dyes, in all cases a first‐order kinetic behaviour was detected. In addition, the influence of inert electrolyte concentration (Na₂SO₄) was assayed. On the other hand, colour removal was considerably faster than the decrease in chemical oxygen demand (COD), which was attributed to the ease of chromophore destruction. Hence, for example for Lissamine Green B the efficiency of sonoelectrochemical decolourisation was 95% compared with 60% of COD removal after 1 h treatment. Additionally, a flow system with total reflux by the electrochemical and the sonoelectrochemical treatment was considered and a similar behaviour to previous experiments was found. CONCLUSIONS: Based on the results obtained, the feasibility of this hybrid technique was demonstrated. Furthermore, an efficient flow system was devised for dye decolourisation, which could be extrapolated to develop a continuous process. Copyright © 2009 Society of Chemical Industry     

Degradation of azo dye C.I. Acid Red 18 using an eco-friendly and continuous electrochemical process

Continuous anodic oxidation of azo dye C.I. Acid Red 18 by using PbO₂ electrode in aqueous solution was studied. To reach the best conditions of the process, the influence of various operating parameters such as pH, current density, hydraulic retention time (HRT) and dye concentration on the removal rate of chemical oxygen demand (COD) and color, as indexes showing the amount of efficiency, was investigated. The findings showed that, respectively, 99.9% and 80.0% of the dye and COD were removed (at optimized conditions). Mineralization current efficiency results indicated that at the beginning of the reaction mineralization occurred quickly at a low current density, whereas at high amounts the rate of mineralization the efficiency decreased. At the optimum conditions, the majority of COD was removed only with 38.2 kWh/kg COD of energy consumption in 120 min. By controlling HO?/dye concentration ratio via the parameters adjustment, particularly HRT and current density, this system can treat Acid Red 18 well even at high concentrations. Furthermore, the voltammetry study illustrated that electroactive intermediates created during the process were mineralized at current density of 8.6mA/cm².     

Treatment of olive mill wastewater by the combination of ultrafiltration and bipolar electrochemical reactor processes

The main purpose of this study was to investigate the removal of the chemical oxygen demand (COD) from olive mill wastewater (OMW) by the combination of ultrafiltration with electrocoagulation process. Ultrafiltration process equipped with CERAVER membrane was used as pre-treatment for electrochemical process. The obtained permeate from the ultrafiltration process allowed COD removal efficiency of about 96% from OMW. Obtained permeate with an average COD of about 1.1 g dm⁻³ was treated by electrochemical reactor equipped with a reactor with bipolar iron plate electrodes. The effect of the experimental parameters such as current density, pH, surface electrode/reactor volume ratio and NaCl concentration on COD removal was assessed. The results showed that the optimum COD removal rate was obtained at a current density of 93.3 A m⁻² and pH ranging from 4.5 to 6.5. At the optimum operational parameters for the experiments, electrocoagulation process could reduce COD from 1.1 g dm⁻³ to 78 mg dm⁻³, allowing direct discharge of the treated OMW as that meets the Algerian wastewater discharge standards (<125 mg dm⁻³).     

Electrochemical decomplexing and oxidation of organic (chelating) additives in effluents from surface treatment and metal finishing

The electrochemical decomplexing and oxidation of two frequently used complexing agents in surface treatment and metal finishing—EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid)—and of organic non‐complexing additives used in nickel‐plating baths were the subject of this study. Using a Ti–RuO₂ electrode, a partial indirect oxidation by in‐situ electrochemical generation of chlorine compounds could be achieved for EDTA and NTA. At a boron‐doped diamond (BDD) electrode however, complete decomplexing and high COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) (up to 95%) removal occurred at an average current density of 2 A dm^?2. It is shown that direct electrochemical oxidation at a BDD electrode resulted in lower energy consumption and higher treatment rates than indirect oxidation at a Ti–RuO₂ electrode. Decomplexing at the BDD electrode occurred at high current efficiencies ranging from 71% to 95% with decomplexing rates in the order of 3.13 mmol (Ah)^?1 and 5.02 mmol (Ah)^?1 for EDTA and NTA respectively. COD removal rates obtained were 0.090 g (Ah)^?1 for EDTA, 0.100 g (Ah)^?1 for NTA and 0.205 g (Ah)^?1 for the nickel‐plating additives. Electrochemical decomplexing and oxidation of common chelating agents can render the subsequent metal precipitation and biological wastewater treatment of surface treatment and metal finishing effluents more efficient. Copyright © 2003 Society of Chemical Industry     

Sodium diclofenac removal from a pharmaceutical wastewater by electro-Fenton process

ABSTRACT

In this study, the experiments were carried out to evaluate the effect of five independent variables on the Chemical Oxygen Demand (COD) removal in a pharmaceutical wastewater contaminated with sodium diclofenac. The parameters were statistically optimized under response surface mythology. The optimum conditions for 97.21% of COD removal experimentally were at reaction time of 59.68 min, current density of 58.47 mA/cm², pH of 2.89, volume ratio of 0.32 ml/l and H₂O₂/Fe²⁺ molar ratio of 3.60.     

Electrochemical removal of boron from water: Adsorption and thermodynamic studies

The present work provides an electrochemical removal of boron from water and its kinetics, thermodynamics, isotherm using mild steel and stainless steel as anode and cathode respectively. The various operating parameters on the removal efficiency of boron were investigated, such as initial boron ion concentration, initial pH, current density and temperature. The results showed that the optimum removal efficiency of 93.2% was achieved at a current density of 0.2 A dm^?2 at pH of 7.0. First‐, second‐order rate equations, Elovich and Intraparticle models were applied to study adsorption kinetics. Adsorption isotherms of boron on Fe(OH)₃ were determined and correlated with isotherm equations such as Langmuir, Freundlich and D‐R models. Thermodynamic parameters, such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°), were also evaluated by Van't Hoff equation. The adsorption process follows second‐order kinetics. The adsorption of boron preferably fits with Langmuir adsorption isotherm suggesting monolayer coverage of adsorbed molecules. The adsorption of boron onto Fe(OH)₃ was found to be spontaneous and endothermic. © 2011 Canadian Society for Chemical Engineering     

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.     

Specific energy consumption in electrochemical treatment of food industry wastewaters

BACKGROUND: Specific energy consumption (SEC) is an important factor in electrochemical treatment of wastewaters. SEC during electrochemical treatment of food industry wastewaters, specifically deproteinated whey wastewater (DWW), simulated sugar beet factory wastewater (SFW) and fruit juice factory wastewater (FJW), were investigated in this study. The effects of operational parameters applied voltage, and electrolyte and wastewater concentrations on SEC were assessed and optimized. RESULTS: SEC values were found in the range of 0.27–148.65, 0.94–375.76 and 0.20–636.40 kWh (kg COD)^?1 for DWW, SFW and FJW, respectively, after 8 h of reaction. Operational parameters were optimized at 25 °C through response surface methodology (RSM) where applied voltage was kept in the range (2–12 V), wastewater concentration and COD removal percent were maximized electrolyte concentration and SEC were minimized. Optimum conditions were estimated as 7.73 V applied voltage and 100% wastewater concentration in the presence of 27.11 g L^?1 supporting electrolyte concentration to achieve 25.02, 67.74 and 43.10% COD removal for DWW, SFW and FJW with corresponding SEC values of 17.85, 22.79 and 80.47 kWh (kg COD)^?1, respectively. CONCLUSIONS: Providing further research on the reduction of SEC values, application of electrochemical treatment to food industry wastewaters with non‐biodegradable components may become an alternative to conventional methods. Copyright © 2012 Society of Chemical Industry     

FEED-FORWARD BACK-PROPAGATION NEURAL NETWORK FOR THE ELECTRO-OXIDATION OF DISTILLERY EFFLUENT

The aim of the present work is to demonstrate the technical feasibility of treating high-strength distillery wastewater in an electrochemical flow reactor and to predict the result using an artificial neural network (ANN) model. The experiments were conducted using oxide coated on expanded titanium (Ti/Ru_0.3Ti_0.7O₂) as anode and stainless steel as cathode in a batch reactor with electrolytic recirculation. Pollutant degradation was measured as chemical oxygen demand (COD) for various operating parameters such as effluent flow rate, current density, and supporting electrolyte concentration. Experiments were conducted for various flow rates, supporting electrolyte concentrations, and current density. An ANN was used for modeling the experimental results. The model was developed using a feed-forward back-propagation network with different layers and neurons. It can be concluded that the network configuration of 3-3-3-1 simulation gives the best result in predicting the experimental results with a high correlation coefficient (R ² = 0.9987). Using this network model, the effluent COD removal can be predicted quickly and easily.     

Use of a PbO2 electrode of a lead-acid battery for the electrochemical degradation of methylene blue

In this work, the electrochemical degradation efficiency of synthetic azo dye, methylene blue, at positive electrode PbO₂ of lead-acid battery was investigated. The structure and morphology of the electrode was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectrometry. The influence of several operating parameters on electro-oxidation of 100 mL of methylene blue solution 100 mg/L was studied. Results indicated that lead-acid battery electrode is effective for removing color and chemical oxygen demand (COD). It is found that current density, the stirring speed, and the supporting electrolyte concentration have a positive effect on decolorization and mineralization, and no significant effect of the distance between the electrodes on methylene blue degradation and COD removal was observed. By contrast, the percentage of color and COD removal decreases with increasing of pH. Kinetic analysis of the results revealed that the COD removal follows a pseudo-first-order kinetics.