Electrochemical oxidation of a textile dye wastewater using a Pt/Ti electrode

Textile dye wastewater (TDW) from a reactive azo dyeing process was treated by an electrochemical oxidation method using Ti/Pt as anode and stainless steel 304 as cathode. Due to the strong oxidizing potential of the chemicals produced (chlorine, oxygen, hydroxyl radicals and other oxidants) when the wastewater was passed through the electrolytic cell the organic pollutants were oxidized to carbon dioxide and water. A number of experiments were run in a batch, laboratory-scale, pilot-plant, and the results are reported here according to residence time and initial addition of HCl in raw wastewater. When of 2 ml of HCl 36% were added and after 18 min of electrolysis at 0.89 A/cm(2), chemical oxygen demand (COD) was reduced by 86%, biochemical oxygen demand (BOD(5)) was reduced by 71%, ADMI color units were reduced by 100%, and TKN was reduced by 35%. The biodegradability of the wastewater was improved because the COD/BOD ratio decreased from 2.16 to 1.52. At the same time the efficiency of the electrode was about 170 g h(-1) A(-1) m(-2). and the mean energy consumption was 21 kW h/kg of COD. These results indicate that this electrolytic method could be used for effective TDW oxidation or as a feasible detoxification and color removal pretreatment stage for biological post treatment.     

Decolorization of dye solution containing Acid Red 14 by electrocoagulation with a comparative investigation of different electrode connections

This study was performed to investigate the variables that influence the efficiency of decolorization of a solution containing an azo dye (Acid Red 14) by electrocoagulation (EC) in order to compare the efficiency of different electrode connections for color removal. Current density, time of electrolysis, interelectrode distance, and pH of the solution were the variables that most influenced color removal. Initially, a simple electrochemical cell was prepared with an anode and a cathode. Then the effect of each variable was studied separately using synthetic wastewater in a batch mode. The efficiency of the method tested was determined by measurement of color removal and reduction of Chemical Oxygen Demand (COD). For dye solutions with COD of approximately 30 ppm and dye concentrations less than 150 ppm, high color removal (93%) was obtained when the pH ranged from 6 to 9, time of electrolysis was approximately 4 min, current density was approximately 80 A/m2, the temperature was approximately 300 K, and interelectrode distance was 1 cm. During the EC process under these conditions, the COD decreased by more than 85%. In the second series of experiment, the efficiency of EC cells with monopolar electrodes in series and parallel connections and an EC cell with bipolar electrodes were compared with results using a simple electrochemical cell. The experimental results showed that an EC cell with several electrodes was more effective than a simple electrochemical cell in color removal. The results also showed that an EC cell with monopolar electrodes had a higher color removal efficiency than an EC cell with bipolar electrodes. Furthermore, within an EC cell, the series connection of the monopolar electrodes was more effective for the treatment process than the parallel connection in color removal.     

Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes

Treatment of textile wastewaters by electrocoagulation using iron and of aluminum electrode materials has been investigated in this paper. The effects of relevant wastewater characteristics such as conductivity and pH, and important process variables such as current density and operating time on the chemical oxygen demand (COD) and turbidity removal efficiencies have been explored. Furthermore, the electrode and energy consumptions for each electrode have been calculated. The results show that iron is superior to aluminum as sacrificial electrode material, from COD removal efficiency and energy consumption points.     

Treatment of the baker's yeast wastewater by electrocoagulation

In the laboratory-scale experiments, treatment of baker's yeast production wastewater has been investigated by electrocoagulation (EC) using a batch reactor. Effects of the process variables such as pH, electrode material (Fe and Al), current density, and operating time are investigated in terms of removal efficiencies of chemical oxygen demand (COD), total organic carbon (TOC), turbidity, and operating cost, respectively. The maximum removal efficiencies of COD, TOC and turbidity under optimal operating conditions, i.e., pH 6.5 for Al electrode and pH 7 for Fe electrode, current density of 70 A/m2 and operating time of 50 min were 71, 53 and 90% for Al electrode and 69, 52 and 56% for Fe electrode, respectively. Al electrode gave 4.4 times higher removal efficiency of turbidity than Fe electrode due to interference from color of dissolved iron. The operating costs for Al and Fe electrodes in terms of $/m3 or $/kg COD were 1.54 and 0.82, 0.51 and 0.27, respectively.     

Treatment of levafix orange textile dye solution by electrocoagulation

The decolorization of the levafix orange textile dye in aqueous solution by electrocoagulation using aluminum sacrificial anode has been investigated. The process performance is analyzed in terms of decolorization efficiency and the important cost-related parameters such as electrode and energy consumptions, as a function of initial pH, conductivity, current density, initial dye concentration and electrolysis time. The present study proves the effectiveness of electrochemical treatment for the textile dye solution. 95% decolorization efficiency may be obtained at suitable operating conditions such as; current density 100 A/m(2), operating time 12 min and initial pH 6.4. The corresponding electrode and energy consumptions during the electrolysis were found to be 1.8 kg Al/kg dye and 35 k Wh/kg dye.     

Contribution to the study of electrocoagulation mechanism in basic textile effluent

Electrocoagulation method with iron electrode is used to treat the industrial textile wastewater in batch reactor. The effects of operating parameters such as time and potential electrolysis on the decolourization and COD removal efficiency have been investigated. The results indicate that electrocoagulation is very efficient and able to achieve 100% colour and 84% COD removal in 3 min at potential 600 mV. The effluent wastewater is very clear and its quality exceed the direct discharge standard. Furthermore, the mechanism of electrocoagulation is elucidated by zeta potential measurement.     

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l(-1)). The CSTR is a 1l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l(-1) d(-1). The FFB is a 1.5l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l(-1) d(-1). The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l(-1) d(-1). The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass (R(TSS/COD)) and on the yield of conversion of substrate on active biomass (R(VVS/COD)) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.     

Arsenic removal by electrocoagulation using combined Al-Fe electrode system and characterization of products

Combination of electrodes, such as aluminum and iron in a single electrochemical cell provide an alternative method for removal of arsenic from water by electrocoagulation. The removal process has been studied with a wide range of arsenic concentration (1–1000 ppm) at different pH (4–10). Analysis of the electrochemically generated by-products by XRD, XPS, SEM/EDAX, FT-IR, and Mössbauer Spectroscopy revealed the expected crystalline iron oxides (magnetite (Fe₃O₄), lepidocrocite (FeO(OH)), iron oxide (FeO)) and aluminum oxides (bayerite (Al(OH)₃), diaspore (AlO(OH)), mansfieldite (AlAsO₄·2(H₂O)), as well as some interaction between the two phases. The amorphous or very fine particular phase was also found in the floc. The substitution of Fe³⁺ ions by Al³⁺ ions in the solid surface has been observed, indicating an alternative removal mechanism of arsenic in these metal hydroxides and oxyhydroxides by providing larger surface area for arsenic adsorption via retarding the crystalline formation of iron oxides.     

Optimization of oil removal from oily wastewater by electrocoagulation using response surface method

Electrocoagulation process with sacrificial aluminium anode was used to separate oil from oily wastewater emulsion. A preliminary experimental study was performed to evaluate the most accurate operating parameters, which are then used for the determination of oil removal efficiency. An experimental design using response surface method (RSM) was then applied and oil separation was estimated by measuring turbidity and chemical oxygen demand (COD). An optimal region characterised with low values of turbidity and COD was found. As part of the optimized process, the main effects of the operational parameters were also investigated. The experimental results indicated that electrocoagulation was very efficient and able to achieve 99% turbidity and 90% chemical oxygen demand (COD) in less than 22 min and current density of 25 mA cm(-2). Analysis of variance (ANOVA) showed a high variance coefficient (R(2)) value of 0.998, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data.     

Decolourisation of real textile waste using electrochemical techniques: effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSA type material. The effect of using different anode materials (Ti/Ru(0.3)Ti(0.7)O(2); Ti/Ir(0.3)Ti(0.7)O(2); Ti/Ru(X)Sn(1-X)O(2), where X=0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO(2) is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L(-1)) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order (E(EO)/kW h m(-3)order(-1)) and energy consumption (E(C)/kW h kg(-1)TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.     

Investigation of the effect of different electrodes and their connections on the removal efficiency of 4-nitrophenol from aqueous solution by electrocoagulation

This study investigates the influence of variables on the removal efficiency of solution containing 4-NP (4-nitrophenol) by D. C. electrocoagulation (EC). The efficiency of different electrode connections and materials (steel 310, Fe, Al, graphite and steel 304) for 4-NP removal is compared. Current density, time of electrolysis, interelectrode distance, supporting electrolyte concentration and stirring rate of the solution were the variables that mostly influenced the 4-NP removal. Initially, a simple electrochemical cell was prepared with an anode and a cathode. Then the effect of each variable was studied separately using aqueous 4-NP in a batch mode. For a solution of 20 mg/L 4-NP+300 mg/L NaCl with chemical oxygen demand (COD) of approximately 40 mg O2/L, almost up to 99% 4-NP and 65% COD were removed, when the pH was about 9, time of electrolysis was approximately 10 min, current density was 100 A m(-2), interelctrode distance was 15 mm and stirring rate was 400 rpm. In the second series of experiments, the efficiency of EC cells with monopolar electrodes in series and parallel connections and an EC cell with bipolar electrodes was compared with that of a simple electrochemical cell. The best results obtained when steel 310 and Fe are used as anodes and employing Al and graphite as anodes would not be satisfactory. Also findings show that the types of sacrificial electrodes are not very significant in the removal of 4-NP. In the real wastewater obtained from Tabriz petrochemical plant 52% removal could be achieved after 10 min with using steel 310 as anode and steel 304 as cathode.     

Detoxification of simulated textile wastewater using a membraneless electrochemical reactor with immobilized peroxidase

Simulated textile wastewater was degraded using a membraneless electrochemical reactor with immobilized peroxidase on the porous Celite. The optimal current density was 10 A m(-2), at which the highest amount of hydrogen (H(2)O(2)) could be generated. The decolorization efficiencies of the simulated wastewater using the electrochemical and electroenzymatic methods were 35% and 92%, respectively. Biodegradability, the ratio of 5-day biochemical oxygen demand to chemical oxygen demand (BOD(5)/COD), was enhanced about 1.88 times when using the electroenzymatic treatment rather than raw wastewater, which could not be achieved by the electrochemical treatment. The toxic unit (TU), calculated using the lethal concentration (LC(50)) of Daphnia magna (D. Magna), of effluent treated by electroenzymatic method was below 1, whereas those of simulated textile wastewater and effluent treated by electrochemical method were 11.4 and 3.9, respectively.     

Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst

Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze redox reactions in presence of air/O2 and water. Here, the potential of a common semiconductor, ZnO, has been explored as an effective catalyst for the photodegradation of two model dyes: Methylene Blue and Eosin Y. A 16 W lamp was the source of UV-radiation in a batch reactor. The effects of process parameters like, catalyst loading, initial dye concentration, airflow rate, UV-radiation intensity, and pH on the extent of photo degradation have been investigated. Substantial reduction of COD, besides removal of colour, was also achieved. A rate equation for the degradation based on Langmuir-Hinshelwood model has been proposed.     

The use of constructed wetland for dye-rich textile wastewater treatment

The objective of the present paper was to examine the treatment efficiency of constructed wetlands (CW) for the dye-rich textile wastewater with special focus on colour reduction. Preliminary, a series of dynamic experiments was performed in the CW model packed with gravel, sand, and zeolitic tuff on three synthetically prepared wastewaters using chemically differ dyestuffs, auxiliaries and chemicals, in order to investigate the potential of low-cost materials as media for textile dye-bath wastewater treatment. The obtained results evidence that applied CW model reduces colour by up to 70%, and COD and TOC by up to 45%. Based on these results, the pilot CW with vertical (VF) and horizontal flow (HF) was constructed near textile factory mainly for cotton and cotton/PES processing with intention to treat real textile wastewater in situ. It was designed for 1 m³/day, covering 80 m², packed with sand and gravel, and planted with Phragmites australis. The average treatment efficiency of the CW for the selected pollution parameters were: COD 84%, BOD₅ 66%, TOC 89%, N_total 52%, N_organic 87%, NH₄-N −331%, sulphate 88%, anion surfactant 80%, total suspended solids (TSS) 93%, and colour 90%, respectively. The results unequivocally proved that the CW could offer an optimal solution to meet the environmental legislation as well as requirements for effective and inexpensive textile wastewater treatment.     

Biological treatment and nanofiltration of denim textile wastewater for reuse

This study aims at coupling of activated sludge treatment with nanofiltration to improve denim textile wastewater quality to reuse criteria. In the activated sludge reactor, the COD removal efficiency was quite high as it was 91+/-2% and 84+/-4% on the basis of total and soluble feed COD, respectively. The color removal efficiency was 75+/-10%, and around 50-70% of removed color was adsorbed on biomass or precipitated within the reactor. The high conductivity of the wastewater, as high as 8 mS/cm, did not adversely affect system performance. Although biological treatment is quite efficient, the wastewater does not meet the reuse criteria. Hence, further treatment to improve treated water quality was investigated using nanofiltration. Dead-end microfiltration (MF) with 5 microm pore size was applied to remove coarse particles before nanofiltration. The color rejection of nanofiltration was almost complete and permeate color was always lower than 10 Pt-Co. Similarly, quite high rejections were observed for COD (80-100%). Permeate conductivity was between 1.98 and 2.67 mS/cm (65% conductivity rejection). Wastewater fluxes were between 31 and 37 L/m2/h at 5.07 bars corresponding to around 45% flux declines compared to clean water fluxes. In conclusion, for denim textile wastewaters nanofiltration after biological treatment can be applied to meet reuse criteria.     

Use of adsorption using granular activated carbon (GAC) for the enhancement of removal of chromium from synthetic wastewater by electrocoagulation

The present work deals with removal of hexavalent chromium from synthetic effluents in a batch stirred electrocoagulation cell with iron-aluminium electrode pair coupled with adsorption using granular activated carbon (GAC). Several working parameters such as pH, current density, adsorbent concentration and operating time were studied in an attempt to achieve higher removal capacity. Results obtained with synthetic wastewater revealed that most effective removal capacities of chromium (VI) could be achieved when the initial pH was near 8. The removal of chromium (VI) during electrocoagulation, is due to the combined effect of chemical precipitation, coprecipitation, sweep coagulation and adsorption. In addition, increasing current density in a range of 6.7-26.7mA/cm2 and operating time from 20 to 100min enhanced the treatment rate to reduce metal ion concentration below admissible legal levels. The addition of GAC as adsorbent resulted in remarkable increase in the removal rate of chromium at lower current densities and operating time, than the conventional electrocoagulation process. The method was found to be highly efficient and relatively fast compared to existing conventional techniques.     

Removal of COD from laundry wastewater by electrocoagulation/electroflotation

The removal efficiency of COD in the treatment of simulated laundry wastewater using electrocoagulation/electroflotation technology is described. The experimental results showed that the removal efficiency was better, reaching to about 62%, when applying ultrasound to the electrocoagulation cell. The solution pH approached neutrality in all experimental runs. The optimal removal efficiency of COD was obtained by using the applied voltage of 5V when considering the energy efficiency and the acceptable removal efficiency simultaneously. The Cl(-) concentration of less than 2500ppm had a positive effect on the removal efficiency. The performance of the monopolar connection of electrodes was better than that of the bipolar connection in this work. In addition, the removal efficiency of using Al electrodes was higher in comparison with using Fe electrodes in the study. The highest COD removal amount per joule was found to be 999mgdm(-3)kWh(-1) while using two Al electrodes, although the removal efficiency increased with the number of Al plates.     

Detoxification of olive mill wastewater by electrocoagulation and sedimentation processes

Olive mill wastewater (OMW) is characterised by its high suspended solids content (SS), high turbidity (NTU), chemical oxygen demand (COD) concentration up to 100 gl(-1) and toxic phenolic compounds concentration up to 10 gl(-1). This study examined the effect of a physico-electrochemical method to detoxify olive mill wastewater prior an anaerobic biotreatment process. The proposed pre-treatment process consisted in a preliminary electrocoagulation step in which most phenolic compounds were polymerised, followed by a sedimentation step. The BOD(5)/COD ratio of the electrocoagulated OMW increased from 0.33, initial value, to 0.58. Furthermore, the sedimentation step yielded the removal of 76.2%, 75% and 71% of phenolic compounds, turbidity and suspended solid, respectively, after 3 days of plain settling. The combination of electrocoagulation and sedimentation allowed a COD reduction and decoloration of about 43% and 90%, respectively. This pre-treatment decreases the inhibition of Vibrio fisheri luminescence by 66.4%. Continuous anaerobic biomethanization experiments conducted in parallel with raw OMW and electrocoagulated OMW before and after sedimentation at a loading rate of 6g COD l(-1)day(-1), proved that the final pre-treated OMW was bioconverted into methane at high yield while raw OMW was very toxic to anaerobic microorganisms.     

Electrochemical oxidation of textile wastewater and its reuse

It is attempted in the present investigation to treat organic pollutant present in the textile effluent using an electrochemical treatment technique. Experiments are carried out in a batch electrochemical cell covering wide range in operating conditions. Due to the strong oxidizing potential of the chemicals produced, the effluent COD is reduced substantially in this treatment technique. The influence of effluent initial concentration, pH, supporting electrolyte concentration and the anode material on pollutant degradation has been critically examined. It is further attempted in the present investigation to reuse the treated wastewater for dyeing purpose. Several cycles of dyeing operations have been performed with the treated textile wastewater and the dye uptake and water quality have been critically examined at each cycle of dyeing process. The results indicate that the electrochemical method is a feasible technique for treatment of textile wastewater and electrochemically treated wastewater can be effectively reused for dyeing application.