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Various techniques such as physical, chemical, biological, advanced oxidation and electrochemical are used for the treatment of industrial effluent. The commonly used conventional biological treatment processes are time consuming, need large operational area and are not effective for effluent containing toxic elements. Advanced oxidation techniques result in high treatment cost and are generally used to obtain high purity grade water. The chemical coagulation technique is slow and generates large amount of sludge. Electrocoagulation has recently attracted attention as a potential technique for treating industrial effluent due to its versatility and environmental compatibility. This technique uses direct current source between metal electrodes immersed in the effluent, which causes the dissolution of electrode plates into the effluent. The metal ions, at an appropriate pH, can form wide range of coagulated species and metal hydroxides that destabilize and aggregate particles or precipitate and adsorb the dissolved contaminants. Therefore, the objective of the present manuscript is to review the potential of electrocoagulation for the treatment of industrial effluents, mainly removal of dyes from textile effluent., (© 2013 Elsevier Ltd. All rights reserved.)

The performance of electrocoagulation (EC) was studied by conducting experiments for the removal of Reactive Orange 4 dye from its synthetic aqueous solution. The effect of operational parameters (initial solution pH, current density, inter-electrode distance, electrolysis time and retention time, solution temperature, conductivity and different electrode combinations) on the efficiency of EC was studied and the results were analysed in terms of colour removal efficiency (CRE), electrical energy consumption (EEC) and operating cost (OC). The effect of different anions on the efficiency of EC was studied by conducting experiments with electrolytes containing chloride, sulphate, carbonate and nitrate ions. The characterisation of EC generated sludge was performed using XRD. A maximum CRE of 95% was obtained for EEC of 1.7 kWh/m3 and OC of 0.45 US $/m3. It was found that the addition of electrolyte containing chloride ions resulted in higher CRE (93–95%) compared to electrolytes containing sulphate and carbonate ions as their presence can lead to passivation of the electrode surface & thereby resulting in a reduction in CRE (60% and 41%, respectively). The addition of sodium chloride as an electrolyte resulted in minimum EEC and OC. The Al/Al electrode combination provided the maximum CRE and least EEC & OC. The increase in solution temperature leads to reduction in CRE and CE due to formation of passive layer on the surface of electrodes. However, a reduction in cell potential and EEC was noticed with an increase in solution temperature. [ABSTRACT FROM AUTHOR]

Textile industries are water intensive and the effluent generated contains salts, dyes, and heavy metals as well as having a high biological oxygen demand (BOD) and chemical oxygen demand (COD), therefore it must be treated before being discharged into the aquatic environment to prevent its contamination. Electrocoagulation (EC) is a promising technique to treat domestic and industrial effluent, where in situ coagulants are produced by sacrificial dissolution of the anode by application of an electric current across the electrodes. The effect of punched-hole electrodes on the performance of EC—color removal efficiency (CRE), electrical energy consumption (EEC), and operating cost (OC)—was studied by varying the number and diameter of holes in the electrode. It was observed that the use of punched electrodes resulted in higher CRE, lower EEC, and lower OC as compared with plane electrodes. The difference in CRE obtained using plane and punched electrodes was found to increase with an increase in current. The effect of punched-hole electrodes on the treatment of real dye effluent was studied and COD removal of 78.79% was obtained using punched-hole electrodes as compared with 69.30% using plane electrodes. The EEC and the OC were found to be 0.5 kW·h/m3 and US$0.424/m3, respectively, for punched-hole electrodes. [ABSTRACT FROM AUTHOR]

Electrocoagulation is a versatile technique used for treating various types of industrial effluent. The material of the construction and shape of the electrodes are crucial in the electrocoagulation process. The effect of the electrode shape on the performance of the electrocoagulation has been studied by performing experiments for the removal of the dye from the synthetic dye solution using punched electrodes and the results have been evaluated in terms of color removal efficiency. The effect of the number of holes, the diameter of the hole, and the configuration of the holes (square, triangular, and random pitch of the holes) on the color removal efficiency was investigated. An increase in the color removal efficiency was obtained using the punched electrode compared with the plane electrode. The effect of the current source (direct and alternating current) on the performance of the electrocoagulation was studied and no significant effect of the current source on the performance of the electrocoagulation was noticed. [ABSTRACT FROM AUTHOR]

Electrochemical treatment of small-scale dyeing unit effluent containing Reactive Yellow 86, Indanthrene Blue RS, Basic GR 4 and Reactive Yellow 145 dyes was carried out with aluminium electrodes in batch mode of operation. The effluent was characterized for various parameters. The experiments were performed for 120 min, keeping the inter-electrode distance at 3 cm with a current density of 0.0625 A/cm2; the colour removal efficiency was determined for each of the four dyes. A colour removal efficiency of >97% was obtained for each of the dyes for an electrolysis time of 120 min. Further experiments were performed using aluminium sulphate as chemical coagulant to compare the colour removal efficiencies obtained by electrocoagulation and chemical coagulation. [ABSTRACT FROM PUBLISHER]

Experiments were performed in batch mode of operation using iron electrodes to remove chromium from effluent by electrocoagulation, and the effect of various operating parameters was investigated. The maximum hexavalent chromium removal efficiency of 100% from a synthetic solution containing hexavalent chromium was obtained for an electrolysis time of 15 min at the optimum current density of , interelectrode distance 0.5 cm, and solution pH of 4. The real electroplating industry effluent was characterized using the standard diphenylcarbazide (DPC) method. A 100% chromium removal efficiency was obtained for both trivalent and hexavalent chromium, for an electrolysis time of 45 min at 4 pH. It was found that Cr(VI) is initially reduced to Cr(III) in the acidic medium. An increase in the pH of the effluent was also noticed in the acidic medium due to the generation of hydroxyl ions. Experiments were performed for the removal of chromium using ferric chloride as the coagulant, and it was found that electrocoagulation is more efficient and relatively faster compared to chemical coagulation. [ABSTRACT FROM AUTHOR]