Electrocoagulation Treatment of Electroplating Wastewater: A Review

Electrochemical methods such as electrocoagulation (EC), electrooxidation (EO), and electroreduction (ER) are promising technologies to remove organics and heavy metals contained in industrial effluents discharged from numerous industries such as electroplating, textile, and metal processing. EC is widely applicable to treat wastewater that has a wide range of pollutants as well as being applicable to treating organic pollutants having a chemical oxygen demand (COD) range of 1,000-13,000 mg/L, and metals concentration in the range of 10-2,500 mg/L depending on the type of pollutants/metals. Several parameters such as pH, current density, electrode gap, electrolysis time, and agitation speed plays a major role during EC. Various laboratory results show that EC works effectively in the pH range 2-8, current density 20-200 A/m(2), electrode gap 1.5-3 cm, electrolysis time 10-150 min, and stirrer speed 30-200 rpm for the reactor size 1-2.5 L depending on the type of wastewater/effluent. Moreover, this process has been proved to be versatile and environmentally friendly. This review mainly focuses on the separation of heavy metals from electroplating effluent (EPE), including other pollutants removal from various industrial effluents such as textile, distillery, paint, and tannery. EC operation is oriented on the supply of direct current in metal electrodes and, consequently, metal ions released into the solution. This results in an increased metal concentration in the solution that finally precipitates as metal hydroxides along with pollutants. Numerous techniques are available to treat heavy metals bearing effluent, which includes precipitation, adsorption, bioadsorption, ion exchange, and membrane separation. These methods have several limitations in term of high operating costs and a large amount of sludge generation, while the EC process has several advantages over conventional technologies such as requirement of less external chemicals, easier installation, lower secondary pollutants formation, odor and color removal, and lower residence time. However, high electricity consumption due to formation of oxide film on the surface of the electrode is a major drawback of this process because oxide film works as an electric insulator. Overall, the EC method has wide potential to treat different kinds of effluents. (c) 2020 American Society of Civil Engineers.