Electrocoagulation Separation Processes
Nael Yasri, Jinguang Hu, Md Golam Kibria, Edward P.L. Roberts
Abstract
The process of electrocoagulation is a highly effective method to remediate effluent streams and to separate problematic pollutants before the discharge of the treated water. Interest in this technology has increased due to its broad range of applications, zero—or minimal—chemical dosing requirements, low waste production, and low cost. The process of electrocoagulation is emerging as an effective alternative to conventional water treatment processes for the separation of a wide range of pollutants. This chapter explores the principles of the electrocoagulation process, and its implementation for the separation of pollutants from wastewater streams. The technology relies on the combination of electrochemical and coagulation processes. Key factors that influence the performance include the electrode material (usually iron or aluminum), current density, electrical charge per unit volume, and solution pH. Commercial electrocoagulation systems are normally operated at constant current (5–20 mA/cm2) to ensure effective treatment. Electrode fouling can present a significant operational challenge but can be mitigated by alternating current operation. Dosing of the coagulant in the electrocoagulation process obeys Faraday’s law of electrochemical dissolution (the Coulombic efficiency is typically close to 100%), which facilitates process automation and control. The electrocoagulation performance can be characterized in terms of the Coulombic efficiency (>95%), electrical energy per unit volume (typically 0.5 kWhr/m3), and the separation efficiency (often >95%). Design parameters must be selected by considering economic, performance and operational factors. The interelectrode gap (typically <15 mm) must consider flow distribution, the risk of plugging due to fouling or coagulated solids, and the cell resistance (and hence energy consumption). Selection of the operating current density is dependent upon the solution conductivity (and hence energy consumption), the total area of electrode required for effective treatment, and the lifetime of the electrodes.