Electrocoagulation processes: A general review about role of electro-generated flocs in pollutant removal

Electrocoagulation (EC) is an acclaimed environmentally adequate approach to wastewater treatment. It is simple and economical by way of reducing the amount of chemical dosage, sludge generation and disposal, and the high costs involved in traditional chemical coagulation (CC). This paper discusses the mechanisms of pollutant removal by electro-generated hydroxide and oxyhydroxide flocs during EC process. The flocs’ generation and formation with Fe, Al and other metal electrodes, and the influence of operating conditions (pH, current density, electrolyte composition, etc.) on floc structure are reviewed. Further, revisions were provided on recent studies about new areas in electro-generated (oxy)hydroxide flocs such as layered double hydroxides (LDHs) and green rusts (GR), common characterization techniques, and factors promoting EC floc production. Results clearly indicate that during EC, the most proposed removal mechanisms of (oxy)hydroxide flocs towards oxyanions, cationic heavy metals, and organic pollutants are adsorption and coprecipitation, charge neutralization and surface complexation, and direct/indirect radical oxidation respectively. EC process alone which has low radical generation is less efficient when treating organic pollutants. Consequently, coupling and combination of AOP-EC generates suitable amounts of radicals and flocs for organic pollutant removal.