Chemical and Electro-coagulation Techniques in Coagulation-Floccculation in Water and Wastewater Treatment- A Review

Abstract

Chemical and electrocoagulation are widely used coagulation methods employed in water and wastewater treatment. Both coagulation processes are effective in removing a wide range of impurities which include dissolved organic matter in form of chemical and biological oxygen demand, pathogens, oils, and colloidal particles as well as heavy metals. The present review has revealed that the mode of action of both coagulation methods is based on charge neutralization and floc formation. The effectiveness of both coagulation techniques depend on factors such as pH, coagulation dose, coagulant type, current density, applied voltage, water and wastewater  type, type of electrode, as well as size and number of electrodes. The commonly used chemical coagulants are inorganic coagulants based on aluminum and iron salts. However, there have been considerable successes in the development of pre-hydrolyzed inorganic coagulants which have the added advantage over traditional inorganic coagulants in that they function well over a wide range of pH and water temperatures. Electrocoagulation has been proposed as an alternative method to chemical coagulation because it is environmental friendly and cheap to operate. Nonetheless, most researchers are of the opinion that there are still some uncertainties regarding the understanding of its optimal performance and design mechanism.