Industrial wastewater treatment by electrocoagulation and conventional coagulation

This research was postulated in order to increase the knowledge on the electrochemically-assisted-coagulation of industrial wastewaters using aluminium anodes. Hence, the aim of this work has been the study of the electrocoagulation process to treat aqueous synthetic effluents polluted with colloidal particles, organic matter, or Oil-in-Water emulsions, using aluminium electrodes. This general aim has been divided in several partial objectives: (1) Characterization of the chemical and electrochemical dissolution of aluminium sheets, when they are used as electrodes in the electrocoagulation process. (2) Characterization of the hydrolyzed aluminium species generated in the conventional coagulation and electrocoagulation processes. (3) Mathematical modelling of the electrodissolution of aluminium sheets when they are used as electrodes in the electrocoagulation process. (4) Study of the influence of the wastewater characteristics and of the operation conditions on the electrocoagulation of wastewaters polluted with kaolin (as model of colloidal suspension), Eriochrome Black T (as model of wastewater polluted with dissolved organic matter), and with O/W emulsions. (5) Comparison of the conventional and electrochemical coagulation processes in the treatment of wastewaters polluted with kaolin, EBT and O/W emulsions. (6) Preliminary comparison of the operating costs, for the dosing of coagulant by the conventional and the electrochemical technologies. (7) Mathematical modelling of the conventional and electrochemical coagulation of wastewaters polluted with kaolin, EBT and O/W emulsions.; It has been found that in the electrochemical cell, the aluminium added to the electrolyte comes from both chemical (corrosion) and electrochemical dissolution processes. As well, it was observed that the speciation of aluminium in an aqueous solution does not depend directly on the dosing technology, but on the total concentration of aluminium and pH. The studies of electrocoagulation of wastewaters with aluminium electrodes have shown that this process can be successfully applied in the treatment of wastes polluted with kaolin, EBT and O/W emulsions. Regarding the comparison, there are not significant differences between the efficiencies obtained by the conventional and the electrochemical technologies, when the same values of pH and aluminium concentration are attained in the reaction system. Finally, the economical evaluation showed lower operating costs for the electrochemical process for low and intermediate aluminium doses.