Continuous electrocoagulation of synthetic colloid-polluted wastes

The electrocoagulation of a synthetic wastewater has been studied in this work. The electrochemical process was carried out in a continuous single-flow electrochemical cell equipped with aluminum electrodes. Kaolin suspensions were used as a model of wastes polluted with colloids, as clays behave as hydrophobic colloids in water. The results obtained were useful to clarify the mechanisms that are involved in the electrocoagulation of this kind of waste and also to study the influence of the different operation conditions in the process. It has been found that the more important variables in the process were the aluminum concentration generated in the system and the pH. The concentration of aluminum generated in the electrochemical cell was always over the expected value (superfaradaic efficiencies) due to the important contribution of the chemical dissolution of the electrodes. This chemical dissolution of the electrodes depended strongly on the pH. A larger concentration of aluminum in the waste did not result in greater process efficiencies. For acidic pHs, a small concentration of aluminum achieved good coagulation efficiencies (80% removal of turbidity), while for alkaline pHs neither high nor low concentrations of aluminum yielded good coagulation results. For pHs close to neutral, a large concentration of aluminum was required to achieve good results. Two primary coagulation mechanisms can explain the experimental behavior of the system: at acid pH the neutralization of the superficial charge of the clays and at neutral pH (and also at high concentrations of aluminum) the enmeshment of the kaolin particles into a sweep floc.