Application of response surface methodology in the modeling of cadmium removal from aqueous environment by electrocoagulation process

Background: Discharging effluents containing heavy metals is very harmful due to accumulative property and non-biodegradability of them. Electrocoagulation, due to easy operation and less chemical consumption, is being considered as a process for removal of heavy metals from aqueous environments. Objective: The aim of the study was to evaluate the effects of variables influencing the removal of cadmium from aqueous environment during electrocoagulation and to develop a model for predicting the results. Methods: This experimental study was performed in a batch electrocoagulation reactor using aluminum electrodes. Direct current was supplied using D.C power supply. Cadmium concentrations were measured using standard methods for the examination of water and wastewater. Response surface methodology and central composite design were used to determine the effects of variables (pH, initial concentration of cadmium, electric current density, reaction time and distance between electrodes) on the removal of cadmium, to design the experiments, to prepare the prediction model for cadmium removal and to optimize the variables.  Findings: The optimal removal efficiency in the conditions of pH; 8.32, current density; 2.965mA/cm2, initial concentration; 65.5 mg/L, reaction time; 54 min and distance between electrodes: 0.723cm was 97.5%. Also R2, Adj.R2 and Pred. R2 were 0.98, 0.97 and 0.96, respectively, which indicates a good fit of the data on quadratic equations. The interactions of all variables were significant in the removal of cadmium by electrocoagulation. The quadratic model is a suitable model for predicting the removal of cadmium using electrocoagulation. Conclusion: Electrocoagulation equipped with aluminum electrodes has high performances in cadmium removal from aqueous environment. This process can be used in primary or supplementary treatment of industrial wastewater containing this heavy metal.