Application of Response Surface Methodology for the Optimization of Cu and Zn Removals by Sorption on Pre-treated Oil Palm Frond (OPF)

The increase in the usage of heavy metals in various industrial processes results in increasing heavy metal wastes that need further treatment. Cu and Zn remain hazardous even at low concentration and it is a clear necessity that they be removed from the effluent. The performance of oil palm frond (OPF) pre-treated with NaOH as asorbent to remove Cu and Zn from aqueous solution was optimized in this study. 2 g of OPF was treated for 300 min in a 250 ml of 1.0 M NaOH solution to improve its sorption ability. Response Surface Methodology (RSM) based on the Three-Variable Composite Face Centered Design was employed as an experimental model to evaluatethe effects of initial Zn and Cu concentration (5-100 mg/l), pH of the solution (2-9) and biomass loading (0.5-2.0 g) on the sorption process carried out at 25°C. The solution pH, initial metal concentration and biomass loading were used as the main process variables while the sorption performance was based on the removal efficiency. The coefficient of determination, R^2, was found to be 0.96 and 0.97 for Cu and Zn removals, respectively. The initial concentration of 89 mg/l, biomass loading of 1.7 g and initial pH of 4.5 were found to be the optimum conditions for the maximum Cu removal of 91.0%, corresponding to sorption capacity of 11.9 mg/g. The optimum conditions for the highest Zn removal of 80.5 %% or sorption capacity of 9.0 mg/g were found to be at an initial concentration of 76 mg/l, biomass loading of 1.7 and initial pH of 5.5.