Modeling of Copper removal from aqueous solution by Populus nigra sawdust using central composite design

Background and objectives: The release of heavy metals into the environment, especially to the water resources is one of the main environmental concerns of the last few years. Copper is a common heavy metal in agricultural and industrial activities which significantly contributes in the pollution of surface and ground water resources. Since copper is a widely used material, its removal from aqueous solutions is a main challenge in water purification. Sawdust as a cost effective and locally available bioadsorbent, is a promising material for the removal of heavy metals especially copper from aqueous solutions. The aim of this study was to quantitative modeling of the effects of pH, copper concentration, sawdust dosage, and contact time on the copper removal from aqueous solutions.
Materials and methods:In this study, the sawdust of Populus nigra withgrain size of 250-600‌μm, was used as a bioadsorbent for the removal of copper from synthetic aqueous solution. Sawdust sample was washed with distilled water and dried inthe laboratory conditions. The sorption of copper on sawdust has been studied by using the batch technique. The central composite design was carried out with aqueous solution of copper with various concentrations ranging from 1-25 mgl-1. The range of variation for the other variables including pH, sawdust dosage and contact time are 2-10, 5-25 gl-1, and 5-185 minutes, respectively. At the end of the each experiment, the equilibrium concentration of the copper was determined by atomic adsorption spectrometer and the removal percentage of the copper was calculated from the difference between the initial and equilibrium concentrations.
Results:The results of the central composite design model demonstrated the high efficiency (R2= 0.907 and RMSE=3.34%) of the predictive model for copper removal by sawdust. Pareto analysis of the central composite design model indicated that, among four variables, contact time, sawdust dosage, pH and initial copper concentrationshave the highest effects on the copper removal respectively.Increasing of the pH at the range of 2 to 7, leads to the increase of the copper removal. The copper removal was also increased at high contact times and sawdust dosages.There was a negative relationship between the initial copper concentration and the removal percentage of the copper.
Conclusion: It has been demonstrated that the Populus nigra sawdust can be considered as a suitable bioadsorbent of heavy metals. The efficiency of the copper removal by sawdust may be reach up to the 94 percent especially at low initial concentrations of the copper. Adjustment of the pH of the solution at the range of 6 to 7 leads to the high efficiency of copper removal by sawdust. Considering the low cost and availability of sawdust, it can be recommended as a bioadsorbent for purification of water resources from copper pollution.