Optimization of heavy metal biosorption onto freshwater algae (Chlorella coloniales) using response surface methodology (RSM)

Abstract

In this study, the interaction of the initial metal concentration, time of reaction and Chlorella coloniales algae dose were taken for the biosorption of Cr, Cd, Co, Fe and As from aqueous solutions using the Box–Behnken design. The regression equation coefficients were calculated and the data confirmed the validity of second-order polynomial equation for the removal of Cr, Cd, Co, Fe and As with Chlorella coloniales algae. Analysis of variance (ANOVA) showed a high coefficient of determination value (R2) for Cr, Cd, Co, Fe, and As, being respectively 0.998, 0.998, 0.995, 0.998 and 0.994. Heavy metal biosorption increased with the increase in time of reaction from 30 h to 100 h then smoothly steadily decreased. The biosorption capacity of Chlorella coloniales increased when initial Cd concentration was increased from 5 to 12 mg/L, and then no change was seen with further increasing in initial Cd concentration. At low concentrations of heavy metal, Chlorella coloniales showed its effectiveness for Cr, Co, Fe and As bioaccumulation, but at high concentrations of heavy metal bioaccumulation efficiency decreased Under optimal value of process parameters, maximum efficiencies for the removal of Cr, Cd, Co, Fe, and As were 97.8, 97.05, 95.15, 98.6 and 96.5% respectively. The results of the present study suggest that use of C. Coloniales algae can be a good alternative to the current expensive methods of removing heavy metals from aqueous solution.