Optimization of process parameters for the removal of chromium(VI) and nickel(II) from aqueous solutions by mixed biosorbents (custard apple seeds and Aspergillus niger) using response surface methodology

Abstract

The mixture of custard apple seeds and Aspergillus niger was used as biosorbents for the removal of chromium(VI) and nickel(II) from the contaminated water. The batch biosorption process was carried out and it was influenced by the different operating parameters such as initial metal ion concentration, pH, temperature, and biomass loading. The essential process variables were optimized using response surface methodology (RSM) based on the central composite design (CCD) experiments. The ANOVA data obtained from the RSM studies were analyzed using a second-degree polynomial equation and the study of the determination of contour plots showed the interactions among the variables of the biosorption system. The optimum conditions for the removal of chromium(VI) was found to be: initial chromium(VI) concentration = 100 mg/L; pH 3.0; temperature = 36°C, and biosorbent loading = 10 g/L. At these optimized conditions, the maximum removal of chromium(VI) was found to be of 95.7%. The optimum conditions for the removal of nickel(II) was found to be: initial nickel(II) concentration = 100 mg/L; pH 5.6; temperature = 30°C, and biosorbent loading = 10 g/L. At these optimized conditions, the maximum removal of nickel(II) was found to be of 96.41%. The mixed biosorbents showed better adsorption properties towards the removal of chromium(VI) and nickel(II) ions from the aqueous solutions. These low-cost biosorption methods can be effectively adopted for the removal of metal ions from the industrial effluents.

Keywords:

• Aspergillus niger
• Biosorption
• Custard apple seeds
• Heavy metals
• Response surface methodology