Adsorption of crystal violet from aqueous solution onto sugarcane bagasse: central composite design for optimization of process variables

The adsorption of crystal violet (CV) from aqueous solution by sugarcane bagasse (SCB), an agro-industrial residue, was investigated in a batch experimental setup. A two level four factor (2⁴) full factorial central composite design (CCD) with the help of Design Expert Version 7.1.6 (Stat-Ease, USA) was used for adsorption process optimization and evaluation of interaction effects of different operating parameters: agitation speed (80–180 rpm), initial solution pH (4.0–8.0), initial dye concentration (100–200 mg L^–1), and adsorbent dose (2–5 g L^–1). A multiple coefficient of determination (R²) value of 0.98, model F value of 266.36 and its low P-value (<0.0001) along with lower value of coefficient of variation (2.70%) indicated the fitness of the response surface quadratic model developed during the present study. Numerical optimization applying desirability function was used to identify the optimum conditions for maximum removal of CV. The optimum conditions were found to be agitation speed = 165 rpm, initial solution pH = 8.0, initial dye concentration = 200 mg L^–1 and adsorbent dose = 2.0 g L^–1. A confirmatory experiment was performed to evaluate the accuracy of the optimization procedure and maximum CV removal of 93.21% was achieved under the optimized conditions.