Modeling and optimization of adsorption parameters for hexavalent chromium removal from wastewater using Box-Behnken design and response surface methodology

Chromium discharged from industries has the potential to severely damage the environment. This study focuses on the optimization of adsorption parameters for successful elimination of hexavalent chromium, i.e., Cr(VI) from wastewater by utilizing activated carbon. The study used an economical Box-Behnken Design (BBD) and response surface methodology (RSM), as a novel approach to design the experiments for pH varied from 2 to 6, adsorbent dosage and contact time ranging from 0.8 to 1.6 g/L and 30–150 min respectively. Thereafter, using BBD-RSM, the adsorption parameters were modelled, and optimized to get maximum Cr(VI) removal. A second-order regression model was developed, which predicted a removal of 98.6% with a desirability function of 0.989 at the optimum pH of 2, contact time of 150 min, and the adsorbent dose of 1.2 g/L. Kinetic studies showed that a pseudo-second-order model, with R² of 0.999 fitted well, indicating chemisorption. Additionally, equilibrium studies conformed to a Langmuir isotherm with an R² value greater than 0.98, indicating monolayer adsorption onto the surface of activated carbon. Hence, these models, combined with the optimization of adsorption parameters, enabled high removal efficiencies of Cr(VI) from wastewater and a reliable prediction of adsorption behavior.