Process Optimization and Modeling the Adsorption of Polycyclic Aromatic-Congo Red Dye onto Delonix regia Pod-Derived Activated Carbon

Abstract

This study was carried out to optimize the batch adsorption of a polycyclic aromatic dye from a simulated textile wastewater onto Delonix regia-derived activated carbon (DRP-AC) under the influence of contact time, agitation rate, and initial dye concentration as process variables. Congo red (CR) dye was used as the model pollutant. Response Surface Methodology (RSM) with a D-Optimal experimental design was employed for this study having three factors and three levels as independent variables and percentage dye removal as the dependent variable (response). The kinetics and CR adsorption equilibrium were investigated and modeled. The CR adsorption data fitted well to a second-order quadratic regression model with a high coefficient of determination ( = 0.9999) using Design-Expert Statistical program (v. 6.0.8). The regression model indicated that the percentage dye removal was significantly (p < 0.05) impacted upon by the linear, quadratic, and interactive effects of contact time, agitation rate, and initial dye concentration. The optimum values for the dye adsorption process conditions to elicit a maximum percentage dye removal of 79.7% were found to be: 140 min (contact time), 165 rpm (agitation rate), and 300 mg/L (initial dye concentration). The CR dye adsorption kinetics followed pseudo-first-order kinetics while the mechanism of adsorption was controlled by intraparticle diffusion. The CR equilibrium adsorption can well be described by the Langmuir isotherm model (R2 = 0.9951). The maximum monolayer adsorption capacity () was found to be 17.12 mg/g. Therefore, DRP-AC has the potential for polycyclic aromatic dye adsorption from wastewaters.