Comparative study of Central Composite and Box-Behnken design for the optimization of malachite green dye adsorption onto Sal seed activated char

Abstract

Aim : Malachite green dye is extensively used for coloring purpose, as therapeutic agent and as a biocide in the aquaculture industry. The presence of dye in the industrial effluents is an environmental concern, and therefore it's removal is inevitable. Sal seed activated char was utilised for the removal of dye from aqueous solution through adsorption process. The purpose of the present study was to examine and optimize the effect of adsorbent dose, pH and initial dye concentration on dye adsorption Central Composite Design (CCD) and Box-Behnken Design (BBD). Methodology : Adsorbent was prepared by pyrolysing raw Sal seeds followed by chemical activation of resultant char using 85 % phosphoric acid. The characterization of activated char was done with SEM, FTIR and XRD. Batch adsorption studies were carried out at different pH, adsorbent doses and initial concentrations of malachite green dye. The experimental data were used as input in the Central Composite Design and Box-Behnken Design. Results : The adsorption was found to be exothermic and spontaneous in the temperature range studied and followed pseudo second order kinetics. Freundlich isotherm was in good agreement with the experimental data. The percentage removal of malachite green dye increased with pH and adsorbent dose, whereas it decreased with the initial dye concentration. The optimum values obtained for the pH, adsorbate concentration , adsorbent dose and dye removal were 10, 50 mg l-1, 1.2 g l and 96.3% for Box- Behnken Design and 9.89, 12.5 mg l-1, 1.7g l-1, and 100% f o r Central Composite Design, respectively. Interpretation : Central Composite Design was found to be better in comparison to Box- Behnken Design for the optimization of malachite green dye adsorption onto Sal seed activated char.