Optimisation of Methylene Blue Adsorption onto Biosorbent from Palm Kernel Shell: A Design of Experiments (DOE) Approach

The treatment of effluents produced by the textile industries in Nigeria leaves much to be desired because there has always been the complex problem of eliminating the synthetic dyes in the effluents such as methylene blue (MB) that do not respond well to the traditional cleaning mechanisms; the situation has ledto the needto explore yet another cheap alternative biosorbent (in this case palm kernel shell) to increase the potential of the adsorption of the dyes. This study explores the potential of using activated carbon derived from palm kernel shells, a locally available agricultural waste, to remove MB from water solutions. The palm kernel shells were carbonised in a muffle furnace, and adsorption experiments were optimised using the Box–Behnken design within the response surface methodology framework. Key variables, including dye concentration, adsorbent dose, and contact time, were examined to assess their effect on dye removal efficiency. Statistical analysis identified a significant model with an F-value of53.83 and p-values less than 0.05 for all factors. Optimal conditions achieved approximately 77% dye removal at an adsorbent dose of0.75 g/100 mL, a contact time of35 minutes, and a dye concentration of133 mg/l. The regression model showed a predicted R² of0.8990 and an adjusted R² of0.9674, indicating high model accuracy. Adsorption isotherms were also analysed, with the Freundlich model fitting better (R² = 0.845) than the Langmuir model (R² = 0.754), suggesting adsorption occurs on a heterogeneous surface. Fourier Transform Infrared Spectroscopy (FTIR) analysis confirmed the presence of active functional groups before and after adsorption. The study demonstrates that activated carbon from palm kernel shells is a practical, low-cost adsorbent for treating textile effluent containing methylene blue.