Efficient adsorption of methylene blue onto raw olive pomace from Moroccan industrial oil mills: Linear and nonlinear isotherm and kinetic modeling with error analysis

Abstract

Dye-contaminated wastewater poses significant environmental risks, particularly to aquatic ecosystems, due to its toxicity and persistence. This study evaluates the potential of raw olive pomace (OP), a lignocellulosic byproduct of Moroccan olive oil production, for the adsorption of Methylene Blue (MB), a cationic dye. A comparative modeling approach using both linear and non-linear methods, combined with statistical error analysis, was employed to rigorously interpret the experimental data. The OP was characterized using FTIR, XRD, TGA/DTA, BET, and SEM techniques. The influence of pH (4–10), initial MB concentration (10–300 mg/L), and contact time (0–180 min) was investigated at the optimal adsorbent mass (0.05 g). A maximum removal efficiency of 98.6 % was achieved. Adsorption data were fitted to Langmuir and Freundlich isotherms and to pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models, in both linear and non-linear forms. The Langmuir model provided the best fit, with maximum adsorption capacities of 232.55 mg/g (linear form) and 252.08 mg/g (non-linear form) at pH 8. Kinetic studies indicated that the PSO model best described the adsorption behavior, suggesting chemisorption as the rate-limiting step. Non-linear modeling was performed using Excel Solver, and error functions (NSD, ARE, χ², RMSE) confirmed the accuracy and reliability of the selected models. These findings demonstrate that raw OP is a highly effective, low-cost, and environmentally friendly biosorbent for the removal of Methylene Blue from aqueous solutions.