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Olive activated biochar (OAB) was prepared from waste de-oiled olive pomace (sansa esausta, SE) through carbonization followed by combined KOH and thermal activation. The activation process was optimized using central composite design (CCD) with pyrolysis temperature, activation time and KOH to pyrolized SE mass ratio (KOH/PSE) as independent variables, and yield, methylene blue number (MBN) and iodine number (ID) as responses. Optimized OAB was subjected to fixed bed adsorption of 100 mg L−1 methylene blue dye. Numerical optimization resulted in optimum process setting of 362°C pyrolysis temperature, 61-min activation time and 0.81 KOH/PSE under which the optimized activated biochar produced 31% OAB, MBN of 679 and ID of 899. Thomas and Yoon-Nelson models best fit the fixed bed adsorption data implying that methylene blue adsorption conforms to Langmuir isotherm and obeys pseudo-second order reversible reaction kinetics with no axial dispersion. The theoretical adsorption capacity of OAB is 131 mg g−1 with theoretical time required for 50% sorbate breakthrough of 54.69 h. These results show the potential application of OAB in dye adsorption.