Activated carbon (AC) was prepared from sapelli wood sawdust using a microwave heating process. The biomass was mixed with inorganic components (lime + ZnCl₂ and FeCl₃) to form a homogeneous paste. The AC samples are denoted as AC-1A (100 g sapelli wood sawdust + 20 g lime + 80 g ZnCl₂), AC-2A (150 g sapelli wood sawdust + 20 g lime + 80 g ZnCl₂), AC-1B (100 g sapelli wood sawdust + 20 g lime + 40 g ZnCl₂ + 40 g FeCl₃), and AC-2B (150 g sapelli wood sawdust + 20 g lime + 40 g ZnCl₂ + 40 g FeCl₃). The samples were placed in a microwave oven and pyrolyzed under nitrogen flow. To increase their porosity, the pyrolyzed samples were subjected to a leaching process (with 6 mol L⁻¹ HCl) under reflux to eliminate inorganic components. Several analytical techniques such as Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and N₂ isotherm and vapor adsorption analyses were performed to characterize the AC materials. The samples presented high Brunauer–Emmett–Teller (BET) surface areas, up to 941.08 m² g⁻¹ for AC-1A. The AC materials were tested for their o-cresol removal ability by determining the best fits to equilibrium and kinetic data using the Sips isotherm and fractional-order model, respectively. The maximum adsorption capacity of the AC samples as obtained from the Sips model was correlated with the surface area. The proposed adsorption mechanism suggests that hydrogen bonding, donor–acceptor complexation, and π–π interactions play key roles. The adsorbents were also tested for treatment of simulated industrial effluents, showing very good efficiency. Almost complete regeneration of the AC adsorbents was achieved using 10 % EtOH + 5 mol L⁻¹ NaOH as eluent. These results demonstrate that sapelli wood sawdust is a promising precursor for preparation of AC to remove o-cresol from aqueous solution.