<p>This study examines the preparation and application of biochar (BC) derived from fermentation residues (FRs) of chlortetracycline (CTC) production, aiming to identify sub-optimal preparation conditions for effective polysaccharide removal. BC was prepared through carbonization at 400&#xa0;°C for 1&#xa0;h, followed by steam activation at 700–900&#xa0;°C for 1–3&#xa0;h. The activated BC effectively removed CTC and eliminated inorganic compounds present in synthetic fermentation media, except for CaCO₃, from fermentation residues. The optimal preparation conditions yielded a surface area of 289.88&#xa0;m²⋅g^− 1 at 700&#xa0;°C for 1&#xa0;h. Adsorption tests on polysaccharide-rich tapioca starch wastewater, with concentrations ranging from 1,250 to 10,000 mg⋅L^− 1, achieved removal efficiencies of 57–70% and COD reductions of 20–58%. Adsorption isotherms were modeled using Langmuir, Freundlich, and Sips equations, with Freundlich providing the best fit based on the lowest χ² value. The maximum adsorption capacities of the virgin BC were 500 mg⋅g^− 1 (Langmuir) and 526 mg⋅g^− 1 (Sips), outperforming the ferric nitrate-impregnated BC (Fe-BC). Kinetic analysis followed a pseudo-second-order model, and thermodynamic results indicated a spontaneous, endothermic process, consistent with computational modeling via the adsorption locator module. Mechanistic studies revealed that polysaccharide adsorption on virgin BC was dominated by hydrogen bonding, π–π stacking, and dipole–dipole interactions, whereas Fe-BC additionally benefited from ligand exchange and electrostatic attraction at Fe sites. Consequently, virgin BC exhibited superior polysaccharide removal, while Fe-BC achieved greater COD reduction. These results demonstrate the potential of BC-based adsorbents as cost-effective and efficient materials for treating polysaccharide-containing wastewater.</p> Graphical Abstract <p></p>