The increasing global demand for sustainable wastewater management in the food manufacturing industry underscores the need for efficient, environmentally friendly, and cost-effective treatment solutions. This study investigated the application of starch derivative-functionalised biochar (FBSD) as an adsorption-based polishing treatment for food manufacturing wastewater. FBSD was prepared from rice husk biochar and evaluated for its ability to reduce Chemical Oxygen Demand (COD) and colour in actual wastewater collected from the secondary clarifier of an industrial wastewater treatment facility. The adsorption performance of FBSD was assessed through COD reduction, colour removal, iodine adsorption number, and regeneration capability over three consecutive cycles. The functionalised biochar exhibited a high initial iodine adsorption number of 650.24 ± 0.03 mg/g, indicating substantial adsorption potential. Treatment with FBSD reduced COD from 160.00 ± 0.00 mg/L to 15.00 ± 0.00 mg/L, corresponding to a removal efficiency of 90.63%, while colour decreased from 315.00 ± 1.73 ADMI to 5.00 ± 0.00 ADMI, achieving 98.41% removal. The adsorbent maintained satisfactory performance during the first regeneration cycle but exhibited a gradual decline in adsorption efficiency with repeated regeneration due to the loss of active adsorption sites. A preliminary economic assessment indicated that although FBSD offers environmental benefits through the utilisation of agricultural biomass, further process optimisation and scale-up are required to improve its economic competitiveness with commercial activated carbon. Overall, the findings demonstrate the potential of FBSD as a sustainable polishing adsorbent for industrial wastewater treatment applications.