AbstractIn this study, crude lignin extracted from the black liquor generated by a pulp and paper mill was modified by different doses of irradiation. The crude and irradiation-modified lignins were used to treat wastewater that was generated during the production of starch glucoamylase. Changes to the physical and chemical properties and structure of the irradiation-modified lignins were determined using scanning electron microscopy, solubility analysis, elemental analysis, analysis of phenolic hydroxyl group, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. Irradiation reduced the phenolic hydroxyl content in the lignin but increased its solubility by about 40%; analysis revealed that irradiation also destroyed the skeletal structure of the benzene ring in the lignin. After four minutes of settling, the total nitrogen (TN) and chemical oxygen demand (COD) in the wastewater reached 7.0 mg/L and 1573.1 mg/L, respectively. The settled solids content and protein recovery were 1.12 g/L and 98%, respectively. This study suggested that irradiation-modified lignin extracted from black liquor generated in the pulp and paper industry can be used to treat wastewater from the production of starch glucoamylase.