Increased biogas residue related to the rapid development of anaerobic fermentation has become an urgent environmental problem. The pyrolysis of biogas residue into biochar is one of the most promising treatments. In this study, biochar derived from biogas residue was prepared, and the degradation efficiency of phenol by permanganate (KMnO₄) increased from 25.3% to 73.4% in 60 min in the presence of biogas residue biochar (BRB). KMnO₄ reacted with BRB to produce intermediate manganese dioxide (MnO₂), while BRB was activated. The specific surface area increased by 132.25%, and the oxygen-containing functional groups C=O, C−O, and COOH increased after the reaction. The generated MnO₂ complexed with BRB to form MnO₂@BRB. The newly formed MnO₂@BRB catalyzed KMnO₄ to remove phenol, which explains the high removal efficiency of phenol. A significant removal rate was also observed for antibiotics and chlorophenols, which suggested that the KMnO₄/BRB system has a relatively high ability to oxidize organic pollutants. In addition, the co-existing metal ions and the natural environment had little influence on the removal efficiency of the KMnO₄/BRB system. This work provides a novel technology for the resource utilization of biogas residue and improved organic pollutant removal efficiency of KMnO₄ in the presence of BRB. Graphical abstract