<p>Macromolecular humic acid (HA) is highly resistant to degradation in wastewater treatment system. Although catalytic wet air oxidation (CWAO) processes can degrade HA, they typically require relatively high temperatures (&gt; 200 °C) to achieve effective degradation. In this study, the effect of hydrogen peroxide (H₂O₂) as a radical promoter on the CWAO of HA was investigated using a catalyst of HNO₃-modified activated carbon (ACNA). Compared with the conventional CWAO process, the addition of H₂O₂ (44% of the stoichiometric amount needed for complete mineralization of HA) significantly increased the degradation of HA. For example, under moderate conditions of 150 °C and 0.5&#xa0;MPa O₂, a 4-h treatment with H₂O₂ achieved a 97.9% reduction in absorbance at 436 nm (Abs₄₃₆) and a 56.9% removal of chemical oxygen demand (COD). In contrast, the conventional system without H₂O₂ under the same conditions only reached an 82.4% reduction in Abs₄₃₆ and a 39.8% removal of COD. In addition, adding H₂O₂ to the CWAO system (H₂O₂-CWAO) significantly enhanced the biodegradability of HA solution. For instance, the BOD₅/COD ratio increased from 0.19 in the CWAO system to 0.68 in the H₂O₂-CWAO system. ACNA showed high stability during HA degradation in the H₂O₂-CWAO system, with only minor loss of activity (based on COD removal efficiency) over three cycles. Moreover, the effectiveness of this system was further demonstrated by treating stabilized landfill leachate, increasing the BOD₅/COD ratio from 0.08 to 0.49.</p>