<p>This work established constructed wetlands (CWs) using different types of biochar as substrates and comparatively analyzed the purification performance of sludge biochar (SBC) and woodchip biochar (WBC). Three groups of systems were designed: a control group using gravel as the filler (Control-CWs), a system with SBC and gravel mixed substrate (SBC-CWs), and a system with WBC and gravel mixed substrate (WBC-CWs). During operation, the removal efficiencies of COD, NH₄⁺-N, NO₃⁻-N, and PO₄³⁻-P were monitored. Results showed that the introduction of biochar improved pollutant removal in constructed wetlands, with the SBC-CWs system exhibiting significantly enhanced performance under the current experimental conditions. This superiority was primarily attributed to the synergistic mechanism of substrate adsorption and the selective enrichment of functional microorganisms. The average removal rates of COD, NH₄⁺-N, NO₃⁻-N, and PO₄³⁻-P reached 58.98%, 93.50%, 90.59%, and 81.94%, respectively, all exceeding those of the control group. In comparison, the WBC-CWs system achieved moderate removal efficiencies between the SBC-CWs and control groups. Microbial community analysis revealed that the SBC-CWs enriched denitrifying and phosphorus-accumulating functional genera (e.g., <i>Thauera</i>, <i>Hydrogenophaga</i>, <i>Rhodocyclaceae</i>, and <i>Pseudomonas</i>), which promoted synergistic nitrogen and phosphorus removal. Overall, sludge biochar enables sustainable sludge reuse while improving nitrogen, phosphorus, and organic matter removal in constructed wetlands, offering an efficient and eco-friendly wastewater treatment strategy.</p>