Constructed Wetlands (CWs) have emerged as an effective, eco-friendly solution for wastewater treatment, employing a combination of plants, substrates, and microbes. These systems are particularly valuable for managing low-strength wastewaters, such as urban runoff or sewage plant tail water, aligning with stringent discharge standards. Yet, the challenge of treating wastewater laden with heavy metals and a low carbon-to-nitrogen (C/N) ratio persists, highlighting the need for innovative substrate integration to enhance pollutant removal efficiency.

A recent study has demonstrated the successful application of biochar and pyrite in CWs, significantly improving the removal of organics, total nitrogen (TN), total phosphorus (TP), and heavy metals. Remarkably, these systems achieved removal efficiencies of up to 95.78% for organics, 98.78% for TN, 96.22% for TP, and 99.91% for heavy metals. The research uncovered that pyrite oxidation played a crucial role in TP and heavy metals removal by facilitating the complexation with ferric hydroxide. Furthermore, the presence of protein-like substances was identified as a key factor in stabilizing heavy metals.

The incorporation of biochar and pyrite not only enhanced heterotrophic and autotrophic denitrification processes but also promoted the proliferation of functional bacteria related to autotrophic denitrification. This study offers a promising insight into the application of CWs augmented with biochar and pyrite for treating low C/N wastewater, underscoring the potential for these materials to address the limitations of traditional CW systems in removing nitrogen, phosphorus, and heavy metals. Through this innovative approach, the study paves the way for more sustainable, efficient wastewater treatment methodologies, leveraging the synergistic effects of biochar and pyrite to enhance CW performance.