Zhang, et al (2024) Distinct roles of biochar and pyrite substrates in enhancing nutrient and heavy metals removal in intermittent-aerated constructed wetlands: Performances and mechanism. Environmental Research. https://doi.org/10.1016/j.envres.2024.119393

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Constructed wetlands are an effective and eco-friendly solution for treating sewage, removing both nutrients and heavy metals. Recent research explores how biochar and pyrite can improve the efficiency of these systems, focusing on their roles in nitrogen and phosphorus removal.

Biochar, a carbon-rich substrate, significantly enhances nitrogen removal through a process called heterotrophic denitrification. It provides a carbon source, which is essential for the microorganisms responsible for this process. On the other hand, pyrite, an iron sulfide mineral, excels at phosphorus removal due to its ability to promote sulfur-iron autotrophic denitrification.

The study found that while heavy metals like copper, lead, and cadmium were effectively removed by both biochar and pyrite, the presence of these metals hindered phosphorus removal but did not significantly impact nitrogen removal. This highlights the robustness of nitrogen removal processes even under metal stress.

Microbial communities in the wetlands shifted depending on the substrate used and the presence of heavy metals. Specifically, Thiobacillus and Ferritrophicum, bacteria involved in sulfur and iron denitrification, were more prevalent in pyrite-based systems. This indicates that pyrite fosters a specific microbial environment beneficial for phosphorus removal.

In conclusion, the study demonstrates that integrating biochar and pyrite into constructed wetlands can enhance their performance. Biochar is particularly effective for nitrogen removal, while pyrite is better suited for phosphorus removal. These findings are crucial for optimizing constructed wetland designs to treat wastewater more efficiently, even in the presence of heavy metals.