Siderite as a Functional Substrate for Enhanced Nitrate and Phosphate Removal in Tidal Flow Constructed Wetlands

Constructed wetlands (CWs) are acknowledged as an effective and sustainable ecological technology for the treatment of wastewater, especially in the removal of nitrate and phosphate. This study investigated the application of natural siderite as a substrate in laboratory-scale tidal flow CWs to enhance simultaneous nitrate and phosphate removal. A systematic study was conducted to evaluate the impact of critical operational parameters, including siderite dosage, influent COD/N ratio, and hydraulic retention time (HRT) on system performance. Moreover, the corresponding changes in microbial community structure were explored. The results indicated that siderite significantly improved the elimination of nitrate and phosphate. Denitrification efficiency exhibited a strong dependence on both siderite dosage and organic carbon availability. The nitrate removal increased by 19.01 ± 6.37% compared to the non-siderite control under an optimal condition. Phosphorus removal demonstrated a primary reliance on the proportion of siderite, reaching a maximum removal improvement of 77.68 ± 26.27%. Analysis of microbial diversity revealed that siderite enhanced both richness and evenness of the microbial community and facilitated the proliferation of essential denitrifying genera, specifically Dechloromonas and Thiobacillus.