Research on performance differences and mechanisms of sulfur-iron composite packing materials prepared from different...

To address the structural instability and limited nutrient removal of traditional fillers, this study fabricated four novel composite fillers-incorporating zero-valent iron (Fe⁰), siderite (FeCO₃), pyrite (FeS₂), and calcium carbonate-via a melt-encapsulation method. Batch and continuous experiments systematically revealed distinct nitrogen and phosphorus removal mechanisms and microbial architectures among these fillers. While all exhibited denitrification potential, S-FeCO₃ demonstrated superior shock resistance, maintaining 78.36-94.71 % nitrogen removal and reducing sulfate accumulation by 30.92 %. Conversely, S-Fe⁰ caused significant nitrite accumulation (2.83 mg/L). For phosphorus, S-FeCO₃ (80.53-84.49 %) significantly outperformed S-FeS₂ (70.84-78.57 %) and S-Fe⁰. Microbial analysis showed a transition from Thiobacillus dominance in S-CaCO₃ to Thiobacillus-Ferritrophicum co-dominance in iron-coupled systems. At the molecular level, sulfur-iron coupling up-regulated key denitrification genes (narG, nirS, nirK, nosZ) by accelerating electron transfer and relieving Fur-mediated repression, providing a systematic strategy for filler optimization in simultaneous nutrient removal processes.