Comparative effects of siderite, goethite, and hematite on nitrogen loss and nitrogenous gases release during municipal sludge aerobic composting.

Despite iron ores exhibiting the potential to regulate microbial nitrogen transformation, their roles in municipal sludge aerobic composting remain unclear. This study evaluated the effects of siderite, goethite, and hematite on nitrogen loss and nitrogenous gases emissions during sludge aerobic composting. Results showed that all three iron ores increased ROS and Fe(II) concentrations, with goethite and hematite increasing nitrogen retention by 13.13% and 18.18%. Goethite and hematite regulated pH and Fe(II) dynamics and increased the abundance of hao and nxrA genes, thereby enhancing nitrification and reducing NH3 accumulation by 7.28 mg/kg and 60.94 mg/kg. Additionally, goethite and hematite reduced N2O accumulation by 27.9% ± 6.2% and 9.9% ± 5.0% through the upregulation of the nosZ gene. Microbial community analysis revealed that goethite and hematite promoted the enrichment of key nitrification- and denitrification-related genera, thereby enhancing nitrogen retention. In contrast, siderite-induced alkalinity increased NH3 and N2O emissions, resulting in a 7.01% reduction in nitrogen retention. This study highlights the distinct regulatory effects of different iron ores on nitrogen transformation during aerobic composting.