Porous Fe3O4@BC Coupled with an Electric Field Facilitates Nitrogen Retention During Composting

This study synthesized a novel Fe3O4/biochar composite (Fe3O4@BC) characterized by a porous structure and a high electron-donating capacity. The effect of Fe3O4@BC on ammonia emission and nitrogen loss during electric-field-assisted composting was investigated, and its underlying mechanism in nitrogen transformation was elucidated. Results demonstrated that the addition of an appropriate amount of Fe3O4@BC reduced cumulative NH3 emission and total nitrogen loss by 30.00% and 4.03%, respectively. The favorable changes in gas emissions could be attributed to Fe3O4@BC-mediated modulation of key core microbial taxa. Under the electric-field-coupled condition, Fe3O4@BC addition significantly promoted the proliferation of Actinobacteria, such as Thermobifida and Corynebacterium, during the high-temperature phase, while concurrently suppressing the activity of Firmicutes. The shift in core microbial communities optimized key nitrogen transformation processes, including ammonification and nitrification, ultimately leading to reduced NH3 emission. This study highlights the application potential of Fe3O4@BC in enhancing nitrogen retention and mitigating emissions during composting.