A bio-nonbio hybrid for synergistic nitrogen removal and N(2)O mitigation in aquaculture wastewater.

Conventional heterotrophic denitrification is often associated with high energy consumption and substantial NO emissions, limiting the sustainability of biological nitrogen removal. In this study, a bio-nonbio hybrid was developed by integrating Comamonas testosteroni FJ17 with biologically-derived carbon quantum dots (bio-CQDs) wherein bio-CQDs act as regulatory molecule, to achieve synergistic denitrification and greenhouse gas mitigation in aquaculture wastewater. GC-MS and nitrogen mass balance analyses demonstrated that bio-CQDs reduced NO emissions by 21.12%. Mechanistic analysis revealed that bio-CQDs facilitated extracellular electron transfer by reducing charge transfer resistance, enhancing the activity of the electron transport chain, and increasing cytochrome c levels, thereby enhancing electron transfer from donors to acceptors. This process further stimulated cellular energy metabolism and the secretion of extracellular polymers (EPS), triggering the formation of protein-rich matrix structures, and enhanced microbial aggregation, which in turn accelerating electron transfer and facilitating the reduction of NO to N. Under continuous-flow reactor operation HRT = 16 h, DO = 3.0 mg·L, the hybrid consistently achieved Class IA effluent standards using real aquaculture wastewater. Overall, this study elucidates the dual regulatory and adaptive response role of bio-CQDs in microbial denitrification and provides a scalable, low-carbon strategy for energy-efficient nitrogen removal and greenhouse gas emission reduction.