The combination of nanobubble aeration and iron-based multi-carbon source composites achieves efficient aquaculture wastewater nitrogen removal

[Display omitted] •Nanobubble aeration improved dissolved oxygen levels in water and sediment.•The NIMCSC system exhibited the best aerobic denitrification performance.•The abundance of key indigenous aerobic denitrifiers significantly increased.•Genes related to N metabolism, electron production, and transfer were upregulated. The primary constraints for efficient nitrogen removal in aquaculture ponds by indigenous aerobic denitrifiers are oxygen depletion in sediment and the shortage of electron donors. This study innovatively combined nanobubble aeration with iron-based multi-carbon source composites to stimulate aerobic denitrifiers, significantly improving the sediment's oxygen level and supplementing the electron donors of the system. Compared with the systems that incorporated multi-carbon source composites (MCSC) or iron-based multi-carbon source composites (IMCSC) under diffused air aeration conditions, the system that employed nanobubble aeration and iron-based multi-carbon source composites (NIMCSC) demonstrated an increase in total nitrogen (TN) elimination rate by 14.07% and 7.46%, respectively, reaching 89.75%. Microbial community analysisrevealed that the NIMCSC systemenriched the mixotrophic aerobic denitrifiers and fostered a symbiotic relationship among the bacterial communities. Moreover, compared with the MCSC and IMCSC systems, the NIMCSC system highlighted a significant increase in the average abundance of key indigenous aerobic denitrifiers. Meanwhile, the production and transfer process of electrons were stimulated, providing more energy and electron donors and assisting various abundant key functional enzymes to achieve efficient mixotrophic aerobic denitrification in the NIMCSC system. This study presenteda novel approach to achieve efficient aquaculture wastewater nitrogen removal.