Aerobic denitrification affects gaseous nitrogen loss in biofloc-based recirculating aquaculture system

Abstract Biofloc-based recirculating aquaculture system (BRAS) is beneficial for nitrogen recovery and culturing turbidity-intolerant fish. BRAS and traditional flow-through system were established to evaluate nitrogen mass balance for 90 days. In comparison with the flow-through system, BRAS increased the nitrogen recovery in the forms of fish and biofloc biomass by 3.2% and 11.9%, respectively. However, BRAS showed a significantly high level of gaseous nitrogen loss (64.4%). Aerobic denitrifiers such as bacteria belonging to the genera Hydrogenophaga, Flavobacterium, Rhodobacter, Pseudomonas, Zoogloea, and Dechloromonas were observed in both systems through Illumina Miseq sequencing. Hydrogenophaga, an autotrophic denitrifier, was predominant in the flow-through system (17% ± 7%). In BRAS, the relative abundance of napA, which is a functional marker for aerobic denitrification, together with nirK and nosZ, significantly increased. These findings indicate that increased aerobic denitrification may be a key factor for the increased gaseous nitrogen loss in BRAS.