Application of Biofloc-Down flow hanging sponge system to remove nitrogen components in recirculating zero water...

This study presents a novel approach to sustainable aquaculture by integrating biofloc technology (BFT) with a compact down-flow hanging sponge (DHS) reactor. The integrated BFT-DHS system effectively removed nitrogen compounds while maintaining ammonia-nitrogen (NH₄⁺-N) concentrations below 1 mg-N L^-1 without water exchange. Application of this system in a tank bred with juvenile Oreochromis niloticus showed a high NH₄⁺-N removal rate of up to 97 % and nitrite (NO₂^- -N) concentrations were maintained at 0.1 ± 0.1 mg-N L^-1. Microbial analysis revealed Gordonia as the predominant genus in the biofloc contributing to heterotrophic nitrification, while the Peptostreptococcaceae family dominated the DHS reactor. Heterotrophic nitrification seemed to be the primary process for enhanced nitrogen removal. Pathogenic bacteria, Vibrio sp. was absent throughout the study. This study highlights the potential integration of BFT and DHS system for sustainable aquaculture practice with effective nitrogen removal.