Intensive aquaculture systems often contain high concentrations of nitrate and phosphate, leading to environmental and economic burdens. Bioflocs technology, a novel approach in aquaculture, addresses these issues by removing these nutrients and producing protein rich microbial biomass. This study explored a novel single stage oxic process for simultaneous rapid recovery of phosphate and nitrate using different carbon addition strategies in bioflocs growth reactors.
Our findings revealed that bioflocs rapidly and effectively assimilated nutrients from high concentration environments. The phosphate removal mechanism involved biomass formation, achieving simultaneous removal efficiencies of 5.5 ± 0.2 mgP/gTSS/d for phosphate and 41.8 ± 2.0 mgN/gTSS/d for nitrate, harvesting biofloc concentrations of 3599 ± 33 mg/L. The crude protein content of the bioflocs exceeded 50%, with essential amino acid indices over 0.9, indicating potential for high quality aquafeed. Actinobacteriota and Bacteroidota were dominant during the phosphorus removal process, with significant proliferation of Nakamurella. Additionally, gene amplification related to assimilation, aerobic denitrification and inorganic phosphate transport was observed, suggesting biofloc technology is a promising method for efficient phosphate and nitrate removal.
This study also investigated the effects of different carbon sources on this process. Results revealed that phosphate removal rate in the glucose group was 0.61± 0.02 mg/L/h, significantly higher than those in the acetate (0.28± 0.01 mg/L/h) and propionate (0.29 ±0.03 mg/L/h) groups (p < 0.05). However, the three groups observed no significant differences in nitrate removal rates (p > 0.05). The superior performance of the glucose group in simultaneous nitrogen and phosphorus removal is likely due to the higher biomass synthesis. In contrast, nitrate removal in the acetate and propionate groups was primarily driven by denitrification, resulting in lower sludge production and reduced phosphate uptake. For practical application of bioflocs in simultaneous nitrogen and phosphorus removal, glucose is recommended as the optimal carbon source. This research promotes the circular economy by recovering nutrients, reducing reliance on traditional feed sources, and minimizing environmental contamination