Synergistic effects of soybean oligosaccharides and Chlorella pyrenoidosa on water quality and microbial community structure in biofloc system

This study explored the synergistic effects of soybean oligosaccharides (SBOS) and Chlorella pyrenoidosa on water quality and microbial community structure of aquaculture effluent in a biofloc system. Five experimental treatments were designed including CON group (control, no treatment), GLU group (glucose), SBOS group (2.5% SBOS and 97.5% glucose), CP group (glucose and Chlorella pyrenoidosa ), and CS group (2.5% SBOS, 97.5% glucose and Chlorella pyrenoidosa ). Chlorella pyrenoidosa were included at a concentration of 5.37×10⁵ cells/mL for selected treatments. Each treatment had 5 replicates, and C/N ratio was 15. Over the nine-day experimental period, combination of SBOS and Chlorella pyrenoidosa demonstrated significant synergistic effects on water quality improvement and biofloc formation ( P  < 0.05). Specifically, in CS group, nitrate concentrations were significantly reduced on day 1, nitrite nitrogen concentrations exhibited a marked reduction on day 5, and both nitrite and total nitrogen concentrations showed significant reductions on day 7 compared to GLU group ( P  < 0.05). Biofloc volume (FV) in CS group showed a significant increase on day 3 compared to both CON and GLU groups ( P  < 0.05). Turbidity (NTU) was significantly lower in all experimental groups compared to CON group ( P  < 0.05). Compared with other experimental groups, the abundance of Aeromonasaceae decreased significantly, and Bacillus and Mycobacteria increased significantly in CS group, which contributed to the enhanced nitrogen cycling and degradation of organic matter degradation pathway ( P  < 0.05). These findings suggest that SBOS and Chlorella pyrenoidosa exhibit synergistic effects in treatment of effluent in biofloc system, and efficiently remove nitrogen and optimize microbial community structure.