Abstract:For the trend and necessary to limit water exchange and control disease, biofloc technology (BFT) has been widely applied in aquaculture. The carbon source supplement is the base and core of BFT, which will significantly affect the water quality, food conversion ratio (FCR) and the immune capacity in rearing animals. To explore the influence of carbon source supply tactics on the treatment of waste water discharged by recirculating aquaculture system (RAS), research was conducted, based on simulated aquaculture wastewater as the research object. In addition, the sucrose, sodium acetate and glycerol were used as carbon source, and three kinds of C/N ratio (5, 10 and 15) were evaluated for each type of carbon source respectively. Results showed that nitrification and assimilation occurred in the experimental groups. At the low C/N ratio (C/N ratio is 5), the nitrification intensity of different carbon source had extremely difference（P<0.05), but in the stable stage of each system, ammonia nitrogen removal rates all achieved over 90%. Moreover, sodium acetate system was quicker to reach the stable stage (4d), and less affected by C/N ratio. While with the C/N ratio increasing, the groups of sucrose and glycerol required less time to achieve stabilization (24d reduce to 12d), and the ammonia nitrogen removal efficiencies were improved gradually(sucrose, increasing from 87% to 99%; glycerol, from 83% to 98%). Secondly, different carbon source and C/N ratio had various effects on alkalinity of biofloc system. At system stable stage, with the increase of C/N ratio, the alkalinity of sodium acetate groups was raised slowly, and maintained high concentrations, which were not suitable for aquaculture reuse, but the groups of sucrose and glycerol were relatively stable, which were all less than 200mg/L (CaCO3). In addition, combined with biofloc sludge volume index (SVI), settlement performance of biofloc had no significant influence on the removal efficiency of ammonia nitrogen（P>0.05). At a low C/N ratio(C/N ratio is 5), the difference of EPS polysaccharide contents of three carbon source was not significant （P>0.05), and with the increase of C/N ratio, EPS polysaccharide of three carbon source had different contents and change tendencies.
