Influencing factors on nitrite removal by bagasse bioflocs and the succession of attached microbial communities

Nitrite accumulation is a common phenomenon that occurs during intensive shrimp culture and affects the physiological state of shrimp. As a new biofloc technology with plant fibers as a flocculation carrier, bagasse bioflocs are essential for removing nitrite and enhancing water quality. In this study, the characteristics, principles and factors influencing bagasse bioflocs in the process of nitrite removal were explored, and the changes in microbial community succession and function were analyzed. The results showed that the nitrite treatment process of bagasse bioflocs involves nitrification by attached microbes, which converts nitrite (NO2 -N) into nitrate (NO3 -N). Within a certain range, the higher the concentration of bagasse bioflocs in water is, the greater the removal rate of NO2 -N in water. The removal efficiency of NO2 -N was basically the same at different initial concentrations of NO2 -N, salinities (15-30) and pH values (6.5-8.0). During the continuous removal of nitrite by bagasse bioflocs, the removal efficiency of NO2 -N tended to increase, stabilize, and then decrease. Moreover, the microbial community structure successive, and the proportion of nitrifying or denitrifying bacteria such as Chloroflexi, Firmicutes, SBR1031, and Bacillus increased significantly. However, nitrification is inhibited in the later stage due to the increase in nitrate reduction, which results in a decrease in the nitrite removal efficiency of bagasse bioflocs. This study indicated that bagasse bioflocs can effectively remove nitrite through nitrification, but it was also found that removal efficiency has an upper limit on activation time and power. In the future, it is also necessary to explore control methods to accelerate and enhance the nitrite removal efficiency and extend the duration of the reaction peak period to improve the application of bagasse bioflocs.