Construction of sequential batch biofilm reactor in marine aquaculture wastewater and its nitrogen removal performance and microbial community structure analysis

【Objective】 Evaluation of ammonia nitrogen removal efficiency and biofilm characteristics in sequential batch reactor（SBR）and sequential batch biofilm reactor（SBBR）under varying salinity conditions was conducted，microbial community structure for efficient ammonia nitrogen removal in high-salinity conditions was investigated to provide reference for the development and application of high-efficiency microbial nitrification technology in marine aquaculture. 【Method】 SBR and SBBR were used to inoculate the same activated sludge in order to simulate the treatment conditions of mariculture wastewater. Both sets of reactors were initially started without the addition of salt and operated steadily for 15 d. Subsequently，the salinity in the reactors was gradually increased to 1.0%，2.0%，3.0% and 4%. The nitrification performance，microbial community structure and metabolic gene abundance of each reactor stage were evaluated using scanning electron microscopy-energy dispersive spectroscopy，N-（1-naphthyl）-ethylenediamine photometry， Nessler’s reagent photometry and metagenomic sequencing analysis. 【Result】 The salinity greatly affected the nitrification performance of SBR. In a high salt environment（3.0% and 4.0%），the removal rate of ammonia nitrogen was only 43.18% and 37.97% for SBR. The salinity change had no obvious effect on the nitration function of SBBR，SBBR could still achieve efficient nitrification with a removal rate of ammonia nitrogen of 98.00% even at a salinity of 4.0%. Compared to SBR，the microbial community in SBBR demonstrated higher species abundance and diversity，with a relatively more stable community structure. Notably，the relative abundances of Gelidibacter and Nitrosomonas were not affected by salinity changes. Denitrification bacteria such as Paracoccus，Thauera and Pseudomonas also exhibited higher relative abundance in SBBR. The key denitrification genes norB and nosZ showed higher abundance in SBBR compared to SBR， and showed stronger synergistic effects. 【Conclusion】 SBBR using sponge biofilm carriers can achieve short-term nitrification and nitrogen removal startup under high-salinity conditions，while maintaining the stability of microbial community structure. This facilitates multiple nitrogen removal pathways and enhances the synergistic effects of nitrogen removal genes. Compared to conventional activated sludge processes，the denitrification performance of SBBR is greatly improved，offering an effective solution for nitrogen removal in seawater aquaculture wastewater under high-salinity conditions.