[Start-up of Partial Nitritation AGS-SBR and Analysis of Its Microbial Community Composition]

The mature aerobic granular sludge (AGS) was inoculated in an sequencing batch reactor (SBR) to treat the simulation wastewater with low carbon nitrogen ratio (COD/N). The start-up characteristics of partial nitritation (PN) based on gradually increasing influent ammonia concentration strategy were investigated. The reactor was operated at dissolved oxygen (DO) of 0.8 mg·L^-1, pH 7.5-8.5 and 30℃.The PN was realized in the AGS-SBR within 60 days. From day 61 and onwards, the nitrite accumulation efficiency of 80% was achieved throughout the experiment. Meanwhile, the total nitrogen average removal rate was maintained at a relatively high level of 64.54%, and the effluent NO₂^--N/NH₄⁺-N ratio reached 1.16, which was a suitable mixture to feed subsequent anammox. Finally, we also investigated the bacterial abundances in AGS-SBR in the PN period (PN-AGS-SBR) through Illumina 16S rRNA gene MiSeq sequencing. The dominant microbial communities at genus level were subjected to sequence analysis. The results revealed that the relative abundance of Candidate-division-TM7-norank was 68.63%, Saprospiraceae-uncultured was 8.26%, Thauera was 4.63%, Denitratisoma was 3.16%, Anaerolineaceae-uncultured was 1.63% and Anaerovorax was 1.39%, respectively. Nitrosomonas, Thauera, Denitratisoma and Bacillu were considered as the main organisms responsible for nitrogen removal. Meanwhile, various denitrification pathways, such as autotrophic denitrification, the denitrification and anaerobic ammonia oxidation of nitrogen, coexisted in PN-AGS-SBR system.