The rapid start-up of the partial nitritation process in a laboratory-scale aerobic granular sludge-sequencing batch reactor was successful by controlling low dissolved oxygen and gradually increasing the influent ammonia levels. The microbial community dynamics were analyzed by high-throughput sequencing and quantitative polymerase chain reaction. The microbial communities were significantly affected by the different influent NH4+-N concentrations (77.84, 119.42, 170.31, and 252.21 mg/L) in Phases I, II, III, and IV. The sludge Shannon index in Phases I, II, III, and IV was 3.9, 4.39, 3.47, and 2.13, respectively, which was higher than that of the inoculated sludge (1.62). The dominant class transformed from Alphaproteobacteria and Gammaproteobacteria in Phase I to Betaproteobacteria in Phase IV. Furthermore, Sphingobacteria and Clostridia were the dominant bacteria in Phases III and IV. The quantitative polymerase chain reaction (qPCR) results suggested that Nitrosomonadaceae_uncultured belonging to ammonia-oxidizing bacterium was the dominant species, but the relative abundance of nitrite-oxidizing bacteria (mainly Nitrospira and Nitrobacter) was extremely rare in Phase IV. Furthermore, Thauera, Denitratisoma, and Planctomycetacia were the dominant functional nitrogen removal microbes in Phases III and IV. Some nitrogen removal pathways such as partial nitritation, denitrification, and anaerobic ammonium oxidation co-existed in the partial nitritation process.
Keywords: Anaerobic ammonium oxidation; Denitrification; Microbial community structure; Partial nitritation; Quantitative polymerase chain reaction.