Microbial Community Characteristics of Shortcut Nitrification Start-up in Different MBR-Inoculated Sludges

Abstract

In order to clarify the microbial community characteristics of the shortcut nitrification start-up with different inoculated sludges in the membrane bioreactor (MBR), the MBR was inoculated with nitrification sludge (R1), anaerobic nitrification sludge (R2) and 1:1 mixed inoculated anaerobic nitrification and denitrification sludge (R3). The results showed that the combination of intermittent aeration and shortened hydraulic retention time (HRT) successfully achieved the shortcut nitrification by R1, R2 and R3 reactors after 46 d, 8 d and 30 d respectively, with the R2 reactor exhibiting the shortest start-up period. During stable operations, the average nitrite accumulation rates of R1, R2 and R3 reactors were 92%, 93% and 94% respectively, and the R3 reactor showed a more stable shortcut nitrification. The results of analyses using ACE, Chao, Shannon, and Simpson diversity indices showed that the microbial abundance and diversity levels of R1 and R2 were significantly lower than that of the inoculant during the stable operation period, while the species abundance in the R3 reactor was slightly reduced and the diversity level was slightly changed. The main bacteria in the three reactors were Proteobacteria and Bacteroidetes after the successful start-up of shortcut nitrification, and the relative abundance of Proteobacteria was increased compared with the inoculated sludge. Proteobacteria were the main denitrifying bacteria, with β-Proteobacteria being the dominant bacteria of the shortcut nitrification system in the three reactors, accounting for 59.6%, 63.6% and 69.3% respectively. Through further analysis, the next dominant bacteria in R1, R2 and R3 were all Nitrosomonas, with 12.8%, 20.2% and 19.7% respectively. Compared with the R1 reactor, there was a certain proportion of shortcut nitrification bacteria in the sludge of the R2 and R3 reactors, which was more favorable to the operation of the shortcut nitrification system.