[Diversity of operation performance and microbial community structures in MBRs and CAS processes at low temperature]

In this paper, the performance of membrane bioreactors (MBR) and conventional activated sludge (CAS) processes at low temperature was investigated by analyzing their effluent quality and microbial viability. 454 high-throughput pyrosequencing was also applied to study the microbial community structures. The results of three systems (two MBRs: R1 with high sludge concentration, R2 with low sludge concentration, and one CAS: R3) showed that the average removal rate of NH4(+) -N was 99.7%, 99.7% and 59.7%, respectively, and the average removal rate of TN was 85.2%, 56.1% and 58.8%, respectively. R2 showed the highest specific ammonium uptake rate (SAUR), followed by R1 and R3; R1 showed the highest specific nitrate uptake rate (SNUR), followed by R2 and R3. It could be concluded that MBRs with high sludge concentration had a better performance of nitrogen removal under low temperature operation. 454 high-throughput pyrosequencing analysis revealed that the microbial richness was R2 > R3 > R1, and the microbial diversity was R2 > R1 > R3 at 97% sequence identity. The microbial structure and bacterial abundance were quite different between MBR and CAS systems. The dominant nitrifier in this research was Nitrospira, and the total relative abundance of nitrifiers in R1, R2, R3 was 1.22%, 1.64% and 0.15%, respectively. The Zoogloea, Thauera, Comamonadaceae and Comamonas might be the dominant denitrifers in this study, and the total relative abundance of denitrifier in R1, R2, and R3 was 5.8%, 4.52% and 15.21% respectively. MBR's characteristics of long solid retention time, high sludge concentration and low total nitrogen loading well supported the accumulation of nitrifiers and denitrifiers, and improved the performance of biological nitrogen removal at low temperature.