Study On Enhanced Nitrogen Removal And Microbial Community Structure Evolution By Aerobic Granular Sludge At Low Temperature

For the urban sewage with low temperature and low carbon ratio in northern China,the mainstream activated sludge process can no longer meet the industry standards.Aerobic granular sludge(AGS)has the characteristics of complete sludge-water separation,compact structure and efficient nitrogen removal performance,which makes up for the deficiency of activated sludge process.The cultivation of AGS is mostly based on the water quality environment of artificial water distribution,and the artificial water distribution can not fully simulate the water quality characteristics of domestic sewage.Therefore,it is proposed to cultivate AGS in different water quality environments,and to explore the microbial community evolution process during the formation of AGS and strengthen the denitrification performance of AGS system in low temperature environment,so as to provide reference for AGS process to treat sewage.(1)AGS granulation.Simulated sewage is easier to cultivate AGS than domestic sewage.The R1 system was successfully started on the 35 th day of the simulated sewage stage,and the particle size was mainly distributed between 0.22-0.90 mm.On the 60 th day of the R2 system,the AGS system was successfully started;on the 120 th day,the particle size was mainly distributed in 0.55-1.25 mm.The filamentous bacteria throughout the AGS play a skeleton role.A large number of bacilli and cocci are distributed on the surface of the granular sludge,and a large amount of EPS is adhered to it.The Zeta potential of the sludge surface continues to decline,which improves the sludge coagulation performance.At the same time,the content of PN in EPS components increased significantly,which played an important role in the formation and stable operation of AGS.(2)AGS on pollutant removal effect.In the process of AGS granulation and operation,it showed excellent removal effect on pollutants.After the C/P ratio was reduced in the R2 system,the removal rate of TP was between 71.0-74.5%.Under A/O operation mode and low temperature stage,the removal efficiency of TP increased by6.5% on average.After reducing the C/N ratio,the removal rate of TN remained at 60.6-70.6%;after changing the A/O operation mode,the removal rate of TN increased by5.8% on average,and it still maintained an upward trend in the low temperature environment.(3)Microbial community evolution in AGS.Alpha diversity analysis showed that the microbial diversity of R1 system was higher than that of R2 system.The microbial diversity of R1 and R2 decreased with the operation of the system,and the R2 system improved the species diversity under the A/O mode of low temperature environment.The analysis of microbial community components at the phylum level showed that R1 and R2 systems showed similar dominant phyla,and the main dominant phyla were Proteobacteria,Patescibacteria,Actinobacteroia,and Bacteroidota.The microbial community components of R1 and R2 systems were different at the class level.The dominant bacteria were similar after AGS maturation.The main dominant bacteria were Saccharimonadia,Gammaproteobacteria,Alphaproteobacteria,Actinobacteria,and Bacteroidia.During the granulation and maturation of aerobic sludge,unclassified＿o＿＿Saccharimonadale,Zoogloea,Azoarcus and other bacteria with EPS secretion function became dominant bacteria,which promoted the formation of AGS.The A/O operation mode and low temperature stage of R2 system had more abundant microbial community diversity and higher abundance,and most of the bacteria were related to denitrification.