Study On The Dynamic Change Characteristics And Influencing Factors Of Microbial Structures In The Activated Sludge Of Shenzhen Wastewater Treatment Plants

At present activated sludge process is the most widely used biological treatment technology for municipal wastewater.The bacterial community structures in activated sludge is closely related to the performance of wastewater treatment plants(WWTPs).Therefore,the analysis of bacterial structures in activated sludge as well as its dynamic changes and influencing factors have become hotspots in academic research,especially for the study of important functional bacteria and key functional genes.Nitrogen cycle-related functional microorganisms are one of the main functional bacterial groups in activated sludge,which play key roles to determine the nitrogen removal from wastewater.In the implementation of the upgrading plan of WWTPs in Shenzhen,the total nitrogen discharge of effluent is required to be controlled below 10 mg/L,which puts forward higher requirements for the wastewater treatment capacity of Shenzhen.However,the bacterial structures,and its changing characteristics and influencing factors in the activated sludge of Shenzhen WWTPs are not very clear.The main functional groups such as bacteria for nitrogen removal and the functional genes have not been elusively studied.Therefore,in this study,activated sludge samples were collected from the aerobic tanks of NS and FT WWTPs with different treatment processes in Shenzhen.Total DNA of activated sludge samples was extracted and high throughput sequencing based metagenomics was performed,combined with bioinformatic analysis and water quality measurement,to reveal the dynamic change characteristics and main influencing factors of the bacterial community structure.The monthly samples of NS WWTP were collected from July 2016 to August 2018,and those of FT WWTP were collected from September 2017 to August 2018,thus 38 samples in total.The main research contents include the analysis of the diversity and dynamic changes of the bacterial community structures in activated sludge;the correlation analysis among the bacterial structure,environmental factors,and wastewater treatment performance;the comparison of bacterial community in activated sludge uncovered by different sequencing methods(Illumina and Nanopore sequencing technology);the screening of nitrogen cycling species and relatedmetabolic genes in activated sludge;and the construction of nitrogen cycling gene database,etc.Research indicates as follows:(1)In the bacterial community of activated sludge,a small number of persistent species(such as Thauera,Thiomonas,Accumulibacter,etc.)account for a high abundance of the total bacterial community,and they are important for maintaining the stability of the activated sludge system.(2)The phenomenon of seasonal change and succession of bacterial community in activated sludge is found in WWTPs,and environmental temperature may be an important factors affecting the changes of bacterial community.(3)There are lots of synchronous,delayed and advanced correlation patterns between the structure of the bacterial community in activated sludge,environmental factors,and wastewater treatment performance.The synchronous correlation patterns are frequently observed between bacterial communities.The correlation between environmental factors and bacterial community is mainly identified as asynchronous correlation.(4)Temperature and sequencing methods have significant effects on sample clustering at the level of typical functional bacterial and nitrogen cycle related genes,and sequencing methods are one of the key factors affecting the clustering of bacteria at the genus classification level.This study deeply explored the bacterial community structure in activated sludge and its dynamic changes and influencing factors to provide theoretical guide for improving the treatment capacity of WWPTs and implementing the upgrading plan.In the future,we should use a variety of technical means to have a more comprehensive understanding of the activated sludge bacterial community,so as to maximize the ecological and engineering value of the activated sludge bacterial community in the field of sewage treatment.