Study On The Correlation Between Activated Sludge Properties And Microbial Community Structure In Urban Wastewater Treatment System

With the increasing emphasis on ecological environmental protection in China,sewage discharge standards have become increasingly strict.Urban sewage treatment plants have beening playing an important role in the degradation of pollutants in sewage.Activated sludge process is the most widely used method in urban sewage treatment.Moreover,activated sludge is the main carrier for degrading pollutants,the physicochemical properties and microbial community structure of which are worth further investigation.In this study,17 activated sludge samples and 2 samples of biological membranes attached to different fillers were collected from 9 urban sewage treatment plants in 7 cities across the country,concerning 6 different treatment processes.A variety of statistical methods were used to comprehensively analyze the characteristics of activated sludge in different biological systems.Illumina high-throughput sequencing was used to analyze the differences and similarities of microbial community composition from three levels,i.e.phylum,class,and genus.Bivariate correlation analysis and canonical correlation analysis were carried out to identifiy the relationship between the characteristics and microbial community structure of activated sludge.The results showed that the physicochemical properties of activated sludge in different biological treatment systems were significantly correlated,and the phosphorus in activated sludge also had high bioavailability and mobility.Where the samples were collected is the main factor affecting the content of heavy metals in activated sludge,while the sampling time had little effect on the heavy metal content.The Zn and Mn in the sludge were highly mobile and bioavailable,while the speciation of Pb,Cr,and Cu were relatively stable.The results of high-throughput sequencing indicated that the warm-season samples had higher bio-diversity and richness than the cold-season samples,and different processes would lead to differences in microbial community structure.Different from A~2/O and oxidation ditch,?-proteobacteria and?-proteobacteria were the dominant strains in SBR process and?-proteobacteria abundance was relatively lower,which reflected higher ammonia oxidation efficiency.The structure of microbial community in the urban sewage treatment system was ecologically coherent.But the relative abundance of Nitrospira in biofilm samples was much higher than that of activated sludge samples,which showed better nitrification performance.The season and geographical were the main factors causing the differences in microbial community structure.The physicochemical properties of activated sludge such as pH,C/N value,S and Ca content were closely related to microbial community structure.Acid-soluble Zn,among all heavy metal specices,was the most important influential factor on?diversity index.Canonical correlation analysis showed that the microbial community structure of activated sludge was significantly associated with heavy metals,including Mn,Zn,Cr,and Ni.These heavy metals are all essential elements for the growth and reproduction of microorganism in activated sludge.In addition to the monitoring of conventional pollutants in the actual scale urban wastewater treatment plants,it is necessary to strengthen the monitoring and management of the physiochemical properties and heavy metal content of activated sludge.The properties of activated sludge will affect the microbial communities strcture and become the constraints of wastewater treatment efficiency.