Analysis Of Microbial Community Structures And Compositions Of Extracellular Polymeric Substances In A Wastewater Treatment Plant

A2/O process is a widely used biological wastewater treatment process. In the system of biological wastewater treatment, the removal of the pollutants essentially depends on the microbial metabolism. The pollutants removal efficiency is directly influenced by the species, numbers and community structures of the microorganisms. Therefore, it is necessary to study on the microbial community structures in the biological wastewater treatment process. The anaerobic, anoxic and aerobic sludge samples was obtained from an A2/O process in an urban wastewater treatment plant. The sequences of intracellular DNA were acquired by Mi Seq high throughput sequencing technology. The results showed that the diversity of the microorganisms in the system was very high. The dominant bacterial phylums in the aerobic and anaerobic tanks were Proteobacteria(the most dominant phylum), Firmicutes, Bacteroidetes, and Chloroflexi;The dominant bacterial phylums in the anoxic tank were Bacteroidete(the most dominant phylum),Planctomycetes, Proteobacteria, Acidobacteria, and Firmicutes。The most dominant genus in the three sludge samples was Terrimonas。The community structure of the nitrifying bacteria in the whole system was relatively single, that the AOB contained only Nitrosomonas and the NOB was only constituted of Nitrospira. On the contrary, the community structure of the denitrifying bacteria was very complicated. Moreover, amounts of aerobic denitrifying bacteria were detected in the aerobic sludge, while few autotrophic denitrifying bacteria were found in the whole system.As an important constituent of activated sludge flocs, EPS plays a significant role in the adsorption of metal ions and organic pollutants, the formation and maintenance of microbial aggregates, and the protection of microbes from external environmental stresses. EPS was extracted by ultrasound from sludges in the urban wastewater treatment plant and a hyperhaline wastewater treatment system. The contents of protein and polysaccharide in the EPS were measured. The results showed that protein was the dominant constituent of the EPS. Proteins and polysaccharides were demonstrated existing in the EPS by fourier transform infrared spectroscopy and three-dimensional excitation-emission matrix. Furthermore, humic acids might exist in the EPS of the high salinity anaerobic sludge sample. The results of the aggregation test indicated that EPS was conductive to the aggregation of sludges, and EPS of aerobic sludges was more beneficial to sludge aggregation than that of anaerobic sludges. EPS of hyperhaline anaerobic sludge was found having little effect on sludge aggregation.As the dominant composition of EPS, the property of extracellular proteins largely determines the character of EPS, and further influences the character and function of sludge aggregates. Shot gun technology based on LC-MS/MS was used to identified the proteins extracted from EPS, and 130, 108 and 114 proteins in anaerobic, anoxic and aerobic samples from the urban wastewater treatment plant were classified, respectively. The results of GOA showed that, the main biological processes, origins, and molecular functions of the extracellular proteins from the three sludge samples were the same. Metabolic process,cellular process,and single-organis process were the three dominant biological processes of the extracellular proteins. Most proteins derived from cytolysis, and their major molecular functions were catalytic activity and binding activity. The results exhibited the potential roles of extracellular proteins in binding multivalence cations and organic molecules, as well as in catalysis and degradation. The structure difference between anaerobic and aerobic sludges could be associated with their catalytic activities proteins.The microbial community structers, composition and properties of EPS, and varieties and functions of extracellular proteins in the A2/O system were revealed in this study. The conclusions of this study helped to better understand the properties of activated sludge, and provided theoretical basis of macro control in biological wastewater treatment process.