Research On Microbial Community Ecology In MBR And GSBR

In this study, membrane bioreactor(MBR) and granular sequencing batch reactor(GSBR) were thoroughly investigated in terms of pollutants removal performance, the succession procedure of microbial communities, population dynamics and quantification of ammonia-oxidizing bacteria(AOB) and spatial distribution characteristics of functionally important microorganisms. A polyphasic approach incorporating the traditional monitoring methods for wastewater and sludge, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), Real-time quantitative PCR and fluorescence in situ hybridization (FISH) was applied to investigate the microbial community structures in the two systems.The main research results were summarized as follows:1) The noticeable change was taken place in microbial structure during the initial operation of MBR. In the process of experiment, the populations such as Pseudomonas and Aeromonas hydrophila were found to be stably the predominant species, the primary communities such as Bacillus sp died out, and the secondary microbial communities such as Enterococcus faecalis,Comamonas sp and Fusobacterium sp increased. The preponderant bacteria (such as Comamonas sp) that increased during the later stage of operation intensified the producing and accumulation of membrane pollutants. The content of EPS in membrane fouling was about 4 times as much as that in active biomass, which were mainly maken up of macromolecule substances(over 12000D) and polysaccharide and protein were the most important pollutant.2) In the process of MBR, variation of AOB community was slower. Comamonas sp, Uncultured Nitrosomonas sp, Uncultured Nitrosospira sp and Uncultured beta Proteobacterium clone nsc162 were dominated species in AOB population. The amount of AOB increased significantly after domestication. Nevertheless, ammonia-oxidizing activity of biomass decreased along with the increase of MLSS.3) In GSBR, the improvement of sludge sedimentation performance occurred earlier than the formation of granular sludge and was not effect by the variance of particle size of sludge. Rod-shaped bacteria and filamentous bacteria served as a means of building frames and supporting structures in the primary period of granulation, as well as the large granules were packed with spherical bacteria. During the sludge granulation, microbial community structures changed gently. In granular sludge, most species were belonging to Proteobacteria and the polyphosphate-accumulating organisms (PAO) were found to be the dominant genera. The initial predominant communities such as Bacteroidetes died out gradually, and the secondary microbial communities such as Nitrosospira and Thauera became dominant groups.4) In GSBR, the variation of AOB was remarkable in the period of sludge inoculation, and diversity of population was reduced rapidly. Subsequently, AOB community structure tended to be stable along with the improvement of sludge sedimentation performance. In seed sludge, most of Nitrosomonas sp. was remained in GSBR; however, all of Nitrosospira sp. was gradually eliminated during sludge granulation. The amount of AOB increased gradually after undergoing the early stage of wash-out. However, ammonia-oxidizing activity of biomass decreased along with the increase of MLSS.5) In the granular sludge that particle diameter was less than 0.6mm, AOB, nitrite oxidizing bacteria (NOB) and PAO distributed evenly in the whole of granular space. In the granular sludge that particle diameter was over 0.9mm; AOB was mainly located in the surface area of the granule, while NOB and PAO were in the subsurface layer. The core areas of granular provided suitable environment for the growth of denitrifying bacteria.