| In this study, we compared the characteristics of the two types of MBR, the composite membrane bioreacter (CMBR) and the submerged membrane bioreacter (SMBR), through the treatment of domestic wastewater. We aimed emphatically at the characteristic of the membrane biological reactor (MBR) wastewater treatment process, the relationships among EPS, the activity of sludge and the microbial community structure of the process which was researched with molecular biological method, such as polymerase chain reaction (PCR) and temperature gradient gel eletrophoresis (TGGE). The genomic DNA of microbial communities was extracted directly. After the 16S rRNA genes (V3 region) were amplified using the universal primers. These PCR products were separated by TGGE. Then the DNA finger printings of the sludge samples were taken pictures, which represent the charecterstic of the microbial community structure of the different sludge samples. The differences of the microbial community structure between the two MBRs were also studied.The results showed that under the condition of long-term operation, hydraulic retention time (HRT) of 6h, dissolved oxygen (DO) of 2.5 mg/L, the pH value of 7~8, the two MBR modes have similar removal effect of COD, NH3-N and turbidity. Averagely, more than 95% of COD was removed with the effluent content of less than 20 mg/L, more than 90% of NH3-N was removed with the effluent content of less than 1 mg/L, and more than 99% of turbidity was removed. However, the average removal of TN in CMBR was 14% higher than that in SMBR.In this study, mixed liquor suspended solids (MLSS), sludge viscosity, median diameter of sludge, Zeta potential, SVI value, EPS, distribution of relative molecular mass of organic matter were all analyzed. The results showed that sludge concentration in the SMBR was higher than in the CMBR since there was carrier in CMBR which is helpful to retard membrane fouling. Moreover, the Zeta potential and the ratio of protein and polysaccharide were positively correlated. With the increase of the ratio of protein and polysaccharides during the running time, the Zeta potential increased, and so did the SVI value.The change was taken place in the first week after sludge was inoculated in the lab-scale MBR. UPGMA cluster analysis of TGGE profiles demonstrated significant differences in community structure related to run time that can be divided into three stages: inoculation period, acclimation period and stable period. Retrieved partial 16S rRNA gene sequences were mostly related to Proteobacteria, Bacteroidetes and Firmicutes classes. There were more Actinobacteria classes in the SMBR than in the CMBR. And Actinobacteria are a class of filamentous fungi, which are likely to exacerbate membrane fouling.Canonical correspondence analysis (CCA) suggested that the community structure of the SMBR was similar to the CMBR, but was different from the seed sludge. In the process of experiment, some kinds of species have been stably possessed high preponderant degrees, as well as the primary communities died out, and the second microbial communities increased. Species such asα-Proteobacterium were found in all the four samples, indicating that these species are wildly existed. Species such as Sphingomonas sp. were dominant species in the seed sludge, but were disappear in the SMBR and CMBR under the condition of stable operation. Species such as Saprospiraceae bacterium were non-dominant species and then become the dominant species. Species such as Sphingobacterium mizutaii and Actinobacterium were only found on the carriers. These two types of micro-organisms may affect the removal of the nitrogen. |
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