# Nitrogen Removal Using a Membrane Bioreactor with Rubber Particles as the Fouling Reducer
## 3 Results & Discussion
### Nutrient Removal by a Reactor with Intermittent Aeration
#### 3.2.3 PCR-DGGE Analysis of the Microiflora in the MBR with Intermittent Aeration  
Different samples of bacterial populations were analyzed and compared using PCR-DGGE analysis targeting eubacterial 16S rDNA. Figure 9 shows the PCR-DGGE profiles of each sample showing various band patterns. The relative diversity of the microbial community and the degree of abundance of each microbial group is closely associated with the number of bands and the band intensity in the gel, respectively [21]. It was found that several dominant populations were severely inhibited using short non-aeration periods. In addition, the microbial population differed according to the intermittent aeration period. Regardless of the intermittent aeration period, bands A, B, D, H, I, K, L, and M were present in the sludge; among these bands, A and H were bright, while the intensities of B, D, and I were not clear, indicating low microbial activity. Further, bands C, F, J, and P were detected using longer aeration periods, whereas bands E, G, N, and O appeared when using longer non-aeration periods. These results suggest that the microbial diversities differ substantially according to the intermittent aeration period in the reactor.  
Depending on the sequences of gel bands, the accession numbers of closely related 16s rDNA were classified using the NCBI BLAST program. The affiliations and the similarity of the gel bands based on their sequences are listed in Table 2. Three major bacterial taxa were identified; four sequences were related to phylum _proteobacteria_, four were related to bacteria, four were related to _Firmicutesute_, and four were related to the phylum _Acidobacteria_. The growth of _Dysgonomonasissi_, uncultured _Acidobacteria_ bacterium, _Pantoea_ sp., and the bacterium enrichment culture were stimulated with relatively long aeration periods in an intermittently aerated reactor. However, _Lactobacillus harbinensis_, _Erythbroacterilotrolis_, _Phybucaderdiazotrophicus_, and _Mycobacterium_ sp., as represented by bands E, G, N, and O in Figure 9, respectively, were dominant when longer non-aeration periods were used.  
Figure 9: Denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rDNA extracted from the sludge. The values of 40/20, 30/30, 20/40, and 10/50 figures on the top of the graph represent the aeration/non-aeration periods during intermittent aeration. Alphabetic bands were excised, purified, and re-amplified to determine their sequences. The gradient concentration of the denaturant used was 40–60%.  
Among these, the contributions of _Dysgonomonas_, _Acidobacteria_, and _Pantoa_ sp. to the nitrification process have already been reported in previous studies [22; 23; 24]. _Lactobacillus_, _Erylthrobacter_, and _Mycobacterium_ are known to be microflora associated with the denitrification process used in wastewater treatment plants [25; 26; 27]. However, the contribution of _Pytbobacter_ to the denitrification process has yet to be reported. Further studies based on independent incubation should be conducted to confirm the contributions of each species to nitrification or denitrification.