S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Chemical and Biological Engineering (화학생물공학부) Theses (Ph.D. / Sc.D._화학생물공학부)
Analysis of Microbial Communities in Membrane Bioreactors with and without Quorum Quenching
하폐수 처리용 분리막 생물반응기에서 정족수 감지 억제 유무에 따른 미생물 군집 분석
- 공과대학 화학생물공학부
- Issue Date
- 서울대학교 대학원
- Membrane bioreactor (MBR); Quorum sensing; Quorum quenching; Biofilm; Activated sludge; Biofouling control; Microbial community
- 학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2016. 8. 이정학.
- Membrane bioreactors (MBRs) are hampered particularly by membrane biofouling, resulting from microbial growth on the membrane surface and microbial production of membrane foulants in activated sludge. To mitigate biofouling, quorum quenching (QQ) has been stand out as an innovative technique in MBRs. Although the biological understanding of the effect of QQ and biofouling mechanism is crucial for the development of biofouling control strategies, the information of the microbial ecology is not sufficient in both QQ-MBR and full-scale MBRs. Therefore the investigation of microbial community in QQ-MBR and full-scale MBRs are required for the successful biofouling control in real MBRs.
Firstly, the microbial communities were investigated in relation to the QQ effect on biofilm in an anoxic/oxic (A/O) MBR. Two laboratory-scale MBRs with and without QQ-beads (QQ-bacteria encapsulated in bead) were operated in parallel. TMP (transmembrane pressure) rise-up in QQ-MBR was delayed by approximately 100~110% compared with those in conventional-and vacant (bead without QQ-bacteria)-MBRs. The principal coordinate analysis based on weighted UniFrac distance matric revealed that QQ had effect on microbial community in biofilm. The results of correspondence analysis revealed that QQ had effect on both bacterial composition and the change rate of bacterial composition in biofilm.
Secondly, the microbial communities of activated sludge were investigated in relation to the effect of QQ on A/O MBR for 91 days. The system performance (e.g., COD, TN removal efficiency) was stable over the period regardless of the presence of QQ beads. However, the average floc size in the QQ-MBR was substantially lower than that in the control-MBR (p<0.05). QQ affected the bacterial compositions of activated sludge. The network analysis revealed that QQ had effects on the microbial interactions of activated sludge.
Lastly, the microbial communities of biofilm and activated sludge were scrutinized from 10 full-scale MBR plants. Overall, Flavobacterium, Dechloromonas and Nitrospira were abundant in order of abundance in biofilm, whereas Dechloromonas, Flavobacterium and Haliscomenobacter in activated sludge. The proportions of known quorum sensing bacterial genera ranged 1.39 to 11.57% in biofilm and 3.19 to 12.14% in activated sludge. Effects of ten environmental factors on community change were investigated using Spearman correlation. MLSS, HRT, F/M ratio and SADm explained the variation of microbial composition in the biofilm, whereas only MLSS did in the activated sludge. Microbial networks were constructed with the 10 environmental factors. The network results revealed that there were different topological characteristics between the biofilm and activated sludge networks. These results indicated that the different microbial associations were responsible for the variation of community composition between the biofilm and activated sludge.
The information of microbial communities in QQ-MBR and full-scale MBRs could provide new insights to develop biofouling control strategies in real MBRs.