Study On Sludge Thickening And Digestion Integrated Reactor Microbial Community Structure And Function

Due to the mountainous terrain of Three Gorges Reservoir Area, it risks the severepollution of the surplus sludge from the WWTPs, which is easily washed away into thesurrounding water body. Accordingly, sludge treatment and disposal in the reservoirarea is of particular importance. However, the WWTPs built in the Three Gorgesreservoir area lack of the technologies in the reduction and stabilization of the sludge;meanwhile, the traditional sludge anaerobic treatment processes are subjected tolow-load, long digestion duration, high costs, and etc. From a comprehensiveperspective, the development of a new efficient sludge treatment technology, especiallyfocusing on the volume reduction and stabilization of was very urgent.Combining modern high-rate anaerobic reactor theory with gravity concentrationtank for the first time, the research group has successfully developed the Two-phaseIntegrated Sludge Thickening and Digestion reactor （TISTD） to achieve integration ofthickening and digestion and the enhancement of the functions. The laboratory testsshowed that the effectiveness of TISTD is way better than the conventionalconcentrated tank and digester. In essence, the TISTD reactor still follows thethree-stage theory of the anaerobic digestion process; therefore, its performance isclosely associated with the two functional microbial populations inside the reactor:acid-producing bacteria and the methanogens. The acid-producing bacteria are capableof degrading organics into volatile fatty acids, from which the methanogens utilize anddegrade into methane, carbon dioxide and other gases in order to achieve the reductionof sludge. Besides these two major bacterial populations, the system contained variousmicroorganisms. The stability and efficiency of the reactor depended largely on theactivity of microbial diversity and dominant species. The stability and efficiency of thereactor under different operation conditions has certain correlation with the change ofthe microbial structure in the system. In this study, the traditional isolation and culturemethods and16S rDNA sequence analysis were used to study the distribution ofmicroorganisms and the predominant species under the optimal operating conditions inthe TISTD reactor. The sludge samples were taken during the start-up period and thesteady state with sludge feeding rate of20%,30%,40%and50%. Then the wholegenome was analyzed by PCR-TGGE fingerprinting technology to acquire themicrobial structure and ecological changes in the reactor at various stages. Additionally, dehydrogenase activity of anaerobic sludge was measured to reveal the dynamicvariation of the metabolic processes in the reactor at different stages. All the resultscomprehensively unraveled the mechanisms of the microbiological reactions in theTISTD under moderate temperature and provided some insights for the furtherapplication of the reactor and process improvement. The main results are as follows:①The efficacy under different sludge feeding rate （20%,30%,40%and50%）showed that the optimal sludge feeding rate was30%, and the hydraulic retention timewas3.33d. When the water content and the ratio of VS/TS were in the range of99.4⁹9.6%and0.62⁰.77and the water content and the ratio of VS/TS of effluentsludge was in the range89.5%⁹3.5%and0.21⁰.28respectively and the suspendedsolids in effluent water were in the range of0.15⁰.6g/L, the thickening and digestionefficacy of the TISTD were way better than conventional gravitational thickening tankand anaerobic digester.②Under an optical microscope, many protozoan amoeba, bean-shaped insect,flagellates and ciliates can be detected in the outer reaction chamber; Scanning electronmicroscope provided us with the complicated microbial community structure and cellmorphology. The predominant strains, enriched by anaerobic morphology isolation andculture, were shown to be short rod-shaped, filamentous and spherical. Threepredominant bacteria were identified as Bacillus and methanogenic genus by16S rDNAsequence analysis, indicating that TISTD realized biophase separation effectively duringthe anaerobic digestion in the reactor making the outer reaction chamber favorable forBacillus to thicken and acidify the sludge while the inner chamber suitable for archaeaand methanogens to digest the sludge and produce methane.③TGGE profiles with many a significantly strips at different positions duringdifferent stages illustrated that the microbial populations inside the reactor were quitediverse under the moderate temperature condition and also the predominant populationsvaried. As the load of the reactor changed, the microbial community structure andpopulation showed a significant change dynamically, which indicated the significanceof the cooperation of all the microbial populations in the achievement of the efficiencyof TISTD. The analysis of the typical bands tapping recovery showed that, the strains inclose relationship with the predominant ones in anaerobic sludge TISTD reactor systemwere uncultured strains.④The anaerobic sludge dehydrogenase activity was measured for acomprehensive understanding of the structural and functional diversity of the microbial community in the reactor system. Dehydrogenase activity showed the similar trend inthe outer and inner chamber of the reactor, which increased first and then decreased. Butthe dehydrogenase activity of the sludge from the inner reaction chamber was alwayslower than that from the outer reaction chamber. According to the dehydrogenaseactivity curve, the optimal sludge-feeding rate of TISTD reactor was30%, at whichpoint the dehydrogenase activity was80.1μg L^-1 h^-1in the inner reaction chamber and97.7μg L^-1 h^-1in the outer reaction chamber.