| IFAS (Integrated Fixed-Film Activated Sludge) process has practical significance in municipal sewage treatment plant upgrading for those developing countries with serious water contamination and eutrophicationThis dissertation aims to reveal the linkage between the effectiveness of IFAS system and the variation of the significant denitrification bacteria in different seasons. In this research, molecular biology & ecology technologies such as quantitative PCR, high-throughput sequencing are applied in the tests to detect the variation of total bacteria and some significant nitrification bacterias such as Nitrospira in population and diversity aspects under different seasons, meanwhile, other detection methods are taken to monitor the nitrogen removal trend in the selected IFAS system to verify and contrast the accuracy of the research. Both suspended (the active sludge) and attached (Biological membrane) phases in the IFAS system were used to be the detection objects. This study can provide theoretical basis for the improvement of IFAS on nitrification and denitrification from the perspective of the microorganism performance, therefore, this research is of great significance both in theoretical and practical way.The main conclusions can be listed as follows:1、IFAS system operational situationThe system performs a stable situation. TN、NH4+ -N and other organic matter such as CODcr and BOD5 can be removed effectively, provide a good environment for the experimental sampling. TN and NHU+-N emission can reach the Level I B emission standard even in the winter, and the removal of CODcr and BOD5 mainly up to 90% and 95% which shows a high effective.2、Bacterial diversity situationThe total bacteria in suspended phase performs a higher status than in attached phase in both species evenness and species richness aspects, which indicates that the suspended phase is more advantage for bacterial diversity formation. And the advantage of species richness and species diversity of the attached phase in the 2nd aeration tank trends a descend way compared with the 4th aeration tank.3、 Community structure situationUnder the Phylum level, the predominant bacteria were Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, Chloroflexi, TM7, Planctomycetes and Nitrospirae. Among them, Nitrospirae as the significant denitrification species shows a higher existence(4.6% vs 1.4% and 7.7% vs 1.7%) in the attached phase which reveals that the biofilm have stronger enrichment of predominant species. Under the Genus level, Pseudomonas is the most predominant species which takes the proportion of more than 50% either in biofilm or active sludge. Furthermore, biofilm in the 4th tank contains the least genus of bacteria which indicates its situation is to the disadvantage of community diversity but to the advantage of the predominant species.4、The variation of NitrospiraNitrospira with the species abundance exceeds 1%, is the main nitrifying bacteria flora in two phases, which indicates it is the predominant species in the aeration tanks of the IFAS system and is of great significance on the nitrogen removal.The number of Nitrospira in biofilm and the 4th tank are higher than that in active sludge and the 2nd tank. And the 2nd Tank Nitrospira bacteria number shows a positive correlation and strong regularity with season temperature variation, meanwhile, the number of Nitrospira bacterial in the 4th tank, except for March, trends a decline way from winter to summer.The activity of Nitrospira in biofilm is higher than that of suspended sludge phase. And in winter, the activity of the Nitrospira in the 4th tank bacteria were higher than the 2nd tank, and as temperatures rising, the activity of Nitrospira in the 2nd tank bacterial activity gradually approached that in 4th tank..As a conclusion, in those lower temperature winter months, the nitration efficiency of the 4th tank biofilm phase is the highest which indicates that the 4th tank is the main place of nitrification in the system especially in the winter. |
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