Study On Biofilm Growth Dynamics And Microbial Community Structure In Gravity Sewers

As an important part of the urban drainage system, the sewer systems are responsible for urban waste water collection and delivery capabilities. Recent studies have shown that sewers are similar to biochemical reactor, in which it happens a large number of biochemical reactions, and it appears some phenomenon such as biodegradation, the production of H2 S, CH4 and sewer corrosion. The sewer biofilm is the main place that biochemical reactions taking place, biofilm structure composition and reaction characteristics determines the occurrence of these phenomena. In the sewer, the special hydraulic conditions and substrate concentration are the major factor that affects the growth of biofilm.Therefore, a sewer biofilm reactor was setup to investigate the biofilm growth characteristics and structure properties under different substrate concentration and shear stress. In the biofilm growth, microelectrode testing technology was used to test the thickness of the biofilm. In the same time, the biofilm density and extracellular polymeric substances was analysised. The 454 high-throughput sequencing techniques was used to analyzed the mature biofilms microbial community structure under different shear stress conditions. This article give a investigation that the effect of shear stress and substrate concentration on biofilm growth process and biofilm structure in the view of both macroscopic and molecular biology perspective, which provides theoretical basis and foundation for future practical applications.The main achievements of this article are summarized as follows:① In the biofilm growth process, the biofilm thickness increased gradually with time, after reaching the maximum biofilm thickness, then the biofilm thickness decreased to a certain extent, finally tends to be stable; biofilm density gradually increased and reached a maximum value, then the biofilm density decreases and reaches a steady value; The biofilm extracellular polymeric substances content increased gradually, when the EPS content reached a certain peak, there will be reduced to a certain extent and eventually converge to a steady state. The results show that: when the biofilm growth equilibrium, biofilm thickness shear stress under the condition of different size as follows: L(F=1.29pa)> L(F=1.12pa)> L(F=1.45pa); the relationship of the biofilm density: TS(F=1.45pa)> TS(F=1.29pa)> TS(F=1.12pa);The size of the content of EPS in bio film is: EPS(F=1.29pa)> EPS(F=1.12pa)>EPS(F=1.45pa)。② High throughput sequencing results showed that the sewer biofilm has a high bacterial diversity. A common dominant bacteria in biofilm under different slope are Proteobacteria, Bacteroidetes,Firmicutes and Candidate_division_TM7. Shear stress has a significant influence on the microbial community structure of biofilm and the number of denitrification bacteria and sulfate reducing bacteria.③ In a certain range, the biofilm thickness and EPS first increased and then decreased with the increase of shear stress, while the biofilm density increased gradually, the biofilm thickness and EPS have the same variation trend. The main component of different slope of biofilm EPS are protein, humus and polysaccharide, in addition the protein and polysaccharide content was significantly higher than that of humus.④ For the steady state biofilm, increase the substrate concentration under the same shear stress conditions or increase the shear stress and substrate concentration at the same time, the biofilm thickness becomes smaller, the biofilm density becomes larger, and the biofilm extracellular polymers is also become smaller.⑤ Developed a new comprehensive model combined sewer fluid dynamics and biofilm growth dynamics. And the verified results show that the model has a high accuracy. This model has a positive guiding role for the practical experiments.By studying the effects of shear stress and substrate concentration on the biofilm growth process, using high-throughput sequencing method to analyze the microbial community structure of mature biofilm, and establish the drainage fluid dynamics and growth of biofilm dynamics coupling model. It provides a theoretical basis for the idea of sewer as a reactor and future actual application promotion, and it provides important academic significance and application prospect.