Study On Microbial Community Structure And Metabolism Characteristic Of A+OSA Excess Sludge Reduction Process

With the rapid development of economy and the acceleration of urbanization in our country, huge amount of excess activated sludge was produced due to increasing of wastewater treatment. An ideal approach was in-situ excess sludge minimization in the process of sewage treatment, coupled with less adverse effects on process performance and sludge characteristics. Oxic-settling-anaerobic(OSA) process which could result in good sludge reduction rate with a simple modification of conventional sewage treatment process and less power consumption has always been one of the focuses of current research. Since the sludge reduction mechanism of the OSA process still remains controversial, the process optimization control and practical application of the OSA process was restricted. The study on mechanism of the OSA process was mostly based on the efficiency evaluation of sludge reduction at the present stage. Although the mechanism of sludge decay playing a leading role in OSA process is widely accepted, no direct evidence was supplied to prove it. Since the restrictiveness of the analytics techniques in the previous study, there were relative few researches of the interpretation of micro-ecology in the OSA process. However, the system interpretation of the microbial community structure and microbial metabolism in the OSA process could not only obtain the direct evidence to prove sludge decay, but also the possible functionally related microorganisms associated with sludge reduction could be identified. Meanwhile, microbial metabolism during sludge decay in the SHT of the OSA process could also be interpreted. The methods for enhancement of sludge reduction rate of A+OSA process were offered based on the experimental results. The research results may provide a theoretical reference for enhancement of sludge reduction rate and process optimization of A+OSA process. The activated sludge from anoxic-oxic-settling-anaerobic(A+OSA) was as the main studying object in this thesis, the microbial community and metabolism characteristics were studied. The sludge reduction mechanism and microbial active mechanism of the OSA process was also illustrated.The sludge reduction in the A+OSA process was actually the microbial biomass decrease, the sludge decay mechanism of the A+OSA process could be explained through living microbial biomass and community involved in the sludge reduction analysis. Based on the changes of phospholipids fatty acid(PLFAs) content of microbial cell in the activated sludge from the A+OSA process, the living microbial biomass and community variation was quantitative analyzed. The living microbial biomass in the sludge holding tank(SHT) of the A+OSA process was reduced, and the living microbial community was separated from the AO process. This confirmed that sludge decay existed in the SHT of the A+OSA process. Gram-negative(G-) bacteria and aerobe bacteria were involved in the sludge decay of SHT. Meanwhile, the growth of fungi could be inhibited in the A+OSA sludge reduction process.The microbial species which were reduced and involved in the sludge reduction in the A+OSA process could be illustrated by bacterial and eukaryotic population and their relative abundance analysis in the A+OSA process. The possible functionally related microorganisms associated with sludge reduction could be identified in the A+OSA process. The qualitative and quantitative analysis of microbial community by means of highly sensitive high-throughput sequencing indicated that sludge decay occurred in the SHT of the A+OSA process. Meanwhile, the bacteria and eukaryotic community diversity indexes of the A+OSA process were lower than that of reference process; the bacteria community richness indexes between different tanks of the A+OSA process was basically identical, the eukaryotic community richness indexes was increased in the A+OSA process. The homogeneity of bacteria community in the different tanks of the A+OSA process was improved due to the insertion of SHT, and the bacteria communities of the A+OSA was separated from the AO process based on the hierarchical cluster analysis. Compared to the relative contents of different bacteria in the AO process, the dominated β-proteobacteria was the main bacteria which relative content was reduced in the A+OSA process. However, the anaerobic fermentative bacteria Sphingobacteria was enriched in the A+OSA process which may have key functions in reducing the sludge from the A+OSA process. The selected enriched Oligohymenophorea in the SHT of the A+OSA process showed that the microfauna′s predations may occurred in the A+OSA process, which contributed to sludge reduction in this process.In the A+OSA process, parts of the microorganisms were reduced in the SHT, which could induce the excess sludge reduction. While some of microorganisms were enriched in the SHT of the A+OSA process, the enriched one may be the sludge reduction functionally related microorganisms. It would help further confirm the functionally related microorganisms by building a simulation anaerobic-starvation environment similar to SHT for the growth of microbes from the A+OSA process and reference process. The analysis results of dynamic changes of bacteria community from the A+OSA process and reference process which were batch culture in the anaerobic-starvation environment showed that batch culture have a more significant impact on the bacteria community from reference process than that from the A+OSA process. Moreover, the bacteria community of the A+OSA process had better community structure robustness. The relative content of β-proteobacteria was significantly reduced both in the two processes, the anaerobic fermentative bacteria Sphingobacteria was enriched through using the secondary substrates generated from dead bacteria. The conclusion could confirm that the Sphingobacteria was the functionally related bacteria.The lower sludge production rate in the A+OSA process was mainly owing to the microbes decay and the secondary substrates generated from these groups used by the fermentative bacteria. The analysis of microbial metabolism during the sludge reduction in the A+OSA process would explain the mechanism of sludge microbe decay. The high-throughput sequencing was used to characterize the microbial metagenomics of the A+OSA processes. The microbial genome of the A+OSA process were classified into various functional genes based on the clusters of orthologous groups of proteins(COG) classification systems. The ratios of gene regulation type of metabolism including cell motility, signal transduction mechanisms, carbohydrate transport and metabolism and amino acid transport and metabolism was slight increased, while the ratios of gene regulation type of metabolism including cell wall/membrane/envelope biogenesis and replication, recombination and repair was decreased in the A+OSA process. The changes of metabolic regulation on genetic level of the A+OSA process were conductive endogenous decay and cell lysis of the reduced microorganisms. Meanwhile, substrate utilization ability of functionally related microorganisms under starvation environment was strengthened. The analysis of intracellular metabolite distribution on the molecular level could also investigate the microbial metabolic process. The result showed that the main heterogeneity intracellular metabolite between the A+OSA process and AO process were organic acids, amino acids and the derivatives, parts of nucleic acid components and amines. The 3-Hydroxybutyrate and 2-Hydroxybutyrate used for synthesize energy storage compounds decrease in the A+OSA process was helpful to weaken endogenous metabolism and enhance cell lysis of reduced microorganisms.The increase of amino acids and the derivatives, parts of nucleic acid components and amines of microorganisms in the A+OSA process could prompt to withstand the unfavorable habitat in SHT. The analysis of intracellular metabolite on the molecular level and metabolic regulation on the genetic level are verified mutually in this study, which interpreted the mechanism of microbial metabolism during microorganisms decay in the A+OSA process.