Microbial Population Analysis In The Optimum Operation Of Denitrification And Phosphorus Removal By ABR-MBR Process

In this study,ABR-MBR combined process was used to treat domestic sewage with low C/N ratio.In order to reveal the evolution of functional populations of denitrifying phosphorus removal in the ABR-MBR combined process,Miseq high-throughput sequencing technology was used investigating the microbial community structure in different stages of operation.The obtained results could be used to reveal the relationship between microbial community characteristics and reactor performance under different operating parameters.Moreover,theoretical support for the change of system efficiency could be obtained based on the observed microbial diversity,population abundance and dominant microbial community distribution.Furthermore,this study could provide theoretical basis for the application of denitrifying phosphorus removal process in engineering practice,and provide technical support for the development of new denitrifying phosphorus removal process.The main contents and conclusions are as follows.?1?The stability of the ABR-MBR combined process was maintained under different conditions.When the HRT was 12h,9h,6h and hence the inflow volume load was increased from 1.02 kg·?m³.d?^-11 to 2.55 kg·?m³.d?^-1,the process showed an effective and stable COD,nitrogen and phosphorus removal performance.In addition,during the operation of the system,the diversity and richness of the microbial population were maintained at a high level,and the functional microorganisms were also stable in the system.Therefore,the diversity of overall microbial population and the structural stability of the functional microorganisms in the system guaranteed the stable and efficient performance of the ABR-MBR process.?2?The ABR-MBR process could be successfully started up treating wastewater with low C/N ratio.The temperature and pH was maintained at?30±2??and 7.1-7.4,respectively.The DO concentration in the MBR was maintained at 1-2 mg·L^-1.Results indicated that increasing the reflux ratio of nitrifying solution from 150%to300%can promote the enrichment of denitrifying phosphorus bacteria?DPBs?,and hence promoted the startup and the stable operation of the system.The system maintained high microbial diversity throughout the operation.The dominant phyla were Proteobacteria and Bacteroidetes with the maximum abundance of 55.13%and7.76%,respectively.The main subgroups of the Proteobacteria were related to Gamaproteobacteria.The functional phosphorus removal bacteria were Aeromonas,Pseudomonas and Flavobacterium.The Aeromonas was extensively enriched.The relative abundance of Gamaproteobacteria of the phylum Proteobacteria increased from 5.30%to 41.49%and remained dominant in the subsequent operation of the system.It showed that the phosphorus removal efficiency of the system was closely related to the relative abundance of functional phosphorus removal microorganism.The diversity of microbial population and the structural stability of functional microorganisms in the system provide a guarantee for the stable operation and efficient performance of the ABR-MBR process.?3?The denitrifying phosphorus removal could be effectively achieve in the ABR-MBR process under different HRT conditions.The effect of the research on the system was tested at the influent COD at 380 mg·L^-1,DO of MBR reactor at 0.5-1.0mg·L^-1,with the HRT of ABR change of 12h,9h and 6h respectively.It can be found that when the HRT was 6h,the system efficiency decreased and the microbial diversity of system energy also showed a decreasing trend.In addition,when the HRT was 9 h,the system operated most stably,and the average removal rates of TP and TN were 94.87%and 73.15%respectively.The Rhodocyclales and Sphingobacteriales bacteria in the system were the dominant functional bacteria,and the total proportion of Denitratisoma,Dechloromonas and Thauera in the class of Betaproteobacteria reached 71.51%,indicating that the efficiency of the system is closely related to the abundance,species and activity of functional dominant microorganisms within the system.?4?The ABR-MBR process can achieved short-cut nitrification stably in the MBR reactor under different influent volumetric loads.The numbers of ammonia oxidizing bacteria?AOB?can be significantly increased and inhibited by recovering the HRT at 9h,keeping the DO of MBR at 0.5-1.0 mg·L^-11 and gradually increasing the inflow volume load of ABR from 1.02 kg·?m³.d?^-11 to 2.55 kg·?m³.d?^-1,so that the short-cut nitrification can be achieved efficiently and stably.In the MBR short-cut nitrification system,the dominant microorganism is Nitrosomonas.With the influent volumetric loading rate increase,the relative abundance of Nitrosomonas in the system increased from 1.02%to 22.87%,and the nitrite accumulation rate?NAR?of the system also increased gradually and finally reached to over 60%.The results showed that the rapid increase of AOB promoted the realization of the short-cut nitrification in the system.