Microbial Community Structure And Process Control Strategy Of Denitrifying Phosphorus Removal

The municipal wastewater in south China is characterized as low carbon to nitrogen ratio (C/N), and the effluent nitrogen and phosphorus of traditional processes are often beyond the discharge standard for the low C/N wastewater treatment. The denitrifying phosphorus removal has become the popular research due to its advantage of simultaneous nitrogen and phosphorus removal, carbon and energy requirement reducing and lower sludge production. In the current study, aiming at the further understanding of denitrifying phosphorus removal process and promotion of its practical application, the operation performance of denitrifying phosphorus removal based two sludge process in pilot scale for low C/N municipal wastewater treatment was firstly investigated. Then the community structure and the core phosphorus removal organisms were systematically compared based on high-throughput sequencing of16S rRNA gene. The effects of both electron acceptor and electron donor (carbon source) on denitrifying phosphorus removal performance and community structure were investigated to provide theoretical principal for process optimization. Finally, metagenome sequencing was further employed to study the community structure and functional genes of denitrifying phosphorus removal.Firstly, treatment efficiency on low C/N wastewater of the A2N process on pilot scale was investigated, and favorable denitrifying phosphorus removal performance was obtained. Effluent concentrations of COD, NO-3-N and TP were respectively38,0.25and0.41mg/L for the A+2N phase, with NH4-N concentration was still as high as8.81mg/L. The NH+4-N could be further nitrified in the secondary BAF and the SS could also be intercepted, with final COD, NH+4-N, NO-3-N and TP concentration reduced to30,1.02,7.5and0.32mg/L, respectively. Analysis of denitrifying phosphorus removal and denitrification showed that there is good linear relationship between phosphorus uptaken and phosphorus released, and also the nitrate denitrified.The denitrifying phosphorus removal efficiency and traditional aerobic phosphorus removal was compared based on SBRs operated under strict anaerobic-anoxic (A-A) and anaerobic-oxic (A-O) conditions. Then the community structure and the core phosphorus removal organisms were systematically compared based on the operation performance and16S rRNA gene based high-throughput sequencing. Results showed that the aerobic phosphorus removal sludge had relatively higher diversity than denitrifying phosphorus removal sludge. Taxonomy analysis showed that denitrifying phosphorus removal sludge had distinct microbial community structure with aerobic phosphorus removal sludge. During the whole acclimation phase, dominant microbial community in denitrifying phosphorus removal sludge had a significant shift compared with the seed sludge, while there was only slight abundance fluctuation of major taxonomies in aerobic phosphorus removal sludge. Dechloromonas-like organisms were the dominant phosphorus removal bacteria in denitrifying phosphorus removal sludge and characterized as facultative bacteria; Ca. Accumulibacter was the dominant phosphorus removal bacteria in aerobic phosphorus removal sludge. Abundances of phosphorus accumulating organisms and glycogen accumulating organisms were16.9%and12.8%,5.26%and6.19%during stable operation, respectively.For the investigation of effect of electreon acceptor on denitrifying phosphorus removal, operation performances and community structure of phosphorus removal sludge with different electron acceptor in three parallel SBRs were compared. TP removal rates of phosphorus removal sludge with nitrate, nitrite and oxygen as electron acceptor were84.8%,78.5%and87.4%respectively, with the nitrite based denitrifying phosphorus removal efficiency comparatively lower. Moreover, electron utilization efficiency of denitrifying phosphorus removal sludge with nitrate as electron acceptor was higher than nitrite, with P/e-of2.21and1.51mol-P/mol-e-respectively. The two denitrifying phosphorus removal sludge demonstrated similar community structure and the potential public health hazards of non-aeration activated sludge systems were revealed. With the assistance of post-aeration for nitrate based denitrifying phosphorus removal sludge, settling ability could be obviously improved and further phosphorus removal could be achieved during post-aeration with increased aeration time. However, the anoxic phosphorus uptake was deteriorated, which was likely a result of shifted microbial community structure. Post-aeration of approximately10min was proposed for denitrifying phosphorus removal.As the electron donor, the effect of carbon sources on denitrifying phosphorus removal and the microbial community structure was then investigated. TP removal rates of sludge with acetate, propionate and glycerol as the sole carbon sources were averaged at82.5%,91.8%and79.2%respectively, with propionate proved as the optimal carbon source for denitrifying phosphorus removal. Organic substrate utilization efficiencies (P/C) in anaerobic phase were0.209,0.261and0.195mol-P/mol-C; electron acceptor utilization efficiencies (P/N) were0.745,0.760and0.569mol-P/mol-N, respectively. From acclimation to stable operation stages, PAO abundances increased from4.54%,4.38%and1.57%to9.53%,41.5%and7.96%, and GAO abundances varied from1.54%,2.22%and1.18%to6.92%,1.18%and1.79%. Propionate was the optimal carbon source for enrichment of PAO and inhibition of GAO, and selective hydrolysis was proposed to produce more proportion of propionate during the digestion and hydrolysis of sludge from primary settling tank or excess sludge.Finally, the microbial community structure and functional genes were further investigated based on high-throughput sequencing of metagenome. Organisms in the denitrifying phosphorus removal sludge were constituted with97.2%of bacteria,0.96% of Archaea,1.63%of eukaryote and etc. Proteobacteria was the most dominant phylum of denitrifying phosphorus removal sludge. Within Proteobacteria, β-Proteobacteria was the most class, followed by α-, γ-and δ-Proteobacteria. Metabolisms of Carbohydrates, Protein and Amino Acids as well as the Derivatives, were most abundant in denitrifying phosphorus removal sludge. The ppk genes of denitrifying phosphorus removal bacteria were distinct from aerobic phosphorus removal sludge, and also different from Dechloromonas.Based on the findings of16S rRNA gene and metagenome based investigation of denitrifying phosphorus removal, it was suggested that DPAO (Dechloromonas-related PAO) was a type of novel phosphorus removal bacteria that different from PAO (Ca. Accumulibacter), and16S rRNA genes was similar with Dechloromonas, but had different functional genes with Dechloromonas. Moreover, DPAO was dominant under anaerobic-anoxic condition and also had active activity under anaerobic-aerobic condition; while PAO couldn’t tolerate the strict anaerobic-anoxic condition actively.