[Start-up and Optimization of Denitrifying Phosphorus Removal in ABR-MBR Coupling Process]

The feasibility of the denitrifying phosphorus removal process in the ABR-MBR system with no sludge reflux and high concentration of seeding activated sludge (25 g ·L^-1, in MLSS) in the ABR was investigated. The characteristics of the microbial community in the denitrifying phosphorus removal compartment were also evaluated. The denitrifying phosphorus removal function was achieved by gradually increasing the reflux ratio (R) from 0% to 200%. During the stable operation, the average removal rates of COD, PO₄^3--P, and TN in the system were 88.28%, 54.45%, and 61.93%, respectively. When the influent loading rate, NO^--N reflux ratio, and hydraulic retention time (HRT) of ABR and MBR were 0.8 kg ·(m³ ·d)^-1, 150%, and 9 h and 3.3 h, respectively, the average VFA concentration of 80.58 mg ·L^-1, ρ(NO₂^--N)/ρ(NO₃^--N) reflux ratio of 1.68, and PO₄^3--P and TN removal rates of 64.94% and 62.95% were obtained. The short-cut nitrification denitrifying phosphorus removal was achieved in the ABR-MBR system. Batch tests showed that denitrifying phosphorus removal bacteria (DPAOs) were the main functional bacteria in the ABR, with anaerobic phosphorus release and anoxic phosphorus uptake of 3.73 mg ·L^-1 and 10.22 mg ·L^-1, respectively. High throughput sequencing results showed that Proteobacteria and Bacteroidetes were the dominant phyla in the phosphorus removal compartment, accounting for 23.49%-53.66% and 16.55%-21.78% of the total phyla, respectively. Thauera, Thiothrix, Pseudomonas, norank_ f_Rhodocyclaceae, and unclassification_ f_Rhodocyclaceae in Proteobacteria, and Sphingobacteriales in Bacteroidetes were the potential denitrifying phosphorus removal microorganisms.