Impact of (O/A)n operation on nitrogen and phosphorus removal performance of a simultaneous nitrification and endogenous denitrification phosphorus removal system

Abstract:

To enhance the synergistic effects of denitrifying phosphate accumulating organisms (DPAOs) and denitrifying glycogen accumulating organisms (DGAOs) in the denitrification phosphorus removal technology, three identical SBR reactors (R1, R2, R3) were set up in the experiment. These reactors operated under a periodic aerobic/anoxic (O/A)_n aeration mode with n values of 1,2, and 3, respectively, to run a simultaneous nitrification endogenous denitrification and phosphorus removal (SNEDPR) system. By comparing the operational conditions of the three reactors over 70 days, the pollutant treatment performance and the activity of functional bacteria were investigated. The results show that under the condition of similar internal carbon storage during the anoxic phase, the R3 reactor operated with (O/A)₃ achieved the highest pollutant removal rates on the 71st day, with 89.38% for total nitrogen (TN), 91.78% for total phosphorus (TP), and 90.20% for chemical oxygen demand (COD), demonstrating the best pollutant removal effect, and also had a higher TP removal rate during the anoxic phase. The typical cycles indicated that on the last aerobic stage of the 70st day, the ratio of NO-₂-N to total nitrogen was 42.41%, 49.83%, and 52.33%, respectively, confirming that increasing the n value in (O/A)_n operation enhances the system′s NTR. Analysis of sludge characteristics revealed that in the R3 reactor, MLSS(mixed liquor suspended solids) and MLVSS(mixed liquor volatile suspended solids) increased steadily, with a low SVI(sludge volume index). The unit VSS extracellular polymeric substances (EPS) content reached 85.27 mg/g by the 70st day, indicating good sludge structure and settling performance. Microbial community analysis showed a higher relative abundance of DPAOs and DGAOs in R3, suggesting that increasing the aeration cycle of (O/A)_n is beneficial for the enrichment of functional bacteria. Increasing the n value in (O/A)_n operation can effectively enhance the synergistic action between DPAOs and DGAOs, improve the nitrogen and phosphorus removal efficiency of the SNEDPR system, and reduce the reliance on external carbon sources.