Feasibility of Partial Nitrification Combined with Nitrite-Denitrification Phosphorus Removal and Simultaneous Nitrification–Endogenous Denitrification for Synchronous Chemical Oxygen Demand, Nitrogen, and Phosphorus Removal

A combination of partial nitrification and nitrite-denitrifying phosphorus removal and simultaneous nitrification-endogenous denitrification (nDNPR-SNED) in two sequencing batch reactors was developed for synchronous chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) removal by regulating dissolved oxygen (DO) and influent nitrite concentrations. COD, total nitrogen, and P removal efficiencies of 87.4 ± 0.5, 91.6 ± 1.1, and 97.8 ± 0.6% were obtained after 112 days of anaerobic/anoxic/aerobic operation. Mass balance analysis confirmed that 91.9% of the COD was stored as intracellular carbon at the anaerobic stage, and 99.6% of PO43––P and 99.8% of NO2––N were eliminated via the nDNPR process at the anoxic stage, and at the aerobic stage, the SNED process contributed to 68.7% nitrogen removal. Genera of Candidatus Competibacter, Dechloromonas, Ellin6067, and Nitrospirae were the dominant consortia with a relative abundance of 26.5, 16.5, 1.0, and 1.1%, respectively. In the metabolic pathway model, β-hydroxybutyrate was the main endogenous driving force for nitrogen and phosphorus removal. Compared with conventional biological nitrogen and phosphorus removal processes, the combined process could achieve 6.7% saving in the total cost. The proposed approach provides an economic and technical alternative for C-, N-, and P-laden wastewater treatment, reducing both carbon demand and aeration consumption.