[Stable Nitrite Accumulation and Phosphorus Removal from High-nitrate and Municipal Wastewaters in a Combined Process of Partial Denitrification and Denitrifying Phosphorus Removal (PD-DPR)]

In this study, a novel process combining partial denitrification (PD, NO₃^--N→NO₂^--N) and denitrifying phosphorus removal (DPR) in an anaerobic-anoxic-aerobic sequencing batch reactor (SBR) was developed. By comprehensively controlling the influent C/N ratio, anaerobic drainage ratio, and anoxic duration, the nitrite accumulation and phosphorus removal performance of a system treating high-strength nitrate and municipal wastewaters was investigated. The results showed that, after 140 days, the nitrate-to-nitrite transformation ratio (NTR) was 80.1%, and PO₄^3--P removal efficiency was 97.64%. In the anaerobic stage (180 min), glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) efficiently utilized the carbon source in municipal wastewater to enhance intracellular carbon storage. In the anoxic stage (150 min), denitrifying GAOs (DGAOs) and heterotrophic denitrifying bacteria (DOHOs) carried out endogenous and exogenous short-range denitrification, respectively, to achieve stable nitrite accumulation; simultaneously, denitrifying PAOs (DPAOs) carried out denitrifying phosphorus uptake to achieve efficient phosphorus removal. In the aerobic stage (10 min), without initiating ammonia/nitrite oxidation, PAOs absorbed excessive phosphorus, which improved the phosphorus removal performance of the system. The effluent NO₂^--N/NH₄⁺-N of a ratio of 1.31:1 (close to the theoretical value of ANAMMOX process, 1.32:1), with little PO₄^3--P and COD (0.30 and 12.94 mg·L^-1), meets the requirements for deep-level nitrogen removal by coupling with ANAMMOX process.