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Abstract Elimination of nitrogen pollution from wastewater containing high-strength nitrate (NO 3 −-N) is a significant issue to prevent deterioration of water quality and eutrophication of receiving water body. Traditional denitrification process faces several challenges including the huge organic carbon demand, intermediate products accumulation, and long acclimatization period. In this study, an efficient solution was given by a novel two-stage Partial Denitrification (PD)-Anammox process. High NO 3 −-N (1000 mg N/L) wastewater and municipal sewage (COD: 182.5 mg/L, ammonia (NH 4 +-N): 58.3 mg/L) were simultaneously introduced to the PD reactor for NO 3 −-N converting to NO 2 −-N. The NH 4 +-N and NO 2 −-N in effluent of PD were removed in subsequent anammox reactor. Results showed that a satisfactory nitrogen removal was achieved by optimizing the volume ratios of influent NO 3 −-N and municipal sewage, as well as the external organic matter dosage. The NO 3 −-N removal efficiency reached up to 95.8% without accommodation period, along with the NH 4 +-N removal achieving 92.8%. Anammox contributed to 78.9% of TN removal despite the high COD (76.5–98.6 mg/L) in PD effluent was introduced, indicating the significant stability of the integrated process. The microbial analysis suggested that the Candidatus Brocadia , identified as anammox bacteria, cooperated stable with denitrifying bacteria in 215-day operation. The PD-Anammox process offers an economically and technically attractive approach in the high NO 3 −-N wastewater treatment since it has great advantages of much low carbon demand, minimal sludge production, enabling simultaneous treatment of municipal sewage, and avoiding the common issues in traditional denitrification process. Graphical abstract Unlabelled Image Highlights • Simultaneous treatment of high-strength nitrate and municipal sewage was demonstrated. • Nitrate removal efficiency reached up to 95.8% at influent nitrate of 1000 mg/L. • Municipal sewage was treated with nitrogen removal efficiency of 92.8%. • Anammox and denitrifying bacteria cooperated for advanced nitrogen removal. • Partial-denitrification combining with anammox is an economic and efficient option. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • DEAMOX maintained stable performance for high-strength NO 3 −-N and NH 4 +-N removal. • TN removal efficiency achieved 96.7% with both NO 3 −-N and NH 4 +-N over 800 mg L−1. • Step-feed of organic carbon significantly improved NO 2 −-N production in PD process. • Anammox bacteria was more tolerant to NO 2 −-N in DEAMOX system than single anammox. • Functional groups cooperated stably with anammox responsible for 88.9% TN removal. Abstract The innovative DEnitrifying AMmonium OXidation (DEAMOX) process, coupling partial-denitrification (PD) with anammox, was designed for treating high-strength nitrate (NO 3 −-N) and ammonia (NH 4 +-N) wastewater for the first time. With influent total nitrogen (TN) up to 1600 mg L−1 (NO 3 −-N/NH 4 +-N of 1.0), DEAMOX process proved to be relatively stable for simultaneously removing NO 3 −-N and NH 4 +-N. The step-feeding organic carbon (OC) demonstrated as an efficient strategy for avoiding NO 2 −-N consumption by denitrification, facilitating the increased of NO 3 −-N to NO 2 −-N transformation ratio (NTR) to 99% at COD/NO 3 −-N of 1.77. The TN removal was significantly enhanced to 96.7% with the considerably high anammox contribution of 88.9%. Also, the inhibitory effect of high NO 2 −-N accumulation on denitrifying bacteria could be mitigated. High-throughput sequencing revealed a relatively stable cooperation of functional groups in DEAMOX system. Genus Thauera possibly capable of NO 2 −-N accumulation remained dominant (39.81% to 44.09%), while Candidatus Brocadia responsible for anammox was detected with much lower percentage (2.01% to 1.81%). Results of qPCR confirmed the evident growth of anammox bacteria under increasing nitrogen and organic loading. The DEAMOX process offers a significantly stable and efficient method in treating high-strength NO 3 −-N and NH 4 +-N wastewater. [ABSTRACT FROM AUTHOR]