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Multi-zonal anaerobic ammonium oxidation for mainstream municipal wastewater treatment

Nature Sustainability (2026)Cite this article

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Abstract

Biological nitrogen removal is a main contributor to the carbon footprint of municipal wastewater treatment plants (MWWTPs). Anaerobic ammonium oxidation (anammox) is key to decarbonizing MWWTPs. However, anammox technology has long been developed following the ‘hotspot’ concept, which spatially confines anammox to specific zones in MWWTPs, leaving its potential underexploited in mainstream treatment. Here we propose a ‘multi-zonal anammox’ concept to expand the anammox process throughout the whole MWWTP mainstream. It allows the implementation of anammox in existing MWWTPs with minimal reconstruction requirements. We evaluated the feasibility of this concept in an anaerobic–anoxic–oxic (A2O) biosystem, which is one of the most widely used processes in MWWTPs. During a 2-year-long operation, anammox bacteria highly self-enriched and contributed to nitrogen removal throughout the mainstream, with relative abundances reaching 4.8%, 5.7–10.0% and 0.2–1.0% in anaerobic, anoxic and oxic zones, respectively. The multi-zonal anammox enhanced nitrogen removal efficiency by 20%, reduced aerating electricity input by 20%, mitigated nitrous oxide emissions by 66% and eliminated the need for supplemental organic carbon. Overall, this work opens a promising avenue for implementing the anammox process, paving the way towards sustainable wastewater management.

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Fig. 1: Set-up and operation of the A2O biosystem.
Fig. 2: Anammox empowering nitrogen removal across functional zones.
Fig. 3: Spatiotemporal characteristics of anammox bacteria enrichment and transcription.
Fig. 4: Bacterial community structure and functional characteristics.
Fig. 5: The proposed potential niche cycle mechanism of anammox bacteria in the hybrid process (flocs + biofilms).

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Data availability

Raw sequencing data are available in the NCBI Sequence Read Archive (SRA) with the accession codes PRJNA1178615 and PRJNA1355498. Source data are provided with this paper.

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Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (grant nos. 52131004, Y.P.; U23A20675, L.Z. and Y.P.), the Higher Education Discipline Innovation Project (111 Project, D16003, Y.P.), the Funding Projects of Beijing Municipal Commission of Education (Y.P.), the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation (grant nos. BX20250323, Q.Z.; 2025M781157, Q.Z.) and the Shanghai Tongji Gaotingyao Environmental Science & Technology Development Foundation (Q.Z.).

Author information

Authors and Affiliations

  1. National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Engineering Research Center of Beijing, Beijing University of Technology, Beijing, People’s Republic of China

    Qi Zhao, Liang Zhang, Yang Zhao, Jianwei Li, Luyao Wang, Xiyao Li & Yongzhen Peng

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  1. Qi Zhao
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  2. Liang Zhang
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  3. Yang Zhao
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Contributions

The project was conceived and led by Y.P. Q.Z., L.Z., Y.Z., J.L., L.W. and X.L. contributed to the chemical, microbial and statistical analyses. Q.Z. wrote the manuscript, and Y.P. and L.Z. contributed to its commenting and revision. All authors discussed and interpreted the results and contributed to the manuscript.

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Correspondence to Yongzhen Peng.

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Nature Sustainability thanks Fangang Meng and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Zhao, Q., Zhang, L., Zhao, Y. et al. Multi-zonal anaerobic ammonium oxidation for mainstream municipal wastewater treatment. Nat Sustain (2026). https://doi.org/10.1038/s41893-026-01786-y

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