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. 2026 Jan 21:294:123832.
doi: 10.1016/j.envres.2026.123832. Online ahead of print.

Multi-strategy rehabilitation enhances nitrogen removal in a one-stage partial nitritation/anammox reactor

Xinyu Wan  1 , Zhicheng Zhao  1 , Yunpeng Zhao  1 , Wan Sun  1 , Shilong Liu  2 , Xiangyu Han  2 , Xi Lu  3 , Yasong Chen  4 , Weiwei Cai  5
Affiliations

Multi-strategy rehabilitation enhances nitrogen removal in a one-stage partial nitritation/anammox reactor

Xinyu Wan et al. Environ Res. .

Abstract

The one-stage granular PNA process is a promising low-carbon technology, yet its application is bottlenecked by unstable performance. In this study, a deteriorated granular sludge one-stage PNA reactor was rehabilitated using various operating strategies, resulting in an increase in total nitrogen removal rates from 0.2 to 0.8 kg N m3 d-1 and achieving a nitrogen removal efficiency of 80 %. Direct control of the airflow rate, rather than using dissolved oxygen (DO) as an indicator, successfully suppressed nitrite-oxidizing bacteria (NOB). Additionally, long-term addition of exogenous hydrazine (N2H4) effectively suppressed NOB, enhanced anammox activity, and strengthened the granulation process, with these effects persisting even after N2H4 addition ceased. The innovation lies in moving beyond conventional wastewater process parameters (like DO, FA, FNA) to implement practical control strategies (airflow rate, exogenous metabolite addition) that directly target and exploit the inherent properties of granular sludge ecosystems for effective, long-lasting system rehabilitation.

Keywords: Anammox; Granular sludge; Hydrazine; NOB suppression; Nitrogen removal; One-stage partial nitritation/anammox.

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Conflict of interest statement

Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Yunpeng Zhao reports financial support was provided by National Natural Science Foundation of China. Xinyu Wan reports financial support was provided by Hubei Provincial Natural Science Foundation. Xinyu Wan reports financial support was provided by China Three Gorges Corporation. Xinyu Wan, Zhicheng Zhao, Yunpeng Zhao, Wan Sun, Xi Lu, Yasong Chen reports a relationship with China Three Gorges Corporation that includes: employment and funding grants. Weiwei Cai reports a relationship with Beijing Jiaotong University that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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