Hydrazine-driven granulation and functional differentiation in partial nitrification-anammox systems: size-dependent
Xinyu Wan1, Yasong Chen1, Shilong Liu2
1National Engineering Research Center of Eco-Environment in the Yangtze River Economic Belt, China Three Gorges Corporation, Wuhan 430014, PR China.
Abstract:
Hydrazine (N2H4) was investigated as a metabolic regulator to accelerate granulation and functional recovery in anammox systems. Low-dose N2H4 (5 mg N2H4 L-1) triggered a 386.6% surge in nitrogen removal rate, significantly outperforming high-nitrogen-load controls. Mechanistically, N2H4 acted as an energy shuttle, stimulating protein-rich extracellular polymeric substance (EPS) secretion. This induced a unique "selective pressure" that eliminated unstable small particles and drove a morphological transition toward large granules (mean size 2.38 mm). These structural shifts created prolonged oxygen mass-transfer limitations, facilitating a more stable ecological niche that suppressed NOB and protected the AnAOB core. Crucially, the system maintained functional stability for 33 days after dosing ceased, demonstrating a sustained structural and functional robustness rather than a transient stimulation. Overall, these findings position N2H4 as a high-efficiency, short-term "bio-catalyst" for rapid start-up or emergency recovery in full-scale anammox engineering.
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