Unveiling novel steady-state phosphorus removal equilibrium in partial nitritation/Anammox-hydroxyapatite process:
Yangkai Liu1, Yanxiao Wei2, Zhenpeng Cao1
1Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, School of Hydraulic and Ocean Engineering, Changsha University of Science & Technology, Changsha 410114, China.
Abstract:
The partial nitritation/Anammox-hydroxyapatite (PN/A-HAP) process enables economical nitrogen and phosphorus removal. This study conducted long-term continuous experiments to evaluate the feasibility of the single-stage PN/A-HAP reactor for low-phosphorus wastewater treatment. An equilibrium limitation of the total phosphorus concentration in the effluent (TP-eff) under controlled conditions was identified. With influent NH4+-N at 350 mg/L, hydraulic retention time of 6 h, and calcium to total phosphorus ratio of 4.0, an airlift internal partition bioreactor consistently maintained TP-eff at 2.0 ± 0.3 mg/L in the PN/A-HAP system, even as the total phosphorus concentration in the influent (TP-inf) reduction from 20 to 5 mg/L. This stability results from limitations in phosphorus removal capacity imposed by the saturation index, phosphorus loading rate, and hydroxyapatite crystallization. These findings expand the understanding of the phosphorus removal boundaries and sustainability potential of the PN/A-HAP system, emphasizing advanced post-treatment strategies to further reduce TP-eff.
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