Performance stability and recovery strategy of pre-denitrification coupled partial nitritation/anammox-hydroxyapatite processes for enhanced organic matter, nitrogen and phosphorus removal from swine manure digestate

• A pre-denitrification PN/A-HAP process for enhanced SMD treatment was evaluated. • The removal efficiencies for N, COD, and P were 94%, 52%, and 32%, respectively. • Pre-denitrification improved NRE by 5% and augmented stability of PN/A-HAP process. • Low Ca/P ratio (0.17) induced PN/A-HAP particle cleavage and process collapse. • Anammox-HAP sludge restored process stability through reformed PN/A-HAP particles. Achieving efficient treatment of high concentrations of NH 4 + -N and organic matter, while addressing NO 3 – -N residue, poses a challenge for the Anammox process. Herein, a novel two-stage pre-denitrification coupled partial nitritation/anammox-hydroxyapatite (PN/A-HAP) process was developed for treating swine manure digestate. The pre-denitrification reactor eliminated the inhibition of organic matter and NH 4 + -N on anammox bacteria while converting NO x - to N 2 . Furthermore, it enhanced PN/A-HAP particles, achieving a mean particle size of 1184 μm along and an excellent settling velocity of 2.6 m/h. Short-term exposure to a low Ca/P ratio of 0.17 led to the initial fragmentation of PN/A-HAP particles, while subsequent fragmentation caused by the inhibition of anammox bacteria and shear stress ultimately resulted in the collapse of the two-stage process. A strategy involving the addition of mature Anammox-HAP sludge demonstrated a restoration of process stability. This study advocates for the application of the anammox process in swine wastewater treatment.