Microbial succession and operational strategies unlocking high-rate performance in IC-Anammox-HAP granular system

This study assessed the nitrogen and phosphorus removal performance of the high-rate anaerobic ammonium oxidation-hydroxyapatite (Anammox-HAP) in an internal circulation (IC) reactor. Under the dual-circulation strategy, a nitrogen removal rate of 23.3 gN/L/d and a phosphorus removal rate of 0.79 gP/L/d were achieved with synthetic wastewater. Long-term operation fostered co-enrichment of biomass and inorganic in granules significantly, improving their mechanical strength and settling performance. Microbial community analysis demonstrated that elevating influent total nitrogen concentration effectively phased out heterotrophic nitrifying aerobic denitrifying bacteria (Acinetobacter and Exiguobacterium), establishing dominance of Anammox bacteria (Ca. Kuenenia) and denitrifying bacteria (OLB13, SJA-28, and Denitratisoma). Comparatively, reducing hydraulic retention time enhanced specific anammox activity effectively. A novel "Rupture-Recycle-Restart" strategy enabled recovery of HAP cores from over-mineralized granules and achieved rapid restart-up of the reactor and regranulation of broken sludge within 11 days. This work demonstrates the feasibility and application potential of the IC-Anammox-HAP system.