Simultaneous removal of nitrogen and phosphorus from methane fermentation permeate by hydroxyapatite microgranule type one-stage partial nitrification/anammox process

In this study, the feasibility of an air-lift one-stage partial nitrification/anammox (PNA) reactor to treat high-nutrient permeate from high-solid anaerobic membrane bioreactor was evaluated. The high concentration of calcium and phosphorus in the permeate promoted spontaneous hydroxyapatite (HAP) formation without Ca/P ratio regulation or alkalinity addition. This consequently enhanced the settleability of microgranules, maintaining an SVI around 35 mL/g even when particle size was below 100 μm. At an influent NH 4 + -N concentration of 2059 ± 80 mg/L and nitrogen loading rate (NLR) of 1.03 g-N/L/d, free nitrous acid (FNA) inhibition briefly affected performance, yet the system showed rapid recovery following sludge flushing and re-feeding. Biomass growth rate, microbial community structure, and activity measurements before and after inhibition underscored the stability and resilience of HAP-based microgranules. Consequently, efficient nitrogen removal (88.9 ± 6.1 %), phosphorus removal (71.1 %), and comparable COD removal (37.5 %) were achieved even at high influent NH 4 + -N concentrations (1822 ± 97 mg/L) without the need for excessive dilution or recirculation. • AnMBR permeate with high concentration of nutrients was treated by one stage HAP-PNA process. • Stable simultaneous removal of N, P and COD was obtained during long term operation. • Permeate feeding enabled HAP-microgranule formation without extra chemical addition. • HAP-microgranule with about 100 μm had good settleability and stable microbial structure. • Candidatus Kuenenia , Nitrosomonas and Denitratisoma were the top 3 functional bacteria.