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 mu m. At an influent NH4+-N concentration of 2059 f 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 f 6.1 %), phosphorus removal (71.1 %), and comparable COD removal (37.5 %) were achieved even at high influent NH4+-N concentrations (1822 f 97 mg/L) without the need for excessive dilution or recirculation.