Phosphorus recovery coupling with one-stage partial nitritation/anammox process for the treatment of high-nutrient permeate from anaerobic membrane bioreactor treating concentrated organic sludge

High-solid anaerobic membrane bioreactors (AnMBRs) are widely applied in solid waste treatment; however, the nutrient removal of the permeate, which possesses high mineral content, nitrogen, and COD concentration, is challenging. In this study, a hydroxyapatite-based one-stage partial nitritation/anammox (HAP-PNA) process was combined with an AnMBR treating concentrated organic sludge for permeate polishing, focusing on the enhancement of phosphorus recovery by influent Ca/P ratio optimization, alkalinity control and the effect of HAP formation on nitrogen removal. The total nitrogen and phosphorus concentrations of high-solid AnMBR permeate were 737 ± 5 mg/L and 90.9 ± 1.9 mg/L, respectively. The reactor operated at the nitrogen loading rate of 0.73 kg-N/m3/d and realized 81.6% nitrogen removal efficiency (NRE) and 0.6 kg-N/m3/d nitrogen removal rate. Denitrification reduced the nitrate produced during the anammox reaction, promoting a 25.7% COD removal and improving the NRE. The phosphorus removal efficiency (PRE) and sludge settleability were significantly enhanced by the addition of calcium, and a maximum PRE of 73.2% was achieved when the influent Ca/P ratio was 2.7. The reactor showed high stability and nitrogen removal performance, even when the phosphorus removal rate/nitrogen removal rate ratio was as high as 0.12. This study demonstrates the excellent capability of the one-stage HAP-PNA process for permeate treatment with high phosphorus content.