Importance of controlling phosphate concentration in nitritation–anammox reactor operation

Abstract

The effect of phosphate on anaerobic ammonium oxidation (anammox) was investigated in an integrated fixed film activated sludge-sequencing batch reactor (IFAS-SBR) treating raw digester sludge thickening lagoon supernatants before and after Ostara® treatment (for phosphorus recovery). At a similar nitrogen loading rate (NLR) of 0.31 kg N m⁻³ d⁻¹, pre-Ostara® lagoon supernatant feeding (with a phosphorus concentration of 235 ± 15.4 mg PO₄³-P L⁻¹) adversely impacted anammox activities, which were significantly improved from 55 ± 9.8% to 88.2 ± 3.6% when post-Ostara® feeding (with a phosphorus concentration of 32 ± 5.4 mg PO₄³-P L⁻¹) was applied. A higher nitrogen removal rate of 0.30 ± 0.01 kg N m⁻³ d⁻¹ was achieved with the post-Ostara® feeding compared to that with the pre-Ostara® feeding. Batch experiments confirmed that the phosphate concentration was the major inhibitor of anammox bacteria, and that anammox bacteria in biofilms showed greater tolerance to phosphate stress than anammox bacteria in flocs. Nitritation–anammox was successfully applied with 100% raw post-Ostara® supernatant feeding and intermittent aeration. High throughput sequencing indicated that the dominant ammonium oxidizing bacteria (AOB) in the IFAS-SBR, Nitrosomonas, facilitated nitritation, and that Candidatus Brocadia was the dominant bacteria responsible for the anaerobic ammonia oxidation observed. Compared to pre-Ostara® feeding, post-Ostara® feeding facilitated greater relative abundance of anammox bacteria. The highest abundance of Nitrosomonas and Candidatus Brocadia was 4.2% and 13.9%, respectively, which was observed in the reactor with the post-Ostara® feeding.