Role of comammox bacteria in granular bioreactor for nitrogen removal via partial nitritation/anammox

In this study, two bioprocess models were first constructed with the newly-discovered comammox process described as one-step and two-step nitrification and evaluated against relevant experimental data. The validated models were then applied to reveal the potential effect of comammox bacteria on the granular bioreactor particularly suitable for undertaking partial nitritation/anammox (PN/A) under different operating conditions of bulk dissolved oxygen (DO) and influent NH₄⁺. The results showed although comammox bacteria-based PN/A could achieve > 80.0 % total nitrogen (TN) removal over a relatively wider range of bulk DO and influent NH₄⁺ (i.e., 0.25–0.40 g‐O₂/m³ and 470–870 g‐N/m³, respectively) without significant nitrous oxide (N₂O) production (< 0.1 %), the bulk DO should be finely controlled based on the influent NH₄⁺ to avoid the undesired full nitrification by comammox bacteria. Comparatively, conventional ammonium‐oxidizing bacteria (AOB)-based PN/A not only required higher bulk DO to achieve > 80.0 % TN removal but also suffered from 1.7 %∼2.8 % N₂O production.