Impact of comammox process on membrane-aerated biofilm reactor for autotrophic nitrogen removal

Abstract

This study compared the simulation results of the side-stream membrane-aerated biofilm reactor (MABR) in terms of total nitrogen (TN) removal and N₂O production obtained by the conventional comammox-exclusive biological nitrogen removal (BNR) model and the novel BNR model with comammox-related model structures/parameters. Even though the conventional comammox-exclusive MABR obtained >85 % TN removal over a wide range of substrate conditions and achieved up to ∼92.0 % TN removal, it suffered from 0.90 %-4.80 % N₂O production. Comparatively, despite the significantly lower N₂O production (0.01 %-0.06 %), due to the undesired full nitrification of comammox bacteria, the novel comammox-inclusive MABR failed to provide adequate nitrite for anammox bacteria under exceeding substrate conditions and only obtained the maximum ∼88.0 % TN removal through comammox bacteria-based partial nitritation/anammox. Both MABRs should be operated at a moderate hydraulic retention time (e.g., 4.0 d) with a sufficient biofilm thickness (e.g., ≥300 μm) to attain efficient TN removal and reduced N₂O production.