Influences of granule properties on the performance of autotrophic nitrogen removal granular reactor: A model-based...

This work studied the impacts of key granule properties on the granular reactor performing partial nitritation/anammox from the modeling perspective. The results could guide not only future reliable modeling but also practical startup/operation of the reactor. To achieve high total nitrogen (TN) removal whilst avoiding significant N₂O production, inoculated granules should be big and anammox-enriched. The optimum boundary layer thickness for maximum TN removal increased with the decreasing diffusivity of soluble components in the granule structure. Even though a thick boundary layer could protect anammox bacteria from elevated dissolved oxygen (DO) (e.g., 0.5 g-O₂/m³) and obtain high TN removal (>90.0%) and low N₂O production (<1.8%), even complete removal of the boundary layer would fail to provide sufficient substrate for anammox and therefore couldn't increase TN removal to 90.0% and decrease N₂O production to <2.4% at insufficient DO (e.g., 0.3 g-O₂/m³ in the presence of lifted influent NH₄⁺ concentration).