Upflow blanket filter anammox (UBFA) system treating low-nitrogen wastewater: high-efficient nitrogen removal, granules formation, N₂O emission, and microbial succession

This research provides an important approach for low-nitrogen wastewater treatment through anaerobic ammonium oxidation (Anammox), and Anammox granule sludge (AnGS) in the Upflow. Blanket Filter Anammox (UBFA) system through shortening the hydraulic retention time was successfully cultivated. The percentage of medium granules (1.0–2.0 mm) with the highest Anammox activity increased from 0 to 28.5%, and the proportion of flocs (0–200 μm) reduced from 84.5% to 17.6%. Through the multidimensional analysis of AnGS, the relationship between AnGS and EPS secretion, low SVI, high PN/PS, multiple filamentous bacteria, and AnAOB were explored. Microelectrode tracing tests demonstrated that the main anammox reaction active layer was 0–1500 μm, and the highest activity was observed at 200–400 μm, whereas denitrification activity and N₂O production were mainly distributed in the granules deep layer of 1500–2500 μm. The research showed that Candidatus Brocadia and Candidatus Kuenenia were the predominant anammox species in the UBFA system, while the abundance of AnAOB was higher in medium granules.