Novel anammox granules formation from conventional activated sludge for municipal wastewater treatment through flocs management

The direct integration of anammox process into municipal wastewater treatment has caused widespread concern, but the lack of anammox seeds limited its real application. This study successfully cultivated anammox granules (322.0 μm) from conventional activated sludge treating municipal wastewater. Through ultra-low floc sludge retention times of 8d, nitrifiers on flocs were eliminated and partial nitrification was realized. Furthermore, highly bacteria-enriched granules were initially formed, with Nitrosomonas and Ca. Competibacter 4-fold higher than that of flocs. Specific staining results revealed the microbial interaction with Ca. Brocadia, considering that Ca. Competibacter and Nitrosomonas correspondingly identified in the inner and outer layers of granules. The percentage of Ca. Brocadia present on the granules increased substantially from 0.0 % to 3.0 %, accompanied by a nitrogen removal rate of 0.3 kg·m−3·d−1. Our findings revealed a valuable reference for the anammox bacteria in-situ enrichment under mainstream conditions, which provides theoretical guidance for anammox-based processes practical application.