Spatial profiling of granular sludge and microbial sub-communities in an anammox EGSB reactor under varying upward flow velocities

The upward flow velocity significantly influences the spatial characteristics of granular sludge and microbial sub-communities in the anaerobic ammonium oxidation expanded granular sludge bed (anammox-EGSB) reactor. This study examines the spatial characteristics of granular sludge and microbial sub-community distribution at various upward flow velocities by adjusting the reflux rate. Elevated upward flow velocity (12.0 m/h) significantly enhances anammox granular characteristics (color, structure, and particle size) and minimizes spatial variations in particle morphology, extracellular polymeric substances (EPS) (proteins, polysaccharides, humic acids), and microbial sub-community structures. Despite the increase in upward flow velocity reducing anammox potential in the abundant sub-community, it fosters microbial synergy, thus optimizing nitrogen removal potential across each region of the reactor. Additionally, the abundant sub-community primarily contributes to nitrogen cycling and is significantly impacted by fulvic-like organic substances, whereas the rare sub-community mainly maintains microbial system stability. The transient sub-community helps sustain nitrogen balance and facilitates organic matter degradation, thereby stabilizing both rare and abundant sub-communities' structure and function. Furthermore, rare and abundant sub-communities display distinct co-occurrence patterns, with the rare sub-community demonstrating greater taxonomic diversity. These findings contribute to optimizing the parameters of the EGSB reactor in actual operation.