Stratification patterns of anammox granular sludge bed: Linking particle size distribution to microbial activity and...

Anammox granular sludge processes are an attractive and efficient biotechnology in the field of wastewater treatment. In this study, the stratification patterns of anammox granular sludge bed (GSB) at steady states were illustrated and its relationship to microbial activity and community were systematically investigated under different nitrogen loading rates (NLRs). Morphological observation and quantitive particle size distribution analysis demonstrated that the GSB at low NLR was mainly composed of micro and fine granules with a big difference between bottom and top sludge layers. But at high NLR, the volumetric mean diameter (VMD) of GSB increased with the size distribution width (Span) declined forming a more homogeneous and coarse granules population. The particle size distribution parameters of GSB could be fast characterized by the optical lightness (L*) parameter (r = -0.771, p < 0.01, n = 16) and held a significant correlation with the nitrogen removal rate (NRR) of anammox system (r > 0.9, p < 0.05). The microbial spatial distribution patterns of different sludge layers were further investigated by high-throughput sequencing. The microbial community α-diversity index and microbial abundance matrix proved that the community structure tend to coverage at high NLR. Significant difference of the relative abundance of microbial community was detected under different NLRs. The VMD of GSB held a significant correlation with the relative abundance of AnAOB (r = 0.556, p < 0.01, n = 16) and other common accompanying bacteria (Denitratisoma and Chloroflexi). This study proved that the apparent particle size distribution patterns of GSB could be a potential auxiliary indicator to reflect the microbial activity and community, which can facilitate the innovative process monitor of anammox system based on visual features.