Characteristics and mechanism of hollow anammox granular sludge with different settling properties

The characteristics and mechanism of hollow anammox granular sludge with different settling property were investigated through the analysis of morphology, structure and microbial community. According to settling property, the granules from an anammox continuous stirred-tank reactor were classified into settling granules (SG) benign floating granules (BFG) and malignant floating granules (MFG). As the settling performance deteriorated, the extracellular polymeric substances (EPS) content of the granules increased. The microstructure showed that the number of pores changed significantly for SG, BFG, and MFG. Transfer distance increased with increasing particle size. The analysis of EPS and rheological properties indicated that EPS is a key driving force of floating and proliferation in the lifecycle of hollow anammox granule. The results of microbial community revealed that EPS-hydrolyzing bacteria were biological factors that weaken structure strength of granule.