Granulation is initiated by initial precursors serving as carriers or nuclei for new bacterial growth.
These loosely adhered bacterial aggregates are strengthened by extracellular polymeric substances (EPSs) excreted by bacteria andform firmly attached initial granules [11]. The selective pressure,
chemical oxygen demand (COD) loading rate, and settling time ofthe divalent metal ions and many other factors affect the start-upof aerobic granulation [12–15].