ConclusionsThe present study found that ZVI enhances aerobic granulation.ZVI significantly decreased the start-up time from 64 to 43 days andimproved the removal efficiencies for COD and NH4+-N. Maturegranules augmented with ZVI had better physical characteristicsand EPS content (especially of protein). 3D-EEM showed that ZVIgenerated organic material diversity (especially protein diversity).ZVI augmentation also enhanced the diversity of the microbial com-munity