Formation of Aerobic Granular Sludge in Sequencing Batch Reactor: Comparison of Different Divalent Metal Ions as Cofactors

The two sequencing batch reactors (SBRs) were operated to investigate the different effect of Ca2+ and Mg2+ augmentation on aerobic granulation. R1 was augmented with Ca2+ at 40 mg/L, while Mg2+ was added to R2 with 40 mg/L. Results indicated that R1 had a faster granulation process, and aerobic granulation reached the steady state after 60 cycles in R1 but 80 cycles in R2. The mean diameter of the mature granules in R1 was 1.6 mm which was consistently larva than that (0.8 mm) in R2, and aerobic granules in R1 also showed a higher physical strength. However, the mature granules in R2 had the higher production yield of polysaccharides and proteins, and aerobic granules in R2 experienced a faster substrate biodegradation. Microbial and genetic characteristics in mature granules were analyzed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The results revealed that Mg2+ addition led to higher microbial diversity in mature granules. In addition, the uncultured bacterium (AB447697) was major specie in R1, and beta-proteobacterium was dominant in R2.