Calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors

This study investigated calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors (SBRs) supplemented with different calcium concentrations of 0, 50 and 100 mg Ca2+ l−1, respectively. Results showed that high calcium concentration would favor the formation of big and fast-settling denitrifying granules. Extracellular proteins (PN) were found to increase, whereas extracellular polysaccharides (PS) almost remained unchanged with granulation in all three SBRs. Moreover, the PN contents in mature denitrifying granules were positively related to feed calcium concentration. These suggested that PN would play a more important role than PS in denitrifying granulation process. It was also revealed that about 2.5–2.9% of calcium in denitrifying granules was bound with extracellular polymeric substances (EPS), and further helped to strengthen the structure of denitrifying granules. Mature denitrifying granules cultured with 50 mg Ca2+ l−1 exhibited the highest specific denitrification rate (DNR) of 1040 mg N g−1 VSS d−1.