Development of denitrifying granules in sequencing batch reactors

Abstract

This study investigated characteristics of denitrifying granules developed in sequencing batch reactors (SBRs) run at different cycle times. The complete denitrification was achieved in the denitrifying granular sludge SBRs. Results showed that the mean size and settleability of denitrifying granules were inversely related to the SBR cycle time, i.e., bigger and faster-settling denitrifying granules were obtained at a shorter cycle time. Meanwhile, a higher initial denitrifying granulation rate was observed at a shorter cycle time, indicating that the shorter cycle time would favor rapid denitrifying granulation. It was found that the content of extracellular polysaccharides in biomass almost remained unchanged in the course of denitrifying granulation, however a substantial increase in the content of extracellular proteins was recorded, i.e. denitrifying granulation would be more related to extracellular proteins instead of polysaccharides. Furthermore, denitrifying granules cultivated at the shorter cycle time exhibited higher mechanical strength which was found to be determined by cell surface charge density. This study offer insights on the characteristics of denitrifying granules, which indeed are essential for actual application of denitrifying granular sludge bioreactor for nitrogen removal from wastewater.