Aerobic Sludge Granulation and Simultaneous Partial Nitrification, Denitrification, and Phosphorus Removal in an AOA-SBR with Low Dissolved Oxygen

Coupling simultaneous partial nitrification, denitrification, and phosphorus removal with aerobic granular sludge (AGS) (SPNDPR-AGS) is promising but challenging to low-carbon wastewater treatment. In this study, extremely low dissolved oxygen around 0.30 mg/L was set in an anaerobic/oxic/anoxic (AOA) mode sequencing batch reactor for the initiation of SPNDPR-AGS, accelerated by gradually decreasing the settling time. Experimental results revealed that AGS formation was essentially completed within 45 days and an average particle size of 497 μm was obtained after maturation over operation. Denitrifying glycogen-accumulating organisms Candidatus_Competibacter predominated up to 50.2% of the community, which favored the secretion of polysaccharide (PS), enhancing the sludge viscosity and aggregation among the sludge particles. In addition, the alkaline microenvironment within the AGS facilitated the precipitation of phosphate inorganic crystals, thus forming the nucleating cores to initiate sludge granulation. The high ammonia-oxidizing bacteria to nitrite-oxidizing bacteria ratio of 3.3 and the average nitrite accumulation rate of 89.2 ± 8.0% indicated that SPNDPR-AGS was successfully achieved and could be continuously stabilized. This study provides new insights into the theoretical and engineering aspects of AGS for green and low-carbon–water management.