| The cultivation of aerobic granules in a large pilot-scale SBR was investigated using domestic wastewater. After operation of 210 days, the granules with a diameter of 330 μm were successfully formed by seeding anaerobic digested sludge. Results showed that, during the first three months of operation under low organic load of influent, removal efficiencies of pollutants increased steadily including COD, NH+4-N, total nitrogen (TN) and total phosphorous (TP). Meanwhile, microorganisms related to nitrogen and phosphorous were enriched. The organic load was enhanced since cycle time was shortened to 6 h, and the operational performance of the reactor still remained stable. Moreover, the average particle size of the sludge started to increase, along with excellent settling ability and high bioactivity. After the formation of aerobic granules, Sludge volume index (SVI) was maintained at 30 mL·g-1 and the mixed liquor suspended solid (MLSS) concentration in the SBR reached 8.8 g·L-1. MLVSS/MLSS ratio of the sludge increased to 82% with a high oxygen uptake rate (OUR) of 5.32 mg·(min·L)-1. Bacillus was dominant on the outer layer of granules, while cocci were mainly located inside. The average COD and TP removal efficiencies kept at 90% and NH+4-N was almost completely depleted, NO-3-N and NO-2-N were not accumulated in the effluent. The aerobic granules were also capable of achieving simultaneous nitrification and denitrification (SND) in a single SBR cycle, which resulted in a high TN removal efficiency of 80%. |
