Abstract: To address the issue of prolonged granulation time and poor stability of aerobic granular sludge (AGS) in domestic wastewater treatment, a gradual transition approach is proposed by gradually introducing domestic wastewater into artificial water, aiming to investigate the granulation process of AGS and its denitrification and decarbonization efficiency. AGS was cultivated in four sequencing batch reactors (SBRs), and the inoculum used was the settled sludge from the secondary sedimentation tank of the A²/O process in a wastewater treatment plant. At a temperature of 25 ℃, R1 received artificial water for the first 17 days, followed by a switch to domestic wastewater on the 18th day. In R2, the artificial water proportion was gradually reduced over stages until domestic wastewater reaches 100%. R3 only received artificial water throughout the experiment, while R4 operated at a lower temperature of 15 ℃ and received artificial water. The results revealed that water quality and temperature variations caused increased fluctuations in protein (PN) and polysaccharide (PS) content in the extracellular polymeric substances (EPS) of R1 and R4. R2 and R3 exhibited an upward trend in PN and PS content, and the settling velocity of AGS increased with higher PN content. At 25 ℃, the sludge volume index (SVI) showed a negative correlation with EPS. Successful cultivation of AGS was achieved at both temperatures. Specifically, at 25 ℃, the gradual transition approach by introducing domestic wastewater into artificial water resulted in a shorter granulation time of AGS in real domestic wastewater, along with enhanced settling performance. These research findings provide valuable insights for AGS-based treatment of domestic wastewater.

Key words: water quality, aerobic granular sludge (AGS), extracellular polymer substances (EPS), nitrogen and carbon removal, domestic sewage