<p>Aerobic granular sludge (AGS) technology has proven to have distinguished features and performance in nutrient removal, yet still few studies have elaborated profound insight into the conditions that lead to the most effective nutrient removal. The novelty of this study lies in revealing the best conditions for nutrients removal by exploring distinct characteristics and pollutants removal performance between anaerobic–aerobic (AO) and anaerobic–aerobic-anoxic (AOA) conditions in the AGS process. AGS was performed in two SBRs under two different conditions, anaerobic–oxic/aerobic (A-O) in R1 and anaerobic-oxic-anoxic (A-O-A) in R2. Results show that both reactors achieved notable performance, with COD removal of 97% for R1 and 93% for R2, 100% for both R1 and R2 in NH₄ removal, and PO₄ removal of 97.8% for R1 and 96.7% for R2. The two conditions yielded distinct biomass growth, granule profiles, microbial diversity, and nitrogen removal mechanisms. The A-O condition resulted in average biomass growth of 4242&#xa0;mg/L and 51% granules, which was higher than the A-O-A condition of 2700&#xa0;mg/L and 38% granules, in addition to larger granule size. Meanwhile, higher microbial diversity was found in the A-O-A system than in the A-O system. R2 performed complete nitrogen removal without leaving NO₃ residue, unlike R1, which faces challenges due to the unattainable SND mechanism, attributed to the small granule size. From this study, significant strategies were obtained in developing and implementing AGS for efficient nutrient removal.</p>