AbstractThe anaerobic/aerobic sequencing batch reactor (SBR) (A/O-SBR) system has been a major focus of recent research because of its high nitrogen (N) and phosphorus (P) removal efficiencies in wastewater treatment plants. The feasibility of using the A/O-SBR system in plateau regions (altitude 3,000 m) remains unclear. In this study, two A/O-SBR systems were established, and the effect of atmospheric pressure on nutrient removal performance was studied. High N and P removal efficiencies of 90.19%±3.96% and 98.83%±1.90%, respectively, were achieved in the A/O-SBR system under low atmospheric pressure (72 kPa, called R2). The A/O-SBR system under low atmospheric pressure had higher P-uptake activity (24 mg/L), indicating that P removal was higher in R2 than in the A/O-SBR system under normal atmospheric pressure (97 kPa, called R1). The 16S rDNA sequencing analysis showed that the abundance of denitrifying glycogen accumulating organisms was higher in R2 than in R1, which was opposite to the pattern of P-accumulating organisms (PAOs), denitrifying PAOs, and ammonia-oxidizing bacteria. Batch tests were consistent with the microbial community analysis. Therefore, efficient N and P removal performance was achieved under low atmospheric pressure, and the functional microbial abundance and microbial activities related to N and P removal were significantly affected. The results of this study have implications for removing pollutants during wastewater treatment in plateau regions.