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Three identical sequencing batch reactors(SBRs) were operated to investigate the efects of various idle times on the biological phosphorus(P) removal. The idle times were set to 3 hr(R1), 10 hr(R2) and 17 hr(R3). The results showed that the idle time of a SBR had potential impact on biological phosphorus removal, especially when the influent phosphorus concentration increased. The phosphorus removal efciencies of the R2 and R3 systems declined dramatically compared with the stable R1 system, and the P- release and P-uptake rates of the R3 system in particular decreased dramatically. The PCR-DGGE analysis showed that uncultured Pseudomonas sp.(GQ183242.1) and β-Proteobacteria(AY823971) were the dominant phosphorus removal bacteria for the R1 and R2 systems, while uncultured γ-Proteobacteria were the dominant phosphorus removal bacteria for the R3 system. Glycogen-accumulating organisms(GAOs), such as uncultured Sphingomonas sp.(AM889077), were found in the R2 and R3 systems. Overall, the R1 system was the most stable and exhibited the best phosphorus removal efciency. It was found that although the idle time can be prolonged to allow the formation of intracellular polymers when the phosphorus concentration of the influent is low, systems with a long idle time can become unstable when the influent phosphorus concentration is increased.