Enhanced biological phosphorus removal performance and microbial population changes at high organic loading rates

A laboratory-scale sequencing batch reactor was operated and the dynamics of Rhodocyclus-related phosphorus-accumulating organisms (PAOs) population was monitored. After the system reached a steady state and showed a stable enhanced biological phosphorus removal status, the organic loading rate was increased from 160 to 1,020 g COD m(-3) cycle(-1) in five steps. When the P storage capacity reached maximum at 330 g COD m(-3) cycle(-1), the system lost the stability and the effluent phosphorus concentration fluctuated. As the organic loading rate increased from 160 to 1,020 g COD m(-3) cycle(-1), the PAO population decreased from 83.8 +/- 4.9 to 32.2 +/- 16.2% and internal polyphosphate content decreased from 0.20 to 0.03 mg P mg VSS-1. Phosphate-accumulating metabolism was weakened as the organic loading rate increased and PAO population decreased concomitantly, whereas glycogen-accumulating metabolism increased at high organic loading rates as supported by the increased intracellular glycogen content and production of a higher fraction of intracellular poly-p-hydroxyl valerate.