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Temperature and sludge age were found to be important factors in determining the outcome of competition between polyphosphateaccumulating organisms (PAOs) and glycogen-accumulating non-polyphosphate organisms (GAOs) and the resultant stability of enhanced-biologicalphosphorus removal (EBPR). At 208C and a 10-day sludge age, PAOs were dominant in an anaerobic/aerobic (A/O) sequencing-batch reactor (SBR), as a result of their higher anaerobic-acetate-uptake rate and aerobic-biomass yield than GAOs. However, at 308C and a 10-day sludge age, GAOs were able to outcompete PAOs in the A/O SBR because of their higher anaerobic-acetateuptake rate than PAOs. At 308C and a 5-day sludge age, GAOs coexisted with PAOs in the A/O SBR, resulting in unstable EBPR performance. At 308C, reducing the sludge age from 5 to 3 days improved the EBPR efficiency drastically, and the EBPR performance was stable. The maximum specificanaerobic-acetate-uptake rates of GAO-enriched sludge were affected by temperature with the Arrhenius temperature coefficient h of 0.042 (8C 21 ) between 10 and 308C. The effect of sludge age (5 and 10 days) on the maximum specific-anaerobic-acetate-uptake rates of GAO-enriched activated sludge, however, was not significant. For the PAO-enriched activated sludge, the maximum specific-anaerobic-acetate-uptake rate did not change significantly between 20 and 308C, but significantly increased from 0.38 to 0.52 mmol-C/ mmol-C/h as the sludge age decreased from 10 to 3 days at 308C. Water Environ. Res., 78, 4 (2006).

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