COMPETITION BETWEEN POLYPHOSPHATE- AND GLYCOGEN-ACCUMULATING ORGANISMS IN ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL SYSTEMS—EFFECT OF TEMPERATURE AND SLUDGE AGE

This study has demonstrated that temperature and sludge age are important factors in determining the outcome of competition between polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating non-poly-P organisms (GAOs) and the resultant stability of enhanced biological phosphorus removal (EBPR). At 20°C and 10-day sludge age, PAOs were dominant in an anaerobic/aerobic (A/O) sequencing batch reactor (SBR) due to the advantage of anaerobic acetate uptake rate and aerobic biomass yield; however, at 30°C and 10-day sludge age, GAOs were able to out-compete PAOs in the A/O SBR due to the advantage of anaerobic acetate uptake. At 30°C and 5-day sludge age, PAOs and GAOs coexisted in the A/O SBR, resulting in unstable EBPR performance. After reducing the sludge age from 5 to 3 days, the EBPR efficiency improved drastically, and the EBPR performance was stable. The specific anaerobic acetate uptake rates of GAO-enriched activated sludge were significantly affected by temperature with the Arrhenius temperature coefficient  of 0.047 (°C−1) between 10 and 30°C. The effect of sludge age (5 and 10 days) on the specific anaerobic acetate uptake rates of GAO-enriched activated sludge, however, was not significant. For the PAO-enriched activated sludge, the specific anaerobic acetate uptake rate did not change significantly between 20 and 30°C but increased as sludge age decreased from 10 to 3 days.