Effects of pH on the rates of aerobic metabolism of phosphate-accumulatingand glycogen-accumulating organisms

The effect of pH on the aerobic metabolism of phosphorus-accumulating organ isms (PAOs) and glycogen-accumulating organisms (GAOs) was studied using ae robic batch experiments performed at pH 6.5, 7.0, and 7.5. For PAOs, the ra tes of phosphate uptake, polyhydroxy-alkanoates consumption, and biomass gr owth observed at pH 6.5 were 42, 70, and 53%, respectively, of the rates ob served at pH 7.0. In contrast, the rates for GAOs were relatively independe nt of pH for the range tested. The results suggest that the stability of bi ological excess phosphorus removal (BEPR) is strongly dependent on the pH i n the aerobic zone. If the pH is low, growth of PAOs will be inhibited wher eas the growth of GAOs will be only mildly affected. This may lead to the p roliferation of GAOs in BEPR systems, resulting in reduced phosphorus remov al.