Stoichiometry and kinetics of acetate uptake under anaerobic conditions byan enriched culture of phosphorus-accumulating organisms at different pHs

The effect of pH on the stoichiometry and kinetics of acetate uptake by pho sphorus-accumulating organisms (PAOs) was studied. The stoichiometry of gly cogen consumption and poly-P-hydroxy-alkanoates (PHA) accumulation was inde pendent of the pH over the range 6.5 to 8.0. It was again demonstrated that the amount of phosphorus released per acetate taken up (P/Hac ratio) was l inearly dependent on pH, because of additional energy requirements for acet ate transport at higher pH. The slope of this relationship was similar to t hat in previously published work, but the absolute values were different, i ndicating that the P/Hac ratio is the most variable stoichiometric paramete r associated with the anaerobic metabolism of PAOs. A kinetic expression fo r acetate-uptake rate was developed and tested. it assumes a zero-order for m when the polyphosphate content of the biomass is not limiting. When the p olyphosphate content becomes low, the rate is significantly decreased. The expression was tested in situations in which polyphosphate was a limiting f actor in the rate of acetate uptake, in which the glycogen content of the b iomass became very low, and in which both glycogen and polyphosphate were p resent in excess. The model was able to simulate the three situations adequ ately. Additionally, the rate of acetate uptake was independent of the pH f or the range studied (6.5 to 8.0). (C) 2001 John Wiley st Sons, Inc.