Evaluation of the capacity of phosphorus-accumulating organisms to use nitrate and oxygen as final electron acceptors: A theoretical study on population dynamics

Ability of phosphorus-accumulating organisms (PAOs) capable of using both n itrate and oxygen as terminal electron accepters to compete successfully in biological excess phosphorus removal (BEPR) systems was assessed relative to purely aerobic PAOs. The anoxic-aerobic population has a significant com petitive disadvantage when competing with PAOs that can only use oxygen bec ause of a lower thermodynamic efficiency of anoxic growth compared to aerob ic growth. This causes less efficient use of stored poly-beta-hydroxy-butyr ate under anoxic conditions, leading to the washout of the anoxic-aerobic p opulation from the system. This analysis provides a potential explanation o f why growth of denitrifying PAOs (DPAOs) has not been observed in some BEP R systems. This work also suggests that introduction of even a small aerobi c zones in a BEPR system will strongly affect accumulation of DPAOs. In add ition, a hypothetical model to describe acetate uptake under anoxic conditi ons was developed. and simulations performed with it produced results that agree with experimental observations published in the literature.