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 nitrate 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 competitive disadvantage when competing with PAOs that can only use oxygen because of a lower thermodynamic efficiency of anoxic growth compared to aerobic growth. This causes less efficient use of stored poly-beta-hydroxy-butyrate under anoxic conditions, leading to the washout of the anoxic-aerobic population from the system. This analysis provides a potential explanation of why growth of denitrifying PAOs (DPAOs) has not been observed in some BEPR systems. This work also suggests that introduction of even a small aerobic zones in a BEPR system will strongly affect accumulation of DPAOs. In addition, a hypothetical model to describe acetate uptake under anoxic conditions was developed. and simulations performed with it produced results that agree with experimental observations published in the literature.