What conditions are necessary for PAOs to effectively populate a mixed liquor?

Phosphate-accumulating organisms (PAOs) require both anaerobic and aerobic conditions to effectively thrive within a mixed liquor. During the anaerobic phase, these organisms utilize stored polyhydroxyalkanoates (PHA) as a source of energy, which helps them take up excess phosphorus from the wastewater. This process allows them to accumulate phosphorus in their cells.

Once the mixed liquor is transitioned to aerobic conditions, the PAOs continue to metabolize and grow while releasing the stored PHA. In turn, they uptake phosphorus from the surrounding environment, leading to a net decrease in phosphorus levels in the mixed liquor. This dual-phase approach is essential for their survival and effective phosphorus removal.

The choice of aerobic only or strictly anaerobic conditions would not provide the necessary environment for PAOs to perform their functions. Anoxic conditions alone also wouldn't support the full metabolic processes required for optimal phosphorus removal by PAOs. Hence, the combination of anaerobic and aerobic conditions is critical for PAOs to flourish and effectively contribute to wastewater treatment.