What happens to excess phosphorus absorbed by PAOs during anaerobic conditions?

Phosphorus-accumulating organisms (PAOs) play a crucial role in wastewater treatment, particularly in the biological removal of phosphorus from wastewater. Under anaerobic conditions, PAOs absorb excess phosphorus from their environment and store it in their cells. This accumulation happens because PAOs take up phosphorus in the form of polyphosphate when environmental conditions favor their growth, specifically in the absence of oxygen.

During these anaerobic phases, while they absorb phosphorus, they also metabolize volatile fatty acids (VFAs), which serve as a carbon source. The ability to store phosphorus in their cells allows PAOs to outcompete other microorganisms for available nutrients once the conditions change, such as during subsequent aerobic phases. This strategy minimizes the amount of phosphorus released back into the environment and is essential for achieving effective phosphorus removal in wastewater treatment processes.

Other options, such as the release of phosphorus back into the environment or its breakdown for energy, do not accurately describe the behavior of PAOs during anaerobic conditions, as their primary function is to store the phosphorus rather than to release or decompose it. Evaporation into gas is also not applicable since phosphorus does not exist in a gaseous state under normal conditions. Thus, the correct understanding focuses on the cellular