Which of the following processes can hinder the effectiveness of PAOs in biological phosphorus removal systems?

The effectiveness of phosphorus accumulating organisms (PAOs) in biological phosphorus removal systems can be significantly hindered by the presence of filamentous organisms. PAOs are specialized bacteria that thrive in conditions where they can uptake and store phosphorus. However, when filamentous organisms are present, they can form excessive biomass that leads to poor settling characteristics during the sedimentation phase of wastewater treatment.

This excessive filamentous growth can create "bulking," where the mixed liquor does not settle properly, resulting in a loss of PAOs during the secondary clarifier stage. As a result, the overall efficiency of phosphorus removal can decline due to reduced biomass retention of the beneficial PAOs. Maintaining a balanced microbial community in these systems is crucial for optimal phosphorus removal, and filamentous organisms can disrupt this balance.

While other factors such as the presence of oxygen, high temperatures, and low pH levels can also affect biological processes, the specific impact of filamentous organisms on PAOs makes this option particularly critical in the context of phosphorus removal efficiency. Thus, the presence of filamentous organisms stands out as a key hindering factor in the performance of biological phosphorus removal systems.