New insights in the competition of polyphosphate-accumulating organisms and glycogen-accumulating organisms under glycogen accumulating metabolism with trace Poly-P using flow cytometry

In enhanced biological phosphorus removal (EBPR) from wastewater, the metabolism pathway of polyphosphate accumulating organisms (PAOs) converted from polyphosphate accumulating metabolism (PAM) to glycogen accumulating metabolism (GAM) under a high ratio of carbon to phosphorus (C/P). This study investigated the competition mechanism between PAOs and glycogen accumulating organisms (GAOs) under GAM pathway. Low acetic acid (HAC) concentration made the GAM of PAOs outcompete GAOs in high C/P ratio (100:1), and the effect of influent acetate concentration on GAOs was stronger than PAOs. Candidates Accumulibacter clades IIC and IID were the main dominant PAOs, and Thiothrix caldifontis (potential PAOs) was discovered and significantly increased from 0.53% to 5.75%. Flow cytometry results indicated that PAOs had higher specific surface area and lower nucleic acid content than GAOs, and high C/P promoted GAM rather than GAOs growth, which maybe important reasons causing PAOs dominant growth. PAOs dominance under GAM ensured stable performance of EBPR when C/P ratio in real wastewater increased.