Enhanced Biological Phosphate Removal (EBPR) - strategies for favoring growth of PAO (Phosphate Accumulating Organisms) vs GAO (Glycogen Accumulating Organisms)

While looking into research on the problems with GAO in biological phosphate removal systems, I found an interesting thesis by Carlos Manuel LÓPEZ VÁZQUEZ titled "The Competition between Polyphosphate-Accumulating Organisms and Glycogen-Accumulating Organisms: Temperature Effects and Modelling."

In this study, he evaluated the impact of temperature, pH, and Acetate/Priopionate ratios on phosphate accumulation. The main findings were:

• PAO dominate at temperatures below 20oC with GAO becoming favored above 30oC.
• Acetate/Propionate ratios between 75:25 - 50:50 favored PAO
• PAO having a positive correlation with higher pH 

While we are still not completely certain of all the bacteria involved in phosphate accumulation ecological niche, we can use finding from this study to favor their growth. So if you have a problem maintaining a proper ratio of PAO to GAO in the EBPR system, you can try to favor PAO by increasing pH and lowering SRT (PAO have higher growth rates in general).