In the world of biological nutrient removal (BNR), few microbial players are as pivotal—and as finicky—as polyphosphate-accumulating organisms (PAOs). These microscopic workhorses drive enhanced biological phosphorus removal (EBPR), helping facilities meet stringent discharge limits while reducing chemical dependency. But cultivating a thriving PAO population isn’t just about luck—it’s about strategy.
Here’s how operators and engineers can tip the microbial scales in favor of PAOs.
🌊 1. Create the Right Feast: Carbon Source Matters
PAOs thrive on volatile fatty acids (VFAs), especially acetate and propionate. These short-chain carbon sources fuel their luxury uptake of phosphorus during the aerobic phase.
The competition between PAOs and GAOs for organic acids is influenced by several environmental and operational factors, including:
PAOs rely on a precise sequence of anaerobic and aerobic conditions to perform their phosphorus magic.
Not all PAOs are created equal. Candidatus Accumulibacter phosphatis is the poster child, but other species like Tetrasphaera also contribute—sometimes under different conditions.
PAOs are sensitive to their surroundings. Dialing in the right parameters can make or break EBPR performance.
Here’s how operators and engineers can tip the microbial scales in favor of PAOs.
🌊 1. Create the Right Feast: Carbon Source Matters
PAOs thrive on volatile fatty acids (VFAs), especially acetate and propionate. These short-chain carbon sources fuel their luxury uptake of phosphorus during the aerobic phase.
- Primary sludge fermentation is a cost-effective way to boost VFA availability.
- Side-stream EBPR processes can enhance VFA production and PAO selection.
- Avoid excessive long-chain fatty acids or complex organics—they tend to favor glycogen-accumulating organisms (GAOs), PAOs’ less helpful cousins.
The competition between PAOs and GAOs for organic acids is influenced by several environmental and operational factors, including:
- Temperature: PAO dominate at temperatures below 20 Deg C with GAO becoming favored above 30 Deg C.
- Organic Acid Ratios: Acetate:Propionate ratios between 75:25 - 50:50 favored PAO
- pH: PAO having a positive correlation with higher pH
PAOs rely on a precise sequence of anaerobic and aerobic conditions to perform their phosphorus magic.
- Anaerobic zone: PAOs release phosphorus and store VFAs as polyhydroxyalkanoates (PHAs).
- Aerobic zone: They use PHAs to take up phosphorus and store it as polyphosphate.
- Adequate hydraulic retention time (HRT) in the anaerobic zone.
- Minimal oxygen intrusion—leaky mixers or poor zone separation can sabotage PAO activity.
Not all PAOs are created equal. Candidatus Accumulibacter phosphatis is the poster child, but other species like Tetrasphaera also contribute—sometimes under different conditions.
- Use molecular tools like qPCR or MCA to track PAO abundance and diversity.
- Watch for GAO encroachment—high glycogen storage with low phosphorus uptake is a red flag.
PAOs are sensitive to their surroundings. Dialing in the right parameters can make or break EBPR performance.
Avoid sudden shifts—PAOs prefer stability over surprises.
💡 Final Thoughts
Encouraging PAO growth isn’t just a microbial game—it’s a systems-level challenge that blends biology, chemistry, and operational finesse. By tuning carbon sources, optimizing zone conditions, and monitoring microbial trends, facilities can unlock the full potential of EBPR and move toward more sustainable phosphorus removal.
Want to dive deeper into PAO dynamics or explore how MCA can illuminate your microbial community? Let’s connect—I’d love to hear how your facility is tackling phosphorus removal.
💡 Final Thoughts
Encouraging PAO growth isn’t just a microbial game—it’s a systems-level challenge that blends biology, chemistry, and operational finesse. By tuning carbon sources, optimizing zone conditions, and monitoring microbial trends, facilities can unlock the full potential of EBPR and move toward more sustainable phosphorus removal.
Want to dive deeper into PAO dynamics or explore how MCA can illuminate your microbial community? Let’s connect—I’d love to hear how your facility is tackling phosphorus removal.
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