Seven Factors for Stable Phosphorus Removal

Across the world, excess phosphorus is a common challenge in wastewater treatment. Whether in industrial parks, municipal sewage, or wastewater from food, chemical, and pharmaceutical plants, phosphorus removal efficiency often decides if discharge standards can be met.

This article summarizes seven core factors that affect phosphorus removal (biological & chemical methods). It serves as a practical guide for environmental engineers and project operators.

 

🔹 Seven Factors Affecting Phosphorus Removal

1. 💧 Influent Quality and pH

• pH should be 6.5–8.0.
• Too low pH → suppresses PAOs (phosphorus accumulating organisms), weakens phosphorus release and uptake.
• Also reduces the coagulation performance of chemical agents. ⚠️ pH control is the first step for stable phosphorus removal.

 

2. 🔬 Phosphorus Forms

• Inorganic phosphorus + organic phosphorus exist in wastewater.
• Some organic phosphorus (e.g., phosphite) cannot be removed by standard coagulants. 👉 Pre-treatment or advanced oxidation may be required.

 

3. 🌬️ Dissolved Oxygen (DO) Control

Biological phosphorus removal relies on anaerobic–aerobic cycling:

• Anaerobic zone → DO < 0.2 mg/L → PAOs release phosphorus.
• Aerobic zone → DO ≥ 2.0 mg/L → PAOs absorb extra phosphorus. ⚠️ Wrong DO control breaks the biological cycle.

 

4. 🔄 Return Flow and Oxygen Carryover

• If return flow from the aerobic end has too much DO, the anaerobic zone is disturbed.
• This suppresses phosphorus release. ✅ Control internal recycle ratio and monitor DO in return flow.

 

5. 🍃 Organic Substrate (e.g., COD)

• PAOs need VFAs and other carbon sources to form poly-P granules.
• Too little organic substrate → phosphorus release and uptake are limited. 👉 Consider adding carbon or improving hydrolysis-acidification.

 

6. ⏳ Anaerobic Retention Time

• If too short → large molecules cannot degrade → PAOs cannot take up enough carbon.
• This reduces phosphorus release and weakens aerobic absorption. ⚠️ Adjust SRT (sludge retention time) and HRT (hydraulic retention time) based on influent quality.

 

7. 🧱 Sludge Age (SRT) and Sludge Wasting

• To keep PAOs active, the sludge age should be 10–15 days.
• Too long → sludge aging → stored phosphorus may be released again. 👉 Timely sludge wasting is critical for stable phosphorus removal.

 

⚗️ Chemical Phosphorus Removal: Three Key Points

When using aluminum salts or iron salts, check:

1. ✅ pH adjustment is correct
2. ✅ Dosage is sufficient
3. ✅ Mixing and reaction time are reasonable

⚠️ Poor operation can cause chemical waste, reduced efficiency, and higher sludge production.