pH Control in Wastewater Treatment

In modern wastewater treatment systems, pH is not only a basic monitoring index but also a critical control parameter.

Even small pH changes may cause serious problems:

❌ poor flocculation,

❌ weak phosphorus removal,

❌ incomplete denitrification,

❌ sludge bulking by filamentous bacteria.

This article explains how pH affects five main treatment stages, giving engineers practical guidance.

 

⚗️ Physical-Chemical Treatment: pH and Flocculation

In coagulation, sedimentation, or flotation units, pH should stay between 6.5–8.0.

• pH > 9 → higher chemical use, weaker flocculation.
• pH < 6 → poor floc formation, hard to settle. 👉 Especially during phosphorus removal or chemical dosing in final clarifiers, unstable pH can cause SS increase and turbidity problems.

 

🧪 Anaerobic Stage: pH Affects PAOs and Methanogens

In UASB and anaerobic tanks, pH should stay at 6.5–8.0.

• Too low pH → PAOs cannot release phosphorus well.
• Methanogens lose activity → VFA accumulates → acidification → upstream biological treatment becomes unstable.

 

💧 Denitrification: pH Needs Precise Balance

The denitrification process produces alkalinity, which gives some buffering. But when pH < 6.8 or > 7.5, denitrifying bacteria loses activity. ⚠️ This leaves nitrate in effluent and makes total nitrogen harder to meet standards.

 

🌬️ Aerobic Nitrification: Low pH Blocks Nitrifiers

Nitrification consumes a lot of alkalinity, so real-timepH monitoring is needed.

• pH < 7.0 → nitrifiers slow down → ammonia removal drops → risk of NH₄⁺ discharge.

 

🦠 Filamentous Bacteria Growth: Low pH Favors Expansion

At pH 4.5–6.5, filamentous bacteria grow faster than floc-forming bacteria.

• Result → sludge bulking, poor settling, and effluent quality risk.
• Often linked with nutrient imbalance + low pH conditions.

 

🔑 Key to Stability: Dynamic pH Control

For both industrial wastewater and municipal treatment plants, pH control is now a key factor of stable and smart operation.

Best practice:

✅ Online pH monitoring

✅ Alkalinity adjustment strategy

✅ Automatic dosing systems

→ Together, these achieve “front-end stability, mid-process buffering, and final-stage correction.”