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Managing Foam Issues in Activated Sludge Systems: A Practical Guide for Malaysian Industries

Foam formation in wastewater treatment plants is a significant operational challenge. If left unchecked, it disrupts biological treatment processes, reduces efficiency, and increases maintenance costs.
Many Malaysian industries—such as palm oil refineries, petrochemical plants, and food processing facilities—face severe foaming issues due to the nature of their wastewater. Understanding the causes and solutions is crucial to maintaining a stable and efficient treatment system.
In this article, we will explore the five most common types of foam issues in activated sludge systems and provide practical, industry-specific solutions.

1. White, Light Foam

Appearance: Light, white, frothy foam floating on the aeration tank surface.
Industries Affected: Palm oil mills, chemical manufacturing plants, and new wastewater treatment plants in startup phase.
Causes:

• Low sludge age (High F/M Ratio) – The bacterial community in the aeration tank is still developing.
• Excessive aeration – High oxygen levels cause fine bubbles to form frothy foam.
• Presence of detergents – Industrial and domestic wastewater often contain surfactants that cause foam.

Solutions:
✅ Increase Sludge Age – Adjust the Food-to-Microorganism (F/M) ratio by optimizing sludge wasting (WAS). A higher sludge age stabilizes the microbial population, reducing foam.
✅ Reduce Aeration Intensity – If DO levels exceed 2.5 mg/L, reduce aeration rates to prevent excessive turbulence.
✅ Seed with Mature Sludge – Introduce sludge from a stable treatment plant to accelerate biomass development.
✅ Foam Control Spraying – Use water sprays or anti-foam agents to suppress foam temporarily.

2. Persistent, Light Brown Foam

Appearance: Thick, sticky, stable light brown foam that doesn’t easily dissipate.
Industries Affected: Petrochemical refineries, palm oil industries, and wastewater treatment plants handling high fat & oil content.
Causes:

• Overgrowth of filamentous bacteria such as Nocardia and Microthrix Parvicella.
• High levels of fats, oils, and grease (FOG) in the influent.
• Low dissolved oxygen (DO) and a low F/M ratio, which promotes filamentous bacteria growth.

Solutions:
✅ Surface Chlorination or Hydrogen Peroxide Dosing – Apply chlorine (5-10 mg/L) or H₂O₂ to kill filamentous bacteria in the foam layer.
✅ Install Foam Skimmers – Use foam skimming systems to physically remove excess foam from the surface.
✅ Optimize Nutrient Balance (N/P Ratio) – Adjust the nitrogen-to-phosphorus ratio to discourage filamentous bacteria. The recommended ratio is 100:5:1 (BOD:N:P).
✅ Improve Aeration and Mixing – Increase DO levels to 2.0 - 2.5 mg/L and ensure proper mixing to limit filamentous growth.

3. Dark Brown, Thick, and Sticky Foam

Appearance: Extremely viscous, dark brown foam that is difficult to remove.
Industries Affected: Palm oil refinery wastewater, chemical plants, and food processing industries with long sludge retention times.
Causes:

• Growth of Nocardia and Mycobacterium, which produce sticky extracellular polymers.
• Low sludge age (MLSS too low) or improper sludge wasting, causing excess bacteria growth.

Solutions:
✅ Increase Sludge Wasting (WAS) – Removing excess sludge prevents overgrowth of Nocardia and Mycobacterium. Maintain a sludge age of 10-15 days.
✅ Apply Surface Chlorination – Dosing sodium hypochlorite (NaClO) or hydrogen peroxide (H₂O₂) helps kill foam-producing bacteria.
✅ Optimize Aeration Patterns – Reduce turbulence in the aeration tank to prevent excess foaming.
✅ Install Foam Removal Equipment – Use floating decanters or foam skimmers to remove thick foam.

4. Green Foam with Algal Growth

Appearance: Greenish foam with visible algal mats forming on the surface.
Industries Affected: Industrial wastewater treatment plants with lagoons, ponds, or extended aeration systems exposed to sunlight.
Causes:

• High nitrogen and phosphorus levels, promoting algae growth.
• Low pH and stagnant water conditions, allowing algae to thrive.
• Excess sunlight exposure, accelerating algal blooms.

Solutions:
✅ Adjust Nutrient Levels – Reduce nitrogen and phosphorus concentrations to prevent excessive algae growth.
✅ Maintain pH Stability – Keep pH between 6.5 - 7.5 to prevent conditions that favor algae.
✅ Increase Flow Rates – Reduce hydraulic retention time (HRT) to limit stagnant conditions that promote algae growth.
✅ Install Covers or Shade Structures – Reduce direct sunlight exposure to prevent algal blooms.

5. Sudden, Light Foam Due to Detergents or Toxic Shock

Appearance: Rapidly forming, light and stable foam that appears suddenly and persists.
Industries Affected: Laundry wastewater treatment plants, food processing industries, and industrial sites using surfactants.
Causes:

• Presence of high concentrations of detergents and surfactants in the influent.
• Toxic shock events, where chemicals or sudden pH shifts cause microbial stress.
• Poor sludge floc formation, leading to dispersed bacteria and foaming.

Solutions:
✅ Monitor and Regulate Influent Quality – Industrial wastewater pre-treatment is crucial. Implement oil-water separators or chemical treatment before biological treatment.
✅ Increase Return Activated Sludge (RAS) Ratio – Adjust the RAS rate (50-100%) to maintain a stable microbial community.
✅ Use Defoaming Agents – Apply silicone-based or alcohol-based defoamers in emergency situations to break foam instantly.
✅ Improve Pre-Treatment – Install grease traps, dissolved air flotation (DAF), or equalization tanks to remove surfactants and toxic compounds before biological treatment.

Conclusion: Effective Foam Management for Malaysian Industries
Managing foam in activated sludge systems requires a combination of process control, chemical treatment, and proper sludge management. By addressing the root causes of foaming—whether it’s filamentous bacteria, high oil content, detergents, or aeration issues—industries can reduce downtime, lower operating costs, and improve wastewater treatment efficiency.
✅ Need expert consultation on foam control in wastewater treatment?
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