Part 3: 🌊 Troubleshooting High Sludge Blanket in Secondary ClarifierA. High Secondary Clarifier Sludge Blanket1. Diagnostic Tools and Calcula...
Published on by Hossein Ataei Far, Deputy Manager of the Research, Technology Development, and Industry Relations Center at NWWEC
A. High Secondary Clarifier Sludge Blanket
1. Diagnostic Tools and Calculations 🔍
Accurate diagnosis of the sludge blanket issue is critical for effective treatment. Use the following tools and calculations:
Settleometer Test: Measure sludge settleability, tracking its settling velocity and compacting capability.
Microscopic Examination of MLSS: Identify the health of microbial communities and assess the presence of undesirable filaments.
Sludge Volume Index (SVI) and Sludge Density Index (SDI): Calculate and interpret these indices to pinpoint compaction problems or assess biomass stability.
SVI: High values often suggest filamentous bulking.
SDI: Indicates the density and compactness of the biomass.
References: 1, 3
2. High SVI, Low SDI
a. Filamentous Bulking 🦠
Filamentous bulking is often a result of excessive filamentous bacteria that hinder sludge settling. Mitigation measures include:
Causes and Corrective Actions: Low Dissolved Oxygen (DO): Ensure aeration tanks maintain 2–3 mg/L of DO.
Organic Loading Rate Imbalances: Monitor F/M (food-to-microorganism) ratios to prevent underloading or overloading.
Nutrient Deficiency: Optimize the Carbon:Nitrogen: Phosphorus (C: N:P) ratio, typically 100:5:1.
Septic Conditions: Reduce sulfide production from anaerobic conditions upstream by aerating influent or adjusting flow rates.
Specific Filamentous Bacteria: Microthrix parvicella: Tends to thrive under low DO and high FOG (fats, oils, and grease) conditions; apply selective chemical treatments or increase wasting to control growth.
Hydrogen Peroxide or Chlorination: Apply selectively for short-term control while addressing root causes.
References: 2, 3, 4
3. Normal SVI, SDI
If indices appear normal, other factors may contribute to sludge blanket elevation:
a. Excessive Biomass 🌱
High biomass concentrations can overwhelm clarifiers. Actions include:
Recalculate CRT (Critical Retention Time) and Wasting Rate: Optimize to reduce sludge buildup.
Enhance Sludge Handling: Check for poor compaction in sludge storage or improper thickening.
Check for Solids Carryover: Prevent WAS (Waste Activated Sludge) bypass from primary clarifiers.
References: 1, 3
b. Inadequate Return Sludge Rate (RAS) 💧
Insufficient RAS rates can cause sludge blankets to rise. Recommendations:
Control and Adjust RAS Pumps: Calibrate pump speeds to balance sludge removal.
Mechanical Maintenance: Ensure pumps and valves are operational and free of debris.
References 📚
[1] State of Michigan Department of Environmental Quality - Activated Sludge Process Control.
[2] AquaFix, Microthrix Bulking in Summer.
[3] Jenkins, Richard D., Manual on Activated Sludge Bulking and Foaming Problems.
[4] WEF (Water Environment Federation), Filamentous Bacteria in Activated Sludge.
You can see this picture on the Lil' Critters in the Sludge website: https://lnkd.in/dtAQBeNB