Secondary clarifiers are an integral component of wastewater treatment systems, facilitating the critical separation of activated sludge biomass from biologically treated effluents. A common operational challenge is the presence of floating solids in secondary clarifiers. This condition negatively impacts the quality of the final effluent and the overall efficiency of the treatment process.
A comprehensive understanding of the factors contributing to solids floating in secondary clarifiers is essential for effective operational management. What are the main mechanisms driving this phenomenon?
In addition, what proactive strategies can be implemented to mitigate and prevent its occurrence, thereby ensuring continued and optimal performance of the wastewater treatment system?
Solids Floating in Secondary Clarifiers
In principle, secondary clarifiers function to settle activated sludge after the aeration process, so that the wastewater that comes out of the system has a quality that meets environmental quality standards. However, in practice, sludge flotation or floating sludge is often found, namely a condition where the activated sludge does not settle, but instead floats on the surface.
This problem can appear suddenly or gradually, and is often accompanied by a decrease in effluent quality, such as an increase in TSS (Total Suspended Solids) or COD (Chemical Oxygen Demand).
When solids float, the clarifier system loses its basic function. Activated sludge that should be returned to the aeration pond (Return Activated Sludge – RAS) or partially discharged as excess sludge, is instead retained on the surface. This causes an imbalance in the mass of microorganisms, potential short circuiting in the clarifier, and an increased risk of biomass release into the environment.
Read Also: Why Is There Too Much Sludge in My Clarifier?
Serious Impact on WWTP Performance
The problem of floating solids is not something that can be ignored. If not handled immediately, the impact can be widespread.
1. Decrease in Effluent Water Quality
Floating sludge that is carried into the effluent causes an increase in TSS and may contain pathogenic microorganisms, nitrogen, and phosphorus that are not properly degraded. This risks causing failure to meet environmental quality standards.
2. Decreased Process Efficiency
With the retention of activated sludge, the amount of biomass in the system becomes unstable. This affects the system’s ability to break down organic loads (BOD and COD) and ultimately decreases the efficiency of the biological process.
3. Overloading the Tertiary Treatment System
If the facility has an advanced filtration process, increased TSS can cause overloading and accelerate fouling of the filter or membrane system.
4. Operational Issues and Additional Costs
Floating sludge requires extra handling, both manually and chemically, which of course has an impact on increasing operational costs and the need for additional labor.
Identify Causes and Integrated Corrections
Before taking corrective action, it is important to identify the root cause of the floating solids. Some common causes include:
1. Lack of Dissolved Oxygen (DO)
If the DO level in the aeration basin is too low, bacteria will switch to anoxic or anaerobic conditions, producing gases such as methane or nitrogen. These gases become trapped in the sludge floc and cause the floc to float in the clarifier.
2. Sludge Bulking
Sludge bulking occurs when the sludge floc becomes light and does not settle properly. This is often caused by the growth of excess filaments such as Nocardia, Microthrix parvicella, or Type 021N, which have the ability to float.
3. Organic Overload
When the organic load is too high, the system cannot completely decompose the organic compounds. This can accelerate the formation of gases in the floc and cause flotation.
Read Also: How to Reduce Organic Content in Raw Water
4. Suboptimal Return Sludge Rate
Setting the return sludge rate (RAS) too low causes the activated sludge to settle too long at the bottom of the clarifier, resulting in local anaerobic conditions and gas production.
5. Chemical Dosage Errors
Using inappropriate chemicals such as polymers, coagulants, or defoamers can also worsen flocculation and cause the sludge to be lighter or form bubbles.
Lautan Air Indonesia’s Solution Approach
As a company with more than 40 years of experience in the field of water solutions, Lautan Air Indonesia offers a comprehensive and integrated approach to addressing floating sludge problems in secondary clarifiers. Here are the services and solutions we can provide:
1. System Audit and Root Cause Analysis
Our technical team can conduct field visits to identify the root causes of floating solids. This analysis includes evaluation of process parameters, visual inspection, and laboratory testing.
2. Operational Recommendations and O&M Support
Based on the analysis results, we will provide operational guidance including RAS/WAS rate adjustments, DO control, and clarifier cleaning strategies. We also provide Operation & Maintenance services to ensure the system runs optimally.
3. Selection of the Right Chemicals
We provide a variety of water treatment chemicals such as:
- Coagulants: PAC, Alum, ACH, to improve flocculation
- Polymers: Anionic/Cationic to strengthen flocs
- Defoamer & Odor Control: to handle odors and bubbles caused by gas
Our chemical selection is based on jar tests and compatibility with existing systems.
4. Equipment Replacement or Repair
If damage is found to the clarifier system such as agitators, skimmers, sludge scrapers, or aerators, we also provide equipment supply and installation services according to industry technical specifications.
5. Operator Training and Periodic Monitoring
We believe that human resources are the key to the success of the system. Therefore, we provide technical training for WWTP operators to be able to manage the clarifier system properly, including early detection of potential floating sludge.
The problem of floating solids in the secondary clarifier can be a sign of systemic disturbances in wastewater treatment. A comprehensive approach is needed, starting from process analysis, operational improvements, to chemical solutions and equipment to overcome it.
Lautan Air Indonesia is here as your trusted partner in industrial water and wastewater management. With decades of experience, comprehensive services, and professional technical support, we are ready to help you maintain the performance of your wastewater treatment system so that it remains reliable and in accordance with regulations. Contact Lautan Air Indonesia now for further consultation.