How a Clarifier Tank Works in Wastewater Systems?
In any modern wastewater treatment system, separating solids from liquid is one of the most crucial steps. This is where the clarifier tank plays a vital role. Whether used in municipal sewage treatment or industrial effluent plants, a wastewater clarifier tank helps in settling out suspended solids and clarifying water before it moves to the next treatment stage.
In this blog, we’ll dive into how a clarifier water tank works, the difference between a secondary clarifier tank and other types, and compare a clarifier vs a sedimentation tank to clarify common misconceptions.
What is a Clarifier Tank?
A clarifier tank is a settling tank designed to remove solid particulates from liquids through the process of sedimentation. It allows heavier particles to settle to the bottom (forming sludge), while clearer water flows out from the top. Clarifiers are essential in both primary and secondary stages of wastewater treatment.
Depending on the treatment phase, they are categorized as:
- Primary Clarifier Tank: Used to settle raw solids and organic matter early in the treatment process.
- Secondary Clarifier Tank: Receives biologically treated water (from aeration tanks) to remove microbial biomass and other residual solids.
How a Clarifier Water Tank Works?
Here’s a step-by-step look at the working process of a wastewater clarifier tank:
1. Influential Entry
Wastewater enters the tank through a central or side inlet, often fitted with energy-dissipating structures to reduce flow turbulence. This allows for the uniform distribution of water within the tank.
2. Settling Zone
As water remains in the tank, gravity causes suspended solids to settle to the bottom of the tank. The settling time and tank design are calibrated to allow maximum removal of particles.
3. Sludge Collection
The settled solids form a sludge layer at the bottom. A mechanical scraper or rake slowly rotates to push the sludge toward a central hopper for removal and further treatment.
4. Effluent Discharge
The clarified water, now mostly free of solids, rises to the surface and is collected through weirs (typically around the tank’s edge) and sent to the next stage—usually filtration or disinfection.
5. Scum Removal
Light materials like oil, grease, or foam float to the surface. A scum skimmer collects these substances separately for proper disposal.
Secondary Clarifier Tank in Biological Treatment
A secondary clarifier tank comes into play after the biological treatment process (e.g., activated sludge process or trickling filter). It separates the microbial floc or biomass from the treated water.
- Purpose: To settle activated sludge so that the clear water can move to tertiary treatment or be discharged.
- Sludge Return: A portion of the settled biomass (return activated sludge) is recycled back to the aeration tank to maintain microbial activity.
- Excess Sludge: The remaining sludge is directed to sludge handling units for thickening or digestion.
Clarifier vs Sedimentation Tank: Are They the Same?
The terms are often used interchangeably, but there are subtle differences:
| Feature | Clarifier Tank | Sedimentation Tank |
| Application | Specific to wastewater systems | Broader use in water and wastewater |
| Design | Typically includes scrapers, scum removal, weirs | Simpler design, used for gravity settling |
| Stages Used In | Primary and secondary treatment | Mainly primary treatment |
| Purpose | Clarify water by removing suspended solids | Remove raw solids through gravity |
In essence, all clarifiers are sedimentation tanks, but not all sedimentation tanks are designed with the enhanced features of a clarifier water tank.
Benefits of Using a Clarifier in Wastewater Systems
- Improved Water Quality: Removes up to 60–70% of suspended solids in primary clarifiers and even more in secondary clarifiers.
- Energy Efficiency: Operates largely by gravity, minimizing energy use.
- Enhanced Process Control: Supports consistent downstream treatment performance.
- Compact Footprint: Especially important for industrial sites with limited space.
- Customizable: Can be adapted for various flows, loadings, and effluent quality standards.
Applications Across Industries
- Municipal sewage treatment plants
- Textile and dyeing industries
- Food and beverage processing
- Chemical and pharmaceutical manufacturing
- Steel and mining wastewater treatment
Each of these sectors uses clarifier tanks tailored to their effluent types and flow volumes.
Ion Exchange Delivers Advanced Wastewater Treatment Solution for Industries
Ion Exchange is enabling sustainable operations at Chiripal Poly Films, one of India’s leading manufacturers of flexible packaging solutions and a part of the Chiripal Group conglomerate. Specializing in Biaxially-Oriented Polypropylene (BOPP) films, Biaxially-Oriented Polyethylene Terephthalate (BOPET) films, and PET resin chips, Chiripal’s manufacturing process uses Mono-Ethylene Glycol (MEG) and Ethyl Acetate (EA), resulting in effluents with high toxicity and elevated BOD and COD levels.
To treat this complex chemical wastewater, Ion Exchange is supplying a 200 m³/day Effluent Treatment Plant (ETP) featuring primary, secondary, and tertiary treatment systems. The primary stage includes a bar screen, oil skimmer, equalisation-cum-neutralisation tank, and guard pond; the secondary stage consists of an anaerobic process, clarification, and an extended aeration system. The tertiary treatment involves a chlorine contact tank and a sludge treatment system, enabling the recycling and reuse of treated water for process and utility applications, thereby supporting Chiripal Poly Films’ sustainability goals.
Conclusion
A clarifier tank is a cornerstone of any wastewater treatment system—reliable, low-energy, and highly effective. Whether as a secondary clarifier tank after biological treatment or as a primary settling basin, its role in separating solids ensures the success of subsequent purification stages. Understanding the design, function, and distinction between clarifier vs sedimentation tank can help industries and municipalities operate more efficiently and meet environmental standards.
