secondary clarifier

Secondary Clarifiers: The Final Clean-Up Crew in Wastewater Treatment

Wastewater treatment plants utilize a multi-stage process to transform raw sewage into safe and reusable water. While primary treatment removes large solids, the heart of the cleaning operation lies in the secondary treatment stage. Here, the focus shifts to biological processes that break down organic matter, leaving behind a clear effluent. But before this treated water is discharged, it needs a final polish, which is where secondary clarifiers come in.

What is a Secondary Clarifier?

A secondary clarifier is a large, cylindrical or rectangular tank that follows the biological treatment processes. Its primary function is to settle out the remaining suspended solids that have been broken down but not completely removed. These solids, often called biosolids, are the byproduct of the biological treatment process and need to be separated from the treated water.

How do Secondary Clarifiers Work?

Imagine a large, shallow pool with a slow, gentle current. This is essentially what a secondary clarifier looks like. The treated water enters the tank at one end, flowing slowly across the surface. As the water travels, its velocity decreases, allowing the heavier biosolids to settle to the bottom.

The settled biosolids, collected at the bottom of the tank, are then removed and further processed for beneficial reuse or disposal. The now-clear water, free of most suspended matter, flows out of the clarifier and may undergo further disinfection before being discharged or reused.

Types of Secondary Clarifiers:

• Circular Clarifiers: These are commonly found in larger treatment plants and feature a central rotating arm that scrapes the settled biosolids towards a collection point.
• Rectangular Clarifiers: These are often used in smaller plants and utilize a chain-and-flight system to remove the settled biosolids.
• Lamella Clarifiers: These utilize inclined plates to increase the surface area for settling, allowing for more efficient removal of solids.

Importance of Secondary Clarifiers:

Secondary clarifiers play a crucial role in wastewater treatment by:

• Producing a clear effluent: This ensures that the discharged water meets environmental regulations and is safe for reuse or discharge.
• Removing biosolids: These can be used as fertilizer or fuel, creating a valuable resource from waste.
• Protecting downstream environments: By removing suspended solids, secondary clarifiers prevent water pollution and protect aquatic ecosystems.

Conclusion:

Secondary clarifiers are the finishing touch in the wastewater treatment process. By removing remaining suspended solids, they ensure the treated water is clean and safe. As the final step in this crucial process, they play a vital role in protecting our environment and providing a valuable resource for future use.