What does the term "return activated sludge" (RAS) mean?

The term "return activated sludge" (RAS) refers specifically to the portion of sludge that is returned to the aeration tank from the secondary clarifier after the treatment process. This material is essential to the wastewater treatment process as it contains viable microorganisms that help maintain the biological treatment system's efficiency. By returning this settled sludge back to the aeration tank, the system ensures that there is a sufficient population of microorganisms available to continue breaking down organic matter in incoming wastewater.

In essence, this practice enhances the treatment process by continually recycling the active biological agents that are crucial for the decomposition of pollutants. The correct understanding of RAS is important for maintaining the balance of the treatment system and achieving effective wastewater treatment outcomes.