Thickening vs. clarification: the separation of a slurry into a clear supernatant liquid and a thick sludge with high solids concentration is termed

Introduction / Context:
Gravity settlers operate in several modes. Clarification emphasizes a clear overflow (low solids), while thickening emphasizes a concentrated underflow (high solids). The umbrella term for separation by settling under gravity is sedimentation.

Given Data / Assumptions:

• A suspension (slurry) is allowed to settle.
• Two outputs: clear supernatant and thickened sludge.

Concept / Approach:
When settling separates phases by gravity without size-based hydraulic classification, it is sedimentation. Clarification is a subset of sedimentation focusing on overflow clarity; thickening is another subset focusing on dense underflow. The question’s wording covers both outcomes simultaneously, so the best general term is sedimentation.

Step-by-Step Solution:
Identify phenomenon: gravity settling of suspended solids.Map to general term: sedimentation.Select "sedimentation" accordingly.

Verification / Alternative check:
Thickeners are sometimes called sedimentation tanks, and clarifiers are clarifying sedimentation basins; both are unit operations of sedimentation.

Why Other Options Are Wrong:
Classification: hydraulic size separation with rising/overflow streams, not simple settling to two products.Clarification: stresses only the clear overflow, not the thick sludge.Decantation: the mechanical act of pouring off supernatant; not the separation mechanism itself.

Common Pitfalls:
Using "clarification" generically when the process objective is actually thickening; design criteria differ.

Final Answer:
sedimentation