Design depth for sedimentation basins: In conventional plain sedimentation tanks used in water or wastewater treatment, what is the typical maximum liquid depth adopted for design?

Introduction / Context:
Sedimentation tanks (clarifiers) remove settleable solids by gravity. Their geometry—especially depth—affects sludge storage, vertical velocity profile, and constructability. Many codes and handbooks recommend standard depth ranges to balance performance and cost.

Given Data / Assumptions:

• Plain sedimentation (no tube modules or high-rate internals).
• Conventional design practice.
• Looking for the typical upper bound of depth range.

Concept / Approach:
Typical liquid depths for conventional rectangular or circular basins are about 3.0–4.5 m. A higher depth can increase cost and complicate sludge removal without proportional performance gains. Hence, designers cap depth around well-established maxima.

Step-by-Step Solution:
Identify standard range: approximately 3.0 to 4.5 m.Select the maximum commonly used value within this band.Hence choose 4.5 m as the typical maximum design depth.

Verification / Alternative check:
Worked examples for conventional clarifiers routinely adopt 3.0–4.5 m depth with side water depth not exceeding ~4.5 m unless special design features are provided.

Why Other Options Are Wrong:
3.0–4.0 m: valid within range but not the maximum.5.5 m: exceeds common practice for plain sedimentation without special internals.

Common Pitfalls:

• Confusing high-rate clarifiers (lamella/tube settlers) with conventional tanks.
• Assuming deeper is always better; sludge handling and mixing considerations impose practical limits.

Final Answer:
4.5 m