Sewage treatment process selection: In an Imhoff tank, what treatment actions occur to raw sewage during operation?

Introduction:
An Imhoff tank is a two-story unit used in primary wastewater treatment. Understanding its functions guides plant design and operation.

Given Data / Assumptions:

• Raw sewage enters the Imhoff tank.
• Gravity separation and sludge handling occur internally.
• No mechanical aeration is provided.

Concept / Approach:
The upper compartment allows sedimentation of suspended solids. The lower compartment isolates settled sludge for anaerobic digestion, reducing volume and odors.

Step-by-Step Solution:
Step 1: Inflow passes to the upper chamber for sedimentation.Step 2: Solids settle through slots to the lower digestion chamber.Step 3: Anaerobic digestion stabilizes sludge, producing gas.

Verification / Alternative check:
Classic Imhoff design diagrams show distinct settling and digestion zones with gas vents.

Why Other Options Are Wrong:
Filtration and aeration are not core functions of an Imhoff tank; choosing only one of sedimentation or digestion ignores the two-stage design.

Common Pitfalls:
Confusing Imhoff tanks with septic tanks or primary clarifiers; Imhoff integrates sedimentation with isolated sludge digestion.

Final Answer:
Both sedimentation and digestion