Where are “sludge banks” most likely to form if raw or insufficiently treated sewage is disposed of into natural water bodies?

Introduction / Context:
Sludge banks are accumulations of settleable solids on the bed near outfalls. They are an environmental hazard, causing odor, anaerobic conditions, and ecological damage. Understanding where they most commonly occur informs outfall design and treatment requirements.

Given Data / Assumptions:

• Discharge of raw/partially treated sewage via marine outfalls.
• Settling and deposition are possible near the outfall zone.
• Shallow coastal conditions with limited dispersion may exist.

Concept / Approach:

Marine (sea) outfalls, especially in shallow or low-energy coastal waters, are prone to deposition if outfall length, diffuser design, or treatment level are inadequate. Persistent deposition forms “sludge banks.” While lakes and rivers can also experience deposits, classical sanitary engineering terminology frequently associates “sludge banks” with marine outfalls that fail to provide adequate dilution and dispersion.

Step-by-Step Solution:

Verification / Alternative check:

Historical cases of coastal pollution show sludge accumulations down-current of inadequately designed ocean outfalls.

Why Other Options Are Wrong:

Rivers and lakes can accrue sediments, but the term “sludge bank” is most commonly applied to marine coastal deposits near sewage outfalls.

Common Pitfalls:

Confusing general sedimentation in lakes/rivers with specific sewage sludge banks; ignoring the role of diffuser depth and current regime.

Final Answer:

seas