Skimming tanks in wastewater treatment are primarily provided for what purpose?
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ARemoval of grease and oil from sewage
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BRemoval of settled sludge from tank bottoms
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CDebris screening with self-cleansing bar racks
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DFine grit removal as an improved grit chamber
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EAir scouring of aeration basins
Answer
Correct Answer: Removal of grease and oil from sewage
Explanation
Introduction / Context:Grease and oil can foul downstream processes and cause scum accumulation. Skimming tanks (or grease traps) are used in preliminary treatment to remove floating matter.
Given Data / Assumptions:
- Municipal sewage with fats, oils, and grease (FOG).
- Tank equipped with baffles and skimming mechanisms.
Concept / Approach:Skimming relies on gravity separation: lower-density oils/grease rise to the surface and are collected by scrapers or weirs, preventing carryover.
Step-by-Step Solution:Step 1: Recognize FOG removal as the skimming tank function.Step 2: Distinguish from grit chambers (remove heavy inorganic grit) and screens (remove coarse debris).Step 3: Select the option describing grease/oil removal.
Verification / Alternative check:Plant schematics show skimming tanks downstream of screening/grit removal or integrated with primary clarifiers as scum removal systems.
Why Other Options Are Wrong:
- Sludge removal is a function of sludge hoppers/valves, not skimming.
- Screens handle coarse solids, not oils.
- Grit chambers remove sand/gravel; skimmers handle floatables.
Common Pitfalls:Confusing grit removal with skimming; neglecting grease control leads to scum blankets and odor issues.
Final Answer:Removal of grease and oil from sewage