If the sewage contains greases and fatty oils, they are removed in
- AGrit chambers
- BDetritus tanks
- CSedimentation tanks
- DSkimming tanksCorrect
Solution
Concept
Removal of grease and oil in sewage treatment
Formula
NONE
Step-by-step solution
1. Grease, oils, and fats in sewage have lower specific gravity than water and float to the surface. 2. Skimming tanks utilize air flotation to push floating oil and grease to the surface layer for skimming. 3. Therefore, greases and fatty oils present in sewage are removed in skimming tanks. Answer: D
Explanation
Skimming tanks are specialized units in wastewater treatment designed to trap lighter-than-water substances that float on the liquid surface. As sewage flows through slowly, fats, oils, and greases rise to the top where they can be mechanically skimmed off before reaching biological treatment stages.
Why the other options are wrong
A) Grit chambers remove heavy inorganic sand, gravel, and grit. B) Detritus tanks remove fine inorganic solids and organic matter. C) Sedimentation tanks remove settleable organic and inorganic suspended solids.
Shortcut
Skim the fat: Skimming tanks remove greases and fatty oils.
Common mistake
Confusing skimming tanks designed for floating fats and oils with grit chambers or detritus tanks designed for inorganic solids.
Correct answer: D) Skimming tanks