The correct answer is C. Skimming tanks.
Grease and fatty oils are removed in skimming tanks by skimming, which is the process of removing floating material from the surface of a liquid. Skimming tanks are typically rectangular or circular tanks with a sloping bottom. The sewage enters the tank at the top and flows down the sloped bottom. As the sewage flows, the grease and fatty oils float to the surface and are skimmed off.
Grit chambers are used to remove grit, sand, and other coarse material from sewage. Detritus tanks are used to remove settleable solids from sewage. Sedimentation tanks are used to remove suspended solids from sewage.
Here is a diagram of a skimming tank:
[Diagram of a skimming tank]
The sewage enters the tank at the top and flows down the sloped bottom. As the sewage flows, the grease and fatty oils float to the surface and are skimmed off. The settled solids are removed from the bottom of the tank.