The correct answer is A. Imhoff tanks.
Imhoff tanks are anaerobic sewage treatment units. They are used to treat sewage by allowing anaerobic bacteria to decompose organic matter. The tanks are divided into two sections: a sedimentation tank and a digestion tank. The sedimentation tank allows solids to settle out of the sewage, while the digestion tank allows the anaerobic bacteria to decompose the organic matter.
Trickling filters and sludge sedimentation tanks are aerobic sewage treatment units. They are used to treat sewage by allowing aerobic bacteria to decompose organic matter. Trickling filters are filled with rocks or other media that provide a surface for the bacteria to grow on. The sewage is sprayed over the rocks, and the bacteria decompose the organic matter. Sludge sedimentation tanks allow solids to settle out of the sewage.
The correct answer is A. Imhoff tanks.