The correct answer is: A. Large suspended organic solids.
Primary treatment is the first step in the treatment of sewage. It is a physical process that removes large suspended organic solids from the sewage. These solids can include food particles, paper, and human waste.
Primary treatment is typically carried out in a sedimentation tank. The sewage is allowed to flow slowly through the tank, and the solids settle to the bottom. The settled solids are then removed from the tank and disposed of.
Primary treatment is an important step in the treatment of sewage. It removes a significant amount of the solids from the sewage, which helps to improve the quality of the effluent.
The other options are incorrect because they are not removed during primary treatment.
- Option B: Oil and grease are removed during secondary treatment.
- Option C: Sand and grit are removed during preliminary treatment.
- Option D: Floating materials are removed during preliminary treatment.