Which of the following is NOT considered a type of preliminary treatment?

• A. Screening and Grit Removal
• B. Odor Control
• C. Flow Equalization
• D. Aeration

Answer: (B)

The question tests which operation is not classified as preliminary treatment. Preliminary treatment is about removing large solids and protecting downstream processes, so activities like screening to remove debris and grit removal to remove heavy inorganic particles are classic early steps. Flow equalization also fits here because it smooths out inflow variations, helping downstream units operate more consistently. Aeration, on the other hand, is part of secondary treatment where microorganisms are supplied with oxygen to break down organic matter. Odor control is important for plant operation, but it isn’t a treatment step that removes solids or conditions the flow; it’s a control measure that can be applied at various points. Therefore, odor control is not considered a type of preliminary treatment.