Which feature is associated with an oxidation ditch?

• A. Circular or oval geometry; variation of extended aeration; organic load 12-15 lbs BOD per 1000 ft3.
• B. Linear straight ditch with fixed aeration.
• C. A fixed-film trickling filter with biofilm.
• D. A batch reactor with no aeration.

Answer: (A)

An oxidation ditch is a circular or oval, continuous-flow treatment channel designed to operate as a long, extended-aeration system. The circular/oval geometry is key because it promotes steady mixing and a consistent flow path, enabling prolonged contact and stable aerobic conditions for the microbial community to break down organic matter. The organic loading described—around 12–15 pounds of BOD per 1,000 cubic feet—fits this setup, reflecting a moderate load that a circle/oval ditch can handle with continuous aeration and mixing to keep everything well circulated and oxygen-rich. The other configurations don’t match: a straight ditch with fixed aeration lacks the circular geometry and the same uniform, looped flow; a fixed-film trickling filter relies on a biofilm on media rather than a circulating mixed liquor in a ditch; a batch reactor with no aeration doesn’t provide continuous, aerobic conditions or the looping flow that define an oxidation ditch.