What is the optimal DO range for typical aerobic wastewater treatment?

• A. 0-1 mg/L
• B. 1.0-3.0 mg/L
• C. 1.5-3.5 mg/L
• D. 2.0-4.0 mg/L

Answer: (B)

Dissolved oxygen must be enough for aerobic microorganisms to efficiently break down organic matter, but not so high that aeration costs become wasteful. In typical aerobic wastewater treatment, a DO range of about 1 to 3 mg/L provides a reliable balance: it keeps the aeration basin oxic so microbes can activity oxidize BOD and, if needed, support nitrification, while avoiding the extra energy expense of maintaining very high DO. If DO falls below about 1 mg/L, conditions can become insufficient for aerobic metabolism, leading to poor treatment performance and odors. Pushing DO much above 3 mg/L generally wastes energy without substantial additional treatment benefits, since most systems operate effectively within the 1–3 mg/L window. Hence, 1.0–3.0 mg/L is the typical optimal range.