What is the typical range for dissolved oxygen (DO) in aeration tanks used in activated sludge processes?

What is the typical range for dissolved oxygen (DO) in aeration tanks used in activated sludge processes?

• A. Approximately 0 to 1 mg/L.
• B. Approximately 2 to 4 mg/L.
• C. Approximately 6 to 8 mg/L.
• D. Approximately 10 to 12 mg/L.

Answer: (B)

Maintaining enough oxygen in the aeration tank is essential for the aerobic microbes to effectively oxidize organic matter. A dissolved oxygen level around 2 to 4 mg/L provides reliable biodegradation while balancing energy use; it keeps the mixed liquor aerobic and supports stable sludge characteristics without wasting energy. If DO is too low (near 0–1 mg/L), anaerobic zones can form, leading to odors and poor treatment performance. Conversely, keeping DO much higher (6–8 mg/L or more) wastes blower energy and offers diminishing returns for treatment efficiency.

Maintaining enough oxygen in the aeration tank is essential for the aerobic microbes to effectively oxidize organic matter. A dissolved oxygen level around 2 to 4 mg/L provides reliable biodegradation while balancing energy use; it keeps the mixed liquor aerobic and supports stable sludge characteristics without wasting energy. If DO is too low (near 0–1 mg/L), anaerobic zones can form, leading to odors and poor treatment performance. Conversely, keeping DO much higher (6–8 mg/L or more) wastes blower energy and offers diminishing returns for treatment efficiency.