What are advantages of aerobic digestion?

• A. Operation is complex and requires high capital cost.
• B. Lower BOD in the supernatant; odorless humus-like product; operation is easy; low capital cost.
• C. High energy consumption and poor stability.
• D. Produces methane.

Answer: (B)

Aerobic digestion uses oxygen to feed aerobic bacteria that oxidize the organic matter in sludge. Because the organics are consumed, the liquid portion (the supernatant) ends up with a lower BOD, and the solids become a stable, odor-free, humus-like product that’s easier to handle and dewater. The process is relatively straightforward to operate and typically incurs lower capital costs than methods that require gas collection, heating, or complex downstream treatment. Methane production is not a feature of aerobic digestion—methane is produced in anaerobic digestion, which is why that outcome isn’t listed as an advantage here. The combination of lower BOD in the supernatant, odorless stable solids, easy operation, and lower capital cost captures the main advantages of aerobic digestion.