What is the approximate air requirement per pound of BOD removed in a conventional activated sludge aeration tank?

• A. 500-700
• B. 1500-1700
• C. 1000-1200
• D. 2000-2500

Answer: (C)

Oxygen supply drives BOD removal in an aeration tank. The air you blow in must deliver enough oxygen to the microorganisms to oxidize the organic matter, and because not all the air’s oxygen is effectively transferred and used, you end up needing more air than the simple oxygen demand would suggest. For a typical conventional activated sludge system, field data and design practice converge on about 1,000 to 1,200 standard cubic feet of air per pound of BOD removed. This range reflects the usual oxygen demand of the biomass plus the practical transfer efficiency and DO targets used in such plants.

The other ranges would either understate or overstate the typical requirement for a conventional setup. If the number is too low, it wouldn’t meet the actual oxygen needs; if it’s much higher, that indicates conditions beyond a standard plant’s normal operation, such as very high nitrification demand or poor transfer efficiency.