What type of bacteria is used to feed on BOD in the activated sludge process?

• A. Aerobic
• B. Anaerobic
• C. Facultative
• D. Microaerophilic

Answer: (A)

In the activated sludge process, the fresh air added during aeration creates an aerobic environment. Under these oxygen-rich conditions, aerobic bacteria use the organic matter in the wastewater (BOD) as food and oxygen as the electron acceptor. They oxidize this organic material to carbon dioxide and water, which is how BOD is removed from the wastewater.

Anaerobic bacteria operate without oxygen and aren’t active in the aerated tanks. Facultative bacteria can live with or without oxygen, but the process is designed to maximize removal under aerobic conditions, so aerobic bacteria do the main work. Microaerophilic organisms prefer very low oxygen levels, which aren’t the conditions maintained in normal activated-sludge aeration.