Question

In aerobic biological waste treatment, microorganisms utilize which compound as the primary electron acceptor during the degradation of organic matter?

• A. Oxygen
• B. Carbon dioxide
• C. Nitrate
• D. Sulfate

Hint:

• Aerobic processes occur in the presence of oxygen.
• In aerobic respiration, organic matter is oxidized (loses electrons).
• Oxygen (O$_2$) is the terminal electron acceptor, being reduced to water (H$_2$O).
• This is a highly efficient energy-yielding process used in many wastewater treatment systems.
• Nitrate, sulfate, and CO$_2$ can be electron acceptors in anaerobic respiration or other metabolic pathways.

Answer 1

The Correct Option is A

Aerobic biological waste treatment processes rely on microorganisms that perform aerobic respiration to degrade organic pollutants. In aerobic respiration:

• Organic matter (e.g., carbohydrates, proteins, fats in wastewater) serves as the primary source of electrons (electron donor) and carbon for microbial growth.
• Microorganisms oxidize this organic matter to extract energy.
• The electrons removed from the organic matter are passed down an electron transport chain.
• Molecular oxygen (O$_2$) acts as the terminal (or final) electron acceptor in this chain. When oxygen accepts these electrons (along with protons), it is reduced to water (H$_2$O).

This use of oxygen as the terminal electron acceptor is the defining characteristic of aerobic respiration and, consequently, aerobic treatment processes (e.g., activated sludge process, trickling filters). Other options:

• Carbon dioxide (CO$_2$): Can be a carbon source for autotrophs or a product of respiration, but not typically the primary terminal electron acceptor in organic matter degradation for energy by heterotrophs. Some microbes (methanogens, acetogens) can use CO$_2$ as an electron acceptor in anaerobic conditions, but this is not typical for aerobic waste treatment.
• Nitrate (NO$_3^-$): Can serve as a terminal electron acceptor in anaerobic respiration (denitrification).
• Sulfate (SO$_4^{2-}$): Can serve as a terminal electron acceptor in anaerobic respiration (sulfate reduction).

Therefore, in aerobic processes, oxygen is the primary electron acceptor. \[ \boxed{\text{Oxygen}} \]