Tennessee Wastewater Operator Practice Exam

If a heterotrophic bacterium is placed under anoxic conditions, what will it produce?

1. Oxygen and ammonia

2. CBOD and nitrogen gas

3. N2, CO2, and H2O using nitrate

4. Carbon dioxide and glucose

The correct answer is: N2, CO2, and H2O using nitrate

A heterotrophic bacterium, which relies on organic compounds for its carbon and energy needs, metabolizes these compounds in the absence of oxygen (anoxic conditions). Under such conditions, many heterotrophic bacteria can utilize nitrate as a terminal electron acceptor in a process called denitrification. During denitrification, the bacteria convert nitrate (NO3-) into nitrogen gas (N2), along with the production of carbon dioxide (CO2) and water (H2O) as by-products. This process is essential in the nitrogen cycle as it helps to reduce excess nitrates in the environment and returns nitrogen to the atmosphere. This metabolic process explains why the correct answer reflects the production of nitrogen gas, carbon dioxide, and water when a heterotrophic bacterium is in anoxic conditions. Other options do not accurately describe the biochemical processes that occur under these specific environmental conditions or involve the wrong by-products.