Tennessee Wastewater Operator Practice Exam

What toxic gas is produced by sulfate reducing bacteria under anaerobic conditions?

1. Carbon dioxide

2. Methane

3. Hydrogen sulfide

4. Ammonia

The correct answer is: Hydrogen sulfide

Sulfate-reducing bacteria are anaerobic microorganisms that thrive in environments devoid of oxygen, often in wetlands, sediments, or in the treatment of wastewater. Under anaerobic conditions, these bacteria use sulfate as a terminal electron acceptor during their metabolic processes. This reduction transforms sulfate into hydrogen sulfide, which is a highly toxic gas recognized for its characteristic smell of rotten eggs. Hydrogen sulfide is dangerous not only because of its toxicity but also due to its flammability at higher concentrations. In wastewater treatment, its presence is an important factor to monitor because it can lead to corrosion of infrastructure and pose health risks to workers. Other gases like carbon dioxide and methane may also be produced by various microbial processes but are not direct products of sulfate reduction. Ammonia, while produced in anaerobic digesters as a product of protein breakdown, is also not a product of sulfate reduction specifically. Thus, hydrogen sulfide is the correct answer as it is the definitive toxic gas produced by sulfate-reducing bacteria under anaerobic conditions.