Wastewater New York State Practice Exam

In wastewater treatment, which compound is primarily responsible for the formation of foul odors during anaerobic digestion?

1. Carbon dioxide

2. Hydrogen sulfide

3. Methane

4. Ammonia

The correct answer is: Hydrogen sulfide

Hydrogen sulfide is primarily responsible for the formation of foul odors during anaerobic digestion due to its distinctive and unpleasant smell reminiscent of rotten eggs. This compound is a byproduct of the breakdown of organic matter under anaerobic conditions, where sulfate-reducing bacteria convert sulfates present in the waste into hydrogen sulfide. The presence of hydrogen sulfide can significantly contribute to the overall odor in wastewater treatment facilities and can pose health risks at elevated concentrations, making its control essential in managing odor emissions. While carbon dioxide, methane, and ammonia can also contribute to the overall gas composition in anaerobic digestion, they do not share the same level of odor potency as hydrogen sulfide. Carbon dioxide is generally odorless, methane has a slight odor when mixed with gas odorants, and ammonia, although pungent, is not the primary compound responsible for the specific foul odor associated with anaerobic digestion.