California Wastewater Treatment Operator Practice Exam

What creates hydrogen sulfide?

1. anaerobic sludge digestion

2. aerobic sludge digestion

3. fermentation

4. decomposing organic matter under anaerobic conditions

The correct answer is: decomposing organic matter under anaerobic conditions

The process that creates hydrogen sulfide primarily occurs during the decomposition of organic matter under anaerobic conditions. In environments where oxygen is scarce, such as in certain types of wastewater treatment facilities or stagnant water, bacteria break down organic material. This process results in the production of hydrogen sulfide, which is a colorless gas known for its characteristic rotten egg smell. Anaerobic sludge digestion specifically refers to the digestion process that occurs in controlled environments where organic solids are broken down by bacteria without the presence of oxygen, also leading to hydrogen sulfide production, but the broader context of decomposing organic matter under anaerobic conditions encompasses a wider range of processes and environments where hydrogen sulfide may be generated. While aerobic sludge digestion is characterized by the presence of oxygen and does not produce hydrogen sulfide, fermentation can produce various byproducts, including acids and gases, but it is not the primary mechanism for hydrogen sulfide generation when discussing anaerobic degradation directly. Thus, the focus on decomposing organic matter under anaerobic conditions captures the essence of hydrogen sulfide production effectively.