Texas Wastewater Class B Practice Exam

What triggers facultative bacteria to change from aerobic to anaerobic conditions in sludge systems?

1. Insufficient Nutrients

2. Excessive Heat

3. Lack of Dissolved Oxygen

4. High pH Levels

The correct answer is: Lack of Dissolved Oxygen

Facultative bacteria are capable of existing in both aerobic and anaerobic environments, allowing them to adapt to varying conditions. The correct choice pertains to the lack of dissolved oxygen, which is crucial for aerobic processes. When dissolved oxygen levels drop significantly, the aerobic conditions cannot be maintained, prompting facultative bacteria to switch to anaerobic metabolism. In this state, they continue to decompose organic matter, but through fermentation or other anaerobic processes, resulting in different end products compared to aerobic respiration. The other options, while potentially impactful to the microbial environment, do not directly trigger the shift from aerobic to anaerobic conditions. Insufficient nutrients may inhibit bacterial growth but doesn't necessarily induce a change in metabolic processes. Excessive heat could affect the viability of the bacteria, but it doesn't directly influence the oxygen availability that prompts the anaerobic metabolic switch. High pH levels can affect microbial activity as well, but again, they are not a direct trigger for changing the bacterial environment from aerobic to anaerobic.