Tennessee Wastewater Operator Practice Exam

What is an indicator that a toxic compound has entered an anaerobic digester?

1. Decreased temperature

2. Decrease in volatile acid concentration

3. Increase in volatile acid concentration

4. Stable pH levels

The correct answer is: Increase in volatile acid concentration

An increase in volatile acid concentration is a clear indicator that a toxic compound has entered an anaerobic digester. This occurs because toxic compounds can disrupt the microbial community that is essential for the digestion process, leading to an imbalance. When this microbial community is affected, it can result in the overproduction of volatile fatty acids, as certain bacteria may proliferate in the absence or reduction of their competitors. This increase in volatile acids can indicate that the process is becoming less efficient and that the environment within the digester is becoming more acidic, which is often a sign of distress among the microbial populations responsible for breaking down organic matter. In a healthy anaerobic digester, you would expect stable or appropriate levels of volatile acids, as the digestion process should maintain a balance between acid production and their consumption by methanogenic bacteria. An increase in these acids can be a detrimental signal for the operational integrity of the digester, often prompting the need for intervention or adjustments in management to restore balance and efficiency.