Florida Wastewater Practice Test

Which two stages are present in an anaerobic digester?

1. Combustion and Methanogenesis

2. Acid formation and Gas formation

3. Fermentation and Aeration

4. Inhibition and Digestion

The correct answer is: Acid formation and Gas formation

In an anaerobic digester, the process of breaking down organic materials without the presence of oxygen occurs in two primary stages: acid formation and gas formation. During acid formation, organic matter is hydrolyzed into simpler compounds. This is followed by the conversion of these compounds into volatile fatty acids, which creates an environment conducive for methanogens. It is in the second stage, gas formation, that the volatile fatty acids are further processed by methanogenic bacteria that convert them into methane and carbon dioxide. This methane is the biogas that can be captured and utilized as a renewable energy source. The other options do not accurately reflect the anaerobic digestion process. Combustion is an aerobic process rather than an anaerobic one, and fermentation can occur in both aerobic and anaerobic conditions; however, aeration is not applicable in anaerobic digestion since it introduces oxygen, which would disrupt the entire process. Similarly, inhibition refers to factors that may negatively affect the process rather than distinct stages. Thus, the correct stages present in an anaerobic digester are indeed acid formation and gas formation.