Florida Wastewater Practice Test

What are the two reaction-forming stages of anaerobic digestion?

1. Acid and methane

2. Aerobic and anaerobic

3. Nitrification and denitrification

4. Oxidation and reduction

The correct answer is: Acid and methane

The two reaction-forming stages of anaerobic digestion are indeed the acid and methane stages. During the anaerobic digestion process, organic matter is broken down by microorganisms in the absence of oxygen. The first stage of this process is characterized by the hydrolysis and acidogenesis phases, where complex organic materials are converted into simpler compounds, primarily fatty acids and alcohols. This is the acid stage, where acids are formed as intermediates. Following the acid stage, the process transitions into the methanogenesis stage. In this phase, methanogenic bacteria consume the fatty acids and other byproducts produced in the first stage to generate methane gas as a byproduct. This methane-rich biogas is what is typically harnessed for energy or other uses. While other options presented contain relevant waste treatment processes, they do not accurately describe the stages involved specifically in anaerobic digestion. The aerobic and anaerobic option refers to contrasting types of microbial processes, nitrification and denitrification pertain to nitrogen cycle processes, and oxidation and reduction are broader biochemical processes that do not specifically describe the unique stages of anaerobic digestion. Therefore, the acid and methane stages are distinctly recognized as the key phases that characterize the anaerobic digestion process.