California Wastewater Treatment Operator Practice Exam

What is the methane content in a properly operating anaerobic digester?

1. 35 to 40% by volume

2. 45 to 50% by volume

3. 55 to 60% by volume

4. 65 to 70% by volume

The correct answer is: 65 to 70% by volume

In a properly operating anaerobic digester, the methane content typically falls within the range of 55 to 70% by volume. This range is significant because methane is the primary product of anaerobic digestion, which is a process that breaks down organic materials in the absence of oxygen, producing biogas as a byproduct. The biogas not only contains methane but also carbon dioxide and trace amounts of other gases. The efficiency of the anaerobic digestion process is influenced by several factors, including the type of organic material being digested, the temperature, and the retention time. When operating optimally, the digester maintains a balance that maximizes methane production, which is crucial for energy recovery and effective waste management. Understanding these dynamics is essential because methane is a valuable energy source and its concentration impacts the overall efficiency of the system. As such, a digester operating effectively would produce biogas with methane concentrations in the higher range of approximately 55 to 70%.