The primary indicator of an upset in your anaerobic digester is __________.

The primary indicator of an upset in an anaerobic digester is an increase in volatile acids combined with a decrease in alkalinity. This condition is significant because the biological processes within the digester rely on a balanced relationship between acid production and the buffer capacity provided by alkalinity.

When the digester functions normally, microorganisms break down organic material, producing methane and carbon dioxide while converting volatile acids into stable compounds that do not disrupt the process. An upset condition typically signifies that the rate of volatile acid production has outpaced the system’s ability to neutralize these acids, leading to a rise in volatile acids (also known as VFAs) and a corresponding drop in alkalinity. This imbalance can lead to a decrease in pH, further stressing the microbial population and impairing digestion efficiency.

The other indicators mentioned, such as excess gas production or changes in pH and carbon dioxide levels, may occur as a result of various operational conditions, but they are not as direct an indicator of the specific disruption in the acid-base balance that is critical in the anaerobic digestion process. Therefore, monitoring volatile acids and alkalinity levels is vital for maintaining optimal conditions in an anaerobic digester.