An anaerobic digester is considered to be failing when__________.

An anaerobic digester is a critical component in wastewater treatment, particularly for stabilizing organic matter and producing biogas. It operates under an anaerobic environment, which means that it doesn’t require oxygen to function. The performance of an anaerobic digester can be assessed based on several key indicators, and a failure can be inferred from changes in these indicators.

When considering the provided options, all the listed conditions indicate poor performance or impending failure of the anaerobic digester.

The decrease in the numbers of methane-forming microorganisms suggests that the digestion process is hampered. Methanogens are essential for the conversion of volatile fatty acids into methane, which is a key product of the digestion process. If their population diminishes significantly, it implies that the digester's ability to produce biogas is compromised.

An increase in volatile acid concentration is another sign of operational issues. Under normal conditions, volatile acids are converted by methanogens into methane. When these acids accumulate, it indicates that the process is out of balance, possibly due to a lack of sufficient microorganisms or operational conditions that are not optimal.

Additionally, a decrease in the alkalinity of the sludge can signal trouble. Alkalinity acts as a buffer in the anaerobic digestion process,