When an anaerobic digester is upset, what is the first sign observed?

The first sign observed when an anaerobic digester is upset is a decreased alkalinity and increased volatile acid concentration. This condition occurs because an upset in the digester often leads to an overproduction of volatile fatty acids (VFAs) due to increased activity from acid-producing bacteria, typically as a result of factors such as changes in the feed stock, temperature, or retention time.

As the concentration of these acids rises, it tends to lower the alkalinity of the digesting sludge because alkalinity serves as a buffer against pH changes, and it can diminish when volatile organic acids are in excess. If this imbalance continues, it can lead to a drop in pH, potentially harming the microbial communities necessary for effective digestion. Maintaining a balance between alkalinity and volatile acid concentration is critical for healthy anaerobic digestion processes, making these indicators vital for detecting upsets early on.