What should an operator do if the volatile acid/alkalinity ratio is increasing in an anaerobic digester?

When the volatile acid to alkalinity ratio is increasing in an anaerobic digester, it indicates an imbalance between acid production and the buffering capacity of the digester. A higher ratio suggests that acids are being produced faster than they can be neutralized by the alkalinity, which can lead to a drop in pH and potentially harm the stability of the digestion process.

Reducing the sludge feed and removal rate is the appropriate response in this situation because it allows the digester more time to stabilize and for the microorganisms to process the existing organic matter effectively. By slowing down the input of additional sludge, you provide an opportunity for the microorganisms to convert the excess volatile acids into biogas and mitigate the potential for acid accumulation.

This careful manipulation of the feed rate helps to restore balance in the digester, avoiding further increases in the volatile acid/alkalinity ratio, and ensures that the digestion process continues efficiently. Other options, such as increasing the sludge feed rate, stopping mixing, or lowering temperature settings, would not address the root cause of the problem and could exacerbate the situation, leading to poor digester performance.