High acid production in an anaerobic digester could result in what condition?

High acid production in an anaerobic digester leads to the condition often referred to as the digester becoming "sour." When there is an excess of volatile fatty acids (VFAs) in the digester, it can negatively impact the overall pH balance of the system, causing it to drop. This sourness indicates that the anaerobic digestion process is not functioning optimally, as the microorganisms responsible for breaking down the organic material are struggling to maintain a stable and appropriate environment. A sour digester typically signals that additional adjustments are needed, such as addressing the feedstock composition or managing retention times, to restore balance and promote healthy microbial activity.

In contrast, an increase in temperature or presence of excess oxygen is not typically associated with high acid production in anaerobic digestion; these conditions would suggest different underlying issues. Efficient operation in a digester would typically involve a balanced pH and a healthy environment for methanogens, not an excess of acids. Thus, the correct choice highlights a critical challenge in maintaining optimal anaerobic digestion conditions.