Which factor is NOT a potential cause of foaming in anaerobic digesters?

Foaming in anaerobic digesters is generally caused by specific microbial activity, environmental changes, and operational factors. Excessive aeration is not applicable to anaerobic digesters, as these systems operate without oxygen. In fact, introducing oxygen into anaerobic conditions can disrupt the fermentation process and favor aerobic microorganisms, leading to issues rather than the foaming typically associated with anaerobic conditions.

The other factors listed, such as Nocardia, fluctuating temperature, and inadequate mixing, can indeed contribute to foaming in anaerobic digesters. Nocardia is a genus of bacteria that can lead to foaming issues in such systems. Fluctuating temperatures can affect microbial activity and lead to instability, while inadequate mixing may lead to stratification within the digester, causing localized conditions that promote foam formation. Thus, excessive aeration stands apart fundamentally as it contradicts the anaerobic environment crucial for proper digestion processes.