Tennessee Wastewater Operator Practice Exam

What is the most common cause of foaming in a digester?

1. High temperatures

2. Excessive nutrient levels

3. Filamentous bacteria

4. Low organic load

The correct answer is: Filamentous bacteria

Foaming in a digester is primarily associated with the presence and activity of filamentous bacteria. These microorganisms can multiply excessively under certain conditions, leading to an imbalance in the microbial population. When filamentous bacteria become dominant, they can create a stable foam layer due to their long, hair-like structures, which trap gas bubbles produced during the anaerobic digestion process. This foam can interfere with the digester's efficiency and may hinder gas collection. In contrast, high temperatures might affect the digestion process by increasing the activity of all bacteria and possibly leading to other issues, but they are not the primary cause of foaming. Excessive nutrient levels, while potentially problematic, do not specifically lead to the foaming characteristic of filamentous growth. Low organic load could reduce the overall activity in the digester but is unlikely to induce foaming since foaming is more related to the specific growth patterns of filamentous bacteria. This understanding of filamentous bacteria's role in foaming is crucial for wastewater operators, as controlling and managing these populations can enhance digester performance and minimize operational problems.