Tennessee Wastewater Operator Practice Exam

What effect does slug loading with VS have on an aerobic digester?

1. Increases pH

2. May cause foaming

3. Improves settling

4. Decreases DO levels

The correct answer is: May cause foaming

Slug loading with volatile solids (VS) into an aerobic digester can indeed lead to foaming. This occurs primarily due to the rapid decomposition of the organic matter introduced in a concentrated form, which can produce a surge of gas during the digestion process. This gas includes carbon dioxide and methane, which can accumulate in the digester and create conditions ripe for foaming. When there is a sudden increase in the organic load, the microbial population may struggle to keep pace, leading to the generation of excess gas as a byproduct of their metabolic activity. This gas can rise and create a frothy layer at the surface of the digester, resulting in foaming. Such foaming can interfere with normal operation and efficiency, sometimes causing operational issues such as overflow or reduced treatment capacity. In contrast, while slug loading could affect other parameters of the digester operation, such as potentially lowering dissolved oxygen (DO) levels due to organic matter degradation, the most immediate and recognizable outcome of such slug loading is the foaming effect.