Tennessee Wastewater Operator Practice Exam

What typically causes a rapid rise event in an anaerobic digester?

1. Excessive mixing

2. Improper chemical dosing

3. Over or under mixing

4. Increased feed rates

The correct answer is: Over or under mixing

A rapid rise event in an anaerobic digester is commonly associated with the mixing dynamics within the system. Over or under mixing can disturb the delicate balance of microbial populations necessary for effective digestion. Proper mixing is crucial to ensure that substrate is evenly distributed and that microbial communities have optimal contact with the waste material. If mixing is excessive, it may lead to excessive shear forces that can damage the microorganisms involved in the digestion process. Conversely, insufficient mixing can cause stratification, where heavier solids settle at the bottom, limiting contact with the microorganisms and leading to reduced biogas production. Therefore, the choice indicating that both over and under mixing can cause issues aligns with the understanding that maintaining the right balance in mixing is critical for the health and efficiency of an anaerobic digestion process. Other options focus on individual factors that, while potentially disruptive, do not encompass the broader impact of mixing dynamics within digesters in the same comprehensive way.