Tennessee Wastewater Operator Practice Exam

Continuous mixing in a digester is crucial to prevent:

1. Biological decay

2. Scum from floating to the top

3. Unbalanced pH levels

4. Accumulation of heavy metals

The correct answer is: Scum from floating to the top

Continuous mixing in a digester is crucial to prevent scum from floating to the top. In anaerobic digesters, the mixing process ensures that the organic solids are evenly distributed throughout the tank. This is important because without proper mixing, scum can accumulate on the surface, potentially forming a thick layer that can interfere with gas production and the overall efficiency of the digestion process. The presence of scum can hinder proper gas transfer and reduce the surface area available for anaerobic bacteria to thrive, ultimately decreasing the efficiency of the digestion process. By continually mixing the contents of the digester, operators can help keep solids suspended, promote even degradation of organic materials, and enhance biogas production. While biological decay, unbalanced pH levels, and accumulation of heavy metals are important considerations in the management of wastewater and digesters, they are not directly mitigated through continuous mixing in the same way that scum accumulation is addressed.