Tennessee Wastewater Operator Practice Exam

What happens to the water level in the digester after a decant cycle?

1. It remains the same

2. It increases significantly

3. It decreases and the hydraulic detention time shortens

4. It fluctuates continuously

The correct answer is: It decreases and the hydraulic detention time shortens

During a decant cycle in a digester, the process involves removing some of the liquid from the digester while retaining the settled solids. This removal causes the water level in the digester to decrease because a portion of the liquid content is being extracted. As the volume of liquid is reduced, the hydraulic detention time, which is the amount of time the wastewater spends in the digester, shortens due to the decreased volume of water present. This decreased water level means that the digestion process can become more efficient, as the remaining solids have a higher concentration and the conditions for biological activity can improve. Understanding these dynamics is crucial for operators to manage digestion effectively and maintain optimal treatment conditions in wastewater treatment facilities.