Tennessee Wastewater Operator Practice Exam

When should chlorine addition to an activated sludge process be stopped?

1. When there are no visible sheaths

2. When only empty sheaths remain

3. After the sludge has settled

4. Once the pH levels drop

The correct answer is: When only empty sheaths remain

Chlorine addition to an activated sludge process is typically stopped when only empty sheaths remain. This condition indicates that the chlorine has effectively inactivated the microorganisms responsible for the sheaths, and the potential risks associated with disinfection have been mitigated. By stopping chlorine addition at this point, operators can prevent unnecessary chemical usage and further adverse effects on the biological processes necessary for effective wastewater treatment. Continuing to add chlorine beyond this point may disrupt the balance of the microbial community that is crucial for the activated sludge process. In the context of other options: the presence of visible sheaths suggests that some microorganisms may still be viable, indicating that more chlorine may be needed. Stopping chlorine addition after the sludge has settled does not specifically assess the condition of the microorganisms and may lead to inadequate disinfection. Lastly, monitoring pH levels is critical for ensuring the effectiveness of chlorine but does not directly quantify the status of microbial inactivation or the necessity for further chlorine treatment.