California Wastewater Treatment Operator Practice Exam

What can result from insufficient contact time during disinfection?

1. Pathogens may remain active in the treated water

2. The disinfectant will become ineffective

3. The system will become overloaded

4. There will be too much oxygen in the water

The correct answer is: Pathogens may remain active in the treated water

When disinfection is applied in wastewater treatment, sufficient contact time is crucial for ensuring that pathogens are effectively inactivated. Insufficient contact time means that the duration during which the disinfectant is in contact with the water is not long enough for the disinfectant to act upon the microorganisms effectively. As a result, pathogens such as bacteria, viruses, and protozoans may remain alive and potentially active in the treated water. This can lead to health hazards if the water is released back into the environment or reused, as these pathogens can cause diseases in humans and animals. The other options do not accurately address the specific consequences of insufficient contact time. For instance, while it might be argued that a disinfectant could lose its effectiveness over time, the primary reason for disinfection failures relates directly to the inadequate exposure of pathogens to the disinfectant, not merely the disinfectant's efficacy. Additionally, system overloads and excessive oxygen levels pertain to other operational issues within wastewater treatment systems rather than the direct impact of contact time during disinfection.