Ontario Operator-in-Training (OIT) Practice Exam

Which method is used to achieve secondary disinfection in wastewater treatment?

1. Ozonation

2. Chlorination or chloramination

3. Filtration

4. Ultraviolet light treatment

The correct answer is: Chlorination or chloramination

Secondary disinfection in wastewater treatment is crucial for eliminating pathogens that may remain after the primary treatment processes. Chlorination or chloramination is widely used in this context because it effectively targets and inactivates a broad range of microorganisms, ensuring that the treated water does not pose a public health risk when discharged or reused. Chlorination involves adding chlorine to the effluent, which reacts with the pathogens and leads to their inactivation. Chloramination, on the other hand, uses a combination of chlorine and ammonia, resulting in a longer-lasting disinfectant residual compared to chlorine alone. This is particularly beneficial for ongoing protection against microbial regrowth in the distribution system or in storage. While other methods like ozonation, filtration, and ultraviolet light treatment are also effective in specific circumstances, they do not provide the same persistent disinfection residual that chlorination or chloramination does. For instance, ozonation is more effective at oxidizing organic material but does not leave a residual disinfectant. Similarly, ultraviolet light treatment effectively inactivates pathogens but requires careful monitoring and does not leave any residual disinfectant in the water. Filtration can remove some microorganisms but is not a method of disinfection on its own. Therefore, chlorination or chloramination stands out as the method specifically