Ontario Operator-in-Training (OIT) Practice Exam

What is meant by the term 'contact time' in water disinfection?

1. The amount of chlorine needed for complete disinfection

2. The time chlorine is allowed to react in water for disinfection

3. The frequency of chlorine dosage application

4. The time taken to filter the water after chlorination

The correct answer is: The time chlorine is allowed to react in water for disinfection

The term 'contact time' in water disinfection refers to the duration that disinfectants, such as chlorine, are allowed to remain in contact with the water being treated. This time is crucial because the effectiveness of disinfection relies on both the concentration of the disinfectant and the length of time it is in contact with pathogens. A longer contact time generally increases the likelihood that the disinfectant will effectively kill or inactivate harmful microorganisms present in the water. The second option accurately captures this concept, emphasizing the importance of allowing sufficient time for the chemical reaction between the disinfectant and contaminants to occur. This reaction is essential for achieving effective disinfection, ensuring that water is safe for consumption and use. In contrast, other options focus on different aspects of the disinfection process. The amount of chlorine needed pertains to dosage rather than time. The frequency of chlorine dosage relates to how often chlorine is applied, which does not directly address the interaction time with water. Lastly, the filtration process after chlorination is a separate phase in water treatment and not specifically linked to the disinfectant's reaction time.