Ontario Operator-in-Training (OIT) Practice Exam

What is chlorine demand?

1. The total amount of chlorine used

2. The difference between chlorine added and chlorine remaining

3. The residual chlorine after disinfection

4. The amount of chlorine in the atmosphere

The correct answer is: The difference between chlorine added and chlorine remaining

Chlorine demand is defined as the difference between the amount of chlorine that is added to a water system and the chlorine that remains in the water after a certain period of time. It represents the quantity of chlorine that has been utilized in the water to react with contaminants such as organic matter, pathogens, and other substances that can consume chlorine. Understanding chlorine demand is crucial for operators because it helps them determine how much chlorine needs to be added to achieve effective disinfection and ensure water safety. High chlorine demand can indicate the presence of substances that require more chlorine to achieve desired disinfection levels, impacting water treatment processes and efficiency. The other choices do not accurately capture the concept of chlorine demand. The total amount of chlorine used does not take into account the chlorine that remains after treatment. The residual chlorine refers to what is left after the disinfection process, while the amount of chlorine in the atmosphere is unrelated to water treatment processes directly.