Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

What is the term for the amount of chlorine used up by reacting with iron, organics, or bacteria?

1. Residual

2. Demand

3. Concentration

4. Usage Rate

The correct answer is: Demand

The term that describes the amount of chlorine consumed during reactions with substances such as iron, organics, or bacteria is "demand." In water treatment processes, chlorine is added to disinfect water, but not all of the chlorine remains in the water as a free disinfectant. Some of it is consumed by these reactions before it can effectively disinfect the water. When assessing water quality and the effectiveness of chlorination, understanding chlorine demand is crucial. It provides insight into how much chlorine must be added to achieve the desired disinfection levels. It's an important consideration in managing water treatment processes, ensuring that sufficient chlorine is available after accounting for the amount that has reacted with impurities. Residual refers to the amount of chlorine remaining after reactions have taken place, concentration measures how much chlorine is present relative to the volume of water, and usage rate would indicate the volume of chlorine used over a specified time. These terms are related but do not specifically address the consumption of chlorine by reactions with contaminants.