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

In chisine dosage, what does the term demand plus desired refer to?

1. Residual

2. Concentration

3. Flow rate

4. pH levels

The correct answer is: Residual

In chlorine dosage, the term "demand plus desired" specifically refers to the residual. This concept is essential in water treatment processes using chlorine as a disinfectant. Chlorine demand is the amount of chlorine that is consumed by organic and inorganic substances in the water, including bacteria, viruses, and other contaminants. When determining how much chlorine to add, you first need to account for this demand. After meeting the demand, any additional chlorine that remains in the water is referred to as the residual, which is the chlorine concentration that continues to disinfect after the initial application. Thus, when considering the overall chlorine dosage, you must calculate both the amount required to satisfy the initial demand and any additional chlorine needed to achieve the desired residual concentration in the water. This ensures that the water remains disinfected throughout the distribution system, protecting public health. Other terms listed, like concentration, flow rate, and pH levels, do not directly relate to the concept of satisfying both the demand for chlorine and achieving the desired residual in the context of chlorine dosage.