If the chlorine demand is 2.3 mg/L and the desired chlorine residual is 0.2 mg/L, what dosage is required?

To determine the required chlorine dosage, you start by adding the chlorine demand to the desired chlorine residual. The chlorine demand indicates how much chlorine is needed to react with contaminants in the water before any residual is available for disinfection.

In this scenario, the chlorine demand is 2.3 mg/L, which means that 2.3 mg/L of chlorine is required to satisfy the need for disinfection. Additionally, a desired residual of 0.2 mg/L is needed for effective ongoing disinfection after the demand has been met.

Thus, the total dosage required can be calculated as follows:

Chlorine Demand + Desired Residual = Required Dosage

2.3 mg/L + 0.2 mg/L = 2.5 mg/L

Therefore, the required dosage of chlorine in this situation is 2.5 mg/L, which corresponds to the correct answer. This value ensures that both the demand is satisfied and that the desired residual for effective disinfection remains in the water.