Question

a water sample has a chlorine demand of 1.8 mg/l. the operator requires a residual chlorine concentration of 0.4 mg/l after 20 minutes of contact. what chlorine dose should be applied?

1.4 mg/l
1.8 mg/l
3.0 mg/l
2.2 mg/l

Explanation:

State the chlorine dose formula

$$ \text{Chlorine Dose} = \text{Chlorine Demand} + \text{Chlorine Residual} $$

Substitute the given values

$$
LATEXBLOCK0
$$

Calculate the required dose

$$ \text{Chlorine Dose} = 1.8\text{ mg/L} + 0.4\text{ mg/L} = 2.2\text{ mg/L} $$

Answer:

• (A) 1.4 mg/L
• (B) 1.8 mg/L
• (C) 3.0 mg/L
• (D) 2.2 mg/L (Correct answer)