Question

The most common water disinfection method is chlorination. For a mid-sized water treatment plant, 28 lbs of chlorine (Cl2) are added daily to disinfect 6 million gallons of water. a) What is the concentration of chlorine in water (in mg/L) when it is just dosed into water? b) Chlorine is a strong oxidizer and it is consumed by oxidizable substances in water, including microorganisms. The term chlorine demand refers to the amount of chlorine consumed during disinfection. The term chlorine residue is the concentration of chlorine remains after treatment. Chlorine residue ensures continued protection of water quality in the distribution system. If the water exiting the treatment plant has a chlorine residue of 0.2 mg/L, what is the chlorine demand (in mg/L)?

Answer 1

(a) 8.0 mg/l

(b) 7.8 mg/l

Step-by-step explanation:

(a) We can calculate the chlorine concentration as

`C_(Cl2)=(28lbs)/(6,000,000gal)*(453,592.37)/(1lb)*(3.78541l)/(1gal)\\\\C_(Cl2)=8,0 mg/l`

(b) In a steady system, the chlorine consumed is equal to the original chlorine concentration less the chlorine residue.

`C_(consumed) = C_(0)-C_(residue)\\C_(consumed) = 8.0-0.2 = 7.8 mg/l\\`