Calculation of Chlorine Required to Treat Water

Problem 1. How much chlorine in lb/hr will be required to treat 10mgd water with 0.4 mg/l of chlorine (use 1mg/l = 8.34 lb/mgd)?
Exam Name: PGCL 2017
Solution:
 1 mg/l = 8.34 l/mgd
∴0.4 mg/l = (0.4 * 8.34) lb/mgd
                 = 3.336 lb/mgd


Daily Cl₂ required= 10 * 3.336
                              = 33.36 lb/day
                              =1.39 lb/hr

Answer: 1.39 lb/hr

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Problem 2. Have to disinfect 1000000 liter of water having chlorine 0.5 ppm and bleaching powder contains 25% of chlorine. Determine the amount of  bleaching powder requires disinfecting the water.
Exam Name: Easteni Refinery Ltd. 2017
Solution:

Cl₂ required = 0.5 mg/l
Total Cl₂ required =  (0.5*1000000) mg
                              = 500000mg
                              = 0.5 Kg


For 25 Kg Cl₂,  required Chlorine =100 Kg
 ∴  for 0.5 Kg Cl₂,  required Chlorine ={(100/25)*0.5} Kg
                                                             = 2 Kg

Answer: 2Kg

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Problem 3. It is required to disinfect 500000 gpd of water with 0.3 mg/l chlorine. If bleaching powder is used (which contains 25% of available chlorine). How many Kg of bleaching powder are needed to treat the daily flow of water?
Exam Name: West region Gas Company Ltd. 2014
 

Solution: 

Total Cl₂ required = (500000*0.3*3.785)/10⁶ Kg
                              = 0.568 Kg


      For 25 Kg Cl₂,  required Chlorine =100 Kg
 ∴  for 0.568 Kg Cl₂,  required Chlorine ={(100/25)*0.568} Kg
                                                                 = 2.272 Kg

Answer: 2.272Kg

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