2. Routine operation and maintenance processes in a water treatment plant includ

Question

2. Routine operation and maintenance processes in a water treatment plant include chemical feed, mixing, coagulation, flocculation, sedimentation, filtration, chlorination, fluoridation, pH adjustment, and pumping. You are asked to review the treatment processes for a 3.0 MGD plant and provide answers for the following equations.
(a) The gas chlorination system is set to feed chlorine at a rate of 16 lb/day into a daily water flow of 3,000,000 gallons for Spring operation. The chlorine residual is 0.4 mg/L. Estimate the chlorine demand (mg/L).

Answer: 0.24

(b) The water treatment plant uses filters that are 10 ft in diameter. If the filters are backwashed at 15 gpm/ft2 for 12 minutes, estimate the amount (gallons per wash) of wash water used.

Answer: 14,130

Explanation / Answer

a)

Daily water flow =3,000,000 gallons/Day

Chlorine residual = 0.4 mg/L

Chlorine usage=16 lb/day=(16lb*1kg/2.204lb)/day=7.25kg/day=7.25x10e6mg/day

Chlorine required=(7.25x10e6mg/day)/(3,000,000) gallons/Day

=2.41mg/gallon=2.41mg chlorine/gallon*gallon/3.785L=0.565mg/L

chlorine demand (mg/L)=Total Chlorine usage-Residual chlorine

=0.565mg/L-0.4 mg/L=0.165mgL

b) Filter Diameter=10ft

Area=(pi*D2)/4=3.14159*100/4=78.53ft2

total gallons=15 gpm/ft2 for 12 minutes=180gallons/ft2

gallons per wash=total gallons*Total area=180gallons/ft2*78.53ft2=14137gallons

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