Assignment 7 Math Worksheet

Each question is worth 20 points. Partial credit may be awarded.

1. Determine the chlorinator setting (lb/day) required to treat a flow of 5.25 MGD with a chlorine dose of 6.5 mg/L.

Feed Rate = Chlorine (mg/L) x Flow (MGD) x 8.34 lb/gal

Feed Rate =

Feed Rate =

1. A pipeline that is 10 inches in diameter and 1250 ft long is to be treated with a chlorine dose of 32 mg/L. How many lb of chlorine will this require?

First, determine the gallon volume in the pipeline:

Volume (gal) = 0.785 x D2 x length x 7.48 gal/cu ft

Volume (gal) =

Volume (gal) =

Next, calculate the amount of chlorine required:

Feed Rate = Chlorine (mg/L) x Flow (MGD) x 8.34 lb/gal

Feed Rate =

Feed Rate =

2. The chlorine dosage for water is 3.2 mg/L. If the chlorine residual after a 30-minute contact time is found to be 0.9 mg/L, what is the chlorine demand (in mg/L)?

Chlorine Demand = Chlorine Dose - Chlorine Residual

Chlorine Demand =

Chlorine Demand =

3. What should the chlorinator setting be (lb/day) to treat a flow of 2.42 MGD if the chlorine demand is 3.8 mg/L and a chlorine residual of 0.7 mg/L is desired?

First, determine the chlorine dosage (in mg/L):

Chlorine Dose = Chlorine Demand + Chlorine Residual

Chlorine Dose =

Chlorine Dose =

Next, calculate the chlorine feed rate in lb/day:

Feed Rate = Chlorine (mg/L) x Flow (MGD) x 8.34 lb/gal

Feed Rate =

Feed Rate =

4. A chlorinator setting is increased by 12 lb/day. The chlorine residual before the increased dosage was 0.8 mg/L. After the increased chlorine dose, the chlorine residual was 1.2 mg/L. The average flow rate being chlorinated is 1.45 MGD. Is the water being chlorinated beyond the breakpoint?

First, calculate the expected increase in chlorine residual:

Feed Rate = Chlorine (mg/L) x Flow (MGD) x 8.34 lb/gal

________________ = x mg/L x _________________ x ____________________

x mg/L = _____________________ / (________________ x ___________________)

x mg/L =

Actual increase in residual is:

________________________ - _________________________ = __________________________