Water Treatment Processes - Mathematics and Statistics for the Environment - page 620

■ EXAMPLE 23.38
Problem: Calculate the actual chemical feed rate (lb/day) if a container is placed under a chemical
feeder and a total of 1.6 lb is collected during a 20-min period.

Solution: First calculate the lb/min feed rate:

Chemical applied(lb)
Len

1.6 lb
20 min

Chemical feed rate = = = lb/min 0.08

gthofapplication(min)

Then calculate the lb/day feed rate:

Chemical feed rate = 0.08 lb/min × 1440 min/day = 115 lb/day

23.4.6.1 Solution Chemical Feeder Calibration
As with other calibration calculations, the actual solution chemical feed rate is determined and
then compared with the feed rate indicated by the instrumentation. To calculate the actual solution
chemical feed rate, first express the solution feed rate in MGD. When the MGD solution flow rate
has been calculated, use the mg/L equation to determine chemical dosage in lb/day. If solution feed
is expressed as mL/min, first convert mL/min flow rate to gpd flow rate:

(mL/min) 1440 min/day
3785 mL/gal

×

gpd = (23.35)

Then calculate chemical dosage:

Chemical dosage (lb/day) = Chemical (mg/L) × Flow (MGD) × 8.34 lb/day (23.36)

■ EXAMPLE 23.39
Problem: A calibration test is conducted for a solution chemical feeder. During a 5-min test, the
pump delivered 940 mg/L of the 1.20% polymer solution. (Assume that the polymer solution weighs
8.34 lb/gal.) What is the polymer dosage rate in lb/day?

Solution: The flow rate must be expressed as MGD; therefore, the mL/min solution flow rate must
first be converted to gpd and then MGD. The mL/min flow rate is calculated as

(940 mL)/(5 min) = 188 mL/min

Next convert the mL/min flow rate to gpd flow rate:

188 mL/min 1440 min/day
3785 mL/gal

×

= 72 gpd

Then calculate the polymer feed rate:

Polymer feed rate = 12,000 mg/L × 0.000072 MGD × 8.34 lb/day = 7.2 lb/day

■ EXAMPLE 23.40
Problem: A calibration test is conducted for a solution chemical feeder. During a 24-hr period, the
solution feeder delivers a total of 100 gal of solution. The polymer solution is a 1.2% solution. What
is the lb/day feed rate? (Assume that the polymer solution weighs 8.34 lb/gal.)