Wastewater Calculations - Mathematics and Statistics for the Environment - page 712

Chemical applied(lb)
Len

Feed rate (lb/min) = (24.104)

gthofapplication(min)

■ EXAMPLE 24.76
Problem: Calculate the actual chemical feed rate (lb/day) if a container is placed under a chemical
feeder and a total of 2.2 lb is collected during a 30-min period.

Solution: First calculate the lb/min feed rate:

Chemical applied(lb)
Len

2.2 lb
30 min

Feed rate (lb/min) = = = lb/min 0.07

gthofapplication(min)

Then calculate the lb/day feed rate:

Chemical feed rate (lb/day) = (0.07 lb/min × 1440 min/day) = 101 lb/day

■ EXAMPLE 24.77
Problem: A chemical feeder is to be calibrated. The container to be used to collect chemical is
placed under the chemical feeder and weighed (0.35 lb). After 30 min, the weight of the container
and chemical is found to be 2.2 lb. Based on this test, what is the actual chemical feed rate in lb/day?

Note: The chemical applied is the weight of the container and chemical minus the weight of the
empty container.

Solution: First calculate the lb/min feed rate:

Chemical applied(lb)
Len

Feed rate (lb/min) =

gthofapplication(min)

2.2 lb-0.35 lb
3

1.85 lb
30 min

= = = 0.062lb/min

0 min

Then calculate the lb/day feed rate:

0.062 lb/min × 1440 min/day = 89 lb/day

When the chemical feeder is used for a solution, the calibration calculation is slightly more difficult
than that for a dry chemical feeder. As with other calibration calculations, the actual chemical feed
rate is determined and then compared with the feed rate indicated by the instrumentation. The cal-
culations used for solution feeder calibration are as follows:

(mL/min) 1440 min/day
3785 m

×

Flow rate (gpd) = (24.105)

L/gal

Then calculate chemical dosage (lb/day):

Chemical (lb/day) = Chemical (mg/L) × Flow (MGD) × 8.34 lb/day (24.106)