Water Treatment Processes - Mathematics and Statistics for the Environment - page 619

23.4.5.2 Determining Percent Strength of Mixed Solutions
The percent strength of solution mixture is determined using the following equation:

Sol.1(lb)Sol.1(%strength)
1

× Sol.2(lb)Sol.2(%strength)

100

×

+

00

%Strength = ×100 (23.32)

Sol. 11(lb)Sol.2(lb) +

■ EXAMPLE 23.36
Problem: If 12 lb of a 10% strength solution is mixed with 40 lb of a 1% strength solution, what is
the percent strength of the solution mixture?

Solution:

Sol.1(lb)Sol.1(%str × ength) Sol.2(lb)Sol.2(%strength)

1

×

+

100 00

%Strengthof mix = × 100

Sol.1(lb)Sol.2(lb) +

( ) + ( ) 12 lb × 0.1 40 lb × 0.1

×= +

12 . lb 0.40 lb

= 100 ×=.% 100 31

12 lb + 40 lb 5 2 lb

23.4.6 d ry C hemiCal F eeder C alibration
Occasionally, we need to perform a calibration calculation to compare the actual chemical feed
rate with the feed rate indicated by the instrumentation. To calculate the actual feed rate for a dry
chemical feeder, place a container under the feeder, weigh the container when empty, then weigh
the container again after a specified length of time (e.g., 30 min). The actual chemical feed rate can
be calculated using the following equation:

dd(lb)
Lengthofapplication(min)

Chemical applie

Chemical feed rate (lb/min) = (23.33)

If desired, the chemical feed rate can be converted to lb/day:

Chemical feed rate (lb/day) = Feed rate (lb/m in) × 1440 min/day (23.34)

■ EXAMPLE 23.37
Problem: Calculate the actual chemical feed rate (lb/day) if a container is placed under a chemical
feeder and a total of 2 lb is collected during a 30-min period.

Solution: First calculate the lb/min feed rate:

Chemical applied(lb)
Len

2lb
30 min

Chemical feed rate = = = 0.06 l lb/min

gthofapplication(min)

Then calculate the lb/day feed rate:

Chemical feed rate = 0.06 lb/min × 1440 min/day = 86.4 lb/day