Page 213 - Water and wastewater engineering

5-16 WATER AND WASTEWATER ENGINEERING

The following example illustrates the complete design of the storage and handling system for one
chemical.

Example 5-4. Design the coagulant chemical handling and storage system for Boiling Water,
Arizona using the following design data:
3
Average daily design flow rate 38,000 m /d
Coagulant ferric chloride
Maximum dosage 50 mg/L as FeCl 3
Shipping time 1 week
Summer temperature frequently exceeds 40 C

Solution:
a. Off-loading piping
From Table 5-5, select a 100 mm diameter schedule 80 PVC pipe with a notation to

check manufacturer’s data for temperature limitations.
b. Storage tank
(1) From Appendix A select FRP for tank material. The tank should be located indoors
in a cool location.
(2) From Appendix A, note that ferric chloride is shipped as a 40% solution with
100% active ingredient. At the maximum dosage, the daily mass of ferric chloride
used is
3
3
,
(50 mg/L )(38 000 m /d )(10 L/m 3 )(10 6 kg/mg) 1 900 kg/d
,
)
and the mass of solution required is
1 900 kg/d
,
4750 kg/d
,
040
.
(3) Noting, from Table 5-1 , that coagulants are noninterruptible, the volume to be held
in two tanks for redundancy is 30-days supply plus two times the shipping time.
(4750 kg/d )(30 d ( )(7d 209 0000 kg
2
))
,
,
(4) Using the density of ferric chloride from Appendix A, the volume of solution to be
stored is
,
209 000 kg 3
.
3 145 14 or 150 m
1 440 kg/m
,
c. Feeder
Two feeder pumps are required to meet redundancy requirements.
From Table 5-3 , a piston metering pump with PVC or PE coated piston is selected.
Checking the capacity