Page 219 - Water and wastewater engineering

5-22 WATER AND WASTEWATER ENGINEERING

5. Describe a method to keep track of the inventory in a dry chemical silo.
6. Explain why the percent concentration of some liquid chemicals is important in han-
dling and storage.
7. Given the plans for secondary containment of a storage area, identify the components
that would need to be checked to meet acceptable design criteria.
8. Explain the purpose of a day tank.
9. Define MSDS.

With the use of this text, you should be able to do the following:

10. Design a chemical storage tank or silo.
11. Design a secondary containment system given the dimensions of a storage tank or silo.
12. Examine a set of drawings to verify safety features for a chlorine gas feed and storage
system.
13. Select an appropriate feeder for a given chemical.
14. Given a chemical and material or two chemicals, use appropriate charts to determine
whether or not they are incompatible.

5-10 PROBLEMS

5-1. Design a storage silo for lime for a water treatment plant with a design average day
3
capacity of 0.23 m /s. The maximum dose is estimated to be 133 mg/L as CaO.
The local supplier has current contracts with other municipalities that specify
3
85% purity and an average bulk density of 960 kg/m . Shipping time is
normally two weeks. Provide a dimensioned drawing of the silo with recom-
mended appurtenances.
5-2. Design a storage silo for soda ash for a water treatment plant with a design average day
3
capacity of 0.23 m /s. The maximum dose is estimated to be 106 mg/L as Na 2 CO 3 . The
local supplier has current contracts with other municipalities that specify 99% purity
3
and an average bulk density of 800 kg/m . Shipping time is normally 10 working days.
Provide a dimensioned drawing of the silo with recommended appurtenances.
5-3. Mule Shoe is to provide fluoride to augment the natural fluoride in the water supply.
The natural fluoride concentration is 0.25 mg/L. The design concentration is 1.0 mg/L.
3
The flow rate is 0.057 m /s. The municipal water authority has decide to use
45 kg polyethylene kegs of fluorosilicic acid (H 2 SiF 6 ) provided by the chemical
supplier as their storage system. Commercial strength is 40% H 2 SiF 6 . Estimate the
number of kegs they must store if delivery is once a month.
5-4. For safety and security reasons, the city of Alum Rock has decided to replace its chlo-
rine gas disinfection system with a sodium hypochlorite (NaOCl) system. You have
been tasked with the design of the storage tank(s) for sodium hypochlorite that is to
replace the gas cylinders. The existing storage system consists of twelve 900 kg