Civil Engineering Reference
In-Depth Information
CHAPTER 24
Chemical Storage and
Feeding Systems
INTRODUCTION
The importance of the design of chemical systems in a water treatment plant cannot
be overemphasized. Although the chemical systems account for a only relatively small
percentage of the capital costs of a water treatment plant, they usually account for a
large percentage of the annual operation and maintenance costs. Proper design of these
systems can reduce operation and maintenance costs and improve treatment efficiency.
This chapter describes specific design considerations for liquid, solid, and gaseous
chemical systems. The groups of chemicals used for particular water treatment func-
tions are discussed, and the specific chemicals in each group are listed, as well as their
pertinent physical data and characteristics. The rationale for selecting a particular
chemical is presented and explained. Important design considerations for each type of
chemical system are discussed, including the selection of chemical form, delivery,
storage, feeding, conveyance methods, and safety.
CHEMICAL SELECTION
Function of Chemicals
Chemicals are used for coagulation and as coagulation aids, for softening, taste and
odor control, disinfection, dechlorination, fluoridation, fluoride adjustments, pH ad-
justments, corrosion control, and removal of certain constituents such as iron, man-
ganese, and heavy metals. Each of these functional classifications contains a variety
of chemicals that can be used for the same purpose, and in some cases the chemicals
serve more than one purpose. Table 24-1 describes the chemicals within these various
unit processes.
Coagulants
In most instances, surface waters require the use of a coagulant, while
well waters do not. Aluminum sulfate (alum) is the most widely used coagulant. It is
available in lump, ground, or liquid form and can be shipped in bulk or in 100-pound
(45.4-kg) bags for dry forms, and drums, totes, and bulk for liquid form. However, it
may be appropriate to use a coagulant other than aluminum sulfate, such as those
listed in Table 24-1.
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