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2.12 CHAPTER TWO

that options permitted in the regulations be explored to achieve both effective and eco-
nomic water treatment plant designs.

Treatment Train Alternatives
In developing a water treatment train, the multiple treatment capabilities of the different
methods and materials should all be considered to both simplify and reduce the cost of
facility construction and operation. A treatment train should not be considered simply as
a sequence of process steps. In essence, a treatment train encompasses a combination of
processes that, when integrated, achieve the desired water quality changes and improve-
meats.
Multiple capabilities of the different options in Table 2.4, Most Common Drinking
Water Treatment Processes, are grouped in Table 2.5. Comparison demonstrates why rapid
sand filtration with coagulation is the most common type of water treatment in use. This
type of filter plant reduces the content of particulate matter, pathogens, disinfection by-
product precursors, and color. If a filter is fitted with a GAC medium, the feature of taste
and odor control is added, and color and precursor reduction are enhanced. With the ad-
dition of preozonation, the effective life of the GAC medium is increased because or-
ganics are removed more through biological action. In addition, preozonation, or appli-
cation of another oxidant, will condition dissolved iron and manganese for removal in the
filter media.
Options and supplementary features that may be considered in developing baseline
rapid sand filtration trains are illustrated in Figure 2.1. Basic treatment facilities are shown
in solid boxes with options shown dashed.
Figure 2.1 illustrates the flexibility and broad treatment capabilities of the several op-
tions that may be adapted for many treatment requirements. For instance, different coag-
ulants may be considered that can be afforded high- to low-energy flocculation to pro-
duce a floc size and density best suited to the particular settling device or filter medium.
Flocculation will also agglomerate some dissolved as well as suspended organic matter.
Small, light, and floatable solids may best be removed by dissolved air flotation rather

TABLE 2.5 Common Multipurpose Treatment Measures
Treatment measure Quality improvement
Filtration (all) Particulate reduction
Bacteria, virus, cyst reduction
Coagulation, rapid sand Precursors and by-product reduction
filtration (additional) Color removal
Oxidation Pathogen inactivation
Partial organics reductions
Non- to biodegradable organics
Color removal
Taste and odor control
Iron and manganese reduction*
GAC media Rapid sand filter particulate removal
Color removal
Precursor and by-product reduction
Additional reduction with preoxidation
Taste and odor control
*With filtration.