Civil Engineering Reference
In-Depth Information
CHAPTER 25
Package Water Treatment Systems
INTRODUCTION
Conventional water treatment systems include the following unit processes:
Coagulation with a primary coagulant such as alum or ferric chloride and
•
Flocculation
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Sedimentation
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Filtration
•
Conventional systems for large plants are most often custom designed and almost
completely constructed on site. There is considerable economy of scale in designing
and constructing conventional systems, and they can be very expensive for small flows.
Package systems are an alternative for small systems, with a capacity of about 3 mgd
or less. Package systems include the same unit processes that are predesigned and
constructed modular units in a factory, including the control system. The modular units
are then assembled on site and are often skid mounted.
As of 1998, it is estimated that over 2,000 package units, ranging in capacity from
5 gpm to 20 mgd, are in service in the United States. These represent only a fraction
of the potential applications of modular units. Assuming an annual average per capita
water consumption of 150 gpd, water systems serving a population of 10,000 persons
would require a 1.5-mgd-capacity treatment plant. In 1998, there were over 42,000
small community water systems that served populations of 10,000 or less. For many
of these communities, treatment is required to meet the Safe Drinking Water Act
standards.
Package units can be used to treat water supplies for communities as well as non-
community water systems, such as those for factories, schools, recreational areas, state
parks, construction camps, ski resorts, remote military installations, and other locations
where potable water is not available from a municipal supply. Several state agencies
have mounted package units on trailers for emergency water treatment. Their compact
size, low cost, minimal installation requirements, and ability to operate virtually un-
attended make them an attractive option in locations where revenues are not sufficient
to pay for a full-time operator.
Package systems covered in this chapter are designed to provide treatment that is
equivalent to conventional systems that are custom designed and constructed. There-
fore, the choice between a custom system and a package system is primarily a matter
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