concrete plant at the Contractor's option. Among
the factors to be considered are initial cost,
maintenance costs, life expectancy, and possible
need for relocation during period of useful life.
Steel plant is generally more economical in first
cost than concrete plant; however, maintenance costs
may be higher. Concrete plant would have a higher
life expectancy in highly corrosive soils. Small
steel plants are suitable for relocation. Concrete
plant is considered as plant having outer walls of
concrete regardless of material used for interior
walls or partitions. Steel plants are considered as
plants having outer walls of steel and bottom of
steel or concrete (except that all-steel would be
needed for relocatable plants).
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Cathodic protection shall be provided for the steel-fabricated sewage
treatment plant when installed below grade. This protection shall consist
of installing one 7.71 kg 17 pound magnesium anode package not less than
every 7.62 m 25 feet along the outer steel shell of the plant. The anodes
shall be securely connected with solderless electrical connectors to the
shell with not less than No. 8 copper wire, factory installed.
2.17
TREATMENT AND PAINTING
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NOTE: Delete reference to comminutor when not
required for plant. For plants of 1.09 L/s 25,000
GPD capacity and below, the comminutor and bar
screen unit may be omitted, and in lieu thereof, a
screening basket provided in the aeration tank. For
installations in which all sewage has passed through
a comminutor and bar screen upstream of the plant, a
comminutor and bar screen unit need not be provided
as a part of the plant equipment.
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NOTE: Delete requirement for aeration tank
detention time when complete mixing type is
specified.
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NOTE: Delete reference either to chlorinator or to
hypochlorinator. Hypochlorinator should be
specified for all plants 4.38 L/s 100,000 GPD
capacity and below. Chlorinator should be specified
for all plants 6.57 L/s 150,000 GPD capacity and
above. Between 4.38 and 6.57 L/s 100,000 and
150,000 GPD capacity either is suitable. Selection
should be made on basis of existing station or base
practices, local availability, and comparative costs.
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Except as otherwise specified, equipment shall be treated and painted in
accordance with the manufacturer's standard practice. All exposed surfaces
of ferrous metals, other than piping, including those to be submerged,
SECTION 11375N
Page 82
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