20. Whether, for extended aeration type plant,
eventual conversion to step aeration type is
anticipated.
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Tanks shall be suitable for support by and anchorage to a concrete base.
Steel tools shall be in accordance with the applicable requirements of AWWA
D100 for shop fabrication and welding of AWWA D100. All shop welding shall
be done by a qualified welder. Steel tank walls and bottom shall be
structural steel plate. All structural steel shapes used for reinforcing
and bracing shall be 6 mm 1/4 inch in the thinnest section. Placement of
reinforcing and bracing shall not adversely affect performance
characteristics with aeration tank. All welded steel structural members
shall be joined by electric arc welding with fillets of adequate section
for the joint involved. All sides, compartment partitions, tank bottoms,
braces, and corners shall be continuously welded inside and out and ground
smooth before priming. Water tightness shall be provided by means of
welding. Common partitions shall be reinforced to withstand pressures
resulting from liquid level differentials which would occur when any
individual compartment(s) is dewatered while contiguous compartments remain
at normal operating liquid level.
2.7.7
Special Requirements for Circular Plant with Concentric Inner Tank
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NOTE: Delete the paragraph for plants of less than
1.31 L/s 30,000 GPD. This plant configuration
appears to be available only above this capacity.
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NOTE: Delete optional wording in eighth sentence
when steel plant only is required. This
specification is structured for steel plant only,
concrete plant only, or steel or 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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The annular zone between the inner and outer walls shall be the aeration
chamber and the aerobic digester zone, and may also have a chlorine contact
zone. The inner circular tank shall be the settling tank. The aeration
zone shall have an influent distribution channel (influent launder) for the
uniform distribution of the raw sewage. The settling tank shall have an
effluent launder for the uniform collection of the clarified liquid from
SECTION 11375N
Page 33
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