Civil Engineering Reference
In-Depth Information
Drainage
Basins should be provided with a means for dewatering. Basin bottoms
should slope toward the drain at a slope of not less than 1 in 12 where mechanical
sludge collection equipment is not used. Minimum diameter of the drain line is 8
inches (200 mm).
Overflow
An overflow weir (or pipe) should be installed that will establish the max-
imum water level desired on top of the filters. It should discharge with a free fall at
a location where the discharge will be seen.
Inlet-to-Outlet Distance
The minimum horizontal distance from basin inlet to out-
let should be 10 feet (3.0 m).
Safety
Permanent ladders or handholds should be provided for safety on the inside
walls of basins above the water level. Guardrails should be included. Flushing lines
or hydrants should not include interconnection of the potable water with nonpotable
water.
Sludge Collection
Mechanical sludge collection equipment should be provided.
Sludge Disposal
Provision should be made for the operator to observe or sample
sludge being withdrawn from the unit.
Solids Contact Units
Units are acceptable for combined softening and clarification where water character-
istics are not variable, and flow rates are uniform. The units should be designed for
the maximum uniform rate and should be adjustable to changes in flow that are less
than the design rate and for changes in water characteristics. A minimum of two units
is recommended.
Installation of Equipment
A manufacturer's representative should supervise instal-
lation and initial operation of all mechanical equipment. There should be adequate
piping with suitable sampling taps so located as to permit the collection of samples
of water from critical portions of the units.
Chemical Feed
Chemicals should be applied at such points and by such means as
to ensure satisfactory mixing of the chemicals with the water.
Mixing
Mixing devices employed should be so constructed as to:
Provide good mixing of the raw water with previously formed sludge particles.
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Prevent deposition of solids in the mixing zone.
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Flocculation
Flocculation equipment should have the following features:
Be adjustable for varying energy input.
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Provide for coagulation to occur in a separate chamber or baffled zone within the
unit.
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Provide a flocculation and mixing period of not less than 30 minutes.
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