TM 5-813-3/AFM 88-10, Vol 3
including gullet, will be approximately 14 feet by 18
Use double, V-notch, effluent weirs with in-
feet, Use vitrified clay tile or similar underdrains and
board, effluent launder.
gravel layer as recommended by manufacturer. Pro-
Approximate total weir length, each basin: 225
vide rate controllers and filter level control equip-
ment. Establish overall depth of filter cell at 15 feet.
Assume an arbitrary operating floor elevation of 15
Flocculator units should have variable speed drives
feet. Significant filter elevations and related depths
and be powered to yield a G value of approximately 50
will be approximately as follows:
see-l at mid-speed and a water temperature of 50F.
Elevation, ft.
Filter cell bottom
0.00
Provide piping and valves so that either basin can be
Top of underdrains (+ 10")
0.83
bypassed while maintaining following secondary units
1.67
Top of gravel (+ 10")
in service. Provide basin overflow and basin cover
Top of coarse sand (+ 4")
2.00
structure if climatic conditions require. Provide basin
2.67
Top of filter sand ( + 8")
sludge withdrawal piping to point of sludge disposal.
Top of anthracite (+20")
4.33
Sludge pumps will be required if gravity sludge flow is
Bottom of surface wash equip
not feasible.
ment(+2")
4.50
f. Second-stage flow division structure. Provide sec-
5.67
Bottom of troughs (+ 14")
ond-stage flow division structure identical to first-
Operating water level (7' above
stage. This structure allows combining the flows from
11.33
anthracite)
the two, parallel-operating, first-stage sedimentation
Depth of water above bottom of filter cell =
units followed by their division into two equal flows,
11.33-0.0000 = 11.33 ft.
which are then directed to the second-stage rapid-mix
Freeboard = 15.00-11.33 = 3,67 ft.
basins. Use of this flow division structure provides
All four filters, each operated at 2 gpm per square
maximum flexibility and optimum use of plant facili-
ties when one first- or second-stage rapid mix or floc-
(4)(14)(14)(2)(1440)
foot, theoretically will produce
culator-clarifier is out of service for repair or mainte-
106
nance.
or 2.25792 million gallons of water in 24 hours. As-
g. Second-stage mixing and sedimentation.
suming two filters washed at 15 gpm per square foot
(1) Rapid mix. Provide two second-stage rapid-
for 15 minutes each in each 24-hour period, wash wa-
mix units identical to those used for first-stage rapid
mixing.
(2) Flocculation-sedimentation. Provide two me-
chanically equipped, circular, flocculator-clarifiers
million gallons for normal backwash, or about 4 per-
identical in size to those used in the first-stage. These
cent of production. Surface washing will require an
units will provide 30 minutes flocculation time and 3
hours sedimentation time. Total time for flocculation,
(2)(14)(14)(0,5)(15)
additional
or 0.00294 million
both stages, is 60 minutes. Total sedimentation time,
106
both stages, is 6 hours.
gallons. Total down-time, each filter, is assumed to be
h. Filtration. Determine number of filter units.
20 minutes. The theoretical net water production for
delivery to service will be as follows:
-- Theoretical total production 2.25792 mgd
Filter configuration will consist of two filters, side by
Less due to filter down-time 0.01568
side, along both sides of a gallery sized to accommo-
Less wash water required
date filter piping, valves controls, etc. Main influent
Net theoretical production
header pipe will be sized for a velocity not to exceed
2,1511 mgd
available for service
1.5 feet per second. Calculated pipe diameter is 20.4
Under actual operating conditions, with the filter-rate
inches. Use 24-inch pipe giving actual velocity of 1.08
and level control equipment specified, the filters re-
feet per second. Use 12-inch pipes to supply individual
maining in service will automatically compensate for
filters. At a rate of 2 gmp per square foot, total filtra-
production lost as a result of a filter being out of serv-
tion area required will be 1530/2 or 765 square feet or
ice for washing or repair, Level control insures that fil-
191 square feet of medium area per filter. Provide 14
ter outflow will always match inflow. In addition to
feet by 14 feet medium area. Use dual-media filters
flow and level control equipment, provide automatic
with 8 inches of filter-grade sand, 4 inches of coarse
filter shut-off and alarm equipment, to be activated at
sand, and 20 inches of filter-grade anthracite,
maximum allowable clearwell level, and also provide
equipped with rotary surface wash. Actual filter cells,
filter high-level alarm. Provide all essential piping,
B-3
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