Page 474 - Water and wastewater engineering

GRANULAR FILTRATION 11-47

With the use of this text, you should be able to do the following:

9. Perform a grain size analysis and determine the effective size and uniformity coef-
ficient.

10. Calculate the headloss through a clean stratified filter bed and determine if it is
excessive.
11. Calculate the depth of an expanded filter bed during backwash and locate the backwash
trough elevation with respect to the top of the filter bed during filtration.
12. Calculate the number and size of filter beds given the maximum day flow rate and the
filtration rate.

13. Calculate the equivalent diameter for a filter media having a specific gravity different
from sand.
14. Design a backwash system including the layout for the placement of backwash troughs,
size of the troughs, trough elevation, and the volume of backwash tank.
15. Determine gullet dimensions (depth and width) given the length, backwash flow rate,
and wash water velocity in the effluent pipe.
16. Calculate the maximum headloss that can be achieved without creating a negative pres-
sure in the filter media.

11-9 PROBLEMS
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11-1. For a flow of 0.8 m /s, how many rapid sand filter boxes of dimensions 10 m 20 m
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3
are needed for a hydraulic loading rate of 110 m /d · m ?
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11-2. If a dual-media filter with a hydraulic loading rate of 300 m /d · m were built instead
of the standard filter in Problem 11-1 , how many filter boxes would be required?
11-3. The water flow meter at the Troublesome Creek water plant is malfunctioning. The
plant superintendent tells you the four dual media filters (each 5.00 m 10.0 m) are
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loaded at a velocity of 280 m/d. What is the flow rate through the filters in m /s?
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11-4. A plant expansion is planned for Urbana. The new design flow rate is 1.0 m /s.
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2
A deep bed monomedia filter with a design loading rate of 600 m /d · m of filter
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is to be used. If each filter box is limited to 50 m of surface area, how many filter
boxes will be required? Check the design loading with one filter box out of service.
Propose an alternative design if the design loading rate is exceeded with one filter
box out of service.
11-5. The Orono Sand and Gravel Company has made a bid to supply sand for Eau Gaul-
lie’s new sand filter. The request for bids stipulated that the sand have an effective
size in the range 0.35 to 0.55 mm and a uniformity coefficient in the range 1.3 to 1.7.
Orono supplied the following sieve analysis as evidence that their sand will meet the
specifications. Perform a grain size analysis (semilog plot) and determine whether or
not the sand meets the specifications. Use a spreadsheet program you have written to
plot the data and fit a curve.