Page 480 - Water and wastewater engineering

GRANULAR FILTRATION 11-53

Gullet dimensions
Backwash water volume
Backwash tank volume
Maximum allowable filtration headloss
Depth of filter box
Backwash tank low water elevation

11-27. Design the structural components of a dual-media rapid filter for the city of Apple
3
Valley. The maximum day flow rate is 45,000 m /d. The design criteria and media
analyses are given below. Assume a 525 mm diameter pipe from the gullet is to carry
the wash water at a velocity of 1.5 m/s. Verify that the sand meets the GLUMRB
recommendations for E and U. Adjust the grain size distribution if the sand does not
meet the specification. Also verify that largest grain size anthracite coal will have the
same approximate settling velocity as the finest sand grain size.
Filtration rate 15 m/h
Water temperature 12 C
Backwash 85 m/h
Trial gullet width 0.8 m
Underdrain 30 cm deep fine screen
Gravel support none required
Surface wash revolving arms at GLUMRB recommended rate
Air scour at GLUMRB recommended rate

Media characteristics
Parameter Sand Anthracite coal
Depth 0.30 m 0.50 m
Sand specific gravity 2.65 1.60
Shape factor 0.75 0.75
Stratified bed porosity 0.47 0.60

Media analysis
Sand Anthracite
U.S. Standard mass percent coal mass percent
Sieve No. retained retained
4–7 9.9
7–8 13.0
8–10 28.0
10–12 20.0
12–14 13.3
14–16 8.62 (continued)