Page 479 - Water and wastewater engineering

11-52 WATER AND WASTEWATER ENGINEERING

below. Assume a 375 mm diameter pipe from the gullet is to carry the wash water at
a velocity of 1.2 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.

Depth 0.50 m
3
2
Filtration rate 150 m /d · m
Sand specific gravity 2.65
Shape factor 0.75
Stratified bed porosity 0.40
Water temperature 10 C
Trial backwash velocity 65 m/h
Trial gullet width 0.5 m
Underdrain 30 cm deep filter block with 1 mm orifice
Gravel support 32 cm in 4 layers
Surface wash revolving arms at GLUMRB recommended rate

Sand analysis
U.S. Standard Mass percent
Sieve No. retained

10–14 2.0
14–20 16.5
20–25 15.4
25–30 38.2
30–35 15.9
35–40 6.5
40–50 4.4
50–60 1.0

0.5
NOTE: geometric mean diameter of successive sieves is d g ( d 1 d 2 ) .

The following is to be provided to complete this portion of the filter design:
Clean bed headloss
Backwash velocity
Depth of expanded bed
Number of filter beds
Area of an individual filter bed
Plan dimensions
Backwash trough layout
Maximum backwash water trough flow rate
Backwash trough dimensions
Backwash trough weir elevation above undisturbed bed