Page 477 - Water and wastewater engineering

11-50 WATER AND WASTEWATER ENGINEERING

Sand analysis

U.S. Standard Mass percent
Sieve No. retained
8–12 0.01
12–16 0.39
16–20 5.70
20–30 25.90
30–40 44.00
40–50 20.20
50–70 3.70
70–100 0.10

11-11. Determine the height of the expanded bed for the sand used in Problem 11-10 if the
backwash rate is 1,000 m/d.
11-12. The rapid sand filter being designed for Laramie has the characteristics shown below.
Using the Rose equation, determine the headloss for the clean filter bed in a stratified
condition.

Depth 0.75 m
2
3
Filtration rate 230 m /d · m
Sand specific gravity 2.80
Shape factor 0.80
Stratified bed porosity 0.50
Water temperature 5 C

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

8–12 0.00
12–16 0.40
16–20 13.10
20–30 54.50
30–40 30.20
40–50 1.785
50–70 0.015

11-13. Determine the maximum backwash rate and the height of the expanded bed for the
sand used in Problem 11-12 .

11-14. As noted in Example 11-2 , the headloss was too high. Rework the example without
the 100–140 sieve fraction to see how much this would improve the headloss charac-
teristics. Assume that the fraction above sieve size number 8 does not contribute to
the headloss and that recalculation of the percentages is not required.