Page 470 - Water and wastewater engineering

GRANULAR FILTRATION 11-43

TABLE 11-10
Design criteria for tri-media filters
Reported
Parameter range Recommended

Anthracite coal on top
Effective size 0.9–1.4 mm
Uniformity coefficient 1.4–1.75
Shape factor (f) 0.46–0.73
Porosity 0.53–0.60
Specific gravity 1.45–1.75
Depth of medium 0.4–0.5 m
Sand in middle

Effective size 0.45–0.55 mm
Uniformity coefficient 1.4–1.65
Shape factor (f) 0.7–0.95
Porosity 0.4–0.47
Specific gravity 2.65
Depth of medium 0.15–0.3 m
Garnet on bottom
Effective size 0.20–0.35 mm
Uniformity coefficient 1.2–2.0
Shape factor (f) 0.6
Specific gravity 3.6–4.2
Depth of medium 0.075–0.15 m
Filtration rate 10–25 m/h 15 m/h
Backwash rate 37–45 m/h
a
Backwash duration 10–20 min 15 min
Surface wash rate
Revolving arms 1.2–1.8 m/h
Fixed arms 4.9–10 m/h
Underdrain
Pipe lateral Yes
Block Yes
Air scour No—if total depth of medium
0.75 m
2
3
Air scour 0.6–1.5 m /min · m if total medium
depth 1 m
a
Actual off -line time will be 30 min because of the time required to drain the filter and gradually come
up to the full backwash rate. An additional 30–40 minutes off-line is required for “filter-to-waste” to
clear the bed of wash water and dislodged turbidity. If air scour is provided, the time will be even longer
because of the necessity of sequencing the air scour and wash water.
Sources: Castro et al., 2005; Cleasby and Logsdon, 1999; Kawamura, 2000; MWH, 2005; Reynolds and
Richardson, 1996.