Page 469 - Water and wastewater engineering

11-42 WATER AND WASTEWATER ENGINEERING

TABLE 11-9
Design criteria for dual-media filters
Reported GLUMRB
Parameter range recommendation Recommended

Anthracite coal on top
Effective size 0.9–1.4 mm 0.8–1.2 mm
Uniformity coefficient 1.3–1.8 1.85
Shape factor (f) 0.46–0.73
Porosity 0.53–0.60
Specific gravity 1.45–1.75
Depth of medium 0.4–0.6 m
Sand on bottom
Effective size 0.35–0.7 mm 0.45–0.55 mm
Uniformity coefficient 1.3–1.8 1.65
Shape factor (f) 0.7–0.95
Porosity 0.4–0.47
Specific gravity 2.65
Depth of medium 0.3–0.75 m 0.6 m and 0.76 m
Filtration rate 7–20 m/h 15 m/h
Backwash rate 30–60 m/h 24 m/h
Backwash duration a 10–20 min 15 min
Surface wash rate
Revolving arms 1.2–1.8 m/h 1.2 m/h
Fixed arms 4.9–10 m/h 4.9 m/h
Underdrain
Pipe lateral Yes
Block Yes
Air scour No—if total depth of medium
0.75 m
3
2
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; GLUMRB, 2003; Kawamura, 2000; MWH, 2005; Reynolds and
Richardson, 1996.