Water and Wastewater Engineering - Sciences Club

11-42 WATER AND WASTEWATER ENGINEERING
TABLE 11-9
Design criteria for dual-media filters
Parameter
Reported
range
GLUMRB
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
Sand on bottom
0.4–0.6 m
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
Surface wash rate
10–20 min �15 min
Revolving arms 1.2–1.8 m/h �1.2 m/h
Fixed arms
Underdrain
4.9–10 m/h �4.9 m/h
Pipe lateral Yes
Block Yes
Air scour No—if total depth of medium
�0.75 m
Air scour 0.6–1.5 m 3 /min · m 2 if total
medium depth � 1 m
a
A ctual 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.