Page 471 - Water and wastewater engineering

11-44 WATER AND WASTEWATER ENGINEERING

TABLE 11-11
Design criteria for deep-bed monomedium filters
Reported range
Parameter of values Recommended

Anthracite coal
Effective size 0.9–1.0 mm
Uniformity coefficient 1.4–1.7
Shape factor (f) 0.46–0.73
Specific gravity 1.45–1.75
Porosity 0.53–0.60
Depth of medium 0.9–1.8 m
Filtration rate 10–25 m/h 15 m/h
Backwash rate 37–45 m/h
Backwash duration a 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 No
Block Yes
Air scour Yes
3
Air scour 0.6–1.5 m /min · m 2
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.

TABLE 11-12
Wash trough design criteria
Parameter Criterion
Length 6m
Interval Particle travel distance 1 m
Height to weir edge
Sand filter Expansion depth of trough 0.15 to 0.3 m
Anthracite 1.1–1.2 m
Freeboard 5 cm
Installation Weirs level

Sources: Castro et al., 2005; Cleasby and Logsdon, 1999; GLUMRB, 2003.