Page 438 - Water and wastewater engineering

GRANULAR FILTRATION 11-11

0.0
Natural sand
0.2 E = 0.44,
U = 3.0

Depth, m 0.4 Filter sand
E = 0.50,
U = 1.35
0.6
0.8 Monodisperse sand
E = 0.61, U = 1.0
1.0
0.0 0.2 0.4 0.6 0.8 1.0
Filtrate quality, C/C o
FIGURE 11-5
Effect of media uniformity on solids penetration in
filter bed.
( Source: MWH, 2005.)

0.0
Monomedia,
= 1
0.5 Monomedia,
Depth in filter, m 1.0
= 0.25

Dual media,
= 1 Anthracite
1.5
sand
Dual media,
= 0.25
2.0
0.0 0.2 0.4 0.6 0.8 1.0
Particle concentration, C/C o
FIGURE 11-6
Effect of attachment efficiency on effluent from
monomedia and dual-media filters.
( Source: MWH, 2005.)

The rate expression describes a first-order removal with depth proportional to the local par-
ticle concentration in the water:
C
C (11-4)
z

where C concentration of particles in suspension, mg/L
1

filter coefficient, m
z depth in filter, m
Based on laboratory and pilot scale studies, the filter coefficient is inversely proportional to the
filtration rate, grain size, and the square of the viscosity (Cleasby and Logsdon, 1999).