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.01 .1 1 5 10 50 90 95 99 99.9 99.990.1
1
10
Percent of Media with Smaller Diameter
Naturally Occurring Sand
Processed Filter Sand
20 30 70 80
ParticleDiameter,mm
Size Distribution of Typical Naturally Occurring and Processed Filter Sand
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Typical properties of filter media used in rapid filters*
PROPERTY UNIT GARNET LLMENITE SAND ANTHRACITE GAC
Effective Size, ES mm 0.2 - 0.4 0.2 - 0.4 0.4 - 0.8 0.8 - 2.0 0.8 - 2.0
Uniformity Coefficient,
UCUC 1.3 - 1.7 1.3 - 1.7 1.3 - 1.7 1.3 - 1.7 1.3 - 2.4
Density, g/mL 3.6 - 4.2 4.5 - 5.0 2.65 1.4 - 1.8 1.3 - 1.7
Porosity, % 45 - 58 Not available 40 - 43 47 - 52Not
available
Hardness Moh 6.5 -7.5 5.6 7 2 - 3 Low
* = Not Available
Figure by MIT OCW.
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5 4 3 2 1
Section through filterPressure at Bottom of Media (m of water)
0
0
D
D
Head Curves - as Filter
Becomes Dirty
Head Curve -
Clean Filter
Head Curve - No Flow
Depth Over
which Negative
Pressure Occurs
Curve Representing
Increase in Depth to
Lines 1 to 5 represent the changes in pressure through the filter as the media becomes blinded.
Line 5 results in the development of negative pressures within the media.
MEDIA
Clean Sand with Time
DepthofWater(m)
DEVELOPMENT OF NEGATIVE PRESSURE IN THE RAPID GRAVITY FILTER
WATER
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100
10-1
10-2
10-3
10-4
10-5
10-6
10-8 10-7 10-6 10-5 10-4
Sedimentation = 2650 kg/m3
Sedimentation = 1050 kg/m3
Sum 2
Sum 1
Interception
Particle Diameter, m
Diffusion
TransportEfficiency
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10-2 10210-4
10-3
10-2
10-1
10-1 1
1
10
40
60
80
100
Experimental Data
Th ti l M d l
d = 0.397 mm
oC
f = 0.36
v0 = 2 gpm / sq.ft.
a = l (assumed)
Experimental Data
Theoretical Model
T = 23
L = 5.5 in.
RemovalEfficiencyofFilter(%)
Single-CollectorEfficiency
Comparison of Theoretical Model and Experimental Data
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70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
0 0.5 1
0 0.5 1
Depth(cm)
Sand
Anthracite
= 1.0
= 0.1
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Filter Media
Graded Gravel
Underdrain
30 in. max
24 to 30 in.
8 to 16 in.
Wash Trough
Cross Section of a Granular- Media Gravity Filter
Figure by MIT OCW.
S JSIM 2001 D t b J Ad d E i t l E i t Th U d d i
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2
Slit platesGravel layer
Beams
Porous concrete
layer
Figures by MIT OCW.
Wash Trough
Typical Pipe Lateral Underdrain Installation
Filter Media
Manifold
Pipe Laterals
Waste Gullet
Source: F.B. Leopold Company, 2003. Filtration, The Process, Underdrain Types.
http://www.fbleopold.com/water/filtration/underdrain.htm. Accessed February 21, 2005.
Source: JSIM, 2001. Database on Japanese Advanced Environmental Equipment, The Underdrain
System for Rapid Filter and GAC Adsorption Filter. Japan Society of Industrial Machinery
Manufacturers. http://nett21.gec.jp/JSIM_DATA/WATER/WATER_6/html/Doc_307.html. Accessed February 21, 2005.
Source: F.B. Leopold Company, 2003. Filtration, The Process, Underdrain Types.
http://www.fbleopold.com/water/filtration/underdrain.htm. Accessed February 21, 2005.