l07 Filtration

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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.

l07 Filtration

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