2025 Nelsen Corporation Catalog - Catalog - Page 430
17 Multi-Media Depth Filter Design Parameters/Activated Carbon Bed Contact Times
Technical & Engineering
Design parameters of a typical multi-media depth filter are as follows:
Bed Depth................................................................................................................................................................................... 30 - 39 inches – 5 Layers
Bottom Layer...............................................................................................Gravel 1/4" x 1/8", Larger tanks have a combination
(support bed) ............................................................................................................................................... of 1/2" x 1/4" and 1/4" x 1/8" Gravel
Fourth Layer .................................................................................................................................................................................................................. #8-12 Garnet
Third Layer..............................................................................................................................................................................................................#30 - 40 Garnet
Second Layer..................................................................................................................................................................................... Filter Sand – .45 - .55
Top Layer ................................................................................................................................................................................................ Anthracite or Filter-Ag
Backwash Rate................................................................................................................................................................................................13-18 gpm/sq. ft.
Service Flow Rate..............................................................12 gpm/sq. ft. or higher, depending upon local conditions
A support bed is mandatory and
a specially designed distributor to
handle high backwash rates.
MEDIA IN POUNDS
100 lbs/cu. ft.
140 lbs/cu. ft.
130 lbs/cu. ft.
100 lbs/cu. ft.
50 lbs/cu. ft.
25 lbs/cu. ft.
130 lbs/cu. ft.
Gravel
Garnet #8-12
Garnet #30-40
Sand .45 - .55
Antracite
Filter Ag
Garnet #30-40
An effluent water quality will be in
the 10-20 micron range.
– 50 lbs./bag
– 50 lbs./bag
– 50 lbs./bag
– 50 lbs./bag
– 50 lbs./bag
– 25 lbs./bag
– 50 lbs./bag
Multi-Media Filter Loading Table in Pounds
Tank Diameter, Inches
Tank Height, Inches
10
44/54
12
48
13
54
14
65
Anthracite
Filter Ag
25
12.5
50
20
50
25
50
30
Filter Sand
35
50
50
100
16
65
18
65
21
62
24
72
30
72
36
72
42
72
48
72
100
50
150
75
250
100
350
150
450
225
600
300
800
400
150
200
300
400
700
800
1000
100
100
200
300
500
600
800
50
50
100
200
200
300
400
—
50
—
100
—
100
200
100
300
100
400
200
600
300
Top Layer (Select One)
100
45
Second Layer
100
Third Layer
25
Garnet, #30-40
25
50
75
100
Fourth Layer
20
Garnet, #8-12
25
25
25
50
Bottom Layer
—
12.5
Gravel, 1/2 x 1/4
Gravel, 1/4 x 1/8
—
20
—
25
—
25
—
50
Activated Carbon Systems - Determining System Size
for Necessary Contact Times
Step 1: Determine exactly what the contaminant is and whether or not there are other factors
that will influence the carbon's effectiveness.
Step 2: Identify the contact time best suited for the contaminant.
(See chart to the right for typical EBCTs - Empty Bed Contact Time)
Step 3: Correspond the required time to the EBCT (minutes) and read across the "Service Flow
Rates" row to desired flow rate. Follow the column down to the required tank size best
suited to your application.
Contaminant
EBCT Minutes
Free Chlorine
1-2
Taste/Odor
3-5
MTBE
9-13
Chloramines
5**
Iron
4**
Hydrogen Sulfide
3**
**w/Catalytic Carbon
Activated Carbon Bed Contact Times
Tank Diameter, Inches
Cubic Foot Load
10
1
12
2
2
Empty Bed Contact
3
Times @ flow rate
through 1 sq. ft. of bed
5
area in minutes
9
Backwash Flow Rate - (GPM)
3.7
2.5
1.5
0.8
4
7.5
5
3
1.6
7
17 - 10
13
2.5
14
16
18
3.5
4
5
Service Flow Rates - GPM
9.5
11.2
15
19
6.3
7.5
10
12
3.8
4.5
6
8
2.0
2.5
3.3
4
9
10
15
15
21
7
24
10
30
15
36
20
42
30
48
40
30
20
12
6.6
30
37
25
15
8
50
56
37
22
12
50
74
50
30
16
70
111
45
45
24
95
148
100
60
32
125
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