2.6 Design of Diffuser Wall

Diffuser wall divides the flocculation tank from the clarifier. Suitable numbers of openings are provided in the diffuser wall through which water after flocculation enters the clarifier. Design criteria governing the design of Diffuser Wall and the values adopted are as follows:

Design Parameter
Ref 1
Adopted
Opening Area
(As percentage of flow Crossection)
2 – 5

Velocity through Orifice

- Dividing ist & 2nd Floc Basin
- Dividing Floc & Sedimentation Basin


0.55 M/s
0.35 M/s



0.35 M/s
Headloss Across Baffle
- Dividing ist & 2nd Floc Basin
- Dividing Floc & Sedimentation Basin

7 - 9 mm
3 – 4 mm


4 mm
Submergence of highest port
15 mm

Clearance below baffle for sludge
25 mm

1. Water Treatment Principles & Design by MWH (P -765)

Design

Velocity through orifice = 1.15 Ft /s

Flow = 11.67 Cusecs

Total Flow Area = 11.67 /1.15
= 10.14 Ft2

Area of each opening = 5 % of the flow Area
= 0.05 x 10.14
= 0.507 Sft
Diameter of each opening = (0.507 x 4 / 3.14)1/2
= 0.80 Ft
= 9.5 “
No of diffuser openings = 10.14 / 0.49
= 21

Perimeter of the Clarifier = 3.14 x 33.17
= 104.15 Ft

Spacing between the diffuser openings (Center / Center) = 104.15 / 21
= 4.95 Ft
= 5.0 Ft

21 diffuser openings each of 9.5“diameter shall be provided all around the diffuser wall at 5.0 Ft Center to Center. All diffuser openings shall be located 7’-0” above the floor of the Flocculator.