Water and waste water engineering

2. Types of Treatment Based on impurities
No Type of Treatment Name of Unit Function
1. Physical Treatment Screen Large suspended and
floating matter
Grit Chamber Grit
Clarifier's Silt, Sand and Other
heavier matter
2. Chemical Treatment Chemical Reactor Dissolved chemicals
3. Biological Treatment Trickling filter Dissolved organic
chemicals
Activated sludge plant
Rotating biological contactors
Digesters

3. Unit operation in waste water treatment
GC PST TF SST DU
Recycle
SDT
S
SDB
From outfall sewer
Sludge flow
Digested sludge
Disposal
Preliminary
Treatment Treatment Treatment
SecondaryPrimary

4. S = Screen Chamber
GC = Grit Chamber
PST = Primary Sedimentation Tank
TF = Trickling Filter
DU = Disinfection Unit
SST = Secondary Sedimentation Tank
SDB = Sludge Drying Beds
SDT = Sludge Digestion tank

5. Design of Bar Screen
1. Peak wet weather flow
2. Peak dry weather flow
3. Hydraulic Design of influent condition
4. Treatment plant design criteria specified by bureau of Indian
standard
5. Equipment, manufactures, their specifications
6. Velocity through bar
7. Information on existing facility plant is to be expanded
8. Bar spacing & head loss constraint through rack & plant
9. Existing site plan with contour
10. Velocities through screen chamber

6. Design Criteria for horizontal Grit
Chamber
1. Detention time 40 to 60 sec
2. Horizontal flow velocity 15 to 30 cm/s
3. Surface overflow ratio = 500 to 1500 m3/m2/day.
4. Length to Breadth Ratio = 6 to 15
5. Length to Depth Ratio = 10 to 30
6. Depth = (1.5 to 2) + free board
7. Free Board = 0.75 to 1m

7. Design criteria for Aerated grid chamber
No Design Parameter Range Remarks
1. Dimension
Depth
2 to 5m Width of Basin is
limited to prevent
turbulence in TankLength 7.5 to 20m
Width 2.5 to 7m
w/d Ratio 1.1 to 5.1
2. Transverse Velocity
at Surface
0.6 to 8 m/s
3. Detention Time 2 to 5min If GC is used to
remove grit <0.2mm
4. Air Supply 4.6 to 12.4 litre/ second /meter
length of tank

8. Design of Primary Sedimentation Tanks
1. Surface Over Flow rate (m3 /m2/day)
(a) Primary Clarification to Secondary Treatment
(a) Avg flow = 30 to 50
(b) Peak flow = 70 to 130
(b) Primary Clarification with waste activated sludge return
(a) Avg flow = 25 to 35
(b) Peak flow = 45 to 80
2. Detention Period = 4 to 8 hours
3. Velocity of flow = 15 to 30 cm/min
4. Weir loading rate = < 370 m3/m2/day.

9. 5. Dimension
Dimension
Rectangular
Length 10 to 100m
Width 3 to 24m
l/w ratio 1 to 75m
l/d ratio 4 to 25m
Side water depth 2.5 to 3m
Circular
Diameter 3 to 60m
Side water depth 3 to 6m

10. Thank You
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