Circular Clarifiers for the treatment of waste water

1. Clarifiers
Presented By:
Ghulam Murtaza
Presented To:
Engr. Waqas Qamar
Roll No:
12063123-046

2. Contents……
 What is clarifier???
 Types of Clarifier
 Working Principle
 Primary Clarifier
 Sludge Process

3. Continu…..
 Secondary Clarifier
 Designing Parameters (Calculations)

5. What is clarifier???
 Clarifiers are settling tanks built for continuous removal of
solids being deposited by sedimentation.
 A clarifier is generally used to remove solid particulates or
suspended solids from liquid for clarification.

6. Types of Clarifiers
There are two types of Clarifiers
 Rectangular Clarifiers
 Circular Clarifiers
 Inclined Plate Clarifiers

7. Effluent
Launder
Effluent
Weir
Scum
Trough
Flights
Drive
Unit
Drive
Chain
Drive
Gear
Idler
Sprockets
Sludge
Withdrawal
Pipe
Sludge
Trough
Inlet
Baffle
Inlet
Rectangular Clarifier

8. Overflow Box
Clarifier
Influent
Sludge Discharge
Clarifier
Effluent
Sludge
Hopper
Flocculation Tank
Flash
Mix Tank
Coagulant
Feed
Feed Box
Discharge FlumesDistribution Orifice
Inclined Plates
Inclined Plate Clarifier (Lamella)

9. Circular Clarifiers Operation
 Circular clarifiers use slowly rotating rake arms to separate
solid particulate.
 A liquid feed with suspended solids is fed into a tank with
a diameter of 5 to 500 feet.
 As the particles settle, angled rake arms move the
concentrated slurry toward the center of the tank, where it
is removed.

10. Primary Clarifier
 Primary clarification is the physical treatment process of
removing solids before biological treatment.
 Floatable material (scum) are removed from the surface by
skimmers and settle able solids (sludge) are collected on
the bottom by a rakes.
 The expected range for percent removal in a primary
clarifier is 90%-95% settle able solids, 40%-60%
suspended solids

13. Activated sludge Process
 The activated sludge process is widely used for biological
wastewater treatment all over the world.
 An activated sludge wastewater treatment system always has an
aeration tank and secondary clarifier, which function as a unit to
remove organic matter and suspended solids from the
wastewater.

16. Secondary Clarifier
 Microorganisms such as bacteria and protozoa can use the small
particles and dissolved organic matter not removed in primary
clarifier as food.
 In a secondary clarifier which operates in the same manner as the
primary clarifier described previously. Some of the solids
collected in the secondary clarifier (return activated sludge) are
sent back to the aeration tank.

17. Cont….
 secondary clarifier effectively separates the biological floc
and colloidal solids to produce wastewater with very low
levels of organic material and suspended matter.

19. Efficiency of solid Removal related to
Characteristics of solid
 Stokes law
VF = Fall Velocity
(ρ - ρo) = Density difference between particle and water
n = viscosity of water
g = gravitational acceleration constant
d = diameter of the particle

20. Particle Size versus Settling Time
Particle Size
mm
Order of Size Time to Settle
1.0 Coarse Sand 3 Seconds
0.1 Fine Sand 38 Seconds
0.01 Silt 33 Minutes
0.001 Bacteria 55 Hours
0.0001 Colloidal 230 Days
0.00001 Colloidal 6.3 Years

21. Calculations (Designing Parameters)
 Hydraulic Loading
 Solid Loading

22. Hydraulic Loading
 Detention Time (DT)
The time it takes for a water to
travel from inlet to outlet.
Typical Design Value = 2 – 3 Hours

23. Calculate the Detention Time in HOURS for a clarifier with a
volume of 25,000 gallons that receives a flow of 310,000
gal/day.
Detention Time =
Volume
Flow
=
25,000 gallons
310,000 gallons/day
= 0.08 Days
0.08 Days X 24 hours/days = 1.9 Hours

24. Hydraulic Loading
 Surface Overflow Rate
The flow in gallons per day into
the clarifier per square foot of surface area.

25. Continu……..
SOR, gpd/ft2 =
Flow, gallons/day
Surface Area, ft2
Typical Design Value = 400 - 800 gal/day/ft2

26. SOR, gpd/ft2 =
Flow, gallons/day
Surface Area, ft2
Calculate the Surface Overflow Rate for a clarifier that is 50 ft
long, 15 ft wide, 12 ft deep, and receives a flow of 338,000 gallons
per day.
= 50 ft. X 15 ft. = 750 ft2Surface Area, ft2
338,000 gallons per day
750 ft2
SOR, gpd/ft2 =
= 451 gpd/ft2

27. Solid Loading
The pounds per day of solids in the clarifier influent per
square foot of surface area.
Typical Design Value = Max 30 lbs./d/ft2

28. Pounds =
Concentration
Of STUFF
In the
Water
Conc. x Flow (or Volume) x 8.34 Lbs./gallon
X
Quantity
Of Water
The STUFF
Is In
Weight
Of The
Water
X
“Pounds Equation”

29. SLR, lbs./d/ft2 =
Solids, lbs./day
Surface Area, ft2
Calculate the Solids Loading Rate for a clarifier with a 50 ft diameter
and a depth of 12 feet, and receives a flow of 2.4 MGD with a
suspended solids concentration of 1800 mg/L.
SA = 3.14 X 25 ft. X 25 ft. = 1962.5 ft2
1800 mg/L X 2.4 MGD X 8.34 lbs./gal = 36,029 lbs./d
36,029 lbs./day
1962.5 ft2
= 18.4 lbs./d/ft2
Solids, lbs./day =
SLR, lbs./d/ft2 =