ClarifiersPresented By:

Ghulam Murtaza

Presented To:

Engr. Waqas Qamar

Roll No:

12063123-046

Contents……

What is clarifier???

Types of Clarifier

Working Principle

Primary Clarifier

Sludge Process

Continu…..

Secondary Clarifier

Designing Parameters (Calculations)

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.

Types of Clarifiers

There are two types of Clarifiers

Rectangular Clarifiers

Circular Clarifiers

Inclined Plate Clarifiers

Effluent

Launder

Effluent

Weir

Scum

TroughFlights

Drive

Unit

Drive

Chain

Drive

GearIdler

Sprockets

Sludge

Withdrawal

Pipe

Sludge

Trough

Inlet

BaffleInlet

Rectangular Clarifier

Overflow Box

Clarifier

Influent

Sludge Discharge

Clarifier

Effluent

Sludge

Hopper

Flocculation Tank

Flash

Mix Tank

Coagulant

Feed

Feed BoxDischarge FlumesDistribution Orifice

Inclined Plates

Inclined Plate Clarifier (Lamella)

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.

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

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.

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.

Cont….

secondary clarifier effectively separates the biological floc

and colloidal solids to produce wastewater with very low

levels of organic material and suspended matter.

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

Particle Size versus Settling Time

Particle Size

mmOrder 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

Calculations (Designing Parameters)

Hydraulic Loading

Solid Loading

Hydraulic Loading

Detention Time (DT)

The time it takes for a water to

travel from inlet to outlet.

Typical Design Value = 2 – 3 Hours

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

Hydraulic Loading

Surface Overflow Rate

The flow in gallons per day into

the clarifier per square foot of surface area.

Continu……..

SOR, gpd/ft2 = Flow, gallons/day

Surface Area, ft2

Typical Design Value = 400 - 800 gal/day/ft2

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 ft2SOR, gpd/ft2 =

= 451 gpd/ft2

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

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”

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 =