clarifiers

CLARIFIERSCLARIFIERS

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit

Provide Quiescent Area

Separation of Solids

FloatableSettleable

ClarifiersSedimentation Basins

Settling Tanks

CLARIFIERSCLARIFIERS

Clarifiers

Efficiency of Solids Removal Related To:

1. Characteristics of the Solids

2. Characteristics of the Water

3. Characteristics of the Clarifier

StokeStoke’’s Laws Law

2(p - po)g 9n

(d/2)2VF =

VF = Fall Velocity(p - po) = Density difference between

particle and watern = viscosity of waterg = gravitational acceleration constantd = diameter of the particle

StokeStoke’’s Laws Law

VF = Fall Velocity(p - po) = Density difference between

particle and watern = viscosity of waterg = gravitational acceleration constantd = diameter of the particle

Forget the FormulaForget the FormulaRemember the Removal Remember the Removal

Efficiency Depends on Several Efficiency Depends on Several FactorsFactors

Particle Size versus Settling Time

Particle Sizemm 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

Clarifiers

Efficiency of Solids Removal Related To:

1. Characteristics of the Solids

2. Characteristics of the Water

3. Characteristics of the Clarifier

StokeStoke’’s Laws Law

VF = Fall Velocity(p - po) = Density difference between

particle and watern = viscosity of waterg = gravitational acceleration constantd = diameter of the particle

Forget the FormulaForget the FormulaRemember the Removal Remember the Removal

Efficiency Depends on Several Efficiency Depends on Several FactorsFactors

Warm WaterLess DenseLess Viscous

Solids Settle More Readily in Warm WaterThan in Cold Water

Cold Water More Dense

More Viscous

Warm Water - Greater Efficiency of Clarification

Settling RateSettling Rate

Cool Water- Less Efficiency of Clarification

Clarifiers

Efficiency of Solids Removal Related To:

1. Characteristics of the Solids

2. Characteristics of the Water

3. Characteristics of the Clarifier

Clarifiers

Efficiency of Solids Removal Related To:

3. Characteristics of the ClarifierSurface Area

DepthHydraulic Loading

Solids Loading

Clarifiers

Efficiency of Solids Removal Related To:

3. Characteristics of the ClarifierSurface Area

DepthHydraulic Loading

Solids LoadingDesign

OperationMaintenance

Clarifiers

Efficiency of Solids Removal Related To:

3. Characteristics of the Clarifier

Flow Characteristics in the Clarifier

Flow Must be Dispersed Evenly Throughout

Higher Flow (Horizontal Velocity) in One Part of Tank

(Detention Time vs. Fall Velocity)

Density Currents

Currents Within the Tank Carry Solids Through the Tank. 

Not the Same as Excessive Hydraulic Load

Clarifier Short CircuitingClarifier Short Circuiting

Clarifier Short CircuitingClarifier Short Circuiting

Missing or poor influent baffling

Causes

Clarifier Short CircuitingClarifier Short Circuiting

Missing or poor influent baffling

Causes

Clarifier Short CircuitingClarifier Short Circuiting

Missing or poor influent baffling

Causes

Clarifier Short CircuitingClarifier Short Circuiting

Uneven effluent weirs

Plant growth or thrash in effluent weirs

Causes

Clarifier Short CircuitingClarifier Short Circuiting

Temperature stratification between influent & clarifier water temperatures.

Causes

Clarifier Short CircuitingClarifier Short Circuiting

Monitoring for Short Circuiting

Visual Observation

Flow Over Weir

Solids Over Weir

Clarifier Short CircuitingClarifier Short Circuiting

Monitoring for Short Circuiting

Dye Testing

Higher Flow (Horizontal Velocity) in One Part of TankDensity Currents

Clarifier Short CircuitingClarifier Short Circuiting

Clarifier Short CircuitingClarifier Short Circuiting

• Missing or poor influent baffling

• Uneven effluent weirs

• Plant growth or thrash in effluent weirs

• Temperature stratification between influent & clarifier water temperatures.

Causes

Clarifiers

Efficiency of Solids Removal Related To:

1. Characteristics of the Solids

2. Characteristics of the Water

3. Characteristics of the Clarifier

Clarifiers

Types of ClarifiersTypes of ClarifiersInclined Plate

(Lamella)

Rectangular

Circular

Inclined Plate(Lamella)

Overflow Box

Clarifier Influent

Sludge Discharge

Clarifier Effluent

SludgeHopper

Flocculation Tank

FlashMix Tank

Coagulant Feed

Feed BoxDischarge FlumesDistribution Orifice

Inclined Plates

Types of ClarifiersTypes of Clarifiers – – Inclined Plate (Lamella)Inclined Plate (Lamella)

Types of ClarifiersTypes of Clarifiers – – Inclined Plate (Lamella)Inclined Plate (Lamella)

Increased settling efficiency due to increased surface area

Smaller Area Needed for Installation

Types of ClarifiersTypes of Clarifiers – – Inclined Plate (Lamella)Inclined Plate (Lamella)

Increased settling efficiency due to increased surface area

Smaller Area Needed for Installation

Types of ClarifiersTypes of Clarifiers – – Inclined Plate (Lamella)Inclined Plate (Lamella)

Seldom Used With Organic WastesBiological Growths Reduce Efficiency

Mostly Industrial Applications

Types of ClarifiersTypes of Clarifiers – – Inclined Plate (Lamella)Inclined Plate (Lamella)

Rectangular Clarifiers

EffluentLaunder

EffluentWeir

ScumTrough

Flights

DriveUnit

DriveChain

DriveGear

IdlerSprockets

Sludge Withdrawal

Pipe

SludgeTrough

InletBaffleInlet

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

InletBaffleInlet

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Influent baffling

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

FloatableSettleable

EffluentLaunder

EffluentWeir

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Effluent

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

FloatableSettleable

Rails

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Solids Removal Mechanism

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

DriveChain

DriveUnit

DriveGear

IdlerSprockets

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Flights

Rails

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Flights

Wear Shoes Rails

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Wear Shoes Rails

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Prevent Wear on the Flights Where They Contact the Rails

Transfer Wear to the Shoe Instead of the Flights

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Flights

Sludge

Sludge Withdrawal

Pipe

SludgeTrough

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Flights

Scum

Scum RemovalScum

Trough

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Scum Removal

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Scum Removal

EffluentLaunder

EffluentWeir

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Effluent

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Effluent Weir – “V Notch”

Flow = Velocity X Area

As Flow Increases, Area Increases

And As Area Increases, Velocity Decreases

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Flow = Velocity X Area

Effluent Weir – “V Notch”

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Effluent Weir – “V Notch”

Helps Keep Velocity Constant

Reduces Solids Build-up Behind Weir

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Single Weir

Finger Weirs

Effluent Weirs

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Effluent Weirs

EffluentLaunder

EffluentWeir

ScumTrough

Flights

DriveUnit

DriveChain

DriveGear

IdlerSprockets

Sludge Withdrawal

Pipe

SludgeTrough

InletBaffleInlet

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

Monitor for Short Circuiting

Visual Observation

Flow Over Weir

Solids Over Weir

Dye Testing

Secondary Rectangular Clarifiers – Most Important

Consider Baffles

Circular Clarifiers

Circular ClarifierCircular Clarifier

Circular ClarifierCircular Clarifier

Influent typically enters the basin from the center rather than from one end. 

Circular ClarifierCircular Clarifier

Influent

Influent typically enters the basin from the center rather than from one end. 

Circular ClarifierCircular Clarifier

Influent

A Circular Baffle Directs Flow 

Center Baffle

Circular ClarifierCircular Clarifier

A Circular Baffle Directs Flow 

Circular ClarifierCircular Clarifier

Influent

Solids Settle

Scraped to Sump

Removed by Pumping Center Baffle

Sludge Sump

Sludge Plow

Circular ClarifierCircular ClarifierSolids Settle

Scraped to Sump

Removed by Pumping 

Circular ClarifierCircular ClarifierSolids Settle

Scraped to Sump

Removed by Pumping 

Circular ClarifierCircular Clarifier

Influent

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum 

Drive UnitSkimmer Arm

ScumBaffle

Circular ClarifierCircular Clarifier

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum 

Circular ClarifierCircular Clarifier

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum 

Circular ClarifierCircular Clarifier

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum 

Circular ClarifierCircular Clarifier

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum 

Circular ClarifierCircular Clarifier

Influent

The Water Flows to the Effluent Weir Around the Circumference of the Clarifier 

Center Baffle Effluent Weir

Sludge Sump

Sludge Plow

Circular Clarifier Outlet

Effluent

EffluentLaunder

EffluentWeir

ScumBaffle

1 2 3OuterWall

InnerWall

SuspendedIn Clarifier

The Launder and Weir May Be

Effluent Launder/Weir Inside Clarifier (#2)Can Create Water Current

• Loss of solids over weir.

• Baffles used to redirect & slow water currents.

STAMFORD BAFFLE MC KINNEY BAFFLE

Other Clarifier Baffles

Clarifier Short CircuitingClarifier Short Circuiting

• Missing or poor effluent baffling

• Uneven effluent weirs

• Plant growth or thrash in effluent weirs

• Temperature stratification between influent & clarifier water temperatures.

ClarifierVariations

Rectangular Tank

Circular Sludge Collection and Skimming

“Squirqular” Clarifier

Clarifier VariationsClarifier Variations

Peripheral FeedPeripheral Discharge

Clarifier VariationsClarifier Variations

Peripheral Feed

Center Discharge

Clarifier VariationsClarifier Variations

Radial Discharge Peripheral Feed

Clarifier VariationsClarifier Variations

Tow Bro Clarifier

Clarifier VariationsClarifier Variations

Spiral Sludge Collector

Clarifier VariationsClarifier Variations

Telescoping Valves for RAS Return

Clarifier VariationsClarifier Variations

Many OthersMany Others

Each Designed to Address Particular Concern

Clarifier VariationsClarifier Variations

Drive MechanismLubrication (Manufacturers Specs.)

Observe Proper Operation (2/Day)

Clarifier OperationClarifier Operation

Routine Inspection & Maintenance

Sludge Judge Daily (Each Shift)

Clarifier OperationClarifier Operation

Rectangular ClarifiersSludge Collection System

Operating SmoothlyFloating SludgeFrequent Shear Pin or Breaker Failure

Clarifier OperationClarifier Operation

Circular ClarifiersSkimmer/Sludge Collector

Operating SmoothlyScum Trough Plugged

CleaningWeirs – Launder - Center Well

Clarifier OperationClarifier Operation

TheHardWay

TheEasyWay

Clarifier OperationClarifier Operation

Clarifier OperationClarifier Operation

Clarifier OperationClarifier Operation

Limit Growth ?

Clarifier OperationClarifier Operation

Limit Growth ?

Covers Block Sunlight Limits Algae Growth

Clarifier OperationClarifier Operation

Limit Growth ?

Covers Block Sunlight Limits Algae Growth

Provides Cold Weather Protection

Clarifier OperationClarifier Operation

Monitoring for Short Circuiting

Visual Observation

Flow Over Weir

Solids Over Weir

Dye Testing

Clarifier OperationClarifier Operation

Routine Inspection & Maintenance

Sludge Judge Daily (Each Shift)

Cleaning

Monitoring for Short Circuiting

Also IncludesCalculating and Monitoring Loading

Clarifier OperationClarifier Operation

Detention TimeSurface Overflow Rate

Weir Overflow RateSolids Loading Rate

CLARIFIERSCLARIFIERS

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit