CLARIFIERS Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit

CLARIFIERSCLARIFIERS

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit

Provide Quiescent Area

Separation of Solids

FloatableSettleable

ClarifiersSedimentation Basins

Settling Tanks


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




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








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





Clarifiers


3. Characteristics of the ClarifierSurface Area

DepthHydraulic Loading

Solids Loading

Clarifiers


3. Characteristics of the ClarifierSurface Area

DepthHydraulic Loading

Solids LoadingDesign

OperationMaintenance

Clarifiers



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


Missing or poor influent baffling

Causes



Causes



Causes


Uneven effluent weirs

Plant growth or thrash in effluent weirs

Causes


Temperature stratification between influent & clarifier water temperatures.

Causes


Monitoring for Short Circuiting

Visual Observation

Flow Over Weir

Solids Over Weir



Dye Testing

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



• Missing or poor influent baffling

• Uneven effluent weirs

• Plant growth or thrash in effluent weirs

• Temperature stratification between influent & clarifier water temperatures.

Causes

Clarifiers





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)


Increased settling efficiency due to increased surface area

Smaller Area Needed for Installation


Increased settling efficiency due to increased surface area

Smaller Area Needed for Installation


Seldom Used With Organic WastesBiological Growths Reduce Efficiency

Mostly Industrial Applications


Rectangular Clarifiers

EffluentLaunder

EffluentWeir

ScumTrough

Flights

DriveUnit

DriveChain

DriveGear

IdlerSprockets

Sludge Withdrawal

Pipe

SludgeTrough

InletBaffleInlet

Types of ClarifiersTypes of Clarifiers – – RectangularRectangular

InletBaffleInlet


Influent baffling



FloatableSettleable

EffluentLaunder

EffluentWeir


Effluent


FloatableSettleable

Rails


Solids Removal Mechanism


DriveChain

DriveUnit

DriveGear

IdlerSprockets


Flights

Rails


Flights

Wear Shoes Rails


Wear Shoes Rails


Prevent Wear on the Flights Where They Contact the Rails

Transfer Wear to the Shoe Instead of the Flights


Flights

Sludge

Sludge Withdrawal

Pipe

SludgeTrough



Flights

Scum

Scum RemovalScum

Trough


Scum Removal


Scum Removal

EffluentLaunder

EffluentWeir


Effluent


Effluent Weir – “V Notch”

Flow = Velocity X Area

As Flow Increases, Area Increases

And As Area Increases, Velocity Decreases


Flow = Velocity X Area




Helps Keep Velocity Constant

Reduces Solids Build-up Behind Weir


Single Weir

Finger Weirs

Effluent Weirs


Effluent Weirs

EffluentLaunder

EffluentWeir

ScumTrough

Flights

DriveUnit

DriveChain

DriveGear

IdlerSprockets

Sludge Withdrawal

Pipe

SludgeTrough

InletBaffleInlet


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


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


Influent

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


Influent

A Circular Baffle Directs Flow

Center Baffle


A Circular Baffle Directs Flow


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


Influent

Drive Mechanism Also Drives Skimmer Arm to Remove Floating Scum

Drive UnitSkimmer Arm

ScumBaffle










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


• 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


Peripheral Feed

Center Discharge


Radial Discharge Peripheral Feed


Tow Bro Clarifier


Spiral Sludge Collector


Telescoping Valves for RAS Return


Many OthersMany Others

Each Designed to Address Particular Concern


Drive MechanismLubrication (Manufacturers Specs.)

Observe Proper Operation (2/Day)

Clarifier OperationClarifier Operation

Routine Inspection & Maintenance

Sludge Judge Daily (Each Shift)


Rectangular ClarifiersSludge Collection System

Operating SmoothlyFloating SludgeFrequent Shear Pin or Breaker Failure


Circular ClarifiersSkimmer/Sludge Collector

Operating SmoothlyScum Trough Plugged

CleaningWeirs – Launder - Center Well


TheHardWay

TheEasyWay




Limit Growth ?


Limit Growth ?

Covers Block Sunlight Limits Algae Growth


Limit Growth ?

Covers Block Sunlight Limits Algae Growth

Provides Cold Weather Protection



Visual Observation

Flow Over Weir

Solids Over Weir

Dye Testing


Routine Inspection & Maintenance

Sludge Judge Daily (Each Shift)

Cleaning


Also IncludesCalculating and Monitoring Loading


Detention TimeSurface Overflow Rate

Weir Overflow RateSolids Loading Rate


Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit

Documents

CLARIFIERS Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit