CHEMICAL CLARIFICATION – COAGULATION METHODS

CHEMICAL CLARIFICATION – CHEMICAL CLARIFICATION – COAGULATION METHODSCOAGULATION METHODS


Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit

CLARIFICATIONCLARIFICATIONCLARIFICATIONCLARIFICATIONRemoval of

Settleable and Floatable Solids

•Increase Removal Amount(More Solids Out)

•Increase Removal Rates(Solids Settle Faster)

CHEMICALCHEMICALCLARIFICATIONCLARIFICATION


•Less Solids

•More Sludge



(in effluent)

(for disposal)

Stoke’s LawStoke’s 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

2(p - po)g 9n

(d/2)2VF =




2(p - po)g 9n

(d/2)2VF =




2(p - po)g 9n

(d/2)2VF =




•Increase Particle Size(Average Diameter)



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

•Increase Particle Size

•Encourage Contact



CHEMICAL CLARIFICATION

1. Coagulation2. Flocculation

3. Separation

Coagulation

•Rapid Mixing

•“Pin-point” Floc Formation

•Chemical Addition

FlocculationFlocculation• Slow Mixing

• Floc Growth

• Increased Diameter

Solids SeparationSolids SeparationSolids SeparationSolids Separation

• Clarified Liquid• Concentrated Suspension

(sludge)

Usually Gravity Settling

Other Processes(dissolved air flotation, etc.)

•Increase Particle Size

•Encourage Contact



* Fine Suspended Particles Have an Electrostatic Charge (Usually +)

* Encourage Contact

* Destabilize Charges

Natural Stabilizing ForceKeeps Solids Apart

Like Charges Repel

Purpose of Chemical Clarification

Mechanisms

•Electrostatic Charge Reduction

•Interparticle Bridging

•Physical Enmeshment

Electrostatic Charge Reduction

• Solid Particles have an Electrostatic Charge

usually negative

solids repel one another

• Add Chemical to Neutralize Charge

positive charge (cationic)

• Must Not Overdose

excess positive charge

Interparticle Bridging• Polyelectrolytes (polymers)

long chainselectrostatic charges

• Adsorb on the Charged Particles

bridges particles together

NegativeColloidalParticles

Cationic Polymer Unit

Interparticle Bridging

Interparticle Bridging• Polyelectrolytes (polymers)

long chainselectrostatic charges

• Adsorb on the Charged Particles

bridges particles together

•Must Not Overdose

Physical Enmeshment• Ions Combine with Hydroxyl Ions

OH -

• Gelatinous Precipitate Forms

flakes

void spaces

• Collects Particles as it Forms

co-precipitate

enlarges the floc

Mechanisms

•Electrostatic Charge Reduction

•Interparticle Bridging

•Physical Enmeshment

CHEMICAL CHEMICAL CLARIFICATIONCLARIFICATION


1. Coagulation1. Coagulation2. Flocculation2. Flocculation3. Separation3. Separation

COAGULATION

FLOCCULATION

Rapid MixAdequate Contact

Slow MixingIncrease Floc Size

PROCESS CONTROL

1. Provide complete mixing.

2. Control mixing for floc.

3. Control chemical dose.

Chemical TreatmentChemical TreatmentChemical TreatmentChemical Treatment

Addition of

Positive Ions (Cations)

orPolymers

CHEMICAL TREATMENTCHEMICAL TREATMENT

Aluminum Sulfate (Al+3)

Calcium Hydroxide (Ca+2)

Ferric (Iron) Chloride (Fe+3)

Positive Ions Added by AddingMetal Salts

Such As

Metal Salts UsedMetal Salts UsedMost Common

Alum (Aluminum Sulfate)Alum (Aluminum Sulfate)Ferric ChlorideFerric ChlorideLime ( Calcium Hydroxide)Lime ( Calcium Hydroxide)

Others

Sodium AluminateSodium AluminateFerric SulfateFerric SulfateFerrous SulfateFerrous SulfateFerrous ChlorideFerrous Chloride

Aluminum Sulfate (Dry)Al2(SO4)3

. 14 H2O

“Alum” or “Filter Alum”

Available in Various GradesLump (rarely used)

Ground (granulated)Rice

Powdered

Feeds Easilydoesn’t “bulk”

Aluminum Sulfate (Dry)Al2(SO4)3

. 14 H2O

Irritantskinmucus membraneseyes

Irritantskinmucus membraneseyes

Must be kept dryMust be kept drycake to solid lumpcake to solid lumpcorrosivecorrosiveequipment must be cleanedequipment must be cleaned

Dosage Approximately 75 - 250 mg/LDosage Approximately 75 - 250 mg/L

Aluminum Sulfate (Liquid)Al2(SO4)3

Approximately 11 pounds / gallonApproximately 5.4 pounds of “dry”/gal

Ease of Handling vs. Transportation Costs

Corrosiveequipment must be protected

Supports Bacterial Growth / Deposits

Reduces Alkalinity

Ferric Chloride Ferric Chloride (FeCl(FeCl33))Anhydrous

Absorbs Moisture from the AirCorrosive with WaterReleases Heat as it is Dissolved

CrystalAbsorbs MoistureReleases Less Heat

LiquidLined ContainersShipped at 30 - 40 %Approximately 12 pounds per gallon

Ferric Chloride Ferric Chloride (FeCl(FeCl33))

Corrosiveequipment must be protected

Stains

Safety Concerns

Dosage Approximately 45 - 90 mg/L

LIMEHydrated Lime

Ca(OH)2

CoagulantpH AdjustmentAbsorbs Moisture

Quicklime (anhydrous)CaOAbsorbs MoistureMust be “Slaked”Heat GeneratedCosts vs. Handling

LIMEErode or Wear Equipment

Scale Build-up

LIMEErode or Wear Equipment

Scale Build-up

Dosage Approximately 200 - 400 mg/L

Irritantskineyesmucus membraneslungs

Polymeric Flocculants“Polyelectrolytes”

“Polymers”

Organic Compounds - Repeating Units

Long Chain - High Molecular Weight

PolymersPolymersPolymersPolymers

Classified By:Classified By:

ChargeCharge

Charge DensityCharge Density

Size (Length)Size (Length)

PolymersPolymersPolymersPolymers

Charge:Charge:

““Cationic” - positive chargeCationic” - positive charge

““Anionic” - negative chargeAnionic” - negative charge

““Nonionic” - no free chargeNonionic” - no free charge

PolymersPolymersPolymersPolymersCharge Density:Charge Density:

Relative Number of Locations Along Relative Number of Locations Along the Chain That Carry a Chargethe Chain That Carry a Charge

Percent of Maximum PossiblePercent of Maximum Possible

Low Charge (<25%)Low Charge (<25%)Medium Charge (25 -50%)Medium Charge (25 -50%)High Charge (>50%)High Charge (>50%)

PolymersPolymersPolymersPolymersSize (Length):Size (Length):

Designated by Molecular WeightDesignated by Molecular Weight““Low” - <10,000 gm/moleLow” - <10,000 gm/mole

““Medium” - 10,000 to 100,000 gm/moleMedium” - 10,000 to 100,000 gm/mole

““High” - 100,000 to 1,000,000 gm/moleHigh” - 100,000 to 1,000,000 gm/mole

““Very High” - 1,000,000 to 10,000,000 gm/moleVery High” - 1,000,000 to 10,000,000 gm/mole

““Ultrahigh” - >10,000,000 gm/moleUltrahigh” - >10,000,000 gm/mole

AnionicPolymers

CationicPolymers

NonionicPolymers

0 % +100 %-100 % +50 %-50 %

MW = 104 gm/moleLow MW

MW = 105 gm/moleMedium MW

MW = 106 gm/moleHigh MW

MW = 107 gm/moleVery High MW

MW > 107 gm/moleUltrahigh MW

Flocculatingafter

Coagulation

SludgeDewatering

Coagulation

POLYMER MAP

PolymersPolymersPolymersPolymersAvailable as:

LiquidDryGelEmulsion

Must be Dilutedusually <1%

Can Be Very Viscousmay build up in pipes and pumpsclean regularly

salt water - dilute bleach

PolymersDry Polymers:

absorb moisture - ineffectivemay form “fish-eyes”aged for maximum efficiency

2 hours minimum7 days maximum

Polymers

Considered Non-Hazardous

Extremely SlipperyClean Up Immediately

SaltChlorineDrying AgentsAbsorbent Materials

PolymersPolymers

Dosage Rateusually less than 1 mg/L(0.25 to 1.5 mg/L)

Overdose Worse Than No PolymerOverdose Worse Than No Polymer



1. Coagulation1. Coagulation2. Flocculation2. Flocculation3. Separation3. Separation

PROCESS CONTROLPROCESS CONTROLPROCESS CONTROLPROCESS CONTROL

1. Provide complete 1. Provide complete mixing.mixing.

2. Control mixing for 2. Control mixing for flocculation.flocculation.

3. Control chemical dose.3. Control chemical dose.

Equipment



Dry Chemical Feeders

VOLUMETRIC

Measures chemical amount by VOLUME

GRAVIMETRIC

Measures chemical amount by WEIGHT

VOLUMETRIC FEEDERSLess Expensive

Low Delivery Rate

Less Accurate

Screw Feed Mechanism

Volumetric Screw Feeder

ChemicalChemicalHopperHopper

ChemicalChemicalHopperHopper

DriveMechanism

RotatingFeed Screw

MixingTank

Gravimetric Feeders

Loss-in-Weight Gravimetric Feeders

Belt Gravimetric Feeders

Highly AccurateClose Dosage Control

Chemical Cost Savings

Intermediate Cost

Accurate & Reliable

Gravimetric FeederGravimetric FeederGravimetric FeederGravimetric Feeder

HopperScale Beam

Control Wedge

Endless Belt

Slide Gate

GRAVIMETRIC BELT FEEDER

WEIGH BELTWEIGH BELT

CHEMICALHOPPER

WEIGHDECK

VERTICALVERTICALGATEGATE

WEIGHBEAM

GRAVIMETRIC FEEDERS

ADVANTAGES

1. Calibration normally not required

2. Greater accuracy and dependability

3. Incorporation of totalizer

4. Automatic proportioning

5. Low maintenance; simple operation

BULKSTORAGE

BINDAY HOPPER

FEEDER

DISSOLVER

HOLDINGTANK

WATER SUPPLY

PUMP TOAPPLICATION

GRAVITY TOAPPLICATION

TYPICAL DRY CHEMICAL FEED SYSTEMTYPICAL DRY CHEMICAL FEED SYSTEM

CHEMICALHOPPER

MIXER

WATERSUPPLY

TOAPPLICATION

FEEDER

Loss-in-weight Gravimetric Feeder

SCALE DRYFEEDER

DISPERSER

WATER SUPPLY

MIXER

MIXING TANK

SCALE

DRYFEEDER

DISPERSER

WATER SUPPLY

MIXER

MIXING TANK

TRANSFERPUMPMETERING

PUMP

APPLICATIONPOINT

POLYMER FEED SYSTEM

AGINGTANK

HOLDINGTANK

Liquid Feeders

Rotary Dippers

Rotometers

Metering Pumps

METERING PUMPS

POSITIVE DISPLACEMENT

Gear

Diaphragm

Plunger

GEAR PUMP

Gear

Gear

Suction Discharge

GEAR PUMP

Suction Discharge

PLUNGER PUMP

PLUNGERSUCTION

VALVE

DISCHARGEVALVE

DIAPHRAGM METERING PUMP

SUCTION STROKE

INTAKE

OPEN

CLOSED

ECCENTRIC DRIVE

DIAPHRAGM

PLUNGER

PUMPINGCHAMBER

CHECK VALVEASSEMBLY

DIAPHRAGM METERING PUMP

DISCHARGE STROKE

OPEN

CLOSED

ECCENTRIC DRIVE

DIAPHRAGM

PLUNGER

PUMPINGCHAMBER

CHECK VALVEASSEMBLY

HYDRAULICFLUID

OUTLET

DIAPHRAGM PUMP

Treatment Process

Coagulation

Flocculation

Separation

MIXING

Initial Rapid Mixing

Uniform Dispersion

Efficient Application

Feed

Impeller

Overflow

FLASH MIX TANKFLASH MIX TANK

FLASH MIX TANKFLASH MIX TANK

FLOCCULATIONFLOCCULATIONFLOCCULATIONFLOCCULATION

Gentle Mixing

Particle Contact

In Biological Process

Feed

ImpellerOverflow

FLOCCULATION TANKFLOCCULATION TANK

Typical Mechanically Mixed Flocculating ClarifierTypical Mechanically Mixed Flocculating Clarifier

Influent

Effluent

Flocculation

Chamber

SlowMixers

CircularBaffle

Treatment Process

Coagulation

Flocculation

Separation

Prepared ByMichigan Department of Environmental Quality

Operator Training and Certification Unit



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CHEMICAL CLARIFICATION – COAGULATION METHODS

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