Coagulation/Flocculation and Jar Testing

Department of Civil and Environmental EngineeringCEEN 330 – Environmental Field Session

Overview Coagulation overview Calculations of dosing Jar testing procedures Turbidity measurement procedures pH measurements Review of Mn measurement procedures

FlocculatorRapid mix

Coagulation/Flocculation

Turbidity in Water:Colloid Surface Phenomena Electrostatic force

principal force contributing to stability of suspension electrically charged particles

Van der Waals force attraction between any two masses opposing force to electrostatic forces

Satisfy Electroneutrality

Double Layer Model of Colloidal Particles

Forces Acting on Colloids

Destabilization Mechanisms Compression of the double layer (DLVO Theory)

increasing the ionic strength

Compression of Double Layer

Destabilization Mechanisms Compression of the double layer (DLVO Theory)

increasing the ionic strength Adsorption and charge neutralization

adding a coagulant (metal salt)

Charge Neutralization

Destabilization Mechanisms Compression of the double layer (DLVO Theory)

increasing the ionic strength Adsorption and charge neutralization

adding a coagulant (metal salt) Enmeshment in a precipitate (“sweep-floc coagulation”)

high coagulant dose (metal salt) coagulant forms insoluble precipitates dominant mechanism applied (pH 6-8)

Al2(SO4) 3

+

Sweep-Floc Coagulation

Al2(SO4) 3

+ +

Al2(SO4) 3

Sweep-Floc Coagulation

colloids are enmeshed

Restabilization

Destabilization Mechanisms Compression of the double layer (DLVO Theory)

increasing the ionic strength Adsorption and charge neutralization

adding a coagulant (metal salt) Enmeshment in a precipitate (“sweep-floc

coagulation”) high coagulant dose (metal salt) coagulant forms insoluble precipitates dominant mechanism applied (pH 6-8)

Interparticle bridging synthetic organic polymer

Destabilization of Colloidal ParticlesMetals salts used for destabilization: aluminum sulfate (alum) aluminum chloride ferric sulfate ferric chloride ferrous sulfate

Coagulation Using Different Coagulants

Design of coagulation processes The design of coagulation process involves:

Selection of proper coagulant chemicals and their dosing Design of rapid mixing and flocculation basins

Coagulation (chemical conditioning) Flocculation (physical conditioning)

Sedimentation

Sedimentation Removal of largest particles for increased filtration

run times Achieves about 1-log removal (90%) of particles Extra buffering for raw water upset Required in treatment of many surface waters

Mechanism and Types of Sedimentation Physical treatment process that utilizes gravity to

separate solids from liquids Types of sedimentation

Type I: discrete settling (i.e., settling of silt; pre-sedimentation)

Type II: flocculant settling (i.e., coagulated surface water) Type III: hindered settling/zone settling (i.e., upper

portion of sludge blanket in sludge thickener) Type IV: compression settling (i.e., lower portion of a

gravity sludge thickener)

Gravity filters:• 2-3 m head• housed in open

concrete or steel tanks• large and small systems

Pressure filters:• higher head• housed in closed steel

vessels• costly; small systems

Media Filtration

Granular Media Filtration Theory Particles being captured can be 100-1,000 times

smaller than the pores Obviously not straining

Mechanisms of Filtration Transport to the Media Surface Attachment

Transport Mechanisms During Granular Media FiltrationA. SedimentationB. InterceptionC. Brownian Diffusion

Collector

A

B

C

Disinfection – Chlorine/ClO2

Regulations and Water Quality Standards Federal Requirements

0.3 NTU (95%) not to exceed 1 (1.49) Fe secondary maximum contaminant level: 0.3 mg/L Mn secondary maximum contaminant level: 0.050 mg/L

Complaints received when Mn is > 0.015 mg/L

Golden WTP: Level III Partnership for Safe Water Quality 0.1 NTU (95%) (15 minute intervals) Strict SOP’s for Operations Stringent Reporting Guidelines 2nd plant in State, 7th in the Nation

Jar Testing A laboratory procedure to determine the optimal pH

and the optimum coagulant dose to achieve best turbidity removal and evaluate the removal of other constituents of interest (e.g., TOC, hardness, Mn2+)

Jar testing simulates the coagulation, flocculation, and sedimentation processes

Coagulant of Choice for the Current Field Session The City of Golden uses Fe2(SO4)3 as a primary

coagulant and PolyDADMAC as polymeric coagulation aid

For this field session we will chose from one of three coagulants: aluminum sulfate (alum) aluminum chloride ferric sulfate

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AlCl3•6H2O 241.34 g/mol

AlCl3·6 H2O + 3HCO3¯ Al(OH)3(am)+ 3CO2 + 6H2O + 3Cl ¯

1 mole of aluminum chloride consumes 3 moles of bicarbonate (HCO3-)

Aluminum Chemistry

If alkalinity is not enough, pH will drop Lime (CaO/Ca(OH)2) or soda ash (Na2CO3) may be

needed to neutralize the acid

AlCl3·6 H2O + 3HCO3¯ Al(OH)3(am)+ 3CO2 + 6H2O + 3Cl ¯

If 100 mg/L of aluminum chloride is to be added to achieve complete coagulation. How much alkalinity is consumed in mg/L as CaCO3?

241.4 mg aluminum chloride consumes 183 mg HCO3-

100 mg aluminum chloride will consume ((183/241.4) x 100) mg HCO3-

= 76 mg HCO3

-

Alkalinity in mg/L as CaCO3 = 76 x (50/61)

= 62 mg/L as CaCO3

241.4 mg 183 mg

Exercise #1: Alkalinity Calculation

Al 27 g/mol

Cl 35.5

g/mol

H 1 g/mol

C 12 g/mol

O 16 g/mol

Coagulation pH @ 25 °C

Mini-Pilot Flow Diagram

FeedTankKMnO4

Flocculation Basin

Coagulant

Constanthead

Chlorine

BackwashLine

BackwashWaste

pHpH adjustment

Overflow

Turbidity meter

Turbidity meter

Exercise #1 For a typical Al3+ dose of 8 mg/L, determine the

weight of AlCl3 6H∙ 2O that will be added to every liter of water

A small water treatment system is operated continuously at 4 L/min. The maximum capacity of the dosing pump is 5 mL/min. If the maximum dose of Al3+ is 16 mg/L, what is the maximum concentration of hydrated AlCl3 in the stock feed solution?

Jar Testing – General Procedure Fill six jars with raw water sample (1 Liter) Place the jars under the jar testing apparatus and lower the

mixers into the jars. Make sure the paddles will turn without scratching the sides of the jar.

Adjust water properties Rapid mix at 200 rpm Quickly (!) add the appropriate dose of coagulant to all jars Continue rapid mixing for 1 minute Reduce stirring speed to 25-30 rpm and continue mixing for 20

minutes

Jar Testing – General Procedure Turn off mixers after the 20 minutes flocculation step Pull the mixers up and secure them (make sure they don’t

touch the top of the holder) Allow flocs to settle for 30 minutes Draw 15 ml sample from each jar for turbidity measurement

(s l o w l y and 1” below the surface) Identify the jar with the lowest residual turbidity

Draw and filter samples for DOC analysis

Jar Testing – Determination of optimal pH Fill six jars with raw water sample (1 Liter) Adjust pH in the jars while mixing using H2SO4/HCl or

NaOH/lime (pH: 5.5, 6.0, 6.5, 7.0, 7.5, 8.0) Add same dose of the selected coagulant to each jar Follow the next steps of the general procedure

Optimal pH: 6.3

For example….

The pH with the lowest residual turbidity will be the optimal pH…

Determination of Optimal Coagulant Dose Repeat all previous preparation steps This time adjust pH of all jars to optimal pH while

mixing Add different doses of the selected coagulant to the

jars (coagulant dose: 10, 20, 30, 40, 50, 60 mg/L) Follow the next steps of the general procedure

Coagulant Dose mg/L

Optimum coagulant dose: 12.5 mg/L

For example….

The jar with the lowest residual turbidity will determine the optimal coagulant dose… Plot residual turbidity against coagulant dose

Teams’ Tasks This afternoon we will be working in groups Group 1: ambient pH; dose optimization (Fe2(SO4)3

Group 2: ambient pH; dose optimization (Fe2(SO4)3; KMnO4 dose of 1.5 mg/L

Group 3: ambient pH; dose optimization (AlCl3) Group 4: ambient pH; dose optimization (AlCl3); KMnO4

dose of 1.5 mg/L Group 5: ambient pH; dose optimization (FeCl3)

Analysis This afternoon we will bring ~20 gallons of river

water for jar testing The same water will be used for both jar testing and

mini-pilot experiments on Tuesday, Wednesday, and Thursday

Measurements on feed water: pH, Mn, turbidity, temperature, TOC

Measurements on jar-testing supernatant: Turbidity, pH, Mn, and TOC on optimized dose

Turbidity Measurement

Make sure the test vials are clean before using them Transfer approximately 10 ml of water sample into a test vial

using a pipette When collecting a sample from the jar of settled water, obtain the

sample about 1” below the surface of the water Calibrate the turbidimeter for the range in which the test water

falls (the instrument itself will be pre-calibrated) Wipe the sides and bottom of the test vial with a Kim-Wipes and

place the sample in the turbidimeter Cover the vial and read and record the results Repeat as needed

Mn Measurement

Mn Measurement

Mn Measurement

pH Measurement You will be using portable pH meters Make sure that the meters are calibrated and follow

the calibration guidelines in the manual using pH 4, 7, and 10 buffers

Rinse the probe thoroughly with DI water between measurements and calibrations and gently dry the tip with Kim-Wipes before the next measurement

Make sure that the probe is stored in electrolyte solution or in wet environment if it is not in use

TOC Measurement You will collect samples in 17 ml vials We will analyze the samples for you using a carbon

analyzed (GE Sievers 5310 C)

Alkalinity and Hardness Measurement Titration methods

Tuesday We will meet in the labs at 8:00 am for start of

experiments (please bring and hand-in the pre-lab and reports)

In the afternoon we will continue experiments and later in the evening we will gather in the classroom to present and share the experimental result

Teams

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6

MichelleBonfanti

JessZielinski

Christopher Allan Waechter

Shaunta Oehlerking

Jordan Partin

Emma Ely

SarahFischer

StephenByers

PaigeBecker

Haley Salzwedel

Travis Ramos

Caroline Ike

KaraDavis

Richard Sebastian-Coleman

OliviaCain

Audra Agajanian

Logan Yamamoto

Frances Marlin

RosaFoth

BrennaEads

Eric Hake

Cameron Colley-Holck

Isaac Avila

Justin Ripley

MarisaLaRouche

MatthewGreff

Dalton Ellis

Jessica Allen

Graham Cottle

Dulguun Tumurbat

MelissaMitton

LauraLeonard

Xiojian Guo

Sarah Hurley

Christopher Marks

Neelha S. Mudigonda

AlejandraRuiz

KeeganO'Day

Laila Maksut

Calculate the required mL of stock solutions to achieve desired doses of coagulant in 2 L water sample

Generate a table:

Group work

Jar 1 2 3 4 5 6

Fe or Al dose (mg/L) 0 5 10 15 20 25

Required stock solution (mL)

Turbidity (NTU)

Group 1 & 2: 25 g/L Fe2(SO4)3 stock solution

Group 3 & 4: 25 g/L AlCl36H2O stock solution

Group 5: 25 g/L alum, Al2(SO4)314 H2O stock solution