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
Com
mon
inor
gani
c co
agul
ants
, coa
gula
tion
aids
, an
d pH
and
Alk
alin
ity A
djus
ting
Chem
ical
s133.3
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