VAN LEEUWEN 2011 Coagulation and Flocculation

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Coagulation andFlocculation in

Water Treatment

J(Hans) van Leeuwen


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Introduction

The need to clarify water

esthetics and health

!olloids " im#art color and tur$idity

to water " aesthetical acce#ta$ility

%icro$es are colloids too


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COAGULATION &FLOCCULATION

Removal of colloidal

substances from water

Potable water reuirements

!ealt!" aest!etics" economic

olloids

#i$e of colloids %

li&!t waves

'rownian motion

#tabilit( of colloids


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What is Coagulation? Coagulation is the destabilization of colloids by addition of

chemicals that neutralize the negative charges

The chemicals are known as coagulants, usually higher valence

cationic salts (Al3+, Fe3+ etc.

!oagulation is essentially a chemical "rocess

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What is Flocculation? Flocculation is the agglomeration of destabilized "articles into

a large size "articles known as flocs which can be effectively removed

by sedimentation or flotation.


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Coagulation aim



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Why coagulation and flocculation?Various sizes of particles in raw water

Particle diameter (mm) Type ettling !elocity

"# Pe$$le #%&' ms

" Course sand #%' ms

#%" Fine sand #%* mmin

#%#" ilt +%* md

#%###"#%###" ("# micron)("# micron) ,arge colloids,arge colloids #%' my#%' my#%#####" (" nano)#%#####" (" nano) mall colloidsmall colloids ' mmillion y' mmillion y

Colloids – so small: gravity settling not possible

G r

a v I t y s

e t t l I n g


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Colloid ta$ility

------

------

Repulsion

Colloid - A Colloid - B

!olloids have a net ne*ative surface char*e

+lectrostatic force #revents them from a**lomeration

,rownian motion -ee#s the colloids in sus#ension

H2O

Colloid

.m#ossi$le to remove colloids $y *ravity settlin*


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Colloidal interaction



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Charge reduction



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Colloids can be destabilized by charge

neutralization

Positively charges ions (Na+, Mg2+, l!+,"e!+ etc#$ neutralize the colloidal negative

charges and thus destabilize them#

%ith destabilization, colloids aggregate insize and start to settle

Colloid -esta$ilization


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"orce analysis on colloids

The integral of thecombined forces is

the energy barrier


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Flocculation aids



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Floc formation with polymers

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Jar Tests

Determination of optimum pH

The ar test " a la$oratory #rocedure to determine the o#timum #H

and the o#timum coa*ulant dose

ar test simulates the coa*ulation and flocculation #rocesses

ill the ars with raw water sam#le

('00 or 1000 mL) " usually 6 ars

dust #H of the ars while miin*

usin* H24& or 5a4H/lime

(#H '708 '7'8 6708 67'8 708 7')

dd same dose of the selected

coa*ulant (alum or iron) to each ar

(!oa*ulant dose ' or 10 m*/L)Jar Test


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Jar Test set-up

9a#id mi each ar at 100 to 1'0 r#m for 1 minute7 The ra#id mihel#s to dis#erse the coa*ulant throu*hout each container

9educe the stirrin* s#eed to 2' to 30 r#m

and continue miin* for 1' to 20 mins

This slower miin* s#eed hel#s

#romote floc formation $yenhancin* #article collisions:

which lead to lar*er flocs

Turn off the miers and allow

flocs to settle for 30 to &' mins %easure the final residual

tur$idity in each ar

;lot residual tur$idity a*ainst #H

Jar Tests – determining optimum


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Optimum pH: 6.3

Jar Tests – optimum pH


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&ptimum coagulant dose

#e"eat all the "revious ste"s

This time ad$ust "% of all $ars at

o"timum (&.3 found from first test

while mi'ing using %)* or

a*%-lime

Add different doses of the selected

coagulant (alum or iron to each $ar

(!oagulant dose /0 10 20 20 2/0 mg-4

#a"id mi' each $ar at 2 to 2/ r"m for 2 minute. The ra"id

mi' hel"s to dis"erse the coagulant throughout each container

#educe the stirring s"eed to / to 3 r"m for 2/ to mins


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Turn off the miers and allow flocs to settle for 30 to &' mins

Then measure the final residual tur$idity in each ar

;lot residual tur$idity

a*ainst coa*ulant dose

Coagulant Dose mg/L

.ptimum coagulant dose/ "%0 mg,

The coagulant dose with

the lowest residualturbidity will be the

o"timum coagulant dose

&ptimum coagulant dose


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• Hydraulic Jump: Hydraulic Jump creates turbulence and

tus elp better mi!ing"

• Mechanical mixing

• In-line flash mixing

In#lo$

Cemical

#eeding

Cemical

#eeding

In#lo$

%ac& mi! impeller #lat-blade impeller

Coagulant


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http://www.math.rug.nl/~veldman/menger/uz.mpg


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In#lo$

Cemical

#eeding

In#lo$

Cemical

#eeding


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'elative coagulating poer

5a< = 18 %*2< = 30 l3< > 10008 e3< > 1000

)ypical coagulants

luminum sulfate l2(4&)371& H24

.ron salt? erric sulfate e2(4&)3

.ron salt? erric chloride e2!l3

;olyaluminum chloride (;!) l2(4H)3!l3


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1luminum Chemistry

1 mole of alum consumes 6 moles of bicarbonate (HC'(-)

*l+,'.)(". H+' 0 1HC'(- ⇔ +*l,'H)(↓0 1C'+ 0 .H+' 0 ('.-+

I# al&alinity is not enoug2 pH $ill reduce greatly

Lime or sodium carbonate may be needed to neutrali3e te acid"

(Optimum pH: ! " 6!#

$it% alum addition& '%at %appens to 'ater pH

*l+,'.)(". H+' ⇔ +*l,'H)(↓0 4H+' 0 (H+'.-+


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1l'2 species as a function of p3



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1l4alinity calculation

*l+,'.)(". H+' 0 1HC'(- ⇔ +*l,'H)(↓0 1C'+ 0 .H+' 0 ('.-+

)* m+ ,66 m+

If 200 mg/L of alum to be added to achieve complete coagulation.

How much alkalinity is consumed in mg/L as CaCO!

'& m* alum consumes 366 m* H!43?

200 m* alum will consume (366/'&) 200 m* H!43?

= 123 m* H!43?

l-alinity in m*/L as !a!43 = 123 ('0/61)

= 101 m*/L as !a!43


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Iron Chemistry

5eCl(0 (HC'(- ⇔ 5e,'H)(↓0 (C'+ 0 (Cl-

$it% iron salt addition& '%at %appens to 'ater pH

($ider pH ran+e of: * " ) Best pH ran+e of *! " !#

1 mole of .eCl, consumes , moles of bicarbonate (HC'(-)

I# al&alinity is not enoug2 pH $ill reduce greatly due to ydrocloric

acid #ormation" Lime or sodium carbonate may be needed to neutrali3e

te acid" Lime is te ceapest"

If 200 mg/L of fe""ic chlo"ide is added fo" coagulation# how

much alkalinity is consumed in mg/L as CaCO!

56ercise/ 1l4alinity calculation


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Fe species as a function of p3



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COA/0AT A3D4

Ot%er substances t%ancoa+ulants used:- Cla5 minerals

- 4ilicates

- ol5mers

ol5mers are often

eit%er anionic or

cationic to aidcoa+ulation!

ol5mers also

reinforce flocs


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FLOCCULATION

"locculation * agglomeration o colloids by collisions to orm separable locs

-amples * mil., blood, seaater

Mechanisms * peri.inetic, collisions rom /ronian motion * ortho.inetic, induced collisions through stirring

&rtho.inetic locculation 0elocity gradient, relative movement beteen colloids in a luid body

'M1 velocity gradient

Camp No# t )ypical 2- 345 * 346


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Typical layout of a water treatment plant


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Topics of -iscussion

The #lace of flocculation within a watertreatment #rocess

The use of coa*ulation and flocculationin the water industry

oftenin* e#aration of flocs $y settlin*

and flotation


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lide ( o# +6

http://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/tsld013.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/index.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld027.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld014.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld012.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld001.htm


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Transport 7echanisms

5 Brownian motion for relatively small "articles which follow random motion and collide with

other "articles ("erikinetic motion

5 Differential settling 6articles with different

settling velocities in the vertical alignment collide

when one overtakes the other (orthokinetic motion

7esign o "locculator (1lo 8 entle mi-ing$

Flocculators are designed mainly to "rovide enough inter"article

contacts to achieve "articles agglomeration so that they can be

effectively removed by sedimentation or flotation


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Cross #lo$ 5locculator ,sectional vie$)

7lan ,top vie$)

$ " a n

s v e " s

e p a d

d l e

L

H

8

Mechanical "locculator


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Hydraulic Flocculation

• Horizontally baffled tank

Plan view horizontal flow!

• "ertically baffled tank

L Isometric "iew vertical flow!

L

8

H

The water flows horizontally.

The baffle walls hel" to create

turbulence and thus facilitate mi'ing

The water flows vertically. The baffle

walls hel" to create turbulence and thusfacilitate mi'ing


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ttp://$$$"environmental-center"com/maga3ine/i$a/9$s/art."pd#

Hydraulic Flocculation


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3ydraulic flocculators


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3ydraulic flocculators/ simple technology


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Hydraulic Flocculation: Pipe


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Hydraulic Flocculation: Pipe


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Hydraulic Flocculation:Large stirrers


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7echanical flocculators

http://www.myersequipment.com/_vti_bin/shtml.exe/horizontal.html/map


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7ecahnical flocculators

http://www.myersequipment.com/_vti_bin/shtml.exe/vertical.html/map


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7echanical flocculators

http://www.myersequipment.com/_vti_bin/shtml.exe/walking.html/map


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1nother mechanicalflocculator

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lide +1 o# +6

-ifferential settling flocculation

http://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld001.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld025.htmhttp://www.even.tamuk.edu/pipeline/academics/processes1/particle%20contact%20mechanisms/sld001.htm


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Flocculators integrated with settling


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Flocculators integrated with settling


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Flocculators $oth sides of settling


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Flocculator perforated wall (in $ac4ground)


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7elocit5 /radient: relative velocity o# te t$o #luid particles/distance

G dv/dy ";/;" ; s-

Mixing and Power

#he degree of mixing is measured by 7elocit5 /radient (/#

Hi+%er / 8alue& intenser mi9in+

: ! 1 m

m/s

3n mi9er desi+n& t%e follo'in+ e;uation is useful

G velocity gradient2 s

-<

7 7o$er input2 8

= >an& volume2 m(<

µ Dynamic viscosity2 ,7a"s)

/ 8alue for coa+ulation:


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+

=i9in+ time: , to 6 4 in-line blender 1-2 sec

/ 8alue for flocculation: 2 to > 4-1

=i9in+ time: 2 to 6 min3n t%e flocculator desi+n& /t (also ?no'n Camp o!# a product

of / and t is commonl5 used as a desi+n parameter

T5pical /t for flocculation is 2 9 1* - 1

Large G and small > gives small but dense #loc

mall G and large > gives big but ligt #locs

8e need big as $ell as dense #locs

$ic can be obtained by designing

#locculator $it di##erent G values 1 2 ,/1:* /2:, /,:2

C l l ti


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o'er Calculation

@hat horse#ower level do we need to su##ly to a flocculation

$asin to #rovide a A value of 100s?1

and a At of 100:000 for 10%AB flowC (iven: µ = 07 10?3 ;a7s8 1 h# = &'7 watts)

olution

9etention time: t = At/A = 100:000/100 = 1000 secs

Dolume of locculation $asin: D = (07&3 m3/sec) (1000 sec)

= &3 m3

; = A2 D µ = 1002 &3 07 10?3 = 300 @

= 300/&6 = '72 h#


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%)' )')MN) N'9 CC;)


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0iscosity of water is a measure of its resistance to flow

The cgs unit is the Poise, 1 gcm-1s-1.

Water viscosity is c. 1cP = 0.01P = 0.001 Pa.s

Pa = N/m2 or kgms-2 m-2 , so Pa.s = kgms-2 m-2 s = kgm-1s-1

This could also have een derived !rom going !rom

gcm-1s-1, multi"lying y 100/1000.

There!ore 1cP = 0.001kgm-1s-1

734CO43T@ =A40=T


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Calculation of Velocity 8radient

Calculate t%e 8elocit5 +radient in a flocculator& '%ere

t%e re;uired ener+5 is 1 J! .lo' rate is *=d&

retention time 2 min

7olume& 7 *(2* 9 62# ! m,

.lo' rate * 9 1 *6!, s

2* 9 6 9 6

EEEEE EEEEEEEEEEEEEEEEE /

√

7

√

1 9 *6!,!19!

2> s-1


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Calculate height re9uired for hydraulic flocculator

Calculate te ead di##erence in $ater troug a

ydraulic #locculator2 $ere te re?uired energy

input is J/L and te #lo$ rate is . @L/d"

o'er ener+5time

1 J 9 s ?+s 9 )!> 9 %

T%erefore& % 1)!> m !12m


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Calculate Camp :o

Calculate t%e Camp o for t%e %5draulic

flocculator in t%e pre8ious e9ample

Camp o /!t

2> 9 2 9 6

,,&

('it%in t%e boundaries of 2& " 2&#


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7here F 8 drag force,

!9

8 dimensionless drag coefficient for "lates moving faces normal to direction of motion

A 8 cross:sectional area of the "addles, m

υ 8 relative velocity between "addles and fluid, m-s

ρ 8 density, 2 kg-m3

The "ower in"ut can be com"uted as the "roduct of drag force and velocity

6 8 Fυ 8 !9Aρν3-

;f this is substituted in the e 8 !9Aρν3- µ>

C D A ρυ 2

2

" = C7ρ2 >2

ADD .OCC0ATO4


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What you need to 4now

How to determine the velocity

*radient and volume: chemical

and ener*y reEuirements for

flocculation

,e a$le to siFe settlin* tan-s on

the $asis of #article settlin* rates

and identify im#ortant Fones inthe settlin* tan-

oftenin* calculations

-isinfection ;yproducts/ 1


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-isinfection $yproducts are formed when disinfectants used in water treatment "lants react with bromide and-or natural

organic matter (i.e., decaying vegetation "resent in the source water. 9ifferent disinfectants "roduce different ty"es or amounts

of disinfection by"roducts. 9isinfection by"roducts for which regulations have been established have been identified in drinking

water, including trihalomethanes, haloacetic acids, bromate, and chlorite. ::::::::::::::::::::::::

Trihalomethanes (T37) are a grou" of four chemicals that are formed along with other disinfection by"roducts when chlorine or

other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic and inorganic

matter in water. The trihalomethanes are chloroform, bromodichloromethane, dibromochloromethane, and bromoform. ?6A has

"ublished the )tage 2 9isinfectants-9isinfection @y"roducts #ule to regulate total trihalomethanes (TT% at a ma'imum

allowable annual average level of B "arts "er billion. This standard re"laced the current standard of a ma'imum allowable

annual average level of 2 "arts "er billion in 9ecember 2 for large surface water "ublic water systems. The standard

became effective for the first time in 9ecember 3 for small surface water and all ground water systems. ::::::::::::::::::::::::

3aloacetic 1cids (3110) are a grou" of chemicals that are formed along with other disinfection by"roducts when chlorine or

other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic and inorganic

matter in water. The regulated haloacetic acids, known as %AA/, are monochloroacetic acid, dichloroacetic acid, trichloroacetic

acid, monobromoacetic acid, and dibromoacetic acid. ?6A has "ublished the )tage 2 9isinfectants-9isinfection @y"roducts #ule

to regulate %AA/ at & "arts "er billion annual average. This standard became effective for large surface water "ublic water

systems in 9ecember 2 and for small surface water and all ground water "ublic water systems in 9ecember 3. :::::::::::::

;romate is a chemical that is formed when ozone used to disinfect drinking water reacts with naturally occurring bromide found

in source water. ?6A has established the )tage 2 9isinfectants-9isinfection @y"roducts #ule to regulate bromate at annual

average of 2 "arts "er billion in drinking water. This standard will become effective for large "ublic water systems by 9ecember2 and for small surface water and all ground "ublic water systems in 9ecember 3. ::::::::::::::::::::::::

Chlorite is a by"roduct formed when chlorine dio'ide is used to disinfect water. ?6A has "ublished the )tage2

9isinfectants-9isinfection @y"roducts #ule to regulate chlorite at a monthly average level of 2 "art "er million in drinking water.

This standard became effective for large surface water "ublic water systems in 9ecember 2 and for small surface water and

all ground water "ublic water systems in 9ecember 3


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VAN LEEUWEN 2011 Coagulation and Flocculation

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