ARMENANTE ny Adsorption with Granular Activated Carbon.pdf

7/27/2019 ARMENANTE ny Adsorption with Granular Activated Carbon.pdf

1/103

PIERO M. ARMENANTENJIT

Adsorption withGranular Activated Carbon(GAC)


2/103


Adsorption Processes Utilizing

Granular Activated Carbon (GAC)

for Wastewater Treatment

In all these processes the wastewater is

contacted with granular activated carbon (GAC)typically in a semi-batch or continuous operation.Processes that utilize this type of carbon include:

Fixed-bed or expanded-bed adsorption

Moving-bed adsorption Fluidized-bed adsorption


3/103


Fixed-Bed and Expanded-Bed

Adsorption Systems

Wastewaterin

Wastewaterout

Wastewaterout

Wastewaterin

Fixed-Bed Expanded-Bed


4/103


Modes of Operation of Fixed-Bed and

Expanded-Bed Systems

Downflow Fixed-bed

Upflow

-Expanded-bed (if the wastewater velocityexpands the bed by about 10% or higher)

- Fixed-bed


5/103


Downflow Fixed-Bed Adsorbers This is the most common type of adsorption

column for wastewater treatment

These columns must be provided with a system forthe removal of spent carbon and the addition of

fresh or regenerated carbon

Because or their construction and operationdownflow fixed-bed adsorbers also acts as depth

filters for particles that can be contained in the

wastewater

Therefore this adsorption column must also beprovided with facilities for backwashing (including

air scouring, if necessary)


6/103


Typical GAC Contactor

After Metcalf and Eddy, Wastewater Eng ineer ing, 1991, p. 316


7/103


Characteristics of Commercial Adsorbers

Height of packing 3 - 9 m (10 - 30 ft)

Particle size 8 - 40 mesh

Hydraulic loading 1.4 - 6.8 L/m2 s (2 -10 gpm/ft2)

Residence time 10 - 60 min (typically 20 -30 min)

Typical carbon

requirements- pretreatment

- tertiary treatment

(in g carbon/m3 wastewater)60 - 200

25 - 50Operating pressure < 20 KPa/m of bed

After Sundstrom and Klei, Wastewater Treatment, 1979, p. 270 and

Metcalf and Eddy, Wastewater Eng ineer ing, 1991, p. 753


8/103


Properties of Commercially Available

Carbons

After Eckenfelder, Indu str ial Water Pol lut io n Control, 1989, p. 268


9/103


Downflow Fixed-Bed Adsorbers in

SeriesWastewater in


10/103


Downflow Fixed-Bed Adsorbers in

ParallelWastewater in


11/103


Granular Activated Carbon Process Flow Diagram

After Corbitt, R. A. 1990, The Standard Handbook of Environmental Engineering,p. 6.199


12/103

Results of Adsorption

Tests on TypicalIndustrial Wastewaters


13/103


Upflow Expanded-Bed Adsorbers

In general, most upflow adsorbing columnsoperate in the expanded-bed mode

Expanded-bed adsorbers are used when thewastewater fed to the column contains asignificant fraction of suspended particles

Since the bed is always expanded the columndoes not act as a filter for the suspendedparticles


14/103


Upflow Fixed-Bed Adsorbers in

Series

Wastewater in


15/103


Moving-Bed Adsorption

Carbon in

Carbon out

Wastewaterout

Wastewaterin


16/103


Fluidized-Bed Adsorption

Wastewaterout

Wastewaterin


17/103


Adsorption Beds as Filter Beds and

Heavy Metal Adsorbers

GAC beds are sometimes used as deep-bed

filters (as well as adsorbers)

the capital cost associated with dual purposeadsorber-filter beds is typically lower than

separate beds

the regeneration of the adsorptive capacity of

the bed should be followed by the removal of

solids via bed fluidization

most heavy metals are also adsorbed on

activated carbon beds


18/103


Biological Reactions in Adsorption Beds

The presence of organic material in a typical activated

carbon bed coupled with the presence of

microorganisms in the wastewater makes the bed an

ideal breeding ground. This can have both negative

and positive effects:

the microorganisms may contribute to thebreakdown of pollutants adsorbed on the bed, thus

improving its performance

the presence of excessive organic material and the

typical lack of oxygen may result in anaerobicgrowth (associate with the potential for odor

generation) and the plugging of the bed due to

excessive growth


19/103


Most Important Design Factors in

Fixed-Bed Adsorption Systems

Particle size

Diameter of column

Flow rate of incoming wastewater (orresidence time)

Height of adsorption bed

Pressure drop

Time required to achieve breakthrough

(Time of exhaustion)


20/103


Analysis of Fixed-Bed

Adsorption Systems


21/103


Steps Involved in AdsorptionAs the wastewater moves through a fixed bed of

carbon the pollutant to be adsorbed will move from

the wastewater to the carbon bed. Several steps are

involved in the overall adsorption process of a

single molecule of pollutant: Mass transfer step. Mass transfer from the bulk

of the wastewater to the surface of the carbon

particle through the boundary layer around the

particle

Dif fusio n step. Internal diffusion through a pore

Adso rpt ion step. Adsorption on to the surface ofthe particle


22/103

PIERO M. ARMENANTE

NJIT

Relative Magnitude of the Rates

Involved in Adsorption Process

In most wastewater treatment applications the

overall adsorption process is dominated by masstransfer, especially intrapart ic lemass transfer. A

qualitative ranking of the magnitude of theresistances is:

External interpart ic le mass transfer step slow to not-so-slow, depending on the operation

Intrapart ic le dif fus ion s tep typically slow

Adso rpt ion step typically fast


23/103

External InterparticleMass Transfer Film

Intraparticle

Diffusion

Adsorption

LiquidBulk

Pore


24/103

PIERO M. ARMENANTE

NJIT

Effect of Carbon Particle Size on

Pressure Drop and Intraparticle Mass

Transfer

The size of the activated carbon particle has an

opposite impact on the pressure drop across thebed and the intraparticle diffusion resistance (andhence on the overall adsorption process)


25/103

PIERO M. ARMENANTE

NJIT


Pressure Drop

The effect of particle size, Dp, on pressure drop,

P, can be determined recalling equations suchas the Ergun Equation for pressure drop in

granular media:

( )PL

Du

p p

L s= +

1501 175

13

2

Re.

or the Fair-Hatch equation (laminar flow):

( )P k

L

Du

p

s=

361

2

3 2


26/103

PIERO M. ARMENANTE

NJIT


Pressure Drop

The pressure drop in a carbon bed is inversely

proportional to the particle size. In particular it is:

P Dp1

forturbulentflow through granular media, and:

PDp

12

forlaminarflow in granular media.


27/103

PIERO M. ARMENANTE

NJIT


Intraparticle Mass TransferAs a first approximation the effect of particle size on

the intraparticle mass transfer of pollutant can be

estimated as follows:

pollutant transferred inside the particlebed volume

pollutant transferred inside the particle

bed volume

D dCd r

AV

DC

r DD

C

D D

D

p

p

p p p

p

6 0

0

12

12


28/103

PIERO M. ARMENANTE

NJIT


Pressure Drop and Diffusion Resistance

Larger carbonparticle size

Smaller carbonparticle size

Smaller pressuredrop

Larger pressuredrop

Smaller mass of

pollutant diffusinginside the particle

Larger mass of

pollutant diffusinginside the particle


29/103

PIERO M. ARMENANTE

NJIT

Size of Activated Carbon Particles Used

in Fixed-Bed Adsorption

Typically carbon particle sizes between 0.4 and2.5 mm are used in fixed bed adsorptionapplications

This size range results from a practicalcompromise between limiting the pressuredrops on one hand and providing adequate

surface area and promote mass transfer for

pollutant adsorption on the other Larger sizes also minimize losses during

carbon handling and packed bed operation


30/103

PIERO M. ARMENANTE

NJIT

Adsorption Zone and Adsorption Wave

In fixed bed adsorption, at any given time the

bed can be divided into three approximatezones, i.e., the saturated zone(containing carbon nearly

saturated with the pollutants),followed by the adsorpt ion

zone(were adsorption actuallytakes place), followed by azone in which the carbon contains little or no

adsorbed pollutant The size and location of the three zones within

the bed change with time

AdsorptionZone

SaturatedZone


31/103

PIERO M. ARMENANTE

NJIT


(continued)

As the wastewater enters the bed it firstencounters the saturated zone in which thecarbon is already nearly saturated with the

pollutant (this is not true for fresh completelyclean beds just being put on line, of course).Practically no adsorption occurs in thesaturated zone

As more wastewater travels through the bedthe saturated zone expands progressivelythrough the bed, eventually including it

completely


32/103

PIERO M. ARMENANTE

NJIT


(continued)

Pollutant adsorption occurs nearly exclusivelyover a portion of the bed called the adsorpt ionzone, downstream of the saturated zone

The concentration of pollutant in the carbonvaries from near saturation (at the beginning ofthe adsorption zone) to near zero (toward the

end of the adsorption zone). Conversely, the

pollutant concentration in the wastewaterincontact (at thattime) with the carbon changesfrom nearly full load (at the beginning of the

adsorption zone) to nearly zero (at the end)


33/103

PIERO M. ARMENANTE

NJIT


(continued) At any given time the portion of the bed

downstream of the adsorption zone containsvery little adsorbed pollutant since the

wastewater it is in contact with has alreadybeen nearly completely depleted of thepollutant(s)

As time goes by a greater portion of the bed

becomes saturated with the pollutant and theadsorption zone moves downstream formingan adso rpt ion wave


34/103

PIERO M. ARMENANTE

NJIT

Breakpoint and Breakthrough Curve

Eventually the forward part of the adsorptionwave reaches the end of the bed. When this

happens the bed begins to release wastewaterhaving a concentration of pollutant higher than

the desired value (typically 5-10% of theinfluent concentration). This point is called thebreakpoint

The corresponding curve of pollutantconcentration in the effluent vs. time is called

the breakthrough curve


35/103

PIERO M. ARMENANTE

NJIT

Exhaustion Point and Bed Saturation

Past the breakpoint the pollutant concentrationin the effluent rises rapidly (i.e., the

breakthrough curve is typically steep), until itreaches an arbitrarily defined exhaust ion po int

where the column approaches saturation If more wastewater is passed through the bed

the entire carbon content of the bed becomessaturated. Then, the wastewater leaving the

bed has, for all practical purposes, the same

concentration of pollutant as the incomingwastewater


36/103

PIERO M. ARMENANTE

NJIT

Breakpoint and Breakthrough Curve

Cumulative Wastewater Volume

C

dsorption

Zone

C CC C

Co Co Co Co

B E

Breakpoint

Breakthrough

Curve

Exhaustion

Point


37/103

PIERO M. ARMENANTE

NJIT

Concentration of Adsorbate in the

Carbon Along a Fixed-Bed Column

Position Along Fixed-Bed Column

q

dsorption

Zone

C CC C

Co Co Co Co

B E

1 2 3 4

1 2 3 4


38/103

PIERO M. ARMENANTE

NJIT

Evolution of Concentration Profiles in in the Wastewater Leaving

the Column and in the Carbon Bed as a Function of Time

Cumulative Wastewater Volume

C

Breakpoint

Breakthrough

Curve

Exhaustion

Point

t1 t2 t3t4

Position Along Fixed-Bed Column

q

t1 t2 t3 t4


39/103

PIERO M. ARMENANTE

NJIT

Progressive Saturation of Adsorber in

Column as a Function of Time

Position Along

the Column

q q q q

tF t tB tE


40/103

PIERO M. ARMENANTE

NJIT

Typical Breakthrough Curves

After Eckenfelder, Ind us tr ial Water Pol lut ion Control, 1989, p. 272


41/103

PIERO M. ARMENANTE

NJIT

Shapes of Breakthrough Curves

V

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

C/Co

VB VE

Short Depth of Adsorption Zone

V

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

C/Co

VB VE

Large Depth of Adsorption Zone


42/103

PIERO M. ARMENANTE

NJIT

Analysis of Fixed-Bed Adsorption

ColumnsThe primary objectives of such an analysis are:

determination of the total (maximum) column

adsorption capacity; determination of the depth of the adsorption

zone and the shape of the breakthrough curve;

determination of the breakpoint, including the

volume of wastewater that can be treatedbefore the breakpoint is reached, the time atwhich this happens, and the degree of columnsaturation at breakpoint.


43/103

PIERO M. ARMENANTE

NJIT

Total Column Adsorption Capacity

If the adsorption equilibrium curve is known thenby knowing the volume of the column and its void

fraction, one can calculate the total cumulativevolume of wastewater, Vmax, that cou ldbe treated

if the column became completely saturated:( )V SL

q

CSL

q

Cs

So

o

sapp

So

o

max = =1

where: S= column cross sectional area

L = height of packing

= void fraction

qSo= g(Co) = value ofqin equilibrium with Co

sand s app= real and apparent density of solid


44/103

PIERO M. ARMENANTE

NJIT

Approaches to the Design of

Adsorption ColumnsMany different approaches are available. In general,

partial differential equations can be written,

incorporating the different mass transfer and

adsorption mechanisms. Typically these models arecomplex and require numerical solutions.

Other models rely on experimental data and the use of

simpler models to interpret them so as to produce

satisfactory designs. These models can be used to

size the column by determining the depth of theadsorption zone, the shape of the breakthrough curve,

the time at breakpoint and the pollutant removed at

breakpoint.


45/103

PIERO M. ARMENANTE

NJIT

Models Examined Here

Three models will be examined here in somedetail:

Simplified Method for Estimation of Fixed-BedAdsorption Performance

Design of Adsorption Columns Based onCapacity of Adsorption Zone (Mass TransferModel)

Design of Adsorption Columns Based on BedDepth Service Time (BDST) Method (SurfaceReaction Model)


46/103

PIERO M. ARMENANTE

NJIT

Simplified Method for the Estimation

of Fixed-Bed Adsorption PerformanceSimplifying assumptions:

the pollutant concentration in the effluent

wastewater from the column increases linearlywith time until it reaches the breakpoint value,CB

at breakpoint the average concentration of

pollutant in the bed is only a fraction, , of the

saturation value (typically 50%)

the wastewater flow rate to the column isconstant and equal to Q


47/103

PIERO M. ARMENANTE

NJIT


of Fixed-Bed Adsorption PerformanceFrom a mass balance for the pollutant atbreakpoint it is:

M q B q B Qt C C

Qt CB so B oB

B o= = =

2

where:

M = cumulative mass of pollutant adsorbed atbreakpoint

B= mass of carbon in bed = s appS L , and:

q K Cso F on= 1


48/103

PIERO M. ARMENANTE

NJIT


of Fixed-Bed Adsorption PerformanceHence, the time required to reach breakthroughis:

t

q B

Q CC

K C B

Q CCB

B

o

B

F o

n

o

B=

= 2 2

1

The cumulative volume of wastewater, VB, treatedat breakpoint is given by:

V Q tB B=


49/103

PIERO M. ARMENANTE

NJIT

Design of Adsorption Columns Based

on Capacity of Adsorption Zone(Mass Transfer Model)

This model assumes that the adsorption zone has

a constant shape that moves down the columnwith time and that the process is controlled by themass transfer around the carbon pellets.


50/103

PIERO M. ARMENANTE

NJIT

DefinitionsL = height of packed bed

tF= time required for the adsorption zone to form

tL = time required for the fully formed adsorptionzone to move down the length of the column, L ,

until the effluent concentration is equal to CE

tE= time required for the effluent concentration toreach the exhaustion point, CE

tA = time, required for the adsorption zone to

move its own height down the column


51/103

PIERO M. ARMENANTE

NJIT

Time Required to Exhaust the BedThe time, tE, required for the effluent concentration to

reach the exhaustion point, CE, is equal to the sum of:

the time, tF, required for the adsorption zone toform

the time, tL, required for the fully formedadsorption zone to move down the length of the

column, L , until the effluent concentration is equal

to CE

Then, it is:

t t tE F L= +

i.e.: t t tL E F=


52/103

PIERO M. ARMENANTE

NJIT

Time Required to Exhaust the Bed

The time, tE, required for the effluentconcentration to reach the exhaustion point, CE, is

also equal to:

tV

Q

V S

Q SEE E

= =where:

VE = cumulative wastewater volume passedthrough the column during the time interval

0 - tE

Q = wastewater flow rate


53/103

PIERO M. ARMENANTE

NJIT

Time Required for Adsorption Zone

to Move Its Own HeightThe time, tA, required for the adsorption zone to

move its own height down the column is:

tV V

QA E B

where:

VB = cumulative wastewater volume passedthrough the column during the time interval0 - tB

tB= time required for the effluent concentration toreach the breakpoint, CB


54/103

PIERO M. ARMENANTE

NJIT

Adsorption Wave Velocity

The velocity, uA, of the adsorption zone (equal tothe wave velocity, uw) is given by:

uL

t

L

t tu

L

tW

L E F

AA

A

= =

= =

which can be rearranged to give:

L

L

t

t

t

t tA A

L

A

E F

= =

where:L = height of column

LA = height of adsorption zone


55/103

PIERO M. ARMENANTE

NJIT

Fractional Pollutant Removed in the

Adsorption ZoneIf additional wastewater is passed through thecolumn after the effluent concentration hasreached the breakpoint, CB, more pollutant will be

removed until the effluent concentration becomesequal to CE. This extra amount of pollutant is:

( )m C C dV oV

V

B

E

= This amount is only a fraction of that which could

be removed if the adsorption zone was not at theend of the column, in which case it would be:

( )m C V V s o E B=


56/103

PIERO M. ARMENANTE

NJIT


Adsorption ZoneThe fractional pollutant removal capacity at theend of the column, f, is then:

( )( )

fm

m

C C dV

C V Vs

oV

V

o E B

B

E

= =

The fractional pollutant removal capacity, f, canbe determined experimentally by monitoring the

effluent concentration (after the breakpoint) as afunction of the effluent cumulative volume.


57/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone

fm

m

C

Cd

V V

V Vs o

B

E B

= =

1

0

1

0 0.2 0.4 0.6 0.8 1

(V-VB)/(VE-VB)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

C/Co

C /CB o

C /CE o

Experimental

Points


58/103

PIERO M. ARMENANTE

NJIT

Pollutant Removed in the Adsorption

Zone: Large fValue (f 1)

CE/Co

CB/CoExperimentalPoints

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

(V-VB)/(VE-VB)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

C/Co

f = Gray Area


59/103

PIERO M. ARMENANTE

NJIT


Zone: Large fValue (f1) If f1, then the adsorption zone at the end of the

column already contains a significant amount of the

adsorbate and has the potential for adsorbing very

little extra pollutant. This implies that, in general, the wastewater

saturates the carbon layer by layer and that the

transition zone from the fully saturated carbon zone

to the unsaturated zone is short. This typically

occurs when the wastewater velocity is low. This also means that the adsorption zone is quiteshort and the t ime requ ired for i ts format ion is clo seto zero.


60/103

PIERO M. ARMENANTE

NJIT


Zone: Small fValue (f0)

0 0.2 0.4 0.6 0.8 1

(V-VB)/(VE-VB)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

C/Co

f = Gray Area

ExperimentalPoints

CB/Co

CE/Co


61/103

PIERO M. ARMENANTE

NJIT


Zone: Small fValue (f0) If f0, then the adsorption zone at the end of the

column contains little adsorbate in the carbon. Hence it

has the potential for adsorbing nearly as much as a

similar zone made of fresh carbon.

This implies that, in general, the wastewater does notsaturate the carbon layer by layer, but that the

transition zone from the fully saturated carbon zone to

the unsaturated zone is gradual. This typically occurs

when the wastewater velocity is high.

This also means that the adsorption zone is quite deepand the t ime required for i ts formation is large and

nearly equal to that needed for the adsorpt io n zone to

move a distance equal to i ts depth.


62/103

PIERO M. ARMENANTE

NJIT

Time Required for the Formation of

the Adsorption Zone As the wastewater first enters a column containing fresh

(or regenerated) activated carbon the adsorption zone is

not established. The time required for the formation of

the adsorption zone can be estimated from:

( )t f tF A= 1

When f1, the length of the adsorption zone is quitesmall and the time for the formation of the adsorption

zone, tF, is nearly zero (layer-by-layer buildup);

When f0, the length of the adsorption zone is quiteextended and the time for the formation of the

adsorption zone, tF, is significant.


63/103

PIERO M. ARMENANTE

NJIT

Height of Adsorption Zone

Recalling that it is:L

L

t

t

t

t t

A A

L

A

E F

= =

it is possible now to eliminate tF from the

expression of the LA/L ratio to get:

( )

L

L

t

t

t

t f t

A A

L

A

E A

= = 1

which can also be expressed in terms of the

corresponding cumulative volumes as:

( )( )L

L

V V

V f V V

A E B

E E B

=

1


64/103

PIERO M. ARMENANTE

NJIT

Height of Adsorption Zone

The equation:

( ) ( ) ( )

L

L

V V

V f V V

V

S

V

SV

Sf

V

S

V

S

A E B

E E B

E B

E E B'=

=

11

can be use to experimentally determine the heightof the adsorption zone, LA, from experimental labdata (since only the ratios Vi/S are important).

The experiments should be conducted for thesame value of the ratio Q/S. Then the value ofLAcan be determined provided the height of the testcolumn (L ') is known.


65/103

PIERO M. ARMENANTE

NJIT

Interpretation of Experimental Data

A common way to collect information on theperformance of an adsorption column and toscale up the results consists insetting up a column as high as

that eventually to be used inthe full scale application, butof much smaller diameter

Data are then collected bydetermining the time at

breakpoint, tB, at differentpoints (ports) along thecolumn

Port

Port


66/103

PIERO M. ARMENANTE

NJIT

Experimental Determination of

the fValueThe fvalue can be determined experimentally by

obtaining Cvs. Vdata as the adsorption zonepasses through the sampling port. Since VBand

VE can also be determined with this approachthen fcan be calculated from its definition:

( )

( )

fm

m

C C dV

C V Vs

oV

V

o E B

B

E

= =


67/103

PIERO M. ARMENANTE

NJIT

Degree of Column Saturation at

BreakpointThe degree of column saturation at breakpoint, ,is defined as the fraction of column saturation atbreakpoint, i.e.:

= Amount of pollutant in column at breakpointMaximum theoretical amount of pollutant in column

The value of is within the range 0 - 1, and is

proportional to the degree of utilization of theactivated carbon packing at breakpoint, i.e.,before the column must be shut down for carbonreplacement or regeneration.


68/103

PIERO M. ARMENANTE

NJIT


Breakpoint (continued)

SaturatedZone

C C

Co Co

B o

Column atbreakpoint

Saturatedcolumn

Adsorption

Zone

( ) ( ) ( ) ( )

( )( ) ( )

= = +

=

= +

M

M

S L L q SL f q

SL qS L L q SL f q

SL q

S

A s So A s So

s So

A s app So A s app So

s app So

1 1 1

11


69/103

PIERO M. ARMENANTE

NJIT


Breakpoint (continued)By simplification one can obtain the following

equation for:

( ) ( ) = = + MML L L f

LS

A A 1

i.e.:

= = M

M

L f L

LS

A

If f and LA have been determined can becalculated for any column of length L .


70/103

PIERO M. ARMENANTE

NJIT

Calculation of Cumulative Pollutant

Removal at BreakpointOnce is known it is possible to determine thecumulative amount of pollutant, M, removed bythe time the breakpoint is reached (and the

column must be taken off line):

M M q SL K C SLS So sapp F o sappn= = =

1

where Co is the pollutant concentration in the

incoming wastewater.


71/103

PIERO M. ARMENANTE

NJIT

Calculation of Breakpoint Time

The breakpoint time, tB, can be calculated as:

tB =cumulative amount of pollutant adsorbed at breakpoint

rate of pollutant fed to column

i.e.:

tM

QCB

o

=

at which time the column must be taken off line.

The cumulative volume of wastewater, VB, treatedat breakpoint is given by:

V Q tB B=


72/103

PIERO M. ARMENANTE

NJIT

Alternative Determination of the

Adsorption Zone ProfileAn alternative method to determine the profile and

length of the adsorption zone (and hence the fvalue and LA) is to model the adsorption zone as if

it were an independent column operating atsteady state and having a cont inuousinput of

both solid activated carbon and wastewater.

This approach is equivalent to assume that the

frame of reference moves with the adsorptionwave.


73/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone ProfileCo

CE

CB

C=0

CE

CB qB

qE

LLALA

dZ

Q

Qq

qso

qE

qB

q=0


74/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Mass Balance In performing a mass balance for such a continuous

column the assumption is made that the incoming

and outgoing streams are nearlyin equilibrium (if

they were really in equilibrium the column will be

infinitely high).

This implies that the incoming wastewater (pollutantconcentration: Co) encounters a carbon which is

practically saturated with the pollutant at that

concentration (qSo).

Similarly the wastewater leaving the column containspractically no pollutant, and so does the fresh

incoming carbon.


75/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Mass BalanceA material balance around the entire continuouscolumn gives:

( ) ( )Q C Q qo q So

0 0

where:

Q= wastewater flow rate

QP= carbon flow rate

Co= pollutant concentration in incomingwastewater

qSo= pollutant concentration in spent carbon


76/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Mass BalanceSimilarly, a material balance between the bottomof the column and a generic section gives:

( ) ( )Q C Q qq

0 0

Hence, the operating line (mass balance) for the

continuous column is:

C

q

C

q

Q

Q

o

So

q= =

Remark: the points (CE, qE) and (CB, qB) must lieon the operating line.


77/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Mass Balance

q(g solute/g carbon)

C

(g/L)

Isotherm

Operating Line

Qq/Q

qB qE qSo

CB

CE

Co

C

C*

q


78/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Mass Balancein a Differential Section of the Column

Assuming that external (or external-internal) masstransfer dominates the overall adsorption

phenomenon a differential balance for thepollutant in an infinitesimally thin layer of thecolumn yields:

Rate of pollutant removal from the wastewater =

Rate of pollutant transfer to the carbon


79/103

PIERO M. ARMENANTE

NJIT

Alternative Determination of the Adsorption

Zone Profile: Mass Balance in a DifferentialSection of the Column

In mathematical terms the previous equation can be

written as:

( )QS dC u dC K a C C dz s L= = *

KL = mass transfer coefficient between the bulk of the

wastewater and the surface of the carbon (m/s)

a= external surface area of carbon particles per unit

bed volumeC*= concentration of pollutant in the wastewater that

would be in equilibrium with the adsorbed

concentration, q


80/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Integrationof Mass Balance Equation

Integration of the previous equation yields:

z uK a

dCC C

C C Cs

L C

C

B E

B

=

'' '*

for

In addition it is:

L uK a

dCC CA

s

L C

C

B

E

= '' '*


81/103

PIERO M. ARMENANTE

NJIT


Adsorption Zone Profile: Calculation offFrom the previous equations it is:

z

L

V V

V V

dC

C C

dC

C C

z L V V V A

B

E B

C

C

C

C A B E

B

B

E

=

=

< <

Date post:	14-Apr-2018
Category:	Documents
Upload:	pippo2378793
View:	234 times
Download:	5 times

ARMENANTE ny Adsorption with Granular Activated Carbon.pdf

Documents