MA THEM A TICAL M ODELING

5. 1 Adsorption Experiments

5. 1 . 1 Kinetic Studies

The rate equation of phenol and naphthalene adsorption on GAC can be expressed as:

( 1 )

Where k is the rate coefficient and n is the order of the equation. To determine the rate of the reaction and the rate coefficient, three rate models (zero-, first- and second­

order) were fitted to the experimental data of the kinetic studies for phenol and naphthalene. The rate parameters along with R2 coefficient obtained from the linearized form of the three rate models were calculated as summarized in Table 5. 1 .

Table 5. 1 Rate parameters of l inearized kinetic equations of phenol and naphthalene adsorbed on GAC

Phenol Naphthalene

Order of rate Slope Intercept Rl Slope Intercept Rl equation

o Order - 1 .4725 47.285 0.3653 -0.35 1 4 1 1 .42 1 0.4588

1 st Order -0.075 3 .6769 0.7005 -0. 1 089 2.3828 0.88 7 1

20d Order 0.0078 0.0208 0.9578 0. 1 355 0.2734 <Y.92 1 4

As obvious from the values of R2 (Table 5 . 1 ), the use of a second-order rate fonnulation for the sorption of both phenol and naphthalene on GAC would be better than the other two rate models. Thus. the rate equations for the two compounds are written as:

For phenol:

For naphthalene:

dC

^{CAe =} - 0 . 0078

C

²

dt

dC _{CAe = _} 0 . l 3 5 5 C ² dt

(2)

(3)

Where dC _CAe

is the rate of change of concentration due to adsorption on GAC.

dt

Figure 5 . 1 and 5 .2 show that the calculated values of this model were successfully fitted with the measured concentrations.

100

i

⁷⁵

'-'

= 0 :c CI:

!:: ⁼ _� 50

CJ =

U 0

'0 ₌

� 25

f

•

o 20

Measu red V a l ues

I

C a l c u la ted V a l ues

40 T i m e (bours)

60 80

Figure 5 . 1 Comparison between measured and calculated concentrations of phenol removed by GAC (Co phenol = 1 00 ppm; Xo= 50 mg; V=20 ml; ^{. �.� -}

T= 25 °C; r shaking= 1 20 rpm)

0 1

30 r---_

r---

•

M easu red Va l u es Calcu lated Values

o 20 40 60

Time (hou rs)

Figure 5 .2 Comparison between measured and calculated concentrations of naphthalene removed by GAC (Co naphthalene = 30 _ppm; Xo= 20 mg; V=20 ml;

T= 25 °C; r shaking= 1 20 rpm)

5. 1 .2 Isotherm Studies

The non-competitive Langmuir, Freundlich and Redlich-Peterson isotherm models have been shown to be suitable for describing mono-component adsorption equilibrium of metal ions, inorganic matters, and organic species by algal, fungal and bacterial cells, suspended cells, activated carbon, sediment, peat, etc ( Rao and Viraraghavan 2002).

In this study, adsorption isotherm data were analyzed with different models to evaluate the equilibrium sorption parameters. Three isotherm models: Langmuir, Freundlich and linear models were fitted with the experimental results of the isotherm study for phenol and naphthalene. The R2 values of the three fitted equations were determined in order to determine the suitability of these models to the employed experimental conditions.

The Langmuir model assumes uniform energies of adsorption onto the surface (Geankoplis, 1 993). For a single solute, the Langmuir isothenn, which applied to adsorption on completely homogeneou surface with negligible interaction adsorbed molecules, is represented by the following equation:

"

q

QK

^{I e}

1 + K I e (4)

=

Where qO is the ratio between the amounts of sorbate (S) per mass of adsorbent (mg/g) to the equilibrium concentration of the adsorbate (Ceq) in the solution (mgIL) and Q is the asymptotic maximum solid phase. The linearized form of the Langmuir equation

is written as:

1 S

= 1 1 1

------ + ^-

K

^{L B} C ^eq B ⁽⁵⁾

Where B and KL are Langmuir constants related to maximum adsorption capacity and energy of adsorption, respectively. Both parameters are functions of the characteristics of the system as well as time. The essential characteristics of Langmuir isotherm can be expressed in term of dimensionless constant separation factor or equilibrium parameter RL, which is defined by Weber and Chakkravotri as quoted by Asku and Yener ( 1 998).

R ^{I. = (6)}

Where Co is the initial concentration mg/L. RL values between 0 and 1 indicate favorable adsorption for all the initial concentration studies. The Freundlich isothenn equation is commonly written as:

s (7)

0 7

Where Kf and nf are Freundlich constants related to adsorption capacity and adsorption intensity, respectively. The adsorption data are analyzed using the logarithmic form of the Freundlich isotherm as shown by the following equation:

loge S ) ⁼ loge

K

^f ) + n f log( C eq ) ₍₈₎

The experimental measurements of the adsorption isotherms for phenol and naphthalene are also analyzed using a linear model :

S ⁼

KlinCeq

⁽⁹⁾

Where Klin is the linear sorption distribution coefficient. Values of the sorption parameters resulting from the best fit of the three models along with the values of R2 are listed in Table 5 .2. Based on the values of the determination coefficient, it would appear that Freundlich equation gives the best representation of the experimental isotherm data.

1 50

Y = 84.0886 * X R-sq uared = 0.9 1 0285

1 00

,-., _<>

--ell ell E '-' rJ)

Y ⁼ 1 .824 1 1 * X 50 _<> R-squ a red ⁼ 0.863689

D N a p h t h a lene

<> ^Phenol ��

0

0 ^{2 0} 40 60 ⁸⁰

Ceq ( m g/I)

Figure 5.3 Linear adsorption isotherms of phenol and naphthalene on GAC

\�.!

^{p�enol =}

1 00 ppm; Co naphthalene = 30 ^ppm; T= 25 °C; r shaking= 1 20 rpm)

0.05 0.04

--^ell 0.03

� 6

'-'

rJ) -- -;

0.01

y ⁼ 0.0277464 * X + 0.0 1 22773 R- q u a red = 0.89 1 7 1 2

Y ⁼ 0.00391 645 ^{* X +} 0.0081 0744 R-sq uared ⁼ 0.8871 04

2

N a p h th a le n e

<> P h e n o l 4

l ICeq ( l/mg)

6 8

Figure 5.4 Linearized Langmuir adsorption isotherms of phenol and naphthalene on GAC (Co phenol = 1 00 ppm; Co naphthalene = 30 ppm; T= 25 °C; r shaking= 1 20 rpm)

2.50 2.25

2.00

--rJ)

'-' _ell 1 .75

0

1 .50 1 .25 1 .00

- 1

Y ⁼ 0.588241 * X + 1 .95845 R-sq u a red ⁼ 0.958 1 06

, .

�

Y ⁼ 0.309789 * X + 1 .4455 R-sq ua red = 0.963289

" I

L. N a p h t h a l e n e I

<> ----P h e n o l

�

0 1 2

log (Ceq)

Figure 5.5 Linearized Freundlich adsorption isotherms of phenol and naphthalene on GAC (Co phenol = 1 00 ^ppm; Co naphthalene = 30 ^ppm; T= 25 °C; r shaking= 1 20 rpm)

� 1

. . ... .,� -

According to R2 coefficients of the three models, which were determined and summarized in Table 5 .2, the three isotherms had high R2 coefficients. Consequently, it would appear that Freundl ich equation gives a good representation of the experimental isotherm data.

Table 5 .2 Comparison of the l inear, Langmuir and Freundl ich constants with R2 coefficients obtained from the adsorption i sotherm models of phenol and naphthalene

on GAC

Isotherm Models Adsorption System

Model Parameters Phenol + GAC Naphthalene + GAC

Langmuir _KL 0.4424826 2.070 1 0 1

Equation B 8 1 .45 1 1 3339 1 23 .3434

R--r 0.89 1 7 1 2 0.8871 4

Freundlich Kr 27.893306 90.876 1 66

Equation nr 0.309789 0.58824 1

R2 0.963289 0.9581 6

Linear Klin 1 .824 84.089

Equation _{R2 0.8636 0.9 103}

The maximum adsorption capacity (B) was 1 23 .34 mg/g GAC for naphthalene and was 8 1 .45 1 1 mg/g for phenol . This magnitude of B, the Langmuir constant, indicated that the amount of pol lutant per unit weight of sorbent to form complete monolayer on the surface was significantly high for both phenol and naphthalene. Moreover, this value was higher for naphthalene than for phenol because naphthalene ^IS a hydrophobic chemical in water that tends to be removed by the solid phase.

A large value of KL related to the binding energy also implied strong bonding of phenol and naphthalene to the GAC. The binging energy with GAC was higher for naphthalene than for phenol by 8 orders of magnitude. The dimension separation factor, RL was calculated from the Langmuir isotherm for phenol and naphthalene as fol lows:

R ( phenol ) = 1 = 0 .022 1

L 1 + ( ( 0 .44248 ) * ( 1 00 »

( 1 0)

-. ::...� -

1

RJ. (naphthalene) ⁼ 1 ₌ 0 0 1 58

1 + « 2.070 1 0 1) * (30)) . ( 1 1 )

The values for both phenol and naphthalene were less than 1 .0 (RL < 1 ) indicating a highly favorable sorption for all pollutant .

5.2 Biological Removal Experiments

The differential method of analysis was used to determine the order of removal rate reaction when using bacteria alone. This is based on the assumption that the rate of reaction is proportional to the nth power of the concentration.

dC

^bacteria

dt - K

_bactena ^.

C

^{n baclena} ( 1 2)

Where Kbaclena is the degradation rate constant and nbacteria is the order of the degradation reaction. The value of n for phenol degraded by P I 0 and for naphthalene degraded by N 1 6 can be determined using the following expression (Tchobanoglous and Schroeder, 1 985):

n =

1

og (

^_

dC

_� t 1 ) ^_

loge

^_

dC

_� ^{t 2 )}

log C

^{t 1 -}

log C

^{t 2 ( 1 3)}

As a result, ^nbactena for Phenol is 3 . 1 84 and for naphthalene is 3.84. The values of

Kbacleria for the two compounds were determined by substitution in the rate equation at different times and taking the average. Based on this, it was found that K for phenol is 2 .6748 * 1 0-6 and for naphthalene is 4.90368* 1 0-6.

For phenol:

dC

^bactena

dt

^{= _}

( 2 . 6748

^{* 1 0}

- 6 ) C

^{3 1 838}

. ... �� -

( 1 4)

-:

c

1 C 2 1 838

( log( ⁰ »

1 0

^{2 . 1 838} ( 2 . 1 838 KC ⁰ 2 1 838 / + 1 )

( 1 5)

de

^{ba tena}

Where

dt

is the change of concentration due to the biological removal of chemicals by bacteria (biosorption and biodegradation). Figures 5 .6 and 5.7 show good agreement between the model and the experimental (measured) data for both phenol and naphthalene.

1 00

•

Measu red Values

l

Calculated Values

'-" 7 5

c 0 ---=

�

E c ⁵⁰

8 g

_Q,> ^{2 5 :}

f

^•

0

0 1 00 2 0 0 300 400

Time ( h o u rs)

Figure 5.6 Comparison between measured and calculated concentrations of phenol removed by bacteria alone (Co phenol ⁼ 1 00 ppm; V=200 ml basal solution; 1 00 vol.%

active bacteria; T= 25 °C; r shaking= 1 20 rpm)

For Naphthalene:

dC

^bactena

dt

^_

( 4 . 90368

*

1 0 - 6 ) c

^{3 84 1 ( 1 6)}

-:

�

'-'

= 0

;c:l

� �

₌

a

_�

� =

i �

1 C 2 84 1

(^--Iog( ^___.!!..o --::--,:--^__

C ^{1 0}

^{2 . 84 1} ( 2 . 84 1 KC (12 84 1 1+ I ) ))

40

• Measu red V a l ues

3 0 C a l c u la ted V a l ues

2 0

1 0

0

0 1 00 2 0 0 300

T i m e ( ho u rs )

400

Figure 5 . 7 Comparison between measured and calculated concentrations of naphthalene removed by bacteria alone (Co naphthalene = 30 ppm; V=200 ml

basal sol ution; 1 00 vol.% active bacteria; T= 25 °C; r shaking= 1 20 rpm)

5.3 Inactive Biological Activated Carbon

( 1 7)

In this system, chemicals were adsorbed on the active sites of both GAC and the cell walls of inactive microorganisms. The kinetic models of phenol and naphthalene sorption using GAC and 1 00% (vol.) of bacterial suspension were fitted with 0-, 1 51_, 2nd -, and 3rd -order of adsorption equations. The parameters of the rate equations were shown in Figures 5.8, 5.9, 5 . 1 0 and 5 . 1 1 and in Table 5.3 and R2 of each order are calculated in order to select the best-fit equation.

1 20

1 00 Y (pbenol) = -0.854266 * X + 58.6304

80 60 40

R-squared ⁼ 0.656 1 22

Y (naptbaleoe)= -0.2385 1 7 * X + 20. 1 954

R-squared ^{= 0.686539}

[ <> pbenol

I L n a phtba lene

20 r:1"""'" ^__

<>

o �---�--^____L-^____�����

o 20 40

Time ( h o u rs )

60 80

Figure 5 . 8 R 2 coefficient and rate parameters of zero order linearized kinetic equation of phenol and naphthalene biologically adsorbed by inactive P7 and N 1 7

6

4

--0" e.>

U '-"

-c 2

o o

Y (naphthalene) ⁼ -0.0250359 '" X + 4.0 1 023 R-sq ua red ⁼ 0.805029

Y (phenol) ⁼ -0.0 1 73838 '" X + 2.97656

R-squa red ⁼ 0.8 1 3 1 52

1 L <>

^_'__phenol naph thalene

20 40

Time (bours) ^{60 80}

Figure 5.9 R2 coefficient and rate parameters of 1 51-order l inearized kinetic equation of phenol and naphthalene biologically adsorbed by inactive P7 and N 1 7

0.200

�

^{0. 1 00}

0.000

o

Y ( p benol) = 0.00090898 " X + 0.0 1 88 1 53 R-sq u a red = 0.9 1 70 1 3

Y ( n a ptba lene)= 0.00 1 32 77 1 .. X + 0.0527742 R-sq u a red = 0.867045

20

<> ^phenol

40 T i m e ( ho^{urs )}

n a p h t halene

60 80

Figure 5 . 1 0 R2 coefficient and rate parameters of 2nd -order l inearized kinetic equation of phenol and naphthalene biologically adsorbed by inactive P7 and N I 7

�

_-.!.­

<

00400

g

^{0 . 2 00}

Y ( p b e n o l ) = 0.00232523 .. X + 0. 1 36357 R-sq ua red = 0.867 1 24

Y ( n a p t b a len e) = 0.0024429 .. X + 0.22705 1 R-sq u a red = 0.862574

n a p h t halene 0.000 L-^{______�� ______}-L ^{________� ______}�

o ^{2 0 40}

Ti m e ( ho u rs) ^{6 0 80}

Figure 5 . 1 1 R2 coefficient and rate parameters of ³ rd -order linearized kinetic equation of phenol and naphthalene biologically adsorbed by inactive P7 and N 1 7

.. ... -;0.

;I I

Table 5.3 R2 coefficient and rate parameters of linearized kinetic equations of phenol and naphthalene biologically adsorbed by inactive bacteria

Order of rate equation

o Order 1 st Order 2nd Order 3rd Order

Slope -0.854266 -0. 0 1 7384 9.089E-4 2.325E-3

Phenol

Intercept R2 58.6304 0.656 2.97656 0.8 l 3 0.0 1 882 0.9 1 7 0. 1 3635 0.867

Naphthalene

Slope Intercept R2 -0.23852 20. 1 954 0.6865 -0.025036 4.01 023 0.805

1 .327E-3 0.05277 0.867 2.443E-3 0.22705 0.8626

Based on the values of the correlation coefficient presented in Table 5.3 the rate -: kinetics of adsorption of both phenol and naphthalene on GAC can be approximated

as a second-order. The two equations are written as:

For phenol:

For naphthalene:

de

_moclBAC

Where

dt

dCinactBAC

=

^-0.000

9

⁰⁸

9

^{C 2}

dt

dC inactBAC

=

-0.00 1 327 C 2 dt

( 1 8)

( 1 9)

is the change of concentration due to the removal of chemicals inside inactive BAC (GAC and inactive microorganisms) and CinactBAC is the concentration of chemical inside inactive BAC . Figures 5 . 1 2 and 5. 1 3 show the fitting of this model with the experimental (measured) data for both phenol and naphthalene .

. . ;': :::;;:'�. -

1

1 00

-..

, -

M easu red Va l ues

l

⁷⁵ Ca lcu la ted Valu es

'-"

= 0 '.J:l

�

_{= 50}

� �

8 _-

=

0 = 25

-= �

�

..

_•

0

0 20 40 60 80

T i m e ( h o u rs)

Figure 5 . 1 2 Experimental and calculated values of phenol removal by inactive BAC (p7+GAC) (Co phenol = 1 00 ppm; Xo = 500 mg; V=200 ml basal solution; 1 00 vol.%

inactive bacteria; T= 25 °C; r shaking= 1 20 rpm)

�

-..

'-' 8

= o

._-

-

� \.0 -=

� � c o

U �

30

20

5 1 0

-

_�

.c - -= c.

Z �

o o

•

Measured Values

I

Calculated Values

L--_______-- --

20

-

40 Time (bours)

•

60 80

Figure 5 . 1 3 Experimental and calculated values of naphthalene removal by inactive BAC (N 1 7+GAC) (Co naphthalene = 30 ^ppm; Xo = 200 mg; V=200 ml basal solUtion; 1 00

vol.% inactive bacteria; T= 25 °C; r shaking= 1 20 rpm)

-:

5.4 Active Biological Activated Carbon

The rate models determined for the adsorption of phenol and naphthalene by inactive BAC were utilized to calculate the concentration of phenol or naphthalene removed by a combined system of GAC and bacteria (active BAC). Figure 5 . 1 4 and 5. 1 5 show the experimental data obtained under BAC conditions and the fit model for the case of inactive BAC.

Measured Values (from active system)

---.

�

e ₇₅

Calculated Values (from inactive s stem

'-'

.� _oW c

eo: I.

... 50

c Q,j CJ C

U Q

-Q = 25

..c Q,j

�

• 0

0 1 00 200 300 400

Time (bours)

Figure 5. 1 4 Experimental and calculated values of phenol removal by inactive and active BAC (p7+GAC) (Co phenol = 1 00 ppm; Xo = 500 mg; V=200 ml basal solution;

1 00 vol.% active and inactive bacteria; T= 25 °C; r shaking= 1 20 rpm)

. . .... � -

30

L

2 0

1 0

o o

Measured Values (from active system) Calculated Value (from inactive system}

1 00 200

T i m e (h o u rs)

•

300 400

Figure 5. 1 5 Experimental and calculated values of naphthalene removal by inactive and active BAC (N 1 7+GAC) (Co phenol = 1 00 _{ppm; Xc =} 500 mg; V=200 ml basal

solution; 1 00 vol.% active and inactive bacteria; T= 25 °C; r shaking= 1 20 rpm)

The measured concentrations of phenol or naphthalene for the active BAC system (experimental data) were compared with those calculated from the kinetic equation controlling the inactive biosorption of the two chemicals. Figures 5 . 1 0 and 5 . 1 1 show that the concentrations obtained with the inactive system, at a given time, is very close to those obtained with an active microorganism. Therefore, the BAC was working as an adsorbing system for both phenol and naphthalene and the role of bacterial degradation is not significant. Inside BAC system, Adsorption of the two chemicals took place on the active sites of GAC and on the cell walls of bacteria.

The removal of phenol and naphthalene from solution in the active BAC system can be modeled as sorption on GAC and biological removal (biosorption and degradation) by the microorganisms. Therefore, the rate of change of concentrations in the active BAC system is given by:

de actBAC

dt ( de bacteria dt

+

de CAe ₎

dt

⁽²⁰⁾

.. ,

Where d

�;8AC

is the change of concentration due to the removal of chemicals

inside active BAC differential method was used to analyze the kinetic data controlling the removal of a phenol and naphthalene by active BAC. When using P l O bacteria combined with GAC, It was found that the rate equation could be expressed as follow :

In case of phenol:

dC

actBAC

dt

d

_C

actBAC dt

- K

^actBAC

C

^{n aclBA(}

- 3 . 5 1 50675

*

1 0 -5 C 3 .212

( 2 1 )

(22)

Where KactBAC is the removal rate constant and nactBAC is the order of reaction inside active BAC system. CactBAc, Cbacteria and COAC are the concentrations of component inside active BAC system, bacterial suspension and GAC system, respectively. The calculated values of this model were successfully fitted with the measured concentrations as shown in Figure 5 . 1 6.

. . ... -::. -

1 00

-..

_s

c. 75 5 c '.c o

...

f _{c 50}

� CJ C o

U '0 _.c

5

^{2 5}

�

o o

•

1 00

M ea s u red V a l u e C a l c u l a ted V a l ues

2 0 0

T i m e (hours) 300

• 400

Figure 5 . 1 6 Measured and calculated concentrations of phenol removed by active BAC (Co phenol = 1 00 _ppm; Xo = 500 mg; V=200 ml basal solution; 1 00 vol.% active

bacteria; T= 25 °C - r shakmg= 1 20 rpm)

Furthermore, the active BAC system is a combination of GAC and bacteria, Therefore, The rate equation is a summation of the equations modeled for biological removal of a chemical by bacteria alone and by GAC alone. Theoretically, the overall removal inside active BAC would equal the removal of a chemical due to both GAC and bacteria. For phenol:

dC actBAC

=

-( K . C

^{nboClerw +}

K C

^nGAc

)

dt bacteria GAC

dC

aCIBAC

=

- 2 . 6748

*

1 0 -6 C 3 . l 838 ^_ 0 . 0078 C 2 dt

(23)

(24)

Where KGAC nGAC are the parameters of rate equation controlling the removal of a chemical by GAC.

1 UJ

.... ,-. -

In case o(naphthalene:

When using N 1 6 bacteria combined with GAC to remove naphthalene, it was found that the rate equation could be expressed as follows

dC ^acfBAC dt

de ^ac/BAC dt

- K bac/ena

^.

C

^nbouena

- K CAC C

^n(,AC

= - 4 . 90368 * 1 0 -6 C3 841 - 0 . 1 3 5 5 C 2

(25)

(26)

Differential method was used to analyze the kinetic data controlling the removal of naphthalene by active BAC. The following kinetic equation describes the removal rate of naphthalene.

dC

^acrBAC

dt - 1 . 8383953

^*

1 0

^{- 4}

C

^{2 . 4542} ₍₂₇₎

The calculated values of this model were successfully fitted with the measured concentrations as shown in Figure 5 . 1 7.

40

E

_c..

�

Measu red Val ues

� = ₀ 30 _L C a l c u lated Va lues

�

�

₌

� 2 0

8

= _�

= �

'i 1 0

.c _...

.c ^c.. •

�

^•

0

0 1 00 200 300 400

T i m e (bours)

Figure 5 . 1 7 Measured and calculated concentrations of naphthalene removed by active BAC (Co naphtheiene = 30 _ppm; Xo = 200 mg; V=200 ml basal solution; 1 00 vol.%

active bacteria; T= _{25 °C; r} shaking= 1 20 _rpm)

5.4. 1 F ree G AC Active Sites Eva l uation

According to the values obtained experimentally, the reduction in phenol concentration using active BAC was less than those adsorbed by GAC. On the other hand, bacteria alone have less removal capability than BAC. Based on these observations, a small fraction of the GAC active sites was used to adsorb the chemical inside active BAC system. This is due to the blockage of these sites by bacteria. At the same time, the pollutant would be adsorbed on the surface of the cell walls and biodegraded by bacteria. So, practically, the overall removal of phenol by active

BAC follows the equation written below.

de ^actBAC

dt de ^bacteria

dt

I V

+

( de

^CAC

^* f )

dt

⁽²⁸⁾

Where f is the fraction of unblocked active site on GAC The d t . .

. e ermmahon 0 f the fraction of active sites on GAC ( 1 :f) that have been occupied and blocked by bacteria in BAC system was based on the overall rate equation of active BAC when using 1 00

% ( 01 . ) of bacterial suspension.

For phenol:

At the same interval of times, the reduction of phenol concentration inside active BAC system can follow the equation below:

Phenol removed active SAC = ( Phenol removed GAc)*f+ Phenol removed b actena . (29)

( C

^{actBAC 0 -}

C

^actBAC

) - (C

^{bacteria 0}

- C

^bacteria

) (C

^{CAC 0 -}

C

^CAC

)

C aclBAC

0 . 452 log 1 7579 . 266

1 0

1 . 36685 I + 1

C

^bacteria 0 . 4579 1 10 1 5 5 1 9 .679

= ^{1 0 9}

0.09065388 1 + 1

C

^GAe

1 + 0 . 74 1 t

^{95 . 522}

f

⁽³⁰⁾

(3 1 )

(32) (33)

It was found that

fphenol lOO%

equaled 0.2585. Where /phenol 1 00% is the fraction of available active sites on GAC when using 1 00 % of bacterial suspension volume to remove phenol. Based on this calculation, only one fourth of the active sites on the surface of GAC were used to adsorb phenol inside the active BAC system. Bacteria were blocked about 75% of the GAC active sites when using 1 00 % (vol .) of bacterial suspension with GAC.

•

... ---t

^-

1

For naphthalene:

Based on Equation (29) and Equation (30):

C ^aCIBAC

Cb

^acfena

.

C ^GAC

0 . 687663 log 1 30 . 72868

1 0 0 .0349489 1 1

0 . 35 1 9 log 1 3634 ^.8746

1 0

0 . 1 92276 1 + 1

22

. 575 1 + 3 . 0589

^t

(34)

(35)

(36)

f

naphthalen e l OO% equaled 0.049. _Where /naphthalene 100% is the fraction of available active sites on GAC when using 1 00 % (voL) of bacterial suspension to remove naphthalene. According to this calculation only 5% of the active sites on the surface of GAC were used to adsorb naphthalene inside the active BAC system. Bacteria, which were considered as a l imiting factor for the adsorption of naphthalene on GAC, were blocked about 95% of the GAC active sites when using 1 00 % (voL) of bacterial suspension with GAC.

5.4.2 Contri butio n of S u rface Sorption

The contribution of biodegradation process in the overall removal of phenol in BAC system was calculated and obtained from the rate equation of inactive BAC. The fraction (a) is ratio of surface biosorption on the bacterial walls to the biological removal of chemical by bacteria (biodegradation + biosorption) as shown in equation below. Inside inactive BAC system, 1 00 % (vol.) of bacterial suspension was used in combination with GAC, which was equivalent to the percentage volume of bacterial suspension of active BAC. Therefore, the fraction if ⁼ 0.2423) of active"HAC was

.

^'

,

used as the ratio of available active sites on the surface of GAC inside the inactive P7 BA

dC surftorp

dt ( dC

bactena

dt

* a

)

⁽³⁷⁾

de _surfsorp Where

dt the rate of changes of concentration due to the surface biosorption on cell walls and Csurfsorp is the concentration of pollutant on the cell walls of bacteria. The overall removal of phenol using inactive BAC can fol low the equations written below.

For phenol:

dC inactBAC

dt ( dC GAC

^*

^{f )}

⁺

dC surfsorp

dt dt

⁽³⁸⁾

The overall rate equation of phenol removed by inactive BAC an be described ^as follows:

dCinactiveB£

=

[(dCGAC

^*

f)

⁺

( dCbaCleria

*

a)]

dt dt dt

( C ^InactBAC

⁰

- C . BAC ^lnact _{) - [(} C GAC

0

- C GAC ₎ * f ]

( C bacteria

0

- C bacteria )

a

phenol

_0.797

When substituting Equation (4 1 ) into Equation (37):

(39)

a

₍₄₀₎

(4 1 )

;:

^;

.. ...,.,:. -

'I

For naphthalene:

de

_surfsorp

dt 0 . 797 * ( de

^bactena

dt )

(42)

The overall rate equation of phenol removed by inactive BAC can be described in Equations (39) _and (40) . The value of a is evaluated below:

de

_surfsorp

dt

a naphtha/en e

=

O. 844

o . 844 * ( de

^bactena

dt )

(43 )

(44)

According to these values about 80% of the overall biological activity for the removal of phenol was due to the surface sorption on the cell walls whereas less than 2 1 % of this activity was due to biodegradation. In case of naphthalene, the contribution of surface biosorption was higher than that for phenol. The ratio (a

)

reached 84.4% of the overall biological activity, whereas only 1 6% of this activity was due to biodegradation. This conclusion is consistent with the similarly in the reduction of concentrations observed when using active BAC and inactive BAC.

5.4.3 F ree GAC Active Sites E n h a ncement

The ratio of surface sorption to biological activity (aphenol ⁼ 0.797, anaphthalene ⁼ 0.844) was used to observe the enhancement of the number of active sites on GAC when reducing the concentration of bacteria used inside inactive BAC. Only 40 and 45 % (vol.) of bacterial suspension was used this time instead of 1 00 % (vol .) in order to calculate (f) for phenol and naphthalene respectively, as written below. Where

C400/0inactBAC

is the concentration of chemical inside inactive BAC when using 40 % of bacterial suspension.

- .. ,--'

J V .J