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 CCHHEEMMIICCAALL  EENNGGIINNEEEERRIINNGG  TTRRAANNSSAACCTTIIOONNSS  
 

VOL. 40, 2014 

A publication of 

The Italian Association 
of Chemical Engineering 

www.aidic.it/cet 
Guest Editor: Renato Del Rosso
Copyright © 2014, AIDIC Servizi S.r.l., 
ISBN 978-88-95608-31-0; ISSN 2283-9216                                                                                     
 

Removal of Phenol from Water by Adsorption onto Sewage 
Sludge Based Adsorbent 

Salim Bousbaa,b, Abdeslam Hassen Meniai*b 
a
Département de Pétrochimie et de Génie des Procédés, Faculté de Technologie, Université 20-Août-1955 Skikda, BP 

26 Route d’El-Hadayek, Skikda 21000, Algérie 
b
Laboratoire de l’Ingénierie des Procédés d’Environnement (LIPE), Faculté de Génie des Procédés Pharmaceutiques, 

Université Constantine 3, Constantine 25000, Algérie 
* meniai@yahoo.fr  

The aim of this study is to evaluate the adsorption performances of sewage sludge based adsorbent SSBA 
for the removal of phenol from water. The SSBA was prepared by chemical activation with H2SO4 in a 
mass ratio of 1:1, followed by a pyrolysis at 650°C for 1 h under inert atmosphere. Phenol removal by 
SSBA was investigated using kinetic and equilibrium experiments. The results demonstrate that phenol 
sorption to the SSBA reached equilibrium at 2 h with the maximum sorption capacity of 26.16 mg.g-1 under 
given experimental conditions (initial Phenol concentration range = 40–200 mg.l-1; adsorbent dose = 5.0 
g.l-1 and temperature = 20°C). The phenol removal was high and relatively constant at (pH<pKa), whereas 
the phenol removal decreased sharply as the solution pH approached a highly alkaline condition 
(pH>pKa).The results indicate that the pseudo second order model was suitable for describing the kinetic 
data. Regarding the equilibrium data, the Freundlich isotherm was fitted well. This study demonstrates that 
SSBA could be used for phenol removal from water. 

1. Introduction 
Phenol is a toxic weak acid causes an unpleasant taste and odour even at low concentrations in water 
(Podkościelny and László, 2007). The major sources of phenol pollution in the aquatic environment are 
wastewaters from paint, pesticide, coal conversion, polymeric resin, petroleum and petrochemicals 
industries. Introducing phenolic compounds into the environment or degradation of these substances 
means the appearance of phenol and its derivatives in the environment. The chlorination of natural waters 
for disinfection produces chlorinated phenols. Phenols are considered as priority pollutants since they are 
harmful to organisms at low concentrations (Ahmaruzzaman, 2008). Treatment of wastewater containing 
phenol is a very important need for environmental protection and has been studied by various techniques 
such as chemical oxidation, biodegradation, membrane filtration, electro coagulation, solvent extraction, 
photo degradation and adsorption. Among these techniques adsorption is still the most popular and widely 
used technique for phenol removal. This work focuses on the removal of phenol from water using a low 
cost adsorbent prepared from sewage sludge by chemical activation with sulphuric acid. 

2. Materials and methods 

2.1. Raw sewage sludge 
Fresh sewage sludge was collected from an urban Wastewater treatment plant (WWTP) of Constantine 
town, in the Northeast of Algeria. The influent treated is mainly domestic and the plant use biological 
treatment process with activated sludge. The sludge used in this study was dewatered surplus sludge 
collected from a sun drying bed, traditionally used as a farmland fertilizer. 
 
2.2 Preparation of the sewage sludge based adsorbent (SSBA) 
Collected sample was air dried at 105°C until constant weight. The resulting solid was ground and sieved 
through 1 mm mesh. Dried sludge was impregnated in (3M) H2SO4 solution with the mass ratio of 1:1. The 

                                                                                                                                                      
 
 
 
 

          DOI: 10.3303/CET1440040 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Bousba S., Meniai A.H., 2014, Removal of phenol from water by adsorption onto sewage sludge based 
adsorbent, Chemical Engineering Transactions, 40, 235-240  DOI: 10.3303/CET1440040

235



mixture was magnetically stirred in a beaker for 48 h at ambient temperature. Then, the excess solution 
was decanted off and the precursor was air dried at 105°C for another 48h. 
After that, 15 g of chemical activated sample was placed into a covered ceramic crucible and placed in 
another big crucible. The cavity between the two crucibles was filled up with fuel coke particles <1 mm, to 
prevent O2 from entering the ceramic crucible during pyrolysis operation (Gascó et al., 2005). Then, the 
sample was pyrolyzed in a muffle furnace. The furnace temperature was gradually increased to 650°C at a 
rate of 10°C/min, and the final temperature of 650°C maintained for 1 h.  
After being pyrolyzed, the sample was washed with 3.0 M HCl to remove the acid-soluble inorganic 
impurities. Then, the sample was thoroughly washed with hot distilled water until constant pH was 
reached. After that, the sample was dried at 105°C for 24 h to constant weight. The resulting solid was 
grounded and sieved to a particle size of 0.125 mm. Finally the powder was stored in desiccators for 
further use. 
 
2.3 Adsorbate 
 
Phenol (C6H5OH) of analytical grade (supplied by Panreac, Spain), was used for the preparation of the 
stock solution (1.0 g.l-1). The experimental solutions of various initial concentrations (C0) were prepared by 
diluting stock solution to the desired concentrations.  
 
2.4 Characterization of SSBA  
The BET surface area of porous SSBA was estimated from adsorption-desorption of N2 at 77.4 K using a 
Quantachrome NOVA-e2200 analyzer. The pHPZC (point of zero charge) of SSBA was determined 
according to the procedure described by (Lopez-Ramon et al., 1999).  
 
2.5 Adsorption tests  
Batch Adsorption tests of phenol were carried out in brown dark bottles (to reduce photo-oxidation of 
phenol). The total volume of the reaction solution was kept at 20ml. The stoppred bottles were 
magnetically shaken at 300 rpm until equilibrium was reached in a thermostat water bath shaker. Blank 
sorption experiments were performed in the absence of adsorbent, and no sorption of phenol by the walls 
of the bottles occurred. The effect of solution pH on the removal of phenol was investigated over the pH 
range from 2–13. The initial solution pH was adjusted using 0.1 and 1.0 N HCl or 0.1 and 1.0 N NaOH. 
Adsorption equilibrium experiments were performed by stirring 20 ml of phenol aqueous solution with initial 
concentration of 40–200 mg.l−1 in each bottle containing 100 mg of SSBA. The solutions were agitated at 
different temperatures 20, 30 and 55 °C, respectively. Adsorption kinetic experiments were basically 
identical to those of equilibrium tests. The aqueous samples were taken out at some intervals. After 
adsorption, the adsorbent samples were separated by centrifugation at 4000 rpm during 15 min and the 
supernatants liquids were analyzed for residual phenol concentration using a double-beam 
spectrophotometer, Shimadzu, model UV-160, at wavelength of 270 nm.  The amount of phenol adsorbed 
onto per gram of adsorbent (qe) and the percentage removal efficiency (R %) were calculated using Eqs. 
(1) and (2), respectively. 
 

 
(1) 

 
(2) 

Where C0 and Ce are initial and equilibrium phenol concentrations, respectively (mg.l
-1), V is phenol 

solution volume (l), m is the mass of adsorbent (g). 

3. Results and discussion 

3.1 Characteristics of SSBA 
The resulting SSBA shows an acceptable development of the specific surface area (162.2 m2/g) compared 
to the raw sludge which is a non-porous material (< 1 m2/g).  The surface area of the SSBA is relatively 
small compared to those of the Commercial Activated Carbon (CAC). The pHPZC of SSBA (4.66) indicate 
that the adsorbent is an acidic material. Therefore, the adsorbent surface is positively charged at pH< 4.66 
and negatively charged at pH> 4.66. 
 

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3.2 Effect of contact time and initial phenol concentration 
 
The effect of contact time on the rate of phenol removal was investigated at different initial concentrations 
(50, 100 and 200 mg.l−1) as shown in Figure 1(a).The results indicate that the contact time to reach 
equilibrium is approximately 120 min for all experiments. Therefore, the chosen contact time of 180 min, 
used in our experiments, is sufficient to reach equilibrium. It was observed that the adsorption process is 
extremely fast. In fact, for all experiments more than 77% of the equilibrium adsorption capacity was 
reached within the first minute. The initial fast adsorption is probably due to the special one-atom-thick 
layered structure of SSBA, which makes phenol contact immediately with the active sites on the surface of 
SSBA. With further increasing time, the diminishing availability of the remaining active sites and the 
decrease in the driving force make it take long time to reach equilibrium. Figure 1(a) also showed that the 
equilibrium adsorption capacity increased from 9 to 23 mg.g−1 with the increasing initial phenol 
concentration from 50 to 200 mg.l−1. When the initial concentrations increased, the mass transfer driving 
force became larger and the interaction between phenol and adsorbent was enhanced, hence resulting in 
higher adsorption capacity. 

Figure 1: (a) Effect of contact time on the adsorption of phenol (adsorbent dose = 5 g.l−1; initial pH 7.0;             
T= 20°C) (b) Determination of the optimal dose of SSBA (C0 = 50 mg.l

-1; initial pH 7.0; T= 20°C; t = 3h) 

3.3 Effect of adsorbent dose 
The effect of adsorbent dose on the adsorption capacity (qe) and the removal percentage (R%) of phenol  
was studied and is shown in Figure 1(b). As the SSBA dose was increased from 0.25 to 20 g.l−1, the 
percentage of adsorbed phenol increased from 10.84 % to 99.76%, whereas the adsorption capacity 
decreases from 22.18 to 2.55 mg g-1. Above 5.0 g.l−1 of adsorbent dose, there was no significant increase 
in the removal rate of phenol, but the adsorption capacity decreased rapidly. Considering qe and R%, 
adsorbent dose of 5.0 g.l−1 was found to be the optimum SSBA dose and was used for all other 
experiments. 
 

3.4 Effect of pH 
Solution pH is one of the most important parameters to determine the adsorption property of an adsorbent 
due to its effect on the surface charge of the adsorbent and on the degree of ionization of adsorbate. 
Phenol as a weak acid with pKa = 10 and it dissociates at pH > pKa, the percentage of the molecular form 
of phenol can be calculated from the Eq(3). 

 
 (3) 

 

 

Pm(%) is the percentage of molecular phenol in the solution. From Eq(3) it can be seen that phenol is 
mainly in molecular form at pH<pKa and in ionic form (phenolate anions) at pH>pKa. In this study the 
effect of solution pH on the removal of phenol was investigated over the initial pH range from 2–13. The 
effect of phenol speciation on the adsorption is better explained by calculating the Pm(%) using Eq(3) at  
different final pH (pH at equilibrium) values and a plot of the Pm(%) and percent of phenol removal (%R) 
versus final pH are shown in Figure 2(a) which clearly shows that phenol removal is pH independent at 
pH<pKa (phenol is mainly in molecular form) and highly influenced when pH>pKa (phenol is mainly in ionic 
form). In fact  when phenol is mainly in molecular form, R% value is higher and constant (R ≈ 80 %) and as 
the pH is increased (pH>pKa),  the phenol ionic form increases which implicate a rapid decrease in R% 

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until it reaches its smallest value of 21% when Pm(%) was practically negligible 1 % at final pH 12. The 
decrease of R% value when pH>pKa is due to the presence of electrostatic repulsion between the 
negatively charged adsorbent surface (pH >pHPZC) and phenol ionic form. Even though the electrostatic 
repulsion at final pH 12, a significant removal of 21 % takes place indicating that chemisorption might be 
involved in the process, similar results were reported by (Bousba and Meniai, 2013) in the case of            
2-chlorophenol removal by SSBA. 

Figure 2: (a) Effect of pH on the removal of phenol (C0 = 100 mg.l
-1; T= 20°C; t = 3 h) (b) Langmuir 

isotherm representation for the adsorption of phenol onto SSBA (T= 20, 30 and 55°C; t = 3 h; C0 = 40-200 
mg.l-1) 
 

3.5 Isotherm analysis 
Several models have been published in the literature to describe the equilibrium adsorption systems. In 
this paper adsorption isotherms were fitted by the two classical models of Langmuir and Freundlich. 
Langmuir: 

 
(4) 

where qm (mg.g
−1) is the theoretical maximum monolayer adsorption capacity at the constant temperature, 

and b (l.mg−1) is the Langmuir constant related to the energy of adsorption.  
The essential features of the Langmuir isotherm can be expressed in terms of a dimensionless separation 
factor RL, which is expressed as: 

 (5) 
where b is Langmuir constant (l.mg−1) and C0 is maximum initial phenol concentration (mg.l

−1). The value 
of RL indicates the shape of Langmuir isotherm to be either unfavorable (RL >1), linear (RL =1),  irreversible 
(RL=0), or favorable (0<RL<1). Also the smaller RL value indicates a highly favourable adsorption. 
Freundlich: 

   (6) 

 
where kF (mg.g

−1(l.mg−1)1/n) and n are Freundlich constants related to the multilayer adsorption capacity 
and the surface heterogeneity, respectively. According to (Hamdaoui and Naffrechoux, 2007) It is 
generally stated that values of n in the range 2–10 represent good, 1–2 moderately difficult, and less than 
1 poor adsorption characteristics. The plot of qe versus Ce for the adsorption of phenol onto SSBA at 20, 
30 and 55 °C according to the non-linear form of Langmuir and Freundlich isotherm models were shown in 
Figures 2(b) and (3a), respectively. The parameters calculated by non-linear regression analysis of 
Langmuir and Freundlich isotherms were given in Table 2. The adsorption capacity of SSBA decrease with 
increase in temperature, indicating that the adsorption process is exothermic in nature. It can be seen from 
Table 2, that the correlation factor R2 is close to the unity for both models, but with a better fit of the 
experimental data by means of Freundlich isotherm, which prove the multilayer adsorption and the 
heterogenity of the SSBA surface. From table 2 it can be seen that the values of Freundlich constant n 
were found to be within the range of 2–10 witch indicate that the SSBA is good adsorbent for phenol.  

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Figure 3: (a) Freundlich isotherm representation for the adsorption of phenol onto SSBA (T= 20, 30 and 
55°C; t = 3 h; C0 = 40-200 mg.l

-1) (b) Plot of the pseudo second-order kinetic for the adsorption of phenol 
onto SSBA (T= 20°C; t= 3 h) 

Table 2:  Langmuir and Freundlich isotherm parameters for phenol adsorption at 20,30 and 55 °C  

 
T (°C)  

Langmuir isotherm  Freundlich isotherm 

Qm (mg.g
−1) b (l.mg−1) R

2 RL kF (mg.g
−1(l.mg−1)1/n)  n R2 

20    26.16 ± 1.77 0.109 ±0.028 0.927 0.04-0.19 6.059 ± 0.229   3.02± 0.09 0.996
30 24.15 ± 1.60 0.073±0.017 0.936 0.06-0.26 4.581 ± 0.319   2.82± 0.14 0.989
55 25.39 ± 1.64 0.041±0.007 0.964 0.11-0.38 3.239 ± 0.120   2.42± 0.05 0.998

 
The comparison of maximum monolayer adsorption of phenol onto various adsorbents was listed in     
Table 3, which showed that sewage sludge based adsorbent SSBA used in present work had a relatively 
quite adsorption capacity of 26.16 mg.g−1 compared to some data of low cost adsorbents obtained from 
the published literature. 

Table 3:  Comparison of the maximum monolayer adsorption of phenol onto various adsorbents 

Qm (mg.g
−1) Adsorbent  References 

59.2 Red mud (Gupta et al., 2004) 
17.1 Coal fly ash (Sarkar and Acharya, 2006) 
13.3 Samla coal (Ahmaruzzaman and Sharma, 2005) 
23.83 Bagasse fly ash (Srivastava et al., 2006) 
26.16 SSBA activated with H2SO4 Present work 
 

3.6 Adsorption kinetics 
The kinetic study is helpful in prediction of adsorption rate constants, equilibrium adsorption capacity and 
adsorption mechanism.  The capability of pseudo-first-order PFO and pseudo-second-order PSO kinetic 
models were examined in this study at three different initial concentation of phenol (50,100,200 mg.l−1) and 
at constant temperature of 20°C. 
The linear form of pseudo first-order model of Lagergren is generally expressed as follows : 

   (7) 

where qe and qt are the adsorption capacity  of phenol per unit weight of SSBA  at equilibrium and at time     
t (min), respectively (mg.g−1), and k1 is the PFO rate constant (min

−1). 
k1 and qe values were determined from the slope and intercept of the plots of ln(qe−qt) versus t (figure not 
shown) for different concentrations of  phenol and are listed in Table 3. From the data in Table 3, it can be 
seen that at all studied concentrations, the correlation coefficients R2 are small. Also, the experimental qe 
values do not agree with the calculated ones, suggesting that the applicability of the PFO model to the 
adsorption processes of phenol onto SSBA is unfeasible. 
The linear form of PSO model is expressed as follows : 
 

239



 
(8) 

where k2 is the PSO rate constant (g.mg
−1.min−1). The values of qe and k2 were determined from the slope 

and intercept of the plot of t/qt versus t. The plot of t/qt versus t at different concentrations is shown in 
Figure 3(b). The data obtained for the PSO kinetic model at different  concentrations is presented in Table 
4.  In this case, the fitting of the expermiental data in the pseudo-second-order equation showed excellent 
linearity with high correlation coefficient (R2 > 0.999). On the other hand, the calculated values of qe 
obtained from the pseudo second order model agreed perfectly with the experimental values of qe at three 
initial concentrations, respectively.  An analysis of the data in Table 4 suggests that the kinetics of 
adsorption of phenol onto SSBA can be explained accurately by the PSO kinetic model. 
 
Table 4: The PFO and PSO kinetic parameters for the adsorption of phenol onto SSBA 

C0 
 (mg.l-1) 

qe exp  
(mg.g−1) 

pseudo first-order model PFO pseudo second-order model PSO 
k1 

(min−1) 
qe cal  

(mg.g−1) 
R2  k2   

(g.mg−1min−1) 
k2qe 

(min-1) 
qe cal  

(mg.g−1) 
R2 

50 9 0.13 8.90 0.8805  0.0978 0.88 9.05 0.9999 
100 15 0.07 10.19 0.5971  0.0560 0.85 15.09 0.9998 
200 23 0.16 64.00 0.8430  0.0920 2.11 23.02 0.9999 

 

4. Conclusions 
The adsorption of phenol from water using SSBA activated with H2SO4 was investigated. Various 
experimental parameters such as contact time, adsorbent dose, initial phenol concentration, temperature 
and solution pH were optimized. The adsorption was found to be highly influenced by initial phenol 
concentration and phenol speciation which is directly related to solution pH. Equilibrium study show that 
the data fit very well in the Freundlich equation of multilayer adsorption but showed small deviation with 
the Langmuir equation, this result indicate the heterogeneity of the adsorbent surface. The values of R2 

obtained from pseudo second-order model were higher than 0.999, indicating that the adsorption process 
obeyed the pseudo second-order model. Finally the adsorption experiments indicated that sewage sludge 
based adsorbent SSBA was efficient adsorbent for the removal of phenol from water.  

References 

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287, 14–24. 

Ahmaruzzaman, M., 2008. Adsorption of phenolic compounds on low-cost adsorbents: A review. 
Advances in Colloid and Interface Science. 143, 48–67. 

Bousba, S., Meniai, A.H, 2013, Adsorption of 2-chlorophenol onto sewage sludge based adsorbent: 
Equilibrium and kinetic study. Chemical Engineering Transactions. 35, 859-864.  

Gascó, G., Blanco, C.G., Guerrero, F., Lázaro, A.M.M., 2005. The influence of organic matter on sewage 
sludge pyrolysis. J. Anal. Appl. Pyrolysis, 74, 413–420. 

Gupta, V.K., Ali, I., Saini, V.K., 2004. Removal of chlorophenols from wastewater using red mud: an 
aluminum industry waste. Environ. Sci. Technol. 38, 4012–4018. 

Hamdaoui, O., Naffrechoux, E, 2007. Modeling of adsorption isotherms of phenol and chlorophenols onto 
granular activated carbon: Part I. Two-parameter models and equations allowing determination of 
thermodynamic parameters.Journal of Hazardous Materials, 147(1), 381-394. 

Lopez-Ramon M.V., Stoeckli F., Moreno-Castilla C., Carrasco-Marin F., 1999, On the characterization of 
acidic and basic surface sites on carbons by various techniques. Carbon, 37, 1215-1221. 

Podkościelny, P., László, K., 2007. Heterogeneity of activated carbons in adsorption of aniline from 
aqueous solutions. Applied Surface Science, 253 (21), 8762-8771.   

Sarkar, M., Acharya, P.K., 2006. Use of fly ash for the removal of phenol and its analogues from 
contaminated water. Waste Manag. 26, 559–570. 

Srivastava, V.C., Swamy, M.M., Mall, I.D., Prasad, B., Mishra, I.M., 2006. Adsorptive removal of phenol by 
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Physicochem. Eng. Asp. 272,89–104. 

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