Enhanced molar sorption ratio for naphthalene through the impregnation of surfactant into chitosan hydrogel beads

Bioresource Technology 101 (2010) 4315–4321

Contents lists available at ScienceDirect

Bioresource Technology journal homepage: www.elsevier.com/locate/biortech

Enhanced molar sorption ratio for naphthalene through the impregnation of surfactant into chitosan hydrogel beads Sudipta Chatterjee a, Dae S. Lee b, Min W. Lee c,*, Seung H. Woo a,* a

Department of Chemical Engineering, Hanbat National University, San 16-1, Deokmyeong-dong, Yuseong-gu, Daejeon 305-719, Republic of Korea Department of Environmental Engineering, Kyungpook National University, Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea c Department of Chemical Engineering, Keimyung University, 2800 Dalgubeoldaero, Dalseo-Gu, Daegu 704-701, Republic of Korea b

a r t i c l e

i n f o

Article history: Received 21 November 2009 Received in revised form 9 January 2010 Accepted 14 January 2010 Available online 25 February 2010 Keywords: Chitosan bead Naphthalene Sorption Surfactant

a b s t r a c t Surfactants in their impregnated forms in chitosan beads (CBs) were used for sorption of naphthalene (NAP) from aqueous solutions. Three different surfactants, Triton X-100 (TX100), cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), were selected for this study. The results showed that surfactant-impregnated CS beads (SICBs) in the form of a separate phase surfactant were very effective for NAP sorption. The calculated molar sorption ratio (MSRB mol NAP/mol surfactant) of the surfactant impregnated into SICBs was much greater than the intrinsic molar solubilization ratio (MSR) in liquid phase. The high MSRB value could be explained by favorable configurations of surfactants in beads, such as micelles in sorbed form. The equilibrium isotherm did not follow Langmuir or Freundlich models, but followed Chapman sigmoidal equation, indicating co-operative sorption of solutes. Using SICBs as a separate phase surfactant may be a valuable tool for remediation of groundwater contaminated with hydrophobic organic compounds. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Hydrophobic organic compounds (HOCs) consist of broad classes of chemicals that appear as persistent organic contaminants in soils and sediments. Certain HOCs, such as polycyclic aromatic hydrocarbons, are of major environmental concern because of their toxicity and restricted biodegradation due to a low aqueous solubility coupled with strong binding or sorption with the soil or sediments (Luthy et al., 1997; Bamforth and Singleton, 2005). Surfactants have been found to be effective agents that can aid in the remediation of subsurface environments contaminated by HOCs (Ko et al., 1998). Surfactants can enhance the removal of HOCs from solid and other sorbed phases by increasing the rates of dissolution and desorption (Zhang et al., 1997). The remediation of HOC contamination in soils by in situ surfactant-enhanced remediation process involves the enhancement of HOC mobility by partitioning it into a mobile surfactant phase. Considerable effort has been given to removing HOCs using the surfactantenhanced remediation because the approach is economical and

* Corresponding authors. Tel.: +82 54 279 8650; fax: +82 42 279 8299 (M.W. Lee), tel.: +82 42 821 1537; fax: +82 42 821 1593 (S.H. Woo). E-mail addresses: [email protected] (M.W. Lee), [email protected] (S.H. Woo). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.01.062

technically feasible (Bramwell and Laha, 2000; Grasso et al., 2001). Depending on the particular site conditions, an alternative remediation approach can be applied by minimizing HOC mobility through sorption to an immobile sorbed surfactant phase (Ko et al., 1998). Surfactants can also be used as permeable reactive barriers to prevent the mobility of certain contaminants from a point source of pollution (Stapleton et al., 1994). Sorbed surfactants contained in solids, such as soils (Yang et al., 2006), clays (Zhu and Zhu, 2008) and activated carbons (Ahn et al., 2008a,b), are also effective for HOC sorption from water. Sorption has been proven to be one of the most effective techniques for the removal of low concentrations of HOCs from large volumes of groundwater, potable water, effluents and aqueous solutions, and there have been a large number of sorption studies conducted on the removal of organic contaminants in soils and minerals with varying organic matter contents (Allen-king et al., 2002; Chiou et al., 1998; Xia and Ball, 1999). Sorption onto activated carbon is often found to be very effective for the removal of organic contaminants from dilute aqueous solutions because of the highly hydrophobic nature, large surface area, and pore volume of carbon (Bautista-Toledo et al., 2005; Cabal et al., 2009). Carbon nanotubes have been studied as sorbents for the removal of HOCs from aqueous media, and in most of these studies they exhibit good sorption capacity towards HOCs (Peng et al., 2003). In some cases, a hypercross-linked polymeric sorbents

4316

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321

Table 1 Chemical properties of NAP and different surfactants. Name

Type a

TX100 CTABa SDSa NAPb

Non-ionic Cationic Anionic –

Chemical formula C14H22O(C2H4O)9.5 C19H42BrN NaC12H25SO4 C10H8

MW (g/mol) 625 365 288 128

CMC (g/L) c

0.106 0.336d 2.33d –

MSRsep (mol/mol) c

0.338 0.263d 0.047d –

Cs (mg/L) – – – 32c

MW: molecular weight; CMC: critical micelle concentration of surfactant in aqueous solution; MSR: molar solubilization ratio of surfactant for NAP (mol NAP/mol surfactant); Cs: aqueous solubility of NAP at 25 °C. a Surfactant. b Contaminant. c Ref. Edwards et al. (1991). d Ref. Roy et al. (1995).

produced by cross-linking polymers of macroporous resins are used for the sorption of organic contaminants (Zhang et al., 2006). Chitosan (CS), a natural linear biopolymer obtained by the alkaline deacetylation of chitin, is the second most abundant biopolymer next to cellulose (Ravi Kumar, 2000). CS is basically a copolymer of glucosamine and N-acetyl-glucosamine residues, while chitin is a straight polymer of N-acetyl-glucosamine units. Due to the presence of multiple functional groups (amino and hydroxyl groups), CS exhibits a high adsorption capacity towards many classes of dyes, especially anionic dyes (Wong et al., 2004), metal ions (Varma et al., 2004), and ionic compounds (Chatterjee et al., 2009a). However, the sorption capacity of CS for HOCs has been reported to be very low. The chemical modification of CS molecules by reagents such as salicylaldehyde and b-cyclodextrin improves the sorption of hydrophobic compounds (Zheng et al., 2004; Li et al., 2009). In this study, three different surfactants, Triton X-100 (TX100), a nonionic surfactant; cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant; and sodium dodecyl sulfate (SDS), were impregnated into CS beads (CBs) to investigate their effects on the sorption of naphthalene (NAP), a polycyclic aromatic hydrocarbon, from an aqueous solution. The main objective of this study was to investigate the efficiency of this surfactant as a separate phase for the sorption of NAP from aqueous solutions. To the best of our knowledge, this represents the first attempt to use surfactants in such a form, which differs from their conventional complementary modes of application for the remediation of HOC contamination.

2. Methods 2.1. Materials CS (>85% deacetylation), NAP (scintillation grade, purity >99%), and three different types of surfactants, including TX100 [octylphenolpoly(ethylene glycol ether)9.5], CTAB, and SDS, were purchased from Sigma Chemical Co., USA. The chemical properties of NAP and the various surfactants used in this study are listed in Table 1. To prepare the aqueous solution of NAP, an excess amount of NAP was added to 100 mL of deionized water in a 250 mL glass bottle (Duran, Germany) fitted with a screw cap. After solubilization for 3 days at 30 °C in a thermostated shaker at 200 rpm, the NAP concentration in the aqueous solution was determined after filtration through a 0.45-lm PVDF filter (Whatman, USA). The NAP concentration in the solution was determined using high-performance liquid chromatography (HPLC, Dionex, USA) with a UV detector at 250 nm. The analytical column contained AcclaimÒ 120, C18 5 lm 120 Å (4.6  150 mm) and the mobile phase was 85% (v/v) acetonitrile and 15% (v/v) deionized water with a flow rate of 1.5 mL/min.

2.2. Preparation of surfactant-impregnated chitosan beads (SICBs) The CBs were prepared by the alkali gelation of the CS-acetic acid solution (10 g/L CS in 2 v% acetic acid) (Chatterjee et al., 2009a). The CS-acetic acid solution was prepared by dissolving 10.0 g of CS powder in 400 mL of 5% (v/v) acetic acid solution. After diluting the CS-acetic acid solution to 1 L with deionized water, the solution was dropped into a precipitation bath containing 1 L of alkaline coagulating mixture (H2O:MeOH:NaOH: 4:5:1, w/w) to form the CBs. The TX100-impregnated CS beads (TCBs) (Chatterjee et al., 2009b) and the CTAB-impregnated CS beads (CCBs) (Chatterjee et al., 2009c) were prepared by adding the desired amounts of TX100 or CTAB solutions from stock solutions (20 g/L) into the CSacetic acid solution, followed by the dropwise addition of the CS/ surfactant solution into the same alkaline solution used for CBs. The steps applied for the SDS-impregnated CS beads (SCBs) (Chatterjee et al., 2009b) formation were similar to the above-mentioned procedure, but the CS was dissolved in the SDS-acetic acid solution to avoid CS–SDS aggregate formation in the final CS/SDS solution. The surfactant concentration in the SICBs was varied from 0.1 to 1.0 g/L bead volume (BV) with respect to the CS concentration (10 g/L BV). The beads prepared in this manner were extensively washed with deionized water to remove alkali and preserved in deionized water. 2.3. Batch sorption studies The TX100, CTAB, and SDS concentrations in SICBs were varied from 0.1 to 1.0 g/L BV to observe the effects of surfactant impregnation on the sorption of NAP with an initial concentration of 15 mg/L. The batch sorption was carried out by adding 0.2 g of the wet forms of TCBs (0.5 g/L BV TX100), CCBs (0.5 g/L BV CTAB) and SCBs (0.8 g/L BV SDS) into 10 mL of an NAP solution of the desired concentration, after which the pH was adjusted to 6 in a 20 mL glass vial fitted with a Teflon-lined screw cap and the sorption process was continued for 24 h at 30 °C in a thermostated shaker at 200 rpm. The sorption of NAP to the glass vial during the batch study was determined by carrying out the same process, only without beads, using an NAP solution of the desired concentration. The experimental solution with the desired NAP concentration was obtained through successive dilutions from a 15 mg/L solution of NAP in deionized water. An equilibrium sorption study with a sorption period of 24 h was carried out with different initial concentrations of NAP (1–15 mg/L) at 30 °C and pH 6. All of the sorption experiments were conducted in triplicate, and the remaining concentration of NAP in the experimental solution after sorption was determined using HPLC. Approximately 1.5 mL of the experimental solution after sorption was collected through centrifugation at 3000 rpm for 30 min. All of the samples taken for the HPLC analyses were measured within 1 h of sampling to avoid sorption onto the wall of the sample glass vial. The amount of

4317

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321

ðC 0  C eq Þ  V W

ð1Þ

where qe is the sorbent capacity, mg/g; C0 is the initial concentration of NAP, mg/L; Ceq is the final or equilibrium concentration of NAP, mg/L; V is the volume of the NAP solution put in contact with the sorbent, L; and W is the dry weight of beads, g. 3. Results and discussion 3.1. General properties of surfactant-impregnated beads The formation of SICBs depends on the surfactant level because excessive foam formation in the CS/surfactant solution at high surfactant concentrations hampers this process. The concentration of each type of surfactant (TX100, CTAB and SDS) was varied from 0.1 g/L BV to 1.0 g/L BV in the CS solution because a surfactant concentration greater than 1.0 g/L BV produced foam in the final solution. The water content of the SICBs determined from the wet weight and the dry weight of the beads was 96.48%, 95.86%, and 96.40% for TCBs (0.5 g/L BV TX100), CCBs (0.5 g/L BV CTAB), and SCBs (0.8 g/L BV SDS), respectively. The water contents of the SICBs were less than that of CBs (96.70%). The porosity of the CCBs was increased from 84.99% to 90.94% after impregnation with 0.5 g/L BV CTAB and the diameter was reduced from 3.65 mm to 2.97 mm (Chatterjee et al., 2009c). The porosities of TCBs and SCBs were found to be 85.95% and 85.35%, respectively (Chatterjee et al., 2009b), indicating that the porosity of the beads was enhanced by the TX100 and the SDS impregnation. The diameters of TCBs and SCBs were reduced to 2.70 mm and 3.21 mm, respectively. Thus, surfactant entrapment into the beads reduced the water content and the size of the beads, and increased the porosity of the beads regardless of the surfactant type used in this study. 3.2. Mass balance during NAP sorption As shown in Fig. 1, the incubation of the NAP solution in 20 mL glass vial for 24 h caused a 30–65% mass loss that depended on the initial concentration of NAP in the solution, and this mass loss, even in absence of the beads, was mainly due to sorption onto the wall of glass vial and the potential volatilization of NAP during the experiments. Thereby, the mass loss during the sorption experiments was taken into account when determining the equilibrium

Equilibrium concentration (Ce , mg/L)

12 Without beads CB TCB (0.5 g/L BV TX100) CCB (0.5 g/L BV CTAB) SCB (0.8 g/L BV SDS) pH 6, 30 0C

10 8 6 4 2 0

0

2

4 6 8 10 12 Initial NAP concentration (C0, mg/L)

14

C 0 ¼ C e;loss þ C e þ qe  fb=l

ð2Þ

where C0 is initial concentration of NAP, mg/L; Ce,loss is equilibrium concentration of NAP in solution without sorbent, considering any loss of NAP such as sorption onto glass vial, mg/L; Ce is final or equilibrium concentration of NAP in liquid with sorbent, mg/L; qe is equilibrium sorption capacity of the sorbent (mg/g); fb/l is the dry weight fraction of the beads in liquid solution (g/L). Thereby, C0 (mg/L) of NAP after sorption is conserved in the system among three parameters: (1) Ce,1oss due to glass wall sorption, (2) Ce remaining in liquid phase, and (3) qe  fb=l (mg/L), the amount sorbed in beads. As for example, for sorption of NAP from a 15 mg/L solution using SICB, the percentage of NAP distributed on glass wall was 30.2%, and 56.3%, 58.4% and 42.1% of NAP (C0 = 15 mg/L solution) were adsorbed by TCB (0.5 g/L BV TX100), CCB (0.5 g/L BV CTAB) and SCB (0.8 g/L BV SDS), respectively (Fig. 1). 3.3. Effect of surfactant dose Fig. 2a shows the effect of surfactant impregnation on sorption of NAP by SICB and surfactant concentration in the beads was

15

(a) 12

NAP sorbed (qe, mg/g)

qe ¼

sorption capacity of the sorbents. The true sorption of the NAP onto the beads can be described by the conservation of the mass of the sorbate in the system after attaining equilibrium. The conserved amount of NAP after equilibrium is given by the equation:

9

6 TCB CCB SCB C0 = 15 mg/L; pH 6

3

0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Surfactant concentration (g/L BV) Molar sorption ratio (MSR B mol NAP/mol surfactant)

NAP sorbed (mg/g) was calculated based on a mass balance equation given below:

1.4 1.2

(b)

MSRB (TCB) MSRB (CCB) MSRB (SCB)

1.0

MSR (TX100) MSR (CTAB) C0 = 15 mg/L; pH 6

0.8 0.6 0.4

MSRsep (TX100)

0.2

MSRsep (CTAB)

0.0

MSRsep (SDS)

0.0

0.3

0.6 0.9 1.2 Surfactant concentration (g/L or g/L BV)

1.5

16

Fig. 1. NAP concentrations in the liquid after sorption on SICBs with various initial NAP concentrations.

Fig. 2. Effect of impregnated surfactant concentrations on NAP sorption (a) and molar sorption ratio (MSRB) in the beads (b). The MSR was obtained from partitioning model calculations in a pure liquid system. MSRsep are intrinsic values in liquid system with separate phase NAP.

4318

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321

Fig. 3. The conceptual model for the partitioning of NAP between micellar pseudophase and aqueous pseudophase in a surfactant-containing liquid system (a), partitioning of NAP between SICBs and the aqueous phase in SICB-containing liquid system (b) and possible configuration of surfactant molecules entrapped in SICBs and its influence on NAP sorption (c). The numbers in (c) denote (1) NAP dissolved in aqueous phase in SICBs, (2) NAP sorbed onto the surface of CS fibers, (3) trapped between CS fibers in the form of self aggregates of NAP, (4) surfactant monomer, (5) sorbed surfactant monomer, (6) normal micelle, (7) different form of micelle with increased MSR (expanded micelle), (8) different form of micelle with decreased MSR (reduced micelle), (9) sorbed micelle (admicelle or spherical micelle), and (10) sorbed hemimicelle.

varied between 0.1 and 1.0 g/L BV. The low sorption capacity of CB (3.56 mg/g) from a 15 mg/L solution indicated that CB without surfactant impregnation was not very effective for sorption of NAP from aqueous solution. The sorption capacity was significantly increased by impregnating surfactants. This increase was not sensitively dependent on the type of the surfactant, while SDS showed somewhat low adsorption capacity. The rate of uptake of NAP was rapid initially and 50% sorption was completed within 5 h for TCB as well as CCB, whereas time required for 50% uptake onto SCB was 7 h (data not shown). The low adsorption capacity and the slow mass transfer in SCB could be described by the fact that SDS amount in the bead (0.8 g/L BV) was well below its CMC (2.33 g/ L). It is noticeable that a moderate range pH variation between 4 and 8 around pKa value of CS (6.3) exhibited negligible effect on its sorption using SICB, suggesting that sorption process is not guided by ionic interactions and not much dependent on charge of CS or surfactant (data not shown). The sorption of NAP onto SICB was found to be increased with increase in surfactant concentration at low loadings, reached maximum and a very small increase in sorption capacity was found with further increase in surfactant concentration. The sorption capacity increased from 3.56 mg/g to 12.06 mg/g after impregnating CB with 0.5 g/L BV TX100 and further increase in TX100 concentration in TCB did not produce any significant increase. Similar trend was found for CCB (12.52 mg/g) and SCB (8.32 mg/g) with 0.5 g/L BV CTAB and 0.8 g/L BV SDS impregnation, respectively. Thereby, for our further sorption study, TCB, CCB and SCB were selected with 0.5 g/L BV TX100, 0.5 g/L BV CTAB and 0.8 g/L BV SDS impregnation, respectively. Here we introduced molar sorption ratio (MSRB), which is defined as mol NAP sorbed per mol surfactant in the beads (Fig. 2b). It should be noticed, in order to determine MSRB of surfactant in SICB for NAP, that qe of CB (3.56 mg/g) has been subtracted from qe value of SICB on basis of molar value. This calculation is based on the assumption that the NAP sorption onto SICB is due to two independent factors (surfactant and CS) for simplicity

and conservative analysis. The MSRB values can show the effectiveness of surfactants in its impregnated form in CB for removal of NAP from aqueous solution. At low concentrations of surfactant (Fig. 2b), the MSRB was low, indicating that most surfactants were sorbed onto CS fibers. With increasing surfactant dose in SICB, MSRB increased to a maximum level most likely due to micelle formation in the beads. After that, MSRB values were decreased with further increase in surfactant concentration due to surfactant aggregation, which will be discussed in more details in a later section. In case of SCB, MSRB pattern was still increasing up to 1 g/L BV because CMC value of SDS (1.56 g/L) is moderately high. The MSRB values of surfactant in SICB were compared with MSR in liquid system (Fig. 3a) and intrinsic MSRsep values in excess presence of separate phase NAP (Fig. 2b). The MSRsep value measures the effectiveness of a particular surfactant for solubilizing NAP in aqueous micellar form in excess presence of separate phase NAP. The MSR value of surfactant in absence of separate phase HOC varies with surfactant dose because of partitioning of HOC between micellar pseudophase and aqueous pseudophase (Edwards et al., 1994). MSR values were calculated from mathematical model (Lee et al., 2007) assuming that surfactant concentration in aqueous solution equals to those in beads for comparison of both systems (Figs. 3a and b). The MSR values of TX100 and CTAB for NAP in the concentration range of 0.1–1 g/L were much lower than MSRB values of TX100 and CTAB in the beads. It is noticeable that there is no MSR value for 0.1–1 g/L SDS in aqueous solution because SDS concentration is below CMC value and micelle does not form. As a conservative approach, the intrinsic MSRsep value that is maximally possible MSR was also compared with MSRB. The values of MSRB for TX100 and CTAB were higher than the MSRsep of TX100 (0.338) and CTAB (0.263) for NAP. SDS in SCB exhibited lower MSRB values than MSRsep value of SDS (0.047) up to 0.2 g/L SDS in the beads and after that, it became significantly higher than intrinsic MSRsep value. The MSRB of TX100 with 0.5 g/L BV impregnation in TCB showed 2.56 times higher value than MSRsep of TX100 for NAP. The MSRB values of CTAB (0.5 g/L

4319

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321

BV impregnation in CCB) and SDS (0.8 g/L BV impregnation in SCB) were also 2.03 times and 3.08 times higher than respective MSRsep values of these surfactants. The high MSRB values of surfactants in SICB for NAP indicate that the system entrapping surfactant into CB is more advantageous than the system containing surfactant in liquid in a dissolved state.

Table 2 Model fitted sorption isotherms of NAP on SICBs.

3.4. Possible configurations of entrapped surfactants in beads and their influence on NAP sorption Fig. 3 illustrates the conceptual model for configuration of surfactant molecules entrapped in SICB and its influence on NAP sorption. Fig. 3a depicts the micellization of surfactant molecules in aqueous solution and partitioning of NAP occurs between micellar pseudophase and aqueous pseudophase. The sorption system containing SICB and NAP in aqueous media is represented in Fig. 3b, where surfactants are present in SICB as a separate phase from liquid. As seen in Fig. 3c, the surfactant molecules entrapped in SICB exist in various forms such as monomers (4), sorbed monomers onto CS fibers (5), micelles as the same form as in pure liquid (6), deformed micelles (7, 8), sorbed micelles onto CS fibers (9) and sorbed hemimicelles (10). Attachment of NAP to CS molecules occurs through direct sorption by hydrophobic interactions (2). Unlike NAP present in a completely dissolved form in pure aqueous phase, NAP can be trapped between CS fibers in the beads in the form of self aggregates (3). The sorption capacity of SICB at various levels of surfactant loading could be described by this conceptual model. At low surfactant concentration in the beads (below CMCB level based on bead volume), surfactant molecules remain as monomers (4) and sorbed monomers (5). It is noticeable that CMCB was not clearly found but it would be higher than CMC value in pure aqueous phase due to the sorption of surfactant onto CS fibers. The low MSRB value of surfactant in the beads at low surfactant loading would be due to interaction between these surfactant monomers and NAP. After that, with increasing surfactant concentration in the beads, micelle is formed and MSRB is also increased. Unlike micelles in pure aqueous phase (Fig. 3a), surfactants in the beads above CMCB level attain various forms of micelles such as normal micelles (6), expanded micelles (7), and reduced micelles (8) due to limited space and interactions with CS fibers. Some of these micelles can sorb onto CS fibers in the form of spherical micelles (9) and hemimicelles (10). These micelles give rise to the increase of MSRB values in SICB, e.g., it has been reported that micelles sorbed onto acitivated carbon can increase their adsorption capacity (Ahn et al., 2008a). The higher MSRB value than MSR or MSRsep as seen in Fig. 2b might be due to the formation of self aggregates of NAP (3), partitioning into the expanded micelles (7) in liquid phase, and sorption onto the expanded micelles in sorbed phase (9) and onto hemimicelles (10). The decrease in MSRB with further increase in surfactant concentration in SICB can be explained by the formation of reduced micelles (8) in liquid or sorbed phase and their interactions with NAP. It is noticeable that reduced micelles (8) could become tight and empty causing very low uptake of NAP. 3.5. Sorption isotherm The equilibrium sorption isotherm data for NAP sorption onto SICB were fitted to Langmuir and Freundlich isotherm models, and Chapman sigmoidal equation (Dupuis and LeHoux, 2007; Irie et al., 2008). Langmuir isotherm model assumes monolayer adsorption onto adsorbent surface with uniform energies of adsorption. The expression of the Langmuir model is:

qe ¼

qm K L C e 1 þ K LCe

ð3Þ

a

a

R2

Sorbent

qm (mg/g)

KL (L/mg)

RL

Langmuir isotherm model TCB CCB SCB

32.39 31.77 28.66

0.321 0.422 0.111

0.172 0.136 0.375

Sorbent

KF

n

R2

Freundlich isotherm model TCB CCB SCB

7.484 9.035 2.761

1.24 1.27 1.17

0.887 0.830 0.840

Sorbent

a

b

c

R2

Chapman sigmoidal equation TCB CCB SCB

12.39 12.77 8.37

2.196 3.594 2.210

2.651 4.501 17.51

0.968 0.960 0.992

0.913 0.861 0.858

C0 is 15 mg/l.

where qm (mg/g) and KL (L/mg) are Langmuir constants related to the adsorption capacity and energy of adsorption, respectively. The value of qm signifies the maximum adsorption capacity (mg/ g) of the adsorbent assuming monolayer adsorption. The essential feature of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor (RL) given by the following equation:

RL ¼

1 ð1 þ K L C 0 Þ

ð4Þ

The value of RL indicates the shape of the isotherm to be unfavorable (RL > 1), favorable (0 < RL < 1), linear (RL = 1), or irreversible (RL = 0). The Freundlich isotherm model is an empirical model based on the assumption that the surface is energetically heterogeneous. It also considers multilayer sorption with intermolecular interactions between the sorbate molecules. The non-linear expression of the Freundlich model is: 1

qe ¼ kF C ne

ð5Þ

KF is the Freundlich constant related to the sorbent capacity of sorbent and n is an empirical parameter representing the heterogeneity of site energies. The expression of the Chapman sigmoidal equation is:

qe ¼ að1  ebC e Þc

ð6Þ

The value of a in the Chapman sigmoidal equation is related to the sorption capacity of sorbent. The constant terms of the Chapman sigmoidal equation (a, b and c) are listed with conventional constant terms of the Langmuir and Freundlich isotherm models along with their non-linear regression coefficients (R2) in Table 2. The RL values obtained for the initial NAP concentration of 15 mg/L indicated that the sorption of NAP onto different varieties of SICBs was a favorable process. The n values in the range between 1.17 and 1.27, suggesting favorability in the sorption system. However, qm and KF values obtained from the Langmuir and Freundlich isotherm models, respectively, could not give the proper information about its real maximum sorption capacity because both isotherm models were not found suitable for explaining the isotherm data due to low R2 value of non-linear curve fitting (Fig. 4). The results exhibited showed that all of the SICBs (TCBs, CCBs, and SCBs) displayed a sigmoid-shaped isotherm or S-type isotherm according to the Giles classification (Hinz, 2001). Each isotherm showed small sorption at low concentrations of NAP in the solution and the sorption increased with an increase in the solute concentration, indicating that solute–solute attractive forces at the

4320

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321

sorption capacity than TCBs and CCBs impregnated with 0.5 g/L BV TX100 and 0.5 g/L CTAB, respectively. While the rising points of the model lines for TCBs and CCBs were around 0.2 mg/L of Ce, SCBs showed a late rising of the model line around 1 mg/L of Ce, resulting in high c value. The low sorption capacity of SCBs could be explained by the fact that the SDS concentration in the SCBs was well below its CMC concentration, while the other two surfactants were impregnated in beads at concentrations higher than their respective CMC concentrations.

14

(a)

NAP sorbed (qe, mg/g)

12 10 8 6 4

Experimental data Langmuir isotherm Freundlich isotherm Chapman sigmoidal equation TCB ( 0.5 g/L BV TX-100) pH 6, 30 0C

2 0

0.0

0.5

1.0

1.5

2.0

3.6. SICBs as separate phase surfactants

2.5

NAP in solution (Ce, mg/L)

14

(b)

NAP sorbed (qe, mg/g)

12 10 8 6 4

Experimental data Langmuir isotherm Freundlich isotherm Chapman sigmoidal equation CCB (0.5 g/L BV CTAB) pH 6, 30 0C

2 0

0.0

0.5

1.0

1.5

2.0

2.5

NAP in solution (Ce, mg/L) 14

Surfactants are well known for their ability to solubilize HOCs by partitioning them into the hydrophobic cores of surfactant micelles above the CMC. This property of the surfactant aids in the remediation of HOC contamination. In our research, when the surfactant was entrapped in a CS bead, the uptake ability (MSRB) of the surfactant in the SICBs was significantly higher than the intrinsic MSR of the same amount of surfactant in a dissolved form due to the various possible configurations of surfactants in the bead. This form of SICB can be regarded as a separate phase surfactant that is able to concentrate the HOC into the SICBs, which is different from the surfactant micelles dissolved in the liquid. This form of surfactant can be easily separated from the contaminated water or wastewater, while surfactant micelles dissolved in liquid should be removed by some treatment, such as adsorption onto activated carbon or filtration (Ahn et al., 2008b). Therefore, the separate phase surfactant can be applied for the treatment of the contaminated groundwater as permeable reactive barriers. However, poor mechanical strength of the SICBs makes it disadvantageous for large-scale applications. Low surfactant loading into the beads is another impediment for its application in HOC remediation processes. Further study is required to improve its mechanical strength by using cross-linking agents or composite materials (Chatterjee et al., 2009d), and for an increase in the surfactant loading into the beads by changing the mixing condition for surfactant during the bead generation step.

(c)

12

NAP sorbed (qe, mg/g)

4. Conclusions 10

Three different surfactants, TX-100, CTAB and SDS in their impregnated forms in CB were used for sorption of NAP from aqueous solutions and SICBs in the form of a separate phase surfactant were found more effective for sorption of NAP than in a dissolved form in water. The calculated MSRB (mol NAP/mol surfactant) of the surfactant impregnated into SICBs was greater than intrinsic molar solubilization ratio (MSR) in liquid phase. Therefore, surfactants in their impregnated form in SICB could be an alternative for treatment of hydrophobic organic compounds in contaminated groundwater or wastewater.

8 6 4

Experimental data Langmuir isotherm Freudlich isotherm Chapman sigmoidal equation SCB (0.8 g/L BV SDS) pH 6, 30 0C

2 0

0

1

2

3

4

5

NAP in solution (Ce, mg/L) Fig. 4. Model fitted sorption isotherms of NAP on SICBs: (a) TCBs; (b) CCBs; (c) SCBs.

surface might cause co-operative sorption (Hinz, 2001). Thus, the Chapman sigmoidal equation appeared to have the best fit with the highest non-linear R2 values for TCBs (0.968), CCBs (0.960), and SCBs (0.992). The a value of the Chapman sigmoidal equation, representing maximum sorption capacity, was almost similar for TCBs (12.39) and CCBs (12.77), indicating that both varieties of beads have similar sorption capacity for NAP. The value of a obtained for SCBs (8.37) was lower than two other varieties of beads, suggesting that SCBs impregnated with 0.8 g/L BV SDS has lower

Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant Number 2009-0079636). References Ahn, C.K., Woo, S.H., Park, J.M., 2008a. Enhanced sorption of phenanthrene on activated carbon in surfactant solution. Carbon 46, 1401–1410. Ahn, C.K., Kim, Y.M., Woo, S.H., Park, J.M., 2008b. Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon. J. Hazard. Mater. 154, 153–160.

S. Chatterjee et al. / Bioresource Technology 101 (2010) 4315–4321 Allen-king, R.M., Grathwohl, P., Ball, W.P., 2002. New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks. Adv. Water Res. 25, 985–1016. Bamforth, S.M., Singleton, I., 2005. Bioremediation of polycyclic aromatic hydrocarbons: current knowledge and future directions. J. Chem. Technol. Biot. 80, 723–736. Bautista-Toledo, I., Ferro-García, M.A., Riverra-Utrilla, J., Moreno-Castilla, C., Fernández, V.F.J., 2005. Bisphenol A removal from water by activated carbon: effects of carbon characteristics and solution chemistry. Environ. Sci. Technol. 39, 6246–6250. Bramwell, D.A.P., Laha, S., 2000. Effects of surfactant addition on the biomineralization and microbial toxicity of phenanthrene. Biodegradation 11, 263–277. Cabal, B., Budinova, T., Ania, C.O., Tsyntsarski, B., Parra, J.B., Petrova, B., 2009. Adsorption of naphthalene from aqueous solution on activated carbons obtained from bean pods. J. Hazard. Mater. 161, 1150–1156. Chatterjee, S., Lee, D.S., Lee, M.W., Woo, S.H., 2009a. Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate. J. Hazard. Mater. 166, 508–513. Chatterjee, S., Lee, D.S., Lee, M.W., Woo, S.H., 2009b. Congo red adsorption from aqueous solutions by chitosan hydrogel beads impregnated with nonionic or anionic surfactant. Bioresour. Technol. 100, 3862–3868. Chatterjee, S., Lee, D.S., Lee, M.W., Woo, S.H., 2009c. Enhanced adsorption of Congo red from aqueous solutions by chitosan hydrogel beads impregnated with cetyl trimethyl ammonium bromide. Bioresour. Technol. 100, 2803–2809. Chatterjee, S., Lee, M.W., Woo, S.H., 2009d. Enhanced mechanical strength of chitosan hydrogel beads by impregnation with carbon nanotubes. Carbon 47, 2933–2936. Chiou, C.T., Mc Groddy, S.E., Kile, D.E., 1998. Partition characteristics of polycyclic aromatic hydrocarbons on soils and sediments. Environ. Sci. Technol. 32, 264– 269. Dupuis, G., LeHoux, J.G., 2007. Recovery of chitosan from aqueous acidic solutions by salting-out. Part 2: use of salts of organic acids. Carbohydr. Polym. 68, 287– 294. Edwards, D.A., Luthy, R.G., Liu, Z., 1991. Solubilization of polycyclic aromatic hydrocarbons in micellar nonionic surfactant solutions. Environ. Sci. Technol. 25, 127–133. Edwards, D.A., Liu, Z., Luthy, R.G., 1994. Surfactant solubilization of organic compounds in soil/aqueous systems. J. Environ. Eng. 120, 5–22. Grasso, D., Subramaniam, K., Pignatello, J.J., Yang, Y., Ratté, D., 2001. Micellar dissorption of polynuclear aromatic hydrocarbons from contaminated soil. Colloids Surf. A 194, 65–74. Hinz, C., 2001. Description of sorption data with isotherm equations. Geoderma 99, 225–243.

4321

Irie, M., Tjandrawinata, R.E.L., Yamashiro, T., Suzuki, K., 2008. Flexural performance of flowable versus conventional light-cured composite resins in a long-term in vitro study. Dent. Mater. J. 27, 300–309. Ko, S.O., Schlautman, M.A., Carraway, E.R., 1998. Partitioning of hydrophobic organic compounds to sorbed surfactants. 1. Experimental studies. Environ. Sci. Technol. 32, 2769–2775. Lee, H.J., Lee, M.W., Lee, D.S., Woo, S.H., Park, J.M., 2007. Estimation of direct-contact fraction for phenanthrene in surfactant solutions by toxicity measurement. J. Biotechnol. 131, 448–457. Li, J.M., Meng, X.G., Hu, C.W., Du, J., 2009. Adsorption of phenol, p-chlorophenol and p-nitrophenol onto functional chitosan. Bioresour. Technol. 100, 1168–1173. Luthy, R.G., Aiken, G.R., Brusseau, M.L., Cunningham, S.D., Gschwend, P.M., Pignatello, J.J., Reinhard, M., Traina, S.J., Weber Jr., W.J., Westall, J.C., 1997. Sequestration of hydrophobic organic contaminants by geosorbents. Environ. Sci. Technol. 31, 3341–3347. Peng, X., Li, Y., Luan, Z., Di, Z., Wang, H., Tian, B., Jia, Z., 2003. Adsorption of 1, 2dichlorobenzene from water to carbon nanotubes. Chem. Phys. Lett. 376, 154– 158. Ravi Kumar, M.N.V., 2000. A review of chitin and chitosan applications. React. Funct. Polym. 46, 1–27. Roy, D., Kongara, S., Valsaraj, K.T., 1995. Application of surfactant solutions and colloidal gas aphron suspensions in flushing naphthalene from a contaminated soil matrix. J. Hazard. Mater. 42, 247–263. Stapleton, M.G., Sparks, D.L., Dentel, S.K., 1994. Sorption of pentachlorophenol to HDTMA-clay as a function of ionic strength and pH. Environ. Sci. Technol. 28, 2330–2335. Varma, A.J., Deshpande, S.V., Kennedy, J.F., 2004. Metal complexation by chitosan and its derivative: a review. Carbohydr. Polym. 55, 77–93. Wong, Y.C., Szeto, Y.S., Cheung, W.H., McKay, G., 2004. Adsorption of acid dyes on chitosan-equilibrium isotherm analyses. Process Biochem. 39, 693–702. Xia, G., Ball, W.P., 1999. Adsorption-partitioning uptake of nine low-polarity organic chemicals on a natural sorbent. Environ. Sci. Technol. 33, 262–269. Yang, K., Zhu, L.Z., Xing, B.S., 2006. Enhanced soil washing of phenanthrene by mixed solutions of TX100 and SDBS. Environ. Sci. Technol. 40, 4274–4280. Zhang, Y., Maier, W.J., Miller, R.M., 1997. Effect of rhamnolipids on the dissolution bioavailability, and biodegradation of phenanthrene. Environ. Sci. Technol. 31, 2211–2217. Zhang, X., Li, A.M., Jiang, Z.M., Zhang, Q.X., 2006. Adsorption of dyes and phenol from water on resin adsorbents: effect of adsorbate size and pore size distribution. J. Hazard. Mater. 137, 1115–1122. Zheng, S., Yang, Z., Jo, D.H., Park, Y.H., 2004. Removal of chlorophenols from groundwater by chitosan sorption. Water Res. 38, 2315–2322. Zhu, R.L., Zhu, L.Z., 2008. Thermodynamics of naphthalene sorption to organoclays: role of surfactant packing density. J. Colloid Interf. Sci. 322, 27–32.