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Separation and Purification Technology 52 (2006) 332–342

Modified cellulose fibres for adsorption of organiccompound in aqueous solution

Fadhel Aloulou a, Sami Boufi a,∗, Jalel Labidi b

a Laboratoire Sciences des Materiaux et Environnement, LMSE-Faculte des sciences de Sfax-Tunisie, Tunisiab “Materials and Technologies” Group, E.U.P. University of the Basque Country, Plaza Europa, 1, 20018 San Sebastian, Spain

Received 23 February 2006; received in revised form 8 May 2006; accepted 9 May 2006

bstract

This paper presents the results of an experimental study of removal of organic contaminant from wastewater using chemically modified cellulosebres. The adsorption capacities of the modified fibres towards various organic molecules were investigated. The ensuing modified fibres appeared

o be efficient absorbent for different dissolved organic molecules in water. The recycling tests revealed that the exhausted substrates coulde regenerated without loosing their capacity. The adsorption isotherm related to different solutes follows the Langmuir model in entire range

f concentration. To confirm the possibility of using the modified cellulose fibres as a sorbent for the removal of dissolved organic pollutant,dsorption breakthrough curves were established under different operating condition such as concentration, flow rate and the column length. Theain advantage of this substrate lies in its relative facile regeneration without a significant loss of its adsorption capacity.2006 Elsevier B.V. All rights reserved.

nm[ttotrptabiscco

eywords: Cellulose fibres; Adsorption; Organic solute; Regeneration

. Introduction

Despite the considerable advances in the field of water treat-ent, the elimination of certain types of products to fulfil the

tandards in force still raises some problems and remains a topicf concern. It is the case of the organic compounds of polyphe-ols type, organochlorinated or aromatic, considered as beinghe most toxic for both living species and fauna. The origin ofhese products is multiple: the chemical industry, leaching andun-off from agricultural and forest land (through the intensivese of pesticides and weed-killers) deposition from aerial appli-ation, discharge from industrial waste [1,2].

In the absence of any treatment, the organic compounds andhe persistent organic pollutants (POP), like certain pesticides,ccumulate in water and favour the risk of contamination of thenderground sources in an irreversible way [3,4]. This effects worsened by the fact that the chemical stability of these

ollutants is high and even their chemical decomposition canenerate very stable products, such as PCB and dioxins, whichre extremely toxic even at very low concentration. Various tech-

∗ Corresponding author. Tel.: +216 74 274 400; fax: +216 74 274 437.E-mail address: sami.boufi@fss.rnu.tn (S. Boufi).

vs

Pt[a

383-5866/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2006.05.008

ologies are available for the water treatment, among them, theost employed are: filtration on granulated activated carbon

5–8], oxidation by oxygen or ozone, photochemical fragmen-ation [9] and the membrane separation [10]. Among the variousechniques cited above, adsorption on activated carbon remainsne of the effective methods to concentrate the organic pollu-ant and lower its concentration from effluent. This property iselated to; the large surface area of the substrate, the adequateore size distribution and the presence of active sites on whichhe organic solutes can be adsorbed through van Der Waals orcid–base interaction. Despite the prolific use of activated car-on and its availability in a variety of configurations and sizes,t suffers from some drawback; activated carbon is quite expen-ive and its regeneration is relatively expensive and leads to aonsiderable loss of the substrate [11–13]. Moreover, activatedarbon could be exhausted prematurely if dissolved compoundsr ions compete for sorption sites on the carbon. These disad-antages brought about searches for a suitable alternative or newubstrate more available at a lower cost.

The use of cellulose as adsorption support is not recent.

revious works highlighted the ability of this natural material

o adsorb a certain number of organic compound as pesticide14,15], and organic dye [16–18]. The ability of cellulose todsorb metal ions was also shown [19–21]. However, the adsorp-

rifica

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2

2

c2n

t

2

b

eamwouwlastfsc

2

as4

2

stsar

2

fuc2tfasiw

2

imfsu

F. Aloulou et al. / Separation and Pu

ion properties of native cellulose are not constant and varyccording to the origin of cellulose and preliminary treatments.n the same way, the adsorption capacity (as well for organicompounds as metal ions) remains very low (from 100 to 1000imes lower) in comparison to activated carbon or zeolite. Thisffect is associated to the low concentration of active sites onhich organic pollutant could be adsorbed [22].In previous studies we have shown that the adsorptions of

ationic surfactant on bleached cellulose fibres greatly enhanceshe aptitude of the substrate to uptake dissolved organic com-ound from aqueous media [23–25]. The improved solutedsorption was ascribed to the accumulation of the organicolutes within the aggregated domains formed by the self-ssembly of surfactant monomers at the cellulose/water inter-ace. The retention capacity depends principally on the amountf surfactant adsorbed and on the structure of the hydrocarbonail of the adsorbed surfactant. The longer the hydrocarbon chainength the higher the solute uptake. Given the ready availabilityf this type of substrate and its low cost, the present approachould be promising in applications related to the removal ofrganic pollutants and toxic substances in waste waters. How-ver, the possible desorption of the surfactant molecules from theellulose surface impeded the regeneration of the substrate byxtraction of the trapped solute once it is exhausted. A chemicalrafting of hydrocarbon structure at a sufficient surface densityo mimic the aggregated domain generated by the adsorbed sur-actant is necessary to overcome this weakness. The introducedhemical structure has to be essentially designed to afford aydrophobic microphase domain on which the organic pollu-ant could be accumulated. In the present work, the potentialsing chemically modified cellulose fibres as a reusable low-ost adsorbent substrate for the removal of dissolved organicompound has been evaluated. The modified substrate is basedn cellulose fibres on which linear alkyl chain has been graftedhrough a heterogeneous esterification reaction of the accessibleellulose hydroxyl groups by octanoic anhydride. The aptitudef the ensued modified substrate to uptake dissolved organicolute in aqueous media has been investigated in a batch and inontinuous operations. The influence of parameters such as flowate, feed concentration, bed length and temperature were alsotudied.

. Experimental section

.1. Materials

The fibres used in this work are commercial microcrystallineellulose: TECHNOCEL-150DM. Their average length is about50 �m and their specific surface, measured by the BET tech-ique using nitrogen as a probe was found to be 2.5 m2 g−1.

Octanoic anhydride and the different organic solutes used inhis work were of analytical grade.

.2. Preparation of modified cellulose fibres

The modifications of the cellulose fibres were carried outy grafting a long hydrocarbon chain through heterogeneous

owcc

tion Technology 52 (2006) 332–342 333

sterification of cellulose surface hydroxyl groups with octanoicnhydride using a solvent exchange procedure. Details of theethod are given elsewhere [26,30]. Cellulose fibres (5 g)ere introduced in the flask containing 110 ml of a mixturef toluene/triethylamine (80/20 v/v). The flask was firstly keptnder reflux (T = 110–120 ◦C) and constant stirring until allater contained on the fibres was evacuated by azeotropic distil-

ation, then octanoic anhydride (5 g) was added drop-wise overperiod of 1 h. The reflux was continued under nitrogen atmo-

phere over a period of 6 h. The obtained product was cooled andhen purified by soxhlet extraction with THF/ethanol (50/50 v/v)or 24 h. The degree of substitution (DS) was determined byaponification and titration according to a well-described pro-edure [27].

.3. FTIR analysis

The FTIR spectra were obtained from KBr pellets withPerkin-Elmer BX II spectrophotometer used in transmis-

ion mode with a resolution of 2 cm−1 in the range of00–4000 cm−1.

.4. CP/MAS 13C solid state NMR

Cross polarization/magic angle spinning (CP/MAS) 13C solidtate NMR experiments were performed with Bruker 300 spec-rometer operating at a 13C frequency of 75 MHz. The spinningpeed was set at 300 Hz. The contact time for CP was 1 msnd the delay time for acquisition was 5 s. Chemical shifts wereeferred to teramethylsilane (TMS).

.5. Batch adsorption studies

Solute adsorption experiments into batch condition were per-ormed by adding organic solute at the desired concentrationsing micro-syringe in a liquid solution containing 1 wt.% ofellulose modified fibres. The suspensions were then stirred for4 h at 25 ◦C to reach the adsorption equilibrium. Fibres werehen isolated by centrifugation and washed two times (10 mlor 0.1 g of fibres) by ethanol to extract the organic solute. Thedsorbed amount of the organic solute was determined by UVpectroscopy on the extracted ethanol fraction. It is worth not-ng that by such extraction procedure we have verified that thehole adsorbed solute was stripped off from the fibres.

.6. Continuous adsorption

Continuous adsorption experiments were carried out undersothermal condition and using a packed column filled with the

odified fibres. The effect of operating conditions: flow rate,eed concentration, adsorbed bed height and temperature weretudied. The packed column employed was a glass jacketed col-mn of 10 mm in diameter and 60 cm long, packed with 5 g

f modified cellulose fibres which were preliminarily kept inater for several hours to reach the equilibrium. Isothermal

onditions in the column were obtained by passing water at aonstant temperature through the jacket. Feed solutions were

334 F. Aloulou et al. / Separation and Purifica

astwmtF

3

ot

TFa1ms1alN

3

tahlascsd

tia(slc

a

Fig. 1. Experimental set-up for dynamic studies.

lso kept at constant temperature in a water bath. The effluentolutions were percolated through the column from the bottomo the top using a precision peristaltic pump. Effluent samplesere collected at regular intervals and the concentrations wereonitored using a UV spectrophotometer. A schematic set-up of

he column used in the continuous adsorption studies is given inig. 1.

. Results and discussion

The adsorbent used in this study is modified cellulose fibresbtained by heterogeneous esterification of bleached microcrys-alline fibres with linear octyl anhydride at a DS level of 0.25.

oami

Fig. 2. FTIR spectra of original cellulose fibres and the modified on

tion Technology 52 (2006) 332–342

he modified fibres were analysed by FTIR and solid state NMR.TIR spectra (Fig. 2) exhibited the presence of ester carbonylbsorption band at 1755 cm−1, methylene peak at 2855 and450 cm−1 (shoulder). The other characteristic peaks of acyloiety are hidden by the overlapping of cellulose bands. The

olid state 13C NMR spectra display the presence of peaks at2–40 ppm assigned to methylene carbon in the acyl moietynd different peaks between 55–110 ppm relative to the cellu-ose backbone. Their respective assignments are depicted on theMR spectra (Fig. 3).

.1. Batch studies

In our previous studies [23–26], we established that a pre-reatment with a cationic surfactant conferred to cellulose fibres

high affinity towards organic compounds. This behaviouras been correlated with the surfactant aggregation at the cel-ulose/water interface which generates hydrophobic domainscting as a reservoir for the accumulation of organic moleculeolutes. By anchoring acyl moiety bearing a long linear hydro-arbon chain onto cellulose fibres, we attempt to mimic thesetructures to preserve the aptitude of the substrate to trap theissolved organic compound from the aqueous solution.

In order to determine the ability of the modified fibreso trap organic compound from aqueous solutions, adsorptionsotherms of different organic solute previously dissolved in anqueous suspension of modified cellulose fibres were establishedFig. 4). For the different compounds, the isotherm displayed ateep increase for concentrations lower than 0.2 mmol l−1 fol-owed by a mild increase and a plateau at a solution concentrationlose to 1 mmol l−1.

The experimental results are best fitted by Langmuir model,s confirmed by the linear curve of Csol/Qads ratio as a function

f Csol (Fig. 5), where Qads,Qmax

ads and Csol are, respectively, thedsorbed amount, the equilibrium solute concentration and theaximum adsorbed amount per unit mass of the substrate. K

s the Langmuir equilibrium constant related to the energy of

e after esterification with octanoic anhydride at a DS = 0.25.

F. Aloulou et al. / Separation and Purification Technology 52 (2006) 332–342 335

TR

O

Fig. 3. CP-MAS 13C NMR spectra of original cellulose fibres and the mod

able 1esults related to the adsorption of different organic solutes on modified cellulose fib

rganic solute Cmax (Langmuir) Cmax (experimental) K

220 210 2

185 180 4

170 170 6

205 207 1

270 267

295 294 6

288 313

286 280 1

a For surfactant treated fibres.b For octyl grafted fibres.c R2 relative to the linear form of the Langmuir equation.

ified one after esterification with octanoic anhydride at a DS = 0.25.

res under equilibrium condition

a (l mol−1) Kb (l mol−1) R2c Solubility (mmol l−1)

750 8600 0.995 22.9

903 14000 0.996 4.46

185 11100 0.996 0.4

771 10400 0.995 16.9

779 21200 0.994 389

360 8900 0.993 0.22

957 15800 0.997

426 8750 0.996 5

336 F. Aloulou et al. / Separation and Purification Technology 52 (2006) 332–342

Fig. 4. Equilibrium adsorption isotherms of different organic solutes onto (a)modified cellulose fibres, and (b) virgin fibres, as a function of the equilibriumsolute concentration at pH 6.5–7 and room temperature.

Fc

a

Q

d

iTtt

i

(

ig. 5. Linear model of the Langmuir adsorption isotherms onto the modifiedellulose fibres at pH 6.5–7 and room temperature.

dsorption:

ads = KQmaxads Csol

1 + KCsol

The experimental values of the Langmuir constants wereetermined using the linear form of the equation:

Csol

Qadsol= 1

KQmaxads

+ Csol

Qmaxads

The adsorption equilibrium constant K, as well as the max-mum concentration of the solute uptake are summarized inable 1. The Freundlich isotherms which are often used to model

he isotherms of activated carbon appeared to be not suitable forhe modified cellulose substrate.

Different remarks could be pointed out from the data depictedn Table 1:

(i) The steep rise of the adsorption isotherm and the high valuesof Langmuir constant (from 8000 up to 15,000) denote thehigh affinity of the substrate toward the efficient trappingof the dissolved organic compounds in aqueous solutions.

(ii) The adsorption capacity seems to be more favoured forthe less soluble compound, but no clear tendency could beestablished between the adsorption coefficient and the sol-ubility. More work is needed to elucidate the mechanismby which the adsorption of organic solute using modifiedcellulose fibres takes place, and the influence of structuralparameters such as solute hydrodynamic volume and solu-bility on the adsorption capacity.

iii) The chemical modification greatly enhanced the ability ofthe cellulose substrate to trap dissolved organic compoundfrom water. The adsorption capacity which does not exceed40 �mol g−1 is raised up to 300 �mol g−1 after the graftingwith octyl chains (Fig. 4b).

rification Technology 52 (2006) 332–342 337

(

2Tmoc1urfeatctamwh

oeg

l

Ft1

F. Aloulou et al. / Separation and Pu

iv) If we compare the results issued from the solute uptakeby chemically modified cellulose fibres and those treatedwith cationic surfactant [23] one can remark that exceptfor trichlorobenzene and quinoline the adsorption capacityof the two substrates are closely the same. However, thechemically grafted substrate displays much higher affinitytoward the solute uptake as indicated by the higher Lang-muir K constant.

The adsorption kinetic of nitrobenzene, trichlorobenzene and-naphthol on modified cellulose fibres is presented in Fig. 6.he relatively long adsorption time denotes the slow diffusionechanism of the organic solute molecule inside the microp-

rous structure of the fibres. Nevertheless, the sorption pro-ess seems to be rapid during the first phase where it attains00 �mol g−1 after 30 min, afterwards the rate of the soluteptake declines appreciably to achieve the adsorption equilib-ium in about 1.5–2.5 h according to the solute structure. Theast phase sorption is probably related to the adsorption by thexternal area or the fibres pore, whereas the second phase isssociated with the diffusion of the solute in the inner part ofhe fibres micropore. Indeed, the high hydrophilic character ofellulose and the presence of an amorphous domains give riseo a highly microporous structure, which greatly increase theccessible surface, once the fibres are wetted by water [28]. Thisicroporous structure arise from salvation and accumulation ofater molecules inside the amorphous domains resulting in aigh expansion of the fibres structure.

In order to study the specific rate constant of solute adsorptionn modified cellulose fibres, the pseudo first and second-orderquations were used. The first-order rate expression of Lager-

reen [29] is given as

og(Qe − Qt) = log Qe − K1

2.303t,

ig. 6. Kinetic data for nitrobenzene, 2-naphthol and trichlorobenzene adsorp-ion on modified cellulose fibres (temperature: 25 ◦C, solute concentration:0−3 mol l−1).

Fo

wa

walisvwooe

3

ap

ig. 7. Plot of pseudo (a) first-order, and (b) second-order model adsorption ofrganic solutes onto modified cellulose fibres.

here Qe and Qt signify the amount adsorbed at equilibrium andt any time, respectively.

The second-order kinetic model [31] is expressed as

t

Qt

= 1

K2Q2e

+ t

Qe,

here K2 (g �mol−1 h−1) is the rate constant of second orderdsorption. The plot of log(Qe − Qt) versus t do not display ainear behaviour over the whole range of contact time indicat-ng that the first-order model is only suitable over the initialtage of the adsorption process. The straight lines in plot of t/Qtersus t (Fig. 7) show a good agreement of experimental dataith second-order kinetic model for the different solutes. Resultsbtained from the second-order model indicated that Qe valuesbtained from the second-order kinetic model are close to thexperimental values (Table 2).

.2. Column studies

Batch isotherms have shown that the modified cellulose fibresre efficient substrates for the uptake of dissolved organic com-ounds in water. To explore the adsorption capacity during

338 F. Aloulou et al. / Separation and Purification Technology 52 (2006) 332–342

Table 2Results related to the second-order model for the adsorption of different organic solutes on modified cellulose fibres

Solute K2 (g �mol−1 h−1) Qe (calculated) (�mol g−1) Qe (experimental) (�mol g−1) R2

N2T

cfittpwc

cw(b

Frfl

oiattacbd

itrobenzene 0.035 195-Naphthol 0.0056 284richlorobenzene 0.0051 303

ontinuous operation, a laboratory column filled with modifiedbres was designed. The ratio (Cs/C0) of the effluent concentra-

ion Cs to the input concentration C0 was plotted against timeo obtain the breakthrough curve at a constant flow rate. For allerformed experiment breakthrough time is defined as the pointhen the concentration of the effluent reaches 5% of the input

oncentration.With the increase of the input flow rate at a constant feed con-

entration and a bed length of 20 cm, the breakthrough curves

ere steeper and occur at a shorter time as the flow rate is raised

Fig. 8a). With 2-naphtol concentration of 10−3 mol l−1, thereakthrough time is reached at 60, 40 and 20 min for a flow rate

ig. 8. Effect of the feed flow rate on the breakthrough curves (a) and on the cor-esponding retained amount vs. time (b) of 2-naphthol uptake under continuousow (bed height 20 cm, temperature: 20 ◦C).

f

cF

Ftc

205 0.9999286 0.9998295 0.9996

f 15, 25 and 40 ml min−1, respectively. This is quite expectedf we take into account the relatively high time needed to reachdsorption equilibrium with modified cellulose fibres. Indeed,he higher the flow rate, the lower is the contact time betweenhe solute and the substrate. Fig. 8b reports the total adsorbedmount of solute versus time. The curves display a linear partorresponding to an increase of the total solute uptake, followedy plateau attributed to the exhaustion of the column whichecreases with the raise of the flow rate and growingly diverges

rom the maximum adsorbed amount at equilibrium condition.

The effect of the inlet concentration on the breakthroughurves at a constant flow rate of 40 ml min−1 is presented inig. 9a for 2-naphthol solute. As expected, the higher the input

ig. 9. Effect of the feed concentration on the breakthrough curves (a) and onhe corresponding retained amount vs. time (b) of 2-Naphthol uptake underontinuous flow (bed height 20 cm, temperature: 20 ◦C).

rification Technology 52 (2006) 332–342 339

ctiTctt

otswdslot2eo

F(2

F. Aloulou et al. / Separation and Pu

oncentration, the lower the breakthrough time is. Nevertheless,he maximum uptake amount of the column before exhaustions increased with the raise in the inlet concentration (Fig. 8b).his effect may be attributed to the increase in the gradient con-entration between the continuous medium and the substrate ashe inlet concentration is rose, which in turn enhances the massransfer between the two phases.

One of the parameters which greatly affect the performancef continuous adsorption is the bed length which will determinehe flow rate of the feed ensuring an efficient trapping of dis-olved pollutant. To study the effect of this factor, the bed lengthas varied by the incorporation of a fine glass sphere (2 mmiameter) within the substrate while maintaining its weight con-tant. Results depicted on Fig. 10 reveal, that with higher bedength both the breakthrough time and the maximum amountf the solute uptake by the column are increased. Their respec-ive value evolves from 140 to 175 min and from 215 up to

73 �mol g−1 as the bed length is raised from 20 to 40 cm. Suchvolutions could be ascribed to the upsurge in the residence timef the solute inside the column allowing therefore a better dif-

ig. 10. Breakthrough curves of 2-naphthol adsorption at various bed lengtha) and the corresponding retained amount vs. time (b) (feed concentration:.5 × 10−4 mol l−1, flow rate: 25 ml min−1, temperature: 20 ◦C).

Fac

fni

anftsa2tatat8tshs

ig. 11. Breakthrough curves of 2-naphthol, nitrobenzene and trichlorobenzenedsorption at (a) and the corresponding retained amount vs. time (b) (feed con-entration: 5 × 10−4 mol l−1, rate: 25 ml min−1,temperature: 20 ◦C).

usion within the inner pore of the modified fibres. It is worthoting that with 40 cm bed length the maximum solute uptakes close to that obtained under equilibrium condition (Table 1).

The effect of the solute solubility on the efficiency of thedsorption with modified cellulose fibres was analysed usingitrobenzene and trichlorobenzene solute that display huge dif-erence in their aqueous solubility. The breakthrough curves andhe corresponding uptake amount for the different solute at a con-tant feed (5 × 10−4 mol l−1) and a fixed bed length of 20 cmre shown in Fig. 11. The breakthrough time for nitrobenzene,-naphthol and trichlorobenzene are 63, 80 and 92 min, respec-ively, and their corresponding maximum uptake is 173, 222nd 285 �mol g−1. The difference noted in the breakthroughime may be related to the difference in the maximum solutedsorbed. However if we compare the efficiency of the soluterapping with respect to equilibrium condition (96%, 78% and4% for trichlorobenzene, 2-naphthol and nitrobenzene, respec-

ively) it seems that in the presence of extremely low solubleolute like trichlorobenzene the trapping efficiency is relativelyigher. Conversely, for nitrobenzene and 2-naphthol solutes noignificant difference is noted in the trapping efficiency even

340 F. Aloulou et al. / Separation and Purification Technology 52 (2006) 332–342

Fig. 12. Effect of the temperature on the breakthrough curves of 2-naphtholc(2

tFa

iawtf21tamtIcwa

w

Far

itnai

3

gpfwrppeaabch

cwessatet

onstant feed concentration (a) and the corresponding retained amount vs. timeb) (feed concentration, 2.5 × 10−4 mol l−1, flow rate:25 ml min−1, temperature:0 ◦C).

hough nitrobenzene is three times more soluble than 2-naphthol.urther work is needed to correlate the solute properties with thedsorption behaviour by alky grafted cellulose fibres.

As the temperature may greatly affects the adsorption capac-ty as well as the diffusion coefficient, the evolution of thedsorption behaviour with temperature under continuous flowas also investigated. Fig. 12 depicts the evolution of the break-

hrough curves and the removed amount of 2-naphthol at dif-erent temperature (feed concentration of 5 × 10−4 mol l−1 and5 ml min−1 flow rate). The breakthrough time is about 140,65 and 185 min at temperatures of 25, 40 and 50 ◦C, respec-ively. The corresponding adsorption capacity is about 250, 260nd 275 �mol g−1. Both the breakthrough time and the maxi-um removed amount are increased by the raise in the column

emperature. This result was ascribed to a thermodynamic effect.ndeed, since the adsorption enthalpy of organic solute by graftedellulose fibres is negative (results shown elsewhere) [30], it

ould be expected that an increase in solution would result in

n enhancement in the adsorption capacity.The effect of the presence of salts on the continuous uptake

ith modified cellulose fibres has also been carried out. Fig. 13

rzsi

ig. 13. Effect of KCl concentration on the breakthrough curves and the retainedmount of 2-naphthol on modified fibres (feed concentration: 10−3 mol l−1, flowate: 15 ml min−1, temperature: 20 ◦C).

llustrates the evolution of the breakthrough curve and the reten-ion amount with the concentration of added KCl using 2-aphthol as solutes. Both of the breakthrough curves and thedsorbed capacity appeared to be unaffected by the raise of theonic strength for salt concentration up to 10−3 mol l−1.

.3. Regeneration of the column

One of the envisaged applications of the system under investi-ation is the use of such substrate to trap dissolved organic com-ounds in wastewater. These systems are worth to be reusableor multiple cycles operation, in order to reduce their cost and toork within a sustainable approach based on using renewable

ecyclable raw material. This is the main driving force whichrompted us to investigate the regeneration ability. Indeed, thisarameter is one of the most important which determine from anconomical point of view, the potential exploitation of a materials an adsorbent. It is worth noting that in most cases, the regener-tion of the saturated adsorbent like activated carbon or zeolitey the elimination of the loaded pollutant is time and energyonsuming. Like wise the cost involved in such treatment is tooigh to reconsider the regeneration of the adsorbent.

Thus, a set of experiments consisting of washing the saturatedolumn by a continuous flow of ethanol (95/5 ethanol/water)as undertaken. Results in Fig. 14 showed that the solute can be

asily recovered and rapidly stripped off from the modified sub-trate. The required volume to completely remove the trappedolute is 340, 310 and 280 ml for trichlorobenzene, 2-naphtholnd nitrobenzene, respectively. When we analyses the desorp-ion curves, we observe that the concentration of the solute inthanol remains constant until the stripped fraction attains a cer-ain level, which is about 60%, 50% and 35%, with respect to the

etained amount, for nitrobenzene 2-naphthol and trichloroben-ene respectively, then it decreases continuously until the totalolute is stripped off. Therefore, it seems that the more solubles the solute in aqueous the easier is the extraction of the trapped

F. Aloulou et al. / Separation and Purifica

Fig. 14. Breakthrough curves of removed 2-naphthol, nitrobenzene andtrichlorobenzene by washing with ethanol and the corresponding removedamount vs. time (solvent flow: 10 ml min−1, temperature: 20 ◦C).

Fa

sbtpo

rlwagtra

4

c

tmimar

•

•

•

bbt

R

[

[[

[[

[[

[

[

ig. 15. Evolution of the maximum adsorption capacity under continuous flows a function of the number washing cycle.

olute. The easy release of the loaded organic compound coulde ascribed to the relatively weak energy of interaction betweenhe organic molecules and the substrate which probably involveurely dispersive interaction between the grafted alkyl chain ofctyl moiety and the solute molecules.

The recycling of the modified substrate was tested within aange of 10 cycles and showed that it can be reused without anyoss of its adsorption capacity, as shown in Fig. 15. The repeatedashing of the modified fibres did not alter significantly the

dsorption capacity of the substrate. This finding is one of thereatest advantages of such modified cellulose fibres comparedo other adsorbents such as activated carbon or zeolites, whichequire an energetically costly treatment and lead inevitably tomore pronounced loss of the adsorption activity.

. Conclusion

Removal of organic contaminant from wastewater usinghemically modified cellulose fibres was studied. The adsorp-

[[

[

tion Technology 52 (2006) 332–342 341

ion capacities of the new adsorbent towards various organicolecules were measured. It was found that the adsorption

sotherm for the studied contaminant follows the Langmuirodel. The experimental study with column filled with the

dsorbent to investigate the effect of operation conditions (flowate, temperature, concentration. . .) has shown that:

the breakthrough time is dependent on the flow rate of thesolution, the residence time and initial contaminant concen-tration,the increase of the adsorption temperature lead to an increaseof the adsorption capacity,the ionic strength of the solution does not affects the adsorp-tion capacity of the modified fibres up to 10−3 mol l−1.

The regeneration of saturated modified cellulose fibres haseen carried out using water/ethanol solution. The new adsor-ent can be regenerated easily and reused for multiple cycles ofreatment without any reduction of its adsorption capacity.

eferences

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