Remediation of hexachlorobenzene contaminated soils by rhamnolipid enhanced soil washing coupled with activated carbon selective adsorption

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Journal of Hazardous Materials 189 (2011) 458464Contents lists available at ScienceDirectJournal of Hazardous Materialsjourna l homepage: www.e lsev ier .comRemed tesoil wa lecJinzhong gtia Environmenta 43007b Nanjing Instit 21004a r t i c lArticle history:Received 16 DReceived in reAccepted 17 FAvailable onlinKeywords:Activated carbBiosurfactantHOCsSoil remediatiSoil washinglectivbon (CB froHCBespecdsorpand aom so% anproceth bioto remove hydrophobic organic compounds from soils. 2011 Elsevier B.V. All rights reserved.1. IntroduRemediacompoundsmental sciewashing iscially for Hmostly ania variety o(PAHs), polRecently, ition of biosenvironmentants [79]enhancing[8,10,11].Rhamnowhich arehydrophilicacids (C8Crevealed thPAHs, oil, a CorresponE-mail add0304-3894/$ doi:10.1016/j.ctiontion of soils contaminated with hydrophobic organic(HOCs) has aroused intensive attention of environ-ntists in the past decades. Surfactant-enhanced soilproposed as an efcient clean-up technology espe-OCs-contaminated soils [13]. Chemical surfactants,onic and nonionic, are proved capable of removingf HOCs, such as polycyclic aromatic hydrocarbonsychlorinated biphenyl and pesticides from soils [46].ncreasing interests have been paid to the applica-urfactants in soil washing, considering their superiortal compatibility relative to the chemical surfac-. For instance, rhamnolipids are widely studied as anagent to remediate soils with HOCs or heavy metalslipids are mostly produced by Pseudomonas aeruginosa,composed of one or two rhamnose molecules as aportion, and up to three molecules of hydroxy fatty14) as a hydrophobic portion. Abundant results haveat rhamnolipids can effectively mobilize or removend PCP in soils [7,12]. More interestingly, it is sug-ding author. Tel.: +86 27 87792159; fax: +86 27 87792159.ress: hust-esri2009@hotmail.com (X. Lu).gested that the residue of rhamnolipids in soils could promote thebiodegradation of residual HOCs [13,14], which is also superior tothe chemical surfactants.However, whatever surfactants are used, post-treatment oftheir washing solutions is required to remove the contaminants,and moreover, to recover/reuse the surfactants. Unfortunately, upto now limited efforts have been devoted into the disposal ofthe washing solutions. Recently, some researchers reported thatadvanced oxidation processes (AOPs), such as photo-Fenton [15],photocatalytic [16,17] and electrochemical treatment [18] couldeffectively destruct the pollutants in surfactants solutions. Never-theless, as AOPs are mostly associated with non-specic hydroxylradical reactions, the presence of high concentrations of surfactantswould inevitably impede the degradation of target contaminants.As a consequence, either a higher treating cost or a lower surfac-tants recovery would be expected. In this sense, the results of Ahnet al. [19] seemmuchmoreappealing,who found that granular acti-vated carbon (GAC) could selectively adsorb phenanthrene fromTriton X-100 solution. A high removal of contaminants (86.5%) anda high recovery of surfactants (93.6%)were obtained byusingDarco2040 activated carbon (AC) at 1 g L1 [19,20]. Furthermore, thespent ACs could be further regenerated via either thermal or chem-icalmethods, and reused for soilwashing solution treatment. Itwassuggested that the adsorption process was simple, fast, and cost-efcient, therefore an applicable alternative to recover surfactantsin soil washing technique [19].see front matter 2011 Elsevier B.V. All rights reserved.jhazmat.2011.02.055iation of hexachlorobenzene contaminashing coupled with activated carbon seWana, Lina Chaia, Xiaohua Lua,, Yusuo Linb, Shenl Science Research Institute, Huazhong University of Science and Technology, Wuhan,ute of Environmental Science, Ministry of Environmental Protection of China, Nanjing,e i n f oecember 2010vised form 16 February 2011ebruary 2011e 23 February 2011onona b s t r a c tThe present study investigates the sesolution by a powdered activated carfurther evaluated on the removal of Hat a dosage of 10g L1 could achieve atrations of 1mgL1 and 3.325g L1, r819%. Successive soil washing-PAC acycle) showed encouraging leachingsolution was applied, HCB leaching frby PAC was nearly 90%. An overall 86respectively, by using the combinedgests that coupling AC adsorption wi/ locate / jhazmatd soils by rhamnolipid enhancedtive adsorptionan Zhangb4, PR China2, PR Chinae adsorption of hexachlorobenzene (HCB) from rhamnolipidPAC). A combined soil washing-PAC adsorption technique ism two soils, a spiked kaolin and a contaminated real soil. PACremoval of 8099% with initial HCB and rhamnolipid concen-tively. The corresponding adsorptive loss of rhamnolipid wastion tests (new soil samplewas subjected towashing for eachdsorption performances for HCB. When 25g L1 rhamnolipidils was 5571% for three cycles of washing, and HCB removald 88% removal of HCB were obtained for kaolin and real soil,ss to wash one soil sample for twice. Our investigation sug-surfactant-enhanced soil washing is a promising alternativeJ. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464 459Table 1Selected physicalchemical properties associated with soils.Property Kaolin Real soilParticle size a1.00.25m0.250.050.050.000.0050.0460 J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464Table 2Composition of present rhamnolipid mix identied by HPLCESIMS.No. Composites Pseudomolecularion, m/zRelativeabundance, %12345678910111213trifuged at 4decanted antionwas suAC1). Then5to the tubethe secondtions wereexperiment2.5. ChemicHCB in tGC equippecolumn (Phdurewas inconcentratisionmat emdiluted appwas below Crhamnolipi3. Results3.1. CharacThe comlisted in Tabof monorhaRhC10C10 aRh2C10C10 owere also cthemixwasmation in Tmix wouldthe result mrhamnolipiover, the C63.1mgL13.2. Effect odesorptionFig. 1athe increasetent with pobserved btions above(MSR) is geffect of rhamnolipid concentration on (a) HCB solubilization and (b) HCBon from kaolin.s which is dened as [2527]CHOC, mic CHOC,cmcCsurf CMCin Csurf is the surfactant concentration added (mol L1), andic, CHOC,cmc are the apparent solubilities of HOCs in sur-s solutions at concentration above CMC (i.e., micelles are) and at CMC (mol L1), respectively. By using above equa-he MSR of rhamnolipid for HCB herein was calculated as04. In comparison, the value is lower than that of a nonionicant, Tween 80 (1.72103 for HCB), while slightly higherat of an anionic surfactant, SDS (3.74.7104 for HCB),ing to the results of Kommalapati et al. [26]. Bordas et al.so reported a lowerMSR of a rhamnolipidmixture for pyrenered with four selected nonionic chemical surfactants.RhC8 305 1.0RhC10 333 11.8RhC12 361 0.7RhC8C10 475 4.6RhC10C10 503 21.6RhC12:1C10 529 6.4RhC10C12 531 7.5Rh2C10 479 6.5Rh2C8C8 593 0.4Rh2C10C8 621 7.7Rh2C10C10 649 20.9Rh2C12:1C10 675 4.7Rh2C12C10 677 6.3000 rpm for 20min, and each group supernatant wered combined. After ltration, 20mL of thewashing solu-bjected to the AC adsorption experiment (designated asmLof the regenerated rhamnolipid solutionwasaddeds containing the precipitated soils (from SW1) to startcycle of washing (designated as SW2). All other opera-the same as the successive soil washing-AC adsorptions described above.al analysishe hexane was determined on a Hewlett-Packard 6890dwith an electron capture detector and a ZB-5 capillaryenomenex, USA). Detailed information for GC proce-cluded in our previous study [21]. Aqueous rhamnolipidonwasestimatedby surface tensionusing a surface ten-ploying the Du Nouy ringmethod [24]. The samplewasropriately to ensure that the rhamnolipid concentrationMC. A calibration curvewas constructedwhich relatedd concentration (mgL1) to surface tension (dyn cm1).and discussionterization of rhamnolipidposition of rhamnolipid identied by HPLCESIMS isle 2. A total of 13 compositeswere detected, with 53.6%mnolipids and 46.4% of dirhamnolipids. Furthermore,ccounted for the largest fraction of 21.6%, followed byf 20.9%. The fractions for RhC10, RhC10C8 and Rh2C10C8onsiderable. The average relative molecular weight ofestimated as 539.8 according to the composition infor-able 2. Correspondingly, the rhamnose content of thebe 44%. Based on the theoretical rhamnose content andeasured by sulfuric acid-phenol method, purity of theFig. 1. EdesorptifactantMSR =whereCHOC,mfactantformedtion, t5.41surfactthan thaccord[25] alcompad used for experiments was calculated as 94.8%. More-MC value determined by the surface tensionmat was, i.e., 0.11mM.f rhamnolipid on HCB solubilization and enhancedindicates that HCB solubility increases linearly withof rhamnolipid concentration (0.0620g L1), consis-revious results that a positive linear relationship wasetween HOCs solubilities and surfactants concentra-CMC [5,25]. Furthermore, themolar solubilization rationerally used to evaluate the solubilization effect of sur-The effespiked kaolorbed correthe range osolutions wand60%, resachieved foalthough thCMC, respetant concenabove effecbe reachedconcentratict of rhamnolipid dosage on HCB desorption from thein is shown in Fig. 1b. Generally, the fraction of HCB des-latedpositivelywith total rhamnolipid concentration inbserved. Particularly, when 10 and 15g L1 rhamnolipidere used, the fractions of HCB desorbed were over 40%pectively.Note that no appreciableHCBdesorptionwasr the rst two rhamnolipid amounts (0.7 and 1.4 g L1),e total concentrationswereaboveCMC(about11and22ctively). Aswell documented, only at an aqueous surfac-tration above CMC (or a total surfactant concentrationtive CMC), enhanced desorption of HOCs from soils can[4,5,8]. It can be found from Fig. 1b that only at totalons above 1.4 g L1, the aqueous rhamnolipid is appar-J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464 461Fig. 2. (a) Adstion as an effecpH 7.0.ently higheof HCB desohigher thanet al. [25].higher rahmclay contenrhamnolipiMoreover, ious rhamnoof total rharhamnolipiequation ofcanwell exptotal rhamntion of rhamet al. [8], whadsorption3.3. SelectivThe perflipid solutioa rather rerange. Approf 2.5 g L1,and 10g L1removal byof HCB in r10g L1. Ontion by ACsexhibits a hicant surfacrange of 2.5the loss warespectivelybetween thTable 3Single-point partition factor for HCB (Kd), rhamnolipid (Kd) and the selectivity (S) ofPAC at variousParametersountmounnolipidterisre votivelty forseleyed hby t= CCinKdolipig1)(mgconequan Taostith torptive removal of HCB and (b) residual aqueous rhamnolipid in solu-t of AC dosage. Initial HCB 1.0mgL1, rhamnolipid 7.5 g L1, time 6h,r than CMC, consistent with the aforementioned resultsrption. The effective CMC herein (22 CMC) seemsmuchthe reported value of 0.4 g L1 (12.1 CMC) by BordasThe difference was probably associated with a muchnolipid adsorption capacity of kaolin due to a highert relative to ne sand [8], and a much lower MSR ofd forHCB than for pyrene (5.4104 versus 7.5103).nspection of Fig. 1b also suggests that fraction of aque-lipid becomes increasingly abundant with the increasemnolipid concentration. By rearranging the results ofPAC am2.5510GAC a2.5510Rham3.37.51520characthe porespeccapaciTheemploof HCBS = KdKdwhererhamnCs (g kand Cenolipidabovelisted iare almtune wd adsorption to kaolin to t the Freundlich model, anCs = 0.104Ce0.40 (r2 =0.972) could be obtained, whichlain the increase in aqueous rhamnolipid fractionwitholipid concentration increasing. A nonlinear adsorp-nolipid to soils was also reported by Mata-Sandovalerein the Langmiur isothermmodel was used to t theof rhamnolipid to three soils.e adsorption of HCB from rhamnolipid solution by ACsormances of selective adsorption of HCB from rhamno-n by GAC and PAC are presented in Fig. 2. PAC showedliable removal efciency of HCB in observed dosageoximately 70% of HCB was adsorbed at a PAC amountand the removal rose up to near 90% and 99% when 5PACwere added, respectively. Comparatively, the HCBGAC at the same dosage was much lower. Only 54%hamnolipid solution was removed at a GAC dosage ofthe other hand, the loss of rhamnolipid due to adsorp-should also be evaluated. Fig. 2b clearly shows that PACigher rhamnolipid adsorption relative toGAC. No signif-tant loss was recorded for GAC for the observed dosage10g L1 (462 J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464Fig. 3. Effect of initial rhamnolipid concentration on selective adsorption of HCB byPAC. PAC dosage 10g L1, time 6h, pH 7.0. Initial HCB 1mgL1.3.4. Enhanced remediation of HCB-contaminated soils by soilwashing coupled with AC adsorptionThe feasibility of coupling PAC selective adsorption withrhamnolipid-enhanced soil washing was tested. As displayed inFig. 4a, when 12.5 g L1 rhamnolipid solution was employed, HCBremoval from kaolin and real soil both declined dramatically as thecycles ofwashing increased. For instance, theHCB removalwas 47%for real soil in SW1, while the efciency dropped down to less than15% in SW3. For the adsorption of HCB in rhamnolipid solution byPAC, the removal were all nearly complete (>98%) for both soils intwo adsorption treatments (AC1 and AC2). Comparatively, the per-formance seemed more encouraging when 25g L1 rhamnolipidsolution was used (Fig. 4b). A total of 67% and 71% of HCB werewashed out for kaolin and real soil in SW1, which were as 1.3 and1.5 times as those for kaolin and real soil at rhamnolipid concen-tration of 12.5 g L1, respectively. Moreover, only a slight decreasein HCB leaching was observed in the following SW2 and SW3 foreither kaolin or real soil. The leaching percentages ofHCB from soilsin SW3 were reduced by 12% and 13% compared with SW1 for thetwo soils, respectively. Furthermore, approximately 89% adsorp-tive removal of HCBwas achieved in AC1, and the efciencies grewup slightly to 94% and 91% for washing solutions from kaolin andreal soil, probably due to a lowering rhamnolipid concentrationvia adsorption to soils in SW2. Noteworthy that the overall HCBremoval of near 90% by 10g L1 PAC is acceptable, given the con-sideration that a further increase in HCB removal means a higherdosage of PAC and a higher loss of rhamnolipid. Interestingly, anapproximately 90% adsorption of pyrene by AC was also proposedas a good goal according to amathematical evaluation by Ahn et al.[19].The variations of aqueous rhamnolipid concentration after eachstep of soil washing or AC adsorption are illustrated in Fig. 4cd.An almost linear decrease in aqueous rhamnolipid concentrationwas recorded for either kaolin or real soil when 12.5 g L1 biosur-factant was applied (Fig. 4c). After two cycles of soil washing andFig. 4. Perform(a) 12.5 and (b7.0.ance of combined soil washing-PAC adsorption process in successive washing of kaolin () 25g L1, and variation of aqueous rhamnolipid at initial concentrations of (c) 12.5 andKL) and real soil (RS): HCB removal at rhamnolipid concentrations of(d) 25g L1. Washing time 48h, adsorption time 6h, PAC 10g L1, pHJ. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464 463Fig. 5. Repeatcombined proAC adsorptiwere aboutThis dramato soil matwashing efcentrationprocessing,(Fig. 4a). Astion, a grad(Fig. 4d). Atant concenaccounted ftents of rhremoval ofHtive loss ofversus 12.5observationgave rise tokaolin (Secit is suggesprocess, higefcient. Hhigher doseproperly hiThe comther evaluaachieve a dthat SW2 co(if measureleaching wiremoval byreal soil, anto SW12athe rhamnoused to wasNote thaments, rhamextent, i.e.,stances, therestored byintervals. Mcient solutto precipitause. It shouHOCs-contations by PAmay be used (alone or after centrifugation) to separate PAC fromrahmnolipid solution. In Addition, other mixing methods such aspumping the soil washing solutions through PAC-packed columnsbe applied to avoid the need of separation. The spent PAC,hileen recluspressorpsibilsorpan bamnoMSRorteHCBremoaquesurfamparm rhorpt7%.tionmnoe succourag L1an a71%B byaqueee wl wae tosamsurfan is ath HOwleds worof Chpmee Keed washing of kaolin and real soil by soil washing-PAC adsorptioncess. Rhamnolipid 25g L1, PAC 10g L1, pH 7.0.on, the residual concentrations of aqueous rhamnolipid3.2 and 2.0 g L1 for kaolin and real soil, respectively.tical loss of aqueous rhamnolipid (due to adsorptionrix and PAC) was the main reason for decreased HCBciency in Fig. 4a. In comparison, the rhamnolipid con-was lower for real soil than for kaolin at all stages ofin accordance with the leaching of HCB from two soilsfor the remediation using 25g L1 rhamnolipid solu-ual reduction in aqueous rhamnolipid was evidencedfter four steps of processing, the residual biosurfac-trations were as high as 16g L1 for both soils, whichor over 64% of the initial concentration. The high con-amnolipid also explained the incomplete adsorptiveCB forAC1andAC2 in Fig. 4b.Note that the less adsorp-biosurfactant with higher initial concentrations (25g L1) was somewhat consistent with aforementioneds, i.e., an increased initial rhamnolipid concentrationa decreased fraction of rhamnolipid adsorbed by eithertion 3.2) or GAC (Section 3.3 and Fig. 3). As a result,ted that for the combined soil washing-AC adsorptionher concentrations of surfactants would be more cost-owever, considering a reduced HCB adsorption (or aof PAC required) at higher rhamnolipid contents, agh dosage of rhamnolipid is suggested.bined soil washing-AC adsorption technique was fur-ted as washing the same portion of soils repeatedly toesirable overall HCB removal. It can be seen from Fig. 5uld leach 4563% of the residual HCB in soils from SW1d by the initial HCB contents in kaolin and real soil, thell be 11.3% and 18.5%). More appealing, the overall HCBcouldmeanwand th4. ConThetive adThe feaPACadsions c(1) Rhtherepofbeofbio(2) Cofroadsof 1trarha(3) Then25as55HCofthrsoitivthebiotiowiAcknoThidationDeveloof Stattwo cycles of washing were 87% and 89% for kaolin andd the nal adsorptive losses of rhamnolipid (subjectedndAC1)were less than25% (data not shown). As a result,lipid solution could be further regenerated by PAC andh another portion of soils.t after a series of soil washing-AC adsorption treat-nolipid concentrationmay decrease to an unfavorableinsufcient for further soil washing. At these circum-capability of the rhamnolipid washing solution can beadding a new portion of rhamnolipid at appropriateoreover, recovery of rhamnolipid from above de-ion canbe also reachedby simply acidifying the solutionte rhamnolipid and re-dissolving the solid for furtherld also be mentioned that for a full-scaled treatment ofined rhamnolipid (or other surfactants) washing solu-C selective adsorption, microltration/ultraltrationShanghai Togy DeveloCenter of Hfor the HPLReferences[1] S. Deshpation for e[2] C.N. Mulltaminate[3] R. Zhangmixtures213229[4] S.O. Ko, Mcompounnol. 32 (1[5] K. Yang, Lsolutions, can be regenerated via thermal ormicrowavemethodsused for soil washing solution treatment.ionsent study investigates the performance of PAC on selec-tion of HCB from biosurfactant rhamnolipid solution.ity of rhamnolipid-enhanced soil washing coupledwithtionwas further veried.Mainobservations and conclu-e summed up as follows:lipid showed a reliable solubilization effect on HCB,was calculated as 5.4104, slightly higher than thed value of SDS for HCB. Signicant enhanced desorptionfrom kaolin was also evidenced, over 60% of HCB couldvedbyusing15g L1 rhamnolipid solution. The fractionous rhamnolipid was found increasing with increasedctant added.ed with GAC, PAC was more efcient to remove HCBamnolipid solution. By using 10g L1 PAC, 99% of HCBion was achieved, with an acceptable rhamnolipid lossFurthermore, an increase in initial rhamnolipid concen-led to a decrease in HCB removal and adsorptive loss oflipid.cessive PAC adsorption-soil washing process achievedging leaching of HCB from kaolin and real soil by usingrhamnolipid as a washing solution and 10g L1 PACbsorbent. The individual HCB removal from soils wasfor three cycles of washing, and the adsorption ofPAC was nearly 90%. In addition, the adsorptive lossous rhamnolipid to soils and PAC was about 35% afterashing and two adsorption treatments. The combinedshing-AC adsorption process was also testied effec-remove 8688% of HCB from both soils by washinge sample for twice. Therefore, it is suggested thatctants-enhanced soil washing coupledwith AC adsorp-promising alternative to remediate soils contaminatedCs.gementsk was supported by the National Natural Science Foun-ina (21077038), the National High-Tech Research andnt (863) Programme (2009AA063103), the Foundationy Laboratory of Coal Combustion (FSKLCC0906), andongji Gao Tingyao Environmental Science & Technol-pment Foundation (STGEF). The Analytical and Testinguazhong University of Science & Technology is thankedCMS analysis for rhamnolipids.nde, B.J. Shiau, D. Wade, D.A. Sabatini, J.H. Harwell, Surfactant selec-nhancing ex-situ soil washing, Water Res. 33 (1999) 351360.igan, R.N. Yong, B.F. Gibbs, Surfactant-enhanced remediation of con-d soil: a review, Eng. Geol. 60 (2001) 371380., P. Somasundaran, Advances in adsorption of surfactants and theirat solid/solution interfaces, Adv. Colloid Interface Sci. 123 (2006)..A. Schlautman, E.R. Carraway, Partitioning of hydrophobic organicds to sorbed surfactants.1. Experimental studies, Environ. Sci. Tech-998) 27692775..Z. Zhu, B.S. Xing, Enhanced soil washing of phenanthrene by mixedof TX100 and SDBS, Environ. Sci. Technol. 40 (2006) 42744280.464 J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464[6] W. Zhou, L. Zhu, Enhanced soil ushing of phenanthrene by anionicnonionicmixed surfactant, Water Res. 42 (2008) 101108.[7] W.H. Noordman, W. Ji, M.L. Brusseau, D.B. Janssen, Effects of rhamnolipid bio-surfactants on removal of phenanthrene from soil, Environ. Sci. Technol. 32(1998) 18061812.[8] J.C.Mata-Sandoval, J. Karns, A. Torrents, Inuenceof rhamnolipids andTritonX-100 on the desorption of pesticides from soils, Environ. Sci. Technol. 36 (2002)46694675.[9] C.N. Mulligan, Environmental applications for biosurfactants, Environ. Pollut.133 (2005) 183198.[10] Y. Asci, M. Nurbas, Y.S. Acikel, A comparative study for the sorption ofCd(II) by soils with different clay contents and mineralogy and the recov-ery of Cd(II) using rhamnolipid biosurfactant, J. Hazard. Mater. 154 (2008)663673.[11] L.Z. Zhu, M. Zhang, Effect of rhamnolipids on the uptake of PAHs by ryegrass,Environ. Pollut. 156 (2008) 4652.[12] L.M.S. Anna, A.U. Soriano, A.C. Gomes, E.P. Menezes, M.L.E. Gutarra, D.M.G.Freire, N. Pereira, Use of biosurfactant in the removal of oil from contaminatedsandy soil, J. Chem. Technol. Biotechnol. 82 (2007) 687691.[13] S. Berselli, G. Milone, P. Canepa, D. Di Gioia, F. Fava, Effects of cyclodextrins,humic substances, and rhamnolipids on the washing of a historically con-taminated soil and on the aerobic bioremediation of the resulting efuents,Biotechnol. Bioeng. 88 (2004) 111120.[14] C.Z. Cui, C. Zeng, X. Wan, D. Chen, J.Y. Zhang, P. Shen, Effect of rhamnolipidson degradation of anthracene by two newly isolated strains, Sphingromonas sp.12A and Pseudomonas sp. 12B, J. Microbiol. Biotechnol. 18 (2008) 6366.[15] R.D. Villa, A.G. Trovo, R.F.P. Nogueira, Soil remediation using a coupled process:soil washing with surfactant followed by photo-Fenton oxidation, J. Hazard.Mater. 174 (2010) 770775.[16] D. Fabbri, A.B. Prevot, V. Zelano, M. Ginepro, E. Pramauro, Removal and degra-dation of aromatic compounds from a highly polluted site by coupling soilwashing with photocatalysis, Chemosphere 71 (2008) 5965.[17] D. Fabbri, A. Crime, M. Davezza, C. Medana, C. Baiocchi, A.B. Prevot, E.Pramauro, Surfactant-assisted removal of swep residues from soil and pho-tocatalytic treatment of the washing wastes, Appl. Catal. B: Environ. 92 (2009)318325.[18] J. Gomez, M.T. Alcantara, M. Pazos, M.A. Sanroman, Remediation of pollutedsoil by a two-stage treatment system: desorption of phenanthrene in soil andelectrochemical treatment to recover the extraction agent, J. Hazard. Mater.173 (2010) 794798.[19] C.K. Ahn, Y.M. Kim, S.H. Woo, J.M. Park, Selective adsorption of phenanthrenedissolved in surfactant solutionusingactivatedcarbon, Chemosphere69 (2007)16811688.[20] C.K. Ahn, M.W. Lee, D.S. Lee, S.H. Woo, J.M. Park, Mathematical evaluation ofactivated carbon adsorption for surfactant recovery in a soil washing process,J. Hazard. Mater. 160 (2008) 1319.[21] J.Z.Wan, S.H. Yuan, K.T.Mak, J. Chen, T.P. Li, L. Lin, X.H. Lu, Enhancedwashing ofHCB contaminated soils by methyl-beta-cyclodextrin combined with ethanol,Chemosphere 75 (2009) 759764.[22] W. Shen, X.K. Li, S.L. Yang, C.F. Ning, Identication of rhamnolipids produced byPseudomonas sp. BS203 with electrospray ionization-mass spectrometry, Chin.J. Anal. Chem. 34 (2006) 6972.[23] Y.M. Zhang, R.M. Miller, Enhanced octadecane dispersion and biodegradationbyaPseudomonas rhamnolipid surfactant (biosurfactant), Appl. Environ.Micro-biol. 58 (1992) 32763282.[24] F.J. Ochoa-Loza,W.H. Noordman, D.B. Janssen, M.L. Brusseau, R.M.Maier, Effectof clays, metal oxides, and organic matter on rhamnolipid biosurfactant sorp-tion by soil, Chemosphere 66 (2007) 16341642.[25] F Bordas, P. Lafrance, R. Villemur, Conditions for effective removal of pyrenefromanarticially contaminated soil usingPseudomonas aeruginosa57SJ rham-nolipids, Environ. Pollut. 138 (2005) 6976.[26] R.R. Kommalapati, K.T. Valsaraj, W.D. Constant, D. Roy, Aqueous solubilityenhancement and desorption of hexachlorobenzene from soil using a plant-based surfactant, Water Res. 31 (1997) 21612170.[27] D. Roy, R.R. Kommalapati, S.S. Mandava, K.T. Valsaraj, W.D. Constant, Soilwashing potential of a natural surfactant, Environ. Sci. Technol. 31 (1997)670675.[28] Y. Fan, B. Wang, S. Yuan, X. Wu, J. Chen, L. Wang, Adsorptive removal of chlo-ramphenicol fromwastewater by NaOHmodied bamboo charcoal, Bioresour.Technol. 101 (2010) 76617664.[29] C.K. Ahn, S.H. Woo, J.M. Park, Enhanced sorption of phenanthrene on activatedcarbon in surfactant solution, Carbon 46 (2008) 14011410.Remediation of hexachlorobenzene contaminated soils by rhamnolipid enhanced soil washing coupled with activated carbon sel...IntroductionMaterials and methodsChemicals and soilsHCB solubilization and enhanced desorption by rhamnolipidAdsorption of HCB from rhamnolipid solution by ACSoil remediation by soil washing coupled with AC adsorptionChemical analysisResults and discussionCharacterization of rhamnolipidEffect of rhamnolipid on HCB solubilization and enhanced desorptionSelective adsorption of HCB from rhamnolipid solution by ACsEnhanced remediation of HCB-contaminated soils by soil washing coupled with AC adsorptionConclusionsAcknowledgementsReferences

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