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) 458464
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Journal of Hazardous Materials
journa l homepage: www.e lsev ier .com
Remed tesoil wa lec
Jinzhong gtia Environmenta 43007b Nanjing Instit 21004
a r t i c l
Article history:Received 16 DReceived in reAccepted 17 FAvailable onlin
Keywords:Activated carbBiosurfactantHOCsSoil remediatiSoil washing
lectivbon (CB froHCBespecdsorpand aom so% anproceth bio
to remove hydrophobic organic compounds from soils. 2011 Elsevier B.V. All rights reserved.
Remediacompoundsmental sciewashing iscially for Hmostly ania variety o(PAHs), polRecently, ition of biosenvironmentants enhancing[8,10,11].
Rhamnowhich arehydrophilicacids (C8Crevealed thPAHs, oil, a
tion 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 . Chemical surfactants,onic and nonionic, are proved capable of removingf HOCs, such as polycyclic aromatic hydrocarbonsychlorinated biphenyl and pesticides from soils .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 metals
lipids 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: firstname.lastname@example.org (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 ,photocatalytic [16,17] and electrochemical treatment  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.  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 .
see front matter 2011 Elsevier B.V. All rights reserved.jhazmat.2011.02.055iation of hexachlorobenzene contaminashing coupled with activated carbon se
Wana, 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 o
ecember 2010vised form 16 February 2011ebruary 2011e 23 February 2011
a b s t r a c t
The 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 / jhazmat
d soils by rhamnolipid enhancedtive adsorption
4, PR China2, PR China
e 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 alternative
J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464 459
Table 1Selected physicalchemical properties associated with soils.
Property Kaolin Real soil
Particle size a
460 J. Wan et al. / Journal of Hazardous Materials 189 (2011) 458464
Table 2Composition of present rhamnolipid mix identied by HPLCESIMS.
No. Composites Pseudomolecularion, m/z
trifuged at 4decanted antionwas suAC1). Then5to the tubethe secondtions wereexperiment
HCB in tGC equippecolumn (Phdurewas inconcentratisionmat emdiluted appwas below Crhamnolipi
The comlisted in Tabof monorhaRhC10C10 aRh2C10C10 owere also cthemixwasmation in Tmix wouldthe result mrhamnolipiover, the C63.1mgL1
3.2. Effect odesorption
Fig. 1athe increasetent with pobserved btions above(MSR) is ge
ffect of rhamnolipid concentration on (a) HCB solubilization and (b) HCBon from kaolin.
s which is dened as 
CHOC, mic CHOC,cmcCsurf CMC
in 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. . 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 6.3
000 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 solutionwasadded
s 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.
he 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 . Aqueous rhamnolipidonwasestimatedby surface tensionusing a surface ten-ploying the Du Nouy ringmethod . The samplewasropriately to ensure that the rhamnolipid concentrationMC. A calibration curvewas constructedwhich related
d concentration (mgL1) to surface tension (dyn cm1).
terization of rhamnolipid
position 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 the
Fig. 1. Edesorpti
whereCHOC,mfactantformedtion, t5.41surfactthan thaccord 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 enhanced
indicates 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