Rhamnolipid Foam Enhanced Remediation of Cadmium

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RHAMNOLIPID FOAM ENHANCED REMEDIATION OF CADMIUM AND NICKEL CONTAMINATED SOIL SUILING WANG and CATHERINE N. MULLIGAN∗ Department of Building, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Boulevard W., ER 303, Montreal, Quebec, H3G 1M8, Canada (∗ author for correspondence; e-mail: mulligan@civil.concordia.ca, Tel: +1-514-848-2424, Fax: +1-514-848-2809) (Received 27 October 2003; accepted 24 March 2004) Abstract. Column experiments were conducted to evaluate the
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  RHAMNOLIPID FOAM ENHANCED REMEDIATION OF CADMIUMAND NICKEL CONTAMINATED SOIL SUILING WANG and CATHERINE N. MULLIGAN ∗  Department of Building, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Boulevard W., ER 303, Montreal, Quebec, H3G 1M8, Canada( ∗ author for correspondence; e-mail: mulligan@civil.concordia.ca, Tel: + 1-514-848-2424,Fax: + 1-514-848-2809) (Received 27 October 2003; accepted 24 March 2004) Abstract. Column experiments were conducted to evaluate the feasibility of using a rhamnolipidfoamtoremoveheavymetals(CdandNi)fromasandysoilcontaminatedwithCd(1706ppm)andNi(2010 ppm). Bestresults wereobtained fromthefoamgenerated by a0.5% rhamnolipid solution withan initial pH value of 10.0 after flushing with 20-pore-volume of solution. These conditions removed73.2%oftheCdand68.1%oftheNi.Removalefficienciesbyfoamgeneratedbyachemicalsurfactant,Triton X-100, were investigated as a comparison. It removed 65.5% of the Cd and 57.3% of the Niunderthesameconditions.Aftera20-pore-volumeliquidsolutionflushing,0.5%rhamnolipid(initialpH 10.0) without foam generation removed 61.7% of the Cd and 51.0% of the Ni, whereas 0.5%Triton X-100 (initial pH 10.0) removed 52.8% of the Cd and 45.2% of the Ni. Distilled water withadjustedpHonlywasalsousedtoflushthroughthecontaminatedsoilcolumnasacontrol.Itremoved17.8% of the Cd and 18.7% of the Ni. This study shows that rhamnolipid foam technology can be aneffective means for the remediation of cadmium and nickel contaminated soil. Keywords: biosurfactant, cadmium, foam, nickel, remediation, rhamnolipid, soil, surfactant, TritonX100 1. Introduction Heavy metals pose a persistent problem at many contaminated sites and are beingadded to soil, water, and air in increasing amounts from a variety of sources, in-cluding industrial, agricultural and military activities, and domestic effluents. Asa result, they are now widely dispersed in the environment in a range of differ-ent physicochemical forms (Roundhill, 2001), and are a source of some concernbecause of their potential reactivity, toxicity, and mobility in the soil (Selim andAmacher, 1996). Thus, heavy metals are included on the EPA’s list of prioritypollutants (Mulligan et al ., 2001a).A number of remediation technologies have been developed for heavy metalcontaminated soils such as soil excavation, thermal extraction for volatile metals(e.g. mercury, arsenic and cadmium as well as their compounds can be evapo-rated at 800 ◦ C), electrokinetics, solidification/stabilization, vitrification, chemicaloxidation, soil flushing, and bioremediation (Mulligan et al ., 2001b). The spe-cific technology selected for the treatment of a contaminated site depends onthe speciation of the contaminants and other site-specific characteristics. Another Water, Air, and Soil Pollution 157: 315–330, 2004. C  2004 Kluwer Academic Publishers. Printed in the Netherlands.  316 S . WANG AND C . N . MULLIGAN important consideration is that the chosen method does not leave toxic residues,which must be subsequently removed (Roundhill, 2001). One or more of these ap-proachesareoftencombinedtogetherformoreefficientandcost-effectivetreatment(Evanko and Dzombak, 1997).Bioremediation has potential for the remediation of heavy metal contaminatedsites. It has been demonstrated that biosurfactants generated by bacteria and yeastscould be used potentially for the environmental remediation of heavy metals fromsoilsandsediments(Miller,1995;Torrens etal .,1998;Mulligan etal .,1999,2001a).Biosurfactantscanenhancethemobilityofheavymetalsbyreducingtheinterfacialtension between the metals and soil and by forming micelles. One more attractivecharacteristic is that they are natural products, may be less toxic to biodegradingbacteria and can be degradable themselves. Therefore, they present effective andnontoxic candidates for the remediation of the contaminated sites. However, theuse of biosurfactant solutions has been limited by a number of parameters, suchas channeling effects, aqueous-phase bypassing, and rate limiting mass transfer(Rothmel et al ., 1998). Moreover, it is difficult to control the migration of the fluidscontainingdissolvedcontaminants(VignonandRubin,1989),whichprobablyleadsto the spreading of the contaminated zone.Biosurfactant foam is being developed as a promising substitute. It not onlyinherits all the merits and remedies the deficiencies, but also improves the removalefficiency.Foamsdisplaypropertiesthatarevastlydifferentfromtheliquids,whichconstitute the foam (Chowdiah et al ., 1998). The simultaneous injection of surfac-tant and air will enhance the flooding efficiency of surfactant flushing even in aheterogeneous porous medium, resulting in higher removal efficiency (Jeong et al .,2000). The use of foam can also provide a better control on the volume of flu-ids injected and the ability to contain the migration of contaminant-laden liquids(Chowdiah et al ., 1998). At the same time, it could be more cost effective due tothe low usage of chemicals and surfactants. Surfactant foam technology has beeninvestigated to remove hydrophobic organic compounds, such as polynuclear aro-matichydrocarbons(PAHs),polychlorinatedbiphenyls(PCBs),pentachlorophenol(PCP), and other chlorinated hydrocarbons from contaminated soils (Peters et al .,1994; Kilbane et al ., 1997; Rothmel et al ., 1998; Jeong et al ., 2000; Mulligan andEftekhari, 2003).The biosurfactant that was used in this study, a rhamnolipid, was from theglycolipid group and was produced by Pseudomonas aeruginosa (Tsujii, 1998).Therearefourtypesofrhamnolipids(Tsujii,1998).Type1(R1)isL-rhamnosyl- β -hydroxydecanoyl- β -hydroxydecanoate of molecular mass 504 Da. Type II (R2) isL-rhamnosyl- β -L-rhamnosyl- β -hydroxydecanoyl- β -hydroxydecanoate of molec-ularmass650Da.Theothertwotypesofrhamnolipidscontaineithertworhamnosesattached to β -hydroxydecanoic acid, or one rhamnose connected to the identicalfatty acid. Rhamnolipid type I and type II are suitable for soil washing and heavymetalremoval.WhiletypeIIIisformetalprocessing,leatherprocessing,lubricants,pulp and paper processing, type IV is usually used in textiles, cleaners, foods, inks,  FOAM ENHANCED REMEDIATION OF CONTAMINATED SOIL 317paints, adhesives, personal care products, agricultural adjuvants, and water treat-ment (JENEIL 2001).Inthisstudy,experimentswerefirstdonetotestthefoamabilityandfoamstabil-ityofJBR425(mixedrhamnolipids)solutions.Next,thepressuregradientbuild-upin the soil column during foam passing through the column was investigated. Then,experiments were conducted to evaluate the feasibility of rhamnolipid foam en-hanced remediation of the heavy metal contaminated soil. Comparisons of themetal removal abilities were made between the biosurfactant, JBR425, and thechemical surfactant, Triton X-100. 2. Materials and Methods 2.1. B IOSURFACTANT  /  SURFACTANT The biosurfactant, JBR425 (mixed rhamnolipids), was obtained from JENEILBiosurfactant Co. (USA). Rhamnolipids are more favored because of their lowtoxicity, high biodegradability, and low surface tensions. The rhamnolipids, usedin this study, were biosurfactants from the glycolipid group made by Pseudomonasaeruginosa with the trademark JBR425 from JENEIL Biosurfactant Co. JBR425is an aqueous solution of rhamnolipid at 25% concentration. It is produced froma sterilized and centrifuged fermentation broth. Two major types of rhamnolipids,RLL (R1) and RRLL (R2), are present in the solution. Several tests done by themanufacturer and independent laboratories (OECD 209ASRIT, OECD 301D andOECD 202) show the degree of biodegradability and toxicity of JBR215 meet theEPA requirements (JENEIL, 2001). The synthetic surfactant, Triton X-100, wasobtained from Sigma Chemical Co. (U.S.A.). The Triton X-series of nonionic sur-factants is prepared by the reaction of octylphenol with ethylene oxide. Both of the two surfactants are commercially available and are widely used as householdand industrial detergents and in other applications. They have also been studied inenvironmental applications (Mulligan et al ., 1999, 2001a; Mulligan and Eftekhari,2003). The characteristics of these surfactants obtained from the material safetydata sheet (MSDS) and other literature are described in Table I.2.2. S OIL TREATMENT The soil sample was obtained from a building site in Montreal, Canada. It waswashed with distilled water and then dried in an oven at 105 ◦ C for 48 h. Large par-ticles werecrushedbymortarandpestle,andthenmixedwithfinesilicasandintheratioof1:4.Consequently,sieveanalysesweredonebyusingasetofUSAstandardtestingsieves.TheparticlesthatpassedthroughtheNo.200sievewerediscardedbe-cause they are not applicable for the column tests. Then the soil was contaminatedartificially in the laboratory with metal salts, in the forms of NiCl 2 · 6H 2 O andCd(NO 3 ) 2 · 6H 2 O,whichweredissolvedwithdistilledwater(4000mg/LofCdand  318 S . WANG AND C . N . MULLIGAN TABLE ICharacteristics of surfactants used in the experimentsSurface tensionSurfactant Type Chemical formula M.W. (g) CMC (g/l) (mN/m)JBR 425 Anionic C 26 H 48 O 9 , C 32 H 58 O 13 573 0.03 a 26 a Triton X-100 Nonionic C 8 H 17 C 6 (OC 2 H 4 ) n OH 620 0.4 33( n = 9–10)JENEIL (2001) and Sigma (1993). a Mulligan et al . (2001a).TABLE IICharacteristics of the contaminated soilOrganic matter content ( % ) 1.0%Cation exchange capacity a (cmoles + / kg) 7.9 (pH = 7.0)Hydraulic conductivity (cm/s) 0.02Heavy metal content (mg metal/kg dry soil) Cd, Ni 1706, 2010Sieve analysis results 84.7% sand and 15.3% siltSpecific gravity 2.43 a Gillman and Sumpter (1986). 4000 mg/L of Ni) and were added together into the soil sample (without adjustingthepHvalue)atthesametime.Thesoilwasleftinthesolutionovertwoweeks,andthen the suspension was shaken on a wrist action shaker at 60 oscillations/min for24h.atroomtemperature(25.0 ± 0.2 ◦ C),andsubsequentlycentrifuged.Thesuper-natant was discarded and the contaminated soil was dried at 105 ◦ C. To measurethe metal concentrations, samples were digested with 6 N HCl and then analy-sis was performed using an atomic absorption (AA) spectrophotometer (PERKINELMER, AAnalyst 100) to measure the metal concentrations. The characteristicsofthecontaminatedsoilweremeasuredbytheUSEPAorASTMmethods(APHA,AWWA, and WPCF, 1995). They are listed in Table II.2.3. E XPERIMENTAL SET - UP AND PROCEDURES A series of experiments was conducted to investigate different parameters involvedin the biosurfactant foam technology in soil remediation. The experimental set-upisshownschematicallyinFigure1.Aplasticcolumn(L = 25cm,D = 2.5cm)withmetalendswasequippedwithcircularporousstoneplates,whichenabledthefoamgeneration in the presence of surfactant solution and air. A pump was used to feedthe surfactant solution. Two flow meters (I and II) were used to control the flow of the solution and the air before entering the foam generation column. The flow ratesof the surfactant solution and air could be varied independently in order to control
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