Surfactant solubilization of polycyclic aromatic hydrocarbons fiom nonaqueous phase liquids

Alex S. Hill Department of Civil Engineering and Applied Mechanics McGiII University, Montreal Octo ber, 1999

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements of the degree of Masterç of Engineering National übw Bibliothèque nationale du Canada Acquisitio~and Aquisitions et Bibliagraphit Services services bibliiraphiques

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Solubilization of naphthalene and phenanthme hma synthesized rnuiti-cornponent non-aqueous phase liquids (NAPL) bj aqueous in polyethoxylated surfactant solutions at supra-CMC dosages was evaiuated in this study. PAHs are abundant at sites contaminated with many chemicdly cornplex NAPLs. such as cod tas. creosotes. and petroleum distillates. Surfactant flushing has been proposed to speed remediation at many contaminated sites. due to surfactant's ability to solubilize these hydrophobie cornpounds. While it is well known that surfactant micei!es cm solubilize significmt amounts of PAHs. this research demonstrates Cor the first time the relationship between NAPL P,U mole hction and the solubiiization capacity of surfactant solutions. Henry's law satisîàctorily described the partitioning of PAHs fiom he'tadecane into water md into surfactant solutions. Selective solubilization of naphthalene over phenanthrene was obsewed. which is believed to be the result of competition for space in the micelle's outer layers. From these results a predictive relationship between NAPL PAH mole fractions and micellar solubilization is presented, La solubilisation de naphtaiène et de phénanthrène provenant d'un liquide à phase non- aqueuse (composés multipIes/synthétisé) a été évalué en utilisant une solution de surfàctants polyethoxyfated à des dosages supra-CMC. Les HAP sont très présents dans les sites contaminés par divers liquides a phase non-aqueuse complexes chimiquement tels que le goudron de houille. les créosotes et les distillats de pétrole. Le passage d'un solution de surfactants au travers du site contaminé a été proposé afin d'accélérer le processus de restauration puisque les surfactants ont la capacité de solubiliser les composés hydrophobe II a été démontré aupanvant que les micelles des surtactants peuvent solubiliser des quantités sigrifkatives de HAP. par contre, ces recherches démontrent pour la première fois le lien entre la fiaction de HAP dans le liquide a phase non-aqueuse et la capacité de solubilisation de [a solution de surîictants. La loi de Henri décrit de façon satisfaisante la répartition des HAP entre une solution d'hexadecane et l'eau ou une solution de surfactants. Une solubitisation sélective favorisant le naphtdine au dépend du phénanthrène fut observée. ceci pouvant ètre le résultat de compétition pour les espaces des couches extérieures des miceiles. De ces résultats on a pu découlé une relation entre la fiaction molaire des HAP dans le liquide à phase non-aqueuse et la solubilisation par les micelles. Acknowiedgments

I would like to express my gratitude to the peopie who have helped to make the completion of this work a rewarding and pleasurable experience. Most Unportant of these is Dr. Subhasis Ghoshal. fiom whom 1 have received superïor guidance and support as my supervisor. which bas made this experience enjoyable and enthralhg. 1 have also benetited îiom the support and encouragement 1 received fiom Dr. I. Nicelt and Dr. R. Gehr. f would dso like to express my gratitude to Daim Brumelis for her technicd expertise and for dways keeping satèty as the hifiest priority. I tvould also like ro rxtend thanks to Sandy Shewchuk-Boyd. Anne-Marie Boyd and Anna Dinolfo for their hetp in deding with the administrative hurdles involved with this work. t tvould iike to thank Tammy Silverstone for her aid in the [ab. most notably for conducting the time-to-equilibrim experiments in the litde vials. 1 have also apprecitited the help and Company of my feliow students: Cathy Pasion. Denise Pinto. Salem Buhari. Moharned Shdie. Mohamed ShariE Man McKernan. Maria Santa Maria Monika Wagner and Angela Keane (mestisted in no particular order). "Thank you3 go out to George. Anne-Marie and Jan Kubanek for Iending me heir cottage while t tvrote this document. and to Paui Chang and Krisia Keiswetter for Ietting me use their car and apartmeat. 1 would also like to thank Troy McGarrigIe and Vera Fnjzynger for being such exceHent proof readers. without whom 1 wouId never have Iearned. how to use the simple comma And frnalIy. pmps to AIex Roy for rranslating my absact and for king there throughout, peace. Table of Contents

Résumé iii

Table of Contenis v

Lirt of Tables viii

Likt of Figures x

List of SymbaLF xiii

1.1, PAH Contamination in the Subsadace I

1.1. I. Subsurface Contamination by Cbrmicaliy Complex NAPLs -i

1.1.2. Remediation of Sites Conraminated with NAPLs Containhg PAHs J

1.1. Objectives 7 1.2.1. Specific Objectives 7 i 2.2. Rrsearch Appmach 8 1.2.3. Organintion of Thesis 9

1.3. Surfactant Solutions 1O 1.3. i. Characterintion of Surfactants IO 1-32. Suri'amt Micelles 11 1.3.3- Nonionic Surfactants 17

1.1, PAH Solubiüty in Aqueous Surfactant Solutions Contacted witb NAPLs 20

I .f.1. NAPL-Water PAH Partitionhg 70 1 A.2. PAH Pmitioninp in Aqueous Surfactant Solutions 25 1-43. ModeIing PAH Partitionhg m Surfactanr Soiutions 28 I=ld. SurFactant Solubilization of PAHs 3 1

2. Equilibriurn Purti~ioningof PAHs Between lVAPLs and Wafer 35

2.1. introduction 35 2.1. t .Theoreticai Fmework 36 2.I.2. Objectives 37

2.2. Materiab and Methods 39 1.1.1. Chernicals 3 9 7.22. NAPL Synthesis and Determination of Maximum NAPL PAH Mole Fmctions 3 9 22.3. Glassware Preparation 4 1 2.2.4. PAH Ultnviolet Spectrophotometry 4 1 2.5. Fluorescence Measurements 49 12.6. Equilibrium Partitioning Experimenrs 5 1

23. Resulh and Discussion 55 2.3.1. Mmimurn NAPL PAH Mole Fractions and Aqueous Solubilities 55 2.32. Equilibrium Partitioning of PAHs Between NAPLs and Water 6 1

2.4. Conclusions 67

3, Effect of NML PAH Mole Fraction on the Solubilizaîion Capacity of Surfactant

3.1. Introduction 68 3.1.1. Theoreticid Framework 68 3.1.7 Approach 73 5. i 2.Objectives 73

31. mate rials and Methods 76 3.2 I . Chemicals 76 3.2.2. Preparation of NAPL-Aqueous Surfactant Solution System 76 32.3. MSR and CMC Determination Expenments 78 3.2.4. Anaiysis of PAHs Concentrations ln Surfactant Solutions 79

3.3. Results and Discussion 83 3.3.1. Effect of Methanol Dilution of the CMC 83 3.32. Determination of the CMC in Aqueous Surfactant Solutions Contacted with Mode1 NAPts - 56 3.3.;. Effect of NAPL PAH Mole Fraction on the MSR 89

4. Partitiorring of PAdls Beîween Three-Component NAPL and Surfactant SoiutwnslOQ

4.1. Introduction IO4 4.1.1. Theoretical Framework IO6 4.12. Objectives IO8

4.2. Materiah and Methods 109 4.2. I .Spihesis of Three-component NAPLç 109 4-27. E~perimenfalSet-Up and Analylical Merbods 109

43. Resulrs an Discussion 111 4.3.1. hqueous Soiubilities of Three-component NAPL Components 111 4.32. Micellar Solubilintion of PAHs Fmm Three-component NAPLs 116

4.4. Conclusions 127

5.1. Future Research 132

vii Table 2.1: NAPL Componenr Physical Data 38 Table 7.7: Comparison of Naphthalene Exrincrion Coeflcients in :Llerhanol und Warer fi = 220 nm) 46 Table 2.3: Comparison of Phenanthrene Exiincrion Coeficients in

Methanof und Varer (3. = 251 nmj 46 Tuhle 7-4: Cornpurison of Phenanthrene Fluorescence Calibrutions in Merhanof und Parer, for Emissions Readings ar 365 nm 50 Tuhle 23: C'isual Observations of PM-Hexadecane iMi~tures.{fier COoling ro 25 "c' 56 Tuhle 2.6: .VAPL Component Properfiesfiorn Experimenrs und Lirerature 58 Tuble 2-1Equilibrium Aqueous Phase PAH Concentrations For PAH Suturated :VAPLs and C~sfals 60 Table 7.8: .Vaphthalene NAPL- Wurer Partirioning Daru wirh Statisrical Purante fers 63 Tuhle 2.9: Phcnanthrene MAPL- Warer Parritioning Data wirh Sratistical Purumeters 63 Table 3.1: Surfactant Characrerhtics and Rqueous Solutions -6 Tuble 3.2: Surfacranr Exrincrion Coeficienrs in Merhanof-Warer Solutions 82 Table 3.3; .Vaphrhulene Concemation in 73% Methanof -3%Water Solurions containing Surfuctanrs XS Tuhle 3.4: CMC Vulues in Aqueous Swfactant Sysrems Y Y Tuble 3.5: Comparison .Y4PLStit$acfant Solution Parritioning Constant Fulttes 98

Tuble 4.1: Cornparison of l/K'y und y' Wuesfor Two-Componenr and

Three-Component :LLAPLs, wiih r-Test Rrsults (u = 0.05) on the Diference of the Mean Values in the Two and Three Component Table X 2: Cornparison of p.cm Values Between Ternary and Binas, iVAPLs 117 Table Al: PAH Lossesjwm the IVAPL in a LV'PL-WaterSystem 144 Table -43: liirlPL PAH Losses in Surfacrmi Sysrems 145 Tuble -43: QSAR estimation of 'Hexadecanefiom Jafierr et al. 1995 146 Table Ad: .Vaphthalene .LISR Daia for Two-Component NAPLs und Cytals I4' Tuble A5: Phenunthrem MSR Data for Two-Component N.4PLs and C'ty~tals 14- Tuble d6: c',~ vr, Y,ond cYIpfor Su~acrantSolutionr Contac~edwith List of Figures

Figure 1.1: Schematic of XAPL Spills 3 Figure 7.1.- .Vaphthaiene in Merhano1 Calibrarion Cune fi = 230 nm) j.5 Fiigure 2.2: Phrnanrhrenr in !Methano1 Calibrarian C7urve

(î- = 3 2 nm) 3j Figure 2.3: .Vaphthaiene in WaferCalibrariun Cime fi = 720 nm) 3.5 Figure 2.4: Phenanthrene in WaferCalibrarion Curve fi = ,'SI nm) 35 Figure 2.3: .Vaphthalene Absurbance in the Presence of fieradecane

IL = 220 nm) 48 Figure 1.6; ..Lbsorbance vs. Hexadecane Concentration [Currrcred ru C?,reoH = I mgiL] rh = 220 nm) 48 Figure 2.-: Fluorescence Emission ar 364 nm vs. Pherimthrene Conce ntrurion 311 Fiivre 2.8: Time to Equilibrium Esperirnental Restclts for a .KiPL- Wafer *rem .tgituteJ ut I 3 rpm (,ph,= O. 17 54 FiLgure 2. Y: -4qurous Phase Equilibrium .Vaphthalene Concrnrrafionvs. .Vuphrhulenr .Wule Fraction in Hrxadecane/iVaphthulene Mirrures j- Figure 2. IO: .4qtieo~~Phase Equilibrim Phenanrhrene Cuncrnrrurion vs. Phrnunthrene .bMe Frucrion in He;radecane/Phenanrhrene .Mixrures 38 Figure 1. II: Equilibrium Rqueous Phase :Vaphhalene Concentration vs. .VA PL .Vuphthalene Mole Fraction 64

Figure 1.12: Equilibrium Aqueous Phuse Phenunthrene Concentrarion tos. .VAPL Phenunthrene ,Mole Fraction 64 Figure 3.1: cnqhTmvs. cd',, in Brq 3jSuluiions Conracted with A

Trou-Componenr LWPL(XIN = 0.01) 79

Figure 3.2 :C"Ph lieoH vs- FJp (Triton,Y-1 O0 in 50% Methmoi Solutio@ 85

Figure 3.3 : lieonW. FAQ (TritonX-1 O0 in 75% Merhami Solutions) 85 Figure 3.4: lMSR vs. X"Ph in Brij 30 So lutions 98

Figure 3.5. ph,, and yMph vs. ,Tph3[in Brij 30 Solutions Y8 Figure 3.6: MSR vs. yph,in Brij 35 Solutions 99

Figure 3.7: .Yphy and y"ph.Vvs. -PPh.yin Brtj 35 Solutions 99 Figiire 3.8: ,MSR vs. ,phvin Tergïtol NP10 Solutions 99

Figure 3. Y: .Yph,und-,""Ph ,/ VS. dr"Ph,,in Tergitol NP1 O Solutions 99 Figure 3.1 O: .LISR vs. ,lmph,rin Triton Xi00 Solufions if10

Figure 3.1 1. .lnUph,und yphLI W. ,Yphin Triton ,Y-1 00 Solutions 1 OU t-Ïmre 3.17: JISR KY. .rp",in Tween 80 Solutions 1O0

Figure 3.13: .yph,und ymph \( VS. .YphC[ in Tweçn 80 Solutions 100

Figure 3.14: .CISR vs. .Vkny in Brij 35 Solutions 101 Fi,qire 3. i j. -vhen,und f "",vs. in Brij 35 Solutions IO1 Figure 3.16: .CISR vs. .phen,in Tween Y0 Solutions IO1

Figure 3.1 7. .Fhe",und f "" ,/ VS. ,vhn in Tween 80 Solutions 101

Figure Il: cNph ,g und phenIQ vs. ,ph", in iV.4 PL- Vuter Systems r.yPkn , = 0.03) und Pph in Wuter Contucted with ,Vaphthalene und Phenanthrene Crystais 1 14

Fieuiue 4.2: cnUphly und cqhen V.Y. lWhin !VA PL- WawSystems

(.rDIPh\ = O. 09) und c~~ ,Q in Wmer Contacted with ?kphthalr!re und Phenunrhrene Crystals 1 14

Fipire 4.3: f' "", und yMphv vs- Total MPL PA H Mole Fruçtion (.ffHJ 11j Figwe 4.4: Estirnured Total YIH,Y vs, Exprrimrnrul Tora1 fAH Fignre 4.5: lMSR vs. -ph,for Brïj rljSolutions Conmcted with ~Mtdti- Componenr 1VAPLs and Naphthalene MSR in Brij 35 Solutions Contacted With Naphrhalene and Phenanthrene Cltals il7 Figure -1.6: .bfSR vs. X'"", for Brij 35 Soliirions Conracted wirh ~blulti- Cornpunent .UPLs and Naphthalene MSR in Brij 35 Solutions Cimtwted CVith :Vuphthalene and Phenanrhrene Crysrals 117 Figzrrr 4. -: .( ,, vs. .ph,in systems where ,ph,iS Vmying und = o. 03 II9 Figure 4.8: y' ,, vs. .rphgn ,in S'stems where .phen,is varying and ,rph, = 0.09 170 Figure 4.9: .Vaphthalene Selecrivis, In Suflactunt Solutions Contact with Terna? .VA PLs und PA H Cysrals 1-13 List of Symbols

HLB - Surfactant hydrophile-Iipophile balance CMC - Critical Micelle Concentration MSR - Molar Solubilization Ratio X - absorbance D - simple dilution ratio EC - EV li&t extinction coefficient k - Boltzmann constant SihT - Signal to Noise ratio f - fbgaciq of species i in a mixture

PI - partial pressure above a mixture. attributable to species i S' - mole fraction of species i n ' - number of moks of species i v - volume of a phase K' - partitionhg constant of species i a' - activity of species i

1 'I - activity coeficienr of species i cl - concentration of species i K'~R - constant used to predict MSR data hm.rv m' - extinction coefficient for multiple PAH systems superscript - species (includes: naph- naphthdene. hex - hexadecane. phen - phenanthrene. surf - surfactant) su bscript - phase (includes: ow - octanol water. AQ - aqueous pseudo-phase. N - NAPL. TOT - aqueous buik phase. AQ - aqueous pseudo- phase. M - miceIIar pseudo-phase. MeOH - in methano1

solutions. O - standard state) 1. Introduction

1.1. PAH CONTAMINATIONIN THE SUBSURFACE

The contamination of soils and gmundwater by polycycIic aromatic hydrocarbon (PAH) compounds has occurred at many locations, including manufactured gas plant sites. wood-treatment facilities. coai coking sites and petroleum facilities (Laue and Loe hr. 1993: Lee et ai.. I992a). PMcontamination at these sites is often the resdt of uncontroIled discharges. spills and leaks of nonaqueous phase liquids (NAPLs) hm storage facilities (Mercer and Cohen, et ai. 1990). PAHs comprise a significant fraction of many chemicaIly complex NAPLs. such as coal car. creosote, diesel hel and petroleurn disti1Iates (Lee er al.. 199%). Widely disnibuted in the environment, PAHs have the potentid to impact human health and the ecology at contaminated sites (Lane and Loehr. 1992). These compounds are considered potential carcinogens linked to lung, stornach and skin cancer in humans. As a result of their hydrophobie ctiaracter they rapidIy bioaccumulate. making hem acutely toxic ro aquatic organisms at low aqueous concentrations (LaGrega et al.. t 994). Due to their Iow aqueous solubitity. PAi-is are slowly but systematicail released hmspiled NAPLs iato the groundwater. For this reason. NAPLs containing significant PAH fractions represent a long term source of contamination that can cause continued deterioncion of the environment (Lane and Loehr. 1992). Often the source of the PAH contamination in the subsurface is immobile. as is the case with NAPLs entrapped within the sail rnatrix (Mercer and Cohen. 1990). Cn these situations, engineered treatment systems chat remove the aqueous phase PMcontamination may be used to e3ect remediation (Edwards et al.. 1991). It has ken demonstrated that adactants incfea~ethe solubility of PAHs in aqueous soIutions, and in this way surfactant aided pump-and-treat technologies may speed the remediation process at sites contaminateci with immobile &-phase NAPLs. 1.1A. Suburface Contamination by Chemically Compfex NAPLs

Many of the NMLs that have caused environmentd contamination have either been us4 in industriai activities or are by-products of industn*al processes. Common NAPLs that have been identified as posing an environmental hazard include. mformer oih contciining PCBs, degreasing solvents such as TCE, coal tar from manufacnired gas plant sites. creosoce at wood treatment sites. steel indwtry coking byproducts and petroleum products such as diesel (Mercer and Cohen 1990). There are many documented NAf L contaminared sites: it is estimaed that there are between 1000-2000 mmufactured gas plant sites (Luthy et al.. 1994) and over 400 wood matment sites using creosote (Muetler et al.. 1989) in the US, It is comrnon to find significant amounts of NAPL conmination at both of these types of sites. Due to the large number of NAPL contaminated sites. a significant amount of attention has ben focuscd on the effects and movement of NAPLs in the subsurtàce (LaGrega et al.. 1994; Mercer and Cohen. 1990: Villaurne, 1985: West and HmeI1. 1992). Figure 1.1 shows a sirnplified picture OCNAPLmigration and dissolutian in the subsurface. Menspilled in sufficient quantities. NAPLs migrate downward due to gmvitational forces. and latedly due to capillq forces. When a Iighter than water XAPL (LNAPL) reaches the +gound water table it will float on top and spread 1ateraiIy through the subsutface matris. On the other hand. a denser that water NAPL (DNAPL). upon reaching the pund water table will continue to traveI downwd untii it reaches an impermeable layer ( LriGrega et al.. t 994). NAPLs can be present in the subsurface eithcr as pools of mobile Free liquid or as gauglia. immobiIized within the soi1 pores. In the rvater-sanrrated subsurface. components of the NAPL wili dissolve into the pundwater resulting in the NAPL king a long term source of ground water contamination (LaGrega et al.. 1994: West and Harweli. 1992). Lighter Than Water Denser Than Water NAPL Spi11 I NAPL Spül

Figure 1.1: Schematic of NAPL Spills f .1.2. Remediation of Sites Contaminated with NAPLs Containing PAHs

PAHs make up a significant fraction of many NMLs found ac conwinated sites (Luthy et al.. 1994: Mercer and Cohen. 1990). Most nocabLe of these are manufactured gas plant coai m. which may contain up to 98 wt% PAHs (Lee et al.. 1992b; Nelson et al.. 1996:

Peters and Luthy. 1993 ): coai tar creosote, containing up to 85 wt% P AHs (Mercer and Cohen. 199(1: Mueller et al.. t 989): and diesel fuel. containing up to 20 wt% aromatic compounds ( Lee et ai.. 1992a). Naphthalene. phenanthrene and pyrene typically make up the largest portion of tfie Pusround in rd-wodd NAPLs (Lee et al.. 1992b: Lane and Loehr. 1992: Peters and Luthy. 1993). although rnany tens and hundreds of individual PAH compounds may be aIso found at fow concentrations in the NAPLs. There have been signiftcant efforts made to clean up NAPL contaminated sites. This is usually iichieved by removing the NAPL hmthe ground or by reducing the residuai concentration of target bazardous compounds wiîhh the NAPL. PAHs have low aqueous solubilities. and often a slow rate of dissolution hmthe NAPL. For this mon aquitèr flushing or other water based remediation technoIogies have proven unsuccessfid or irnpracticable at many sites contaminated with NAPLs comprised largely of PAHs. In recent years several innovative and advanced technologies have been proposed to overcome these difficulties. Surfactant aided soiI-flushhg is one method that has shown promise in speeding the rernoval oEPAHs at NAPL-contamînated sites (West and Hanvell. 1992). When NAPLs are present near the surface, it is possible to directly remove the residuai NAPL by excavation of the contaminated soit. Where pooled NAPL lies derp below the surface. signiticant qumtities of the free NAPL may be removed by extraction through wells. However. at sites where the fiee phase NAPL has been pumped out of the subsurtàce, Iarge amounts of NAPL remain entrapped within the porous rnatrix as residual saturation. Direct extraction and excavation techniques are not feasible at sites where residud NAPL is dispersed throughout the satumted zone. trapped in the soil matrix as gangiia or buried very deep below the surface (LaGrega et al., 1994: Mercer md Cohen. 1990: West and HaniveIl. 1993). In these cases the tnpped NAP t cm bc rernoved by mobilization or by the solubilization of its components into the groundwater. Once NAPL contaminants are solubilized or entrained in the aqueous bulk-phase. enginered removal systems (Le. pump-and-mat or in situ biodegradation) may be used to effect remediation (Edwards et al.. 1991). Conventionai pump-and-treat schemes may require over a hundred years to richieve their target PMconcentrations (Mercer and Cohen. 1990). making them impracticable at many NAPL contaminated sites. Surfactant enhanced aquifer remediation (SEAR) has been proposed as a rnechod to reduce the tirne needed to cIean up NAPL contarninated sites. Sirrfactant Bushing of the subdace can reduce clean up times at NAPL contaminated sites either by mobiIizing the trapped NAPL or increasing the solubility of the NML components (LaGrega et al., 1994; West and Hanvell. 1992). West and HmveIl(t992) state that srrrfâctant aided sotubilization is easier to apply than is surïactant aided NAPL mobiIization, because mobilization of trapped NAPL droplets may lead to dispersion of the conmmhmts. Surfactant enhanced soIubiIization is promising in that it may enhance the rate of PAH dissolution by increasing the driving force for mass trader of PAHs into water. A number of studies have shown that the rate of dissolution of pooled NAPLs is significantly increased in the presence of surfactants in soil column experiments (Mason and Kueper. 1996; Pennel et al., 1993: Abriola et al., 1993). Kanga et al. (1997) found that the solubility and rate of dissolution of methyl-substituted naphthalenes from crude oil containing a variety of PAHs was significantly increased. relative to the values in pure water. in aqueous sotutions containing a biosurfactant (produced by micro organisms) or the industrial surfactant Tween 80. While these laboratory studies have shown that surfactants can _matly enhance the removal rate of many model and real NAPLs. applications in the field have not yielded the same enhancement (West and Harwell. 1992). The process is still not hlly understood and efforts are being taken to develop a rreater understanding oithe factors important to surfactant flushing in the subsurface. b Several field studies have provided evidence that surfactant flushing may be effective under certain circumstances. Fountain et d. (1995). found that at two NAPL contaminated sites surfactant flushing was successfUl. provided that free phase NAPL is present and the hydraulic conductivity is moderate to high. Bourbanaise et ai. (1995) tested the feasibility of using surfactant flushing at a site contaminated with diesel fuel and motor oil. They predicted that surtactant flushing could remove up to 99% of the three to six ring PAHs in the NAPLs. due to increased solubilization and mobilization in the presence of surfactants. They also identified some drawbacks to surfactant flushing. including mobilization of soil fines, increased microbiai degradation in the subsurface which may potentially lead to anaerobic conditions. difficulty in removing sorbed surt'actant from the soil and potential dificdty in treating the recovered leachate. One potential limitation to SEAR is that significant amounts of the srrrfactant may sorb to the soil. resulting in possible negative impacts on hydrophobic organic compound (HOC) contaminant partitioning in the subsurface. KOet al. (1998) studied the effects of surfactant sorption on naphthalene and phenanthrene partitioning in surfactant-kaolinite- water systems. They found that both PAHs partitioned significantly into the surfactant layers adsorbed on clay particles, thereby increasing the PAH transport retardation factor. While increased retardation is desirabLe in comaminant immobilization schemes, it is undesirable wherr one is attempting to remove contaminants from the subsurface. Their results show that the increase in the retardation factor was significantly greater for SDS. an ionic surfactant, than for the nonionic surfactant Tween 80. In a companion paper. Ko and Schlautman (1998) used the results hmthe partitioning studies to develop a mode1 to simulate the performance of SEAR applications at naphthalene, phenanthrene and pyrene contaminated sites. The mode1 resuits suggest that in sandy soils with low organic carbon fractions (43surfactant flushhg would hinder the removal of naphthalene and phenanthrene. but wodd aid in the removal of more hydrophobic PAHs such as pyrene. They also found that Uicreasing the fa, of the soi1 irnproved the ctTectiveness of surfactant flushing Their resuitç suggest that SEAR may be a promising remediation technology for relatively hydrophobic compounds such as pyrene. However. PAH dissolution From NAPLs is often a mass msfer Iimited process (Grimberg et al.. 1994) and their equilibrium partitioning mode1 does not account for the mmuansfer rate of PAHs from their source. As it has been observeci that surfactant micelles can signiticantly increase the rate of PAH and HOC dissolution into aqueous solutions (Grimberg et ai.. 1994: Pnmauro and PeliPeni, 1996). it is probable that surfàctant tlushing rnay be effective at NAPL contaminated sites. Overail. sites conhnated with NAPLs that contain a significant hction of

PAHs rire difficult to rernediate. Positive evidence does exist suggesting that surfactant tlushing rnay be effective in speeding the clem up of such sites. However. as it is a new technology. it is still poorly understood. Therefore. more research must be done to determine its potential at NAPL conmnimted sites where PAHs are present in signiiicant quantities. The overall objective of this research was tu evaIuate the ability of aonionic surtàctmt solutions to solubilize naphthalene and phenanbene fiom multi-component NAPLs. In addition to this. a theoretical basis for predicting the relative MSR of PAHs dissoived hmcomplex NAPLs is provided. It is not possible to predict the solubilization capacity of nonionic surtàctant solutions for PAHs dissolved fiom chernically complex NAPLs based on the Somation provided by prior audies. Furthemore, the relationship between NAPL mole hction and molar solubilization ratio (MSR)in systems containing an ided NAPL has not been contïrmed. LUSO. the interactions between PAHs in micellar solutions that affect the solubilization capacity (SC) of surfactant solutions for PAHs have not been assessed or adequately described. This research has anempted to cnhance the undemanding of the partitioning of PAHs between chemicaily complex NAPLs and nonionic surtictant soIutions.

1.2.1. Specific Objectives

The specific objectives of this research were:

1. TO test the hypothesis that naphthdene and phenanthene partitioning beween hexridecane and water follows Henry's Iaw. and thrit as a consequence these NAPLs provide an appropriate surrogate for ml-world chemicaily complex NAPLs.

2. To deveIop a mathematicd mode[ to predict PAH partitioning berneen complex 'IAPLs and surfactant solutions based on Henry's law for Liquid-liquid equitibrium partitioning.

3. To evaluate the ability of the Henry's Iaw partitioning model to predict the sotubi1ization of naphthdene and phenanthme hmsynthesized twocomponent NAPLs in nonionic strrfactant soIutions. 1. To evaiuate the partitioning behavior of naphthaiene and phenanthrene between three- component NAPLs and &actant solutions.

5. To develop a theoretical framework to explain the cornpetitive interactions between P,4Hs solubilized in micellar solutions.

1.2.2. Research Approach

In this study naphthalene and phenanthrene were chosen as the target PAH compounds because they are usually abundant in coal tar. creosotes and diesel. Moreover. they are considered to be hazardous contaminants, especially when bey are present in groundwater which may be used as drinking water. Two and three-cornponent NAPLs were synthesized by dissolving known quantities of naphthalene andfor phenanthrene in hexadecane. Experiments were performed using these NAPLs to assess the naphthaiene and phenanthrene equilibrium aqueous concenvations in systems containing these NAPLs. Hexadecane was chosen as the bulk NAPL component because it is very similar in charmer to many petroleum products. It is aiso e.utremely water insoIuble and is not sxpected to partition into surfactant micelles to an appreciable extent. Thus. the use of hexadecane ailows for the isolation of PAH partitioning phenornena in NAPL systerns. Aqueous surfactant solutions were created for Brij 30. Brij 35. Tergitoi NPIO. Triton X-100 and Tween 80. These nonionic surfactants were chosen as they have been identitïed in the literature as being appropriate for applications to subsurt'ace remediation due to their low toxicity and physical properties. The surtàctants chosen represent three major structurai classes of nonionic surfactants and cover a wide range of HLBs. Therefore. results of experiments with these five surfactants are considered to be representative of the rnajority of ethoxylated nonionic sirrfactants. The equilibriurn solubility of naphthaiene and phenanthrene was assessed in systems contacting PAH crystals with each of the five noniouic surfactant soIutions. Experiments tvere perfomed to evaluate the equilibrium PAH concentrations in surfactant solutions contacted with various two and three-component NAPLs. The eEerts of NAPL mole hction and aqueous surfactant concentration on the aqueous PAH concentration were assessed in order to determine the relationship beniveen NAPL PAH mole fmction and the MSR. The results obtained from the model systems were used to assess the ability of the Henry's law partitioning mode1 to predict the solubility of PAHs in nonionic surfactant soiutions. The MSRs in multiple PAH systems were evaluated and compared to single PAH systems in order to develop a qualitative theoreticai description of the intenaions of PAHs within micelles.

1.2.3. Organization of Thesis

The research and analysis of results is presented in the next three chapters. Each chapter describes one complete set of experiments. In Chapter 2 the partitioning of naphthalene and phenanthrene between hexadecane and water is modeled based on Henry's law. This provides the rationale and justification for using the synthesized NAPLs as surrogates for rd-world chemically complex NAPLs. In Chaptrr 3. a description of the equilibrium partitioning of naphthalene and phenanthrene benveen hexadecane and surfactant solutions is given. A model based on Henry's law is presented in order to predict the solubilization capacity of surfactant solutions for naphthaiene and phenanthrene in two-component NAPL systerns. Chapter 4 describes the partitioning of naphthalene and phenanthrene benveen three-component NAPLs and surfactant solutions. The results of the partitioning experiments with two and three-component NAPLs are compared. A theory of multipie PAH partitioning in rnicellar systems contacted with complrx NAPLs is presented. based on the two-state model developed by Muke jee

( 1979). The important conclusions and contributions of this research. dong with directions for future research. are discussed in Chapter 5. 1.3.1. Characterization of Surfactants

Surtàctants are amphiphilic molecules with both a hydrophobic moiety and a hydrophilic moiety. Their dual nature causes them to exhibit a number of interesting phenornena Given that the polar group tvill tend to stay very hydrated while non-polar group will tend to avoid contact with water. sirrfactants wiIl collect at interfaces and form colloidai aggregates. called micelles. suspended throughout the solution. Surfactants can be combinations of a wide variety of sub-molecular groups. Properties of a given surtactant in an aqueous solution are detemiinad by the relative charncters of the hydrophobic and hydrophilic groups within the surfactant molecule. Due to their hydrophilic and hydrophobic moieties. surfactants can be dissdved in either polar or non-polar solvents. As SEAR applications involve the use of aqueous swfactaut solutions. this &scussion will be limited to symems in which aqueous solutions of micelle forming surtactants are in contact tvith hydrophobic liquids and sotid surfaces. In aqueous solutions a surfactant's hydrophobic &mupdistorts the water structure around it, which in turn increases in the tÏee energy of the solution (Lindman and Wemerstrom. 1980: Peters et ai.. 1997). Rosen (1989) States that where the hydrophobic group is taken out of contact with the wter the solution's heenergy is lowered . Because surfaces are hi& enerw sites. sirrfactant molecules will collect at these locations. orienting themselves çuch that theù hydmphobic groups are pointed toward the more hydrophobic side of the interface. This results in a decrease in the solution's liee rnergy. Surtàctant adsorption at interfaces also lowers the interfaciai surface tension. thus increasing the interface's wettability. which cm led to the formation of emulsi fications and stable foams (Rosen. 1989: Porter. 1994). At low concentrations. surfactants form simple solutions of unassociated monomers (Prarnauro and Pelizzetti, 1996; Rosen, 1989). Adsorption to surfaces has typicdly be described by an adsorption isotherm. whereby the sdactant concentration at the surfaces increases with increasing surfactant monorner concentration (Pramawo and Pelizzetti. 1996). Surfactants are classifieci accordiig to the charge on the polar head group. The four surfactant classifications are anionic. cationic. nonionic and zwitterionic (containhg both anionic and cationic charges), The character of the head pupa6ects the type of intertaces to which the sudactant will adsorb. For instance. many solid surîàces are negatively charged and cationic surfactants may adsorb with their head groups oriented toward the charged solid surface (Porter. 1994). Nonionic surfactants will tend to adsorb with their hydrophobic tails pointhg toward the most hydrophobic phase at the interface

( Hiemenz. 1986: Pramauro and Pelizzetti, 1996: Rosea 1989). As mentioned above. the cendency for surfactants to adsorb at interfaces is relevant to SEAR applications in two ways: ( 1) it rnay lead to the mobilization of trapped NAPL. due to a lowering of the NAPL-water intedacial tension. and (2) it rnay lead to significant surfactant losses, lowering the effectiveness of surfactant solutions to solubilize HOCs (West and Hmell. 1992). Another way that &actant molecules in aqueous solutions orient thernselves to duce the contact between their hydrophobic tails and water is to coIlect together and fom micelies such that al1 the hydrophobic pups are oriented toward the middle and a11 the hydrophilic groups rue pointed toward the water (Couper. 1984). Micelles form in signiticant numbers when the surfactant concentration is above the critical micelle concentration (CMC). Micelles have the ability to solubilize significant quantities of HOCs and thus nise their apparent solubility in aqueous solutions. A discussion of the process of micellization and the structure of micelles is presented in the following section. The chemicai structure and size of the surfactant tail group abo affects the behavior of surfactant molecules in aqueous solutions. increased hydrophobic taiI lengths or the presence of polyoqqropylene groups in the surfactant's hydrophilic portion generdly increase the tendency of the surfactant to adsorb at interfàces and to tom & micelles. Longer hydrophobic groups ~iliaiso resuit in denser packing of the surfiictant. bath at interfaces and within miceIIes (Rosen, 1989). Branching, ullsaturation or the presence of an aromatic nucleus hthe taii group will uicrease the surfactant's solubility in aqueous solutions leading to an increase in the CMC and looser packing in both the micelles and at interfaces (Lindman and Wemerstrom. 1980: Rosen. 1989). The relative size of the polar pupas compared to the non-polar group will aiso have an effect on the behavior of surfactants in solution. The hydrophile-lipophile balance (HLB) is ofien used to quantiSr this surfactant property (Rosen. 1989: Porter. 1994). In the case of nonionic surtàctants the HLB can be calculated by (Rosen, 1989).

where M,and MLare the formula weights of the hydrophilic and lypophilic rnolecular -moups respectively. Surfactants with an HLB pater than 9 are generally hydrophilic in çharacter whereas those with HLBs beIow 7 are generally hydrophobic (Rosen. 1989: Pramauro and Pelizzetti. 1996: Porter. 1994). In a system containhg both a NAPL and an riqueous phase. surfactants with HLBs pater than 9 wiI1 partition mostly into the riqueous phase (Rosen. 1989). Ifasurtàctan~with an HLB orover 9 is zidded to a YAPL- water system. the surfactant concentration in both phases will increase until mou& surhctant has been added to reach the CMC in the aqueous phase. At surfacmt concenuritions above the CMC any additional surfactant added to the system will be incorporated as micelles in the aqueous phase. Therefore the concentration of unassociated surtictant rnonomers in both phases will remain constant once the CMC has been reachcd in the aqueous phase. Surfactants with an HLB less than seven will partition mostly into the hydrophobic Iiquid phase. there forming reverse micelles in which the hydrophilic groups are oriated toward the center (Porter. 1994).

1.3.2. Surfactant Micelles

.As the concentration of surfactant in an aqueous sotution is increased hmvery low values. there is a point at which a change in the concentration dependence ofa number of equiiibrium and transport propemes occurs (Pmauro and Pelizzetti. 1996). This co~centrationknown as the CMC, corresponds to the concentration at which sigdïcmt numbers of micelles form. It is their presence which causes these changes (Rosen, 1989). Surfactant micelles are of particular interest due to their ability to solubilize hydmphobic organic compounds (HOC) in their core (Edwards et al., 1991 ; Grimberg et ai.. 1994:

Guha et al.. 1998a: Hiemenz 1986; kfvert et al., 1994; ;Pramauro and PeliPetti. 1996: Rosen. 1989: Thangamani and Shreve, 1994; Yeom et al.. 1991). The ability of a surfactant solution to solubilize HOCs in aqueous solutions is dependent on the concentration and character of surfactant micefies. which is in turn determined by the surfactant and bulk solution properties. An understanding ofthe mechanisms involved in micelle formation can therefore provide a theoretical bais for the study of surfactant enhanced solubilization ( Chaiko et al.. 1984: Guha et al.. 1998a; Muke rjee. 1979: Nagarajan et ai.. 1984: Thangamani and Shreve. 1994). For surfactants that fom micelles in aqueous sohtions. the CMC can be interpreted as the solubility limit of surfactant monomen. Above the CMC the concentration of unassociated monomers remains constant in both the aqueous phase and the hydrophobic organic liquid phase (Rosen. 1989). The surface concentration of surtàctant at the system's interthces also stays constant at suriàctant concentration in e'tcess of the CMC. in systems where surfactant bilayers do not form (Porter. 1994: Pramauro and Pelizzetti. 1996: Rosen. 1989). Determination of the CMC can be accornpkished by locating a break in the concentration dependence of any one of a number of bufk solutions propenies including: the air-water interfaciai tension. osmotic presstire. electricai conductivity and detergency. Most commonly the CMC is deterrnined by electricai conductivity. surface tension or light scattering rneasurements (Rosen, 1989). The CMC can also be determined as the concentration at which the apparent aqueous concentration of a HOC begins to rise linearly with increasing surfactant concentration (Grimberg et al.. 1994; Porter. 1994: Rosen. 1989). There have been objections to the use of this method because the CMC can be affected by the solubilization of the XOC into micelles (Linclman and Wennerstrom. 1980: Rosen 1989). However. in systems where the CMC is of interest in pertinence to the surfactant concentration at which solubility enhancement of the HOC in question is fitobserve4 this method of CMC is appropriate (Grimberg et al.. 1994: Rosen, 1989). Assessing the CMC is important in understanding the partitionhg behavior in a eiven system. Industriai surfactants. such as those used in this study. are mixtures of b surfactants defineci by the functiond pqswhich they contain and their average molecular weights. Surfactant mixtures tend to have a less well defined CMC due to the fact that small nurnbers of surfactant aggregates may tom at surtàctant concentrations slightly lower than the measured CMC (Pramam and Pelizzetti. 1996). Micellization is driven by the free energy reduction associated with the removd of the hydrophobic tails fiom the aqueous sotution to a largely hydrophobic environment. Thus. any factor which demases the surfactant's hydrophobic interaction with warer or which increases the Eree energy of micellization (Le. those which increase the repulsive forces between head groups within the micelle) will result in an increasisc in the CMC (Nagmjan and Ruckenstein. 199 1: Porter. 1994: Pramauro and Pelizzetti. 1996). Factors that increase the CMC include: (1) a decrease in the size of the hydrophobic group. (2) incorporation of slightly polarizable pups into the hydrophobic tail. such as hydroxyl groups. aromatic nuclei or polyoxypmpylene. (3) movement of the hydrophilic group to a more centrai region in the molecule. (4) an increase in the polarity or nurnber of hydrophilic groups. (5) a decrease in the solution's ionic strength (most pronounced for critionic and anionic surfactants)and (6) incdtemperature (Rosen, 1989: Nagmjan and Ruckenstein. 199 1 ). The presence of organic additives in the sotution can aIso alter the CMC by changing the îke energy of miceliization. Thesr additives can be divided between CIass 1 and Clriss 11 materials. CIass 1 materiais are those which are absorbed into the micelle and affect free energ of miceltization by altering the interactions between the surfactant molecules within the micelle. GeneraLly polar. Ciass I materiais are beiieved to be absorbed into the micelle's shell amongst the head groups or. in the case of less polar additives. in the region between the core and the shell (referred to as the palisade Iayer), Tt is thought that these materials depress the CMC by reducing the repulsive forces between the head pups (Rosa 1989) or towering the core-water intedaciai tension (Nqarajan and Ruckenstein. 199 1). Ammatic hydrocarbons, which have a slightiy polar character. have been identined to act as CIass 1 matenais in both ionic and nonionic surtàctant solutions (Rosen, 1989; Nagarajan and Ruckenstein, 199 1). This is in

amementb with evidence from spectral anaiysis which suggests that they are solubilized to some extutent in the outer layers of micelles (Chaiko et al.. 1984: Lindman and Wemerstrom. 1980: Nagarajan et ai.. 1954: Nagarajan and Ruckenstein. 199 1: Pramauro and Pelizzetti. 1996: Rosen. 1989). While Class 1 effects are usually observed at low additive concentrations. Class 11 materials cause changes in the CMC at much higher additive concentrations by aitering the chrincter of the solvency of the aqueous solution for surfactant monomers. In gened, Class II materials affect the interactions of the surfàctant hydrophobic tail with the surrounding water. Additives which promote water structure. such as xyiose. tend to decrease the CMC while additives that disrupt the water structure. such as short chain aicohols and water-soluble esters. increase the CMC (Rosen. 1989). Along with the CMC. the size and structure of micelles in solution are important qualities of aqueous surtactant systems. The average number of surfactant moIecules within the micelles in a surfactant solution is termed the aggregation nurnber. The most cornmon micellar structures encountered are srnall spheres. elongated cylinders or rods. large tlnt lamellar discs and vesicles. Knowledge of the aggregation number alone with the shape of micelles in a givcn solution provides insight into the average micelIe volume. Tiie micella. volume and shape are important factors in determining the degee to which a surfactant solution will solubilize HOCs (Lindman and Wemerstrom. 1980: Mukeje. 1979: Nagmjan and Ruckenstein, 1991 :Rosen. 1989). Therefore. it is of interest here to develop an understanding of the factors which affect the structure of micelles. thermodynarnic modeling of micelle formation suggests that for micelles at Low to medium surfactant concentrations the aggregation number of the individual rniceites fdls within a narrow range (Couper. 1984: Nagarajan and Ruckenstein. 1 99 1: Rosen. 1989). A number of general trends are observed for aggregation numbers with changes in the character of the dactant or solution characteristïcs. It has been observed that agpgaîion nurnbers increase rapidly with increased length of the hydrophobic group. dl other conditions remaining unchanged (Hiemenz. 1986; Rosen. 1989). On the other hand. aggregation numbers for sudiactants with polyoxyethylenated (POE) hydrophilic pupsdecrease with increasing head pupsize. tn general, those factors which tend to decrease the CMC increase the aggregation numbers (i-üemenz. 1986). In dilute surfiactant solutions increases in micelie size and aggriegatioa numbers with increasing surfactant concentration is negligibIe (Linhan and Wennerstrom, 1980): therefore. the toul voiume of the micelles in these solutions will increase linearly with increasing surfactant concentration. This has important implications for micellar solubili@ enhancement of HOCs in riqueous solutiorts as the depeof HOC solubilization within the micelle: is a iùnction of the rniceitar volume. The solubilization capaciry is a measme of the amount of a compound that can be solubilized in a surtactant solufion, relative to the amout of surfactant in the micelles. The SC of surfactants with the same hydrophilic head pupgenedly increases with increasing dkyl tail Iength (Linhan and Wennerswm. 1980: Nagarajan and Ruckenstein. 199 1: Rosen. 1989). The size and shape of micelles dso affects the solubilization cripacity of a given &actant (Lindman and Wemerstrom. 1980). Prarnauro and Pelizzetti (1996) state that for hydrocarbons solubilized deep ~ithinthe pdisade Iaycr or in the COR. increasing agpgation number leads to increased amount of solubilized materiai. Therefore. any factor that increases the aggregation number is rxpected to increase the solubiImtion capacity (Linhan and Wemerstrom. 1980: Pmauro and Pelizzetti. 1996: Rosen. 1989). The SC of a given micellar soiution is dependent on the micellar volume availabk for solubilization. Micelles contain differeut regions with varying potarity. and the SC of a given compound within the miceI1e will be deterrnined by the volume of the regions in which the compound is solubilized, as weIl as the concentration of the compound in those regions. Rosen ( 1989) States that there are five locations for soIubilization nithin the miceNe: ( 1) on the miceiie sitrface. (2) between the head groups. (3) in the palisade Iayer-

(4) more deeply within the palisade layer and (5)within the hydrophobie COR. The palisade lqer is the region which marks the transition between the hydrophilic outer layers and the hydrophobic core: it contains both hydmphobic and hydrophdic groups. It shodd be noted that there is no dehite bom- between these layers but that they exist as a continuum. Distinctions are made between the layers to simplifi modeling of the micelle environment (Rosen. 1989). Muke rjee (1979) proposed a two-site model describing micellar solubilization which has become the most commonly accepted hework for evduating the solubilization of HOCs by miceiles (Lindman and Wememrorn, 1980: Nqarajan and

Ruckenstein. 199 1: Porter. 1994: Rosea 1989). In this model. the core is rnodeled ris a hy drophobic liquid-like environment into which other compounds may be absortxd while the micellar shell is modeied as a polar region at which adsorption is possible (Mukerjee. 1979). The locus of HOC solubilization within the micelle varies according to the type of interaction between solute and surfactant. Overall, the SC of a given HOC will depend on the hydrop ho bicity of the HOC's and the relative sizes of the micelle's hydrophobie

core and outer polar regions ( Lindman and Wemerstrom. 1980: Mukejee. 1979: Pmmauro and Pelizzetti, 1996: Rosen. 1989).

1.3.3. Nonionic Surfactants

Nonionic surfactants derive their hydrophilic moiety hmuncharged polar groups. This causes them to behave differently From ionic surfactants in aqueous solutions. especially where mice1la.r qualities are concerned. It has been shown in past studies that nonionic surfactants have the ability to enhance the solubiliy and. in some cases. the biodepdation rates of HOCs (Bourbonais et ai.. 1995: Grimberg et aI.. 1994: Guha et ai.. I998b: Penne1 et al. 1993: Porter. 1994; Zhang et ai., 1997). Recently attention has focused on detennining the possible effitiveness of using a nurnber of nonionic surfactants for SEAR. in light of their nontoxic character. biodegradability and solubilizauon qualirïes (Grimberg et al.. 1994: West and HameII. 1992). The main difference between ionic and nonionic sudactants pertaining to micellization is the lack of charge in the miceliar sheii. This eümiuates the Free energy conmbution due to repulsive forces between the chargeci head grorrps when they are brought in close proximity in micelies. According to Couper (1 984) this reduction in the fkee en= of micelle formation resuits in nonionic srtrfactants having CMC values hpically two orders of magnitude iower than for ionic surfactants. hother important characteristic of nonionic surfactants is their adsorption behavior. .4s clay particles are aegatively charged (LaGrega et al.. 1994). cationic or nvitterionic head wups may adsorb significantly to them. 'Ibis may facilitate bilayer or multi-Iayer sorption. resulting in an iccrease in surfactant tosses due to sorption. Nonionic surfactants do not generally form biiayers when adsorbing to surfaces (Rosen. 1989) and they _eenerally have much higher solubilization capacities han ionic surtàctants (Lindman and Wemerstrorn. 1980). These hctors. dong with their iower CMCs. give nonionic surfactants an advantage over ionic surtàctants in SEAR applications. in chat a pater degree of solubiiization enhancement wodd occur at Iower surtictant concentrations. Thus Iess surfactant would Iikely be required than for ionic surtàctants. resdting in a potential saving in associated chemicai costs. Nonianic surtactants have other characteristics which make hem advantageous for SEMapplications. According to Rosen ( 1989). nonionic surti~ctantsare: ( L ) -ceneraily available free of electrolytes (which mleffect the subsurface biotal. (2) compatible nith ai1 other surfactants in mked miceIIes due to Lack of charge. (2) poor foam stabilizers - advantageous in pumping operations - and. (4) they ofien show an inverse temperature solubility relationship. which suggests that they would be we1L suited to lower tempennire envhnments. The most common 'pes of industrially produced nonionic surfactants avaiIable inciuds: alky l ethoxylates :&(CH2CH20),). &y lphenol ethoxytates. aicoho1 ethoxytates. polyoqethylenated polyoqpropylene glycols. polyoxyethylenated mercaptans, Iong chah carboqiic acid esters and alkanolamides (Rosen. 1989: CIine et al.. 1991 j. Five nonionic surfactants wece selected for this work. Their gened non-toxicity. biodepiability and ability to solubiüze significant quantities of HOCs in aqueous solutions. maice them ideai for SEAR applications. The surfactants seIected for this work are, Brij 30 and Brij 35. (ethoxylated lauryl ethers). Triton X-100 and Tergitol NP10

( phenolic ethoxylates) and Tween 80 (a polyethoxylated sorbitol). aII of which have ben used in other surfactant sokubiiization stuclies. [t has been reported that they dl form sphericai or eIIipsoidal micelles and that the micellar size and aggregation numbers are expected to rem& constant over dilute solution concentration ranges (Le. < 0.2 M) (Grimberg et al., 1994; Jafvsrt et al., 1994; LaGrega et ai., 1994: Luidman and Wennerstrom. 1980). This suggests that it is teasonable to draw conclusions Frorn comparisons of solubiiiition capacities of these surfactants over a range of dilute surtictant concenmtions. 1.4. PAH So~usi~inIN Aau~ous SURFACTANT SOLUTIONS

1.4.1. NAPL-Water PAH Partitioning

Two simple models descnbing liquid-liquid equilibBum pmitioning that have been applied to multi-cornponent NAPL-water systems are Raoult's law and Henry's Law. They both assume that ideal partitioning behavior (where the dissolution of one species is not at-fected by the partitioning of other species) can be used to relate the mole fiactions of ri given species in each of the two iiquid phases when the system is at equilibrium. This allows for prediction of a chernicai species' equilibrium concentration in one phase based on knowledge of the concentration of that particular species in the other phase. Hildebrand and Scott ( 1964) provide a description of Raoult's law and its implications. It is stated that Raoult's Iaw is based on the assumption that al1 the species in ri given mixture are sufficiently alike that an individuai molecule of any one requires the same kinetic energy to escape fiom the mixture as from its own pure liquid. This is rquivalent to assumùig that the entropy of mixing associated with adding n moles ofa constituent to the mixture is the same as adding n moies of the same species to its pure liquid. The vaiidity of this ssurnption is influenced by the relative sizes. shapes and chemical character of the constituent molecules. It is stated that in the absence of hydrogen bonding. differences in the molar volume of non-polar and slightly polar molecules have a srndl effect on the entropy of miuing. Thus it is reasonable to test the applicability of Raoult's law in NAPLs where very littie water. or other polar compounds capable of hydrogen bonding to a sigoificant degree. are present

For a binary mkvture of species i and species j with simiIar molecuiar properties. and assuming that the hgacicy of each component cm be approximated by its partiai pressure. Raoult's law may be written as (Hildebrand and Scott. l964), where the superscripts are used to denote the species of interest, fi and f ', are the species- hgacity in the mixture and in the standard state respectively. p', is the standard reference vapor pressure. A' is the mole fraction in the iiquid and p' is the partial pressure above the mluture. The Raoult's law standard reference state for vapor pressures and Fugacities is the species' pure liquid state (Hildebrand and Scon, 1964; Reid, 1990). According to Hildebrand and Scott (1964). Henry's law differs tiom Raoult's Law in that it allows for the differences between the molecuiar fields of the components in liquid mixtures. For the tendency of a rnolecule to escape fiom a binq mixture to remain constant. regardless of the concentration of the other constituent in the mixnrre. it must be present in very dilute qwtities. At infinite dilution each molecuIe \vil1 be surrounded entirely by molecules of the other species and srnail changes in its concentration will not effect the interactions between molecules unless the dilute species becornes concenmted enough that its moIecules begin to intemct with each other. By this reasoning the Henry's law standard state for a given species is taken as the species at intinite dilution in the solvent of interest. For a binary mixture. Henry's Iaw cm be expressed in a number of ways as it makes littie difference what expression for concentrations are used in dilute systems

( Hildebrand and Scott. 1964).

where nJ is the number of moles of speciesj in the mixture, V is the unit volume. and KJ. K" and KI'' are the Henry's law constants for each of the different fonns. The activity of a species (a')is defined as the ratio of its fugacity in a particular soiution CO its hgacity in the standard reference state (Hildebrand and Scott. 1964: Reid. 1990).

The activity coefficient of viesi (y') in a given phase is defined by.

Combining Equations 1-4 and 1.5 pives. Considering the case where the standard solution is pure liquid i. it cm be seen that Raoult's law is valid for dl cases where y' is eqdto one. The same need not be me for Henry's law to apply. ALI that is needed in these cases is that y' k constant for al1 .Y', over the mge of interea. From Equation 1.6 it cm be seen that the Henry's Iaw constant can be calculated as.

When wo phases are at equilibrium. any constituent's fugacity is equai in both phases. For a NAPL-water system at equilibriurn the following relationship holds.

where the subscnpts .V and rlQ refer to the properties in the NAPL and the aqueous phase respectively. If the activity coefficients in each phase are constant over the concentration ange of interest. Equation 1.7 cm be remanged resulting in,

Ki.., - X', XIw =Yi y/y i 0

where Ki, is a pdtioning constant which relates the equilibrium concentrations of species i in rach of the phases. In situations where Raoult's law or Henry's law adequately descnbe partitioning between phases. partitioning constants cm be hvoked to relate the concentration of rr species in each phase. One that is commonly used is the octano[-water partitioning

constant (K,,). [t is defined as the ratio as the concentration of a moIecular species in octmot to the concentration of the species in water. when the octanol and water phase are in equilibrium (LaGrega et al.. 1994). It is a useN parameter to compare the partitioning behavior of chemicd species. as those species which are more non-polar will have higher K,,, values than polar chemicals. There have been a number of attempts to mode1 the partitionhg of PAHs 6om NAPLs found at contaminated sites. Lee, et ai. (I992a) derived a model, based on Raoult's Law. to describe rhe partitioning of PAHs fiom four dieset fuels into water. The aqueous phase and diesel fuel equilibrium concentrations of 8 PAHs (including naphthalene and phenanthrene) were used to develop a Universal Quasi-Chernical FunctionaI Croup Activity Coefficient (UNIFAC) mode1 to predict the partitioning of other Pus. A diesel-water partitioning constant (Kh}was defined and the LJNIFAC mode1 allowed the prediction of each PM'S Kdwvdue fiom its K,,or aqueous solubitity. They concluded that the deviations from ideality in the partitioning of the 8 studied PAHs were such that their modef yietded error vdues within a fwtor of 2, and thus Raoult's law rnay be acceptable to most field-scale applications. in a second set of studieç by some of the sme authors. the partitioning of the sarne S PAHs between water and coal tars wfis inveçtigated (Lee et al.. 1993b)+ They concluded that modetinç the pmitioning behavior of the PAHs by Raoult's law yielded sufficientiy low mors that it could be applied to fieId situations in which coai tan were in equilibrium with pund waters f Lee et ai., 1 Wb)

Peters and Luhy ( 1993) attempted to mode1 the partitioning behavior of PAHs benveen coal tar and water miscible solvents. Their objective was to investigate the possibility of using solvent extraction as a remediation technique at NAPL contaminated sites. Resuits from expenrnents with a coaI tar containhg over 35 wt% PAHs showed that squilibrium partitioning between coai tar and water. n-buty1amie. acetone or 2- propanol could be adequately modelcd by assuming that Raoult's law was applicabIe in dlcases. They went on to suggest that coal tar couid be treated as a pseudo-component such that the relative concentrations of each of the PAHs would be eqdin each of the solvents as it is in the coal tu.

ln an rittempt to create a synthetic NAPL to mode1 high PMcontent cdtas.

Peters et ai, ( 1997) devetoped a series of homogeneous eutectic NAPLs compriseci entirely of PMswhich are solids at room tempemm in their pure form. They concluded that ideal soiuûon theory adequately described the solubiIity of four PMs in binq and ternary P.4Hs mixtures. They aIso found that assuming that y ', = t for =ch PMIin the NAPLs provided acmtepredictions of equilibrium aqueous concenrrations when the NAPLs were contacted with water. In a Iater study, Mukherji et al. (1997) evaluated the rnass transfer of PAHs fiom similar synthesized NAPLs containing eight PMsdissolved in toluene. They found that y ', values in four synthesized NAPLs were dose to unity for al1 NAPL constituents. and that Raoult's law modeling of the NAPL-water partitioning behavior couid therein be applied. In al1 cases outlined above, the activity coefficients of the PAHs studied remained constant over a wide range of NAPL mole fractions. These results suggest that it is valid to assume ideal equilibriurn partitioning between teai-world NAPLs. containing signiticant quantities of PAHs, and pundwater rit contaminated sites. Therefore any synthesized NAPL used to mode1 PAH partitionhg in the environment shouid be one in which the activity coefficients of the PAHs of interest within the NAPL do not vary significantly over the range of PAHs concentrations studied. Other studies suggest that the aqueous solubility of PAHs may be affected by small quantities of other hydrophobic compounds present in the aqueous phase. Kile and

Chiou ( 1989) found that the aqueous solubility of PCBs and DDT were en!!anced due to the presence of hurnic acid. Similady. Fu and Luthy (1986)found that the presence of water miscible solvents (which were tess polar than water) in the aqueous phase increased the aqueous solubility of 7 PAHs. including naphthaiene and phenanthrene. Since the activity coeficients in this thesis is caiculated based on aqueous concentrations. it wilI be necessary to assess the affect of the other hydrophobic compounds present on aqueous solubilities. For instance, in the case of naphthalene the presence of hexadecane and phenanthrene may taise its aqueous solubiiiq. Chiou and Schmedding (1982) found that when relating the K,,, values for a number of organic compounds (including benzene. naphthaiene and phenanthrene) to their water soIubilities. deviations fiom Raoult's Iaw ideality occurred. These deviations were seen to increase with K,, and were attributed to partitioning water into the octanol phase which nised the activity coefficients of the most hydrophobic compounds. This couid present another complication in modeling NAPL-water partitioning. In this work, water was contacted with two and three-component LNAPLs synthesized by dissolving naphthalene and phenanthrene into hexadecane. The systerns were equilibrated in a temperature controlled environment under gentle mixing conditions to avoid enors in the solubility measurements and emulsification of the NAPL. In the synthesized NAPLs used in this study. it is unlikely that the y ', values for the PAHs will change significantly due to the non-polar character of al1 the NAPL components. as stated by Hildebrand and Scott (1954). Also, as hexadecane is much more hydrophobic than octanol. it is expected that water partitioning into the NAPL will bc minimal and that it wiil not effectr ',\, vdues. Due to hexadecane's extremely low water solubility of0.4 pg/L it is dso unlikeiy that it wilI affect the aqueous solubility of the other PAHs. Several other studies have ernployed similar NAPLs to svaluate the bioavaiiability and mas transfer rates of PAHs. For exarnple. in other studies NAPLs have been synthesized by dissoiving naphthalene or phenanthrene into hexadecane. heptamethy lnonane or diethy lhexyl phthalate (Ghoshai et al.. 1996). Cod W. diesel and creosote al1 contain significant quantities of PiWs (Peters et al.. 1997). thus. it is believed that the mode1 NAPLs are reasonabty represenmive of these ceai-world NAPLs.

1.4.2. PAH Partitioning in Aqueous Surfactant Solutions

The ability of surfactant micei!es to solubiIize sipificant quantities of HOCs is well documented (Bourbonais et al.. 1995: Dunaway et ai., 1995: Hiemenz, 1986: Lindman and Wennersmn. 1980: Nagarajan and Ruckensteia 199 1: Porter. 1994: Pramauro and Pelizzetti. 1996: Rosen. 1989). Men modeling the partitioning of a non-polar compounds in aqueous surfactant solutions. it ha cornmonly been assurned that the micellar-core environment can be treated as a droplet of liquid hydrocarbon (Lindman and Wennerstrom. 1980; Porter. 1994; Pramauro and Pelizzetti, 1996: Rosen 1989). The micelle core is therefore considered to be a third phase in equilibrium with the aqueous phase and the NAPL. However- this rnay be an over simplification as HOCs rnay not always be partitioned exclusiveIy within the hydrophobic micellar core and solubiiization of HOCs rnay alter the micelle's properties (Du~wayet ai., 1995: Guha et al.. 1998~ Hiemenz. 1986; Nagarajan et ai., 1984; Nagarajan and Ruckenstein. 199 1; Pramauro and Pelizzetti. 1996; Rosen. 1989; Tucker, 1995). In order to mode1 the partitionhg of HOCs between micelles. water and a NML. it is necessary to define the boundaries of the phases present. When micelles form in aqueous surfactant solutions. they will typicdly be dispersed throughout the aqueous bulk-phase (Hiemenz 1986: Lindman and Wennerstrom, 1980: Porter. 1994: Pramauro and Pelizzetti. 1996: Rosen. 1989). The dispersed micelles are treated as a single phase. referred to as a pseudo-phase in order to differentiate it fiom a continuous phase such as the NAPL. The aqueous pseudo-phase includes ail of the aqueous solution excluding the micelles (Porter. 1994: Rosen. 1989). but including the unassociated surîàctant monomers, The aqueous bulk-phase refers to the entire aqueous surfactant solution containing both the micellar pseudo-phase and the aqueous pseudo-phase. Together the NML. aqueous pseudo-phase and micellar pseudo-phase comprise a three phase system. PAH partitioning between the NAPL and the aqueous pseudo-phase follows the relationship outlined in the preceding section for a NAPL-water system. Muke jee ( 1979) notes that the association of naphthdene molecules with surfactant monomers is negligible in rnost surfactant solutions. Thus. it is assurned that the aqueous pseudo- phase PAH concentration is equivalent to the aqueous concentration in a NML-water system. tn NNL-surfactant solution systerns it is necessary to consider partitioning into the micellar pseudo-phase. Mukerjee (1979) states that the solubilization of HOCs within micelles is directly associated with the process of micellization and the properties of the solute. Within the micelle core the hydrocarbon chains are flexible. which results in a liquid-like envircnrnent (Hiemenz. 1986). whereas the polar head groups are held in the shell viith much less freedom of motion (Lindman and Wememom. 1980: Nagarajan and Ruckenstein. 199 1: Rosen. 1989). Wlen non-pIar solutes are incorponted into the core the surfactant hydrophobie tdsanain more &dom of motion and the core becomes even more Iiquid-Iike (Nagarajan and Ruckenstein, 1991). It has been suggested that the solubility of a given non-polar compound in the micellar core can be approximated by the solubili~of the compound in the hydrocarbon liquid which is most Iike the surfactant's hydrophobic tail (Prarnauro and Pelizzetti, 1996) and that the radius of the micelle core can be approximated by the length of the hlly stretched hydrophobic tail (Hiemenz. 1986: Rosen 1989). However. the micellar environment is not homogeneous and in each of the different micellar regions. described in Section 1.2.2, solubilization is likely to vary. especially for polar and slightly polar solutes (Dido et al.. 1994: Hiemenz 1986: Lindman and Wememom. 1980; Mukejee, 1979: Nagarajan and Ruckenstein. I99 I: Pramauro and Pelizzetti. 1996: Rosen. 1989). Muke rjee (1979) provides a comprehensive review of the process of micellar solubilization. in which he outlines his two-state solubilization model. According to the two-state model rnicellar solubilization is considered to be a combination of absorption into the hydrophobic core and an adsorption to the polar surface layer. For non-polar compounds it is appropriate to consider solubilization as simple partitioning between the micellar non-polar interior and the aqueous environment (Rosen. 1989: Lindmm and Wennersuom. 1980: Muke rjee. 1979). whereas significant quantities of slightly polar compounds. such as aromatic hydrocarbons, are expected to be solubilized in the shell and at the shell-core interface (Guha et al.. l998a: Hiemenz. 1986: Lindman and Wsnnerstrom. 1980: Muke jee. 1979: Nagarajan and Ruckenstein. 199 1: Prarnauro and Pelizzetti. 1996: Rosen. 1989). Using this model. Muke rjee (1 979) attempted to explain the anomalously high solubilization capacity that micelles have for slightIy polar compounds such as benzene. when compared to non-polar alkanes. He suggested that steric interactions and repulsive forces between surfactant head groups. bound close together in the rnicellar shell, oppose the of micelles. Evidence is provided that slightly polar molecules are solubilized to some extent between the surfactant head groups which may reduce repulsive forces between these groups. This results in a lowering of the CMC and possibly an increase in the micelle core volume which may contribute to the high SC values. For surfactants containing bulky POE head groups, the outer mantle. or palisade layer. can be a locus of solubilization (Mukerjee. 1979). Since the location of solubilization varies according to the type of interaction between solute and surfactant (Rosen. 1989). non-polar aiiphatic compounds would be solubilized to a significant extent only within the micelle's hydrophobie core whereas aromatic hydrocarbons cm be solubilized within the core and the slightly polar paiisade layer (Lindman and Wennerstrom. t 980: Mukerjee, 1979: Nagarajan and Ruckenstein. 199 1 ; Rosen. 1989). Therefore. SC values for aromatic hyrlrocarbons would be higher than values for non- polar aliphatic compounds due to their ability to be absorbed in signiticant quantities within the micelle-s outer layers. and an increase in the size and number of micelles in the solution. It has also been show that the SC of aromatic hydrocarbons in nonionic micelles decreases with increasing solute molecular volume (Rosen 1989: Nagarajan et al.. 1984). Chaiko et al (1984) found that the SC values in ionic and nonionic micelles cm be better predicted when both the solute polarity and molecular volume are considered. nther than just the rnolecular volume. Evidence suggests that SC values increase with decreasing solute molecular volume and increasing polarity (Chaiko et al.. 1 984: Lindrnan and Wennerstrom. 1980: Nagarajan et ai.. 1984: Nagarajan and Ruckenstein. 199 1 : Pramauro and Pelizzetti. 1996: Rosen. 1989).

1.4.3. Modeling PAH Parütioning in Surfactant Solutions in order to assess the solubilizauon capacity of a given surfactant. it is necessary to evaluate the increase in the P.W concentration in the rnicellar pseudo-phase. associated with increasing surfactant concentration. To do this it is ofien useful to measure the PAH concentration in the aqueous bulk-phase (CfmT).which includes the PAH solubilized in the water and the micelles. CdmTcan be calculateci from.

where n ',, and n :,p are the total number of moles of PAH in the rnicellar and aqueous pseudo-phase respectively. Vu is the miceIIar pseudo-phase volume and V,Q is the aqueous pseudo-phase volume. It has ken stated that at low and moderate surfactant concenrrations {i.e. Iess than 5 wt%) V, is much smaiier than VdQ(Grimberg et aI.. 1994)- and thus Equation 1.1 Oa reduces to (t. [Ob)

From Equations 1. lOa and I. lob. it can be seen that a masure of the aqueous bulk-phase PAHconcentration will have both an aqueous and micelhr pseudo-phase contribution and that knowledge of the PAH aqueous pseudo-phase concentntion witl ailow for determination of the micellar pseudo-phase concentration. Measurement of the micellar volume is dZi5cult. in that it is necessary to detemine the aggregation nurnber. micellar size disnibution tunction and the micellar shape by light scattering. viscosity and NhIR chernical shift measuremenrs (Linciman and Wennerstrom. 1980). Even when average micelle volumes are known. the effective micellar volume availrible to a given solute is rarely known. Therefore. the micellar concentration (C.\,)is ofien expressed in terms of the volume of the aqueous bulk-ph=. which cmbe approximated ris the volume of the aqueous pseudo-phase (Grimberg et al.. 1994).

It has been stated that Henry's law partitioning cm be eed to describe partitioning benveen the micelle ruid the aqueous pseudo-phase for ditute solutions of rn- HOCs (Mukejee. I979). For unchargeci solutes, the activity within the micelte cm be treated in the same way as for other Iiquid phases (Dunaway et id.. 1995: Muke rjee. 1979: Tucker. 1995)+ It has ben noted that for nonionic micelles this treatment is most useful. despite its limitations (Mukejee. 1979). The following equation can therefore be used to relate the activities in the micellar and aqueous pseudo-phases at equilibrium.

where the subscript iMdenote~micellar pseudo-phase properties. Once again. it shodd be noted that the activity coefficients are based on the pure liquid standard state such that as X ' -+ 1.7 ' + 1. Assessing the y ', vdues is usehi in deteminhg the nature of the environment within the micelle: y ', near 1 represents an environment similar to that of the pure Iiquid solute. y ', 'rester than unity represents Iess favorable environments whereas y las than unity represents a strong attraction between the aggregate and the solute (Pramauro and Pelizzem. 1996). From Equation 1.13 a partitioning constant can be defined to descnbe the equilibrium partitioning of a given solute between the micellar and the aqueous pseudo- phases.

This has cornmonly been used as an indicator of the depof solubili~enhancement that can be expected for a specific solute in solutions of a particular surfactant (Jahert et al.. 1995: Porter. 1994: West and Hmvell. 1992). Also used to quanti@ this solubi1ization enhancement is the SC. which cm be calculated by the unit mass of solubilized per unit mas of surfactant added to the solution in excess of the CMC (Grimberg et al.. 1994). The MSR is another commonly used parameter that describes the extent of solubilization of a compound into micelles. It is detined as the ratio of the number of moles of solute incorponted into micelles per mole of micellar surfactant. In aqueous surfactant solutions the following equation cm be used to calculate the MSR (Zimmerman et al.. 1999: T!mgamani and Shreve. 1994).

MSR = (C!, - C I (c'*:\~- CMC) (1.14) or in terms of the solute micellar mole hction as (Edwards et ai.. 1994b),

Lising these panmeters the partitioning behavior OF PAHs in surfactant solutions cmbe evaiuated and compared for different systems. The SC and MSR are particularly usehl to assess the ability of a &en surfactant to increase the solubility of PAHs in SEMapplications. The micellar mole fraction and activity coefficient indicate the nature of the micellar environment rxperienced by the solute.

f .4.4. Surfactant Solubilization of PAHs

The hct that nonionic surfactants inmase the aqueous bulk-phase solubility of aromatic hydrocarbons is well documented. Edwards et al. ( 199 1.1994a and I994b) Found that four nonionic surfactants. including Brij 30 and Triton X-100, significantly increased the apparent aqueous solubility of naphthaiene, phenanthme and pyrene in mil-aqueous solution systems. ïhey present a physicochemical model, in which the MSR and K',, were used to describe the distribution of PAHs between the soi1 and micellar solution at various surtàctant concentrations. Their e-qerimental results show that the modd was effective in predicting PAH partitioning and that successive surfrcmt flushing couid achieve better results than a single wash with the same total mass of surfactant added to the system.

Edwards et al. ( 1994a) found that above the CMC the sorption of the nonionic surf'actantTriton X- I O0 was constant and that the apparent aqueous solubili~of naphthalene and phenanthrene therefore increased with increasing surîàctant concentration. Their results suggest that at higher surfactant concentrations surtictant losses and the effect of HOC partitioning to sorbed surfactant may become less important relative to the enhancement of HOC aqueous solubiiities

Jattert et ai. ( 1994) and Jat-vert et aL(1995) present a set of predictive models For the K ',, values based on the measurements of K',, for various PMsand chlorinated mnes in 1 CC nonionic surfactant solutions. Their models suggest that K',, values are strongly dependent on the hydrophobicity of the solute and the size of the hydrophilic and h!drophobic portions of the surfactant molecules. They go on to show that K',, values cm be predicted fiom knowledge of the solute's K,, dong with the nurnber ofcarbons in the surfactant's hydrophilic and hydrophobie groups.

Zimmerman et al ( 1998). in a study of the effect of partitioning of ethoxylated nonionic surtàctants into seven single component NAPLs. found that nonionic surfactant solutions have the ability to solubilize significant amounts of HOCs from NAPLs. They also showed bat the solubilization capacity of a given surfactant wodd be underestimated if surfactant partitioning into the NAPL is overiooked in MSR calculations. The micellar solubilization of four PAHs hmaged coal tar by Brij 25, Triton X- 100 and Tween 80 was studied by Yeom et al (1995). They found that Raoult's law satisfactody described the partitioning of the PAHs hmthe coaI tar in the presence of soi1 ~itha high focdespite the fact that the aged coal tar was not identified as a distinct liquid phase. Mass transfer experiments did not reach equilibriurn due to PAH rnass mtèrlimitations in the coal tar. thus chey were notable to assess the effect of coal tar PAH mole fractions on equilibrium aqueous concentrations. The solubilization of hexadecane in surfactant solutions. studied by Thangrnani and Shreve ( 1994). is also of interest. Hexadecane \vas used in the this work as the bulk NAPL into which the PAWs were dissdved. The authors found that the solubility hexadecane was enhanced in solutions of four biosurfactsuits and one industrial surfactant but that the MSRs were emmely bw in al1 cases (< 2.0 x 10). An increase in the aqueous solubility due to rhe presence of surfactant monorners was also obsewed. This provides lùrther evidence that extremeiy hydrophobie compounds will not be solubilized into aqueous surfactant solutions as much as slightly polar PAHs. It also suggests that hexadecane micellar mole fiactions are likely to be very small in the systems used in this study. Other studies have shown that the presence of surîàctant micelles cm enhance the rate of PAH dissolution into the aqueous phase due to an increase in the apparent aqueous solubility. which is the driving force for mass msfer. Grirnberg et al ( 1994) found that the rate of solid phenanthrene dissolution into six nonionic solutions was sigrûficantly higher than the rate in pure water, despite the fact that the overall mass transfer coefficient decreased with the addition of surfactant. They explained the mas transfer rate increase by showing that the increased solubility of phenanthrene in surfactant solutions outweighed the decrease in the mass transfer coefficient. The ability of surfactant solutions to increase the rate of PAH biodepdation has also been explained by the enhancement of PAH solubilities in the presence of surfactants. tt was shown that the rate of phenaathrene biodegradation was enhanced due to the increase in phenanthrene dissolution rates and solubility, attributable to the presence of micelles in the solution (Zhang et ai.. 1997; Aronstien et ai. 1991). It has even been proposed that increa~edrates of phenanthene biodegradation may be partiaily attributable to the direct avdabilip of a portion of the phenanthrene in the rniceilar core (Guha and Jaf5e. 1996: Guha et A.. 1998). However, in another case three nonionic surf~tantsolutions showed enhanced phenantbrene solubility but inhibited biodemdation.- ptesumably due to interactions between the surfactant molecules and bacteria membranes (Laha and Luthy. 199 1). There has ken Me work done on rnicellar sohbilization of HOCs hmmulti- component NAPLs or in systems containing mulupie PAHs. The snidies rnentioned above mostiy consider single component NAPLs. pure solids or dissolved single compounds. Kmga et d. (1997) studied cmde oil containing only a small mole fraction of the PAHs in question. however rhere ivas no attempt made to relate the PMmole

fmction in the NAPL to the micetlar solubiSizatian capacity. Yeom et ai. ( 1995') did relate the mole tiiiction of coal tar to the SC. but the aged coal tar used was a sotid and equilibriurn sotubilities were not achieved due to mas transfer limitatiuns. To date. the only study of the solubiIization ot'multi-component NAPLs was

presenred in cornpanion papers by Nagruajan et ai. (1984) and Chaiko et al. ( 1984). In

their work it wris observed that the MSR of benzene in ionic surt'act;uits wris only slightly dyected by the presence of cyclohexme and hexane. However. they witnessed a synergetic inmilse in the MSR ot'hexane hmNAPLs containing small mole hctions of benzene. They concluded that sorne degree ot'benzene solubilization had occurred in the outer Iayen ofthe micelles and chat this Iead to an increase in the miceliar core volume. which in tum increased the MSR of n-heme.

Guha et al. (1998a) studied the partitionhg of miunires of naphhaiene. phenanthne and pyrene cqstiils in Triton X- 1 O0 solutions. 'Ihey Lound that in some cases an increase in che surfactant solutions' SC for phenanthtene occurred in the presence of naphthalene. when compared to the SC duesfor sirrfactant soiutions containing no naphthafene. Other results conceniing the partitioning of naphthdene in nvo PMsystems and the partitioning of dI three PMs in solution together were Iess concIusive with some increases in SC values and some decreases in SC values compared to the SCs in siagie PAH systems. They conchdeci that naphthdene Likely increased the SC of the other more hydrophobie PAHs by being solubilized at the core-water interface which lead to an increase in the cote voIume avaiIabIe for soIubiIization. In order to gain a thomugh understanding of remediation processes. it is essential tfiat the solubility of PAHs at sites contaminated with NAPLs be knom. So far. the equilibrium partitioning of PAHs between common real-worid NAPLs and water is well understood. Because surfactant flushing has been considered as a means to increase of dissolution of PAHs fiom NAPLs in the saturated zone, it is important to assess the partitioning parameters of PAH dissolution into surfactant solutions. While the effect of surtàctant micelles on 3 given PAH's apparent solubility in single solute systems is well understood. there is a lack of information on the partitioning behavior of P.4H.s in systems containing multi-component NAPLs. Moreover. a comprehensive undemanding of the dect of NML constituent mole fractions on MSR values in surfactant solutions is Lacking. The effects of changing PAH concentrations in each of the phases present. caused by continued dissolution on the activities of the PAHs in the system. needs to be scertained. This knowledge is criticd for modeiing and assessing PAH dissolution rit NAPL contaminated sites for any surfactant enhanced remediation process. 2. Equilibrium Partitioning of PAHs Between NAPLs and Water

Partitioning of phenanthrene and naphthalene between hexadecane and water was investigated to test the validity of using twocomponent NAPLs to model PAH dissolution fiom real-world NAPLs into water. Past studies have predicted the partitioning of PAHs from chemicallycompIex NAPLs such as creosote by assurning that Raoult's lai or Henry's law can be applied to the system. Both of these models assume chat the aqueous phase concentration of a compound will be a linear function of that compound's concentration in the NAPL. Fmn this it can be assurned that the partitioning behavior of a compound in a system that fits either model is sirnilar to the partitioning behavior of that compound in another system that can be modeled by either Henq's iaw or Raoult's Iaw. in order to test the applicability of Henry's law for the two component NAPLs studied here. partitioning coefficients were developed to describe the dissoiution of naphthalene and phenanthrene. The results hmthese experirnents estabiish the bais for the approach taken in the study conceming NAPL partitioning into surtàctant solutions. presented in Chapter 3. Esperimental results suggest that Raoult's law may be applied to a large number of non-polar mimes (Hildebrand and Scott, 1964). Cheet al. (1991) showed that Raoult's law may be applied to benzene. toluene and naphthalene in a wide range of compleir solvents including hexadecane. Other studies using PAH containing NAPLs such as coai tar. diesel fuel and gasoline give evidence that PAH partïtioning fiom reaI- world NAPLs ofien follows the predictions of Raoult's law (Peters et al.. 1997: Mukherji et ai.. 1997: Lee et al.. l992a: Fu and Luthy. 1986: Cline et al.. 199 1). It was therefore rxpected that naphthaiene and phenanthrene would exhibit ideaI partitioning behavior Lkom hexadecane into water and that these NAPLs would provide an appropriate surrogate for those found at NAPL contaminated sites. The aqueous phase equilibrium concentration of a NAPL constituent can be determined on the basis of multi-component Liquid-liquid equilibriurn theory (Mukheji et ai.. 1997: Lee et ai.. 1992b). as described in Chapter 1. According to this theory, thermodynamic equilibrium is defined as the equality of chemical potentials between phases (Hildebrand and Scott. 1964). Applying the Raoult's Iaw convention for activity coefficients. as stated in Chapter 1. Equation 1.8 can be invoked to relate the equilibrium concentration of a compound in two phases contacted together.

Fu and Luthy ( 1986) stated that the relationship between a crystalline solute's aqueous solubility (expressed as a mole fiaction: -V,4g,t) and its aqueous phase activity coefficient at saturation (Tr.lQ.s

where f", is the reference fugacity of the pure solid i. f is the reference îùgacity of the pure liquid i. 1f the aqueous soiution is sufficiently dilute. with respect to the PAH of interest. the molar concentration of PAH in the aqueous phase can bc estimated as the ratio of the aqueous phase mole fraction to the molar volume of water (Le. CIY=& / VW - and C' ,Q,, - ,r.,Q, / VI,where V, is the molar volume of water and Cw is the molar concentration of PAH in the aqueous phase and cg,is the aqueous solubility of PAH in the aqueous phase ) (Lee et al.. 1992a). Assuming that the aqueous phase activity coetricient of a component is unaffected by the dissolution of the other species comprising the NAPL. Equations 1.7 and 2.1 can be combined with the following result:

cl, = xi, -,',ci, 1 (f (2.2) In a system in which Y.,, does not change as a function ofthe NAPL mole fraction and C?,.lQ.w, does not change due to the presence of other species, a NAPL-water partitioning coefficient (K',) can be defined to estimate the release of PMfiom the NAPL into the aqueous phase (Lee et ai.. t9Wa). Values of the solid-liquid fugacity ratio for naphthaiene and phenanthrene. esùmated based on thermodynamic properties. according to the method described by Mukherji et ai. (1997). are presented in Table 2. l . From Equation 3.3 it cm be seen that these values cm be used to estimate the activity coefficients of PAHs by measuring the aqueous PAH concentrations in NAPL-water systems. The solid-liquid fugacity ratio can dso be used to determine the activity çoetticient in a PAH-saturated NAPL if the maximum dissolvable PAH mole fraction (.Y, (mm))is knotvn. Peters et al. ( 1997) state that for a solid PAH the .r, (ma)cm be related to (f?j/J and -( by.

Equation 2.4 shows that same relationship rxists for ar,v(mar)as did for .Y.,Q, in Equation 2.1. From tkis it can be conciuded that when the activity coefficient of a given compound in solution equals one (i-e.ideal solution). the maximum NAPL mole tiaction will be equal to the solid-liquid hgacity ratio, Atso. if the PAH activity coeficienr in the saturated NAPL is not significantly different fiorn the PAH activity coefticients in unsatucated NAPLs. then C',44in water contacted with saturated NAPL should be equal to

2.1 -2. Objectives

The objective of these experiments was to evaiuate the partitioning of naphthalene and phenanthrene between hexadecrtne and water. From this work the ability of a NAPL- water partitioning coefficient to predict aqueous phase PAH concentrations over a &ide range of PAH mole hctions in the synthesized NAPLs can be assessed. Estimation of the maximum solubility of each PAH in tiexadecane defines the upper litto the range of PAH mole tiactions to be used in Merexperiments. Comparisons are made between C' C' in water contacted with a PAH saturated NAPL and obtained fiom cqd- water systems. in order to mess the effect of water saturation on NAPL PAH activity coeficients. UItimately concIusions are made regarding the validity of using the synthesized NAPLs to mode1 PAH partitiming tiom reai-world NAPLs such as coal tars or creosotes.

Table 2.1: NAPL Component Physical Data Icompound 1 Molecular Melting Boilinq SolidlLiquid UVllR Densiîv Weight point- point FuWci

Phenanthrene 178.24 99.2 340 0.279 256,211 0.98 Compound Molecular Vapor Heat of Henry's Law Log Volume Pressure in Fusion Constant at 25 OC kW (cm31mol) Air (moUL) (kcallrnol) [Log Kd (L atm mort)

Hexadecane 1 332' 1.86E-06 nia 332 O 6.12

Phenanthrene 1 199 6.60E09 4 199 C 4.57 [Sources: * Schwarzenbach et al.. 1993; " Mackq. ei al.. 1992: Chiou and Schmedding, 19821 2.2. MATERIALSAND METHODS

2.2.1. Chemicals

Phenanthrene (purity > 98 %) and scintillation grade naphthaiene (purity > 99 %) were obtained Liom Sigma Aldrich Chemicai Co. (St. Louis, MO). Naphthalene, a two-ring polycyclic aromatic hydrocarbon. is a solid at room temperature with a melting point of 80 "C and a water solubility of approximately 3 1.0 mg/L at 35 OC (Mackay et al.. 1992). Phenanthrene is a three-ring polycyclic aromatic hydrocarbon with a melting point of% "C and is sparingly water soluble with a water solubility of 1.12 mg/(Mackay et al.. 1992). Reagent-grade hexadecane (purity > 99%), a saturated unbranched hydrocarbon. was purchased From Sigma Aldrich Chernical Company. It has a rnelting point of 18.1 "C (Howard and Meylan. 1997) and thus was a liquid under the controlled lab environment of 2s' "C. With a solubility of 0.9 pg/L (Howard and Meylan. 1997). it is considered to be essentially water insoluble. Physical data for the NAPL components is presented in Table 1.1. Al1 NAPL components were used without furthet purification. HPLC grade mehanol, purchased from Fisher Scientific (Fair Lam. NJ), was used for sample dilution in the analysis procedures and to create standard solutions for calibrations. Al1 hater used for dilutions and sample preparation was distilled deionized water. Nitric acid (69- 73% solution). obtained Eiom Anachernia (Montreai. PQ), was used in cleaning rfasstvare. b

2.2.2. NAPL Synthesis and Determination of Maximum NAFL PAH Mole Fractions

Experimrnts were canied out to determine the maximum amount of each PAH that could be dissolved into hexadecane. As NAPL constituent solubüities typically increase si_@ficantly with increasing temperature (Fu and Luthy. 1986; Hildebrand and Scott. 1964). dissolving PAHs into NAPLs at an elevated temperature resuits m NMLs that are supersanrnted with PAH, relative to the solubility at the reference temperature of 25 OC. As the heated mixtures are cooled, dissolvsd PAH will precipitate leaving a PAH saturated NAPL in equilibrium with a crystalline PAH phase. Twoîomponent LNAPLs were synthesized by miving various quaritities of individual PAHs with hexadecane in 8 ml Pyrex vials sealed with polypropylene open- topped caps fitted with Teflon-lined silicone sepm The mixtures were then heated to 60 "C until ail the PAH crystais were cornpletely dissolved into the hexadecane. The vials were then placed on an orbital shaker and agitated at 200 rpm in a temperature controlled environment set to 25 "C. Mer 96 hours the samples were visuaily inspected for crystals. Those in which PAH crystals had precipitated were deemed to have had initial mole fractions above the maximum solubility of the given PAH in hexadecane at 25 "C. From each sample. 2 ml of NAPL was extracted with a 5 ml glass syringe. It has been noted that crystals too small for visual detection may be present in systems contacted with crystalline PAHs and that these rnay etfèct PAH concentration measurements (Grimberg et ai.. 1994). Thus the 2 ml of NAPL was then expressed through a 0.7 pm pore Tetlon tilter to remove any crystais that rnay have been entrained. tn order to reduce the error induced by PAH losses through sorption to the glassware and filter holder surtaces. the filter and syringe were first rinsed with 3 ml of the sample being andyzed. ..\fier filtration, the 2 ml of NAPL was contacted with 25 ml of water in a JO ml Pyrex via1 sealed with polypropylene open topped caps fitted with Teflon-lined silicone septa. NAPLs were added carefully to the viais, after the 25 ml of water. by slowly expressing a strem of NAPL fkom the syringe tip and ailowing it to Ml against the wail of the vial just slightly above the surface of the water. This technique avoided breaking-up of the NAPL into droplets and reduced the chances of NAPL emulsification. The JO ml vials containing NAPL and water were then placed on an orbital shaker and agitated at 175 rpm in a 25 "C temperature-controlled environment. After 96 hom it was assumed that the system had reached equilibrium based on the results of the time to equilibrium e.xperiments descnbed betow. The samples were then removed from the shaker. the aqueous phase was sampled and the equiltkium PAH concentration was mertsured by the methods described below. The maximum PAH mole fraction in the NAPL was estimateci as the point dong the aqueous phase equilibrium PAH concentration vs. mixture mole fraction curve at which the aqueous phase equilibrium concentration showed no increase with indPAH mole fraction in the original mixture.

2.2.3. Glassware Preparation

.Ill glassware. except the syringes. was washed first by soaking for 24 hours in a detergent solution (Sparkleen. Fisher Scientific. NJ). followed by scmbbing and thorough rinsing with tap water aFter which it was placed in an acid bath containing 25% (wlw) niuic acid. The purpose of the acid rinse was to remove any soap that could not be removed by rinsing with water alone. Mer 24 hours the glassware was removed tiom the acid bath and rinsed thoroughiy with distilled water. Glassware that was contaminated with significant amounts of NAPL or PAH crystals was pre-rinsed with methanol prior to soap and acid washing. The syringes. syringe tilter holder. syringe tips and Teflon-lined septa were not acid washed but insteaci were rinsed with methanol and lefi to sit in a methanol bath for a minimum of 24 hours before being rinsed thoroughly with distilled water and dried.

2.2.4. PAH Ultraviolet Spectrophotometry

Measwement of PAH concentntions were made using a Hewlett Packard HP-8453 single beam ultraviolet (UV) spectmphotometer wîth a deuterium lamp. Samples were placcd in a quartz ce11 with a 1.000 cm path length. Table 2.1 includes the commonly reported absorbance peaks for the various NAPL components in aqueous solutions. Examination of naphthdene's absorbance spectra in methanol solutions led to the choice of 220 nm as the peak absorbance wavelength for measurements. Smailer peaks were observed at 254. 263.272 nm but they were not as sensitive to naphhaiene concentration as the peak at 270 nm. thus 220 nrn was chosen as the absorbance wavelength for naphthalene concentration measurements. In the sinde- beam W spectroptiotorneter used, a beam of UV light is passed through the quartz ceIl containing the sample to a detector placed in a straight Iine behind the Iamp and sample. The wavelength of the light is varied over a range set by the user and the intensity of the light beam derit has passed through the sample is measured by the detector. Lower measured intensities are interpreted as the result of higher sample UV 1ight absorbance at the wavelength in question. The liV spectrophotometer interpreted the rneasurements and gave dirnensionless absorbance values as output. Ovrr a typically narrow concentration range the absorbance of a sample will vary linearly with changes in the concentr~tionof the compound of interest (tnçle and Crouch. 1988; Pnmauro and Pelizzetti. 1996). The slope of the absorbance vs. concentration curve hra given wavelength is tenned the extinction coefficient. lt represents the amount of light absarbcd per unit concentration pet unit path length through the sample. As absorbance is ri dimensionless parameter. the extinction coefficient is expressed by the units: L mg-' cm-'. Extinction coefficients are particular to a specific compound's absorbance. measured at a specific wavelength. Standard naphthafene stock solutions were produced by dissolving 1000 mg of naphthalene into 1000 ml of HPLC grade methanol. The mixture was stirred with a Tetlon stimng bead for at least 24 hours. at which tirne al1 the crystdline naphthdene had dissolved. Because naphthaiene is reasoniibly volatile and cm break down when exposed to sunlight. the solution was then placed into 250 ml brown giass bottles sealed with closed-top polypropy lene caps lined with Tetlon lined silicone septa and stored in the dark at 5 "C to reduce volatilization losses. Each bottle was fim rinsed with 50 ml of the standard solution in order to reduce losses due to naphthalene sorption to the glasswm. The linear absorbance response range for naphthalene in methanol solutions wu detemiined to be between O and 2.0 mg/L, for which the absorbance at 220 nrn varied hmO to 1.4. Figure 2.1 shows the results of the initial naphthaiene in methanol solutions calibntion for naphthalene concentrations ranging fiom 0.216 mg/L to 2.47 mgiL, Each point on the calibntion is the mean of three rneasurements made on each of three separately produced samples with the same naphthalene concentration. Enor bars represent the 95% confidence internai (CI) of the means. The linear response range was determined as the range in which the linear regression line fitted to the points passes through each point's 95% confidence range. The minimum detection Iimit was defmd as the minimum concentration for which the mem signal (absorbance) is removed by pater thau four standard deviations from the mean background signai (Skoog and Leary, 1992). In order to tocate this point the signal to noise ratio for each concentration was calculated by,

where SN is the signal to noise ratio, A,, is the mean absorbance at 220 nm for samples containing a given concentration of PAH. a, is the standard deviation of the zero reading (i.e.the standard deviation of absorbance readings for pure HPLC grade methanol at 230

MI) ruid os is the standard deviarion of the absorbance reading. The smple absorbance vas caiculated as the difference between the rneasured absorbance at 220 nm and the zero absorbance as rneasured for each sample at a standard wavelength. From anaiysis of each compound's absorbance spectm it was determined that none of the compounds used in this research absorbed UV light in the wavelength range of 3 10-330 nm. Thus the zero absorbance level was determined by averaging the absorbance reading over this range. Setting a minimum SN ratio of 4 irnplies greater than 99.99% confidence in the observed reading (Skoog and Leary. 1992). It can be seen in Figure 2.1 that the minimum detection limit for naphthaiene was iess than 0.2 mg/L in methanoi sohtions. Cdibration standard solutions with lower naphthalene concentrations were created by volurnemc dilution of the standard stock solutions. These were aiso stored in brown glass botties at 5 "C. Caiibmtion solutions were replaced &er 8 CO 10 weeks to ensure that the concentrations would not change due to volatilization tosses. Before each set of measurements the UV spectrophotometer readings were calibnted with solutions containing 0.3 0.6. 1.O. 1.4 and 1.8 mg/L naphthaiene.

The same procedure was foIIowed for phenanthrene caiibrations. the results of which are presented in Figure 2.3. SpectraI anafysis showed that the absorbance peak most sensitive to phenanthene concentration was at 25 1 am and that the average absorbance between 3 10-330 nm provided an appropriate zero level. The linear absorbance range for phenanthrene in methanol solutions was determined to be between O and 5 rng/L. The minimum detectïon Iimit was assessed at O. 1 mg/t. A range of phcnanthrene cdibntion standard solutions with phenanthrene concentrations of 0.2. 1.0. 2.0.3.0 and 3.0 mg/L were created and stored in the smeway as the naphthaiene standard solutions: thse were used to calibnte the UV spectrophotometer before each set of phenanthrene so1uuon measurements. It is ive11 know that a shift in the absorbance spectrum of a compound can result when the compound is dissolved within a more or Iess hydrophobie environment (Lindmm md Wennerstrom, 1980: Pramaum and Pelizzeni. 1996: Rosen. 1989). Fur this reason. calibrations for naphthalene and phenanthrene were also carried out in sohions in which water comprised over 99% of the solvent. Aqueous naphthalene cdibration standards were created by diluting the stock naphthaiene in methanol solution with water. By dituting this solution Mer.aqueous naphthaiene standard solutions were created wÏth naphthdene concentrations of 0.2.0.6. 1 .O. f -4 ruid 1.8 mgL. Aqueous solutions containing 1 m-fi of phenanthrene were created by adding 2.5 ml of a t 00 mg/L phenanthrene in methanol solution to 240 ml of water in a 250 mi volumetric tlask. As the tlnd mixture wouId have a concentration close to the water solubility of phenanthrene in water at 25 OC. the water \vas heated to 40 "C pnor to the addition of the methmoi solution. in order to avoid precipitation. Mer miving, water was added to bring the total volume to 250 ml. From the I mfi aqueous phenanthrene solution. calibration standard solutions were created with phenanthrene concentrations of 0.05.0.1. 0.25.0.375.0.5.0.56 and 0.75 mg/L. Ai1 aqueous PAH caiibration standards contained less than I % methanol derdilution and thus the presence of methanol on these so iutions' absorbance spectra was considered negligibte. The caiibration results for aqueous solutions of naphthaiene and phenanthrene are presented in Figures 23 and 2.4. Cornparison of the naphthalene absorbance extinction coefficients between solutions in which methanol is the solvent and those in which water comprises greater than 99% of the solvent suggests that there is no si&icant dEerence between the NO. as both extinction coefficients fail within the other's 95% contidence range. As aii naphthalene aqueous equiiibrium concentrations. in systems contacted with NAPLs containhg naphthalene at mole hctions of at least 0.005. were _mater than 1 .j m@L. it was possible to dilute almost ail the sarnples to at least 80% methanol(l:5 dilution) before UV absorbance measurement. For this reason the naphthalene in methano1 solutions extinction coefficient was used for al1 subsequent naphthalene concentration measurements (Table 2.2). From Table 2.2 it can be seen that the extinction coeficients for the phenanthrene in water and phenanthrene in methanol caiibntions do not fail within each other's 95% confidence interval. For this reason al1 aqueous phenanthrene samples ûnalyzed by UV spectrophotometry were measured without dilution with methano1 using the phenanthrene in water extinction coet'ficient.

Table 2.2: Comparison of Naphthalene Extinction Coefficients in Methinol and Water (A = 220 nm) Solvent 95%CI Extinction 95% CI Detection Absorbance Lower Coefficient Upper Tail Limit Reading at Dewon Tail (L mg*' cm") (WlL) Limit Water 0.7049 0.7271 0.7493 0.2 0.14542 Methanol 0.7212 0.7339 0.7466 0.2 O. 14678

Table 2.3: Comparison of Phenanthrene Extinction Coefficientsin Methanol and Water (k= 251 nm) (solvent 1 95% CI Extinction 95% CI Dewon Absorbance 1 Lower Coefficient Upper Tai1 Limit Reading at Detection Tail (L mg*' cm") (mgw Limit Water 0.295 0.325 0.356 0.1 0.0326

A1thoug.h hexadecane is considered essentiaily water insoluble it has been no'ed that the presence of compounds such as benzene. toluene and xylene in the aqueous phase cm increase its aqueous phase solubiiity to 4.7 x 10 'molR. rnost likely hugh cosolvency-like effects (Thangamani and Shreve, 1994). Therefore, it was possible that hexadecane may have been present in the aqueous samptes in sulKcient quanaties to make it necessary to assess the effect of hexadecant on the absorbance of PAH soiutions, Smples were prepared by diluting NAPLs containing both hexadecane and naphthalene ttith methano1 untiI di the NAPL had dissolved, creating a one-phase solution (approximately 100 mg NAPL in 40 ml methmol). These solutions were then diluted furtfier in order to create sarnples covering a range of naphthalene and hexadecane concentrations chat could be andyzed by LJV absorbance. Figure 2.5 shows the ~Iationshipbetween naphthdene concentration and UV absorbance at 320 nm. Despite the variation in hexadecane concenarion hmO to about 2200 m@. the absorbmce vs. naphthalene concentration curve is closely fit by tinear regtession with a dope that tàlls within the naphthalene in methanot extinction coefficient's 95% confidence interval. -4 second plot is show (Figure 2.6) in which the absorbance hm been corrected t'or naphthrilene concenuation to correspond to a concentration of 1 m@L. The correction was based on evidence that the absorbance was a linear fùnction of concenmtion using the equrition.

where fcorr.~is the absorbance corrected to that expected from a 1 m@L naphthdene solution. A, is the absorbance as me&. ph,,is the naphthaiene concentration in the simple and 0.7065 is the inverse of the slope of the linear regession line fit to the data in Figure 2.5. The correlation coefficient between corrected absorbance and hexadecane concentration is 0.15 which suggests that the presence of hexadecane in the solutions has very little effect on the absorbance of naphhaiene solutions at 220 nrn. Men the mean corrected absorbance of samples with hexadecane concentraions less han 100 rnfl is compared to the mean corrected absorbance of simples with fiexadecane concentrations Fater than 100 mgk. it is concluded ttiat they are not - - - Naphthalene . Hexadecane Jnear(Naphthalene )

O 0.2 0.4 0.6 0.8 1 1.2 14 Absorbance (220 nm)

Figure 2.5: Naphthalene Absorbance in the Presence of Hexadecane (k= 220 nm)

l Hexadecane Concentration (mglL) Figure 2.6: Absorbance vs. Hexadecane Concentration [Comcted to c~~~~~~= 1 rn@l (A = 220 am)

significantly different based on the fact that they both faIl within the others 95% confidence intervai. This is strong evidence in favor of disregardmg the effect of hexadecane on the absorbance of PAH soIutions created hmcontact with hexadecane based NAPLs due to its Iow aqueous soIubiIity minimal absorbance over the birange. As this remit agrees with the literature (Howard and MeyIan, 1997) hexadecane concentration was not considered in the rneasurement of aqwous solutions. 2.2.5. Fluorescence Measurements

Due to the Iow queous solubility of phenanthrene. the concentration of phenanthrene present in solutions was ofien below the minimum detection lirnit for UV spectrophotometry. In these situations phenanthene concenmtions were measured by fluorescence using a Shimadzu RF-530 specwfiuorophotometet with a Kenon short arc Imp Light source and off-plane, concave diffraction grating monochromator emission detector. According to Van Durren (19601, the optimal conditions for phenanthrene concentration memurement in polar solvents is ro rneasure the sample's ernission at wavelengths around 360 nm when it is excited by a beam of tight with a wavelength of 250 nm. This was verified in this study by inspection of the emission spectra and excitation spectra for various phenanthrene solutions. When phenanthrene was excited by Iight with ri 250 nrn wavetength. two main peaks were observed. one at 342 nm and une at 364 m. OFthese. the peak at 364 nm was the most intense and provided the most sensitive response to phenanthrene concentration in methmot solutions. Calibntion solutions of phenanthrene in methanol were created according to the rnethods outlined above. Phenanthrene concentration was caiibrated with emission readings at 363 nm with an excitement beam slit width of t O mm and an emission detector slit width of IO mm at the low sensitivity setting. The results of the calibration are presented in Figure 2.7.

The ernission response to phenmthrene has been seen to change when phenanthrene is dissolved in different solvents (Van Durren. 1960). Low molecuiar weight alcohols have been identified as solvents that dIow for reasonably precise measurements of PAH concentrations by fluorescence (Van Durren. 1960)- Therefore methanol was used as the soivent for the caiibntion. However. the samples to be measured were aqueous solutions of phenanthrene. In order to overcome the discrepancy between emission readings in the two solvents, dl samples were diluted with methanol prior to rneasurement. The calibration coefficient - deked as the slope of the concentration vs. emission tine - for phenanthrene in methanol soIutions with 4% deionized distilIed water is presented in Table 2.4. Cornparison of the 95% CI of the 4% water extinction coefficient with the extinction coefficient of phenanthrene in a pure methanol solvent shows that the two are significantly different. Thus the aqueous phenanthrene solutions were diluted 15:1 with rnethanol and the extinction coefficient for phenanthrene in a 96% methanol and 4% water solvent extinction coefficient was used to convert the emission readings to concentrations. The linear response range for the fluorescence readiip was large enough such that no other dilution ratios were used. Sarnples which had phenanthrene concentrations high enough to warrant tùrther dilution were measured by W spectrophotometer. Table 2.1: Cornparison of Phenanthrene Fluorescence Calibrations in Methanol and Water, for Emissions Readings at 364 nm bolvent I 95% CI Calibration 95% CI Detection ~imitl I 1 Lower Tail Coefficient (mg/L) Upper Tail

96% Methanol. 0.112 0.1 15 0.119 I4% Water

hilethano1 4% Waîer -SIN (4% Water) - - Laear ( 4% Waterl imtear(Methanoil

O 0.01 0.02 0.03 O. 0.05 0.06 0.07 0.08 0.09 0.1 Phenanthrene ConeenWation (mgR)

Figure 2.7: Fluorescence Emission at 364 nm vs. Phenanthrene Concentration .Uer the maximum mole Fractions of naphthalene and phenanthme achievabk by completely dissolving the cornpouad in the NAPLs were determinecl a series of two- component NAPLs were synthesized for panitioning experiments. Naphthalene in hexridtxane NMLs were created ~ith~r"P~,~ranging hm 0.005 up to rt mole hction near .V"phr(nm,.Phenanthrene in he~adadecîaeNAPLs were created with .vh",ranging t'rom 0.0 I to a mole fraction near ,pn,(mm).To synthesize each NAPL. the arnount of PAH required to achieve a desired mole hction in approximately 100 ml of hexadecane ivas wveighed out and placed in a 250 ml brown glas bottle. The bottie was placed on a balance and the appropriate mass of hexadecane was added to reach the desired PAH mole hction, The actd PAH mok fraction in the NMLs fefI within 0.5% of the desired mole hction in al1 cases. The bottles were then sealed with closed-top polypropylene caps fitted with Tefion-lined silicon septa and placed on an orbitai shaker ruid agitated at 250 rpm for 73 hours. at which point no crystals remained. NMLs were stored in the dark at room temperature. To ensure that headspace losses would not be sipificant enough to result in reduction in the PAH moIe fraction. NAPLs were stored for a maximum of 12 weeks before use and were also replaced when less than 50 m1 rernained in a bonie. Equilibrium partitionhg of naphthalene and phenanthme between NAFLs and an aqueous phase (C'.,y)was studied by contacthg the MO-component NAPLs with water in a quasi-fully-rnixed batch qstern. Two ml of NAPL were contacted with 25 mI of water in 10 ml Pyrex EPA wals with polypropylene open-topped caps fitted with Tefl on-lined silicone septii, Equilibrium partitionhg was achieved by piacing the vials in an orbital shaker and qitating them at 175 rpm for 96 hours in a temperature controlled environment set to 25 "C. This quasi-completety-mixed system allowed for adquate mixing within both the aqueous phase and NAPL. with no visually observable emuisification of the NAPL over the entire period of contact. Evidence of this is presented below. PAH concentration in the aqueous bulk phase was measured by withdrawing 10 ml aliquots fiom the aqueous bulk phase with a 10 ml stainIess steel tipped glass plunger and banel syringe. Aliquots From the aqueoudcrystailine P.4H system were expressed through a 0.2 pm Teflon fiher attached to the syinge in order to remove any crystais that may have been suspended in the aqueous phe. Other researchers using similar NAPL-water volume ratios have found that at low agitation rates 48 to 73 hours is sufficient to achieve equilibrium partitioning of surtactant and NAPL components (Diailo et al.. i994; Mackay et al.. 1992; Zimmerman et al.. 1999). In order to test the assumpaon that 96 hours is sufficient for the NAPL-wliter and crystals-water systems used here COmach equilibriun. the concentration of naphthalene was assessed at a series of time intervals. Tirne-to-equilibrium experiments were conducted by creating a series olsystems in which 2 ml of NAPL with a naphthalene mole fraction of 0.17 were contacted with 25 ml of water for an extended period. At various times a via1 was removed EFom the shaker and an aliquot was immediately taken from the aqueous phase. after which the solution was sacrificed. The results are presented in Figure 2.8. It can be seen that derabout 5.8 hours the concentration of naphthaiene in the aqueous phase remained constant at 25-77 mg/L (k1.O%). It kvas therefore assurned that 96 hours was sufficient to reach equilibriurn conditions in al1 OF the NUL-water systems studied. For systems in which excess crysta1Iine PAi-is were contacted with water. a series of vials were prepared as mentioned above and the PAH concentration in the aqueous phase was measured afler 24.18.71.96 and 168 hours. The PAH concentration in the aqueous phase did not change significantly aiter 24 hours (Iess than 3%). Therefore 96 hours was considered adequate theto reach equitibrium in al1 crystais-water systems. The riqueous solubility of crydline naphthdene was assessed by contacting 1g of naphthalene with 25 mi of water. The aqueous solubility of naphthalene is most commonly reponed to be between 25.0 and 35.0 mg& (Mackay et al.. 1992: Peters et ai.. 1997: Schwmenbach et ai.. 1993: Yeom et al.. i991) and thus 1 g was Far in excess of the amount of naphthalene that couid be dissoived in 25 ml of water. CrystaIline phenanthrene partitionhg was assessed in systems containing 0.5 g of phenanthrene contacted with 25 ml of water. which is also in excess of the amount that can be solubilized, considering that phenanthme's aqueous sotubility at 25 OC is reported to be between 1.O and 1.6 mgiL (Edwards et al., 199 1: Grimberg et al.. 1994: Mackay et al.. 1992: Yeom et al.. 199 1 ). In ail cases there was excess crystailine PAH remaining in the vials at'ter equilibrium had ken obtained. In order to remove any emulsified NAPL. the aliquots taken from the aqueous phase in the vials were decanted uito LO ml Pyrex centrifuge tubes sealed with closed-top polypropylene caps lined with Teflon-Iined silicone septa and cennihged at 3600 rpm for 45 minutes to separate any emulsified NAPL from the bulk phase. In ail cases. the syringes. tilters and centrifuge tubes were rinsed with 3 ml of solution %om the aqueous bulk phase in order to avoid losses due to PAH sorption to the glrissware. Mer centrifugation the top 2 ml oFsolution was removed by pipette and disposed of. in order to avoid resuspension of any emulsified NAPL. Results of concentration measurements conhned that no ernulsified NAPL was present in the sarnples. It was verified that this rate and duration of centrifugation was sufficient to achieve an acceptable level of separation, In order to ensure that the NAPL PAH concentrations remained neariy constant throughout the contact period. mass balances were performed on the system. Also. to tnck PAH losses due to leakage. a series ofvials containing NAPL and water were prepared and the aqueous phase concentration was measured at various times over an éxtended period (up to 44 days). The amount of PAH lost From the NAPL to the aqueous phase and the headspace were calculated based on the aqueous phase concentration and Henry's law coefficients found in the literature. I O 5 10 15 20 25 30 35 40 45 Tirne (h)

Figure 2.8: Time to Equiiibrium Experimental Results for a NAPL-Wnter System Agitated at 175 rpm (xnnPh,= 0.17) 2.3. RESULTSAND DISCUSSION

2.3.1. Maximum NAPL PAH Mole Fractions and Aqueous Solubilities

The ma,.uimum mole fmction of each PMdissohable in hexadecane (A',(mrrr)) was determined in order to chose an appropriate range of PAH mole fiactions for partitionhg experiments. Knowledge of Al'i-(max) can also give insight into other phenomena. such as the et'fect of saturation of the NML with water on the PAH values and the eiktof hexadecane present in the queous phase on the solubility of the PAHs. Comparison behveen the aqueous concentration in water contacted with saturated NAPLs and in water contacted with crystals will indicate the [email protected] of these effects. Hildebrand and Scott (1964) state that the maximum mole fraction theoretically obtainable by dissolving a solid soIute in a pmnonaqueous solvent can be detemined by assuming that solute tiigacities in the solid and liquid phases are equal when they are in equilibrium. For a system in which pure solid PAH is in equilibrium with a liquid mixture the following equations apply.

and since in this casej" = f", .the toilowing relationship results,

Rearranging Equation 3.7 leads to Equation 2.4 as presented in Section 2.1.

.r,(mar) was esthated by both visual observation and by tracking the increase in C" ,- in the water contacted with the PAH mole fnction in PAH-hexadecane mixtures (.Y,,,). Table 2.5 includes the resuits of observations made regarding the presence of PAH precipitate in the rni~turesafter contact with the aqueous phase. The PAH-

hexadecane mivtures were heated to 60 OC. at which point al1 the crystals dissolved. The visual observations method entaüed estirnatingz.k{mm) as the maximum ,y,, NAPL

From which PAH did not precipitate upon coohg to 25 OC. From these observations .r"~',(mm)appearj to be between 0.21 and 0.23. and ~,,

Table 2.5: Visual Observations of PAH-Eexadecane Mixtures After Cooihg to 25 OC Naphthalene Precipitate Phenanthrene Precipitate Mole Fraction Mole Fraction 17 None 5 None 18 None 5.5 None 19 None 6 None 20 None 6.5 Small Crystafs 21 None 7 Srnall Crystals 23 Crystals formed in NAPL after 7.5 Small Crystals contact with water 25 Crystals 8 Small Crystals 27 Crystals 9 Small Crystals 30 Crystals 1O Larger Crystals which the NAPLs were saturated with the PAH in question. NAPLs taken from mixtures with higher than saturation PAH to hexadecane ratios would not have had increasing .k',\; due to the extraction and filtering of the NAPL prior to contact with water. Thus the constant values suggest that the NAPL mole hction was constant in these systems and .Y,(rnq can be taken as .,Id,, at the Fust point at which Gystops increasing, As the crystals were removed fiom the NAPLs pnor to contact with the aqueous phase and the NML PAH Iosses are assumed to be negligiblc in all cases, C.iQin water contacted with NAPLs taken from mixtures with 2, pater thmk",(mm) represents the c,,Qfor a systern in ivhich water is contacted with a PAH-saturated NAPL. From the graphs it was determined that the maximum naphthalene mole hction dissolvable in hexadecane is 0.19 and the maximum phenanthrene mole hction dissolvable in hexadecane it 0.065. Using these vaIues, dong with estirnates of the PM solid-liquid Cugacity ratios, it was possible to caicdate the PAH activity coeficient in the NAPL bmEquation 2.2 As can be seen from Table 2.6. the activity coetEcient of naphthalene in the NAPL is much lower than bat of phenanthene. This is Likeiy due to phenanthrene's Iarger molecular volume which would cause phenanthrene to disturb the hexadecane liquid structure more than naphthalene ('Hiidebrandand Scott. 1965). These activity coefficients are only valid for P AH-satunted hexdecane. The e ffect of changing PAH mole ti-actions on the NAPL activity cortlïcients is investigated in the next section.

30 ,

,rd,,- 4 w

C O z 20 .. 2

ai to.. E -ai 0.1 9

I O 0.05 0.1 0.15 0.2 0.25 (1.3 Naphthalene Mole Fncüon in Mixture

------Figure 2.9: Aqueous Phase Equilibrium Naphthalene Concentration vs. Naphthalene Mole Fraction in HexadecanefNaphthalene Miartnres Naphthalene Mole Fraction in Mixture

Figure 2.10: Aqueous Phase Equilibrium Phenanthrene Concentration vs. Phenanthrene Mole Fraction in Hexadecane/Phenantbreue Mixtures

Table 2.6: NAPL Component Properties from Experiments and Litcrahire

Compound C1m,t C'*~ur f'd~a! Xi,(max) in Actkity at 25 OC (mgll) at 25 OC (mglL) 25 OC Hexadecane Coefficient [reporteci] [rneasuw [measured) at xl,(max)

Hexadecane 0.0009 a nia - 1 Naphthalene 25.0-35.0 a 26.35 0.306 0.19 1.56 Phenanthene 1.O-1 -6 1.O4 0.279 0.065 4.04 I [' Howard and Meylan. 1997: Mackay et al. 1992: Peters et al.. 1997

There is an apparent contradiction between the maximum solubility of naphthaiene in hexadecane as determined by visud observations of the NAPL mixtures cornpared to the maximum naphthalene mole fraction obtained hmthe measurements, In Tabte 2.5. it is noted that no crystals were visible in either the 0.23 or

0.2 1 mole Fnction mivtures prior to their contact with water. After the 0.23 mole fraction NAPL rntunire had been contacteci with water. a visible naphthdene precipitate formed in the NAPL but stiU no crystals were visible in the 031 mole fiaction mixture. That the precipitation ofcrystais was observable in the 0.23 mole fiaction NAPL mixture is probably due to significant precipitation resulting hmsaturation of the NAPL with water. As naphthalene is considerably hydrophobic, this may cause the naphthalene activity coefficient to rise which in turn would lead to precipitation of some amount of naphthalene. That no crystals were visible in the 0.21 naphthalene mole fraction mixture is most likely due to the shortcomings of the visual observations. In past studies. it has ben noted that filtenng sarnples from systems containhg crystalline PAHs with a 0.1 pm Tetlon tilter was necessary to remove unseen minute crystals that may have been present (Grimberg et ai.. 1994). It is likely that pnor to contact with water the 0.21 and 0.23 naphthaiene mole Fnction mixtures contained crystals that were too small to be visible. The aqueous solubility of each PAH was determined by measwing c,Yin vials containing 25 ml of water contacted with an excess of PAH crystals. By these experiments the aqueous solubility of naphthalene was determined to be 26.35 mg/L. While most of the literature encountered in this work report naphthalene aqueous solubility values of79.0 to 32.0 mgL (Edward's et al.. 1991; Ko et ai., 1998: Peters et al.. 1997: Schwarzenbach et al.. 1993; Yeom et al.. 199 1). Mackay et ai. ( 1992) provide ii comprehensive list of naphthalene solubility rneasurements reported in studies over the last 30 years. Values in this list range from less than 3s' mgiL CO over 35 m&L. it is possible that the value presented in this research is lower than the true aqueous solubility as rigorous solubili~tests are typicaily canied out with extremely pure water and solutes with precise temperanue control over an extended period. In this crise the naphthalene received from the manufacturer was used without further purification and it is possible that there may have been trace arnounts of impurities in the distiIled and deionized water. Al though the contact period here was only four days, sarnpies contacted for 44 days showed no si-d~cantchange in c,4Qafter the initial 24 hours which niggests that equilibriurn was achieved in these systerns. Aiso. values obtained on seven separate occasions ti-iroughout the penod of the experiments were in close agreement with each other (+ 2.3%). In light of this and the solubility values presented by Mackay et ai.

( IW2)- 26.35 mgL. is considered to be an acceptable naphthalene solubility value, The measured aqueous solubility of phenanthrene was 1.O3 mg/L which is in chse agreement with the duespresented in the literabe ( Grimberg et al.. 1994: Mackay et al.. 1992: Schwartenbach et ai, 1993). Wïidebrand and Scott (1964) state that of two compounds the one with the higher melting temperature will tend to be less water soluble udess the substance with the lower melting temperature haa much higher heat of tusion, From Table 2.1 it cmbe seen that the meiting point of phenanthrene is higher than that of naphthalene and the heat of hion of naphthalene is higher than that of phenanthrene. This suggests &at it is reasonable to Fid that the aqueous solubility of phenanthrene is much lower than that of naphthalene. Thus. €rom this point the rneasured C' ,',, values will be used where aqueous solubility values are needed for caIculations. The 9joh CI for naphthalene and phenanthrene C,g,u,values are presented in Table 2.7. [t cm be seen hmFigures 2.9 and 2.10 that C,Qvalues in vials contacted with PAH saturated NULStaken hmPAH-hexadecane rni.mms are within the measured C',,Qm,95% CI for both naphthalene and phenmthrene. From this it cm be conduded that the presence of hexadecane in the aqueous phase did not significantly dTict C',4g,, values. Therefore it is reasonable to estimate NAPL activity coefficient values hmC ,y measurements.

Table 2.7: Equiiibrium Aqueous Phase PAH Concentrations For PAH Saturated NULS and Crystals Item Contacteci 95*h CI Limits ?AH with Watew cLp (mglL) Lower Upper Naphthalene Crystals (Measured) 26.35 25.56 27.14 Log KnaphN= 2-98 Saturated NAPL (Measured) 26.14 25.62 26.66 Saturated NAPL 25.57 24.81 26.34 (Predicted From KiN) Phenanthrene CrystaIs (Measured) 1.O3 0.97 1.O9 Log KPknN= 4.08 Saturateci NAPL (Measured) 1.O4 1.O0 1.O8 Saturated NAPL. 0.97 0.94 0.99 (Predicted From KIN) 2.3.2. Equilibrium Partitioning of PAHs Between NAPLs and Water

Partitioning experiments were carried out by contacting water with NAPLs in which the PMmole fraction were known apriori. However, as the PAH partitioned beween the NAPL. water and headspace. and giver, that there could have been Ieaks hmthe system. it was necessary to mess the PAH losses hmthe NAPL. With this information it was possibIe to accurately describe the partitioning of naphthalene and phenanthrene between hexadecane and water at varying PAH moie hctions. X series of NAFL-water systerns containing NAPLs with naphthalene mole hctions of 0.0 Il. 0.09 and 0.17 were created. Leakage losses from the seded batch systems were assessed by measuring the aqueous concentration of naphthaiene in water contacted with each of the NAPLs for 4.9.24 and 44 days. For the thesets of NAPL- wter systems. conesponding to the rhree ,PPhvvalues. the average correlation coet'ticient between aqueous PAH concentrations and tirne of contact was -0.25, with no one value being less than -0-35-This suggests chat the nqueous phase concentration was not chan& significantly with time over the 44 days. Considering that the -stems used in partitioning experirnents sat for oniy 4 days it \vas assumed that naphthdene leakage losses from the vials were negligible. As naphthdene is more volatile than phenanthrene and PAH leakrtge is expected to involve PAHs escaphg hmthe headspace around the cap. it was assumed that phenanthrene teakage was also negligibte. It ws assurned that hexadecane partitioning into the aqueow phase was minimal. due to its low water solubility. Ttius y, was only expected to change due IO PAH losses to the headspace and the aqueous phase. Using naphthalene's vapor pressure at 25 "C. as presented in Table 2.1. it was possibIe to estirnate the amount of naphthalene Iost hm the NAPL by volatilization into the approximately 13 mi of headspace in the contact vids. This amounted to about 7.3 1x10~mol, which is about O. 1% of the totd amount of naphthaiene in 2 ml of a NML wiih a naphthaiene mole fraction of 0.01. it is assurned that there was no sigdïcmt pressure buiId-up in the vials. thus 0.1% represents the maximum amount of naphthaiene Iost to the head space in the system as the vitpor pressure miII onLy be achieved in systems containing crystals or a naphthdene saturated NAPL. The naphhalene mole fiaction in the NAPL was estiniated to decrease by less than 0.5% due to partitioning into the aqueous bulk phase based on the partitioning coefficient obtained hmthe results of partitionhg experiments presented below. Table AI of the Appendk shows the measured and estimated PAH losses at dierent ,V, for both naphthaiene and phenanthrene. For NAPLs containine naphthalene. losses never exceed 0.5% and for NAPLs containing phenanthrene lusses were always less than O.?O/o. It was therefore assumed that NML PAH losses were negligible and that PAH mole fractions in the NAPLs rernained constant throughout the partitioning experiments. NAPL-water partitionhg experiments were done with two-component NAPLs containing a wide range of naphthalene and phenanthrene mole hctions. Five standard .Y', for each PMwere specified for al1 MerNAPL-water partitioning test. These are shown as the mole t'nction values in bold in Tables 2.8 and 2.9. The results of a series of partitioning experiments. with synthesized two-component NAPLs are presented in Table 3.8 ruid 2.9. In Figures 2.1 1 and 7.12 the partitioning data is presented graphically dong with the lines representing the linear regression curve fit to the data. The error bars in these figures represent the precision of the C',,c!measurements as quantified by the standard mor of the mean memments rit each .y,,,. It can be sen that in both tigures the linear regression line fdls within the crror bars for the mean C',40vaLues at ,r,and that the coetficient of detemination values for both is greater than 0.99. This suggests that both trends have a linear relation. Examinauon of Equation 2.2 indicates that if the activity coefficients of the PAHs in the NAPL were changing as a function of the PAH mole fiaction. the b,Qvs. %, curve would not be a straight line as both d,Q.,and Cfid/lr) are constants. Therefore. the goodness of the straight line fit to the cQvs, 3, curves is evidence that the activity coefficients of the PAHs in question are constant ovrr the range of NAPL mole ffactions considered. Tables 2.8 and 2.9 provide NAPL PAEi acxivity coefficients based on the experimental data calcuiated using Equation 2.2. WhiIe there is a degree of variation in these values there is no apparent trend in activity coefficients with increasing NAPL PAH mole hctions. The activity coefficients obtained hmthe T-b(mm)determination experiments presented above are within the 95% CI of the average y', values obtained from unsaturated NAPLs. This provides Mer support for the validity of the assurnptions that the presence of water in the NAFL does not effect the PAH activity

Table 2.8: Naphthalene NAPGWater Partitionhg Data with Statistical Parameters na n Mean Number of Standard Mean Y P~ Mole Fraction Equilibrium Measurements Deviation N 95%CI in NAPL cmPhAa (moUL) (+ % Mean)

Crystals

1 Calwlated yPh,from linear M (figure 2.1 1) 1.56 -

Table 2.9: Phenanthrene NAPL-Water Partitiooing Data with Statistical Parameters nan Phenanthrene Mean Number of Standard Mean N Mole Fraction Equilibrium Measurements Deviation yPh'nN 95% CI in NAPL cph.n AQ (mou (I % Mean)

0.04 3.26E-06 7 2.38E-07 3.95 2.55 0.05 4.25E-06 6 5.51 E-07 4.13 5.55 Crystals 5.75E-06 5 6.07E-07 - 5.87 m versa7.60 Calculated .phenNfnm linear fit (Figure 212) 4.04 - coefficients and that the hexadecane in the aqueous phase does not change affect the PAH aqueous solubilities. Given this. a NAPL-water partitionhg coefficient (Kv)was detined for each of the PAHs according to Equation 2.3.

O 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Naphtalene Mole Fraction in NAPL

Figure 2.1 1: Equilibrium Aqueous Phase Naphthalene Concentration vs. NAPL Naphthalene Mole Fraction

O 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Phenanthmne Mole Fmtion in NAFL

Figure 2.12: Equilibriam Aqueous Pbase Phenanthrene Concentration vs. NAPL Phenanthrene Mole Fraction NAPL-water partitioning coefficients, calculated as the inverse of the linear tegression line's slope fitted to Gyvs. & data in Figures 2.1 1 and 2.12. are presented in Table 2.7 dong with measured C',,p values in water contacted with saturated NAPLs and in water contacted with PAH crystds. A1so shown is the predicted C',Q value in a saturated NAPL-water system. calculated by dividing the saturation PAH mole fnctions - 0.19 and 0.065 for naphthaiene and phenanthrene. respectively- by the appropriate partition coefficient values. It can be seen that d,,Qvalues in water contacted with saturated NAPLs determined by measurements and by prediction using K', values are in close agreement with d.,g, as they all Mt within the 95% CI for the mean C',,,,- value measured in PAH crysd-water systems. This suggests that the K',values are adequate in describing the partitioning of the two PAHs studied into water from a saturated binq NAPL containing hexadecane over the entire range of naphthalene and phenanthrene mole ti-actions of interest. As values are constant and pater than unity for both naphthalene and phenanthrene in hexadecane over a wide range of y. it can be concluded that the distribution of PAHs between hexadecane and water follows ideal partitioning according ro Henry's latv. That yfv values were greater than one implies that the PAHs were in ri solvent that was less amicable than their own pure Iiquid. That y',values remain constant suggests that interactions between the PAH molecules in hexadecane are not signiticant over the range of mole fractions of interest. This is likely due to the fact that the PAHs have a lower rnolecular volume than hexadecane and thus occupy Iess space in solution. It has been found that in many cases PAHs partition ideally according to Raoult's law from real-world NAPLs. Peters and Luthy (1993) and Lee et al. (1992b) found rhat the partitioning of PAHs hmcoal tar into water followed Raoult's law. Lee et ai.

( 1992a) found that Raoult's law dso accmtely modeled partitioning of PAHs between diesel hel and water. Cheet aI. (1991) found that Raoult's law also described partitioning between NAPLs and water for NAPLs with Iow PAH concentrations such as gasoline. Other studies with complex synthesized NAPLs containing significant arnounts of PAHs (Le. 1 to 60%) has shown that PMpartitionhg foliowed Raoult's law (Chiou and Schmedding. 1982: Lane and Loehr. 1992: Mukheji et al,. 1997: Peters et al.. 1993.

Lane and Loehr ( 1995) even showed that Raoult's Law partitioning occurs in complex NML-water -stems that contain soil. Ghoshd at al. (1996) bund that y"pk, values varied between 2.98 and 1.97 in heptamethylnoaane NAPLs with phvvarying between 0.002 and 0.07. Heptmethylnonane is an alkane with a significant de- of branching and thus the changing -(""phv vaiues were likely the result of its rnoleculat volume. which is smaller than that of hexadecane. Overall. the results here dong with those presented in the literature suggest that ideal partitioning occurs between high PMmole fraction NAPLs and water in the subsurtàce. As naphthaiene and phenanthrene both exhibit ideal partitioning behavior in hexadecane, according to Henry's law. these NAPLs are usehl in modeling the partitioning of PAHs kom NAPLs such as coal tar and diesel hel which contain similar hctions of P.4i-i and dkanes. From the equilibrium aqueous phase concentration data. it crui be concluded that the maximum naphthaiene and phenanthrene mole fractions dissolvable in hexadecane are 0.19 and 0.065. respectively. It appears that the limiting value in a satunted NAPL-water system corresponds closely to that of a P.4H crystai-water system. The aqueous solubilities of naphthalene and phenanthrene were found to be 26-35 mg/L and 1.04 mgL. respectively. These vaiues correspond to the values found in the literature. and thus it is concluded that equilibrium was achieved in the systems studied. Equilibrium partitioning of PAHs between hexadecane and water followed Henry's law predictions closely. Naphthalene's activity coefficient in the NAPL was constant at 1.53 over the range of NAPL mole fnctions studied (0.0 1 to 0.1 T) and phenanthrene's activity coetlicient was constant at 1.12 for NAPL mole fiactions ranging tiom 0.01 to 0.05. Thus. NAPL-water partitioning coetl'icients were defined which were cible to describe the partitioning of PAHs in a NAPL water system over a wide range of.\',. including those çorresponding to PAHs saturated NAPLs. 3. Effect of NAPL PAH Mole Fraction on the Solubilization Capacity of Surfactant Solutions

3.1. Introduction

The equilibriurn partitioning of PAHs bctween NAPLs and surfactant solutions dictates the maximum amount of PMthat rnay be removed hma NAPL when it is cûntacted with surîàcta.solutions. The partitioning will also provide an important parameter for the determination of the rates of dissolution under non-equilibrium conditions. Thus it is necessary to determine the partitioning parameters of PAHs between NAPLs and surfactant solutions. Measurements of the molar solubilization ratio (MSR)and the micelIe-water partitioning coefficient are required to a obtain quantitative description of partitioning. 1t has been show that in surfactant solutions the me equiIibrium aqueous phase concentration of a compound affects its concentration in surfactant micelles (Anderson, 1992: Dunaway et al.. 1995: Edwards et ai.. 1991: Jaftert et al.. 1994: Tucker. 1995: Yoem et al.. 1991). Thus it is hypothesized that where dactant soiutions are contacted with NAPLs. the MSR wiIl aIso be affécted by the NAPL PAH mole hctions. Changes in the MSR and rate of dissolution are particularly relevant to the rnodeling of surfactant- aided dissolution ofP.4Hs from multi-component NMLs in the environment since the PAH mole tiaction in the NAPL will decrease over time with continuous dissolution and subsequent ceaction.

When contacted with aqueous surfactant solutions containing micelles. PAHs partition fiom NMLs into both the aqueous pseudo-phase and the miceUar pseudo-phase. The rniceI1a.r core is comprised of the hydrophobie tails and thus may be modeled as a drop of liquid hydmcarbon (Hiemem. et ai.. 1986: Pramauro and Peüzzetti. 1996: Rosen, 1989) that is smiuitaneously in equilibrium with both the NAPL and the aqueous pseudo-phase. It is expected that the queous pseudo-phase PAH concentration wiil correspond clorely to the aqueous phase concentration in a NAPL-water system. Assuming that the increase in aqueous pseudo-phase PAH concentration due ta PAU association with surfactant monomers is negiigibie. partitioning between the NAPL and the aqueous pseudo-phase cm be modeled according to liquid-liquid equilibriurn theory (Linciman md Wennerstrom. 1980). If the same assumptions regarding the partitioning of PAUs in a NAPL-water systern made in Chapter 2 are applied to NAPL- aqueous pseudo-phase partitioning, then the aqueous pseudo-phase PAH concentration

(c",.,~)cm be estimated by:

CL,,Q= Kix Xiv (2.3)

where .V\, is the PAH mole fraction in the NAPL and K',, is the NAPL-water partitioning coetlïcient. as described in Chapter 2. In this case CIlQ represents the PAU concentrarion in the aqueous pseudo-phase only. whereas represents the PAH concenmtion in the aqueous bulk-phase. ïhere is a general consensus in the literature that it is reasonable to assume that the partitioning of mmatic compounds into the micetlac pseudo-phase cm be modeled according to liquid-liquid equilibrium theory (Grirnberg et al., 1994: Hiernenz et ai.. 1986: Lindrnan and Wennerstrom. 1980; Rosen. 1989). If the solubiIization of PAHs tollows ided Henry's law partitioning, wherein the partial pressure (pi)of a substance is a linear tünction of the concentration ofthat substance in the Liquid phase (Hildebrand and Scott. 1964). then the following relationship holds:

pL= ktfrCLj (3.1 )

where k':', is the Henry's law coefficient and dJisthe concentration of compound i in phase J. At equilibrium. the fugacity of compound i is equal in each phase and, provided that the gaseous phase is ideal. the fugacity is approximateiy quai to the parhl pressure of that compound above the solution (Reid, 1990). Equating the aqueous and micellar pseudo-phase fugacities at equilibriurn Ifdbfandf,q) leads to the foollowing relationships:

f sr = f ..IO (3-2) where C,,,is the rniceilar pseudo-phase concentration, as defined in Chapter 1. and kt,, and kt,,oare the micellar and aqueous pseudo-phase Henry's law coefficients. respectively. From this a micellar partitioning coefficient can be defined as the ratio of the compouncïs aqueous md micettar pseudo-phase Henry's law coettïcients:

The Henry's law coefficient in each phase has physical sipniIicance in that it is equivalent to the Raoult's law convention activity coeficient of the compound at infinite dilution (Hildebrand and Scott. 1964). Henry's Iaw coefficients have been reported in the Iiterature for PAHs in water but not for PAHs in micellar hydrocarbons. Here it will be assumed that k',, and remain constant over the same range of surfactant and PAH concentrations that K',, remains constant. By substituting Equation 3.6 into 3.5 it cmbe shown that the micellar pseudo- phase PACI concentration is a Iinear tùnction of the PAH mole Fraction in the NAPL.

Sincr the micellar core is a liquid phase made up of the surfactant's hydrophobic rails. it is reasonable to assume that the miceIlas volume is a Cunction of the surfactant concentration. It has been suggested that PAH partitioning into the micelle's outer Iayers may etktthe core size by lowering the core water interfacial tension (Guha et al.. I998a). However. Nagarajan et ai. (1984) show that the decrease in the free energy of micellization attributable to the solubilization of aromatic compounds into a micelie's outer layers is offset by an increase in fke energy associated with bringing the hydrophobic aromatic compounds into a closer proximity to water than would be the case if it was solubilized into the core. Thus. they show that the solubiliition of PAHs in the micellar sheII has no affect on K',, Therefore, it is reasonabie to assurne that the micellar volume is not appteciabiy affected by the solubilization of PAH molecules.

Mukejee ( 1979) developed a two-state model to simpIifi the partitionhg of solutes mithin micelles. The two sites within the micelle referred to by this model are the hydrophobic core and the hydrophilic sheU. As was stated in Chapter 1, the hydrophobic tails have significant freedom of motion and thus the core is considered to be in a liquid Iike state. Whereas the hydrophiiic heads are in a bound state in the micelle shell. This was the rationale behind the definition of the two-state model, whereby the incorporation of a solute in the core cm be modeIed as absorption into a liquid. while solubilization into the shell is considered an adsorption process. This concept will be investigated tùrther in Chapter 4. where the competition between PAHs for micellar space is considered. It is well documented that a compound's degree of hydrophobicity will affect the extent of its solubilization in the various regions within a micelle (Lindman and Wennerstrom. 1980; Pramauro and Pelizzetti. 1996: Rosen 1989). Saturated long chain alkanes are extremeIy non-polar (Schwarzenbach et al.. 1990) and tiom this it can deduced that. according to the two state partitioning model. hexadecane will partition entirely into the hydrophobic core. -4romatic compounds have a slightIy polar nature (Pramauro and Pelizzetti. 1996) and may partition to some extent in both the micelle's core and shelI regions. It is usefui to consider the hydrophobicity of naphthalene and phenanthrene when comparing their relative solubilities in surtàctant solutions. From Table 3.1. it cm be seen that naphthalene ha a lower K,, han phenanthrene. It dso has a lower water solubili~and hexadecane-water partitioning coefficient than phenanthrene. From these observations it cm be conciuded that naphthalene is less hydrophobic than phenzinthrene. Therefore. it will partition to a greater extent into the micelles' outer shell than will phenanthrene. according to the two state-model. Grimberp et al. ( 1994) defined the following relationships to describe the concentration of solute within the miceilar pseudo-phase (d,\,)and the micellar pseudo- phase volume. which were used successfuliy to predict the partitioning of phenanthrene in nonionic surtictant solutions.

V, = B(C'"*~,~SMC) where V,, is the total rnicellar pseudo-phase volume in an aqueous solution with a aven s~rfactantconcenmtion (Y!.@) and B is a constant that relates the nwnber of moles of surfactant in rnicellar pseudo-phase to the rnicellar volume. B is a lumped parameter which accounts for the micelle's core and shell volumes. the aggregation number and the micelle shape in a given surfactant solution. From Equations 3.5.3.6 and 3.7 it can be deduced that for systems in which a rnicellar pseudo-phase is in equilibrium with a NAPL containing a certain mole fraction of PAH. C',, is constant at dl surfactant concentrations in excess of the CMC. It is also evident From these equations that the micellar concentration of a given compound is a weighted average of its concentration in al1 the reg ions within the micelle. Detining the MSR as the ratio of the number of moles of PAH solubiiized withui the micelles to the number of moles of surfactant compnsing the micelles and substituting using Equations 2.6 and 3.7 it cm be seen that the MSR is a function of the micellar phase PMconcentration:

MSR = niSt/ nswk, = ciS,B(C'~*.\~-CMC) / V,(C~~*:.,~ -CMC)I = ci, B 1v,~ (3.8) where nt",, is the number of moles of surfactant in the rnicellar pseudo-phase and C>Q is the volume of the aqueous pseudo-phase. Substituthg for C',, using Equation 3 .S and crouping the constants. the MSR can be expressed as a linear function of .Y ,: b

where K' is the NAPL-micellar pseudo-phase partitionhg coeficient. in suff~cientlydilute systems that obey Henry's law at dl sohte concentrations up to saturation. the micellar pseudo-phase activity coefficient can be caiculated by (Dunaway et ai.. 1995).

As in Chapters 1 and 2, the solid-iiquid fugacity ratio CfJ5/fJdis inctuded to correct for the fact that phenanthrene and naphthdene are both soIids in their pure form at the system temperature. Changes in the micellar PAH activity coefficient (y' 3 with the PAH micellar mole hction (YCI)indicate changes in the micellar environment surrounding solubilized PAH molecules (Tucker. 1995). An increase in the micellar activil coetlkient can bt interpreted as the average micellar environment experienced by the PAH becoming less favorable for solubilization. whiIe a decrease in the activity coefficient refiects an increase in the affînity of the PAH for the miceIlar enviroment. (Dunaway et al.. 1995: Tucker. 1995). To mess the validity of Equation 3.9, solutions of t'ive non-ionic swtàctants were contacted with a synthesized two-component NAPL compnsed of either naphthalene or phenanthsene dissolved in hexadecane. Deviation of the results &om this linear relationship - evident from significant changes in the micellar phase PAH activil coetricients - would implicate the ideal Henry's law partitioning assurnption as being inappropriate. This may result hmsubstantial PAH solubilization at locations other than the micelle core. changes in the micellar structure or size. or the failure of the hydrophobic core to behave Iike an ideai liquid solution. Some deviations fiom the ideal partitioning behavior discussed above ma? occur due to changes in the extra-micellar environment. For example. surfactants are known to partition into the NAPL upon contact (Rosen. 1989: Zimrnerman et ai.. 1999). The presence of surfactant molecules in the NAPL rnay alter the PAH activity which wouid attect PAH partiuoning between the NAPL and the micelIes. As explained in Chapter 1. at aqueous surfactant concentrations above the CMC. the sdactant concentration in the NAPL will remain constant (Zimmerman et al.. 1999). If the apparent CMC is detined as the minimum amount of surfactant that an aqueous solution must be charged with that will result in the formation of micelles, then it is evident that the apparent CMC wili be elevated in systems where surfactant partitioning into a NAPL occurs. Because more hydrophobic surfactants (Le. those with lower HLBs) are expected to partition into the NAPL to the greatest extent (Rosen. 1989; Zimmerman et ai., 1999), the increase in the apparent Chic for surfactants with low HLBs (between 9 and 12) wilI be higher than the increase observed for surtàctants with higher HLBs. Evduation of the apparent CMC and the MSR is key to developing an understanding of the partitioning of PAHs in a three-phase system. ïhe apparent CMC can be determined by assessing the minimum aqueous surfactant concentïation that results in a significant rise in the solubility of PAH. The MSR cm be assessed as the dope of the C,,vs. line in solutions with C?<4p -ter that the CMC. Once the apparent CMC is determined. assessing the changes in Cc'4Owith ~5~~at rub-CMC values cm give an indication of the eEect of changes in the NAPL-aqueous pseudo-phase partitioning caused by the presence of surfactant monomers in both phases.

It has been suggested that solubilization methods are not generaily appropriate for determining the true CMC for a given sirrfactant in solution (Linciman and Weniierstrom. 1980). However. this technique is appropriate in this case as it is necessary to determine the et'téct of surfactant partitioning and micellar solubilization of PMon the apparent CMC in ordcr to accurateiy describe the partitioning of PAHs between NAPLs and surfactant solutions. The CMC cmdso be caised by the addition of a Class It materiai such as methmoi. As is discussed in Chapter 1. Claçs II materials alter the nature of the so1vent which ritTects its interaction with the surfactant monomers in solution. Micelles present in solutions may cause quenching of W Iight (Grimberg et al.. 1994) and thus interfere with absorbance measurements by W spectrophotometry or fluorescence measurement. Also. the absorbance specen olPAHs solubilized within micelles may be altered due to the effect of the hydrophobic environment within the micelte (Lindman and We~erstrom,1980). The dilution of samples to surfactant concentrations below the CMC pnor to andysis will eliminate this probIem. However. in solutions with low PAH concentntions relative to the surfactant concentration, such as those contacted witti low .y, NAPLs. dilution with -ter to surfactant concentrations below the CMC often lowers the PAH concentration below the minimum detection iimit by UV spectrophotometry. Methmol was rested for its ability to raise the CMC of the surfactants used so that micelles codd be removed hmthe sampIes with Iess dilution than would be required when ushg water as the diluent. It has been stated that the presence of micetks in samples subject to spectral anaiysis may interfere with the measurement of solute concentrations. For this reason it is desinble to eliminate micelles from samples prior to anaiysis. The hst objective of the experiments presented in this Chapter is to determine the effect of methanol dilution on the CMCs of the tive nonionic surfactants. From this it can be determined if methanol dilution is able to diminate micelles hom sampIes without lowenng the PAH concentrations to levels below the detection limits of the analysis apparatus. The second set of experiments are aimed at determinhg the extent of surtàctant partitioning in to the NAPL phase in the experimentai systems. With this information it is possible to determine the effect of surfactant monomers on the partitioning of P.4Hs between the NAPL and the aqueous pseudo-phase. Finaily the effect of variations in NAPL PAH mole frriction on the MSR in systems in which synthesized hvo-component NAFLs are contacted with nonionic surfactant solutions are determined, Attempts are made to determine the primary factors which affect the soIubiIization capacity of surfactant solution for a PAH compound. The ability of the theoretical mode1 presented in Section 3.1.1 to predict the extent of PAH solubilization in surfactant solutions contacted with multi-component NAPLs containing PAHs is evaiuated. 3.2. Materials and Methods

Five non-ionic surtàctants were used in this study. The surfactants Brij 35 (polyoxyethylene [23] lauryl ether). Brij 30 (polyoxyeihylene [4] Iauryl ether). Tergitol NP 10 (nonylphenolethoxylate), Tween 80 (PolyoxyehtyIene-sorbitanmonolate).Triton X-IO0 (t-octylphenoxypo~yethoxyethaol)were ail purchased fiom Sigma Chemical Company (St. Louis. MO). AI[ surfactants are Iiquids at ambient tempentures except Brij 35 which is a solid. The industrial surfactants are al1 mixtures containhg molecules comprised of the same functionai groups with mean molecular weights as specified in Table 3.1. Surîàctants were used without Merpurification.

Table 3.1: Surfactant Characteristics and Aqueous Solutions Surfactant Formula Molecular HL8 Repo-d Reported Maximum Weight CMC Aggregatio c""",~Studied (gimol) (moUL) n Number (moliL)

Brij-30 a c12E4 363 9.7 2.OE-05 NIA 0.0040 Brij 35 C12E23 1198 16.9 9.2E-05 40 0.0046 Tergitol NP1O a C9PElo 5 683 13.6 5.OE-05 NIA 0.0025 Triton X-100 C8PE9.5 625 13.5 7.70E-04 100-1 55 0.0102 Tween 80 C18S6E20 1310 15 1.2E-05 58 0.0024

Sources: a Edwards et ai.. 199 1: Yeom et al.. 199 1

Standard &actant solutions were made by nwing a known weight of surfactant into

1O00 ml of water. The surfactant concentrations În the standards were between 5- 10 times the maximum surfactant concentration used in the MSR experiments for each surfactant. The sarnples were mixed with a Teflon-coated stirring bead on a magnetic stirrer for 24 hours at whkh tirne visual inspection suggested that al1 the surfactant had dissolved into the water. The standard solutions were msferred into 1 L brown glass bottles sealed with closed-topped polypropylene caps fitted with Teflon septa, The bottles were rinsed with 50 ml of the standard solutions prior to tramferring the solution in order to reduce surfactant losses due to sorption to the glassware. Al1 standard surfactant solutions were stored at 5 "C in the dark except for the Brij 30 solution which appeared to approach its cloud point at 5 "C, becoming a viscous heterogeneous mixture. and was thus stored at ambient temperatures in the dark. All glassware was washed according to the protocol outlined in Chapter 3. In al1 cases. distilled deionized water vas used in preparing solutions and for dilutions where warer is specified as the diluent. Diiute surfactant solutions. ranging in concentration from well below the litennue reported CMC values to the limits specified in Table 3.1 were created by volumetric dilution of the standard solutions. Dilution was done according to the methods outlined in Chapter 3. Solutions were stored for a maximum of one week at ambient tempemures in the dark. Stored solutions were mixed with a Teflon-coated stining bead and magnetic stirrer for 5-1 0 minutes before use. Two-component NAPLs containing naphthalene or phenanthrene dissolved in hexadecane were synthesized according to the methods presented in Chapter 2. All partitioning experiments were camied out using NAPL-surfactant solution systems containing 15 ml of surfactant solution contacted with 2 ml of NAPL. These were created in the same way as the NAPL-water systems in Chapter 2. Care was taken when handling the vials in order to minirnize emulsification of the NAPL. Crystalline PAH- surfactant solution systems were created in the sarne way as the crystalline PAH-water systems in Chapter 2. For each surfactant a senes of NAPL-solution systems with varied surfactant concentrations was created and agitated in the orbital shaker at 150 rpm for 96 hours. in a 25 "C temperature controlled environment At this rate of agitation the NAPL did not break into droplets, and it was assumed that both the NAPL and aqueous phases were coinpIetely rnixed over the time period considered. This assumption was based on the hct that no significant variations in PAH concentration were noticed by sampling at different locations within the aqueous bulk-phase. A series of vials was prepared in order to assess the theneeded for the NAPL- surfactant solution system to reach equilibrium. The effect ~Inaphthaienemole ti-action in the NAPL (,rphV)and the aqueous bulk-phase surfactant concentration (cy)on die time needed to reach equilibrium was investigated by contacting surfactant solutions of various L"?,~ with a series of NAPLs containing a range of .pPhv.At 24 hour intervals one viai from each set was sacrificed and the aqueous buik-phase was analyzed for its PM concentration. €rom these experiments, it was confirmed that 96 hours agitation at 150 rpm was sutxcient to achieve equilibrium in ail cases. These conditions were chus used for dl subsequent partitioning experiments.

3.2.3. MSR AND CMC DETERMINATIONEXPERIMENTS

Figure 3.1 shows the relationship between the aqueous bulk-phase naphthalene concentration and the surfactant concentration in solutions contacted with a NAPL containing a naphthalene mole tiaction of 0.01. This figure illusates the method used to determine the MSR and CMC for a given surfactant when present in solutions contacted rith a NAPL with a specific =y.,. The apparent CMC was assessed as the c*,~ at the point of intlection dong the Cmrvs. Cieline where dmTwas seen to begin to incrwse linearly with increasing cyThe MSR is assessed as the dope of the lineuly incresinç CIMT VS. L~''':,~curve at points above the CMC, The CMC and blSR values were detennined by masuring the CToTin a of senes vials in which NAFLs were contacted with surtictant solutions (see Table 3.1) ranging in surfactant concentrations from 0.01 to as much as 200 times the literature reported CMC values for each surfactant. For al1 surfactant NAPL combinations at least three points were used to fit the MSR line. halysis of the aqueous buik-phase for Cm7-was done according to the methods described below. Sirnilar systems were used to determine the MSR and CMC for surtàctant sotutions contcicted with pure PAH crystais. except that the 2 ml of NAPL was replaced with an excess of PAH crystais in each case. Figure 3.1: M.CMAp in Brij 35 Solutions Contaeted with A Two-Component NAPL = 0.01)

From vials containing surfactant solutions. aliquots of the aqueous bulk-phase were taken and centrihged prior to anaiysis according to the methods outlined in Chapter 1. The total PAH concentration in the dTorwas measured by UV spectrophotometry and tluorescence ernission according to the methods in Chapter 2. except for the cases where the surfactants showed significant absorbante at the waveiengths of interest. or where micelles were present in the sampie. Since the CMC is expected to be significantly increased by the addition of a short chah alcohol due to Class 11 interactions between surfactants and aicohols (Rosen. 1 989). the efect of methanol dilution on the CMC was studied. A senes of vials were prepared containing 3 g of naphthaiene cryds with 25 ml of Triton X-100 solutions containing up to 300 times the CMC concentration in water. Two sets of vials were tested. one in which the solvent was comprised of 50% methano1 and 50% water (vh) and one in which the solvent was comprised of 75% methanol and 25% water (vlv). A third set of vials were prepared in which 3 g of cqstalline naphthaiene was contacted with each of the other four sirrfxtants in a 75% methanol35% water (vh) solution. In these systerns the surfiictant solutions were created by diluting aqueous solutions of known surfactant concentrations with methano1 at a 3 :1 ratio (v/v). In dl cases the viais were agitated at 200 rpm on an orbitai shaker for 96 hours in a temperanire controlled environment set to 25 "C. The methanol-water phase was sampled. filtered and anaiyzed for its naphthdene concentration accordhg to the methods presented in Chapter 2. The CMC in the methanol--ter solution was taken as the intlection point at which the c"~~,,,,vs. r"I, curve (which is similar to the C"Ph,,,VS. cdUrfIQcme in Figure 3.1) showed a dnmatic increase with increasing surfactant concentration. The results of these experiments are presented in Section 3.3.1. It was round that for ail surt'actants. the CMC was increased in the 75% methanol solutions to a level above the m~~imurnsurfactant concentration ever present in the diiuted sarnples analyzed in this work, Therefore. swfactant solutions were diiuted at Im 4: 1 (vlv) with methanol prior to rneasurement by UV spectrophotomeuy. This was assumed to elirninate any micelles from the solutions being anaiyzed. Thus PAH concentration meaçurement in surfactant solutions by UV absorbance anaiysis was conducted using the PM-in-methanol solutions extinction coefficients as presented in Chapter 2. As the presence of micelles cm dso effect fluorescence emission readings (Lindman and Wennermom. 1980). ail surfactant solutions being anaiyzed by tluorescence were tirst diluted 25: I (vlv) with methmol. The 96% methanol. 4% water calibration coetEcient developed in Chapter 2 was used for ai1 subsequent measurements. In some cases the surfactants thernselves absorb significant amounts of LW Iight at the wavelengths of interest for PAH concentration anaiysis. Tween 80. Tergitol NP10 and Triton X-100 ail absorb significaut amounts of light in relation to the absorbance to naphthalene at 220 nm. Tween 80 also absorbeci signiticant amounts of light at 25 1 m. the absorbance wavelength used for phenanthrene concentration rneasurement. Tergitol NP IO and Triton X-100 were not andyzed for their absorbance at 251 nm as they were not used with phenanthrene. Brij 35 and Brij 30 showed no significant absorbance at either 220 nrn or 25 1 nm within the concentration range. snrdied. UV absorbance is an additive phenornenon for solutions in which quenchine does not occur (Ingle and Crouch. 1988). Quenching was assudto be negligibie within the linear response ranges of both the PAHs and surfactants. Thus the e.utinction coetXcient and linear response range for each surfactant were determined at 220 nm and 25 1 nrn according to the procedure outheci in Chapter 2. The surfiactant extinction coefficients presented in Table 3.7 were determined using solutions diluted to at lem 80% methanol in order to ensure that no micelles were present. It was assumed that the surfacmt extinction coefficients did not change significantly in solutions containing higher quruitities of methanol. When analyzing samples containing one of the three UV absorbing surtàctants. the sample was diluted to a level at which the absorbance reading Fe11 within both the surt'actant's and the PrVI's linear response range. As the decrease in the swfactant's LW absorbance conmbution due to surfactant partitioning into the NAPL was not e~pectedto be signiflcant relative to the total concentration of surfactant in the solutions. the surhctant concentration was taken as in the solution at the onset of the partitioning experiment. Thus the surfactant contribution to the absorbance rending could be calculated by

?,(surf) = c"".,~/ ( D x EC) (3.1 1) where .-fmt-jj is the sirrtictant's contribution to the total absorbance reading. D is the volurnetric dilution ratio applied to the sample prior to LiV measurement and EC is the surtictant extinction coefficient (moüL). The net absorbance due to the presence of the PMin question was then taken as the ciifference between the sample's total absorbance reading and the surfactant's absorbance contribution. In Tergitol NP10 and Triton X-100 solutions contacted with NAPLs with .pph, of at least 0.03. and in Tween 80 solution systems withPhhvof at least 0.01. it was possible to obtain si@~cant net naphthalene absorbance readings at 220 nm hm aqueous phase samples after dihion with methanol. Oniy Tween 80 and Brïj 35 were contacted with NAPLs containhg phenanthme. The absorbance readings at 251 nm for Tween 80 soIutions were correcteci for the surfactant's absorbance contribution. It tvas possible to achieve significant net phenankne absorbance readings in Tween 80 solutions contacted with NAPLs with.k?knnVof at lem0.01. Neither Brij 25 nor Tween 80 sulutiaus emitted a signifimtamount of light at 364 nrn under the conditions used for fluorescence measurements. The other surfactant solutions were not assessed for their emission spectra as they were not analyzed by fluorescence. Thus. solutions with low phenanthrene concentrations were measured by tluorescence emission as described in Chapter 2.

Table 3.2: Surfactant Extinction Coefficients in Methanol-Water Solutions 1 = 220 nm 7L = 251 nm [iw [ilmsl < 0.001 Ma Brij 35 < 0.001 c 0.001 Tergitol NP10 0.41 8 nla Triton X-100 .1.366 nla Tween 80 ,0.012 0.007 3.3. Results and Discussion

3.3.1. EFFECTOF METHANOLDILUTION OF THE Cl((tC

The presence of organic additives in surfactant solutions may have marked effects on the CMC. AS elcplained in Chapter 1. organic additives cm act either as Class 1 materials. which affect the CMC by aitering the micelar environment. or as Class II matenals. which cm increase the CMC significantly by altering the nature of the interactions benveen the solvent and the surfactant monomers. Rosen (1989) States that short chah dcohols often act as Class iI materials when present at hi& concentrations. Pramauro and Pelizzetti ( 1996) report that many surfactants that tom micelles in aqueous solutions will not aggregate in methanol due to the greater at't?nity of the monomers for methanol as a solvent. Thus. rnethanol was chosen to dilute samples prior to analysis because af its potential to act as a Class II material. By increasing the CMC through rnethanol dilution it was possible to maintain rneasurable PAH concentrations in solutions to be analyzed while eliminating the üV light quenching effects of surfactant micelles. E.xperiments were canied out to determine the effectiveness of diluting surfactant solutions to 50% and 75% methanol (dv)in order to nise the CMC suficiently to etiminate micelles at the surfactant concentrations of interest. Figures 3.2 and 3.3 show the equiIibrium naphthalene concentration in rnethanol and weer surfactant solutions (~',,,,M) contacted with naphthalene qstais. It cm be seen in both cases that at lower surfactant concentrations is nearly constant. chus the surfactant concentrations in this range are assumed to be below the CMC in these soldons. At higher surfactant concentrations. CqDh,weoHinmases with increasing surfactant concentration. These solutions were assumed to have surfactant concentrations in excess of the CMC. Distinct linear trends are apparent below and above the CMC for both 50% and 75% methanol solutious. Straight lines fit to the supra-CMC data by linear regession are plotted on Figures 3.2 and 3.3. The dashed lines represent the average r"ph,b,emin solutions with c"fMCoHles than the CMC. This was taken as the equiIibrium naphthalene concentration in each methanol-water mixture. The CMC in the methanol-water solutions was detemined to be the surfactant concentration at the intersection of the nvo lines. In Figure 3.2. the CMC in a 50% methanol (vlv) solution for Triton X-IO0 is estimated to be 0.013 moVL. which is about 71 times greater than the CMC for Triton X- 100 solutions in water reported by Yoem et al. (1991) (see Table 3.1). For 75% rnehol (viv) solutions. the CMC is estimated to be about 100 times the reported ltqueous sohtion CMC value. These results suggest that methanol acts as a Class II organic additive. causing a sipiticant nse in the CMC as its concentration in the solution is increased. It is expected that the limiting CMC in solutions with increasing methanol concentrations \?Il be equal to the CMC in pure methanol. This is expected to be significrtntly higher than the CMC in aqueous solutions. due to the less polar nature of methmol as a sohent in comparison to water (Pramauro and Pelizzetti. 1996: Rosen. 1989). For some surtactants. micellar qgregation may not occur in methano1 solutions (Rosen. 1989). ïhe effect of methmol dilution on the formation of micelks was investigated for the other surîàctants. For each case. the most and the least concentnted surtactant solutions used in the MSR experiments were diluted to 75% methanol (v/v). These solutions were then contacted with naphthaiene crystals and the equilibriurn c"@',,~,, was memured. The results of these experiments are presented in Tabte 3.3. It cmbe sccn that in these surfàctant solutions closely matched the average equilibrium c~~~,,~(,in the Triton X- 100 solutions n surtàctant concentrations below the apparent CMC in 75% rnethanol solutions. These results suggest that dilution of the solutions with methanol at ieast a 3: 1 (wiratio \vas suficient to mise the CMC to the point at which no micelles were present in the surfactant solutions of interest. Based on this. the methanol dilutions presented in

Section 3.2.4 were presumed to be sufficient to preclude CO interference of micelles an specal analysis of the simples. 'I'irblc 3.3: Nuphtkulene Ctrnccntration in 75% Mclliunid - 2S1X, Wutcr Solutions conïuining Surfuctnnts Surfactant Cu""(mol/L) v (mmol/L) rriton X-100 3.40E-04 65.61 8.50E-04 62.01 CMC = 0.012 molA 8.50E-03 63.85 0 O00 -I O O 005 O 01 0.015 O 02 0.025 1.70E-02 63.69 Surfactant Concentration (mollL) 2.55E-02 66.41 3.40E-02 71.00 Figure 3.2 : c""'"',,,,,,, vr. c~':~ 5.1OE-02 75.32 .(Triton X-100 in 50% Mclhnnol Sulutions) 3rij 30 2.5OE-04 63.04 1.00E-03 64.15 3rij 35 2.30E-04 62.10 1.15E-03 59.78 rergitol NPI O 1.25~-04 63.42 6.25E-04 64.01 'ween 80 1.50E-04 64.30 6.00E-04 62.19

CMC = 0.017 rnollL

O 001 002 003 004 O05 Surfactant Concentration (mallL)

Figure 3.3 : c"""~,~,,~,W. c""',,~ (Triton X-100 in 75% Mcthanol Soluliuns) 3.3.2. DETERMINATIONOF THE CJ((ICIN AQUEOUSSURFACTANT SOL~~ONS

The apparent CMC was estimated in systems where 2 ml of NAPL was contacted with 25 ml of surfactant solution. Figure 3.1 shows a plot of Crorvs. fiQin Brij 35 solutions contacted with a NUL (,yv = 0.01). The CMC was estimated as the c~!.(, corresponding to the inîlection point where CmTbegan to increase linearly with increased sdactant concentration. The location of the inflection point was assessed to be the point of origin ofa linear tit to the C',, vs. fl.,Qdata for points where CmTwas higher than ,- in NAPL-water systems of a particular -l',. T'he equation of best tit fmm nch linear regression was solved for the at which is equal to Cd,,,:- this vaiue of is retërred to as the measured apparent CMC. tt is possible that solubiiization of PAHs within micelles miiy affect the CMC by acting as Class i materials. Because this effect may be more pronounced in systems with higher PAH concentrations. Brij 35 solutions were contacted with a range of naphthatene containing NAPLs with .yvranging tiom 0.01 to 0.17. The average of the apparent CMC values for a11 .k', was about ntice the CMC reported in the litennue. tt is stated in Chapter 1 that Class 1 materials tend to decrease the CMC by encouraging micelle formation. As the CMC was higher than the reported value and no trend in the CMC was observed with increasing A", (see Table 3.4). it is concluded that CIass 1 effects of naphthalene partitioning into the micelles were insignificant over the range of A',. studied. Thus, the differences between the apparent CMC vaIues and the literature CMC vdues were assumed to be attributable to sirrfactant losses to the NAPL and to sorption to the intertjces within the system. Arornatic compounds are thought to affect the CMC by being solubiIized in the outer layers of the micelle (Linciman and Wennerstrom. 1980: Nagmjan et ai.. 1484). As Brij 35 has the hi&est HLB its micelles wiil have the greatest shell to core volume ratio. Thus, it is expected to be most effected by PAH solubilization in its outer layers. Since there are no apparent Class 1 interactions for Brij 35. it is therefore assdthat CIass I effects due to PAH partitioning are negligibIe for ail the surfactants studied. Also. because phenanthrene is less likely than naphthdene to be solubilized at the core-water interface, due to phenanthrene's more hydrophobie nature and larger molecular volume. it is assumed that phenanthrene will not act a Class 1 material either. The apparent CMC hcrease in Brij 25 solutions contacted with naphthdene crystals is in the order of the increase witnessed in the solutions contacted with NAPL. suggesting that surfactant losses in both systems are due mostly to sorption to the systems' interfaces. The average of the apparent CMC vaIues for al1 Brij 3 systems. shown in Table 3.4. is 2.6 tirnes greater than the reported CMC value. The 95% CI of the average is between 0.83 to 4.2 tirnes the repocted CMC. suggesting that surfactant losses rw not signiticant in these systems. Since Brij 25 has the highest HLB of al1 the surfactants tested it is expected to partition the lest into the NAPL. Therefore. it was necessary to mess the effect of NAPL contact on the apparent CMC for each of the other surfactants. This was riccomplished in systems containing 2 ml of a NAPL with a naphthaiene mole Fraction of 0.19 and in systems containing 2 ml of a NAPL with a phenanthrene mole fnction of 0.04 for Tween 80. Plots of cm,vs. C?TQfor each surfàctant solution contacted with the NAPL are presented in Figures Al to AS in Appendix A. As cm be seen in Table 3.4. the apparent CMC was not signifrcantly different hmthe literature reported CMC in any of the systems. with the exception of those containing Brij 30 solutions. The CMC values for systems containing phenanthrene NAPLs were not significantly different than the CMC vaiues in naphthalene NAPL qstems. which Mersupports the concIusion that Class I interactions were insignificant in these systems. In Brij 30 solutions the apparent CMC was seen to be about 28 times greater than the reported CMC value of Edwards et al. (1 991). This the Fatest increase in CMC observed and, as Brij 30 has a much lower HLB than the other surfactants. it is concluded that Brij 30 partitions into the NAPL significantiy in the systems used hm.

Zimmerman et al. (1999) found htfor ethoxylated surfiactants with HLBs between 14.1 and 17.6. surfactant partitioning into NAPLs increased with decreasing HLB. It was found that surfactant partitioning was greatest into NAPLs with the lowest log K,,, (least hydrophobic). Nonionic surfactants with HLBs greater than 9 are more hydrophilic than hydrophobic in nature. In NAPL-water systems, they will partition predominantly into the aqueous phase and form micelles there. In systems where surîàctant solutions were contacted with tetrachioroethylene (PCE). which has a log Ka,, of 2.88 (Sch~varzenbachet ai.. 1993). Zimmerman et al. (1999) observed that the partitioning of surtàctants into the NAPL was minimal. Because hexadecane is much more hydrophobic, with a log K,, of6.17 (Table ll), surfactant partitioning into the XXPLs used here should be negligible for ail but the surfactants with the lowest HLBs. This is in agreement with the observation that Brij 30 the most hydrophobic of the surtàctants studied. with an HLB of 9.7. was the only surfactant to partition into the NAPL in significant quantities. Since Brij 30 partitioned significdy into the NAPL. its et'fect on the NML mole tiaction was determined. ft was found that Brij 30 partitioning resulted in a 7.8% increase in the nurnber of moles in the NAPL. In NAPL-water systems micelles formed in the aqueous phase at high Brij 30 concentrations. Wherein micelles will only form in one phase in a two phase system (Rosen. 1989). it is concluded that no Brij 30 micelles tormed in NAPL. It also folIows that the surfactant concentration in the NAPL was constant at al1 above the apparent CMC. Thus. A', vaiues were comcted by 7.8% for al1 Brij 20 systems. Whereby Brij 30 was the oniy surfactant that partitioned into the NAPL in significant quantities. it was the only one likeiy to have an effect on the activity of naphthalene in the NAPL. For dl NAPL-surfactant solution ?stems with e,Qlower than the apparent CMC. was withill5% of the expected value according to the partitioning experiments for pure water systems as presented in Chapter 2. This is within the precision of the measurements (determined as 2 3.3% based on the average of the standard errors). Thus- it is conctuded that the partitioning of PAHs between the NAPL and the aqueous pseudo-phase is not sipificantly affected by the presence of surfactant monomes in either phase. Table 3.4: CMC Values in Aqueous Surfactant Systems iurfactant PAH X'N Measured Ratio Measured 1 Apparent CMC Reported CMC (moUL) Naphthalene 0.01 5.06E-04 5.5 0.05 5.1 4E-05 0.6 0.09 2.30E-04 2.5 0.13 6.37E-05 0.7 0.17 3.52E-04 3.8 Crystals 3.64E-04 4. O Phenanthrene 0.04 1.03E-04 1.1 Naphthalene 0.12 5.60E-04 28.0 Naphthalene 0.12 6.46E-05 1.3 Naphthalene 0.1 2 1.86E-04 1.1 Naphthalene 0.1 2 1.43E-05 1.2 Phenanthrene 0.04 3.02E-05 2.5

3.3.3. EFFECT OF NAPL PAH MOLEFRACTION ON THE MSR

The MSR of naphthalene in al1 five non-ionic surfactants was determined in systems containing two-component NAPLs with a range of ,yph,of 0.0 1 to 0.17. Phenanthrene MSR values were determined for Bnj 35 and Tween 80 solutions contacted with NULS with phenanthrene mole fractions ranging hm0.01 to 0.05. From the MSR daia the micellar PAH mole fiactions (y,,,)and activity coefficients were are also calculated. A11 of these results are presented in Figures 3.4 to 3.17. wherein the MSR values are presented in the even numbered figures and the activity coefficients and xiMare presented in the odd nurnbered figures.

Edwards et al.. ( 199 1) state that .T.k, cm be determined in single solute systems by

Xik,= MSR I ( 1 + MSR) (3. 1 3) This equation cmbe used to determine ,y, in micelles contacted with PAH in hexadecane mixtures, assuming that the hexadecane moIe fnction in the rnicellar pseudo- phase is negiigibte. From Equation 3-13 it can be seen that at low MSR values XIM is approximately equal to the MSR. tndeed many of the conclusions in ttiis work are subject to the assumption that hexadecane does not partition significaatly into the aqueous or micellar pseudo-phase. In Chapter 2. it was assumed that NAPL PAH mole fractions are not affected by hexadecane partitioning into water due to hexadecane's extremely low water solubility. It is possible that hexadecane's solubility in the aqueous pseudo-phase is increased by association with surtàctant monomers. Thangamani and Shreve ( 1994) state that hexadecane's water solubility was raised to 4.7~10"mol/L in the presence of hurnic acid. Even if such an increase occurred in the aqueous pseudo-phase concentration of hexadecane it tvould have a negligible effect on the NAPL compositions (less than 0.01%). As micelles are capabie of soiubilizing significant amounts of hydrophohic materids it is not obvious that hexadecme will not be present in significant quantities tvithin the micelles. Based on the quantitative structural-activity relationship (QSAR)

developed by JatVert et al. ( 1995). MSR values were caiculated for crystdline naphthalene. phenanthrene ruid pure Iiquid hexadecane. These values are presented in Table .-13 in Appendix A. The QSAR predicted he'izidecane micellar mole fraction (.Pt!)values of less than 0.003 for ail surfactants based on hexadecane's K,, and the surtàctant structures. Predicted values for crystalline naphthalene and phenanthrene MSRs agree closely with the dues found in this study. which suggests that the mode[ is valid for the systems used here. [t has been noted that aromatic compounds are solubilized to a large extent in the outer layers of micelles. This significantly raises their MSRs relative to those for aiiphatic HOCs. which are solubilized entirely wivlthin the micelle core (Lindrnan and Wennerstrom. 1980: Mukejee. 1979: Rosen. 1989). It is therefore expected that the predicted dues from the QSAR model are significantly higher than the uue l?, values because the model was developed using only aromatic cornpounds. Thus. it cm be concluded that is low enough not to affect the NAPL composition. It is aIso açsumed. due to hexadecane's extremely hydrophobic nature and low predicted ,th-, that it is sotubilized enrirrly within the micelle core in very small quantities. iüus. it may be concluded that the little hexadecane present in miceIles wil1 not alter the micelle structure or affect the partitioning of PAHs into the micelle- Based on the above assumption, it was possible to isolate the partitioning behavior of PAHs in NAPL contacted surfactant solutions. MSRs were detemined for each surfactant contacted with NAPLs of at least five different PAH mole Fractions. ranging fiom 0.01 to just below the X',b{mm),for each surfactant. Since Tergitol NP10 and Triton X-100 both had significant UV absorbance at 220 nm. it was not possible to get a significant net absorbance for naphmene in solutions contacted with NAPLs with .Yph,oIO.0 1. The heowest dpph,that dalwed for measnbk PPhdQfor borh surfactants was 0.03. At each ,V, a minimum oltwo sets of vials were prepared for the determination of the MSR. Each set included four or five vials containing a range of surfactant solutions in excess of the CMC. MSRs were determined as the dope of a straight line fit to the Cdmr vs. C<,data fiom one set of vials. dl containing NAPLs with the sarne .r,. The full set of MSR data is avaitable in Table A4 in the Appendix. The average MSR was calculateci hmat Ieast two sets of data for each surfactant-.r, combination. The error bars on the MSR vs. ,Y', curves indicate the MSR measurernent precision: they represent the standard error of the average of al1 the MSR values. normalized to each measurernent. PAH losses from the NUL due to voIatilizatïon were assumed to be the sarne as those presented in Chapter 2. The change in ,yv due to partitioning of PAH into the surfactant solutions was caiculated based on a mass balance using CmTmeasurements. In al1 cases. PAH losses hmthe NAPL were less than 6% of the totai number of mole ot' PAH in the NAPL. In cases where the PAHpartitioning and losses From the NAPL accounted for an ,Y', reduction of pater than 2% it was suspected that the MSR vdue would be affected. The experiments discussed here aim to detemine whether the MSR changes as a Iinear îünction of Y,. Implicit to this supposition is that Cm,in sotutions with a specific surtactant concentration. will also vary linearly with ,Y' v. Without the knowledge that Iinear relationship existeci between the MSR and,% over a large range of,Y, values. it was assumed that for very small changes in ,y, (Le. less than 6%) the variation in CmT cm be approximateci by a liear relatiomhip with minimal ermr. The following equation was therefore wdto correct dmTin systerns where X,,r changed significantly due to FAH partitionkg:

where CdmT(mm.)and ,k'b{cov.)are the corrected values of CmTand .l?, respectively. .V, (corr.) values are presented in Table A2 in Appendix A. Zimmerman et al. (1999) observed that faheto account for surfactant partitioning into the NAPL can lead to the calcuiation of artitïciaily low MSR values. Thry dso sure that determinhg MSR values fmrn lines tit to Cm, vs. r"',,,data a points above the CMC is a straight forward way to avoid the etTect of surfactant partitioning on MSR values. Using ths method of MSR caiculation. the resuiting MSR values air free of errors associated with surfactant partitioning and CMC changes in the N.4PL systems. it is observed for each surfactant that a Iinear relationship with very litde deviation cxists between the MSR and A' ,.. For dl but a few data points, the lines titted by Iinear regression to the MSR data pass through the error bars. Al1 the coefficients of determination suggest that the fit is good (~30.93).It is also apparent that the rnicellar PAH mole fiaction (T,,) varies IinearIy withY,. Together these resuits indicate that the ratio of rither MSR or ,yv to fvis constant over the range offvstudied. This supports the use of the coefficient. b?rlSR. to predict MSRs fiom NAPL composition data. Considering that iit was assumed that the aqueous pseudo-phase PMconcentrations do not change signnificantly with increased p4@these results also support the ûssumption that ided Henry's law partitioning between the three phases provides a valid model in NAPL-surfiactant solution systerns. as the PAH concentration in one phase bears a Linear relationship to the concentration in each of the other phases. Therefore it cm be concluded ttiat the micelIar pseudo-phase behaves as a simple Gquid phase with respect to PAH partitioning hmthe model NAPL into solutions containing any one of the five nonionic siIrtàcmts used in this study. Other studies have shown similarly that solute concentrations in micelles can ofien be related to the solute concentration in the other phases by equilibrium coefficients. In a study of the partitioning of methane, ethane and propane between a gaseous phase and a miceilar solution, BoIden et. al. ( 1983) found that Henry's law was obeyed. It was also found that the intemicella.solubility of each gas differed fiom the solubility of the gas in solvents compriseci ofthe alkyl chains which make up the hydrophobic tails of the surfactants used. This discrepancy decreased with increasing length in the surtactant's hydrophobic tail. which suggests that in larger micelles the solute's solubility in the core shodd correspond to that in the pure liquid hydrocrirbon. In another study. Tucker ( 1995) used vapor pressure measurements to mdy the solubilization of HOCs by surfactant micellea in that study. the micellar partitioning coefficient for benzene remained nearly constant over a range of ,Yw up to 0.2 in four of the the nonionic surtactants tested, It was therefore assumed that an ideal Henry's law partitioning model would predict partitioning within this range of X ,,. Anderson ( 1992) developed a partitioning mode1 for SDS (sodium dodecylsulfate) systems. In agreement with the results above. it was found that the partitioning of benzene. toluene and o-ylene closely followed an ideal Henry's law model and that k', decreased with increasing surfactant concentrations. There are rnany examples of micellar partitioning coefficients defined in the Iiterature. These are generally simiiar to K',, detined by Equation 3.4 in that they provide a ratio between the miçellar pseudo-phase concentration and the concentration in another

phase. Jafiert et al. ( 1994) define K'wAq as the ratio ofthe MSR to the aqueous phase concentration for a nurnber of HOCs in nine non-ionic surfactants. Based on those results they developed a predictive relationstiip between K' and surfactant qualities based on the nurnber of carbons in a surfactant's hydrophilic head and the hydrophobic tail. The results of JaELert et al.( 1994) are cornpared with the results of this study in Table 3.5.

Dunaway et al. ( 1995) defianother coefficient. K',wAv-as the ratio of the micellar solute mole fraction to 6,,@It is clear hmEquation 3.12 that at Iow MSRs. Y,, can be approximated as being equal to the MSR and therefore the two partitioning coefficients become equal. Compariwn of fwAvvalues to Kr,wvalues in Table 3.5 shows that the results here agree closely to those in the literature. Yaem et ai. (1991), also found that the MSK seemed to Vary as a linear hction of PAH mole iraction for systems containing soil, organic mater and aged coal tar. However. the aged coal tar \vas mostiy likely a solid and no attempt was made to veri@ the presence of free NAPL in their çystem. Using Tween 80, Brij 35 and Triton X-100 they measured the rate of dissolution and final ClTOTfor a nurnber of PAHs. They assurned that the activity coefficients in dl the phases were independent of concentration

and that Raoult's law applied to the coal tar (Le. = 1). Considenng that the presence of free NAPL in their system was not established and equilibrium partitioning was not achieved due to mass transfer limitations in the cod tar, the equilibrium partitioning patterns for PAHs in NAPL-surfactant systems cannot be precisely estabfished from their study. However. if a NAPL phase was present. their results suggest that in real-world NAPLs the PvISR may be predicted provided an accurate estimate of the activity of PAHs in the NAPL is available. blicellar pseudo-phase PAH activity coefficients were cdculated by Equation 3.10. Plotsofthey',,withX'k~(Figures3.5.3.7.3.9.3.l1.3.13.3.15.3.17)showseved interesting trends. For naphthalene in dl surfactants studied PhMinneases sharpiy at the lowest .vph,,,and then decreases gradually at higher .yph,.[t has been sugpeîted that the limiting vaiue of y', should be 1 at X,v= 1 based on thermodynarnic considerations (Dunaway et ai.. 1995: Tucker. 1995). For Tergitol NP 10 and Triton X- 100 micelles. the naphthaiene rnicellar activity coefficient shows less of a sharp rise at the lowest .Y ,,. This is Iikely because the lowest ,Y, used with these surfactants was 0.03 and thus the range of Ad,,, investigated is not as broad as the other surtàctants as low as 0.0 1 ). These results suggest that the micellar environment becomes less arnicable for the PAHs as .Y,,, increases. At low ,vJ,, PAH solubilization likely occurs in the outer shell and palisade and core layer filling spaces between the surfactant molecules and dispiacing water molecules. while at higher ,f, soIubilization occurs predomuiantly within the core (Rosen. 1989). It is thought that PAHs are incorpomted into daceand palisade Iayers which results in a significant altering of the micelIar structure and a lowering of the entropy of the micellar system (Lhdman and Wennerstrom. 1980). The cise in j,, here is atuibuted ta the Uicrease in the difficulty of filling spaces in the palisade Iayer as it becomes more fidl wirh PMImolecules, and to the entropy decrease associated with restnicturing of the miceIIes. As Yb, levels off and begins to decrease it is thought that the partitioning of the PAHs into the core becomes most sigdicant and that as A',, becomes larger the core environment becomes more like the PAH which leads to a steady reduction in y',, with increasing This is supported by the fact bat ssaturated aliphatics and alicyclics and other non polar molecules tend to be absorbed into the core. as is observed in their NbR or LJV spectra (Rosen. 1989). Dunaway et al. (1995) hund that the activity coefficient of benzene in cetylpyridinium chloride (CPC)micelles increased sharpiy at low A', leveled offat intermediate .r,,and showed signs of decreasing at hi& A',,. For hexane in CPC micelles it was seen that as Y, increased. y',, decreased. tending to unity at .Y',, = 1. It should be noted that an .Vw value of 1 has no physical significance: it is a theoretical limit çorresponding to micelles comprised purely of PAH molecules. In most cases reponed in the litentue. .r ,, has a realizable limit between 0.3 and 0.6 (Dunaway et al.. 1995: Tucker. 1995). Variations in -y',, are srnall in al1 systems studied here except at very low naphthalene mole hctions. This supports the validity of using ideal Henry's law partitioning to predict MSRs based on -Yv for the cange ofYvstudied, However. the significant drop in y',, vdues at low A", suggest that at very low ,Y', (Le. less than 0.01 ) Henry's law may not apply . As NAPLs such as coal tar and creosote are typically rich in a varie& of PAHs, often containing significant fractions of one or two primary PAHs. it is likely that the high ,Y, conditions necessary for Henry's taw partitioning apply. Micellar partitioning in systems containing multiple PAHs is Uivestigated in Chapter 4. but considering that the lower fw values are attributabte to the PAH solubilization in the slightly polar paIisade Iayer at very low PAH concentrations. it is likely that a PAH that makes up a significant fnction (Le. greater than 3 mol%) of a mdti-component NAPL will partition ideally into the micelle core according to Henry's iaw. The micellar activity coefficients for phenanthrene in Brij 35 and Tween 80 do not show a sharp increase at the lowest but do exhibit a gradua1 decrease with increasing This is likely due to the fact that phenanthrene is a more hydrophobie and larger molecule. thus it would have more difficulty filling spaces in the outer layers than naphthalene. Therefore. it is most Likely solubilized predorninantly into the micelle core over the rang of ,rkn,tested. However. it is possible that phenanthrene molecules may also be solubilized into the palisade layer. but thrtt it would become saturated with phenanthrene at much iower concentrations due to phenanthrene's greater degree of hydrophobicis. If this is nue. then the sarne sharp increase in fhen,.as was seen with -rph,.may be apparent in systems contacted with a range of NAPLs with -Phen,below 0.01. For condensed rirornatic compounds. the solubiiization capacity has been observed to decrease with increases in molecular size (Rosen. 1989). Crystalline naphthalene has a higher MSR than crystailine phenanduene in solutions of either Brij 35 or Tween 80. as is seen in Figures 3.6.3.12.3.14.3.16. However. results herc suggest that at the same NAPL mole hction. phenanthrene will have a higher MSR than naphthaiene in Brij 35 and Tween 80 solutions (flhrn,, > K"@',,R). Despite this, there is in fact no dimepancy between the Iiterature and the resutts for the NAPL systems employed here. The higher P"",,vaiues are attributed to the fact that naphthalene is more soluble in hrxadecane than is phenanthrene and thus the activity of naphthalene in the NAPL is lower than the activity of phenanhene as the sarne mole fraction. This is supported by the tàct that in systems containing NAPLs satunted with naphthaiene or phenantlirene. .kg"",, values are lower than the ,phVvaiues in Tween 80 and Brij 35. which corresponds to the findings in the PAH qd solubilization experiments. For al1 the surfactants studied the MSR data for PAH crystais corresponds to the sxpected MSR for a saturated. This is analogous to the observation in Chapter 2 that the PAH concentration in watcr contacted with a saturated NAPL wiU be qua1 to its aqueous solubility. From this it can be conctuded that may be estimated by: where ,I?,(mux) is the solubility of the pure compound i in the NAPL rxpmsed as a mok fraction. Using the QSAR model of Jafvert et ai. (1995) MSR values were estirnated for naphthalene and phenanthrene crystals in solutions of each of the tive nonionic surfactants studied in this work. The results are presented in Table A2 in the Appendix. From this it can be seen that the rneasured values are in close agreement with rhe QSAR values estimated hmthe compounds' K,,, (average 18 % deviation). Jafvert developed th& QSAR model from MSR data from six aromatic compounds. including phenanthrene and naphthalene. Therefore. it is concluded that a reasonable estimation of k4 ,,may be obtained for other aromatic compounds by combining the QSAR devetoped by Jaîilen et al ( 1995) with Equation 3.14. l'able 3.5: <'oniparison NAPL-Surfriclant Solution IBartilioningConstant Values

Surfactant PAH KIMSR Log K'WN LW K'WAO Log K'MIAQ (KIhiVN=XIM / CaAQ) (KIhiVAO= MSR/CIAo) (Jafvert et al. 1994) Brij 35 Naphthalene 0.92 2.90 2.94 Phenant hrene 1.57 4.25 4.28 Brij 30 Naphthalene 0.94 2.89 2.95 3.02 Tergitol NP1O Naphthalene 1.15 2.98 3.04 3.09 Triton X-1 O0 Naphthalene 1 .O0 2.80 2.98 3.05 Tween 80 Naphthalene 1.97 3.17 3.27 Phenanthrene 2.25 4.39 4.43

O N4R NA!% Avg Cryeiab , Qysîab Ave -Linear (MN)

O 0.05 O. 1 O 15 O 2 Naphthalene Mole Fraction ln NAPL Figurc 3.5: x"~'"'~and Y"nl'hhl VS. in Brij 30 Solutions Figura 3.4: MSH vs. x""I"'~in Hrij 30 Solutions O NARAve O tapl A iù4R Ave Cryslals . Crysials Crystals Ave Cryslais Ave Lmeat (NAR) ,, ,, - O 3 ,- Linear (NAR Ave )

O 0 05 O 1 O 15 0 2 O 0.05 O. 1 0.15 O. 2 Maphthalene Mole Fraction in NAPL Naphthalene Mole Fraction I ...... - . . . . . --- Figure 3.6: MSH vs. x**')~~in Brij 35 Solutions Figurc 3.8: MSH vu. x"."''~in Tergital NP10 Solutions

1 X Naph (MA) Aclivity Cod. Linear(X Neph.(NAR) )

Figure 3.7: x"*"'~and y''Yph,+, W. x"'"~,,in I3rij 35 Solutions Figure 3.0: x"'~'~~and yll"l''iXI W. x""""~~in Tergitol NP10 Solutions

O O t::::: 3.4. Conclusions it was found that. in methand-water solutions, the CMC of the nonionic surfactants used here increased by a factor of over 70 compared to the values reporteci in the Iiterature. Thus. it was concluded that methanol acts as a Class II organic additive. Dihtion of samples ~ith80% (v/v) methanol prior to andysis was therefore assumed to result in the disassociation of al1 micelles whch precluded W quenching by micelles in the samples. CMC detemination by PAH solubilization rneasurernents in aqueous mrfàcmt solutions conmcted with two-component NAPLs showed that the apparent CMC wris typically increased by a factor of 2-5 over the CMC values reported in the literam. Since this increase was within the limits of the CMC meamernent error it was assumed that surtictant partitioning into the NAPL was negligible. Ody Brij 30. the most hydrophobie of the surfactants studied. had a significant increase in its CMC over the reponed values (28 times pater). This increase was attributed to surfactant partitioning into the NAPL. Tt uïas also concluded that the ability of PAHs to act as CISS 1 materials was minimai as here was no evidence that they lowered the CMC. Expenments in sytems with sub-CMC surfactant solutions suggested that surtàctant partitioning into the NAPL did not affect the PAH activity in the NAPL. nor did the presence of surfàctmt monomers significantly increase the aqueous solubility of PAHs. Ln experiments in which two-component NAPLs were contacted with surfactant solutions with CQin excers of the CMC it was observed that the MSR increased Iinemly with .Yv for ail five surfactants over a wide range of phenanthrene and naphthdene NAPL moIe fractions. Examination of the PAHrniceUar activity coefficients showed that naphthalene was Iikely solubiIized into the micelles' palisade layer at Iow naphthalene concentration but that at higher concentrations naphthalene soIubilization occurred predominantiy into the micelles' core. The same behavior was not observed for phenanthrene. IikeIy because of its higher molecular volume. These dtsagree with evidence fond in the literature. PAH mice1Ia.r activity coefficients were nearly constant in almost di systems snidied. From bis observation. dong with the fatthat MSRs varied linearly with .it was concliided that Henry's Iaw adequately described the partitioning of PAHs in the

NAPL-surfactant solutions studied. Thus, a partitioning coefficient (K.,) LW defrned to predict MSR values fhm NAPL component mole fractions. The combination of this partitioning coefficient with the pure component MSR QSAR mode1 developed by Jafken et al.. (1995). may provide a reasonably accurate (within an order of magnitude) method for estimating MSR values in many NAPL-surfactant solution systems. With this knowledge. it is possible to predict the partitioning of PAHs tiom NAPLs into surî2ctant solutions. This knowledge fomthe bais for investigations into the relative partitioning of PAHs fiom complex multi-component NMLs. Ultimately. this cm be used to predict the rate and extent of PAH dissolution fiom complex NAPLs in surtàcmt tlushing and SEAR operations. 4. Partitioning of PAHs Between Three-Component NAPLs and Surfactant Solutions

NAPLs Cound at most contarninated sites are complex mixnires. often containing signihcant amounts of multiple PAHs. WGle individual PAH mole îiactions in some coal tars and petroleurn based NAPLs may be smdl, collectively they often comprise over 80 mol% of the NAPL (Mercer and Cohen. 1990). For this reason. it is essential to detemine the effect that the presence of one PAH will have on the partitionhg of another PM3 in a NAPL-surfactant solution system. From this. a fundamental understanding of surtàcmt aided dissalution ofreal-wodd chemicdly complex NAPLs becomes possible. A concepniai understanding of phenornena reiated to multiple solute partitioning

tiom NAPLs to surtactant soluuom has emerged tiom the work of Chaiko et al. ( 1984) and Nagarajan et al. ( 1984). These authors found that benzene and toluene MSR values in a nurnber of ionic surfactant solutions were well correlated with the aromatic cornpounds' molecular volumes. A dimensionless constant was developed relating a cornpound's polarity. represented by the compound-water interfacial tension, to its moletular volume: a,v2'3/k~.where a, is the water-solute interfacial tension (dynedcrn). Vis the solute mdecular volume (A3). k is the Bolizmann constant (ergs/K) and T is the absolute temperature (KI. It was obsewed that, for a number of alkanes and aromatic compounds, better correlations could be obtained between MSR values and this dimensionless coefficient than between MSR values and molecular volumes. From this it tvas concluded that prediction of a variety of HOC MSRs can be achieved when molecdar volume and poiarity are both considered. In a second set of experiments. presented by Chaiko et al. (1984) and Nagmjan et

ai. ( 1984). surfactant solutions were contacted with two-cornponent NULS. containing combinations of benzene. cyclohexme and hexane. in these systems, a change in the ratio of the MSRs of the two components wiîh respect to their relative MSRs in single solute systems was observed. This was believed to be the result of selective solubilizntion of one component over the other within the micelles. Results showed that benzene was selectively solubilized over hexane which had a larger mo1ecular volume and was more hydrophobic. Thus. it was concluded that the selectivity of one cornponent over another could be predicted fiom single solute MSR data (Le. the solute with the higher MSR would be selectively solubilized in a two-component systern). It was also suygested that benzene may be solubilized into the region between the rnicellar core and the head group layer (cailed the paiisade layer). It was believed that this would cause a reduction in the rnicellar core-water interfacial tension leriding to an increase in the core volume.

Nagarajan et al. ( 1984) assessed the potential for. and et'fects of. benzene solubilization in the micelle's hydrophobic shell and paiisade layer in rnulti-solute sytems. Based on thermodynmic rnodeling of micelle formation and solubilization, they demonstrated that the keenergy decrease due to the reduction of the core-water interfacial tension. caused by benzene solubilization in the palisade layer. is offset by the increase in frec energy associated with the contacting water molecules with the bemene molecules in the palisade layer. Since values are a function of the fiee cncrgy of solubilization within the micelle. they concluded that K',, values for benzene should be independent ofits locus of solubilization. It was also concluded that the synergetic relritionship which nised the hexane MSR was due to solubilization of benzene micefles in the palisade layer. It was observed that hexane MSR values are increased at low benzene concentrations but rernain relatively unaffected at high concentrations. From this, it can be inferred that benzene solubilization may predominantly take place in the outer iayers at lower benzene concentrations and into the core rit higher benzene concenmtions. This supposition is supported by resuits that showed that in quatemary ammonium solutions. benzene was solubilized primarily at the micelle-water interface at low benzene concentrations but further solubilization was the result of partitioning into the micellar core (Rosen. 1989). Guha et al. (1998a) reported X",values for naphthaiene. phenanthrene and pyrene in aqueous nonionic surfactant solutions containing known concentrations of each of the three PAHs. They concluded that the soIubiIization of one PAH compound into micelles may have an effect on the solubilization of other PAHs present in the system and that micek partitioning coefficients flom single PAH systems may not apply to multiple- PAH systems. Two types of PAH interactions which may affect the micetlm solubilizaîion of other PAHs were proposed by the authors: (1) a decrease in the solubilization of a given PAH due to competition for space withii the micelle core From other more hydrophobic PAHs and. (2) an increase in the solubilization of a given PAH caused by solubilization of less hydrophobic PAHs at core-water interface. which may lead ro an increase in the core volume.

4.1 .l.Theoreücal Framework in this chapter. the theoretical framework which describes the dissolution of PAHs tiom NAPLs into surfactant solutions. is extended to NAPLs containing multiple PAHs. From Equation 2.3 it can be seen that the equilibrium aqueous concentration of a given NAPL constituent (C' ,Q) can increase dur to an increase in its aqueous solubility (C' or its activity coefficient in the NAPL (y',). Hildebrand and Scott (1964)note that C" ,,,,, will increase if the ti-ee energy of solubilization decreases. This may occur due to the altering of the water structure by other hydrophobic molecules present in the solution. This has been witnessed for some PAHs by Kile and Chiou (1989) who observed that the aqueous solubi1ities of PCBs and DDT were increased in the presence of trace quantities DOM and humic acid. It is possible that a similar enhancement in aqueous sotubilities may occur in systems containing both phenanthrene and naphthaiene. The activity coetlicient of a compound will increase if the environment surrounding it becomes less favorable for its soIubilization (Hildebrand and Scott. 1964). The two PAHs, naphthaiene and phenanthrene, are more aiike in nature than either is to hexadecane. Thus. it is uniikeIy that the y', vaIues of the PAHs dlincrease when naphthaiene is added to the two-component NAPLs comptised of hexadecane and phenanthrene. It is most probable that the similar structures of naphthaiene and phenarzttirene wouid lead to a reduction of the f,v values in the three-component NMLs. if my change occurs. It has been suggested by Peters and Luthy (1993) that PAHs may be lumped together as a pseudo-component when describing their partitionhg fiom coal tar into various solvents. including Nater. It was proposed that when Raoult's Iaw holds for each of the PAHs in cdtar, they will maintain the same relative equilibrium molar concentrations in the aqueous phase as in the NAPL. Based on this reasoning Equatiuns 4.1 and 4.2 were proposed by the authors.

(for al1 species i) (4.1 i

(for ail species i) (3.2)

X similar relationship to that presented in Equation 4.2 cm be developed by replacing Cd, with A', . In cases where Raoult's Law does not apply but ideal Henq's Iaw partitioning is used as a valid rnodel. this relationship between d,,pand .Y'\. cm be aitered to inchde the activity coefficients of each component. Furthemore. assuming that over the range of NAPL total PAH mole hctions (,Ptv)studied the individual cornponents' -icdo not change. the tollowing analogous relationship will be valid.

.i\ssessment of the second ratio in Equation 4.3. over a range of ,'il"',,, will provide insight into the applicability of Heq's law for a NAPL of known composition. Negative deviations in the ratio suggest that the weighted average of the is decreasing while positive deviations suggest increasing y'.v values. ..\ similar relationship can be developed to relate the sum of the MSR values to the individual .r, values in a NAPL containhg multiple PAHs. assuming that the MSRof each component is the sarne in a multi-component system as in the single solute system.

(for dl species i)

tn cases where this relationship is valid, the totai MSR can be determineci for a NAPI. provided that the K',,values are known and remain constant for di PAHs present over the concentration range of interest. in some cases this may be an over-simpLifrcation. There is a paucity of information which describes the solubilization of one aromatic compound fiom multi-cornponent mimes. but the few relevant studies suggest that the interactions in multi-component mixtures affect individual MSR values.

4.1.2. Objectives

It has ken noted above and in Chapter 3 that PAH partitioning into micelles is complex in that it may occur in both the outer layers and the core. and because it rnay lead to restrucnuing of the micellar environment. In these experiments. three-component NAPLs containing various concentrations of naphthalene. phenanthrene and hexadecane were contacted with surîàctant solutions in order to examine the ettèct that the presence of one PAH may have on another's NAPL-water-micelle partitioning. The objective was to investigate the validity of applying a linear rnodel based on Henry's law to the prtrtitioning of PAHs between NAPLs and solutions containing micelles. Although several studies have focused on the partitioning of muitiple organic solutes into rnicellar solutions. this study represents the first attempt at modeling the partitioning of multiple PAHs from an ideal NAPL into miceliar solutions. The knowledge gained wiil improve the understanding of surfactant-aided dissolution of PAHs hmNAPLs such as coal tars and creosotes. 4.2. MATERIALSAND METHODS

4.3.1. Synthesis of Three-component NAPLs

Three-component NAPLs comprised of naphthaiene. phenanthrene and hexadecane were synthesized by dissolving crysiailine phenanthrene and naphthalene into hexadecane according to the methods presented in Chapter 2. Phenanthrene mole fractions varied Iiom 0.01 to 0.05 and naphthalene mole fiactions varied Liom 0.01 to 0.17. PAH mole fractions were accurate within t% of the stated vatues. Visual observations of PAH- hexadecane mixtures suggested that the mahum individual PAH mole fractions dissolvable in the three-component were close to those in ihe two component NAPL.

4.3.2. Experimental Set-Up and Analyticaf Methods

Equilibrium partitioning of PAHs between the aqueous bulk-phase and the NAPL was achieved by contacting 2 ml of NAPL with 25 ml of aqueous surfactant solution as described in Chapter 3. A range of solutions. contai~ngvarious concentrations of Brij 33. was created and the MSRs determined in the same ways as in Chapter 3. PAH partitioning in NAPL-water systems was assessed by the methods described in Chapter 2. The aqueous bulk-phase in test systems was sampled according to the methods described in Chapters 2 and 3 and PAH concenmtions were analyzed using UV spectrophotometry and tluorescence emission meaurements. ïhe Brij 35 solutions did not absorb UV light significantly at either 230 nm or 35 1 nm nor did they emit light at 364 nm when excited by 250 nrn light in the specmfluorophotometer. Phenanthrene and naphthalene both absorb sipificant amounts of UV Iight at 220 nm and 231 nm. Thus. it was necessary to separate the contributions of sach to the measured absorbance at both wavelengths. This was achieved by determining the extinction coefficients for each PAH at both 220 nm and 25 1 nm. The contributions at each wavelength were assumed to be additive, an assumption sirnilx to that stated in Chapter 3 for separating surfactant absorbance hmPAH absorbance. For each sample solution the absorbance at 25 1 mand 220 nm was meadsimultaneously and the concentrations of naphthalene and phenanthrene were determined hmEquations 4.5 and 4.6.

In the above equations, dk(cm-') are the net absorbance readings over the 1 cm quartz ceIl width and mrk(L rng-'crn-l) is the extinction coefficient ofcornpound i at the wavelength k. The extinction coefficients for naphthalene at 23 1 nm and phenanthrene at 210 nrn in rnethanol were 0.0 178 L mg-'cm-' and 0.1055 L mg'cm-'. respectively. Mass balances were pertormed on the NAPLs for each PAH. Corrections were made in the C' ,- values. according to the method used in Chapter 3. for systems in which NAPL PAH concenurition changes exceeded 2% due to dissolution. The CMC values for the three-component NAPL system were assessed tiom solubility data according to the methods presented in Chapter 5. CMC values for four NAPLs covering a range of.vhe", and?("phVvaiues did nat show a significant variation tiom the average CMC values for Bnj 35 solutions listed in Chapter 3. It was concluded thrit Brij 35 pmitioning into the YAPL was insignificant according to the sarne rational presented in Chapter 3. The samc was found for syterns in which phenanthrene and naphthalene crystais were contacted with Brij 35 solutions. 4.3.1. Aqueous Solubilities of Threetomponent NAPL Components

Water \vas contacted with naphthalene and phenanthrene crystals simultaneously and the equilibrium aqueous phase PAH concentrations were measured. These concentrations ivere triken as the aqueous solubilities of each PMin water saturated with both naphthalene and phenanthrene. In Table 4.1 the aqueous solubilities of naphthalene and phenanthrene in these systems are compared to the aqueous solubilities obtained by the expenments presented in Chapter 2. It is obsewed that in water containing both naphthalene and phenanthrene is higher than in water containing just naphthalene. The same is observed for the riqueous solubility of phenanthrene in systems containing both PAHs. It is therefore concluded that naphthaiene and phenanthrene exhibit a dege of cosoliwq-like behavior. It was stated above that the equilibrium concentration of a P.Mi in water contacted with a NAPL. at a particuiar ?r",. may be aifècted by the presence of another compound. This can either be the result of an increase in the PAH's NAPL activity coetticient - caused by a change in the nature of the NAPL by addition of another compound - or due to a change in the PAH's aqueous solubility as the result of cosolvency rffects. It has already been observed that naphthalene and phenanthrene exhibit a mild degree of cosolvency-like behavior in the crystalline systems. Further experiments were carried out with three-component NAPLs to determine whether that the presence of naphthalene would affect .p",and if the presence of phenanthrene would

affect 3rmph,. Figure 4.1 shows the equilibrium aqueous concentration of phenanthrene and naphthalene in water contacted with a series NAPLs in which the naphthalene mole fraction varied from 0.0 L to 0.17 and the phenanthrene mole fraction was held constant 3t 0.05. tUso shown in this figure is the naphthalene concentration in water contacted with naphthalene and phenauthme crystals together. In Table 4.1, the dope of the line fit to the Ph,,Qvs. ,ph,v data (represented by 1/Phv)in the three-component NAPL systems. in which pkn,was held constant at 0.03. is compared to that for two- component NAPL systems. From the resuits in this table. it is evident that Yph,,,,values were increased by the presence of phenanthrene in the NAPLs since l/K"ph, is somewhat higher in the three-component NAPL systems than in the two-component NAPL syaerns.

Table 4.1: Camparison of lMiy and Values for Two-Component and Three Component NAPLs, with t-Test Results on the Dinerence of the Mean y', Values in the Two and Three Component NAPLs (a = 0.05)

C'AQ, C.I. 1IK'~ C.I. Conditions (pmoUL) (Lower (moUL) (UpPer Limit) Limit) aphthalene with Phen. 223 +/4.6 1.07E-03 1.1O€-03 1.13E-03 205 +/- 2.7 1.ME43 1.OSE-03 1.06E-03 Phenanthrene with Naph. 6.22 +1- 0.12 8.85E-05 9.49E-05 1.O1 E-04 5.75 +/- 0.30 7.91 E-05 8.33E-05 8.75E-05 Difference of Two and 'hm-Component NAPL Means, t-Test Results (a=O.OS)

Solutes $N n C.I. C.I. (Mean) (Cower (UPP~~ lPIH Limit) Limit) aphthalene with Phen. 1.47 13 -0.209 0.090 - single solute 1.53 7 Phenanthrene with Naph. 3.95 10 -0.51 1 0.166 1 single solute 1 4.12 5 1

The phenanthrene concentration in water contacted with three-component NAPLs. with .\Phen, varying between 0.0 1 and 0.05 and ,Ywh, held constant, is presented in

Figure 4.2. The dope of the line fit to the vs. .Fkn.v data is eornpared for the two and three-component systems in Table 4.2. Similar to the resdts for naphthalene. the aqueous concentrations of phenanthrene are higher in the three-component NAPL systems than in the two component NAPL systems. In both Figures 4.1 and 4.2 it can be observed that the C',g, values in the three- component NAPL systems fit ont0 the vs. ,y, lines at the X,,{mmr) values deterrnined in Chapter 2. This suggests that the PAH concentration in water contacted tiiith a rnulti-component NAPL saturated with that PAH would be equd to the aqueous solubility of the PAH in question. nus. it is believed that the increase in the aqueous Pidi concentrations in three-component NUL systems is due to a rise in the aqueous solubility of naphthaiene and phenanthrene in systerns containing both PAHs. The activity coefficients of phenanthrene and naphthaiene were calculated tiom Equation 7.7 for each of the NAPLs. using the multiple PAH system C,g,vdues. [n Figure 4.3 the three-component NAPL and two-component NML y',\. values are plotted rigainst .kdor,. The error bars show the precision of the y', values around the mean y',. as represenred by the standard error of the calculated 'I)." values. No apparent trend in -Ilv values is obvious fiom this plot. The average y', values in the two-cornponent adthree- component NULSwere cornpared for both PAHs and the resuIts of a t-test (a= 0.05). presented in Table 4.1. show that there was no significant difference betsveen the mean ,. values in the nvo-component and three-component NAPLs. From this it is conciuded that the NAPL activity coefficients of naphthdene and phenanthrene are not affected by the presence of the other PAH in the three-component NAPL systems. Therefore, the increase in Cy,Q values in the three-component NAPL systems cm be rittributed to an increase in the C1'.,s,sotvalues. .A plot of the measured total aqueous PAH concentration vs. the predicted total aqueous concentration fiom Equation 4.3 is show in Figure 4.4. The slope of this line is ciose to unity and the intercept is at (0.0). From this it can be intèrred that PAHs can together be treated as a pseudo-component in qstems in which the y'N values rernain constant and are known. The primary objective of these experiments was to determine the validity of using the synttiesized three-component NAPLs as a surrogate for red-worid complex NAPLs such as coal tar. In this work, it is observed that y', values are not atfécted by the presence or concentration of another PAH, which is in agreement with the resuits of Lee et al. ( 1993). who found that the f,of a number of PAHs were not affected by the composition of four diesel îûels. and Lee et ai. (1992b). who observed the same constancy of y',. values in eight coal tar sarnples. Similady. Lane and Loehr (1992) 1 Figure 41: c~''.,, and W. xPbenyin NAPL-Water Systems (x'", = 0.03) and cnaph,,in Water Contaeted nith Niphthakne and Phenanthrene Crystals

- - Rienantfirene O Ft~enanthrene~ve. A Rien. Oystats Ave.

1 Figure 1.2: cnaPhAQand c"",~ nxnaPb, in NAPL-Water Systems (x~"', = 0.09) and c'"~,~in Water Contacted wïth Naphthalene and Phenanthrene Crystals developed partitionhg coefficients, assuming constant y', values. which could accmtely predict the aqueous concentration of 16 PAHs in water contacted with 9 NAPL-soi1 simples fiom MGP sites and gas holder residue disposai sites. This, dong with the fact that the individual PAHs showed sirnilar dissolution behavior From bimy NAPLs into water contirms the appropriateness of using the spthesized rndti-component NAPLs as swogates for rd-world N-APLs.

Fi yre4.3: fknS and vs. Total NAPL PAEi Mole Fraction (x'*',)

Fiwe41: Estimited Total cPMAQvs. Experiment.1 Total cPmAQVaiues It was also an objective of these experiments to quanti@ the changes in the NAPL-water partitioning behavior of naphthaiene and phenaathrene in th-componenr NAPL systems. From the data presented hm, it cm be concluded that the increases in C',cl,,, values in three-cornponent NAPL qstem are significant but minor (less than 10%). especially in relation to the elevated CmTvaiues obsemed in rnicellar surtàctant solutions. The saine cm be said of the CJQvalues in three-component NAPL systems. Also. it has been shown that ~y'.~values are the sarne in both two and three-comportent NAPLs. Therefore. it is evident that any significant changes in the partitioning behavior observed in the NAPL-surfactant solution systems described below cmbe attributed to changes in the PAH NAPL-miceHe partitioning.

4.3.2. Micellar Solubilizaüon of PAHs From Three-component NAPLs

Naphthalene and phenanthrene MSR values in Brij 35 solutions were assessed in solutions contacted NAPLs containing varying amounts of naphthalene and with .V'"", held consunt at 0.03. The results of thrse experimenl are shown in Figure 4.5. It cmbe seen that as in he nvo-component NAPL systems. the naphthdene MSR values increased Iinearly ivith inmasing ,ph,.[n Table 4.2 the phmvalues. defdas the slope of the MSR vs. line. for both the hnio and three-component NAPL systems. Mt within cach other's 95% CI and hus are not signifcantiy different. However, it is evident hm Table 4.2 and Figure 4.5 that the MSR of phenanthrene in three-component NAPLs with

.irPhrn, = 0.03 is lower than in a two-cornponent NAPL with the same phenanthrene concentration. ln Figure 4.6 the MSR vaiues are presented for naphthaiene and phenanthrene in solutions contacted with three-component WLs. with held constant at 0.09 and .Ph", varying between 0.01 and 0.05. ïhe K"kn, vahe for these systems is compared to flkn,, hmsystems containine two-component NAPLs in Table 4.2. It is obçerved uiat h?kn,ER is lower in solutions contacted wi& the three-componem NAPLs than in those contacted with the two-component NAPLs. This is consisent with the findïngs in the three-component NMLs containhg IPh", = 0.03 presented in Figure 4.5. Therehre ir is conctuded that the presence of naphthaiene in the NAPL iowers the MSR of phenanthrene but that the presence of phenanthrene in the NAPL does not affect naphthalene MSRs.

Table 4.2: Cornparison of K', Vaiua Between Ternary and Binary NAPLs PAH System K'MSR X'N Mean MSR Conditions (at xlN) Naphthalene With Phen. 0.97i 0.04 0.09 0.093 i 0.0085 Single Solute 0.91 8 i 0.03 0.09 0.075 i 0.01 Phenanthrene With Naph. 1.28 i 0.05 0.03 0.0394 i 0.005 Single Solute 1.52 k 0.06 0.03 0.049 i 0.002

Figure 4.5: MSR vs. xnl*,, for Brij 35 Solutions Contacted with Multi-Component NAPLs and Naphthalene MSR in Brij 35 Solutions Contacted With Naphthalene and Phenanthrene Crystals ------. Rien. O (XnW.09)

+ Rien. (*M. 17)

Rien. (XnN=O.Ol)

Fhen. Ctystal

Figure 4.6: MSR vs. x~"'.,, for Bnj 35 Solutions Contaîted with Multi-Component NAPLs and Naphthalene MSR in Brij 35 Solutions Contacted With Naphthalene and Phenanthrene Crystals

These resuhs suggest that the presence of multiple fAHs within micelles af%ects partiùoning behavior between micelles and NAPLs. Pramaum and PeIizzetti ( 1996) note that little attention has been paid to the solubilization of mixtures of solutes but factors that cause stnicturai changes in the micelle or the filling of preferred sites are expected to atTect solubilization in micellar solutions. It is of interest to investigate the effects of PAH mixtures within micelles in order to make predictions regarding the relative solubility of P.4Hs in micellar solutions. Based on the above results, it is believed that the decrease in phenanthrene MSR values were due to cornpetition with naphthalene For space within the micelle. In Chapter 3.7, values were caiculated from Equation 3.10 and these values were used to draw conclusions regarding the nature of the environment experienced by PAHs within micelles. It is evident from inspection of Equation 3.12 that in multi-solute systems .Y.,, cannot be approximated by MSR values. ïhus X',,,values, in systems in which both

component t and j are present in significant quantities within the micelle. are caiculated by. Uçing these .V4blvalues, y', can be calcdated in muitiple solute systems frorn.

= ~~.4~(f.fdi1 WiM ciA~3a 1 (48) which is similar to Equation 3-10 used to calculate y', in two-component NAPL sysrems ewxpt that MSR is repIaced by The relationship between and X',for naphthalene and phenanthrene m presenied in Figurer 4.7 and 4-8. respectively. In Figun 4.7. is increasing rlighdy with increasing .Yphy suggesting that naphthalene solubilimion desplace in an increasingly less favorable environment within the micelle. This is sirnilar to the hndings pmrnted in Chapter 3 where the increase in fVh\. a highec rnicellar naphthalene concentrations was attributed to increased naphthdene soiubilization within the core relative to solubilimtion within the outer shell and palisade Iayer. No trend is evident in the -the",, values with increasing in Figure 4.7. in Figure 4.8 there is no observable trend in the y', values with increasing .Pkn,,. which suggests that the location of PAH solubilization is not aî3ected by increasing the phenanthrene concentration withh the micelle. This agrees with the observations in Chapter 2. and by the same reasoning used there. it is concluded that phenanthrene solubilizafion rakes place predominantly in the micelle core. over the ?ph*\ mge studird. The ratio of naphthalene MSR values to phenanthrene MSR values in the three- component NAPL systerns is higher than in the two-component systerns. Thus. it can be inferred that naphthalene is selectively solubilized over phenanthrene. The naphthalene soIubilization selectivky factor (ph)can be cdcuiated fiom Equation 4.9 (Guha et al.. 1 998a Nagarajan et al.. 1984).

Sn~h= (MSR~"1 MSR~~") I f [ xnVhN I ma,^)] IpphenN 1xphcnN(~~)]) (4.9)

Phrepresents the degree to which the relative MSR values change as a function of the NAPL composition. It can be seen in Figure 4.9 that the highest vaiues ofrphare at the lowest ,y,.This suggests that at low concentrations, naphthaiene is preferentially solubilized over phenanthrene to a larger degree. As arornatic compotmd solubilization at low concentrations is believed to occur predominantly in the hydrophilic sheli and the paiisade layer (Rosen, 1989), the above results suggest that naphthdene successtùlly cornpetes with phenanthrene for space at

Figure 4.2 y', vs. x~''~~,,in systems where xnaPh,is Varying and x""~= 0.03

Renanthrene Naphthakne . . -.

i Fipre 4.8: vs. xphenM,in Systems nhere xPhenYis Varying and x"%= 0.09 Figure 1.9: Naphthalene Selectivity In Surfactant Solutions Contact with Ternary NAPLs and PAH Crystals these micellar locations. This is likely due to the fact that naphthalene is les hydrophobie and has a lower molecular volume than phenanthrene (see Table 2. i ). which endows naphthalene with a pater affinity for the slightly polar environment in the micelle's outer layers. Surfactant head groups in micelles exist in a bound state (Mukerjee. 1979). Thus. soIubi1ization of PAHs in the palisade Iayer and outer shell is most likely attributable to an adsorption process. whereby PAH molecules fil1 spaces between the head groups. In the same way as naphthaiene displaces water molecules due to their relative incompatibility with the palisade Iayer (Rosen, 1989). it may also displace phenanthrene molecules. It is proposed that naphthaiene is more readily adsorbed into the interstitial spaces between bound head groups than phenanthrene and that this leads to lower phenanthrene MSRs in the presence of naphthalene.

Mukerjee ( 1979) noted that the micelle core is a liquid-like enviromnent in wbich sotubilization of HOCs is an absorption process. PAH solubilization in the core, relative to solubilization in the outer layers. is expected to increase at higher PAH miceilar concentrations. in this study it is observed that phenanthrene is not selectively solubilized over naphthalene at higherk", This is evidence that cornpetitive solubilization does not take place in the micelle core. which cm be attributed to the core's liquid-like state. One interesting remit is that the MSR values for both naphthalene and phenanthrene arc significantly higher than expected in either the two-component or the tliree-component NAPL systems when Brij 35 solutions are contacted with an excess of both PAH crystals togethtr, Nagarajan et ai. (1991) state that as the HOC mole fraction in the micelle core increases. the amount of Freedom experienced by the hydrophobic surfactant tails increases. making the core environment more Liquid-like. ln this srudy. the c~stalPAH system may have higher MSRs than expected due to a change in the micrllar core state to a more liquid-like form which wodd enhance PAHsolubilization. This is supported by the fact that the increase in the phenanthrene crystals MSR is larger than the increase in the naphthalene cymls MSR. This may be caused by an increase in the size of the hydrophobic core. hr which phenanthrene has a stronger affinity. hother contributing factor to the eievated MSRs in the crystaIline PMsystem could be a change in the micellar smcture or shape at the highest PAH concentrations. The typical linear relationship between and cYJy was not obsenred nt the higher surfactant concentrations in the crystals ystem, which suggests that a restrucnrring or swelling of the micelles may have occurred. As the MSR of phenanthrene is significantly affected by the soIubilization of naphthalene. P.4i-i~cm not be treated as a pseudo-component when considenng solubilization into surfactant solutions. However. these PAHs are quite different tiom cash other in th& degee of hydrophobicity and moIecular volume. Other PAH combinations in which ail the PAHc are very similar to each other may possibly be treated as pseudo-components (i.e. combinations of various methyi-naphthalenes). tt has been obse~edthat NAPL mixnms of benzene with cychhexane showed no selectivity when their relative MSRs were compared between two-component and single solute -stems. This is most likely due to the fact that these two compounds have simiIar molecular volumes and poIarities (Chaiko et ai.. 1984). It is therefore thought that PAHs with similar polarity-molecular voIume dimensionless numbers may be treated as pseudo- components when considering solubi1ization in surfactant solutions. ïhe interactions of multiple solutes wiihin micelies are not well understood. Three other studies have been identified which attempt to explain the important factors in determining the relative MSRs of various HOCs in multiple solute systems. The tindings in some of these help to describe the theory of mdti-component solubilization in surtàctant micelles. Chaiko et al. (1984) noted that the trend in MSR values of aromatic compounds in solutions of a given surfactant were well correfated with the aromatic compounds' molecular volumes in single solute systems. It dso observed that in two-component solute systems the relative MSRs of the components in single solute systems was a good predictor of the relative MSRs in the two-component systern. The results in this work agree with their tindings: naphthalene has the lower molecular volume and thus hm a higher maimurn MSR in the threecomponent NAPL system. Interactions that dect the relative soiubilization o€'NAPL components within micelles have also been witnessed by Chaiko et al. (1984). They observed an increase in the MSR of hexane in surfactant solutions contacted wirh NAPLs at low beiizene concentrations. From these observations. Chaiko et al. (1984) suggested that solubilization of benzene in the micelie's hydrophilic shell lowered the core-water interîàcial tension Ieading to a rise in the micelle's core volume. which increased the MSR of hexane. If this were the case in the systems used in this work. then it wodd be expected that phenanthrene MSRs should increase in the presence of naphthaiene. However. there are some significant differences between the systems used by Chaiko et al. (19984) and the systems used in this study. which may preclude such an effect on phenanthrene EvlSRs. FinChaiko et ai. (1954) used ionic sudactants for which the thermodynamics of micellization includes a term accouuting for the repulsive forces between the charged head _goups. It has been noted that the IK eiectron cloud of aromatics is polarizable and

that this allows them to be solubilized between the charged hydrophilic head pupsof ionic surîàctant micelles (Rosen, i989). Thus. the presence of benzene arnongst the head groups of ioNc micelles would also dissipate the repulsive forces between the head groups which would lead to a lowering of the free energy of micellization. in the nonionic surfactant solutions used here. this would not have been a factor as the repulsive forces behveen the head groups are significantly smaller. Nagarajan and Ruckenstein (199 1) point out that a11 micellar free energy changes will aiTect the micellar aggregation number and the CMC. Nagrinjan et al. ( 1984) note that the solubilization of benzene in solutions of the ioNc surfactant SDS resulted in a decrease in the CMC by 60% whiie the decrease in the core-water interfaciai tension \vas only decreased by 30%. They also state that the free energy decrease associated with the reduction of the core-water intertàciai tension due to benzene solubilization is offset by the increase in the free energy associated with the proximi~of benzene to the water molecules (Nagarajan et al.. 1984). It is therefore iikely that the increase in hexane miceltar solubilization in the presence of small arnounts of benzene in ionic micelles is due largely to a dissipation of the head group repulsion forces. which would lower the free rncrgy of micellization and increase the MSR of hexane by encouraging micellization. This would not be the case in nonionic surfactant solutions because the repulsive forces between the head pupsare much smaller and the reduction in the fie energÿ of micellization attributed to lowering the core-water interfacial tension would be ottset by the increased contact between the aromatic moiecdes and water in the micelle's outer Iayers. In the systems studied in this work. no reduction in the CMC was observed due to ?AH solubilizrttion. This is evidence that the free energy of micellization was not significantly reduced in the Brij 35 solutions which may explain why the results here differ hmthose of Nagarajan et al. ( 1981) and Chaiko et al. ( 1984). Other factors may have ais0 played a role in the obsewed synergistic solubilization of hexane in the presence of benzene. Chaiko et ai. (1984) used a system in which 1O ml of organic NAPL was contacted with 10 ml of surfactant solution. As was mentioned in Chapter 3. in cases where surfactant partitionhg hto a second liquid phase is significant, the MSR values are aitered when the MSR is detemiined by the value of Cdm,at oniy one FJQ(Zimmerman et ai. 1999). as was the case in their midy. Furthemore. the activity coefficients of the two components were assumed to be constant at dl mole fiactions ranging &om A', = 0.0 to 1.0. Changes in the y', values could also have contributed to the MSR trends observed. Neither of these effects were considered by Chaiko et al. (1984). Thus, as the synergistic effect was observed in ionic surfactant solutions in contact with significant volume of organic liquid. their explanation of the observed synergistic solubilization of hexane in the presence of benzene may not be accurate. [n another study. Guha et al. (1998a) reported the only results to-date regarding the solubilization of multiple PAH mixtures in a nonionic surfactant solution. They found that in some cases two-component and three-cornponent PAH mixtures enhanced PAH soiubilization in Triton X-100 miceiles and in other cases solubilization was decreased due to the presence of other PAHs. They concluded in the end that. based on the conjectures of Chaiko et al. ( 1984). naphthalene was solubilized at the rnicellar core- water interface and that this lowered the interfacial tension which in turn led to an increase in the MSR values for phenanthrene and pyrene. Guha et al. ( 1998a) went on to report that both the phenanthrene and pyrene MSR increased with increasing c""~~,-,, values. Hoviever. there are a nurnber serious shortcomings in the interpretation of the results presented by Guha et ai. ( 199th). First. it should be noted that while the phenanthrene MSR values in systems saturated with phenanthrene were obsewed to increase with increasing naphthdene concentration (C"OPhm7). the sarne was not obsewed for pyrene. If naphthdene increased the core volume then pyrene MSRs should be increased 3t leas as much as was observed for phenanthrene MSRs. because plne is more hydrophobic than phenanthrene. Instead it is observed that pyrene MSRs are reduced by the presence of other PAHs in al1 cases, except in a system saturated with naphthaiene. phenanthrene and pyrene. Overail, their conctusions are based on selectiveiy chosen results. while the remainder of their resuits either contradict their conclusions or provide no evidence in favor of the conclusions made. It shouId also be noted that many of the trends they observe fail within the experünental error of the measurements. For instance, they suggest that increasing naphthalene concentrations hmFhmT= 8 rn@ to 19 mfl resdts in an increase in Pkn,(defined as: CQhen.td[c"f,I x CI'hrnmT]) vaIues hm0.027 to 0.032. However. the precision of the first nurnber is + 0.004 and the precision of the second number is k 0.003'. hmwhich it cm be concluded that the ir"P*,wvalues are not sipifieanrly dinerent. Finaliy. the increse in the p.,valus in ystems satumted with phenmrhrene and naphthalene over systems containing just phenanthrene was the sarne as the increase of kThn,, in systems saturated with both pyrex and phenanthrene. It is unlikely rhat hese increases arc: the result of the !owering of the core-water interfacial tension since neither phenmthrene or pyrene are Iikely to be solubilized in as significant qusuitities in the outer Iayers of micelles as naphthaiene. instead. these increases in K',, vaiues could be attributed to the conversion of the core to more liquid-Iike state, due to the high PAH concentrations within the micelles. as was suggested above.

Considering the above shortcomings in the interpretation of Guha et al. ( I998a). the fact that their conclusions regarding miceIIar solubilization multiple PAN mixtures ditkr hmthe ones in this study is not problematic. Aso. it is concluded that contradictions between the results of Chaiko et al. (1984) and this study are attributabk to their use of ionic surfàctants while this work involvd the use of nonionic surtàctmt solutions. It is ttierefore conctuded that the resuIts of this snidy are vdid and that crimpetition for space in the outer miceiiar Iayers dictates the solubilktion of multiple PAHs in nonionic surfactant solutions. A rise in the aqueous solubility of both naphthalene and phenanthne was observed in systems containing both PAHs, This is presumed to be the effect of cosolvency-like interactions between the two PAHs in water. It was also observed that c.lovalues were higher in water contacted with three-component NAPLs than in water contacted with nvo-component NAPLs. Analysis of the PAH activity coefficients suggests that this increase in C',Q values cari be attributed to the rise in the PAH aqueous solubilities in the three-component system. Thus. it is concluded that the PAHs can be treated as a pseudo- component. in that their relative concentrations in the aqueous phase are predictable tiom their activities in the NAPL. It was therefore concluded that the multiple-PMI NULS are an appropriate .surrogate for rd-world chernically complex NAPLs. It is also concluded that the NAPL-water partitioning behavior of the PAHs is linle changed in the three-component NAPL as compared to the two-component NAPL. Thus. any sipificant changes in the partitioning behavior in the three-component NML systems containing surî'rictants can be attributed to changes in the NAPL-micelle partitioning.

It is observed that phenanthrene PYISR values are lower in three-component NAPL systems. while the PvlSR values of naphthalene remain unchanged. It is concluded that naphthalene is selectively solubilized over phenanthrene within the outer layers of the miceks. This is attributed to naphthalene's less hydrophobic nature and lower molecular volume which cause it to displace phenanthrene molecules fiom the spaces between the surfactant head groups. It is also observed that in solutions contacted with both PAH crystais together. the MSRs of both compounds are mised. This is attributed to changes in the nature of the micelle core and structure at hi& rnicellar PAH concentrations. Ultimately. it is concluded that PAHs with a less hydrophobic nature and lower molecular volume will be selectively solubiiiied into noaionic surfactant miceiles with voluminous outer Iayers. as is the case for the Brij 35. From this. it is proposed that the relative MSRs of nvo PAHs in solutions contacted with a chemicaily complex-NAPL will be predictable hmtheir relative MSRs in single solute systems and their concentration in the NAPL. 5. Conclusions

The overall purpose of this research was to determine the relationship between PAH mole fractions in multi-component NAPLs, and the extent of PMsolubilization observed in nonionic surfactant solutions. NAPLs containing one or two PAHs and hexadecane were used as a simplified mode1 for chemicaily complex NAPLs commonly found at contaminated sites. The molar solubility ratio (MSR) was used to describe the extent of PAH solubilization in NAPL-water systems. The MSR is an important process and design parameter tor surfactant flushing operations and other surfactant enhanced aquifer remediation (SEAR) technologies at contarninated sites. The t-m objective of this work was to test the hypothesis that PAH puiitioning from hexadecane into water would follow Henry's law. This was necessary in order to justi@ the use of the PAH-hexadecane mixtures as surrogates for NULS such as coal m. creosote and diesel hel. found at contarninated sites. Two-component NAPLs (Le. one P.4H compound dissolved in hexadecane) with a wide range of PAH mole fractions (3,varied from 0.01 to the solubility limit of each PAH in hexadecane) were contacted with water. and the aqueous phase PAH concentrations were mecisured. The results indicate that the partitioning of naphthalene and phenanthrene ffom hexadecane into water closely foIIows Henry's law at al1 PAH mole fractions studied. Partitionhg experiments behveen three-component NAPLs (containingnaphthdene. phenanthrene and hexadecane) and water showed that Henry's law behavior is also followed in multi-PAH NAPLs. it has been reported in past studies that the partitioning of PAHs from chemicdly complex NML mixtures such as coai tar and creosote follows can be modeIed by

Raouit's law ( Lee. et al.. 1992% Lee et ai.. 1992b; Peters et al. 1997). A requisite condition for the vdidity of Raoult's law or Henry's law partitioning is that the activity coefficient of the component in question remain constant over the concentration range studied. This proved to be the case in the mode1 NAPL-water systems used in this work Thus. it is Iikely that the partitioning behavior of PAHs hmhexadecane dlbe andogous to that of many cornplex NAPLs and therefore the synthesized NAPLs used in this research are an appmpriate surrogate. The second objective of this research was to develop a PAH partitioning model for NAPL-surfactant systems and to evaluate its vdidity using the model NAPL. A partitioning model based on Henry's law was developed to relate the NAPL PAH mole hction to a surfactant solution's solubiIization capacity. In systems where two- component NAPLs were contacted with nonionic surtactant solutions. it was observed that the MSR was related to the NAFL PMmole fraction by a Iinear function. This vas in a-geement with the predictions of the model. tt was observed tiom experiments that naphthalene. which has the lower hydrophobicity and molecular volume of the two PAHs. was more soluble in the micellar solutions than phenanthrene. This was attributed to significant PAH solubilization in the slightiy polar outer layers of the micelles. The measured MSR values in systems containhg PPLH crystals were plotted with the NAPL MSR data at points conesponding to the maximum dissolvable P.4H concentration in hexadecane. It &as observed that these points fit closely on the NAPL PAH mole fraction vs. MSR lines, and consequently it was concluded that the NAPL- micellar pseudo-phase partitioning coefficient (fi,,&) may be predictable from pure component MSRs. Considering the agreement of the crystalline systems MSRs with the values predicted by the quantitative stmctural-activity relationship (QSAR) developed by

Jahert et al. ( 1995). it is possible that the of other PAH-surfactant combinations ma! be predicted by coupling the QSAR with the model developed here. The hal goal of this work was to evaluate the ability of the partitioning mode1 to predict MSR values in systems containing multiple PAHs. It was observed that MSR values dso followed a linear relationship with NAPL mole hction in threecamponent NML systems. However. the individuai PAH MSR values in the three-component NAPL system did not necessarily correspond to the values in the two-component NPgL system. Obsewed MSR values for naphthalene in the nvo and three component N.@L systems were the same. while the MSR values for phenanthrene were significandy lower in solutions contacted with three-component NMLs than in the two component NAPL system. From these results it ws conciuded that Henry's law provides an adsquate rnodel for the partitioning of PAHs hmtwo-component NAPLs into micellar solutions. However. in the rnulti-PM system studied here. the MSR values were affected by competitive interactions. For this reason. the validity of the assumption that the partitioning of one species does not affect the partitioning of another in multi-component NAPL systems is questionable. tn solutions containing nonionic surfactant micelles, it is postulated that the PAHs with the greatest ability to fil1 spaces in the outer layer should maintain the highest MSRs in multiple P.M systems. Obsewed trends in the PAH micekir activity coefficients suggest that the discrepancies in the phenanthrene MSR values were due to cornpetition between the two Pusfor space in the micelle's outer shell and palisade layer. The surfactants used here al1 contain buiky polyethoxylated hydrophilic groups. Because of this. their outer iayers are sufficiently voluminous that PMpartitioning tvithin this region would account for a significant portion of the total rnicellar solubilization capacity. [t is concluded that compounds will compete for a finite number of interstitial spaces in the outer layers and that the compounds with the greatest aflnity for the micelle's outer regions tvi11 be most successful at filling these spaces. On the other hand. selective solubilization is not expected to occur in the micelle core due to its liquid-like nam. Therefore. in surfactant solutions where solubilization into the outer layers is significant. it is expected that less hydrophobie compounds. and compounds with smaller rnolecular volumes. will be selectively solubilized. From this. it folluws that the selective solubilization of one PAH over another in surfactant solutions contacted with comp1ex NML rni.unues. should be predictable hmknowiedge of their MSR dues in wo-component NAPLs or those of the pure substances. Surtictant tlushing has been proposed as a method of increasing the rate of dissolution of sparingly warer-soluble PAHs fiom complex NAPLs in the subsurface

( Mercer and Cohen IWO: West and Harwell, 1992). Knowledge of the solubility of PAtis in surfactant solutions ailows for predictïon of the extent and rate of PAH dissolution from NAPLs and the rate of PAH biodegradation. This information is key to developing an appropriate remediation strategy at NAPL contaminated sites. Grimberg et al., (1994)state that the rate of solid PAH dissolution into surfactant solutions is increased due to the presence of micelles- The authors show that the drïving force for PMdissolution is the ciifference between the equilibrium aqueous bulk-phase PAH concentration and the aqueous bulk-phase concentration at the theof interest. .As C',, is a function of both the surfactant concentration and the MSR it is apparent that u priori knowledge of MSR vaIues is required for prediction of the mas transfer of P.4Hs From complex NAPLs into surfactant solutions. The resuits presented in this study show that as the PAH concentration in the NAPL decreases. the MSR and apparent solubility in the surfactant solution aiso decrease by a linear relationship to it. This work shows that the apparent solubility of PAHs in nonionic surfactant solutions contacted with multi-component NAPLs is increased due to the presence of micelles in the solution. This increase is predictable by Henry-s law in two-component NAPL systems, while in multiple PAH sq'stems competitive interactions rnay affect the relative MSR vaIues. Considering this. it is possible to estimate the expected increase in PAH mass transfer hmcornpIex NULSand the rate of bidegradation in multiple PAH systems. The reIationships presented above can be used to mode1 surfactant flushing operations at sites containing excess free NUL in the subsurface. The completion of this work has pointed to a number of related research topics that would tùrther develop an understanding of the processes involved in surfactant solubi~izationof

PAHs fiom chemicaily complex NAPLs. In generai, a theoretical approach to determining the locus of PAH solubilization within micelles is needed in order to determine the nanue of possible cornpetitive interactions affecting PAH solubilization in multiple PAH systerns. This theory would need to be tested with a wide range NAPLs in order to develop a predictive model of PAH MSR values in surfactant solutions contacted with cornplex NMLs. This study provides the first step in such a process: the following sxperiments should eventually result in an accurate model of multipie PAH solubilization in surtictant solutions. In Section 3.3.3 it was observed that there was a sipificant drop in naphthaisne micellar pseudo-phase activity coefficients at very low micellar naphthalene concentrations. most likely due to naphthdene solubilization in the outer Iriyers of the micelles. The objective of this work was to study the equilibrium partitioning of P.Ws tiom NXPLs containing large quantities of PM. and thus this decrease in activity coefficients was not investigated further. Examination of this phenomenon in sysrems containing NMLs of very low mole PAH moie hctions may %ivefunher insight into the locus of naphthalene solubilization within micelles. It is believed that the same phenomenon was not observed in phenanthrene solutions because phenanthrene is more hydrophobie and has a larger molecular volume. However. it is possible that a drop in phenanthrene micellar activity coefficients may be observed phenanthrene concentntions Iower than those tested in this mdy. If this phenomenon is observed. it would provide further evidence that PAHs are soiubilized predominantiy into the outer layers of micelles at low PAH concentrations. due to its slightly polar nature as an aromatic compound. Frorn a theoretical point of view this information could help to descrii the selective sotubiliition behavior in multiple PAH systems Determination of MSR values fiom experiments with NAPLs containing very low P.W concentrations would aiso be of use in predicting the rates of PAH mass transfer at very low PAH N.4PL mole frictions. This would also help to develop target levels for PAH removal fiom NAPLs. Funhermore, the competitive interactions between PAHs for space within nonionic surfactant micelles could also be better understood if it was determineci at what concentration range the presence of naphthaiene began to affect the MSR of phenanthrene in micelles. Changes in the MSR values of phemthrene were not observed with changing naphthalene concentration in the system. However. phenanthrene MSR values were signiiïcantly lower in the presence of naphthalene as compared to phenanthrene MSR values in the two-component NAPL systems. hesumably, there is a threshold naphthalene concentration. or mitional range of naphthalene concentrations at which phenanthrene MSRs begin to show the effect of the presence of naphthalene in the micelles. Both of these phenornena wouid iikely be observed at very low P.4H concentrations. Thus. it would be necessq to alter the analysis techniques. making them more sensitive to PAHs concentrations. Van Durren ( 1960) noted that fluorescence rneasurements were 100-1000 times more sensitive to PAH concentrations than UV absorbance measurements. He shows that increasing the excitation and emission detection slit widths in a spectrofluorophotometer increases the sensitivity of the device but lawers the ability of the measurements to differentiate peaks. Fluorescence measurements could likely be calibrated for much lower PPJI: concentration ranges. In multiple PAH systems. it may tint be necasary to use chromatogmphic methods to separate the PMs. Determination of the locus of phenanthrene and naphthdene solubilization within miceIIes would aiso help to deveIop an understanding of the competitive interactions wîthin micelles. Past studies have used shifis in the üV spectm of benzene to determine its location within many ionic and nonionic surfactant miceIles (Lindrnan and Wemerstrom. 1980: Nagarajan et al.. 1984). However. it is questionable whether this is an effective technique since benzene spectra have ben seen to Vary in solvents with similar dielectric constants. Tlrus. it is not certain that spectral analysis cm be used to adequately determine the polanty of the environment surrounding the probe moIecuIe (Nagarajan et ai.. 1984). It has ben proposed that rneasuring the transfer free energies of solutes in miceiles may be the most effective way to determine the locus of sohbitization (Nagarajan et d.. 1984). A cornparison of mas tramfer free energies in single and multiple PMsystems could aid in the devetopment of a theoretical mode1 for predicting quantitatively the relative MSRs in multipie PM-! systems. Intèrences on the Iocus of PAH soIubilUation could dso be drawn fmm experirnents on systems contacthg multiple PAH NAPLs with other nonionic surtàctrtnts. Since cornpetitive solubili~tionbetween PMis is thought to occur in the micetle's outer Iayers. it is likely that surfactants with varied palyethoxylattted head group lengths would show dittéring degres of selectivity for naphthdene over pheoantfirene. Funhermortt. comparing the solubility of the PAHs in the pure alkane liquids. wtüch make up the surfactant tails, to the solubility of the PAHs in the micelles wouId give an indication of the relative pmitioning ot'PAHs between the micelle's core and outer [-ers. It has been suggested that solubilization of PAHs into surfactant micelles ma? affect the CRIC and the suucture of the micelle. Measuring the changes in die riggregation number. which can be done by Light scattering techniques and turbidity merisuremen= (Diallo et al.. 1994). due ro solubiIization would indicate possible changes in the size md structure of micelles. Measuing the CMC by surthce tension techniques would betrer indicate the eCfect of PAH solubilization of the CMC since values couid be compared benveen systems containing PAHs and those fixe of PAHs. Including benzene in the experiments would be usefui in light of the hct that most of the work done to date on selective soIubiIization of aromatic compounds within surt3ctant micelles has focused on benzene- Inclusion of this compound in these systems wouId strengthen the vdidity of cornparisons between the resuits here and those tiom pax studies. While hexadecane provided an ideal bulk NAPL in these experiments. it may dso be useM to test the validity of the results hmthis system using an alkane (such as hexane) which wouid k more solubte in both the aqueous and micellar pseudo- phases. This too wouid help test the ddity of cornparisons made to the work of Nagarajan et al. ( 1984) and Chdo et al. ( 1984). Expanding the experiments to include higher MW PAHs such as pyene and substituted PA& would dso provide valuable information. If data were availabte for a wide range of PAHs it may be possible to develop a QSAR based on considerritions of PAH's structura1 elements (Le. nurnber of rings, degree of substitution) and physical properties ( i.e. polarity, molecdar volume and aqueous solubility). This could be combined with the QSAR developed by Jafvert et al. (1995) to predict the MSRs ofa wide range of multiple PAH surfactant solutions, Finally. it would be of interest to test the ability of the micellar partitioning coetZicients developed in this research to predict the rate of PAH mass tramfer and biodegradation tiom complex NAPLs containing significant quantities of PM+Both the model NAPLs used here and complex NAPLs should be used in order to develop specific values that rnay be used to model these processes in the subsurface. Colurnn tests. including soil. NAPL. and bacteria wodd also be usehl to test the affects ofmrtkctant partitioning and adsorption to soil on the removal rates of PAHs hmcornpiex NAPLs. Knowledge of the apparent solubility can also be used to mode1 the rate of PAH biodegradation at P.W contaminated sites. Guha et al. ( I998b) found that for systems containing naphthalene. phenmthrene and pyrene crystals. muitiple PAHs were simuitaneously biodegraded in surfactant solutions. The authors concluded chat a portion of the PAH solubilized within the micelle was directly bioavailable. From this th. showed that the MSR values could be used to predict the total concentration of biorivaihble PM4 in the aqueous bdk-phase This in tum codd be used to predict biodegradation rates in multi-PAH systems. By coupling an appropriate biodegmdation model to a dissotution modei. it is often possible to predict the rate of removal of PAHs hmsites contaminated hith a fBre NAPL (Ghoshal. et al.. 1996). it is apparent hmthe above discussion that an increase in both rates will remit when surfactant micelles are present in the aqueous phase. It has been show that the MSRs of individuai PAHs are predictabIe Eiom Henry's law. Using this relationship. it is possible to better gredict the rate and extent of PAH removd and biodegradation frorn complex NAPLs contacteci with nonionic surfactant solutions. Overail there is still much to be understood before the rate of removal and reaction of PAHs fiorn free complex NAPLs in the subsurface cm be accurately predicted. The resuits of this study show that surfactant flushing should increase the extent and rates of removd and degradation of PAHs. and that these can to a signifiant deme be predicted by using liquid-liquid partitionhg models such as Henry's law. Nonetheless. work is needed to fdly understand and predict the nature and et'fects of selective solubilization of PAHs from multi-component NMLs. References

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*l'ahlc A3: QSAH cstiiiiiilion id Hexudccnnc froni Jafvert ct al. 1995 Hexadecane Naphthalene Phenanthrene Surfactant y1 y2 log MSR(max) X',,,, (rnax) log MSR(max) MSR(max) log MSR(max) MSR(rnax) KheRWAQ (Predlcted] [Predicted] KnaPhWA,[Predictsd] [Measured] KP~~~~~~[Predicted) [Measured] Tween 80 18 26 5.73 0.00213 0.0021 2.97 0.280 0.28 4.17981 0.136 0.143 12 4 5.66 0.00183 0.0018 2,90 0.240 0.18 4,11258 0.117 nla 12 23 5.50 0.00125 0.0013 2.74 O. 164 0.18 3.94767 O. 0798 O. 099 Tergitol NP10 15 10.5 5.73 0.00212 0.0021 2.97 0.278 0.23 4.17649 0.135 nla Triton X-IO0 14 9.5 5.70 0.00199 0.0020 2.94 O. 260 O. 19 4,14852 O. 127 n/a

wlierc, yl = number ol'csrbons in ilie surl'ucinni's Iiydrophohic tail

y, = number of groiips iti ilic surl'uciniii's Iiydropliilic Iicud (sorbiiun carboiis or cthoxy yroups)

Notc: MSR values calculutcd usiny ( J,o,,,, iis repciricd by Jüfvert cl al., 1995 l'or naphtliulciiç und phenunrhre~ic:

, (44~ and usinb ,,u= 3.97 x 1 W" us reporird by 1-luwwrd uiid Mryliin. (CRC) Table M: Naphthalene MSR Data for Two-Cornpanent NAPLs and Crystals XMpnN Brij 35 TrifOn Tween 80 x*~ Tergitol x"'". Brij 30 X-1 O0 NP10 0.01 0.013 0.027 0.03 0.030 0.009 0.020 0.01 0.012 0.03 0.037 0.009 0.03 0.05 0.055 0.046 0.03 0.05 0.050 0.046 0.05 0.047 0.05 0.056 0.083 0.05 0.048 0 .O9 0.117 0.083 0.09 0.076 0.09 0.086 0.083 0.09 0.084 0.09 0.084 0.120 0.09 0.083 0.09 0.104 0.120 0.1 1 0.13 0.154 0.157 0.1 1 0.13 0.155 0.157 0.13 0.1 11 0.13 0.145 Crystals 0.13 O. 126 0.1 7 0.21 3 Crystals 0.17 O. 157 0.1 7 0.188 0.17 O. 160 0.17 0.195 Crystals 0.191 Crystals 0.220 Crystals 0.179 Crystals 0.280 C rystals 0.208 Crvstals 0.229

Table AS: Phenanthrene MSR Data for Two-Compooeot NAPLs and Crystals

xp-N Brij 35 Tumen 80

0.01 0.018 0.020 0.01 0.017 0.021 0.02 0.032 0.043 0.02 0.033 0.045 0.03 0.050 0.067 0.03 0.049 0.069 0.03 0.050 0.067 0.04 0.060 0,092 0.04 0.062 0.097 0.05 0.075 0.110 0.05 0.079 0.109 Crystals 0.097 O. 142 Crystals 0.101 O, 144 Table A6: <,, - vs and C.5,for Surfactant Solutions Conneted with Three- ~om~onentNAPLs or Crystals ahenanthrene Naphthalene Total MSR MSR MSR 0.0416 0.0108 0.0524

Crystals Crystals Crystals Crystals O O O01 O 002 O 003 O 004 O O O01 O 002 0.003 0.004 0.005 Surfactant Concentration (mollL) Surfactant Concentration (mollL) 1 I Figure Al: Rrij 30 CMC Dctermination Chart Figure A3: Brij 35 CMC Dctermination Chart (xnnPhN= 0.12) (Crystallinc Naphthalene )

u O.HO I O 0.001 0.002 0.003 0.004 0005 O O O01 0002 0.003 0.004 0.005 Surfactant Concentration (mollL) Surfactant Concentration (mollL) Figure A2: Brij 35 CMC Determination Chart Figure Al: Brij 35 CMC Determination Chart (x"'"~~=O, 13) (x""~",= 0.04) O O0002 0.0004 00006 00000 0001 0 00005 O001 0.0015 0.002 0.0025 Surfactant Concentration (mollL) Surfactant Concentration (mollL) lI Figure A5: Tergitol NP10 CMC Determinution Chart Figurc A7: Twccn 80 CMC Determination Chart (xnnphN= O* 1 2) (x"""~= 0.12)

Oh00 1 O 00005 0.001 00015 0.002 0.0025 O 0.0005 O 001 O 0015 O 002 Surfactant Concentration (mollL) Surfactant Concentration (mollL) I I Figure A6: Triton X-100 CMC Dctcrmin~tioiiChart Figurc A8: Twcen 80 CMC Detcrminntion Chnrt (x"'"~,= o. 12) (x-, =O.OU)