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Integrated design of surfactant enhanced DNAPL remediation: Efficient supersolubilization and gradient systems
Abstract
Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in contamination of soils and ground water supplies. This paper summarizes key technical and economic issues for surface active agent (surfactant)-enhanced remediation of such contamination episodes. Laboratory and field results are cited illustrating each of these key issues. Using the design of an upcoming field study as an example, we illustrate the importance of system solubility enhancement, interfacial tension, viscosity and density in selecting a surfactant system. We also show how a site-specific capillary curve can be used to optimize contaminant solubility (super solubilization) while mitigating mobilization and vertical migration. Finally, we demonstrate the potential of a surfactant gradient system to progressively increase the super-solubilization potential without mobilizing trapped oil.
... When a surfactant is added into a system of oil and water, surfactant monomers accumulate at the oil/water interface, lowering the interfacial tension (IFT) between the oil/water interface. Greatly reducing the IFT induce the mobilization that allows the trapped oil to be released from the soil pores and move as its own phase [8,9]. Mobilization is vastly more effective than solubilization in removing oil [10,11,12], but it can also cause the vertical migration of dense non-aqueous phase liquid (DNAPL), which produces new and more complicated contamination problems. ...
... A lower IFT responded to a lower residual saturation of the trapped oil. To prevent mobilization, Sabatini et al. [9] applied the relation founded by Pennell by introducing the gradient concept, in which the IFT of a surfactant system is sequentially adjusted to minimize vertical migration and still maintain its remediation efficiency. By applying this method, the most mobile fraction of trapped oil would be removed by solubilization step by step. ...
... The fraction of the mobilized oil mixture was observed before an increase in solubilization. This is the general trend as observed by other studies [9,11,18]. The remaining trapped oil tends to be solubilized afterwards. ...
Surfactant enhanced remediation is viewed as a potential method for removing organometallic compounds from contaminated aquifers. Dibutyltin dichloride (DBT), as a representative organometallic compound, was applied in sand packed columns to observe its solubilization behavior compared to that of perchloroetylene (PCE), a normal organic solvent. Ottawa sand was used as the porous media. A mixture of DBT and PCE was applied as the contaminant. The tracer study exhibited the plug flow condition with a retention time of 79.9 min. The surfactant solution was a mixture of 3.6 wt% SDHS and 0.4 wt% C16DPDS with various concentrations of CaCl2.The column experiments were carried out by single and gradient surfactant systems. The effluent exhibited a general solubilization pattern for PCE, governed by a rate limiting mechanism. However, the concentration of DBT in the effluent observed in every experiment was just a slice of its solubilization capacity.The adsorption of DBT on the sand was suspected to be the cause of the problem. The solubilization of DBT by a surfactant was ineffective at removing DBT from the contaminated media. It may be concluded that DBT exhibits the properties of both an organic and inorganic compound; it could be solubilized by a surfactant and absorbed strongly on sand. Nevertheless, the results indicate that trapped DBT could be removed by mobilization in the form of a PCE-DBT mixture and that adsorption could be prevented by a very low pH condition.
... The theory behind surfactant flushing applied to aquifer remediation has been studied at the laboratory scale [7][8][9][10][11] and also at the field scale 6, 12-14 . Dwarakanath et al. 7 produced CDCs in the laboratory for two non-aqueous phase liquids (NAPLs) with alluvial aquifer material. ...
... Their results are used later in this paper for comparison purposes. In Sabatini et al. 10 , laboratory and field experiments are used to illustrate key technical and economic issues for surfactant flushing. They used a site-specific capillary curve to optimize the solubilization of denser-than-water NAPLs while avoiding mobilization and vertical migration. ...
... Previous studies on N Ca and CDC [10][11]17 highlighted the site-specific challenges of LNAPL capillary desaturation enhanced by surfactant flushing. Another challenge related to the use of in-situ soil flushing is achieving contact between the surfactant solution and the LNAPL within a heterogeneous source zone. ...
This paper investigates low-concentration (< 1 wt%) surfactant flushing when used as a follow-up technology for multiphase vacuum extraction on heterogeneous sites. Challenges posed by soil permeability, pore-size distribution, mineralogy, light non-aqueous phase liquid (LNAPL) weathering and groundwater hardness were quantified through batch and soil column tests. Compatibility issues between the mixed mineralogy soils, hard groundwater, mixed LNAPL and usual anionic surfactants were observed. The selected solution was a Winsor type I system promoting an interfacial tension of 0.06 mN/m between the site LNAPL and the amphoteric surfactant CAS in aqueous solution at pH 12. Surfactant loses to adsorption and pore media plugging were observed in the fine soil fraction. The capillary desaturation curves (CDC) obtained with the column tests suggested mixed-wettability behavior. The soil permeability strongly influenced LNAPL recovery, as expressed by the relationship obtained between capillary numbers (NCa) and hydraulic gradients. In this case, the critical NCa, marking the onset of capillary desaturation, could only be obtained with realistic hydraulic gradients in the coarse soil fraction. At those gradients, potential LNAPL recovery was 30% at the most. Unlike previously published CDCs, the relationship between NCa (log-scale) and LNAPL recovery was not linear but dependant on residual LNAPL saturation.
... Oil residue in small pores within petroleum reservoirs accounts for 50% to 65% of oil and is trapped by high forces of capillarity as well as interfacial tension between the hydrocarbon and aqueous phases. Different reductions in interfacial tension are needed for the mobilisation of this hydrocarbon [116,117], which is only achieved with the use of surfactant concentrations significantly higher than that required for the formation of micelles [118,119]. In enhanced oil recovery, the use of heat, tensioactive agents, microbial processes and gas injection leads to the recovery of a significant portion of the retained oil. ...
... Surfactants in solutions facilitate the solubilisation, dispersion and desorption of contaminants and allow the reuse of the soil [143]. Decontamination tests have been performed with different synthetic surfactants [144,145], but the desire to replace such compounds with natural surfactants has led to research into the use of biosurfactants [119]. Studies have demonstrated the potential of surfactin, rhamnolipids and sophorolipids [146][147][148]. ...
... The centrifuged microemulsions and ethanol was then used to wash the precipitates and remove the biosurfactant and heptane. The use of biosurfactants is a more ecofriendly approach [119]. Reddy et al. [172] found that silver nanoparticle synthesis could be stabilised for two months using surfactin, which is a biodegradable, renewable stabilising agent with low toxicity [3,119]. ...
In the era of global industrialisation, the exploration of natural resources has served as a source of experimentation for science and advanced technologies, giving rise to the manufacturing
of products with high aggregate value in the world market, such as biosurfactants. Biosurfactants are amphiphilic microbial molecules with hydrophilic and hydrophobic moieties that partition at
liquid/liquid, liquid/gas or liquid/solid interfaces. Such characteristics allow these biomolecules to play a key role in emulsification, foam formation, detergency and dispersal, which are desirable
qualities in different industries. Biosurfactant production is considered one of the key technologies for development in the 21st century. Besides exerting a strong positive impact on the main global problems, biosurfactant production has considerable importance to the implantation of sustainable industrial processes, such as the use of renewable resources and “green” products. Biodegradability and low toxicity have led to the intensification of scientific studies on a wide range of industrial applications for biosurfactants in the field of bioremediation as well as the petroleum, food processing, health, chemical, agricultural and cosmetic industries. In this paper, we offer an extensive review regarding knowledge accumulated over the years and advances achieved in the incorporation of biomolecules in different industries.
... Oil in the petroleum residues is usually trapped in the surface tension between the aqueous medium and hydrocarbons with high capillary forces [170,171]. Biosurfactants could reduce the interfacial tension to release the oil trapped between the oil/water and oil/rock phases [115,[172][173][174]. During biodegradation, biosurfactants increase the availability of the hydrophobic sites for the microbes, and the interaction between the cell surface and the biosurfactant causes membrane changes and reduces the amount of lipopolysaccharide in the cell. ...
... With increasing concentrations, the biosurfactants adsorb zirconia and provide an environment for the flocculation and dispersion of high solids into microparticles [243]. The stability of nanomaterials can be achieved with the help of biosurfactants [173]. ...
Biosurfactants, produced by the microorganisms such as bacteria, fungi, and yeast, possess high biocompatibility and low toxicity, with a wide range of properties such as surface activities and biodegradability. Biosurfactants are classified as glycolipids, lipopeptides, fatty acids, ionic, or polymeric-based biosurfactants. They can be water-loving, water-repelling, or amphiphilic, exhibiting both hydrophilic and hydrophobic characteristics. These unique and broad range capacities have specific applications in many industries. In the petroleum industry, biosurfactants are used in the bioremediation of oil spills. The diverse activities such as anticancer, antiinflammatory, antimicrobial, antibiotic, or antiviral activities of the biosurfactants have found applications in the medical and pharmaceutical industries. In cosmetics, biosurfactants are used in the production of creams, powders, lotions, gels, shampoo, and products such as antioxidants, antinourishing, and antimicrobial agents. The future applications of biosurfactants in nanomedicine, drug delivery, and targeted therapy could open up new avenues in disease treatment, especially in cancer therapeutics.
... The surfactant gradient approach based on the gradient curve (i.e., a normalized capillary/trapping curve) is introduced to maximize the DNAPLs solubilization while minimizing unwanted downward migration (Sabatini et al., 2000;Childs et al., 2004). The trapping curve depicting the relationship between S n and N T , which was adjusted with the van Genuchten equation (Van Genuchten, 1980), was expressed by Eq. (4): The gradient curves, which express the residual DNAPL saturation as a function of microemulsion (i.e., DNAPLs solubilization mixture) viscosity and IFT at specific soil properties and surfactant system flow conditions, were quantified by Eq. (5) and plotted in Fig. 4 (Childs et al., 2004). ...
... In addition, a low viscosity of the microemulsion phase is not only necessary for lowering head loss during surfactant flushing but also for avoiding DNAPLs mobilization (Childs et al., 2004;Tick et al., 2015). In the study of Sabatini et al. (2000), with the CaCl 2 concentration increased from 0 to 1.0 wt% in a determined surfactant formulation system (i.e., ISAeDowfaxeCaCl 2 system), the PCE was extracted over 90% within 5 pore volumes through solubilization. A DNAPL removal study indicated that the PCE was removed over 99% without mobilization by means of surfactant gradient system with a selected surfactant formulation through changing the electrolyte gradient (Pabute, 2004). ...
... Studies of detailed LNAPL and DNAPL recovery mechanisms by surfactant flushing can be found in numerous publications (Pennell et al. 1996 ;Martel et al. 1998c ;Martel et al. 1998d ;Martel et al. 1998b ;Falta 1998 ;Jackson and Dwarakanath 1999 ;Dwarakanath et al. 1999 ;Ramsburg and Pennell 2001 ;Roeder et al. 2001 ;Sabatini et al. 2000 ;Taylor et al. 2001 ;Dwarakanath et al. 2002 ;St-Pierre et al. 2004 ;Jeong and Corapcioglu 2005 ;Robert et al. 2006 ;Bernardez et al. 2009 ;Los Angeles LNAPL Group 2015 ). Laboratory batch and soil column experiments have been used to optimize surfactant solution composition and to quantify contaminant recovery mechanisms in controlled environments, where contact between the contaminant and the surfactant is favored. ...
... It is believed that a relatively simple and robust surfactant solution formulation would be able to achieve such a reduction. In the other scenario, the value of σ ow = 0.005 mN/m corresponds to the higher range of ultralow values obtained with Winsor Type III middle-phase microemulsion systems (Sabatini et al. 2000 ). This reduction could be achieved with a more elaborate and sensitive surfactant solution formulation, using branched anionic surfactants and high salinity. ...
A field tracer test was carried out in a light nonaqueous phase liquid (LNAPL) source zone using a well pattern consisting of one injection well surrounded by four extraction wells (5-spot well pattern). Multilevel sampling was carried out in two observation wells located inside the test cell characterized by heterogeneous lithology. Tracer breakthrough curves showed relatively uniform flow within soil layers. A numerical flow and solute transport model was calibrated on hydraulic heads and tracer breakthrough curves. The model was used to estimate an average accessible porosity of 0.115 for the swept zone and an average longitudinal dispersivity of 0.55 m. The model was further used to optimize the relative effects of viscous forces versus capillary forces under realistic imposed hydraulic gradients and to establish optimal surfactant solution properties. Maximum capillary number (NCa) values between injection and extraction wells were obtained for an injection flow rate of 16 L/min, a total extraction flow rate of 20 L/min, and a surfactant solution with a viscosity of 0.005 Pas. The unconfined nature of the aquifer limited further flow rate or viscosity increases that would have led to unrealistic hydraulic gradients. An NCa range of 3.8 × 10-4 to 7.6 × 10-3 was obtained depending on the magnitude of the simulated LNAPL-water interfacial tension reduction. Finally, surfactant and chase water slug sizing was optimized with a radial form of the simplified Ogata-Banks analytical solution (Ogata and Banks 1961) so that injected concentrations could be maintained in the entire 5-spot cell.
... Micellar solubilization of this type leads to a Winsor type I, oil-in-water emulsion [14,17,18]. Thus, the solubility of NAPL increases largely when the surfactant concentration is well above the critical micelle concentration (CMC) [19]. Although the exact mechanism of solubilization has not been completely elucidated, several models have been proposed, a few of which are described in detail by Zhong et al. [20]. ...
... Edwards et al. showed that the amount of solubilization of polycyclic aromatic hydrocarbons into the aqueous phase was linearly related to the concentration of nonionic surfactant, with more solubilization at higher concentrations [22]. Multiple laboratory tests have executed surfactant-enhanced solubilization of NAPL contaminants and many surfactants have been identified as good candidates for this process [19,20,[23][24][25]. ...
Remediation of petroleum contaminants from aquifers is an ongoing and environmentally relevant challenge. Non-aqueous phase liquids (NAPLs) can infiltrate groundwater reservoirs and pollute the water source leading to health and public safety concerns. NAPLs such as asphaltenes and naphthenic acids possess high adsorptive potential making removal difficult with conventional pump-and-treat techniques. As a result, surfactants and microemulsions have been posited as a means of mobilizing and solubilizing these heavy contaminants for safe and effective removal. Experiments have shown that microemulsions with nonionic surfactants are effective for removing aquifer contaminants, although the exact molecular level mechanism is not clear. To this aim, molecular dynamics simulations were carried out with water, surfactant, and microemulsion solutions. These simulations were compared to determine the effects of surfactants and microemulsions on contaminant removal from calcite mineral surfaces. Results indicate that polar molecules serve as a base layer upon which further non-polar molecules could adsorb. Microemulsions were effective at swelling the oil phase and reducing the overall percentage of polar components, leading to easier removal. In addition, the dissociation of microemulsion micelles at the contaminant-water interface was shown to be a thermodynamically favorable process.
... Most research has focused on the use of synthetic surfactants for the subsurface remediation of NAPL contamination (Cheng et al., 2001;Fiorenza et al., 2000;Sabatini et al., 2000). While several studies have looked at the use of biosurfactants Jenneman et al., 1983;Morán et al., 2000), they have generally looked at the use of single surfactant rather than exploiting the synergism possible with surfactant mixtures. ...
... Several factors are critical to successful implementation of SESR including: (1) minimizing the interfacial tension between surfactant and oil, (2) maximizing the oil solubilization, (3) and minimizing the surfactant loss due to precipitation, phase separation, and adsorption (Austad et al., 2000;Sabatini et al., 2000). Foaming is another concern, especially if air stripping is being considered as a separation process. ...
... The University of Oklahoma conducted side-by-side technology demonstrations of both surfactant solubilization and mobilization at Hill and conducted surfactant solubilzation of DNAPL at Dover AFB. In both cases, the surfactant system was tailored to site-specific contaminant and hydrogeology conditions (Sabatini et al. , 2000Childs et al. 2004;Wood et al. 2005). At Hill AFB, surfactant was injected and extracted using fully screened wells described above in the Hill AFB site description. ...
... • Solubilization is a robust technology that is easier to design and implement than mobilization, and poses less risks due to the potential for vertical NAPL migration. While mobilization has the potential to be much more effective than solubilization, the risks stated above must be balanced with this increased effectiveness (Falta et al. 1999a;Knox et al. 1999;Sabatini et al. 1999) which has led to novel implementation methods such as supersolubilization and gradient technologies (Sabatini et al. 2000). • At most sites, the NAPL is a complex mixture of many different contaminants. ...
Sites contaminated with immiscible nonaqueous phase liquids (NAPLs)
present unique and difficult challenges for remediation. A large breadth
of research has been conducted and it is for the most part agreed
(consensus) that many sites require site specific strategies and that a
significant portion of contaminant mass remains (incomplete removal)
within the subsurface even after aggressive remediation techniques were
implemented. It is the aim of this talk to initiate next step
discussions on proposing new strategies, combined remediation scenarios,
and different means of evaluating risk and cleanup goals. A major part
in doing so involves establishing well-studied contamination sites as
collaborative working "field observatories", assemble and develop
collective data sets to better understand contaminant transport and
factors limiting effective cleanup for the ultimate development of more
effective remediation strategies. Integration and availability to
comprehensive data-sets from "legacy" sites such as Dover AFB, Hill AFB,
Cape Cod, Borden AFB, AFP-44, and other sites wherein the authors have
experience (Little Creek Amphibious Base, Camp Legune, etc) have great
potential to lead to more research and discoveries for more effective
remediation strategies. What is the next step for dealing with NAPL
contaminated sites? We propose a more collaborative approach for solving
some of these most challenging issues for researchers and practitioners
when it comes to cleaning up and understanding difficulties specific to
NAPL-contaminated sites.
... In the remediation of solid surfaces, the critical micellar concentration (cmc) of the surfactants composing the microemulsions is highly important, as the use of this parameter is recommended for the washing method (Sabatini et al. 2000). At values above the cmc, the micellar concentration and, thus, the solubility of the organic contaminant is increased. ...
Microemulsions are important for soil and sediment remediation technology. The characteristics of the surfactants that make up these microemulsions include low sorption into soil or sediments, low surface and interfacial tension, the ability to penetrate tiny pores, and good solubilization of contaminants. This review revealed that microemulsions formulated with nonionic and anionic surfactants have higher recovery efficiencies for hydrophobic contaminants than cationic ones, as evidenced by the surveyed studies reporting effective remediation of soils and sediments using on microemulsions. These microemulsified systems have been found to remove petroleum and its derivatives from soil or sediments at percentages ranging from 40 to 100%. As such, this review can aid with the choice of surfactants used in microemulsions for remediation, such as those with plant-based components, which are promising solutions for the remediation of contaminated soils due to their contaminant extraction efficiency and biodegradability.
... Among surfactant-based microemulsion systems, the binary surfactant mixtures mostly reduce interfacial tension or enhance certain properties (e.g., more oil/water solubilization, less critical micelle concentration), which is better than using a single surfactant [3][4][5][6][7][8][9][10]. Extended surfactants are a novel classification that has been widely used to formulate microemulsions. ...
Optimal condition-based microemulsion is key to achieving great efficiency in oil removal. One useful empirical equation to predict an optimal condition is a hydrophilic–lipophilic deviation (HLD). However, the K constants of each surfactant should be the same to combine the HLD equations for the mixed surfactant. Recently, a normalized hydrophilic-lipophilic deviation (HLDN) was presented to avoid this limitation. This work sought to determine the phase behaviors and predict the optimal salt concentrations, using HLDN for the mixed surfactant. Sodium dihexyl sulfosuccinate (SDHS) as an anionic surfactant, and alcohol alkyl polyglycol ether (AAE(6EO4PO)) as a nonionic surfactant, were both investigated. Alkanes and diesel were used as a model oil. The results showed that AAE(6EO4PO) enforced both the hydrophilic and the hydrophobic characteristics. The Winsor Type I-III transition was influenced by the ethylene oxide, while the propylene oxide presence affected the Winsor Type III-II inversion. For the HLDN equation, the average interaction term was 1.82 ± 0.86, which markedly showed a strong correlation with the fraction of nonionic surfactant in the mixed systems. The predicted optimal salt concentrations using HLDN of SDHS-AAE(6EO4PO) in the diesel systems were close to the experimental results, with an error of <10% that is significantly beneficial due to the shorter time required for optimal determination.
... As a result, several technologies have been developed in the past three decades for DNAPL removal including enhanced dissolution using co-solvent or surfactants (M. Mohammed et al., 2019), in-situ chemical oxidation (Akyol, 2018), bioremediation Ottosen et al., 2021), and nanoremediation (Pak et al., 2020, O. Mohammed et al., techniques which mostly increase the solubility and/or mobility of the DNAPL, leading to significant reduction in remediation time (Rao et al., 1997;Sabatini et al., 2000;Huo et al., 2020). Low molecular weight alcohols are common and strong co-solvents for DNAPL remediation which can significantly increase the solubilization of DNAPLs (Liang and Falta, 2008). ...
Co-solvent flushing into contaminated soils is one of the most effective techniques for Dense Non-Aqueous Phase Liquid (DNAPL) remediation. In addition to the increase of DNAPL solubility, co-solvents (e.g. ethanol) can alter the viscosity and density of aqueous phase and diffusion coefficient of solute. Any changes in these parameters can change the flow behaviour and alter the upscaled DNAPL mass transfer coefficient which is a key parameter controlling soil and groundwater remediation at Darcy-scale. While numerous studies have investigated DNAPL remediation using co-solvents at the Darcy scale, pore-scale modelling of co-solvent enhanced DNAPL remediation has not been well investigated. In this work, a three-dimensional pore-network model was developed to simulate the 1,2-dichlorobenzene (DCB) remediation experiments using ethanol-water flushing solution. The model simulates the effect of changes in solubility, viscosity, density, and diffusion coefficient during co-solvent flushing of the DNAPL. The results of pore network modelling for ethanol-water flushing for the DCB remediation were also validated using the experimental data. In addition to pore-scale modelling, a continuum scale modelling (Darcy-scale) was used for the DCB remediation using ethanol-water flushing. The results of both pore network and continuum scale modelling demonstrated that the ethanol content and flushing velocity influence the interphase mass transfer and DNAPL dissolution process. The results indicated while the mass transfer coefficient decreased in the presence of ethanol, the process of NAPL remediation was improved due to the substantial increase of solubility in the presence of co-solvent. The large scale modelling showed that NAPL bank can be formed in the front of ethanol-water mixture flushing.
... m −1 with Tween 80 [Suchomel et al., 2007]. For PCE, the system's IFT can be reduced by the Aerosol family of surfactants: from 47.8 to b0.01 mN.m −1 [Dwarakanath et al., 1999;Sabatini et al., 2000;Childs et al., 2004], or by Triton X-100 and Tween 80 [Taylor et al., 2001;Harendra and Vipulanandan, 2011]. In this work, the surfactants were introduced at concentrations well below their respective CMC concentrations, in order to avoid DNAPL dissolution and hence the need for costly water treatment technologies [Sabatini et al., 1998;Ahn et al., 2008;Atteia et al., 2013;Maire et al., 2018]. ...
Chemical and thermal enhanced recovery of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) were investigated by using lab-scale 1D cells. Temperature was increased to reduce DNAPL viscosity (and hence increase its mobility), while surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media. Laboratory scale experiments, based on mass balance and indirect monitoring methods (i.e., permittivity, electrical resistivity and optical density), were conducted to quantify the effects of these enhancements. Heating the DNAPL up to 50 °C decreased its viscosity by a factor of two. The addition of a surfactant; i.e., Sodium Dodecyl Benzene Sulfonate (SDBS), at its Critical Micelle Concentration (to prevent DNAPL solubilization), decreased interfacial tensions by a factor of 12. Drainage-imbibition experiments performed in 1D cells provided retention curves (capillary pressure as a function of water saturation) of a two-phase (DNAPL-water) system in experimental glass bead porous media. The observed reduction of residual saturation (Srn) obtained with SDBS was 28% for 0.5 mm-diameter glass beads (GB) and 46% for 0.1 mm GB. No significant decrease in Sm was observed with thermal enhancement. The van Genuchten – Mualem model was found to satisfactorily reproduce the measured retention curves. Indirect measurements of water saturations (Sw) showed that: i. measured permittivities were very close to values modeled with the Complex Refractive Index Model (CRIM); ii. Archie's Law was less successful in reproducing measured electrical resistivities; iii. optical densities provide accurate estimations of Sw. At field scale, the combined monitoring of electrical resistivity (which provides a global picture) and permittivity (which yields locally precise but spatially limited information) is expected to significantly improve the collection of information on residual saturations Srn.
... Other detergency processes like soil cleaning seem to be a future challenge too in the case of high-density (eventually chlorinated) oil contaminants, which must be dissolved in a water phase to be removed (Baran et al., 1996;Baran Jr et al., 1994a, b;Cheng and Sabatini, 2002;Childs et al., 2004;Sabatini et al., 2000). Dissolving solid fats of leather (Haegel et al., 2009;Lamalle et al., 2006) or solid triacylglycerol oils at low temperature is a particular case, which has been analyzed as well (Do et al., 2014;Tanthakit et al., 2010). ...
The research published in the past half century indicates that surfactant interfacial performance in producing low tension or high solubilization with polar oils is not generally attained with pure conventional species exhibiting well‐defined polar and nonpolar parts. The improvement trends reached with surfactant mixtures as well as the introduction of additives like cosurfactants and linkers lead to the introduction of the so‐called extended surfactants, whose structure includes an intermediate polarity spacer between the hydrophilic head and the lipophilic tail. Recent investigations on different kinds of surfactants in a variety of applications—such as detergency, cosmetics, enhanced oil recovery or crude demulsifying, and vegetable oil extraction—indicate that these extended surfactants are likely to be particularly performing with oils containing polar groups, such as triacylglycerols and asphaltenic crudes. Possible applications of extended surfactants in enhanced oil recovery, crude emulsion breaking, detergency and cleaning, medicine and cosmetics vehicles, and natural oil extraction as well as some other cases are quickly reviewed.
... Among the technologies used in EOR, the use of operations to reduce interfacial tension by surfactants is implemented worldwide (Austad and Taugbøl 1995;Al-Wahaibi et al. 2014;Nabipour et al. 2017;Marhaendrajana et al. 2018), because its ability to reduce the interfacial tension between water and oil allows the oil trapped in the pores of the reservoir by capillary forces to be recovered (Van Dyke et al. 1991;Pornsunthorntawee et al. 2008;Li et al. 2012;Guo et al. 2015;Zhang et al. 2015;Kumar and Mandal 2017). However, to achieve a satisfactory result, high concentrations of surfactants are required (Sabatini et al. 2000;Fernandes et al. 2016), which ultimately depends upon high costs for the use of chemical surfactants. ...
In this study, the biosurfactant produced by Pseudomonas aeruginosa was evaluated in view of its ability to be used in Microbial-Enhanced Oil Recovery (MEOR). This microorganism was isolated from a soil artificially contaminated with crude oil and used to produce rhamnolipid using glycerol as the carbon source. The biosurfactant efficiently reduced water surface tension from 72 to 35.26 mN/m at its critical micelle concentration of 127 mg/L and emulsification rate (E24) of 69% for the crude oil. Furthermore, it was demonstrated that the rhamnolipid can recover oil, even 2 months after its production, which shows that its biodegradability is not a disadvantage to the application in MEOR. The best result, for a biosurfactant concentration of 100% above the Critical Micelle Concentration (CMC) and petroleum with API gravity of 21.90, showed that the total recovery factor was 50.45 ± 0.79%, of which 11.91 ± 0.39% corresponds to MEOR.
... Recent oil recovery technologies depend on natural reservoir pressure and /or injection of gas or water into the reservoir to drive the oil to producing wells (Van Hamme et al., 2003;Belyaev et al., 2004). However, these technologies mobilize only about 30-50% of the residual oil contained in the reservoir (Sabatini et al., 2000;Al-Wahaibi et al., 2014). Microbial enhanced oil recovery is potentially low-priced technique in which different microorganisms and their metabolic products are convinced to exploit the remaining trapped oil in the reservoir. ...
Bacterial Profile modification is an efficient process which brings the alteration in permeability of the porous media of the reservoir by selective plugging which eventually recover the residual oil. It is an advantageous and feasible method for residual oil recovery from high permeability zones of the reservoir. In this study, indigenous bacterial consortia, TERIJ-188 was developed from Gujarat oil fields. TERIJ-188 was identified as Thermoanaerobacter sp., Thermoanaerobacter brockii, Thermoanaerobacter italicus, Thermoanaerobacter mathranii, Thermoanaerobacter thermocopriae. The novelty of consortia was that it produces biomass (850 mg l-1), bio-surfactant (500 mg l-1), and volatile fatty acids (495 mg l-1) at 70°C in the span of 10 days, which are adequate to alter the permeability and sweep efficiency of high permeability zones facilitating the displacement of oil. The biosurfactant was analyzed for its functional group by FTIR and NMR techniques which indicate the presence of C-N bond, aldehydes, triacylglycerols. TERIJ-188 showed an effective reduction in permeability at residual oil saturation from 28.3 to 11.3 mD and 19.2% incremental oil recovery in a core flood assay. Pathogenicity test suggested that TERIJ-188 is non-toxic, non-virulent and safe for field implementation.
... However, these concentrations of surfactant were smaller than the critical micellar concentration, indicating that the solubilization was rather small, which was not observed for DBT on this fractional scale. Moreover, the cosolvent effect due to BuOH (Ladaa et al., 2001) and the solubility of PCE (250 mg/L; Sabatini et al., 2000) and DBT (135 mg/L; Damrongsiri et al., 2010) were also negligible in weight fraction units. The negligible level of aqueous surfactant at equilibrium resulted in a miniscule amount of PCE and DBT in the aqueous phase. ...
F-N co-doped TiO2/C/ZnFe2O4 (ZCT-FN) catalyst with excellent UV-Vis photocatalytic activity and recyclable performance was successfully synthesized by the sol-gel method. X-ray power diffraction results showed that ZCT-FN was anatase titanium dioxide with good crystallinity. X-ray photoelectron spectroscopy and UV-Vis revealed that F and N were co-doped into the lattice of TiO2, and a red shift of the absorption edge was brought out owing to F and N co-doping. Comparing to undoped TiO2/C/ZnFe2O4 and TiO2/ZnFe2O4, ZCT-FN exhibited an excellent photocatalytic activity for degradation of methyl orange both under UV- and Vis-light irradiation. Visible light photocatalytic degradation activity of ZCT-FN is nearly 4.2 times higher compared with P25. The high activity of ZCT-FN can be attributed to the synergetic effects of strong absorption and narrow band gap induced by F, N co-doping and narrow band gap semiconductor ZnFe2O4. The carbon layer between outer layer TiO2 and ZnFe2O4 core can effectively suppress the photodissolution behavior of catalyst. Moreover, ZCT-FN can be easily separated after the photocatalytic reaction and remain as stable photocatalytic activity after five cycles. This work not only offers a controllable method for the fabrication of F-N co-doped TiO2/C/ZnFe2O4 core-shell structure hybrids but also provides an effective and conveniently recyclable photocatalyst for the practical application in the purification of wastewater.
... However, these concentrations of surfactant were smaller than the critical micellar concentration, indicating that the solubilization was rather small, which was not observed for DBT on this fractional scale. Moreover, the cosolvent effect due to BuOH (Ladaa et al., 2001) and the solubility of PCE (250 mg/L; Sabatini et al., 2000) and DBT (135 mg/L; Damrongsiri et al., 2010) were also negligible in weight fraction units. The negligible level of aqueous surfactant at equilibrium resulted in a miniscule amount of PCE and DBT in the aqueous phase. ...
... Various enhanced oil recovery (EOR) technologies based on interfacial tension (IFT) reduction by surfactants are used worldwide to increase oil production. However, a reduction of several orders of magnitude in IFT is needed for efficient hydrocarbon mobilization [4,5], implying that high surfactant concentrations are required [6], except to gaseous hydrocarbons. High chemical costs have prevented the widespread use of surfactants for enhanced oil [7]. ...
Effects of nutritional and physicochemical parameters on the production of biosurfactants by Bacillus subtilis RI4914 were evaluated. Effects of three different concentrations of NH4NO3 and/or yeast extract were tested. The treatment with 2.0 g l(-1) of NH4NO3 without yeast extract resulted in the highest biosurfactant, organic acid, solvent and polymer concentrations, and this cultivation condition was selected for the residual oil recovery experiments. The lower interfacial tension between crude oil and the culture supernatant was 0.07 mN/m and this result was achieved at NaCl concentrations up to 120 g l(-1). Culture fluid with 600 mg (-1) biosurfactant and the polymer produced by the bacterium resulted in residual oil recoveries up to 88%. The attainment of low interfacial tensions and high oil recoveries with the biosurfactant concentrations used at high salinity and temperature indicated that B. subtilis RI4914 is an excellent candidate for application in MEOR.
... Various enhanced oil recovery (EOR) technologies based on interfacial tension (IFT) reduction by surfactants are used worldwide to increase oil production. However, a reduction of several orders of magnitude in IFT is needed for efficient hydrocarbon mobilization [4,5], implying that high surfactant concentrations are required [6], except to gaseous hydrocarbons. High chemical costs have prevented the widespread use of surfactants for enhanced oil [7]. ...
... Anionic surfactants are very sensitive to the background electrolyte species and concentration, and as a result, their performance can be improved markedly by the addition, or presence, of salts (Baran et al., 1994;Sabatini et al., 2000). Above a certain threshold of salt concentration, however, the phase behavior of anionic surfactant may be negatively impacted, leading to surfactant precipitation or the formation of highly viscous gels (Shiau et al., 1995). ...
When properly implemented, surfactant and cosolvent flushing technologies can recover substantial quantities of contaminant mass from chlorinated solvent source zones in relatively short time periods. As with most in situ remediation technologies, surfactant and cosolvent flushing are most effective in relatively homogeneous subsurface systems with sufficient permeability to allow for delivery of injected fluid and subsequent recovery of the contaminant. Under ideal conditions, surfactant and cosolvent flushing field trials have consistently resulted in contaminant mass recoveries of greater than 80 to 90% of the contaminant mass, although recoveries on the order of 50 to 70% are more likely at complex sites. Nevertheless, such reductions in contaminant mass hold the potential to reduce source zone longevity and downgradient contaminant mass flux, thereby reducing potential risks to the environment and public health. Recent advances in these technologies have focused on combining aggressive, short-term surfactant flushing technologies with lower impact, long-term strategies such as bioremediation, which hold promise as a means to more effectively achieve remediation goals and reduce overall treatment costs.
... The advantages of this means are high treatment efficiency and short remediation time (7). Therefore, SEAR is considered the most popular technology worldwide (8)(9)(10). Although considerable progress has been made regarding petroleum organic pollutants with SEAR, this technology may lead to two problems without a means for surfactant recovery and recycling (11)(12)(13)(14). ...
This study conducted counter-current solvent extraction to investigate the influence of solvent/solution volumetric ratio, solvent flow rate, and surfactant concentration on extraction efficiency. Fitting formulas for predicting the partition coefficients of the contaminant and surfactant between the aqueous and solvent phases were developed to optimize the counter-current solvent extraction. It is found that the solvent/solution volumetric ratio and the surfactant concentration had greater impact than the solvent flow rate on the extraction efficiency. The relationship between the partition coefficient K and the solvent/solution volumetric ratio or surfactant concentration was closely related to power function. Besides, the accuracy of the fitting formulas was consistent with the experimental results.
... Residual oil present in small pores within the reservoirs comprises 50e65% of oil in place (US DOE, 2012) and is entrapped by high capillary forces and interfacial tension between the hydrocarbon and aqueous phases. Several orders of magnitude reduction in interfacial tension are needed for hydrocarbon mobilization (West and Harwell, 1992;Austad and Taugbøl, 1995;Green and Willhite, 1998), usually achieved by surfactant concentrations significantly above that needed to form micelles (e.g., the critical micelle concentration) (Salager, 1999;Sabatini et al., 1999Sabatini et al., , 2000. Enhanced oil recovery (EOR), e.g., the use of heat, chemicals such as surfactants, microbial processes, and miscible gas injection (Green and Willhite, 1998), has the potential to recover a significant portion of this entrapped oil. ...
Significant amounts of entrapped oil could be potentially recovered from water-flooded reservoirs nearing their economic limit of production via biosurfactant-enhanced oil recovery. However, evidence for the persistence and metabolic activity of injected biosurfactant-producing bacterial species activity is lacking. We injected a glucose-nitrate-mineral nutrient mixture and two lipopeptide biosurfactant-producing Bacillus strains into two wells to correlate in-situ metabolism with oil recovery. Two wells producing from the same Viola formation were each inoculated with about 60 m(3) of tank battery brine with a nutrient mixture containing glucose, sodium nitrate and trace metals and Bacillus licheniformis RS-1 and Bacillus subtilis subsp. subtilis spizizenii NRRL B-23049. Analysis of production water indicated in-situ growth of the injected strains and other heterotrophic fermenting bacteria, metabolism of the nutrients, and biosurfactant production. Both wells had a peak lipopeptide biosurfactant concentration of 20 and 28 mg/L, respectively, which is twice the minimum concentration required to mobilize entrapped oil from sandstone cores. Metabolic products of glucose fermentation in both wells were acetate, 2,3-butanediol, ethanol, formate, lactate, and succinate and cells and these products accounted for 107.6% of the glucose used. The increase in biosurfactant, acids, alcohols and carbon dioxide during the first 5 days after commencement of production corresponded directly with an increase in oil recovery. Wellhead measurements of total produced fluid, the water-to-oil ratio and the percentage of oil showed that about 52.5 m(3) of additional oil (net cumulative increase) occurred during the first 60 days of sampling. These results showed the feasibility of stimulating in-situ biosurfactant production and its potential to improved oil production from mature oil reservoirs. Published by Elsevier Ltd.
... The contamination of soils and groundwater by non-aqueous phase liquids (NAPLs) is a major environmental problem worldwide [1][2][3]. Although not applicable to every situation, surfactant-enhanced aquifer remediation (SEAR) proved a promising technology to clean NAPL contaminants, such as benzene and nitrobenzene from contaminated soils and groundwater [4][5][6][7]. Compared with traditional pump-and-treat remediation, SEAR could overcome the ''tailing effect'', and thus remediation time could be dramatically reduced, thereby improving remediation efficiency. ...
Solvent extraction is an efficient method that separates surfactants and pollutants in pumped groundwater during surfactant-enhanced aquifer remediation (SEAR). This paper addresses the factors that influence the extraction efficiency of solvent extraction method. A series of batch experiments were conducted to verify the effectiveness of solvent extraction by describing the interactions among contaminants, surfactants, and solvents, using factors such as extraction time, solvent/water volumetric ratio, surfactant type and concentration, contaminants type and concentration, solution salinity and solvent equivalent alkyl carbon numbers (EACNs). The surfactants, contaminants, and solvents used were sodium dodecyl sulfate (SDS) and Tween 80, benzene and nitrobenzene, n-hexane, n-decane and n-hexadecane, respectively. The results indicated that (1) the increase in extraction time or solvent/water volumetric ratio caused higher benzene removal efficiency, but the increment of removal was not significant after 2 h or 0.1; (2) surfactant type and concentration significantly affected extraction efficiency. The increase in SDS concentrations could generally increase benzene removal and then decline, whereas benzene removal seldom changed under the studied Tween 80 concentration range. Moreover, Tween 80 losses were much lower than that of SDS. When mixing the two surfactants, benzene was increasingly separated from the aqueous surfactant solutions by increasing the proportion of Tween 80, and surfactant losses almost depended on monomers instead of micelles within the aqueous surfactant solutions; (3) the efficiency of separating benzene from aqueous surfactant solutions was higher than that of nitrobenzene. Furthermore, n-hexane losses in the benzene aqueous solution were higher than that in the nitrobenzene aqueous solution; (4) higher inorganic salt concentration in the aqueous Tween 80 solutions could increase benzene removal and decrease Tween 80 losses, thereby improving extraction efficiency; (5) n-hexane was more suitable to separate benzene from aqueous Tween 80 solutions because its EACN was closest to the EACN of benzene.
... Residual oil present in small pores within the reservoirs comprises 50e65% of oil in place (US DOE, 2012) and is entrapped by high capillary forces and interfacial tension between the hydrocarbon and aqueous phases. Several orders of magnitude reduction in interfacial tension are needed for hydrocarbon mobilization (West and Harwell, 1992;Austad and Taugbøl, 1995;Green and Willhite, 1998), usually achieved by surfactant concentrations significantly above that needed to form micelles (e.g., the critical micelle concentration) (Salager, 1999;Sabatini et al., 1999Sabatini et al., , 2000. Enhanced oil recovery (EOR), e.g., the use of heat, chemicals such as surfactants, microbial processes, and miscible gas injection (Green and Willhite, 1998), has the potential to recover a significant portion of this entrapped oil. ...
The long-term economic potential for enhanced oil recovery (EOR) is large with more than 300 billion barrels of oil remaining in domestic reservoirs after conventional technologies reach their economic limit. Actual EOR production in the United States has never been very large, less than 10% of the total U. S. production even though a number of economic incentives have been used to stimulate the development and application of EOR processes. The U.S. DOE Reservoir Data Base contains more than 600 reservoirs with over 12 billion barrels of unrecoverable oil that are potential targets for microbially enhanced oil recovery (MEOR). If MEOR could be successfully applied to reduce the residual oil saturation by 10% in a quarter of these reservoirs, more than 300 million barrels of oil could be added to the U.S. oil reserve. This would stimulate oil production from domestic reservoirs and reduce our nation's dependence on foreign imports. Laboratory studies have shown that detergent-like molecules called biosurfactants, which are produced by microorganisms, are very effective in mobilizing entrapped oil from model test systems. The biosurfactants are effective at very low concentrations. Given the promising laboratory results, it is important to determine the efficacy of using biosurfactants in actual field applications. The goal of this project is to move biosurfactant-mediated oil recovery from laboratory investigations to actual field applications. In order to meet this goal, several important questions must be answered. First, it is critical to know whether biosurfactant-producing microbes are present in oil formations. If they are present, then it will be important to know whether a nutrient regime can be devised to stimulate their growth and activity in the reservoir. If biosurfactant producers are not present, then a suitable strain must be obtained that can be injected into oil reservoirs. We were successful in answering all three questions. The specific objectives of the project were (1) to determine the prevalence of biosurfactant producers in oil reservoirs, and (2) to develop a nutrient regime that would stimulate biosurfactant production in the oil reservoir.
The surfactant-based microemulsion technique enhances oil-contaminated soil remediation with high removal performance. With the presence of soil in the surfactant–oil–water (SOW) system, surfactants are the key success for this technology due to their activity. This study aimed to investigate the oil removal efficiency of different surfactant mixtures and determine surfactants’ and oil’s material balances in the soil flushing process. The mixed surfactant systems of SDHS-C12-14Ej (j = ethylene oxide group; 1, 5, 9) and SDHS-C16-18E6P4 mixtures were formulated, and a commercial diesel was selected as a model oil. The soil flushing experiment was conducted through the sand pack column with a 0.5 ml/min flow rate at room temperature. It was found that the SDHS-C12-14E1 system (9:1 ratio, 8%wt/v NaCl, Winsor Type III) showed the highest removal efficiency. The intermediate structure (i.e., ethylene oxide: EO) in the SDHS and C12-14Ej is an influent parameter in the surfactant selection for soil remediation. The less EO group in the surfactants, the better sand was decontaminated. The microemulsion types (i.e., I, II, and III) also affected the soil washing/flushing performance. Winsor Type III had the highest oil removal efficiency, followed by Winsor Type I, and II microemulsions. For mass balance in mixed surfactant systems, > 50% of SDHS, an anionic surfactant, remained in the aqueous effluent, while most of C12-14Ej and C16-18E6P4, a nonionic surfactant, solubilized in the oil phase and significantly adsorbed onto the sand.
Surfactants can aid subsurface remediation through three primary mechanisms - solubilization, mobilization and/or emulsification. Among these mechanisms, emulsification in porous media is generally not well studied or well understood; particularly in the context of treating sources containing multicomponent NAPL. The objective of this research was to elucidate the processes responsible for recovery of a multicomponent hydrocarbon NAPL when surfactant solutions are introduced within a porous medium to promote the formation of kinetically-stable oil-in-water emulsions. Emulsifier formulations considered here were selected to offer similar performance characteristics while relying on different families of non-ionic surfactants - nonylphenol ethoxylates or alcohol ethoxylates - for emulsification. The families of surfactants have particular environment relevance, as alcohol ethoxylates are often used where replacement of nonylphenol content is necessary. Results from batch and column studies suggest performance of the two formulations was similar. With both, a synergistic combination of emulsification and mobilization led to recovery of a synthetic gasoline NAPL. The relative contribution of solubilization to the recovery was found to be minor. Moreover, the physical processes associated with emulsification and mobilization acted to limit the amount of preferential recovery (or fractionation) of the multicomponent NAPL.
Microemulsions, as isotropic, transparent, nano size (<100 nm), and thermodynamically stable dispersions, are potentially capable of being used in food formulations, functional foods, pharmaceuticals, and in many other fields for various purposes, particularly for nano-encapsulation, extraction of bioactive compounds and oils, and as nano-reactors. However, their functionalities, and more importantly their oil extraction capability, strongly depend on, and are determined by, their formulation, molecular structures and the type, ratio and functionality of surfactants and co-surfactants. This review extensively describes microemulsions (definition, fabrication, thermodynamic aspects, and applications), and their various mechanisms of oil extraction (roll-up, snap-off, and solubilization including those by Winsor Types I, II, III, and IV systems). Applications of various food grade (natural or synthetic) and extended surfactants for edible oil extraction are then covered based on these concepts.
In-situ microemulsion flushing is an effective remediation technology for the removal of dense non-aqueous phase liquids (DNAPLs) from aquifers. Nitrobenzene (NB) is a typical DNAPL pollutant that is responsible for the serious contamination of many groundwater systems, while its removal using the flushing method has rarely been studied. In this study, bench scale, 1-D column and 2-D tank experiments were conducted to establish an efficient salt-free sodium dodecyl sulfate (SDS)/1-butanol based in-situ microemulsion flushing system for NB contaminated aquifers. Results showed that the NB/SDS/1-butanol/water microemulsion increased dissolved NB concentrations by more than 15-fold compared to the SDS-only solution. The formulation also presented good solubilization capacity at low temperature (5 ℃) and with clay media. NB was effectively removed from the aquifer by solubilization and mobilization via the formation of the microemulsion with the injected SDS/1-butanol solution. The flushing system also reduced the tailing phenomenon in later remediation stages, and exhibited weak reagent adsorption onto aquifer media. Furthermore, the vertical DNAPL migration to deeper aquifer was effectively controlled. Therefore, the constructed in-situ microemulsion flushing system is a highly efficient treatment method for NB contaminated aquifers, with this study providing valuable reference information on the optimal reagent parameters and the remediation mechanism.
Oil spill contamination in soil is still problematic. At the same time, petroleum-contaminated soil in oil reservoirs contain various microbes, which have the ability for biosurfactant production. Extracting these biosurfactants is a very promising and cost-effective strategy for the microbial enhanced oil recovery process. Biosurfactants production using Bacillus licheniformis AnBa7 and Rhodococcus erythropolis sp., isolated from Egyptian crude oils, was enhanced using various carbon sources. The best biosurfactant characteristics were observed when 1% of crude oil was used as a carbon source. The production was further improved by using a developed fed-batch cultivation strategy depends on using 1% Glucose as a single addition at the beginning of the culture. Then 1% of crude oil was added three times during the production process. This strategy enhanced surfactin and trehalose productivity by 1.8 and 4.7 fold higher than the normal conditions, respectively. The surface-active and thermodynamic properties were studied. The results indicated that the calculated values of ΔGmic for surfactin complex, and trehalose complex were −18.47 and −18.28 kJ/mol at 60 °C, respectively while ΔGads values were −30.42 and −29.46 kJ/mol at 60 °C. The interfacial tension (IFT) values of surfactin complex and trehalose complex systems were ranging from 0.75 to 0.19 mN m–1 and from 0.93 to 0.26 mN m–1 at 60 °C, respectively. However, the (IFT) for the blank solution was ∼11.57 mN m–1, and the wettability was changed to an excellent water-wet state (θ = ∼ 17.42–24.0°). The core-flooding studies showed that the enhanced oil recovery for surfactin complex and trehalos complex, at maximum concentration 6 g/L, were 59.21% and 51.83%, respectively. A predicted mechanism was illustrating through the text.
The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12‐14 alcohol ethoxylate (C12 − 14Ej) that contains an ethylene oxide (Ej) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C12 − 14Ej systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C12 − 14E1 was more lipophilic, while SDHS − C12 − 14E9 was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C12 − 14E5 system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.
Pumping experiments were performed in a 2D tank in order to estimate the recovery yield of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) by varying different parameters: permeability of the saturated zone, pumping flow rates, addition of surfactant and heating. Surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media while temperature was increased to reduce DNAPL viscosity (and hence increase its mobility). Chemical enhancement was performed with the addition of Sodium Dodecyl Benzene Sulfonate (SDBS) (at its Critical Micelle Concentration, to avoid DNAPL dissolution) and thermal enhancement was performed at 50 °C (to avoid DNAPL volatilization). The experiments were monitored with photography allowing, on the basis of image interpretation, to convert optical densities (OD) into water saturations (Sw). Image interpretations were compared with modelling results. The two-phase flow modelling was performed with the pressure-pressure formulation using capillary pressure and relative permeability functions based on the van Genuchten – Mualem equations. Measured volumes of DNAPL recovered as well as the displacement of the DNAPL-water interface (radius and height of the cone of depression) are consistent with the modelling results. Furthermore, chemical enhancement results in a significant increase in the recovery rates of DNAPL. The observed improvement in the recovery of DNAPL with chemical enhancement is due to the fact that: (i) the residual saturation inside the cone of depression is lower and (ii) the cone of depression radius and height increase. Thermal enhancement had no beneficial effect on DNAPL recovery rate or yield. This study shows that it is possible to accurately determine water and DNAPL saturations by image interpretation during pumping tests in a 2D tank in the laboratory. For field-scale applications, the two-phase flow model allows to determine remediation yields as well as the volumes of the cone of depression according to the different operating conditions.
Organic liquids with low water solubility are generally described as Non-Aqueous Phase Liquids (NAPLs). They penetrate the soil subsurface as oily liquids (free products), do not mix readily with water, and therefore flow independently from groundwater. They can be divided into two main classes: light NAPLs (LNAPLs), such as refined petroleum products, which are lighter than water; and dense NAPLs (DNAPLs), such as trichloroethylene, which are heavier than water. NAPLs may dissolve in the aqueous phase or evaporate in the gas phase. Due to their toxicity and widespread occurrence, they generate serious environmental and health problems. Most contaminants migrate when they are present as free-phase. Therefore, removing free products is of primary importance for the remediation of any contaminated site. Conventional NAPL remediation consists of pumping the free product until residual saturation is reached (i.e., no more NAPLs can be recovered). This residual saturation may impact gases (vapor phase) or groundwater (dissolved phase) for several years. Decreasing this residual saturation (i.e., increasing the recovery yield of free product) may contribute to reducing: (1) contaminants dissolved into water, (2) the duration of the remediation operation, (3) the extent of plumes and related contaminant concentration levels, and consequently, (4) remediation costs. In this chapter, we present conventional technologies for free product recovery from the practical and theoretical viewpoints: pump-and-treat, skimming, bioslurping, and recovery trenches. This chapter describes the advantages and limitations of these techniques, and discusses innovative technologies such as thermal and chemical enhancement (i.e., surfactants), which aim to increase free product recovery yields and rates.
When surfactants are coupled with persulfate-based ISCO (in situ chemical oxidation) to facilitate the remediation of soil-sorbed hydrophobic organic contaminants or non-aqueous phase liquids, surfactant selection is critical in avoiding excessive nonproductive consumption of persulfate and ensuring proper longevity of persulfate. In this study, the kinetics and mechanisms of the decomposition of persulfate in the presence of simple organic compounds containing primary basic building blocks of nonionic and anionic surfactants were first examined to elucidate the impact of individual building blocks to persulfate decomposition. Further kinetic and mechanistic studies were then carried out in the presence of representative surfactants from the four families of surfactants frequently applied in subsurface remediation. The results indicate that alkyl polyoxyethylene nonionic surfactants significantly accelerated initial persulfate decomposition due to radical-chain processes induced by the oxyethylene functional groups, whereas alkylphenol polyoxyethylene nonionic surfactants retarded initial persulfate decomposition by quenching the radical-chain processes by the aromatic rings. On the other hand, alkyl sulfonate anionic surfactants and alkylbenzene sulfonate surfactants retarded initial persulfate decomposition to some extent; Coulomb repulsion of SO4⁻/S2O8²⁻ and surfactant anion/radical, and entry of surfactant radical anion from the pseudo-aqueous phase into the pseudo-micellar phase may contribute to retarding initial persulfate decomposition. Overall, the results offer insightful structure-based guidance in selecting proper surfactants for surfactant-enhanced persulfate-based ISCO.
Short branched alkyl polyoxypropylene sulfates, sodium isohexyl polyoxypropylene sulfate (i-HPS) and sodium isooctyl polyoxypropylene sulfate (i-OPS) were synthetized via propoxylation, sulfation, and neutralization three-step reactions, and characterized by FT-IR and 1H NMR. Their Krafft points were measured and the results were all below freezing point. Their critical micelle concentrations (cmc) and minimum surface tension (γcmc) determined by equilibrium surface tension were 54.74 mmol L-1 and 32.12 mN m- 1 for i-HPS, 15.57 mmol L-1 and 33.33 mN m-1 for i-OPS, respectively. The measurement of dynamic surface tension indicated that both the equilibrium values of surface tension and the time required for reaching the equilibrium decreased with the increasing concentration of surfactant solutions. The spreading ability on paraffin film researched through dynamic contact angle revealed that the droplet of i-HPS solution presented a minimum contact angle of 58.9°at a concentration of 150 mmol L-1, while the equilibrium contact angle of i-OPS droplet was 52.8°under the same condition. Their salt tolerance measurement showed that 1.0 wt% i-HPS solution and 1.0 wt% i-OPS solution could endure 183.1 g L-1, 143.9 g L-1 NaCl, 206.3 g L-1, 198.4 g L-1 MgCl2, and 229.7 g L- 1, 217.9 g L-1 CaCl2, respectively.
We aimed to investigate how can target and optimize pulmonary delivery distribution by changing physicochemical characteristics of instilled liquid.Therefore, we created a new liquids group: a. eligible for desired distribution within lung because of assorted physicochemical characteristics b. capable of being augmented with a broad range of chemicals inertly c. no interference on respiratory function d. compatible with airway surface liquid We developed forty types of new liquid,were composed of Carboxymethylcellulose sodium,Glycerin and different types of Polysorbates.Viscosity was measured using a Programmable Rheometer and surface tension by KRUSS Tensiometer. We subsequently examined the liquids and delivery protocols by simple and branched glass capillary tube models of airways.Eventually,we explored pulmonary distribution of liquids being augmented with technetium-99m in mechanically ventilated rabbits.We used a single head large field of view gamma camera.Kinematic viscosity between 0.265Stokes and 0.289Stokes,density between 1g/cm3 and 1.5g/cm3 and surface tension between 25dyn/cm and 35dyn/cm were the most acceptable.
Removal of contaminant sources or associated residual free phase pools often suffers from a combination of inefficiency, increased risk of contaminant spreading due to uncontrolled mobilization, and/or high treatment costs. The paper gives a brief overview of results from laboratory and field studies where chemical and biochemical in-situ source control actions are evaluated with respect to their efficiency on changes of source emission. The studies focused on the contaminant group of chlorinated ethenes. Chemical approaches aim to mobilize contaminant phases. By now these studies have been mainly executed in the laboratory and only few pilotscale field studies exist. The results indicate large emission rates at the beginning of the phase displacement but give less information on long-term emission rates. Biostimulation and bioaugmentation approaches revealed increased emission on short time scales and accumulation of cis- Dichloroethylene and Vinylchloride due to incomplete degradation of higher chlorinated solvents in the source zone. On long-term scales emission rates decreased and groundwater plumes were shrinking.
Researchers at Surbec-ART Environmental, Norman, OK, and The University of Oklahoma have completed several field demonstrations using the surfactant flushing technique. Among these, two case studies were presented including Alameda Point, CA, and Spartan Chemical Co Superfund Site, MI. Representative contaminants observed at the sites were trichloroethylene (TCE) and trichloroethane (Alameda Point), and complex mixed wastes of methylene chloride, TCE, ketones, and BTEX (Spartan Chemical). The major goal for these field tests was to demonstrate that significant NAPL removal (> 90%) could be achieved in several pore volumes of surfactant injection and system operation. Another goal was to reduce surfactant use by recycling and reinjecting the surfactant solution treated by an ultrafiltration unit. Samples were collected form the recovered water prior to, and after treatment, for treatment efficiency assessment. Enhanced solubilization was observed for various contaminants throughout the test cell during the surfactant injection phase. Concentrations of the highly water-miscible contaminants, acetone, MEK, and MIBK, showed significant increase during surfactant injection phase. Greater enhancement was observed in the downgradient direction of the flow in the cell. This is an abstract of a paper presented at the 221st ACS National Meeting (San Diego, CA 4/1-5/2001).
In order to realize the formation rules of in-situ reaction zone (IRZ) of sucrose-modified nanoscale zero valent iron (SM-NZVI) in underground aquifer, simulated IRZ was set up in two-dimensional slot, and the influence of particle size of silica sand, groundwater velocity, slurry concentration, injection volume and injection approach on the remediation area of IRZ were invesgated. The results showed that the reaction zone was wider as the medium size and groundwater velocity increased, and the zone in coarse sand was 3times as wide as that in fine sand; when the groundwater velocity increased from 0.1 m/d to 1.0 m/d, the width expanded by 14.9% and 106.4%, respectively. Injecting slurry into underground gradually by several times could let the initial zone width increase by 19.8%. Moreover, lower slurry concentration contributed to the expansion of the zone in both directions of groundwater flow and vertical aquifer. ©, 2015, Zhongguo Huanjing Kexue/China Environmental Science. All right reserved.
This chapter reviews current and future applications of surfactant microemulsion formulations for a variety of cleaning and environmental remediation technologies. It analyzes how the phase behavior, properties, and recent advances in microemulsion formulations relate to the use of microemulsions in cleaning and environmental remediation technologies. It also provides a more detailed description of the use of microemulsions in cleaning technologies, specifically in the areas of hard surface cleaning, laundry, and personal cleaning formulations, along with the use of microemulsions in environmental remediation applications (with a special emphasis on surfactant-enhanced aquifer remediation [SEAR]). In general, two types of cleaning approaches have been identified: oil detachment or mobilization, and oil solubilization. The oil-detachment mechanism requires ultralow interfacial tension and is economically attractive due to the low surfactant concentration needed to achieve substantial levels of oil removal; nonetheless, it is necessary to avoid the formation of wetting films at the end of the washing process. In SEAR-solubilization technologies, the high cost of surfactant has been circumvented by combining separation technologies (air sparging, liquid-liquid extraction, and membrane ultrafiltration) that allow recycling of the surfactant solution.
Within the PHREEQC framework, a dual Monod kinetics formulation has been included, which allows rate dependencies of both substrates, terminal electron acceptors and inhibitors. In this way, PHREEQC will simulate the redox processes under concern both with regard to kinetics and thermodynamics. Furthermore, PHREEQC allows one-dimensional reactive transport to be simulated. The biogeochemical processes involved in transport and biodegradation of dissolved jet-fuel were simulated for two cases by PHREEQC with this Monod kinetics scheme. The column studies of Knudsen (2003) exploring dissolved jet-fuel transport and biodegradation within initially pristine aquifer sediments dominated by pyrite oxidation and calcite dissolution. Pyrite oxidation will compete with aerobic biodegradation, thereby reducing the efficiency of aerobic bioremediation. The 1D column simulations gave reasonable agreement with measured biodegradation, mineralization and pyrite oxidation rate, and reproduced the overall microbial processes well, but they failed to mimic the observed ferrous iron. A dual porosity approach should be included. The second case with a jet-fuel contaminated plume under monitoring was simulated with a 1D PHREEQC column from a plume cross section along the flow direction. The biogeochemical reactions themselves were described reasonably well, but dispersional/diffusional transport effects could not be simulated sufficiently with a 1D column of PHREEQC alone. Here truly coupled models of 3D flow and biogeochemical reactions must be applied.
Remediation of oil spills using soil washing technologies with chemical agents such as surfactants are an advantageous alternative compared to other common techniques. This chapter provides an introduction to the phase behavior of surfactant-oil-water (SOW) systems and an equation of state that describes this phase behavior and the properties of these SOW systems. It provides a connection to the properties of SOW systems with the performance of surfactant-based remediation technologies through the use of dimensionless numbers. The chapter illustrates the use of this integrated approach in designing remediation technologies that can incorporate biocompatible surfactants and improve the performance of these technologies. The hydrophilic-lipophilic difference (HLD)-net-average curvature (NAC) framework, combined with the dimensionless numbers that describe the hydrodynamic conditions, can be used to engineer the design of a new generation of dispersant formulations.
Studies of solubilization of organic contaminants by surfactants are complicated by the fact that the effective surfactant concentration is decreased by partitioning into the organic phase. This paper introduces an experimental setup for surfactant solubilization where the partitioning loss of surfactants is minimized. Using this setup, two anionic (sodium dodecyl sulphate and Spolapon AOS 146) and one nonionic surfactant (Novanik 0633 A) were compared. When comparing solubilization efficacies expressed as multiples of the critical micelle concentration, the two anionic surfactants were able to solubilize a higher amount of polychlorinated biphenyls. For lower surfactant concentrations, solubilization efficacies were similar for all surfactants. However, it is necessary to take into account that the critical micelle concentration of the nonionic surfactant is considerably lower.
The objective of this study is to investigate the performances of permeable reactive barrier (PRB) packed with nanoscale zero-valent iron (NZVI) particles enhanced by surfactant and electrokinetics (EK) on trichloroethylene (TCE) degradation. The optimal operation parameters obtained from the tests conducted in a lab-scale sandbox were the potential gradient of 1 V cm−1, NZVI loading of 5 g, and PRB located behind the anode, and were adopted for the following transport and degradation experiments conducted in the bench-scale sandbox. Chlorinated byproducts were not detected during the lab-scale sandbox tests, i.e. TCE was completely dechlorinated by NZVI particles in the reactive barrier. The results of bench-scale sandbox tests revealed that TX100 surfactant raised the mobility and solubility of TCE in aquifer that increased its availability for further dechlorination of NZVI. Advection and dispersion were the main factors on reduction of TX100 while adsorption of sand had higher influences on the decrease of TCE. The concentrations of TCE in the lower layer are higher than those in the upper layer owing to its dense non-aqueous phase liquid (DNAPL) properties. EK can promote the reactivity of NZVI by releasing H+ near anode. H+ not only participates in TCE dechlorination reaction but also washes away the precipitates on surface of NZVI to maintain its activity. Fe2+ and Cl− were continuously produced accompanying with TCE degradation showing that TCE was dechlorinated by NZVI particles. This study shows that NZVI coupling with EK can promote the degradation of TCE in groundwater.
In this paper we discuss the influence of chemical structures of renewable feedstock oils (RFOs) on the domains of existence and the nano-structures of microemulsions. We compare the results to those of classical microemulsions containing classical n-alkanes. First, the domains of microemulsions obtained from the melt of water, sodium dodecyl sulfate (SDS) as surfactant, 1-pentanol as co-surfactant and different RFOs (or RFO melts) in pseudo-ternary phase diagrams are presented. A surfactant–co-surfactant mass ratio of 1:2 is kept constant and the RFO (or RFO melt) is considered as a pseudo-constituent. Two different fatty methyl ester (FAME) biodiesels from rapeseed and cuphea oils, rapeseed oil, “TBK” biodiesel from rapeseed oil, limonene, and different mixtures of limonene to FAME-rapeseed biodiesel and FAME-rapeseed biodiesel to FAME-cuphea biodiesel are used as RFOs or RFO melts. Second, conductivity data are shown along an experimental path having a constant RFO or RFO melt:(surfactant–co-surfactant) mass ratio, whereas the water content is varied. All obtained data are then compared to data from previous studies with a series of n-alkanes (from n-hexane to n-hexadecane). As the main conclusion it is found that RFOs or RFO melts can easily substitute n-alkanes. From the chemical structure of the oils, it appears that not only the polarity of the oil plays an important role but also does the absolute size of the oil molecules. In all cases microemulsion systems exhibit percolative behavior.
Abstract
Laboratory phase behavior and soil column experiments were conducted using branched alcohol propoxy sulfate surfactants to evaluate their effectiveness in removing gasoline and diesel range hydrocarbons from contaminated groundwater. Very low residual oil saturations were achieved with a much smaller amount of surfactant than typically required in surfactant enhanced aquifer remediation (SEAR). This type of surfactant has been shown to be both robust and efficient even when used at low temperatures and without co-solvent.
Experiments were conducted to evaluate the potential of ether sulfate surfactants with degrees of ethoxylation ranging from one to four per molecule for use in subsurface remediation. It was hypothesized that ethoxylated anionic surfactants will exhibit lower losses in the subsurface due to precipitation and sorption as a function of increasing ethoxylation while maintaining high hydrocarbon solubilization potentials. Results demonstrated that no significant precipitation of surfactant and calcium occurred where the degree of ethoxylation was two or greater. Sorption assays demonstrated that these ethoxylated anionic surfactants were less prone to sorption on soil than nonethoxylated anionic and nonionic surfactants. Furthermore, enhancements in solubilization of naphthalene were evidenced with increasing degrees of ethoxylation, and micelle-water partition coefficients were comparable with those of other high-performance surfactants. Microbial degradation assays indicated that these ethoxylated anionic surfactants served readily as substrates, raising concerns relative to their use in subsurface aerobic systems. However, they could be compatible with a treatment train concluded with a biological unit process.
This paper summarizes a laboratory study to select a suitable surfactant for a surfactant-enhanced aquifer remediation (SEAR) process that integrates surfactant recovery and reinjection. Several anionic, nonionic, and anionic/nonionic mixtures of surfactants with and without co-solvent have been evaluated. Most of these systems showed unacceptable phase behavior with PCE and/or high viscosity and were thus eliminated from further study. The Aerosol MA-80I surfactant demonstrated high solubilization of PCE and low viscosity with PCE; however, due to its high CMC, it is not considered an optimum surfactant for recovery by ultrafiltration. A new surfactant was synthesized especially for this project and found to be the best overall choice due to its excellent solubilization of PCE, low viscosity with PCE and good recovery by filtration due to its low CMC.
Pervaporation is gradually becoming an accepted and practical method for the recovery of volatile organic compounds (VOCs) from aqueous process and waste streams. As the technology has matured, new applications for pervaporation have emerged. One such application is the separation of VOCs from surfactant solutions, such as those used to remediate soils contaminated with chlorinated solvents, thereby enabling the reuse of the surfactant solution. In pervaporation, a nonporous hydrophobic membrane separates the surfactant solution from a vapor phase (vacuum) which extracts the VOC. As a result, pervaporation does not suffer from foaming problems commonly encountered with conventional separation processes. In this paper, the effect of surfactants on process fundamentals and recent experimental results with surfactant solutions will be discussed.
Surfactants can aid pump-and-treat remediation of DNAPL chemicals but, under the conditions examined in this paper, surfactant re-use is necessary to be economical. The most cost effective above ground processes for surfactant regeneration are probably vacuum steam stripping or air stripping/incineration with surfactant recovery from the bleed stream using a combination of ultrafiltration and foam fractionation. The major cost is that of surfactant required to fill the treated zone. If the region of residual saturation is small and well defined, then surfactants may be more economical than pump-and-treat alone.
Two field tests at Hill Air Force Base Operational Unit 2 were completed in May and September of 1996 to demonstrate surfactant remediation of an alluvial aquifer contaminated with DNAPL (dense nonaqueous phase liquid). The DNAPL at Hill OU2 consists primarily of trichloroethene (TCE), 1,1,1-trichloroethane (1,1,1-TCA) and tetrachloroethene (PCE). Sheet piling or other artificial barriers were not installed to isolate the 6.1 x 5.4 m test area from the surrounding aquifer. Hydraulic confinement was achieved by: (1) injecting water into a hydraulic control well south of the surfactant injectors (2) designing the well pattern to take advantage of the alluvial channel confined below and to the east and west by a thick clay aquiclude and (3) extracting at a rate higher than the injection rate within the well pattern. An extensive program of laboratory experimentation, hydrogeological characterization, effluent treatment and predictive modeling was critical in the design of these tests and the success of the project. Simulations were conducted to determine test design variables such as well rates, injected chemical amounts and test duration, and to predict the recovery of contaminants and injected chemicals, degree of hydraulic confinement and pore volume of the aquifer swept by the injected fluids. Partitioning interwell tracer tests were used to estimate the volume and saturation of DNAPL in the swept volume and to assess the performance of the surfactant remediation. Analysis of the Phase I and Phase II results showed high recoveries of all injected chemicals, indicating that hydraulic confinement was achieved without sheet pile boundaries. Approximately 99% of the DNAPL within the swept volume was removed by the surfactant in less than two weeks, leaving a residual DNAPL saturation of about 0.0003. The concentration of dissolved contaminants was reduced from 1100 mg/1 to 8 mg/1 in the central monitoring well during the same time period.
Thermodynamically stable Winsor Type I (oil-in-water), Type II (water-in-oil), and Type III (middle phase) phase behavior systems have been identified for perchloroethylene, with a mixture of sodium sulfosuccinate surfactants in the presence of isopropyl alcohol and appropriate electrolyte concentrations. The surfactant mixture is composed of 65% sodium dihexyl sulfosuccinate (Aerosol MA) and 35% sodium dioctyl sulfosuccinate (Aerosol OT) by weight. All experiments were done at 25°C. The results presented are the electrolyte concentrations and solubilization parameters for the optimum formulations.
Surfactant-enhanced subsurface remediation can dramatically improve contaminant removal rates compared to the traditional pump-and-treat technology. Surfactants can be used to significantly enhance the solubility (solubilization) of non-aqueous phase liquid (NAPL) constituents, or they can be used to reduce interfacial tensions thereby mobilizing the NAPL (mobilization). Both the solubilization and mobilization mechanisms were used to remediate separate portions of a NAPL-contaminated aquifer at Hill AFB, Utah. The demonstrations were conducted in cells contained by steel sheetpiling driven into an underlying impermeable layer. The solubilization demonstration cell showed excessive leakage through the sheetpiling; hence, the surfactant (Dowfax 8390) was not flushed through the entire cell. In spite of less than complete flushing of the cell, contaminant extraction in the solubilization cell was as high as 58% with ten pore volumes of surfactant flushing. In the mobilization cell, two surfactant solutions (Aerosol OT and Tween 80) were injected along with calcium chloride. The surfactant-mobilized NAPL had a higher viscosity than aqueous fluids resulting in reduced hydraulic conductivities and mounding of the solution. In under seven pore volumes, the average contaminant removal for the mobilization cell exceeded 90%. Flushing with water alone would have extracted less than 1% of the contaminant mass in the same time frame. The contaminant removal rates derived from pre- and post-demonstration soil cores are in concert with the contaminant mass removed in the extraction wells and generally agree with the pre- and post-demonstration partitioning tracer tests. The mobilization system was much more efficient than solubilization with both systems being much more efficient than water alone. By contrast, the solubilization system was much easier to design and implement. These demonstrations thus illustrate the exciting potential for surfactants to dramatically improve pump-and-treat remediation of residual oil.
This paper provides a brief summary of some key elements of surfactant enhanced oil recovery technology that are relevant to the application of the use of surfactants to the remediation of contaminated soils. Surfactant screening and laboratory testing, the use of polymers and foams for mobility control, the use of tracers for characterization and performance assessment and modeling and field testing are discussed and important lessons from EOR research and experience are identified for each of these topics. Surfactant enhanced aquifer remediation (SEAR) technology could benefit tremendously from these EOR lessons, which were learned the hard way over more than thirty years.
It is hypothesized that surfactants with twin head groups will exhibit lower losses in the subsurface as compared to single head group surfactants while maintaining high solubilization. The results of this research demonstrated that disulfonates were significantly less susceptible to precipitation than monosulfonates and that disulfonates were less susceptible to sorption than monosulfonates and also less prone to sorption than nonionic surfactants evaluated in other research. Disulfonates also exhibited greater solubilization of naphthalene than monosulfonates and slightly lower solubilization than nonionics. Solubility ratios were evaluated on both a molar (MSR) and weight (WSR) basis, and corresponding miscelle-phase/aqueous-phase partition coefficients (Km and Kw). -from Authors
Liquid-liquid extraction was investigated for use with surfactant enhanced subsurface remediation. A surfactant liquid-liquid extraction model (SLLEM) was developed for batch equilibrium conditions based on contaminant partitioning between micellar, water, and solvent phases. The accuracy of this fundamental model was corroborated with experimental results (using naphthalene and phenanthrene as contaminants and squalane as the extracting solvent). The SLLEM model was then expanded to nonequilibrium conditions. The effectiveness of this nonequilibrium model was corroborated with experimental results from continuous flow hollow fiber membrane systems. The validated models were used to conduct a sensitivity analysis evaluating the effects of surfactants on the removal of the contaminants in liquid-liquid extraction systems. In addition, liquid-liquid extraction is compared to air stripping for surfactant-contaminant separation. Finally, conclusions are drawn as to the impact of surfactants on liquid-liquid extraction processes, and the significance of these impacts on the optimization of surfactant-enhanced subsurface remediation.
In laboratory column studies we evaluated chlorinated solvent removal using food grade surfactant-based solubilization and mobilization systems. We used nonionic sorbitan polyethoxylate monostearate for solubilization experiments, and both bis-2-ethylhexyl sodium sulfosuccinate and sodium mono- and dimethyl naphthalene sulfonate in mobilization studies. Surfactant enhanced mobilization was shown to be more efficient than solubilization for removing tetrachloroethylene. Excellent removal efficiency was maintained even when the mobilization system was varied, demonstrating the robustness of this system for subsurface remediation. The selected food grade surfactants, however, suffered mass losses in the column, probably due to the occurrence of phase separations (e.g., formation of precipitates or liquid crystals). Thus, surfactant losses need to be minimized before using these systems in full-scale applications. This study also demonstrated that surfactant performance was influenced by a variety of factors, such as the type of microemulsion, temperature, and contaminant compositions, that must also be considered in design of field implementations.
Winsor Type I (o/w), Type II (w/o), and Type III (middle phase) microemulsions have been generated for water and perchloroethylene (PCE) in combination with anionic surfactants and the appropriate electrolyte concentration. The surfactant formulation was a combination of sodium dihexyl sulfosuccinate and sulfated Guerbet alcohol ethoxylates and propoxylates. All studies were done at 25-degrees-C and the experimental data presented are electrolyte concentration and solubilization parameter for optimum formulations and width of the three phase regime in salinity space. Many of the results are reminiscent of those obtained with hydrocarbons for the oil phase once it is realized that PCE requires more hydrophilic surfactants than does octane.
A one-dimensional numerical model that simulates the surfactant-enhanced solubilization of pooled DNAPL is presented. Two non-equilibrium expressions describing mass transfer are examined. The mass transfer coefficient is based on the wetting phase Darcy flux, with the mass transfer rate coefficient accounting for the variation of interfacial area available for mass transfer between the DNAPL and the surfactant solution through the pool and over time. The non-wetting phase saturation distribution is calculated as a function of the hydraulic gradient, allowing for exact calculation of the local velocity. The model is calibrated using data from laboratory column experi ments where pooled tetrachloroethylene was solubilized under upward gradient conditions. Upward gradients were utilized to prevent downward pool mobilization in response to a lowering of interfacial tension upon exposure to solubilizing surfactants. Effluent concentrations are generally well predicted by the model, although simulated effluent curves exhibit more tailing than was observed experimentally. Predicted effluent concentrations improve when the equilibrium concentration of organic in surfactant solution is expressed as a function of time.
The potential for nonaqueous phase liquid (NAPL) mobilization is one of the most important considerations in the development and implementation of surfactant-based remediation technologies. Column experiments were performed to investigate the onset and extent of tetrachloroethylene (PCE) mobilization during surfactant flushing. To induce mobilization, the interfacial tension between residual PCE and the aqueous phase was reduced from 47.8 to 0.09 dyn/cm by flushing with different surfactant solutions. The resulting PCE desaturation curves are expressed in terms of a total trapping number (NT), which relates viscous and buoyancy forces to the capillary forces acting to retain organic liquids within a porous medium. The critical value of NT required to initiate PCE mobilization fell within the range of 2 × 10-5 to 5 × 10-5, while complete displacement of PCE was observed as NT approached 1 × 10-3. The interplay of viscous and buoyancy forces during PCE mobilization is illustrated in horizontal column experiments, in which angled banks of PCE were displaced through the columns. These results demonstrate the potential contribution of buoyancy forces to PCE mobilization and provide a novel approach for predicting NAPL displacement during surfactant flushing.
Ground water contamination frequently consists of mixed chlorinated solvents [e.g., tetrachloroethylene (PCE), trichloroethylene (TCE), and trans-1,2- dichloroethylene (DCE)]. In this research, mixtures of the food grade (edible) surfactants bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium mono- and dimethylnaphthalene sulfonate (SMDNS) were used in the formation of middle-phase microemulsions for mixed chlorinated solvents. Microemulsions of binary (e.g., PCE/TCE, PCE/DCE, DCE/TCE) and ternary (PCE/TCE/DCE) chlorinated solvent systems were evaluated. Several empirical correlations were used for describing and/or predicting the phase behavior of the resulting middle-phase microemulsions (e.g., the ideal mixing rule or the nonideal regular mixing theory). The ideal mixing rule provided a good approximation for binary and ternary systems, but experimental deviations from the predictions were significant enough to affect the optimal surfactant system. Nonideal regular mixing theory demonstrated much better predictive capabilities than ideal mixing for the binary and ternary systems. The recognition of nonideal mixing behavior and the resulting predictive correlations will be valuable in the design of groundwater remediation scenarios when surfactants are used for remediation of mixed chlorinated solvents.
A mathematical model is developed to describe surfactant-enhanced solubilization of nonaqueous-phase liquids (NAPLs) in porous media. The model incorporates aqueous-phase transport equations for organic and surfactant components as well as a mass balance for the organic phase. Rate-limited solubilization and surfactant sorption are represented by a linear driving force expression and a Langmuir isotherm, respectively. The model is implemented in a one-dimensional Galerkin finite element simulator which idealizes the entrapped residual organic as a collection of spherical globules. Soil column data for the solubilization of residual dodecane by an aqueous solution of polyoxyethylene (20) sorbitan monooleate are used to evaluate the conceptual model. Input parameters were obtained, where possible, from independent batch experiments. Calibrated model simulations exhibit good agreement with measured effluent concentrations, supporting the utility of the conceptual modeling approach. Sensitivity analyses explore the influence of surfactant concentration and flushing strategy on NAPL recovery. 45 refs., 6 figs., 3 tabs.
The solubilization of dodecane by polyoxyethylene (20) sorbitan monooleate, a nonionic surfactant, was investigated as a potential means of recovering nonaqueous-phase liquids from contaminated aquifers. Residual saturations of dodecane were established by injecting [sup 14]C-labeled dodecane into water-saturated soil columns and displacing the free product with water. Flushing with a 43 g/L surfactant solution increased the concentration of dodecane in the column effluent by 5 orders of magnitude. However, effluent dodecane concentrations were considerably less than the equilibrium value of 3500 mg/L measured in batch studies. Subsequent column experiments conducted at several flow velocities and with periods of flow interruption confirmed the existence of rate-limited, rather than instantaneous, solubilization of residual dodecane. The results of this study demonstrate the sizable capacity of surfactant solutions to enhance the recovery of residual dodecane, even under conditions of rate-limited solubilization. 67 refs., 6 figs., 1 tab.
The economics of surfactant-enhanced subsurface remediation are affected by losses of surfactants due to such phenomena as precipitation, sorption, etc. It is hypothesized that surfactants with twin head groups will exhibit lower losses in the subsurface as compared to single head group surfactants while maintaining high solubilization. The contaminant addressed in this research was naphthalene, and the surfactants evaluated were mono- and disulfonated anionics (sodium dodecylbenzenesulfonate and alkyl diphenyl oxide disulfonates). The results of this research demonstrated that disulfonates were significantly less susceptible to precipitation than monosulfonates and that disulfonates were less susceptible to sorption than monosulfonates and also less prone to sorption than nonionic surfactants evaluated in other research. Disulfonates also exhibited greater solubilization of naphthalene than monosulfonates and slightly lower solubilization than nonionics. Solubility ratios were evaluated on both a molar (MSR) and weight (WSR) basis, and corresponding micelle-phase/aqueous-phase partition coefficients (K(m) and K(w)) were reported. This research demonstrated that disulfonate surfactants are less susceptible to losses than other surfactants evaluated and thus are strong candidates for use in surfactant-enhanced subsurface remediation.
Experimental data are presented on the enhanced apparent solubilities of naphthalene, phenanthrene, and pyrene resulting from solubilization in aqueous solutions of four commercial, nonionic surfactants: an alkyl polyoxyethylene (POE) type, two octylphenol POE types, and a nonylphenol POE type. Apparent solubilities of the polycyclic aromatic hydrocarbon (PAH) compounds in surfactant solutions were determined by radiolabeled techniques. Solubilization of each PAH compound commenced at the surfactant critical micelle concentration and was proportional to the concentration of surfactant in micelle form. The partitioning of organic compounds between surfactant micelles and aqueous solution is characterized by a mole fraction micelle-phase/aqueous-phase partition coefficient, K{sub m}. Values of log K{sub m} for PAH compounds in surfactant solutions of this study range from 4.57 to 6.53. Log K{sub m} appears to be a linear function of log K{sub ow} for a given surfactant solution. A knowledge of partitioning in aqueous surfactant systems is a prerequisite to understanding mechanisms affecting the behavior of hydrophobic organic compounds in soil-water systems in which surfactants play a role in contaminant remediation or facilitated transport.
This paper documents the importance of membrane processes to surfactant-enhanced subsurface remediation and presents results of a field study on these processes. Surfactants enhanced the contaminant (BTEX) concentrations by one to two orders of magnitude over baseline ground water concentrations. The surfactant stream was decontaminated by air stripping in hollow fiber membranes and concentrated using ultrafiltration. Hollow fiber air stripping was able to avoid foaming problems which will be more common in packed tower air strippers. A 10 000 MWCO ultrafilter was able to recover a majority of the surfactant (approaching 80%) despite being hindered by ground water dilution (ground water extraction was four times greater than injection to maintain hydraulic control). A fundamental model of surfactant-reduced stripping efficiency was corroborated by the field results, providing further confidence in the use of this model for design purposes. The high level of surfactant recovery (90%±6%) achieved in a relatively low permeability formation (1 ft/day or 3.5×10−4 cm/s) is also encouraging. These results thus demonstrate the importance of an integrated design to optimize system performance, and illustrate the ability of surfactant-enhanced technologies to expedite subsurface remediation.
An intermediate-scale flow cell experiment was conducted to remove a liquid trichloroethylene Ž . Ž . TCE spill from a saturated, heterogeneous porous medium using pump-and-treat P & T as well Ž . as surfactant flushing SF techniques. Dissolved TCE concentrations were measured at 20 locations, while fluid saturations were obtained with a dual-energy gamma scanner. The behavior Ž .w of the TCE spill has been described by Oostrom et al.. Movement and remediation of TCE in a saturated heterogeneous porous x medium: 1. Spill behavior and initial dissolution, this issue. . A total of six alternating P & T and SF periods were used to remediate the flow cell. A two-well system, consisting of an injection and an extraction well, was used during the first five remediation periods. For the last SF period, a three-well system was employed with two injection wells and one extraction well. During the first P & T period, most entrapped TCE was removed, but TCE saturations in a substantial pool on top of a fine-grained sand layer were largely unaffected. During the first SF period, a dense plume was formed containing solubilized TCE which partially sank into the fine-grained sand. In addition, unstable fingers developed below the liquid TCE in the pool. In several samples, small TCE droplets were found, indicating mobilization of TCE. Most of the samples with concentra-tions larger than 5000 ppm had a milky, emulsion-like appearance. The SF considerably reduced the amount of TCE in the pool on top of the fine-grained sand. During the second P & T period, plume sinking and instabilities were not observed. After starting the second SF period, some unstable fingering and plume sinking resumed, starting at the upstream end of the TCE in the) Corresponding author. Tel.
Surfactant enhanced subsurface remediation is being evaluated as an innovative technology to expedite contaminant extraction from the subsurface. Regulatory approval of this technology will likely be enhanced by use of surfactants with FDA direct food additive status (“edible” surfactants). This research establishes edible surfactant systems capable of solubilizing (via micellar partitioning) and microemulsifying (via middle phase microemulsions) chlorinated solvents (PCE, TCE, and trans 1,2-DCE). Micellar partition coefficients with edible surfactants are observed to be comparable to values previously reported for other surfactants, with solubilization increasing aqueous concentrations by one to two orders of magnitude for the chlorinated organics. Middle phase microemulsion formation is dependent on surfactant structure and cosurfactant concentration. Solubility enhancement in the middle phase systems (microemulsification) is at least one to two orders of magnitude higher than solubilization for the same surfactant concentration, but is much more sensitive to the surfactant system and the contaminant. In addition, successful microemulsion formation is seen to be a function of ground-water temperature and hardness, indicating the need to consider these and additional factors for successful design and implementation of surfactant enhanced subsurface remediation. This research thus establishes a variety of edible surfactant systems that can significantly expedite subsurface remediation of chlorinated solvents, and illustrates the importance of proper selection and design of surfactant systems.
Micellar-enhanced ultrafiltration (MELT) and air stripping were evaluated for surfactant-contaminant separation and surfactant recovery. Two linear alkyl diphenyloxide disulfonate (DPDS) surfactants were evaluated with the contaminants naphthalene and trichloroethylene. A separation model developed from micellar partitioning principles showed a good correlation to batch MEUF studies, whereas flux analysis highlighted concentration polarization effects in relation to hydrophobe length. MEUF effectively concentrated the surfactant-contaminant system (93 to 99 percent retention); however, this did not result in surfactant-contaminant separation. Batch and continuous flow air stripping models were developed based upon air/water ratio, surfactant concentration, and Micellar partitioning; model predictions were validated by experimental data. Sensitivity analyses illustrated the decline in contaminant-surfactant separation with increasing surfactant concentration (e.g., TCE removal efficiency declines from 83 percent to 37 percent as C-16 DPDS concentration increases from 0 to 55 mM). This effect is greater for more hydrophobic contaminants (naphthalene vs. TCE) and surfactants with greater solubilization potential (C16-DPDS vs. C-12 DPDS). The resulting design equations can account for this effect and thus properly size air strippers to achieve the desired removal efficiency in the presence of surfactant micelles. Proper selection and design of surfactant-contaminant separation and surfactant recovery systems are integral to optimizing surfactant-enhanced subsurface remediation.
Over the past four years, we have been developing an in situ surfactant-washing method to decontaminate soil systems. This study addresses another major step in that development: a field test of the surfactant-washing method at a site contaminated with polychlorinated biphenyls (PCBs) and oils. A test plot, 10-ft diameter by 5-ft deep, was selected in an area of high levels of contaminataion. The study involved applying a surfactant solution on the plot to wash the site material and carry the leachate down to the depressed water table, where it was collected by pumping a recovery well installed through the center of the plot. The leachate pumped to the surface was biotreated to degrade the oils and surfactant, and the PCBs were removed from the leachate by an activated carbon system. Soil cores from the test plot indicated concentrations of up to 6,223 mg/kg PCBs and 67,000 mg/kg oils. The test plot initially contained about 15 kg of PCBs and 157 kg of oils. The hydraulic response of the test plot to washing was monitored by measuring the water levels in wells around the test plot and the fluid pressure and saturation through the plot. These real-time data were used to adjust the surfactant-application rate to minimize lateral spread of the surfactant and leachate and the pumping rate to capture all the leachate by the recovery well. The response of contaminant concentrations in the test plot to washing and the performance of the leachate-treatment system were also monitored during the test by collecting and analyzing samples from the recovery well and from the treatment system. An on-site laboratory was used for these analyses. During the 70 days of the washing test, 5,375 gallons of a 0.75% aqueous surfactant solution was applied on the test plot at an average rate of 77 gal/day. During the same period, 10,981 gallons of leachate were recovered at an average rate of 157 gal/day. A total of 1.6 kg of PCBs and 16.9 kg of oils (about 10% of the initial mass) was washed from the test plot during the test. Maximum concentrations of 65 mg/1 PCBs and 709 mg/1 oils were measured in leachate samples. The leachate was adequately treated before it was discharged. These test results indicate that in situ surfactant washing is a promising candidate for the remediation of contaminated soil systems.
A field demonstration of surfactant-enhanced solubilization was completed in a shallow unconfined aquifer located at a Coast Guard Station in Traverse City, Michigan. The primary objectives of the study were: (1) to assess the ability of the vertical circulation well (VCW) system for controlling chemical extractants added to the subsurface; and (2) to assess the behavior of the surfactant solution in the subsurface, with a goal of maximum surfactant recovery. A secondary objective was to demonstrate enhanced removal of PCE and recalcitrant components of a jet fuel. The analytical results showed that the surfactant increased the contaminant mass extracted by 40–fold and 90–fold for the PCE and jet fuel constituents, respectively. The surfactant solution demonstrated minimal sorption (retardation) and did not precipitate in the subsurface formation. In addition, the VCW system was able to capture in excess of 95% of the injected surfactant solution. Additional field testing and full-scale implementation of surfactant-enhanced subsurface remediation should be performed.
A variety of column experiments have been completed for the purpose of selecting and evaluating suitable surfactants for remediation of nonaqueous phase liquids (NAPLs). The various NAPLs tested in the laboratory experiments were tetrachloroethylene (PCE), trichloroethylene (TCE), jet fuel (JP4) and a dense nonaqueous phase liquid from a site at Hill Air Force Base, UT. Both Ottawa sand and Hill field soil were used in these experiments. Surfactant candidates were first screened using phase behavior experiments and only the best ones were selected for the subsequent column experiments. Surfactants which showed high contaminant solubilization, fast coalescence times, and the absence of liquid crystal phases and gels during the phase behavior experiments were tested in soil column experiments. The primary objective of the soil column experiments was to identify surfactants that recovered at least 99% of the contaminant. The secondary objective was to identify surfactants that show low adsorption and little or no loss of hydraulic conductivity during the column experiments. Results demonstrated that up to 99.9% of the contaminants were removed as a result of surfactant flooding of the soil columns. The addition of xanthan gum polymer to the surfactant solution was shown to increase remediation efficiency as a lower volume of surfactant was required for recovering a given volume of NAPL. Based on these experimental results, guidelines for designing highly efficient and robust surfactant floods have been developed and applied to a field demonstration.
Even in the absence of mobilization of dense nonaqueous phase liquid (DNAPL), the microemulsion that forms when the surfactant solubilizes a dense contaminant such as trichloroethylene will be more dense than water and tends to migrate downward. This paper addresses the issue of migration with a new concept: surfactant enhanced aquifer remediation at neutral buoyancy. Laboratory results of surfactant remediation in two-dimensional model aquifers show that downward migration of microemulsion containing solubilized dense contaminants can be reduced to an acceptable level, even in the absence of capillary barriers in the aquifer. One model experiment was designed to exhibit a small degree of vertical migration and full capture of the microemulsion at the extraction well. The second experiment was designed to demonstrate the effect of large buoyancy forces that lead to excessive downward migration of the microemulsion. Density measurements of aqueous solutions containing sodium dihexyl sulfosuccinate surfactant, isopropanol, trichloroethylene, and sodium chloride are presented. A companion paper presents the results of the flow and transport calculations needed for this approach to surfactant flooding.
Winsor Type I (o/w), Type II (w/o), and Type III (middle phase) microemulsions have been produced for water and CCl4, water and trichloroethylene (TCE), and water and 1,2-dichlorobenzene (DCB) with anionic surfactants and appropriate electrolytes. Attempts at producing classical phase behavior with several more polar chlorinated hydrocarbons were unsuccessful. These results are compared to those obtained previously with PCE. All studies were done at 25-degrees-C. The experimental data presented are electrolyte concentration and solubilization parameter for optimum formulations and salinity window for the Type III phase region.
Adsolubilization of contaminants by media-sorbed surfactants is an important phenomenon for surfactant-based environmental technologies. The present research evaluates the impacts of contaminant properties on adsolubilization (e.g., nonpolar, polar, and ionizable organic compounds). In addition, adsolubilization by modified admicelles is investigated (operating below the surfactant's Krafft temperature). The medium and surfactant investigated were alumina and sodium dodecyl sulfate, respectively. Naphthalene, naphthol, and 4-amino-1-naphthalenesulfonic acid were investigated as nonpolar, polar, and ionizable organic compounds, respectively. Variations in adsolubilization results for these compounds are explained based on surfactant fundamentals and contaminant properties. Modified admicelles effectively adsolubilized organic molecules without requiring the presence of surfactant monomers. Implications of these results to surfactant-based environmental technologies are discussed.
Removal of chlorinated solvents in subsurface media using edible surfactants: column studies
- Shiau
Microemulsions and related systems
- Bourrel
Numerical simulation of surfactant flooding to remove pooled DNAPL from porous media
- Mason
Solubilization and mobilization of DNAPLS using direct food additive (Edible) surfactants
- Shiau