Surfactant-Enhanced Soil Washing for Removal of Petroleum Hydrocarbons from Contaminated Soils: A Review

Pedosphere 28(3): 383–410, 2018 doi:10.1016/S1002-0160(18)60027-X ISSN 1002-0160/CN 32-1315/P c 2018 Soil Science Society of China ⃝ Published by Elsevier B.V. and Science Press

Surfactant-Enhanced Soil Washing for Removal of Petroleum Hydrocarbons from Contaminated Soils: A Review Abayneh Ayele BEFKADU and CHEN Quanyuan∗ College of Environmental Science and Engineering, Donghua University, Shanghai 201620 (China) (Received December 15, 2017; revised March 21, 2018)

ABSTRACT An increase in energy demand leads to further exploration, transportation, and utilization of petroleum, which creates severe soil contamination because of recurrent accidents and oil spills. Remediation of these contaminated soils is challenging. Among many treatment methods practiced for remediation of petroleum-contaminated soils, surfactant-enhanced soil washing has been widely practiced as a preferred treatment option, as it is a fast and environmentally accepted method. In this paper, we review research undertaken on various anionic, nonionic, cationic, biological, and mixed surfactants for the remediation of petroleum hydrocarbon-contaminated soils. Upcoming surfactants like gemini and switchable surfactants are summarized. We assess the challenges and opportunities of in-situ and ex-situ soil washing, the mechanisms of surfactant-enhanced soil washing, and the criteria to follow for surfactant selection. Furthermore, we briefly discuss the operational and environmental factors affecting soil washing efficiency and soil and surfactant properties affecting surfactant adsorption. We also describe the advantages of coupling soil washing with effluent treatment and surfactant reuse challenges and opportunities. Moreover, challenges and possible new directions for future research on surfactant-enhanced soil washing are proposed. Key Words: pollution

adsorption, biosurfactant, effluent treatment, gemini surfactant, oil spills, organic contaminants, remediation, soil

Citation: Befkadu A A, Chen Q Y. 2018. Surfactant-enhanced soil washing for removal of petroleum hydrocarbons from contaminated soils: A review. Pedosphere. 28(3): 383–410.

INTRODUCTION Soil is a three-dimensional body continuously interacting with other environmental compartments such as water and air. Thus, its pollution can directly propagate contamination and pose potential risks to human health, water resources, ecosystems, and other environmental receptors (Balachandran et al., 2012; Adhikari and Hartemink, 2016). Exploration, extraction, processing, and utilization of petroleum are increasing owing to a growing demand for energy caused by the rapid growth of industry, which results in the impregnation of soil by toxicological petroleum hydrocarbons (De Figueredo et al., 2014). Petroleum products may be introduced into the soil by mechanisms like leaks and spills from refineries, manufacturing sites, power plants, distribution depots, retail service stations, and disposal land of residual lubricants, through blow-outs from pipes and pumps, pipeline corrosion, and spillages during transportation (Trevors and Saier, 2010; Nogales et al., 2011; Park and Park, 2011; Wu et al., 2017). ∗ Corresponding

author. E-mail: [email protected].

Different bio-physicochemical weathering processes occur on a contaminated soils, and the degree of contaminant weathering depends upon the characteristics of the contaminant and the bio-physicochemical properties of the soil (Gavrilescu, 2014). The most common features that affect the weathering degree of a contaminant in soil are water solubility, vapor pressure, sorption characteristics, biodegradability, and chemical stability of the contaminant. Contaminants with higher water solubility, volatility, and biodegradability are not likely to stay in the soil for long, whereas those with the opposite properties will tend to leach from the soil slowly and ultimately become a continuous source of groundwater pollution (Mayer et al., 2000; AbdelShafy and Mansour, 2016). The bio-physicochemical properties of a soil that affect contaminant weathering in the soil include microbial activity, nutrient status, soil pH, organic matter and clay content, and redox potential of the soil. The presence of high amounts of clay and organic matter in soil will expose a contaminants to complexation reactions and make the contaminant resistant to weathering (Lee, 2010).

384

The longer a contaminant stays in soil, the more the physical, chemical, and biological processes weather the contaminant, resulting in changes in contaminant composition and complexity and leaving the contaminant with higher molecular weight, viscosity, and density, as well as greater binding strength to soil (Chen et al., 2007). Therefore, weathered contaminated soils are usually much harder to remediate than recently contaminated soils. It is essential to remediate contaminated soils to support animal and plant life and also to protect humans and other species from long-term health threats. With the intensification of soil contamination by petroleum hydrocarbons, how to remediate, treat, and control this pollution economically and efficiently is becoming a technical problem for environmental protection (Phillips et al., 2006; Pei et al., 2018). Experts use physical, chemical, or biological techniques—or a combination of these— to treat organically polluted soils in the field. These treatment methods may remove or change organics into less toxic products and reduce the concentration of the contaminants present in soil (ZamudioP´erez et al., 2013). The four major principles of removing contaminants from soil are molecular separation (ion exchange), phase separation (desorption), chemical destruction, and biodegradation (bioremediation). These approaches can be used for many types of contaminants either individually or in combination, but the specific technology selected for contaminated soil will depend on the kind and form of contamination and other site-specific characteristics (Gupta et al., 2010). Different contaminant properties affect the choice of remediation method and the efficiency of soil remediation, and pollutant properties like volatility, water or organic solvent solubility, and chemicalthermal instability affect the choice. Moreover, the adsorption/absorption rate, the magnetic or electrical properties, the surface properties, and the size, shape, and density of the polluted particles also determine the method selection and efficiency of soil remediation (Pienynsku et al., 2000; Onur et al., 2015; Trellu et al., 2016). There are many reported treatment methods for petroleum-contaminated soils, including solidification/stabilization, incineration, bioremediation, electrochemical treatment, solvent extraction, soil washing, thermal desorption, thermal destruction, and vapor extraction (Van Gestel et al., 2003; Zhou and Hua, 2004; Albergaria et al., 2012; Hern´andez-Espri´ u et al., 2013; Seo et al., 2015; Samaksaman et al., 2016; Yu et al., 2016). Soil washing is a simple and efficient technology that has been practiced successfully for many years for the effective removal of hydrocarbons

A. A. BEFKADU AND Q. Y. CHEN

and heavy metals from soil (Dermont et al., 2008). Soil washing usually employs different extractants such as acids, bases, chelating agents, electrolytes, oxidizing agents, and surfactants (Wan et al., 2009; Trellu et al., 2016). Surfactant-enhanced remediation is thought to be an efficient, economical, and quick method for the remediation of soils polluted with hydrophobic organic compounds (Peng et al., 2011; Lim et al., 2016). Surfactants are particularly attractive for such applications as they potentially have low toxicity and better biodegradability than most organic solvent-based systems (Park et al., 2008; Cheng et al., 2017). This review mainly focuses on surfactant-enhanced soil washing of petroleum-contaminated soils. A detailed review focusing on the works undertaken in the past two decades on surfactant-enhanced soil washing is required to give researchers, remediation companies, and decision-makers a tool for decision-making and to enlighten them about present successes, challenges, and future directions. Different brief reviews on remediation technologies for petroleum-contaminated soils have been published in recently years (Mousset et al., 2014a; Von Lau et al., 2014; Mao et al., 2015; Lim et al., 2016), with some older reviews on surfactantenhanced soil washing (Mulligan et al., 2001; Paria, 2008). However, the present review is more focused on critically analyzing the latest and previous works undertaken on surfactant-enhanced soil washing using synthetic surfactants, biosurfactants, and some new class of surfactants, as well as coupling soil washing with effluent treatment technologies, for the remediation of petroleum-contaminated soils. SOIL WASHING METHODS Ex-situ and in-situ methods are the two major broad categories of soil washing. Ex-situ soil washing (ESW) involves excavation of affected land and subsequent treatment of the contaminated soil at the surface. In-situ soil washing (ISW) (soil flushing) treats the contaminated soil in place. The lower cost of excavation and transport and less destruction of the soil ecosystem are the advantages of ISW over ESW. However, long treatment time may render the site unusable during the ISW treatment period. Thus, ESW treatment is a preferred method as it is a relatively fast option and allows redevelopment and other treatment possibilities (Elgh-Dalgren et al., 2009). Ex-situ soil washing Ex-situ soil washing is an ex-situ, water-based process that employs chemical-physical extraction and se-

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

paration processes to remove or transfer organic and inorganic contaminants from soil to a liquid stream (Feng et al., 2001; Dos Santos et al., 2016). Ex-situ soil washing involves two major procedures: i) the dissolution of soil contaminants into the washing solution (comprising water, surfactants, acids, or alcohols) and ii) the simple separation of the fine-grained material of the washed effluent (comprising mainly silt and clay from sand) by high-energy mixing, mechanical shearing, or dispersion (Ceschia et al., 2014). A typical ESW system comprises screening of oversized particles, followed by scrubbing, size separation, dewatering of the washed soil, and finally treatment of washed effluent (Fig. 1). Contaminants are weakly sorbed on sand, as coarse particles have a smaller specific surface area, lower cation exchange capacity (CEC) and organic matter content, and higher permeability. In contrast, fine particles (silt and clay) hold contaminants strongly owing to an accompanying increase in the properties mentioned above. Therefore, soils containing a higher level of fine particles will respond less to surfactantenhanced soil washing than soils containing a larger number of coarse particles (Kuhlman and Greenfield, 1999; Lee et al., 2002). Ex-situ soil washing provides enhanced contact between the washing solution and the contaminated soils as the mixture is physically agitated, which in turn reduces the remediation time and also provides higher contaminant removal efficien-

Fig. 1

385

cy compared with that of ISW (soil flushing) processes (Mousset et al., 2014a). Advances in ESW equipment and the production of new and efficient surfactant classes have made ESW a feasible alternative for different categories of organic contaminants (Kuhlman and Greenfield, 1999; Feng et al., 2001; Mulligan et al., 2001). The principal advantage of ESW lies in its reducing the volume of soil to be treated by concentrating contaminants into fine particles, which ultimately reduces the overall cost (Salehian et al., 2012). The process of ESW is cost-efficient and relatively fast and has the potential to treat and recover large volumes of contaminants (Urum et al., 2006). Other related advantages include the fact that washing in a closed system gives control over ambient environmental conditions, washing has broad applications for various waste groups, and, finally, regulatory and public acceptance are high (Urum et al., 2006; Yuan and Marshall, 2007). The ESW method is efficient for soils containing a significant portion of sand and gravel, but is relatively ineffective for fine-textured soils because a higher interfacial tension is present between the surfactant and the clay particles, which decreases the surfactant concentration in the soil solution (Salehian et al., 2012). Soil treatment time and efficiencies will vary based upon the types of contaminants the soil contain, the desired remediation capabilities, the soil type, and the washing solution used (Cheng and Wong, 2006; Urum et al., 2006; Li et al., 2016). The ESW process

Schematic diagram of an ex-situ soil washing system (adapted from Alternative Remedial Technologies, Inc. (1992)).

386

has some limitations; primarily, excavation affects the natural ecosystem, workers are exposed to hazardous materials, and the efficiency is less for soils with a high amount of clay. When ESW treatment is only a physical process, there is little reduction in the toxicity of the contaminants. If chemical processes are involved, potentially hazardous chemicals used in the remediation process may be difficult to remove from treated soils and may remain on site. Soil flushing Soil flushing is an ISW method that uses a flushing fluid, either water or other extracting solutions, on the surface of contaminated site or injected into the contaminated zone to wash the contaminants from soil and move them to the washing solution (Khan et al., 2004). The extracting solutions can be synthetic surfactants or biosurfactants, cyclodextrins, organic cosolvents, humic acids, or vegetable oils (Ko et al., 2005; G´omez et al., 2010; Zou et al., 2014; Li et al., 2016). An additive is commonly added to water to enhance the contaminant solubility. Surface flooding, leach fields, basin infiltration systems, drains, and infiltration wells can be used to infiltrate flushing solution into soil. For remediating dense nonaqueous phase liquid (NAPL)-contaminated sites, linedrive and push-pull systems have also been used (Boving et al., 2008). During soil flushing, continuous injection of the flushing solution through the injection wells leaches the contaminants from the colloid part to the flushing solution. This contaminant-flushing solution mixture is extracted by downgradient extraction wells. The contaminant-flushing solution mixture is separated and treated, and the treated water is either discharged or re-injected back, as shown in Fig. 2

A. A. BEFKADU AND Q. Y. CHEN

(Salehian et al., 2012). Injecting the flushing solutions into groundwater raises the watertable into the capillary fringe where high concentrations of contaminants are found (Zhu et al., 2005). Three very important factors, the characteristics of soil, the type of soil, and the amount of flushing agent, determine the efficiency of soil flushing (Zhou et al., 2005). The following physical and chemical properties of soil and their variation with depth can affect the effectiveness of soil flushing: the hydraulic permeability, the grain size distribution, the organic matter content, the CEC, and the moisture content. The hydraulic permeability of soil is the single most important factor limiting the effectiveness of soil flushing; it should be approximately at least 1 × 10−7 m s−1 (Navarro and Mart´ınez, 2010). Soil flushing has shown several advantages such as relatively low cost, less environmental disruption, and reduced exposure of workers to hazardous materials compared to the conventional ˇ ab excavation and landfill methods (Zhu et al., 2005; Sv´ et al., 2008). Soil flushing, when combined with proper groundwater treatment techniques, can be an inexpensive method for the remediation of contaminated soils. The use of surfactants for ISW should take into consideration the environmental compatibility of the surfactant in use as toxic and hazardous surfactants may join the groundwater, and the surfactants should also be easily recoverable from the subsurface by natural or anthropogenic processes (Pacwa-Plociniczak et al., 2011; Zhou et al., 2011). The surface charge of surfactants may also result in the dispersion of clay particles, which can lead to clogging of the soil pores, direction change of the surfactant solution, and a reduction in the effectiveness of ISW. Therefore, ISW is plagued by challenges of safe

Fig. 2 Schematic diagram of soil flushing (in-situ soil washing) for removal of petroleum hydrocarbons from contaminated soils (adapted from USEPA (1996)).

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

surfactant application, containing, and recovery (Tsai et al., 2009). The enhanced contact between the contaminant and the surfactant, the speed of remediation, and higher contaminant removal efficiencies make ESW preferable to soil flushing as a remediation method, despite its constraints like the requirement for soil excavation (Mousset et al., 2014a; Trellu et al., 2016). MECHANISMS OF SOIL WASHING

SURFACTANT-ENHANCED

The term surfactant represents a mixed and longchain molecule containing a hydrophobic (nonpolar) hydrocarbon “tail” and a hydrophilic (polar) “head” group. The hydrophilic group is usually a sulfate group, a sulfonate group, a carboxylate group, a quaternary ammonium group, polyoxyethylene, sucrose, or a polypeptide. The most common hydrophobic parts of synthetic surfactants are paraffins, olefins, alkyl benzenes, alkylphenols, and alcohols (Paria, 2008). At lower concentrations, surfactant molecules are present as dispersed monomers; as their concentrations in solution increase, they start forming aggregates. When they reach a particular aqueous concentration that is unique to each surfactant and called the critical micelle concentration (CMC), they form micelles (Vishnyakov et al., 2013). These micelles have a hydrophobic interior (tail) located at the center of the clusters and a hydrophilic exterior (head) facing towards the water (solvent), which enhances the mobilization of hydrophobic compounds into the solution (Zhu et al., 2005; ElghDalgren et al., 2009). At this point, the surfactant exhibits the lowest surface tension, as shown in Fig. 3. The CMC value of a surfactant depends on the type, structure, and composition of the surfactant and the ionic strength, temperature, and presence and types of organic additives of the solution (Perger and BeˇsterRogaˇc, 2007; Szymczyk and Ja´ nczuk, 2007; Dubey,

387

2011; Karakashev and Smoukov, 2017). It is the formation of micelles in the aqueous solution that makes a surfactant to be excellent in solubilizing hydrophobic organic compounds (HOCs) (Ahn et al., 2008b; Ishiguro and Koopal, 2016). Mobilization and solubilization are two processes that explain the mechanisms of surfactant-enhanced remediation of hydrocarbon-contaminated soils (Deshpande et al., 1999; Mulligan et al., 2001). When surfactant monomers accumulate at the soil-contaminant and soil-water interfaces, they increase the contact area between the soil colloid and the contaminant. Also, the surfactant molecules adsorbed on the surface of the contaminant cause repulsion between the head group of the surfactant molecule and the colloid particles, thereby promoting the separation/mobilization of the contaminant from the soil particles (Rosen, 1989). This repulsion lowers the oil-water and oil-soil interfacial tension, which leads to a reduction in the capillary force holding the crude oil and the soil. As a result, the residual oil saturation in the presence of a surfactant is appreciably lower, and more oil is mobilized than with simple water floods alone (Khalladi et al., 2009). Solubilization of contaminants in the soil-surfactant mixture occurs when the concentration of surfactant in the soil solution increases and their adsorption into the soil colloid reaches saturation. After adsorption reaches saturation, the excess surfactant molecules start to aggregate and finally form micelles in the bulk solution. This unique surfactant concentration at which thermodynamically stable micelles begin to form is the CMC (Liu et al., 2014). The formation of micelles at or above the CMC increases the solubility of organic contaminants, as the contaminants are trapped inside the hydrophobic core of micelles by hydrophobic forces, and consequently, their solubility in the aqueous phase increases (Chu and So, 2001; Zhu et al., 2005). Even though solubilization is initiated at the CMC, optimum

Fig. 3 Variation of different physical properties of the solution with surfactant concentration for removal of petroleum hydrocarbons from contaminated soils. CMC = critical micelle concentration

388

removal efficiencies are reported at concentrations far higher than the CMC (Zhou et al., 2013; Yan et al., 2015). The surfactant molecules that form micelles in the aqueous solution orient their hydrophobic nonpolar tails to achieve maximum contact with each other, forming a hydrocarbon-like core, and the hydrophilic heads also make maximum contact with water (Gan et al., 2009). Furthermore, the HOCs tend to partition into hydrocarbon-like micellar cores, giving micelles the capacity to solubilize HOCs (Laha et al., 2009). Surface tension, interfacial tension, adsorption, and detergency properties change with surfactant concentration below the CMC, but there are no variations in those properties at surfactant concentration above the CMC (Paria and Khilar, 2004). Because surfactant molecules partition into soil colloids owing to their amphiphilic nature, the surfactant dose required for micelle formation in the soil solution is greater than that in water alone. The partitioning results in a higher measured CMC for soil-water systems than for the aqueous solutions, and this higher surfactant dose is called the elevated CMC or effective CMC (CMCeff) (ElghDalgren et al., 2009; Laha et al., 2009). Ussawarujikulchai et al. (2008) found that the CMC of Triton X-100 (TX-100), which is 0.3 mmol L−1 in the aqueous system, increased to 0.9–1.7 mmol L−1 in organic soils (CMCeff). Hydrophobic interaction among hydrocarbon chains causes micellization in nonionic surfactants as the hydrophobic groups are easily divided from the surfactant solution. For ionic surfactants, high concentrations are required to overpower the electrostatic repulsion among ionic head groups through micellization (Amirianshoja et al., 2013). The adsorption of surfactants may also increase the hydrophobicity of soil surfaces, which promotes the re-adsorption of the solubilized organic contaminants onto the soil surfaces and further decreases the efficiency of washing (Chu and Chan, 2003; Ishiguro and Koopal, 2016). Thus, a quantitative evaluation of any potential surfactant remediation approach must consider the sorption of surfactants onto soils and subsequent HOC partitioning to each phase to maximize efficiency and minimize cleanup costs (Zhou and Zhu, 2007a). The soil washing process may also result in a loss of fine particles, which affects the mechanical and hydraulic behavior of the tested materials (V´azquez et al., 2010). As would be expected from their use in soil cleaning programs, surfactants have been shown to enhance the solubilization of HOCs from soil, but they can increase the adsorption of HOCs by forming hydrophobic adsorbate layers, or hemimicelles, into which HOCs can partition (Haigh, 1996). Many surfactant molecules may be

A. A. BEFKADU AND Q. Y. CHEN

sorbed efficiently onto soils only as monomers (Zhu et al., 2003). Surfactants may also improve the microbial remediation of HOCs in soils by affecting the accessibility of the HOCs to microorganisms (Onur et al., 2015). Some surfactant combinations exhibit synergistic properties: they show a considerable decrease in surface tension and a lower CMC value than each of the individual members. The measure of the effectiveness of a particular surfactant in solubilizing a given solute is known as the molar solubilization ratio (MSR), the ratio of the number of moles of hydrocarbon solubilized to the number of moles of surfactant in the micelle form. This ratio can be calculated as follows (Edwards et al., 1991; Cheng and Wong, 2006): MSR =

Co − Co,CMC Cs − Cs,CMC

(1)

where Co is the total apparent solubility of the organics in moles per liter in micellar solution at a particular surfactant concentration greater than the CMC, Co,CMC is the apparent solubility of the organics in moles per liter at the CMC, Cs is the molar concentration of the surfactant, and Cs,CMC is the molar concentration of the surfactant at the CMC. The increase in solubilizate concentration per unit increase in micellar surfactant concentration is equivalent to the MSR. In the presence of an excess of hydrophobic organic compounds, the MSR is obtained from the slope of the curve that results when plotting the solubilizate concentration against the surfactant concentration (Edwards et al., 1991; Cheng and Wong, 2006). Use of the micelle-water partition coefficient (Kmc ), which represents the distribution of HOCs between surfactant micelles and the aqueous phase, is an alternative approach used to quantify the surfactant solubilization and may be expressed as follows: Kmc =

MSR Xm = Xa (1 + MSR)SCMC Vw

(2)

where Xm and Xa are the mole fractions of the solubilizate in the micelle and the aqueous phase, respectively, SCMC is the apparent solubility of the HOCs at the CMC of the surfactant, and Vw is the molar volume of water (0.018 05 L mol−1 ) (Zhou and Zhu, 2005). If the values of Kmc are immensely large, it indicates that the solubility of the HOCs in the micelles is greater than that in water. In fact, absorption onto micelles can be 4 to 6 orders of magnitude higher than the corresponding solubilization in water (Edwards et al., 1991). The value of Kmc is dependent on surfactant chemistry, solubilizate chemistry, and temperature.

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

SURFACTANTS USED IN SOIL WASHING Based on their origins, surfactants are classified as synthetic surfactants or biosurfactants. According to the nature of the hydrophilic head groups, synthetic surfactants are classified into four types: cationic, anionic, nonionic, and zwitterionic surfactants (Paria, 2008; Rosen and Kunjappu, 2012). These four types of surfactants have different adsorption characteristics, CMC values, and solubilization capacities, which significantly affect their performance in solubilizing HOCs (Chu and Chan, 2003). Some of the different classes of surfactants commonly used for soil washing are summarized in Table I, with their molecular formulae and weights presented. Besides these commonly used surfactants, germini surfactants, switchable surfactants, and mixed surfactants are also newly used for soil washing. Cationic surfactants Cationic surfactants dissociate in water into an amphiphilic cation and an anion, most often of the halogen type. An enormous proportion of this class consists of nitrogen compounds such as fatty amine salts and quaternary ammonium salts, with one or more long chains of the alkyl type, often coming from natural fatty acids. Cationic surfactants have positively charged head groups and tend to adsorb strongly onto negatively charged surfaces like fabric, hair, bacterial cell membrane of, soil, and sediment via electrostatic

389

interactions (Zhang and Zhu, 2010). Cationic surfactants are a smaller class of surfactants commonly used in fabric softeners, hair conditioners, and antibacterial agents (Koner et al., 2011). Cationic surfactants mostly contain straight alkyl chains of 8–24 carbon atoms, and the most common cationic surfactant compounds are quaternary ammonium compounds (Tadros, 2005). Cationic surfactants are chemically stable and stable to pH and electrolyte changes. They are compatible with nonionic surfactants, but are incompatible with most anionic surfactants. Cationic surfactants have CMC values close to those of anionic surfactants when both have the same alkyl chain length (Varade et al., 2005). Cationic surfactants are not suitable for soil washing because they have a high tendency onto sorb to soil particles and are less environmentally compatible. The firm interaction between the cationic head groups and the negatively charged soil surfaces causes surfactant loss and results in higher concentration demand for micelle formation in solution in comparison to anionic and nonionic surfactants (Zhang and Zhu, 2010; Ishiguro and Koopal, 2016). As a result, anionic and nonionic surfactants have been widely used for surfactant-enhanced soil washing (Yang et al., 2005, 2006; Li et al., 2016). In an experiment conducted to identify factors affecting the selection of surfactants in washing remediation technology, Li et al. (2016) found that anionic and nonionic surfactants achieve better desorption of petroleum hydrocarbons from clay mate-

TABLE I Surfactants commonly used for soil washing Surfactant

Full name/component

Type

SDBS SDS ADBAC

Sodium dodecyl benzene sulfonate Sodium dodecyl sulfate Alkyl dimethyl benzyl ammonium chloride Cetyl trimethy lammonium bromide Alkyl poly glucosides Polyoxyethylene(4)lauryl ether Polyoxyethylene lauryl ether Polyethylene glycol hexadecyl ether Polysorbate 20 Polyoxyethylene sorbitan monooleate Triton X-100 α-l-rhamnopyranosyl-α-l-rhamnopyranosylβ-hydroxydecanoyl-β-hydroxydecanoate Pentacyclic triterpene saponin Cyclic lipopeptide 1,10-(alkane-1,s-diyl)bis(1-dodecyl pyrrolidinium) bromide Disodium 2,3-didodecyl-1,2,3,4butanetetracarboxylate

Anionic synthetic surfactant C18 H29 NaO3 S Anionic synthetic surfactant CH3 (CH2 )11 OSO3 Na Cationic synthetic surfactant C6 H5 CH2 N(CH3 )2 RCl (R = C8 H17 –C18 H37 ) Cationic synthetic surfactant CH3 (CH2 )15 N(Br)(CH3 )3 Nonionic synthetic surfactant C16 H32 O6 Nonionic synthetic surfactant C12 H25 O(CH2 CH2 O)4 H Nonionic synthetic surfactant C12 H25 (OC2 H4 )23 OH Nonionic synthetic surfactant C16 H33 (OCH2 CH2 )20 Nonionic synthetic surfactant C12 H34 O2 C6 H10 O4 (OCH2 CH2 )20 Nonionic synthetic surfactant C18 H34 O2 C6 H10 O4 (OCH2 CH2 )20 Nonionic synthetic surfactant C9 H17 C6 H4 O(OCH2 CH2 )9.5 H Biosurfactant (glycolipid C32 H58 O13 rhamnolipid) Nonionic biosurfactant Zwitterionic biosurfactant Cationic gemini surfactant

CTAB APGs Brij 30 Brij 35 Brij 58 Tween 20 Tween 80 TX-100 Rha-RhaC10 -C10 Saponin Surfactin C12-CsC12 PB GS

Anionic gemini surfactant

Molecular formula

Molecular weight g mol−1 340–352 288.372 Variable 364.45 362.56 1 198 1 124 1 228 1 310 628 650.79

390

rials than cationic surfactants. In most of the reported results, cationic surfactants are not effective in removing organic contaminants (L´opez-Vizca´ıno et al., 2012). Nonionic surfactants Nonionic surfactants are the second largest class of surfactants after anionic surfactants. They do not ionize in aqueous solution because their hydrophilic group, which comprises an ethylene oxide chain of variable length, is of a non-dissociable type, such as alcohol, phenol, ether, ester, or amide (Farn, 2006; ElSayed et al., 2013). As a result, anionic surfactants are compatible with other types of surfactants; they do not form insoluble salts, can be used in strongly acidic solutions, and tend to have low toxicity profiles (Singla et al., 2009). Nonionic surfactants dissolve in the aqueous phase via the formation of intermolecular hydrogen bonds between the hydrophilic groups and water molecules. Micellization is easier for nonionic surfactants because aggregation takes place mainly due to the hydrophobic attraction among nonpolar chains, whereas hydrophilic chains are easily separated in an aqueous phase. Therefore, nonionic surfactants usually have low CMC values (Rosas et al., 2013). In nonionic surfactants, the hydrophilic part commonly comprises polyoxyethylene, sucrose, or polypeptide, and the hydrophobic part is an alkylated phenol derivative, a fatty acid, or a long-chain linear alcohol (Paria, 2008). Compared with anionic surfactants, nonionic surfactants are effective under extreme conditions of salinity and hard water as they are less sensitive to electrolytes and the presence of divalent cations (ElSayed et al., 2013; Rosas et al., 2013). Nonionic surfactants are good detergents, wetting agents, and emulsifiers, and some of them have excellent foaming properties. Some kinds of nonionic surfactants exhibit low toxicity levels, which makes them usable for pharmaceuticals, cosmetics, and food products (Ivankovi´c and Hrenovi´c, 2010). The most abundant nonionic surfactants in use are alcohol ethoxylates (AEOs) and alkylphenol ethoxylates (APEOs) (Gomez et al., 2011). Higher solubilization capabilities in a very dilute solution, better biodegradability, lower tendency to flocculate clay particles, relatively constant properties for salt addition, and much lower CMC values are the qualities of nonionic surfactants that make them preferable over anionic surfactants (Mulligan et al., 2001; Paria and Yuet, 2007; Fabbri et al., 2008). Significant loss of nonionic surfactants by adsorption and consequent partitioning of hydrophobic contaminants into surfactant hemimicelles formed on the

A. A. BEFKADU AND Q. Y. CHEN

soil surface, particularly at a concentration below the CMC, have raised economic feasibility issues. Hydrogen bonding may be considered the primary driving force for nonionic surfactant adsorption onto soil or mineral surfaces, as ionic and chemisorbing groups are absent from nonionic surfactants (Rosas et al., 2013). Surfactant adsorption reduces the amount of surfactant available for micelle formation in the soil solution; therefore, more surfactant is required for the system to be effective (Cowell et al., 2000; Zheng and Obbard, 2002; Muherei, 2008). Anionic surfactants Like all surfactants, anionic surfactants are surfaceactive compounds composed of a hydrophobic alkyl chain connected to hydrophilic groups. Anionic surfactants are the most commonly used, abundant, and inexpensive class of surfactants and are mainly used in detergent formulations and personal care products (Farn, 2006). In aqueous solutions, anionic surfactants dissociate into an amphiphilic anion and a cation; the most frequently found cations are sodium, potassium, ammonium, calcium, and various protonated alkyl amines (Zhou et al., 2005). The anion in anionic surfactants is the carrier of the surfactant properties; it gets its negative charge from the presence of sulfonate, sulfate, phosphate ester, carboxylate, isethionate, soap, or taurate groups in the molecule, and the presence of this polar groups is the basis for classification (Karsa and Porter, 1995). The general formulae of anionic surfactants are as follows: Cn H2n+1 COO− X+ (carboxylates), Cn + + H2n+1 OSO− (sulfates), Cn H2n+1 SO− (sulfo3X 3X − + nates), and Cn H2n+1 OPO(OH)O X (phosphates), where n is in the range 8–16 atoms and the counter ion X+ is usually Na+ (Tadros, 2013). Linear alkyl benzene sulfonates (LASs) are the most widely used and researched anionic surfactants; their popularity is because of their higher efficiency as detergents and the relative ease by which they can be manufactured (Farn, 2006). Anionic surfactants have relatively high removal efficiency and lower adsorption, making them preferable surfactants for washing (Deshpande et al., 1999). However, ionic surfactants exhibit higher CMC values, which results in higher surfactant concentrations in washing residues, and are more prone to precipitate in the presence of multivalent cations (Ca2+ and Mg2+ ) (Fabbri et al., 2008; Muherei, 2008). A significant amount of loss of surfactants by such mechanisms reduces their effective concentration in aqueous solution, which substantially reduces surfactant solubilization and flushing efficiency (Fabbri et al., 2008;

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

Zhou et al., 2013). In addition to their ability to emulsify oil that has reached soil into washing solutions, surfactants can lift soils, including particulates, from surfaces because, unlike cationic surfactants, the negatively charged head groups of anionic surfactants are repelled from most surfaces, which also tend to be slightly negatively charged (Farn, 2006). The vast majority of anionic surfactants generate a significant amount of foam at concentrations above their CMC; this may be a desirable attribute in most cleaning operations, but can also create a problem in some cleaning processes (Srinet et al., 2017). Chu and Chan (2003) found that for similar nonpolar chain lengths, the order of magnitude of solubilization of HOCs by surfactants was: nonionic > anionic > cationic. L´opez-Vizca´ıno et al. (2012) attempted to remove phenanthrene from a kaolinitic clay using three different types of surfactants: sodium dodecyl sulfate (SDS), alkyl dimethyl benzyl ammonium chloride (ADBAC), and polyoxyethylene sorbitan monooleate (Tween 80). Among the tested surfactants, the anionic surfactant SDS achieved higher removal efficiency (90%) than both the nonionic and cationic surfactants (70% and 30%, respectively). They did not explain the reason for the differences in efficiency between the surfactants, but they claimed that it may depend on other factors like surfactant-to-contaminant ratio and fluid dynamic conditions. Yan et al. (2015) attempted to remove nitrobenzene (47.3 mg kg−1 ) from contaminated soils using sodium dodecyl benzene sulfonate (SDBS), Tween 80, and an SDBS-Tween 80 mixture. Superior nitrobenzene removal (76.8%) was achieved using SDBS compared to using both Tween 80 and the SDBS-Tween 80 mixture. Higher desorption efficiency of nitrobenzene was found for SDBS than for Tween 80 at the same concentration owing to the weaker sorption effect on kaolin. They concluded that though the apparent solubility of nitrobenzene in Tween 80 solution is greater than that in SDBS solution, the adsorption amount of surfactant on soil is key to the washing process, which can significantly affect nitrobenzene desorption (Yan et al., 2015).

391

ric surfactants, have pH-dependent charges; they are cationic under acidic solution conditions and anionic under strong alkaline conditions. They are available as zwitterions in only a narrow pH range, and they show maximum surface activity at the isoelectric point (Tadros, 2013). Zwitterionic surfactants are highly compatible with other classes of surfactants, are readily biodegradable, form stable foams, and are less sensitive to temperature and salinity variations (Li et al., 2013). Their high biodegradability and high compatibility with other classes of surfactants indicate that they may have increased importance in future applications (Stefania et al., 2012; R´ıos et al., 2017). Gemini surfactants Gemini surfactants are a relatively new class of surfactants contain two hydrophilic head groups and two hydrophobic tails covalently linked through a spacer unit at or in proximity to the head groups, as shown in Fig. 4 (Zana, 2002a; Kabir-ud-Din et al., 2009; Cashion et al., 2010). Synthetic gemini surfactants include cationic, anionic, zwitterionic, and nonionic functionalities, depending on the incorporated spacer (Menger and Keiper, 2000). The spacer in gemini surfactants can be long or short, flexible or rigid, hydrophilic or hydrophobic (Akba¸s et al., 2014). The length of the spacer in gemini surfactants affects the shape and size of the micelles, which ultimately determine their performance (Zana, 2002b). For a cationic gemini surfactant, the longer the length of the spacer, the less adsorption the gemini molecule and the better its performance (Chorro et al., 1999). The effect of the spacer length on the adsorption of anionic gemini surfactants is the inverse of the effect on cationic gemini surfactants (Paria, 2008).

Zwitterionic surfactants The hydrophilic polar heads in this class of surfactants contain both positive and negative charges; the presence of a dual charge on the same head group makes these surfactants neutral and puts their hydrophilicity between the nonionic and ionic classes. Zwitterionic surfactants, sometimes called amphote-

Fig. 4

Basic structure of a gemini surfactant.

These surfactants have higher surface activities and have shown some unique properties like much lower CMC values, more surface activity, higher efficiency in lowering surface tension, stronger biological activi-

392

ty, better wetting capability, better foaming capability, and better solubilization capability, as compared with the commonly used surfactants (Du et al., 2006; Liu et al., 2010; Akba¸s et al., 2014), and, hence, have more varied industrial applications. Gemini surfactants have a complicated synthetic process; this complex process raises the cost of their production and is an obstacle to their extensive use in remediation processes (Mao et al., 2015). They are commonly utilized as foaming agents, detergents, coaters, softeners, and ingredients in cosmetic and biomedical applications (Chen et al., 2008; Parekh et al., 2011). Owing to a limited number of studies conducted on this surfactant class, the performance of gemini surfactants remains unclear. Switchable surfactants Switchable surfactants are another upcoming class of surfactants having the potential for remediation and related functions. Surfactants that can be switched on and off reversibly by external stimuli like pH (Liu et al., 2012), carbon dioxide (CO2 ) (Yang and Dong, 2016), temperature (Hu et al., 2015), magnetic field (Czaun et al., 2008), light irradiation (Long et al., 2014), and redox conditions (Smith et al., 2017) are known as switchable surfactants. Switchable surfactants have attracted considerable interest in many industrial applications such as cleaning, fuel production, oil recovery and transport, and emulsion polymerization (Jiang et al., 2013). Surfactant-enhanced soil remediation is known to produce a stable contaminant oil-in-water emulsion, which makes separating oil, surfactant, and water difficult. Considering the cost and environmental contamination posed by surfactants, finding a way to recover and reuse surfactants has an economic and ecological advantage. Reversible surfactant-enhanced remediation technology takes advantage of the ability of switchable surfactants to be switched on and off according to the operator’s command to separate the oil and surfactant from the oil-in-water emulsion formed in the soil-washing effluent. The basic procedure is that after washing the contaminated soil with a switchable surfactant, the surfactant in the effluent is switched off, releasing the hydrocarbon contaminant from the emulsion state to float on the surface of the water. By removing the hydrocarbon from the top of the surfactantwater mixture, the washing solution can be reused by switching on the surfactant using its particular stimulus (Ceschia et al., 2014). Of all the above-mentioned environmental triggers, CO2 seems to be ideal for oil and surfactant recovery because CO2 is abundant, biocompatible, easy to remove, and available at relatively

A. A. BEFKADU AND Q. Y. CHEN

low cost (Ceschia et al., 2014; Liu et al., 2016). This class of surfactants has not been widely used in soil remediation, as most switchable surfactants are cationic and are more readily adsorbed on the negatively charged soil particles. To minimize their adsorption, switchable surfactants were mixed with nonionic surfactants, and the mixture reduced the degree of adsorption on soils (Hu et al., 2017). Recently, Ceschia et al. (2014) compared three anionic CO2 -switchable surfactants with TX-100 and SDS and found that the switchable surfactants and TX-100 were able to remove more than 90% of the oil from contaminated sand. Moreover, treatment of the washing solution with CO2 was able to break 90% of the emulsion and recover 99.5% of the switchable surfactants. The use of anionic switchable surfactants has potential as they have lower adsorption than cationic surfactants. Even though switchable surfactants have enormous potential for soil washing, synthesizing them is complicated. Hence, further work on the synthesis and testing of eco-friendly switchable surfactants for the removal of different types of organic contaminants is required. Mixed surfactants The lower efficiency of cationic surfactants, the higher CMC of anionic surfactants, and the sorption of nonionic surfactants onto soil has led scientists to look beyond single surfactant systems. The use of welldesigned surfactant mixtures may significantly alleviate problems of selection. Mixing two or more surfactants in water forms mixed micelles, with the most mixed micelles being ionic-nonionic (Parekh et al., 2011). Some surfactant combinations exhibit synergistic properties: they show considerable improvement in solubilization capacity, decreased surface tension and CMC value, higher cloud point, and lower Krafft point (critical micelle temperature) than each of the individual members. Synergism results in a reduction of the total amount of surfactant used in a particular application, which in turn improves efficiency, and reduces both the cost and the environmental impact (Zhou and Zhu, 2003, 2005, 2007b; Yang et al., 2006; Guo et al., 2009; Kabir-ud-Din et al., 2009; Shi et al., 2015). The addition of nonionic surfactants to an anionic surfactant solution can decrease the precipitation of the anionic surfactant with a multivalent electrolyte such as Ca2+ and Mg2+ , which correspondingly reduces the sorption loss of the anionic surfactant by soil (Zhao et al., 2005; Yang et al., 2006). The sorption of nonionic surfactants can also be inhibited by the presence of anionic surfactants owing to the reduced electrostatic attraction (Paria and Khilar, 2004;

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

Yang et al., 2005; Guo et al., 2009), leading to the formation of more micelles and, hence, more contaminant removal (Yang et al., 2006). Using anionic-nonionic mixed surfactants is shown to be more efficient for solubility enhancement and desorption of HOCs from soil compared with using a single surfactant (Zhou and Zhu, 2004, 2005, 2007b; Muherei, 2008; Guo et al., 2009). Guo et al. (2009) have reported that because of the formation of mixed micelles, the apparent solubilities, MSR, and sorbed Tween 80 concentration are positively correlated with the mass fraction of SDBS in Tween 80-SDBS mixed surfactant solutions. In another study on mixed surfactant systems comprising anionic sodium dodecyl trioxymethylene sulfate (SDES) and gemini surfactants (cationic) at different molar ratios, high interaction and very low CMC were found because of weakening of electrostatic head group repulsion, which favored mixed micelle formation. Gemini surfactants bind tightly with SDES by electrostatic, hydrophobic, and ion-dipole interactions (Parekh et al., 2011). Furthermore, with an increase in the mole fraction of the nonionic surfactant, the CMC values of the mixed surfactants were reported to decrease continuously from the CMC of the pure anionic surfactant down to the CMC of the pure nonionic surfactant (Zhou and Zhu, 2004; Muherei, 2008). Ideal solution theory can predict the mixed CMC values of similarly structured ionic or nonionic surfactants. However, the reported experimental CMC values were lower than the ideal values (Muherei, 2008). The mixtures of different surfactants show more non-ideal behavior and are of both theoretical interest and practical importance (Parekh et al., 2011). The properties of mixed surfactants depend on their structural type and composition, and the tendency to form a micellar structure in mixed surfactant solutions is substantially different from that in simple individual surfactant solutions. Mixed surfactants perform well over a wider range of temperatures, salinities, and hardness conditions than individual surfactants (Holland and Rubingh, 1992). Studies on mixtures of two single-chain surfactants have found that the synergism decreases in the order: anionic-cationic > ionic-zwitterionic > ionic-nonionic (Liu et al., 2014). However, in practice, ionic-nonionic mixtures have lower adsorption to soil and higher contaminant removal efficiency and thus are more widely used than anionic-cationic or cationic-nonionic mixtures (Xu et al., 2006). The nature and charge of the mineral surface determine which surfactant is preferentially adsorbed over

393

the other. On positively charged surfaces where anionic surfactants are densely adsorbed, the presence of a nonionic surfactant decreases the adsorption of the anionic surfactant, and the adsorption of the nonionic surfactant is enhanced, whereas a nonionic surfactant alone shows trace adsorption (Wang and Kwak, 1999; Paria and Khilar, 2004). Interestingly, however, it has been reported that the presence of anionic surfactant retards nonionic surfactant adsorption on clay minerals (Paria and Khilar, 2004; Yang et al., 2005). The extent to which surfactants influence the distribution of HOCs depends principally on the HOC sorption onto the solid phases. Surfactant washing can be ineffective for soils that contain more than 20%–30% silt/clay or considerable quantities of organic matter. In a study (Zhang and Zhu, 2010) conducted on the polycyclic aromatic hydrocarbon (PAH) desorption efficiency of mono and mixed surfactants, Tween 80 mixed with SDBS exhibited higher desorption of PAH than mono surfactants. Adding a small proportion of anionic surfactants to a larger proportion of nonionic surfactants decreases the sorption of nonionic surfactants onto soil and increases the active surfactant ion concentration in solution, which ultimately increases contaminant desorption (Zhang and Zhu, 2010). The salinity or ionic strength of the solution may positively affect the solubilization, CMC reduction, and sorption loss of surfactants in mixed surfactant systems. The addition of salt has less effect on the solubilization of nonionic surfactants, but it can reduce the CMC of anionic surfactants (Li and Chen, 2002). Wei et al. (2015) reported that the addition of salt to nonionic-anionic surfactant mixtures improved the solubilization of pyrene and decreased the CMC of the nonionic-anionic surfactant mixture as the presence of salts reduced the electrostatic repulsion between micelles and increased their Kmc . They found that the presence of salts reduced the sorption of surfactants onto kaolin-rich soil from 15.34 to 11.07 mg g−1 soil. Shi et al. (2015) evaluated the remediation efficiency of mono and mixed surfactants in PAH-contaminated soils from a coke oven plant. The highest removal efficiencies were in the order: TX-100-SDS mixture (9:1) > TX-100-SDS mixture (8:2) > TX-100-SDS mixture (7:3) > TX-100-SDBS mixture (7:3) > TX-100 > SDBS > SDS. From the results, we see that mixed surfactants perform better than mono surfactants, and the mixed surfactants with a high nonionic-to-anionic ratio perform best. Zhou and Zhu (2007b) assessed the desorption of phenanthrene from contaminated soils using TX-100,

394

SDS, and SDS-TX-100 mixture. The mixed surfactants performed better than the individual surfactants in phenanthrene removal as the presence of SDS (anionic) surfactant reduced the sorption of TX-100 (nonionic) onto the soil, which ultimately increased the solubilization of the contaminant because more TX-100 was available in the soil solution for solubilizing the contaminant. In addition, as the mole fraction of SDS in the mixture increased, the amount of TX-100 sorbed onto the soil decreased (Zhou and Zhu, 2007b). Several studies (Zhao et al., 2005; Yang et al., 2006; Yu et al., 2007; Ahn et al., 2010) have reported similar strong restriction of nonionic surfactant sorption at the soil surface by the presence of an anionic surfactant as the formation of mixed micelles and the sorption amount of nonionic surfactants decreased with the increasing mole fraction of the anionic surfactant in the mixed solution. Combined TX-100 and SDBS at a 1:9 mass ratio exhibited the highest phenanthrene desorption (Yang et al., 2006). Biosurfactants Biosurfactants are surface-active compounds of biological origin. They are mostly produced by microorganisms like bacteria, fungi, and yeasts, but can also be extracted from plant and animal parts (Lee et al., 2012). They are soluble in water, form micelles above the CMC, and reduce surface and interfacial tension as synthetic surfactants (Chapr˜ao et al., 2015). They are amphiphilic in nature, with their hydrophilic part usually composed of amino acids, carbohydrates, peptides, and polysaccharides. Their hydrophobic ends are long-chain fatty acids, hydroxy fatty acids, or α-alkylβ-hydroxy fatty acids (Mulligan, 2005). Most biosurfactants are anionic or nonionic; only a few are cationic, such as those containing amine groups. The structures of biosurfactants are characteristic of the producing species and the availability of the carbon source during the growth of the microorganism (Pacwa-Plociniczak et al., 2011). Biosurfactants can be broadly divided by their microbial origin and chemical composition into categories as follows: glycolipids (rhamnolipids, sophorolipids, and trehalolipids); fatty acids, phospholipids, and neutral lipids; polymeric biosurfactants; and particulate biosurfactants (Santos et al., 2016). Because synthetic surfactants are subject to considerable losses via precipitation/adsorption or phase change, are toxic to microorganisms, and have lower biodegradability at higher CMC, they cause secondary contamination and inhibit biodegradation processes. Biosurfactants may be a promising option for soil washing operations in the cleanup of contaminated soils

A. A. BEFKADU AND Q. Y. CHEN

(Zhou et al., 2013; Chapr˜ao et al., 2015; Helmy et al., 2015). When compared with synthetic surfactants, biosurfactants possess distinct advantages including lower toxicity, higher biodegradability and biocompatibility, multifunctional characteristics, and less sensitivity to extreme environmental conditions and thus can be more efficient in the remediation of contaminated soils (Christofi and Ivshina, 2002; Kuyukina et al., 2005). Zou et al. (2014) investigated the surface activity of the biosurfactants produced by Acinetobacter baylyi ZJ2 isolated from a crude oil-contaminated soil sample in China and evaluated its potential application in microbially enhanced oil recovery. They reported that these biosurfactants reduced the surface tension of water from 65 to 35 mN m−1 and the interfacial tension against oil from 45 to 15 mN m−1 . The biosurfactants commonly used for soil remediation include glycolipids (e.g., rhamnolipids, fructose lipids, and sophorolipids), lipopeptide compounds (e.g., surfactin and polymyxin), and humic substances (Mao et al., 2015). The most commonly introduced biosurfactant-producing microorganisms used in microbially enhanced oil recovery processes are Bacillus, Pseudomonas, Clostridium, Corynebacterium, Arthrobacter, and Nocardia species (Kaczorek et al., 2010; Chandankere et al., 2013). Rhamnolipids are among the most commonly studied biosurfactants for the remediation of soils contaminated with HOCs and heavy metals. They are mostly produced by Pseudomonas aeruginosa and are composed of one or two rhamnose molecules as the hydrophilic portion and up to three molecules of hydroxy fatty acids (C8–C14) as the hydrophobic portion (Wanet al., 2011). Lai et al. (2009) tested the total petroleum hydrocarbon (TPH) removal efficiency of rhamnolipid produced by P. aeruginosa, surfactin produced by Bacillus subtilis, and synthetic surfactants such as Tween 80 and TX-100. Their results showed that the biosurfactants exhibited much higher TPH removal efficiency than the synthetic surfactants examined. In a study that compared the washing efficiency of a biosurfactant from Rhodococcus ruber with the synthetic surfactant Tween 60, the biosurfactant was more efficient and was also less adsorbed onto the soil (Kuyukina et al., 2005). The adsorption of rhamnolipid on soil depends on different soil parameters like the clay, metal oxide, and organic matter contents of the soil (Paria, 2008). Zhou et al. (2013) compared the phenanthrenecontaminated soil washing using a plant-derived natural biosurfactant saponin extracted from the fruit pericarps of Sapindus mukorossi with that of Tween 80, a representative synthetic nonionic surfactant. They fo-

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

und that the Sapindus saponin effectively removed phenanthrene from the contaminated soil with an efficiency of 87.4%, only 4.1% less than the efficiency of Tween 80. In a study (Chapr˜ao et al., 2015) conducted to investigate the enhanced biodegradation and removal capabilities of biosurfactants produced by Candida sphaerica and Bacillus sp. on motor oil-contaminated sands, both crude and isolated biosurfactants showed superior effectiveness than Tween 80 and TX-100 under kinetic conditions (70%–90%). The presence of the biosurfactants also increased the degradation rate by 10%–20%, especially during the first 45 d, indicating that the biosurfactants acted as active enhancers of hydrocarbon biodegradation (Chapr˜ao et al., 2015). Conte et al. (2005) reported that humic acid could be utilized as a natural surfactant for the remediation of contaminated soils with efficiency equal to or better than synthetic surfactants. Montoneri et al. (2009) reported that humic acid derived from lignocellulosic biomass plus food wastes was more efficient for PAH removal than SDS at a concentration of 10 g L−1 . In a model soil column study conducted on crude oil desorption using a microbially produced biosurfactant from R. ruber and the synthetic surfactant Tween 60, the oil removal rate of the biosurfactant was 1.4–2.3 times greater than that of Tween 60. The biosurfactant-enhanced oil mobilization was reported to be temperature-related and was slower at 15 ◦ C than at 22–28 ◦ C. Fractional analysis of the removed oil relative to that of the original oil composition showed that crude oil removed by the biosurfactant contained a lower proportion of nonbiodegradable high-molecular-weight paraffin and asphaltene. This result also suggests that oil mobilized by biosurfactants can be readily biodegraded by soil bacteria (Kuyukina et al., 2005). Biosurfactants improve the bioavailability of hydrocarbons to bacterial cells by increasing the area of the aqueoushydrocarbon interface, which enhances the rate of hydrocarbon dissolution and therefore utilization of the hydrocarbons by the bacteria (Banat et al., 2010; Zhang et al., 2010). Ivshina et al. (2016) investigated the removal of PAHs from soil using biosurfactants produced by R. ruber IEGM 231 in soil columns spiked with model mixtures of primary petroleum constituents (a crystalline mixture of single PAHs, a crystalline mixture of PAHs and polycyclic aromatic sulfur heterocycles (PASHs), and an artificially synthesized NAPLcontaining PAHs). They found that the biosurfactants were 2.5 times more efficient than Tween 60 in the NAPL-spiked soil and were similar to Tween 60 in

395

the crystalline-spiked soil. Liao et al. (2016) compared the potential of two biosurfactants (rhamnolipid and soybean lecithin) and a synthetic surfactant (Tween 80) to facilitate the phytoremediation of crude oilcontaminated soil by maize (Zea mays L.). Their findings indicate that biosurfactant-amended phytoremediation may be a useful and green biotechnological approach for the remediation of petroleum hydrocarbonpolluted soils. Morales-Guzm´an et al. (2017) isolated 13 bacterial strains from highly weathered petroleum hydrocarboncontaminated soils and evaluated the emulsifying and diesel degradation potential of each strain. They found a strain with 74.2% diesel emulsification potential, high cell hydrophobicity, and 96% diesel degradation potential. The production of biosurfactants by this class of bacteria allows them to access and degrade usually unavailable hydrocarbons, and in addition they can attach onto hydrophobic surfaces and act as both co-substrate and carbon source for other microorganisms (Onur et al., 2015). These bacteria have enormous potential for bioremediating soils contaminated with weathered petroleum hydrocarbons. One of the factors that affect the efficiency of bioremediation through bacterial action is the low availability and solubility of contaminants because of hydrophobicity and the strong adsorption of contaminants by soil colloids (Chang et al., 2015). However, the presence of emulsifying bacteria mobilizes the contaminants and makes them accessible for degradation. Bacterial strains with both emulsification and degradation potential have also been isolated from contaminated river water and petroleum reservoirs (Chandankere et al., 2013; Zou et al., 2014; Onur et al., 2015). However, further bioremediation studies on the effectiveness of these bacterial strains when inoculated into real contaminated soils are required. In addition to the positive impact on solubilization and desorption of soil contaminants, biosurfactants also stimulate microbes to decompose contaminants, which is favorable to the in-situ bioremediation of soil contaminants. However, the main issue that currently impairs their use in washing is their economically consistent production, and large-scale production remains financially challenging for many types of these products (Von Lau et al., 2014). The exploration of new biosurfactants, the discovery of new fermentation and recovery processes (or the improvement of existing processes), and the use of cheap materials will mean that less expensive biosurfactants can be made available for remediation processes in the future (Chapr˜ao et al., 2015). Plant-derived biosurfactants such as sa-

396

ponin may be less costly since they are plant-derived and easily produced than the other microbially derived biosurfactants (Kobayashi et al., 2012). SURFACTANT SELECTION As different types of surfactant are available, it is necessary to evaluate the relative suitability of a surfactant for washing a target contaminant from soil or aquifer systems. The effectiveness of a surfactant in solubilizing a given organic contaminant depends on several properties, such as solubility, adsorption tendency, CMC, toxicity, biodegradation, contaminant solubilization ability, cost, public and regulatory perception, and ability to be recycled (Deshpande et al., 1999; Mulligan et al., 2001). The CMC, the surface and interfacial tension, and the hydrophilic-lipophilic balance are the three most important parameters that help characterize surfactant activity in solution (Lee et al., 2002). Low adsorption/CMC, solubility at groundwater temperature, and toxicity, high solubility at a concentration less than 3%, low soil dispersion, low surface tension, and elevated biodegradation rate are expected from an ideal surfactant (Deshpande et al., 2000; Mulligan et al., 2001). Among all the synthetic surfactants, nonionic surfactants have gained lots of attention in surfactant-enhanced soil washing studies (Chu and Chan, 2003; Zhu and Zhou, 2008) because of their low concentration requirement, high solubilization capacity, and reduced soil flocculation (Cowell et al., 2000). Surfactant-induced foaming and turbidity are operating conditions that are also important to be considered in surfactant selection (Deshpande et al., 1999). An intrinsic factor affecting the adsorption of nonionic surfactants by soil is the alkyl chain length. In general, the adsorption of nonionic surfactants increases with increasing alkyl chain length (Rao and He, 2006). Nonionic surfactants have relatively high biodegradability and low toxicity to soil microorganisms (Cowell et al., 2000; Chu and Chan, 2003). This rapid degradation of nonionic surfactants in soil also aids in eliminating any adverse long-term impact on the environment as the nonionic surfactants are removed in a short period through biodegradation. Nonionic surfactants are usually preferred over ionic surfactants in soil washing operations as they are relatively biodegradable, have less tendency to flocculate clay particles, and possess lower CMC, which makes them cost-efficient (Cheng et al., 2017). Higher washing efficiency does not always indicate the best choice of surfactant for the selective sorption process and reuse of

A. A. BEFKADU AND Q. Y. CHEN

the surfactant. An ideal surfactant for the soil washing operation is biodegradable, has a high pollutant solubilization ability, and low sorption by soil colloids (Zhou and Zhu, 2007a). However, if surfactant recovery is taken into consideration, the selective sorption capacity of the surfactant onto an adsorbate-like activated carbon will significantly affect surfactant recovery and the overall selection process (Ahn et al., 2008a). Deshpande et al. (1999) conducted an experiment on three different soils using eight types of surfactants and found that the surfactants behaved differently in different soils, calling for bench-scale testing when selecting a surfactant for a given soil contaminant system. They also recommended that evaluating both anionic and nonionic surfactants at concentrations below and above their CMC values is necessary for any surfactant selection procedure. As soil surfaces are negatively charged, they have a high affinity for cationic surfactants, which they readily adsorb. This makes cationic surfactants unavailable for remediation. Therefore, cationic surfactants are rarely used in laboratory and field remediation studies (S´anchez-Mart´ın et al., 2003). Owing to the low CMC values of nonionic surfactants and the weak adsorption tendency of anionic surfactants, nonionic and anionic surfactants are preferred for soil washing (Zhu and Feng, 2003; Yang et al., 2005). The bulk of literature suggests that nonionic surfactants are a better choice for surfactant-enhanced soil washing in comparison to anionic surfactants because of better their washing performance, i.e., lower precipitation tendencies, lower CMC values, and increased solubilization capacity (Zhao et al., 2005; Yu et al., 2007; Alc´antara et al., 2008; Zhu and Zhou, 2008). From the results of the soil washing studies undertaken in the last three decades, we can conclude that surfactants differ significantly in contaminant removal efficiency. The performance of each surfactant is understood to be soil-specific and contaminant typedependent (Table II), which calls for site- and lab-scale treatability studies to be conducted before selecting an appropriate surfactant for a given site (Uhmann and Aspray, 2012). FACTORS INFLUENCING WASHING EFFICIENCY Factors affecting soil washing efficiency can be viewed from three different angles: the properties of the soil, contaminant-related parameters, and processbased parameters. Zhou and Zhu (2007a) studied the efficiency of surfactants in enhancing the desorption of

Sandy loam Sandy loam

Silty loam Loam Silt Crushed and screened clay soil Landfill soil (top layer), silt, sand clay Soil of 13% gravel, 67% sand, and 20% fine fraction Soil of 6% clay, 16% silt, and 78% sand Sandy loam

Sand

Kaolin

37.6% clay Sandy soil Sandy soil Sandy loam Soil of 5.9% sand, 67.5% silt, and 26.6% clay Spiked soil Kaolin Sandy loam

Sandy soil

Soil of 50% sand, 30% clay, and 20% peat

Gharibzadeh et al. (2016) Huguenot et al. (2015)

Mousset et al. (2016)) Villa et al. (2010) Khalladi et al. (2009)) Sri Ranjan et al. (2006)

Chapr˜ ao et al. (2015)

Yan et al. (2015)

Guo et al. (2009)) Salehian et al. (2012) Urum et al. (2006) Tsai et al. (2009) Zhou et al. (2013)

Kobayashi et al. (2012) Wan et al. (2011) Lai et al. (2009)

Urum et al. (2005)

Kuyukina et al. (2005)

b) PAH

Air sparging-assisted stirred tank Column

Batch Batch Batch

Laboratory Column Batch Batch Batch

Laboratory

Laboratory

Laboratory

Laboratory

Field demonstration Laboratory

Laboratory Laboratory Field demonstration Laboratory

Laboratory Laboratory

Scale of remediation

Russia

Companies, UK

Japan Wuhan, China Taiwan, China

Chemical reagent factory, Shanghai, China Nanjing, China Tehran, Iran Companies, UK Taiwan, China Hangzhou, China

Western part of the Trans-Mexican Volcanic Belt geological province Jilin Oilfield, Northeastern China Oil refinery plant in southern Taiwan, China Brazil standard sand

French industrial site Mato Grosso, Brazil Algiers, Algeria Manitoba Province, Canada Pusan, Korea

Tehran, Iran Marne-la-Vallee, France

Soil source

Biosurfactant from Rhodococcus ruber

SDB-Tween 80 mixture (1:1) SDS (0.1%) Rhamnolipid, saponin, SDS Simple Green Sapindus saponin, Tween 80 (3 mg L−1 ) Saponin (10 g L−1 ) Rhamnolipid (25 g L−1 ) Rhamnolipid, surfactin, TX-100, Tween 80 (0.2%) Rhamnolipid (0.1%)

Rhamnolipids, surfactin, Tween 80, TX-100 Biosurfactant, Tween 80, TX-100 SDBS

Natural gums, surfactants (Maranil LAB, SDS, Texapon 40, and Surfacpol G) Alkyl poly glucosides

Tween 80 (2%)

Tween 80 (7.5 mg L−1 ) TX-100 (8.3 mg L−1 ) SDS (8 mmol L−1 ) CTAB (1.5%)

Tween 80 (5 000 mg L−1 ) Tween 80 (5%)

Surfactant(s) useda)

Crude oil

Crude oil

PAH Hexachlorobenzene TPH

p-nitrochlorobenzene Diesel Crude oil Fuel oil Phenanthrene

Nitrobenzene

Motor oil

Oil

Crude oil

PAH DDT, DDE, diesel Diesel Benzene series, naphthalene, phenanthrene Diesel, coal oil, lubricating oil Diesel

Phenanthrene Diesel

Major contaminant(s)b)

65%–82%

52.7% 55%–71% 63%, 62%, 40%, 35% 92%

96.7% 35%–45% 44%, 27%, 46% 90% 87.4%, 91.5%

63%, 62%, 40%, 35% 70%–90% 55%–80% 76.8%

97%

78.51%, 60.13%, 71.27%, 48.19%

88%

74.4% ± 3.5% 920 mg L−1 in effluent 85% ± 6% 66%, 80%, 100% 97% 58.8%–98.9%

Maximum removal efficiency

= Triton X-100; SDS = sodium dodecyl sulfate; CTAB = cetyl trimethy lammonium bromide; SDBS = sodium dodecyl benzene sulfonate. = polycyclic aromatic hydrocarbon; DDT = dichlorodiphenyltrichloroethane; DDE = dichlorodiphenyldichloroethylene; TPH = total petroleum hydrocarbon.

a) TX-100

Lai et al. (2009)

Han et al. (2009)

Hern´ andez-Espri´ u et al. (2013)

Lee et al. (2005)

Soil

Study

Soil washing experiments conducted for remediation of different hydrocarbon-contaminated soils

TABLE II

SOIL WASHING FOR REMOVAL OF HYDROCARBONS 397

398

PAHs from PAH-contaminated soils. They utilized a model to describe and predict the relative efficiency coefficient and critically improved the desorption concentration values for PAH. The ability of surfactants to enhance PAH desorption highly depends on the soil composition, surfactant structure, and PAH properties in both their model and experimental results. Contaminant-related factors The type, concentration, physicochemical form, and degree of weathering of organic contaminants are factors that influence their retention in soil. Zhou and Zhu (2007a) found that the desorption rates of phenanthrene, fluorene, acenaphthene, and naphthalene using TX-100 depended on the type of contaminant. Contaminant removal efficiency was also found to depend on the initial level of contaminant present in soil. Removal efficiency tends to be higher in soils with higher initial organic contaminant levels than in soils with lower initial organic contaminant levels. Salehian et al. (2012) reported an increase in diesel removal efficiency with an increase in diesel concentration. When the diesel content of the soil increased from 1 000 to 2 000 mg kg−1 , the optimum diesel removal efficiency increased from 35% to 45% even though the same concentration of SDS surfactant was used. A possible reason for the increase in removal efficiency is the increased contact area between the surfactant and the contaminant. Weathering degree of contaminant has a greater impact on the efficiency of surfactant-enhanced soil washing. Contaminants that age in soil are subjected to different physical, biological, and chemical processes, and contaminants with higher binding strength to the soil remain. Remediating soils containing aged and weathered contaminants is more challenging than remediating freshly or newly contaminated soils (Chen et al., 2007). Washing operation-related factors The washing process-related factors that affect organic compound removal are the mode of extraction, the type and concentration of extractant, the solution pH, the electrolyte concentration, the liquid-tosoil (L/S) ratio, the stirring speed, the washing temperature, and the retention time (Chang et al., 2000; Urum et al., 2004; Zhou and Zhu, 2007b; Peng et al., 2011). Peng et al. (2011) investigated the different factors influencing the washing efficiency of two selected nonionic surfactants on five target PAHs. Their results revealed that the first four factors, i.e., stirring speed, washing time, surfactant concentration, and L/S ratio,

A. A. BEFKADU AND Q. Y. CHEN

had a significant influence on removal, whereas temperature and on-and-off mode did not have an obvious influence. However, other research showed that temperature variation did influence the crude oil removal for all the soil with different particle-size fractions, and the oil removal efficiency increased as the washing temperature increased (Urum et al., 2004). The increased oil removal efficiency is attributed to the reduced viscosity of the oil fraction, which ultimately increases the oil mobility and interaction with surfactants. Soil washing efficiency has a tendency to increase with increasing stirring speed; however, above a certain level, the removal ratio starts to drop, indicating that the collision between soil particles becomes stronger with increasing stirring speed, which helps the stripping of the adsorbed contaminants because scrubbing of the contaminated soil surfaces generates attrition and abrasion. However, a further increase in stirring speed causes the slurry to move in bulk, which reduces collision, leading to lower removal (Urum et al., 2004; Peng et al., 2011). In most of the research results reported, the soil washing process is time dependent. With increasing washing time, the removal efficiency has a tendency to increase, reach equilibrium after a given period, and sometimes decrease after stabilization (Chang et al., 2000). However, washing for an extended period has an economic implication, and an optimization study is needed. In an experiment conducted using rhamnolipid and SDS at a concentration range of 0.02%–0.2% for crude oil removal, the overall performance in removing crude oil from weathered and non-weathered soils increased as the concentrations of the surfactants increased (Urum et al., 2004). Zhu et al. (2005) also reported the same trend using anionic surfactants LAS and SDS; they found that diesel oil solubilization increased linearly with surfactant dose. As the surfactant concentration in soil solution increases, the contaminants adsorbed on colloids are forced to leave the soil colloid and join the washing solution owing to a reduction in surface tension and an increase in the hydrophobic attraction of the surfactant micelles. Owing to these trends, a proper balance between washing performance, environmental pollution risk, and cost must be found in future research. The L/S ratio is also an important parameter in the soil washing procedure: a higher L/S ratio indicates a greater solubilization capacity. Removal efficiency increases with increasing L/S ratio in a nonlinear pattern. Also, soil washing at a higher L/S ratio means using more water, which requires larger equipment, gre-

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

ater energy usage, and a respective generation of more wastewater for post-treatment. The addition of salt to surfactant solutions was found to reduce interfacial tension, the CMC, and the sorption of surfactants onto soils in many studies (Cai et al., 1996; Hamouda and Karoussi, 2008; Huang et al., 2015; Wei et al., 2015; Kumar and Mandal, 2016). The presence of salts in the surfactant solution greatly enhances the clustering of the surfactants near the interface, thereby reducing interfacial tension (Bera et al., 2012). The reduction in interfacial tension is due to the influence of the synergistic effect of the salt-surfactant mixture, which leads to a decrease in the surface energy of the crude oil in the presence of the surfactant solution when the salinity is increased (Cai et al., 1996). The synergistic effect of salt and surfactant reduces interfacial tension. For ionic surfactants, the reduction of interfacial tension is due to a reduction in the electrical repulsion between ionic head groups, consequently reducing the size of the micelle in the presence of electrolytes. For nonionic surfactants, the reduction of interfacial tension is related to reduced hydrogen bonding (Hamouda and Karoussi, 2008; Kumar and Mandal, 2016). Wei et al. (2015) found that the experimental CMC of the salt-surfactant mixture was lower than the salt-free mixture, indicating a reduction in electrostatic repulsion in the presence of salt. Correspondingly, solubilization of pyrene and a decrease in the sorption of surfactants onto kaolin-rich soil increased in the salt-surfactant mixture solution. Another study on the impact of sodium salt addition to different surfactant solutions on kerosene-contaminated soils showed that sodium salts reduced the surface tension and CMC of ionic surfactants and the re-adsorption of oil with nonionic surfactants and enhanced the washing efficiency of kerosene-contaminated soils (Huang et al., 2015). Urum et al. (2005) also compared the crude oil washing efficiency of distilled water, seawater, and seawater together with SDS for crude oil-contaminated soils and found that seawater and seawater together with SDS were more effective than distilled water. They concluded that the greater removal with seawater may have been caused by the additional electrolyte in the seawater, which reduced the electrostatic repulsion of the surfactant. Soil property-related factors Soil properties like particle-size distribution, mineral composition, organic matter content, pH, and CEC and the presence of other inorganic contaminants affect the contaminant retention capacity of the soil.

399

Zhou and Zhu (2007a) reported that the desorption of phenanthrene was easier in a soil with relatively low organic carbon and clay contents as both clay and organic matter contents were closely related to higher surface area for adsorbing contaminants and surfactants. In a study that compared the effective CMC values of TX-100 under different organic matter levels, it was found that the effective CMC values increased with an increase in organic matter level (Ussawarujikulchai et al., 2008). A higher organic matter level is related to an increased surface area for the adsorption of surfactant, which leaves a minimum amount of surfactant to form micelles. Recently, Li et al. (2016) conducted a study to assess the effect of clay minerals and surfactants on hydrocarbon removal during the washing of petroleumcontaminated soils, and the results indicated that removal efficiency of the same type of surfactants was different depending on the types of clay minerals present. This suggests that knowing the type of clay minerals present could help in surfactant selection. Surfactant sorption by soil colloids One of the factors affecting the effectiveness of surfactant-enhanced soil washing is the sorption of surfactant monomers by colloids (Amirianshoja et al., 2013; Kang and Jeong, 2015; Ishiguro and Koopal, 2016). The sorption of surfactants onto the colloid surface decreases the effectiveness of soil washing as the amount of surfactant available for solubilizing the organic compounds decreases, and surfactant mobility in the soil solution is restricted, which requires addition of more surfactants for the washing to be effective (Wang and Keller, 2008; Kang and Jeong, 2015). In addition to reducing micelle formation, the adsorbed surfactants can increase the soil organic carbon content by increasing the hydrophobicity of the soil and can act as a new partitioning medium for desorbed HOCs, which makes them compete with micelles for contaminants. As a result, the removed, solubilized organic compounds are re-adsorbed onto the soil surface, thereby reducing the overall effectiveness of the system (Deshpande et al., 2000; Mao et al., 2015). The partitioning of phenanthrene and naphthalene to surfactant micelles, kaolinite, and sorbed surfactants demonstrates that surfactant sorption can lead to reduced HOC removal (Ko et al., 1998). Zheng and Obbard (2002) confirmed that surfactant sorption was the cause of high nonionic surfactant CMC values observed in soil-water systems. Adsorption, which is preferential partitioning of solute molecules at the solid-liquid interface, is a complex

400

chemical process that is driven by a combination of electrostatic interactions, chemical interactions, lateral chain-chain associative interactions, hydrogen bonding, and desolvation of the adsorbate species (Zhang and Somasundaran, 2006). In general, most conventional adsorption mechanisms occur by: ion exchange (exchange of surfactant ions adsorbed on the substrate with similarly charged surfactant ions found in the solution); ion pairing (adsorption of surfactant ions found in solution onto unoccupied oppositely charged sites); hydrophobic bonding (an attraction between a hydrophobic group of an adsorbed molecule and a molecule present in the solution); adsorption caused by the polarization of π electrons (when the surfactant contains electron-rich aromatic nuclei, the solid adsorbent has strongly positive sites, and the attraction between the electron-rich aromatic nuclei of the adsorbate and the positive sites on the adsorbent result in adsorption); and adsorption caused by dispersion forces (adsorption caused by the London-van der Waals force between the adsorbate and the adsorbent increases with the increasing molecular weight of the adsorbate) (Paria and Khilar, 2004; Yang et al., 2010). The different physicochemical properties of the soil and surfactant affect the sorption of surfactants onto soil colloids. The organic matter content and mineral composition of the soil and the concentration and chemistry of the applied surfactant solutions significantly influence the degree of sorption (Shen, 2000; Rodr´ıguez-Cruz et al., 2005; S´anchez-Mart´ın et al., 2008; Ussawarujikulchai et al., 2008; Amirianshoja et al., 2013; Bera et al., 2013). Surfactant loss through sorption and precipitation to soil colloidal surfaces threatens the success of surfactant in enhancing remediation of contaminated soil and groundwater (Yang et al., 2005). The existence and length of polyoxyethylene units, the hydrophobic chain length, and the presence of unsaturated carbon in the surfactant structure affect the extent of surfactant sorption. In all cases tested, the less-sorbed surfactants showed higher diesel removal. Surfactants with a greater degree of ethoxylation in their hydrophilic moiety, shorter hydrocarbon chains, and unsaturated carbon in their hydrophobic chains showed less sorption and superior diesel removal (Kim and Lee, 2000). Rodr´ıguez-Cruz et al. (2005) conducted a comparative study on the adsorption of SDS and TX-100 on 18 soils with organic matter (OM) and clay fraction contents varying over a broad range. They found that SDS adsorption was positively correlated with organic matter content and silt fraction contents, but negatively correlated to soil solution pH and clay fraction con-

A. A. BEFKADU AND Q. Y. CHEN

tent. They also found that adsorption was positively correlated with kaolinite content, but negatively correlated with the contents of montmorillonite and illite. Contrarily, the TX-100 adsorption had a highly significant positive correlation with clay fraction content and a significant positive correlation with pH and montmorillonite and illite contents, but an insignificant negative correlation with organic matter and kaolinite contents. Amirianshoja et al. (2013) found a direct relationship between clay content and surfactant adsorption; they reported that with increasing clay in the soil mixture from 5% to 20%, the degree of nonionic surfactant adsorption increased. The adsorption power of the clay minerals for the nonionic surfactants was in order of montmorillonite > illite > kaolinite, but all the adsorbents adsorbed a negligible amount of anionic surfactants. These findings suggest considering of the physicochemical properties of soils (organic matter and clay contents) and the mineralogy of the soil clay fraction when selecting a surfactant for technologies involving the enhanced solubilization and removal of contaminants from soils and sediments (Rodr´ıguez-Cruz et al., 2005). Shen (2000) conducted an experiment to assess the role of soil mineral composition in the sorption of the nonionic surfactant A9PE10 and found that the surfactant sorption capacity of the soil particles decreased progressively with increasing soil maturity or lower Si-to-Al + Fe ratio. Nonetheless, in addition to the surface of the soil colloids, the chemistry of the soil water (e.g., pH and ion species and concentration) plays an important role in nonionic surfactant sorption in soil-water systems (Shen, 2000). S´anchez-Mart´ın et al. (2008) studied adsorption of three surfactants of different nature, TX-100 (nonionic), SDS (anionic), and ADBAC (cationic), on four layered (montmorillonite, illite, muscovite, and kaolinite) and two non-layered (sepiolite and palygorskite) clay minerals. They found that the highest adsorption was obtained for the cationic surfactant ADBAC, except for the minerals kaolinite and sepiolite, which had lower CEC. Montmorillonite and illite had greater adsorption for TX-100, whereas kaolinite and sepiolite showed better affinity to SDS. These affirm the dependence of adsorption of surfactants by clay minerals on both the nature of the surfactants and the structure of the clay minerals. The type of the clay mineral determines the efficiency of this technology and will permit the selection of a cationic, anionic, or nonionic surfactant to be applied. Bera et al. (2013) studied the adsorption of the three types of surfactant, SDS (anionic), cetyl trime-

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

thyl ammonium bromide (CTAB) (cationic), and Tergitol 15-S-7 (nonionic), onto clean sand particles from aqueous solutions. Their results showed that the solution adsorption of SDS on the sand surface increased with increasing salinity owing to the weak electrostatic repulsion between the adsorbed surfactant species. The sand particles exhibited high adsorption efficiency at low pH for anionic and nonionic surfactants. However, they also found an opposite trend for the cationic surfactant. The increasing temperature-dependent adsorption of SDS surfactant decreased as the randomness of the molecules at the solid-solution interface declined over the fixation of the surfactant molecules on the active site of the sand surfaces (Bera et al., 2013). According to an experiment conducted to assess the adsorption of different concentrations of TX100 onto soils, the amount of TX-100 sorbed onto soils increased with an increase in its concentration (Ussawarujikulchai et al., 2008). Compared with the adsorption of single surfactants, the adsorption of mixtures of anionic-cationic, anionic-nonionic, cationic-nonionic, cationic-zwitterionic, and nonionic-nonionic types exhibit synergy at the interfaces because of their ability to minimize the amounts sorbed and thus enhance their effective concentrations. Yang et al. (2005) found that the amounts of TX-100 and SDBS sorbed onto the calcium-saturated montmorillonite surface were significant, but, the adsorption amount of TX-100 decreased when TX-100 was mixed with SDBS, relative to the adsorption of individual TX-100. The formation of mixed micelles is the reason for the negative deviation of the CMC from the ideal mixed CMC and the decrease in sorbed TX-100 and sorbed SDBS in the mixture (Yang et al., 2005). Surfactant sorption on soil is dependent on different interacting factors like organic matter content, the amount of clay, clay mineralogy, the type of surfactant, the chemistry of soil solution (pH, ionic strength, CEC, and concentration), and the soil solution temperature. The pH value controls the degree of sorption and desorption, the solubility, and the activity of potentially degrading microorganisms. The adsorption of anionic surfactants by soil increases as the pH of the soil decreases because in conditions of acidic pH, soil colloids carry higher positive charges than negative charges (Ishiguro and Koopal, 2016). The exchange reaction may alter the pH of the soil solution, especially when hydroxy groups are released. The sorption of cationic surfactants is usually higher than that of anionic and nonionic surfactants as the majority of colloidal soil surfaces are negatively charged. This is why anio-

401

nic and nonionic surfactants are mainly preferable for surfactant-enhanced remediation technologies. SOIL WASHING EFFLUENT TREATMENT METHODS Surfactant-enhanced soil washing moves the contaminants from soil colloids to washing solution, meaning that it is necessary to further treat the contaminant or the surfactant from the soil solution with the aim of cleaning and recovering the extracting agents for further reuse (Fabbri et al., 2008). The leachate usually contains a significant amount of organic pollutants, surfactants, and co-extracted minerals, which require further treatment (Fabbri et al., 2009; Huguenot et al., 2015; Trellu et al., 2016). The presence of surfactants in the washing effluent increases the complexity of the effluent treatment as complete degradation of the washing effluent may lead to the inefficient use of surfactants, removing any chance of reusing the surfactants. To solve these issues, an innovative technology of combining soil washing techniques with other water treatment techniques has been employed, and the current research involving coupling of soil washing with different effluent treatments is presented in Table III. Biological remediation processes (Zamudio-P´erez et al., 2013; Gong et al., 2015), ultrasonic irradiation, electrochemical advanced oxidation processes (EAOPs) (Bandalaet al., 2008; Mousset et al., 2016), heterogeneous photocatalysis (Fabbri et al., 2009; Rosas et al., 2013), technologies based on Fenton reaction chemistry (Tsai et al., 2009; Huguenot et al., 2015), ozonation (Knopp et al., 2016), activated charcoal/biochar adsorption (Li et al., 2014), and activated membrane reactors are the most common treatment methods that are combined with soil washing. The remediation methods mentioned above may reduce the concentration of the contaminants, degrade the contaminants, or increase the bioavailability of recalcitrant organic contaminants from the washing fluid (Aljuboury et al., 2015). Trellu et al. (2016) recently reviewed the mechanisms of organic contaminant removal from soil washing solutions using various treatment methods and examined the main advantages and drawbacks of the different treatment methods. The advanced oxidation process involves the in-situ generation of sufficient concentrations of strong oxidizing agents (e.g., hydroxyl radical, ·OH), which are nonselective, have a short lifespan, are strong oxidants, and can therefore effectively decontaminate the washing solutions (Oturan and Aaron, 2014). The findings of different research indicate that it is possible to couple soil washing and different waste wa-

402

A. A. BEFKADU AND Q. Y. CHEN

TABLE III Soil washing for remediation of hydrocarbon-contaminated soils and their effluent treatment techniques Methoda)

Major contaminant

Reported efficiency

Reference

Soil washing with Tween 80 and biological treatment of effluent

Phenanthrene

Gharibzadeh et al. (2016)

Soil washing with nonionic surfactants and activated carbon absorption of effluent

Phenanthrene

Soil washing with natural and synthetic surfactants followed by effluent treatment with submerged aerobic biofilter

Petroleum

Soil washing with Tween 80 and microbial degradation of effluent

Polycyclic aromatic hydrocarbon (PAH) Phenanthrene

74.4% ± 3.5% phenanthrene removal from the soil and complete biodegradation of washing effluent 84.1% phenanthrene removal by soil washing, 33.9%–56.4% phenanthrene absorption by activated carbon from effluent, and 85%–89% surfactant recovery 31.33% and 55.54% total petroleum hydrocarbon (TPH) removal from soil washed with locust bean gum and Tween 80, respectively, and 73% TPH removal from locust bean gum soil washing effluent 92.6% PAH removal by joint washing and microbial degradation 65% phenanthrene removal by soil flushing with Tween 80 and 96% degradation of phenanthrene from washing solution Tween 80 recovered and reused Higher efficiency of conductive diamond electrochemical oxidation than dimensionally stable anode technology Degradation of 83% of phenanthrene, 90% of anthracene, 77% of pyrene, and 75% of fluoranthene and only 5% reduction in efficiency when reused Regeneration of 50% of Tween 80 and 90% of hydroxypropyl-β-cyclodextrin

G´ omez et al. (2010)

Reuse of 79% of Tween 80 and 89% of hydroxypropyl-β-cyclodextrin and complete degradation of PAH (> 99%) 1% diesel removal with Tween 80 and > 99.5% quasi-complete mineralization of diesel from washing solution Complete PAH degradation and comparable washing capacity of recycled and fresh washing solutions 92% petroleum removal by soil washing with SDS and greater than 90% chemical oxygen demand (COD) removal from the washing effluent using BDD electrolysis and the coupled methods 100% diesel removal from both soil and the washing solution by soil washing and solar photoFenton process > 99% PAH oxidized by Fenton process

Mousset et al. (2016)

Ex-situ soil washing (column soil flushing) with Tween 80 and electrochemical treatment of effluent Surfactant-aided soil washing followed by electrochemical oxidation of effluent

PAH

Soil washing coupled with anodic oxidation using boron-doped diamond anode

PAH

Soil washing coupled with hydroxypropyl-β-cyclodextrin and Tween 80 followed by electro-Fenton oxidation of effluent Soil washing coupled with electroFenton oxidation

Phenanthrene

Ex-situ soil column washing with Tween 80 followed by effluent electroFenton oxidation Recycling electrochemically treated surfactant solutions

Diesel

Sodium dodecyl sulfate-aided soil washing followed by sonolysis, photolysis, and boron-doped diamond (BDD) electrolysis of effluent

Petroleum

Soil washing with TX-100 followed by photo-Fenton oxidation of effluent

Diesel

Soil washing with TX-100 and Igepal CA-720 followed by Fenton oxidation of effluent Soil washing with SDS followed by solar-driven advanced oxidation of effluent Soil washing with SDBS followed by persulfate oxidation of effluent Surfactant-enhanced soil washing followed by coagulation of effluent

PAH

a) SDS

PAH

PAH

Petroleum

Nitrobenzene PAH

35% TPH removal by soil washing with SDS, 69% of COD oxidized from washing solution by photo-Fenton process 76.8% nitrobenzene removal, 97.9% nitrobenzene degradation, 51.6% SDBS degradation 90%, 70%, and 30% PAH washing efficiency with anionic, nonionic, and cationic surfactant, respectively, and > 90% COD removal of washing solution by coagulation

= sodium dodecyl sulfate; TX-100 = Triton X-100; SDBS = sodium dodecyl benzene sulfonate.

Ahn et al. (2008a)

Zamudio-P´ erez et al. (2013)

Gong et al. (2015)

S´ aez et al. (2010)

Trellu et al. (2017)

Mousset et al. (2014b)

Huguenot et al. (2015) Hussein and Ismail (2013) Dos Santos et al. (2016)

Villa et al. (2010)

Saxe et al. (2000)

Bandala et al. (2008) Yan et al. (2015) L´ opez-Vizca´ıno et al. (2012)

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

ter treatment methods to remove organic contaminants from soils and effluent solutions. Wan et al. (2011) investigated the selective adsorption of hexachlorobenzene (HCB) from rhamnolipid solution using powdered activated carbon (PAC). They found that when 25 g L−1 rhamnolipid solution was applied, HCB leaching from soil was 55%–71% for three cycles of washing, and HCB removal by PAC was nearly 90%, whereas the corresponding adsorptive loss of rhamnolipid was 8%–19%. Huguenot et al. (2015) investigated surfactant-enhanced soil washing using a combination of Tween 80 and the electro-Fenton (EF) process for the treatment of soils contaminated with petroleum hydrocarbons. They found that 25 and 920 mg L−1 of the hydrocarbons were leached with Tween 80 concentrations of 1% and 5%, respectively, but accounted for only 1% of the removal of the surfactants present in soil. However, the electro-Fenton treatment achieved quasi-complete mineralization (> 99.5% total organic carbon (TOC) removal) after 32 h of treatment. Zamudio-P´erez et al. (2013) treated the wastewater generated from the surfactant-enhanced washing of real petroleum hydrocarbon-contaminated soil using a submerged aerobic biofilter. Treating the effluent produced by washing the soil with locust bean gum in a biofilter containing microorganisms Corynebacterium jeikeium, Bacillus subtilis, Enterobacter sakazakii, Pseudomonas sp., Aeromonas sobria, and Aeromonas caviae operated at 24 ◦ C, they obtained hydrocarbon degradation efficiency of 73%. The degradation rate of the organic contaminant in the washing solution may depend on the type of surfactant used for washing the contaminant (Rosas et al., 2013; Dos Santos et al., 2016). Dos Santos et al. (2016) reported higher pollutant contaminant removal in effluent containing high levels of SDS than in effluent containing low levels of SDS using boron-doped diamond (BDD) electrolysis, implying that SDS contributed sulfate, a precursor of the persulfate formed in the electrochemical treatment. They also reported the presence of synergism when using two or more remediation methods in combination: coupling ultraviolet (UV) light irradiation, sonolysis, BDD electrolysis, and photolysis exhibited higher contaminant removal efficiency than using each treatment method alone. Villa et al. (2010) investigated the effectiveness of coupling soil washing with photo-Fenton oxidation for the treatment of soil contaminated with dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE) and soil artificially contaminated with diesel. They used 12 times the CMCeff of TX-100 and

403

found removal efficiency of 66%, 80%, and 100% for DDT, DDE, and diesel, respectively, after three subsequent washing cycles. Moreover, the washing solution was treated for 6 h with the solar photo-Fenton process, with dissolved organic carbon degradation efficiency of 99%, 95%, and 100% achieved for DDT, DDE, and diesel, respectively. These results indicate that coupling soil washing with photo-Fenton process is a better option for soil remediation and washing solution treatment. Yan et al. (2015) investigated the combined application of surfactant-enhanced soil washing and persulfate oxidation of nitrobenzene-containing effluent. Using 24.0 mmol L−1 of SDBS at a soil-to-solution ratio of 1:20, they were able to extract 76.8% of the nitrobenzene. Moreover, they found that treating the washing effluent for 15 min with Fe2+ -persulfate and Fe2+ -H2 O2 degraded 97.9% of the nitrobenzene and 51.6% of the SDBS. Chemical oxidation processes for the complete mineralization of organic contaminants are usually expensive as the oxidation intermediates formed during treatment are resistant to complete chemical degradation and consume energy and chemical reagents, with increased costs with increasing treatment time (Mu˜ noz et al., 2005). However, combining the processes with biological treatment is reported to lower operation costs (Oller et al., 2011). The primary challenge for this operation is the biodegradability of the treatment effluent; a 5-day biochemical oxygen demand (BOD5)to-chemical oxygen demand (COD) ratio usually measures the biodegradability, and for biological treatment to be acceptable, this ratio should be more than 33% (Huguenot et al., 2015). Recently, Gharibzadeh et al. (2016) studied surfactant reuse feasibility of bioremediation effluent from the washing of phenanthrene-contaminated soil with Tween 80. They were able to reuse the biologically recycled solution for seven cycles, with removal efficiency of > 99% and > 97% in artificial and real contaminated soils, respectively, indicating the effectiveness of the bioremediation for the reuse of surfactant solutions. In another surfactant reuse study, activated carbon adsorption of the organic contaminants from the washing solution reduced the surfactant requirement by 70% (Ahn et al., 2008b). Using activated carbon for the selective adsorption of organic pollutants is a straightforward and fast technology that may be a reasonable alternative for the recovery of surfactants in soil washing processes. Research has been conducted on both synthetic and real washing effluents (Mousset et al., 2014a, b;

404

A. A. BEFKADU AND Q. Y. CHEN

Aljuboury et al., 2015; Dos Santos et al., 2016). Unlike in real effluents, the amount and type of contaminant in synthetic effluents can fully be controlled (Mousset et al., 2014a, b; Trellu et al., 2016), and thus research on synthetic washing solutions helps in the understanding of the mechanisms involved. However, it does not represent the interaction conditions of the mixed environment. Further studies on coupling soil washing and treatment of real washing effluents are required.

problems related to the toxicity of the degradation products have to be solved. Therefore, to make surfactantenhanced soil washing further economically feasible, further studies on surfactant recovery and reuse are also necessary. There is no ideal single soil contaminant removal technology; the integration of two or more methods may be necessary for the successful remediation of soils, depending on the particular contaminant, the environment, and the operating conditions.

CONCLUSIONS

ACKNOWLEDGEMENT

Research undertaken over the past three decades has explored different methods that improve the efficiency of surfactant-enhanced soil washing. Numerous studies have been conducted on the efficacy of soil washing technology and the main factors affecting washing efficiency. Nonionic surfactants are usually preferred over ionic surfactants owing to their lower CMC values and competent solubilization capability, but they have problem of high adsorption; mixing nonionic surfactants with anionic surfactants minimizes the high adsorption of the nonionic surfactants. It has been reported that the addition of mixed surfactants at a lower anionic-to-nonionic ratio reduces the high adsorptions associated with nonionic surfactants to some extent. However, more studies to determine the proper mixture ratio of anionic to nonionic surfactants for different soils and washing conditions are required. Various types of biosurfactants are reported to be as effective as synthetic surfactants and are an environmentally sustainable option. However, biosurfactants are expensive. Therefore, further research on the economic extraction and production of biosurfactants from cheap materials is required. Gemini surfactants are also attracting more attention owing to their very low CMC values and superior performances than the commonly used surfactants and are critical for the future of surfactant-enhanced soil washing operations. However, they are also costly, which also calls for further research on the economic production of this class of surfactants. The selection and production of surfactants, especially biosurfactants, and studies on field-scale and historically contaminated soils are required. Understanding of site-specific contaminant and soil properties and the effects of weather and operating conditions is crucial for the success of the technology. As soil washing only shifts organic contaminants from soil colloids to washing solution, additional studies on the integration of soil washing with bioremediation and effluent oxidation methods are required. Different oxidation methods have brought success in efficient mineralization of organic contaminants, but some

The financial supports from the National Key Research and Development Program of China (Nos. 2016YFC0400501 and 2016YFC0400502), the Fundamental Research Funds for Central Universities of China (No. 2232018D3-43), and the National Natural Science Foundation of China (No. 21277023) are greatly acknowledged. REFERENCES Abdel-Shafy H I, Mansour M S M. 2016. A review on polycyclic aromatic hydrocarbons: Source, environmental impact, effect on human health and remediation. Egypt J Petrol. 25: 107–123. Adhikari K, Hartemink A E. 2016. Linking soils to ecosystem services—A global review. Geoderma. 262: 101–111. Ahn C K, Kim Y M, Woo S H, Park J M. 2008a. Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon. J Hazard Mater. 154: 153–160. Ahn C K, Lee M W, Lee D S, Woo S H, Park J M. 2008b. Mathematical evaluation of activated carbon adsorption for surfactant recovery in a soil washing process. J Hazard Mater. 160: 13–19. Ahn C K, Woo S H, Park J M. 2010. Selective adsorption of phenanthrene in nonionicanionic surfactant mixtures using activated carbon. Chem Eng J. 158: 115–119. Akba¸s H, Boz M, Elemenli A. 2014. Interaction between cationic gemini surfactant and related single-chain surfactant in aqueous solutions. Fluid Phase Equilib. 370: 95–100. Albergaria J T, Alvim-Ferraz M d C M, Delerue-Matos C. 2012. Remediation of sandy soils contaminated with hydrocarbons and halogenated hydrocarbons by soil vapour extraction. J Environ Manage. 104: 195–201. Alc´ antara M T, G´ omez J, Pazos M, Sanrom´ an M A. 2008. Combined treatment of PAHs contaminated soils using the sequence extraction with surfactant-electrochemical degradation. Chemosphere. 70: 1438–1444. Aljuboury D a d A, Palaniandy P, Aziz H B A, Feroz S. 2015. Treatment of petroleum wastewater using combination of solar photo-two catalyst TiO2 and photo-Fenton process. J Environ Chem Eng. 3: 1117–1124. Alternative Remedial Technologies, Inc. 1992. Soil Washing Demonstration Run for the King of Prussia Technical Site. Alternative Remedial Technologies, Inc., Tampa. Amirianshoja T, Junin R, Kamal Idris A, Rahmani O. 2013. A comparative study of surfactant adsorption by clay minerals. J Petrol Sci Eng. 101: 21–27. Balachandran C, Duraipandiyan V, Balakrishna K, Ignacimuthu

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

S. 2012. Petroleum and polycyclic aromatic hydrocarbons (PAHs) degradation and naphthalene metabolism in Streptomyces sp. (ERI-CPDA-1) isolated from oil contaminated soil. Bioresour Technol. 112: 83–90. Banat I M, Franzetti A, Gandolfi I, Bestetti G, Martinotti M G, Fracchia L, Smyth T J, Marchant R. 2010. Microbial biosurfactants production, applications and future potential. Appl Microbiol Biotechnol. 87: 427–444. Bandala E R, Velasco Y, Torres L G. 2008. Decontamination of soil washing wastewater using solar driven advanced oxidation processes. J Hazard Mater. 160: 402–407. Bera A, Kissmathulla S, Ojha K, Kumar T, Mandal A. 2012. Mechanistic study of wettability alteration of quartz surface induced by nonionic surfactants and interaction between crude oil and quartz in the presence of sodium chloride salt. Energy Fuels. 26: 3634–3643. Bera A, Kumar T, Ojha K, Mandal A. 2013. Adsorption of surfactants on sand surface in enhanced oil recovery: Isotherms, kinetics and thermodynamic studies. Appl Surf Sci. 284: 87–99. Boving T B, Blanford W J, McCray J E, Divine C E, Brusseau M L. 2008. Comparison of line-drive and push-pull flushing schemes. Ground Water Monit Remediat. 28: 75–86. Cai B Y, Yang J T, Guo T M. 1996. Interfacial tension of hydrocarbon + water/brine systems under high pressure. J Chem Eng Data. 41: 493–496. Cashion M P, Li X L, Geng Y, Hunley M T, Long T E. 2010. Gemini surfactant electrospun membranes. Langmuir. 26: 678–683. Ceschia E, Harjani J R, Liang C, Ghoshouni Z, Andrea T, Brown R S, Jessop P G. 2014. Switchable anionic surfactants for the remediation of oil-contaminated sand by soil washing. RSC Adv. 4: 4638–4645. Chandankere R, Yao J, Choi M M F, Masakorala K, Chan Y. 2013. An efficient biosurfactant-producing and crude-oil emulsifying bacterium Bacillus methylotrophicus USTBa isolated from petroleum reservoir. Biochem Eng J. 74: 46–53. Chang M C, Huang C R, Shu H Y. 2000. Effects of surfactants on extraction of phenanthrene in spiked sand. Chemosphere. 41: 1295–1300. Chang Y T, Chou H L, Chao H P, Chang Y J. 2015. The influence of sorption on polyaromatic hydrocarbon biodegradation in the presence of modified nonionic surfactant organoclays. Int Biodeterior Biodegrad. 102: 237–244. Chapr˜ ao M J, Ferreira I N S, Correa P F, Rufino R D, Luna J M, Silva E J, Sarubbo L A. 2015. Application of bacterial and yeast biosurfactants for enhanced removal and biodegradation of motor oil from contaminated sand. Electron J Biotechnol. 18: 471–479. Chen D Y, Xing B S, Xie W B. 2007. Sorption of phenanthrene, naphthalene and o-xylene by soil organic matter fractions. Geoderma. 139: 329–335. Chen L F, Xie H Q, Li Y, Yu W. 2008. Applications of cationic gemini surfactant in preparing multi-walled carbon nanotube contained nanofluids. Colloids Surf A: Physicochem Eng Asp. 330: 176–179. Cheng K Y, Wong J W C. 2006. Effect of synthetic surfactants on the solubilization and distribution of PAHs in water/soilwater systems. Environ Technol. 27: 835–844. Cheng M, Zeng G M, Huang D L, Yang C P, Lai C, Zhang C, Liu Y. 2017. Advantages and challenges of Tween 80 surfactantenhanced technologies for the remediation of soils contaminated with hydrophobic organic compounds. Chem Eng J. 314: 98–113.

405

Chorro M, Chorro C, Dolladille O, Partyka S, Zana R. 1999. Adsorption mechanism of conventional and dimeric cationic surfactants on silica surface: Effect of the state of the surface. J Colloid Interface Sci. 210: 134–143. Christofi N, Ivshina I B. 2002. Microbial surfactants and their use in field studies of soil remediation. J Appl microbiol. 93: 915–929. Chu W, Chan K. 2003. The mechanism of the surfactant-aided soil washing system for hydrophobic and partial hydrophobic organics. Sci Total Environ. 307: 83–92. Chu W, So W S. 2001. Modeling the two stages of surfactantaided soil washing. Water Res. 35: 761–767. Conte P, Agretto A, Spaccini R, Piccolo A. 2005. Soil remediation: humic acids as natural surfactants in the washings of highly contaminated soils. Environ Pollut. 135: 515–522. Cowell M A, Kibbey T C G, Zimmerman J B, Hayes K F. 2000. Partitioning of ethoxylated nonionic surfactants in water/NAPL systems: Effects of surfactant and NAPL properties. Environ Sci Technol. 34: 1583–1588. Czaun M, Hevesi L, Takafuji M, Ihara H. 2008. A novel approach to magneto-responsive polymeric gels assisted by iron nanoparticles as nano cross-linkers. Chem Commun. 2124– 2126. De Figueredo K S L, Mart´ınez-Huitle C A, Teixeira A B R, de Pinho A L S, Vivacqua C A, da Silva D R. 2014. Study of produced water using hydrochemistry and multivariate statistics in different production zones of mature fields in the Potiguar Basin – Brazil. J Petrol Sci Eng. 116: 109–114. Dermont G, Bergeron M, Mercier G, Richer-Lafl` eche M. 2008. Soil washing for metal removal: A review of physical/chemical technologies and field applications. J Hazard Mater. 152: 1–31. Deshpande S, Shiau B J, Wade D, Sabatini D A, Harwell J H. 1999. Surfactant selection for enhancing ex situ soil washing. Water Res. 33: 351–360. Deshpande S, Wesson L, Wade D, Sabatini D A, Harwell J H. 2000. DOWFAX surfactant components for enhancing contaminant solubilization. Water Res. 34: 1030–1036. dos Santos E V, S´ aez C, Ca˜ nizares P, da Silva D R, Mart´ınezHuitle C A, Rodrigo M A. 2016. Treatment of ex-situ soilwashing fluids polluted with petroleum by anodic oxidation, photolysis, sonolysis and combined approaches. Chem Eng J. 310: 581–588. Du X G, Lu Y, Li L, Wang J B, Yang Z Y. 2006. Synthesis and unusual properties of novel alkylbenzene sulfonate gemini surfactants. Colloids Surf A: Physicochem Eng Asp. 290: 132–137. Dubey N. 2011. Micellar properties and related thermodynamic parameters of aqueous anionic surfactants in the presence of monohydric alcohols. J Chem Eng Data. 56: 3291–3300. Edwards D A, Luthy R G, Liu Z B. 1991. Solubilization of polycyclic aromatic hydrocarbons in micellar nonionic surfactant solutions. Environ Sci Technol. 25: 127–133. Elgh-Dalgren K, Arwidsson Z, Camdzija A, Sj¨ oberg R, Rib´ e V, Waara S, Allard B, Von Kronhelm T, Van Hees P A W. 2009. Laboratory and pilot scale soil washing of PAH and arsenic from a wood preservation site: Changes in concentration and toxicity. J Hazard Mater. 172: 1033–1040. ElSayed E M, Prasher S O, Patel R M. 2013. Effect of nonionic surfactant Brij 35 on the fate and transport of oxytetracycline antibiotic in soil. J Environ Manage. 116: 125–134. Fabbri D, Crime A, Davezza M, Medana C, Baiocchi C, Prevot A B, Pramauro E. 2009. Surfactant-assisted removal of swep residues from soil and photocatalytic treatment of the washing wastes. Appl Catal B Environ. 92: 318–325.

406

Fabbri D, Prevot A B, Zelano V, Ginepro M, Pramauro E. 2008. Removal and degradation of aromatic compounds from a highly polluted site by coupling soil washing with photocatalysis. Chemosphere. 71: 59–65. Farn R J. 2006. Chemistry and Technology of Surfactants. Blackwell Publishing Ltd., Oxford. Feng D, Lorenzen L, Aldrich C, Mar´ e P W. 2001. Ex situ diesel contaminated soil washing with mechanical methods. Miner Eng. 14: 1093–1100. Gan S, Lau E V, Ng H K. 2009. Remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). J Hazard Mater. 172: 532–549. Gavrilescu M. 2014. Colloid-mediated transport and the fate of contaminants in soils. In Fanun M (ed.) The Role of Colloidal Systems in Environmental Protection. Elsevier, Amsterdam. pp. 397–451. Gharibzadeh F, Rezaei Kalantary R, Nasseri S, Esrafili A, Azari A. 2016. Reuse of polycyclic aromatic hydrocarbons (PAHs) contaminated soil washing effluent by bioaugmentation/biostimulation process. Sep Purif Technol. 168: 248– 256. ´ 2010. ReG´ omez J, Alc´ antara M T, Pazos M, Sanrom´ an M A. mediation of polluted soil by a two-stage treatment system: Desorption of phenanthrene in soil and electrochemical treatment to recover the extraction agent. J Hazard Mater. 173: 794–798. ´ 2010. Soil G´ omez J, Alc´ antara M T, Pazos M, Sanrom´ an M A. washing using cyclodextrins and their recovery by application of electrochemical technology. Chem Eng J. 159: 53–57. Gomez V, Ferreres L, Pocurull E, Borrull F. 2011. Determination of non-ionic and anionic surfactants in environmental water matrices. Talanta. 84: 859–866. Gong X, Xu X Y, Gong Z Q, Li X J, Jia C Y, Guo M X, Li H B. 2015. Remediation of PAH-contaminated soil at a gas manufacturing plant by a combined two-phase partition system washing and microbial degradation process. Environ Sci Pollut Res. 22: 12001–12010. Guo H Q, Liu Z Y, Yang S G, Sun C. 2009. The feasibility of enhanced soil washing of p-nitrochlorobenzene (pNCB) with SDBS/Tween80 mixed surfactants. J Hazard Mater. 170: 1236–1241. Gupta M K, Srivastava R K, Singh A K. 2010. Bench scale treatability studies of contaminated soil using soil washing technique. J Chem. 7: 73–80. Haigh S D. 1996. A review of the interaction of surfactants with organic contaminants in soil. Sci Total Environ. 185: 161– 170. Hamouda A A, Karoussi O. 2008. Effect of temperature, wettability and relative permeability on oil recovery from oil-wet chalk. Energies. 1: 19–34. Han M, Ji G D, Ni J R. 2009. Washing of field weathered crude oil contaminated soil with an environmentally compatible surfactant, alkyl polyglucoside. Chemosphere. 76: 579–586. Helmy Q, Laksmono R, Kardena E. 2015. Bioremediation of aged petroleum oil contaminated soil: from laboratory scale to full scale application. Proced Chem. 14: 326–333. Hern´ andez-Espri´ u A, S´ anchez-Le´ on E, Mart´ınez-Santos P, Torres L G. 2013. Remediation of a diesel-contaminated soil from a pipeline accidental spill: enhanced biodegradation and soil washing processes using natural gums and surfactants. J Soil Sediment. 13: 152–165. Holland P M, Rubingh D N. 1992. Mixed surfactant systems: An overview. In Holland P M, Rubingh D N (eds.) Mixed Surfactant Systems. American Chemical Society, Washington, D.C. pp. 2–30.

A. A. BEFKADU AND Q. Y. CHEN

Hu X J, Tian S L, Zhan S J, Zhu J X. 2017. Adsorption of switchable surfactant mixed with common nonionic surfactant on montmorillonite: Mechanisms and arrangement models. Appl Clay Sci. 146: 140–146. Hu Y M, Ge L L, Han J, Guo R. 2015. Concentration and temperature induced dual-responsive wormlike micelle to hydrogel transition in ionic liquid-type surfactant [C16imC9]Br aqueous solution without additives. Soft Matter. 11: 5624–5631. Huang Z L, Chen Y Q, Zhou J, Xie M H. 2015. Strengthening effects of sodium salts on washing kerosene contaminated soil with surfactants. Environ Sci (in Chinese). 36: 1849–1855. Huguenot D, Mousset E, van Hullebusch E D, Oturan M A. 2015. Combination of surfactant enhanced soil washing and electro-Fenton process for the treatment of soils contaminated by petroleum hydrocarbons. J Environ Manage. 153: 40–47. Hussein T A, Ismail Z Z. 2013. Validation of recycling electrochemically treated surfactant solutions for washing the PAHs-contaminated soil. Polycycl Aromat Comp. 33: 208– 220. Ishiguro M, Koopal L K. 2016. Surfactant adsorption to soil components and soils. Adv Colloid Interface Sci. 231: 59–102. Ivankovi´ c T, Hrenovi´ c J. 2010. Surfactants in the environment. Arh Hig Rada Toksikol. 61: 95–110. Ivshina I, Kostina L, Krivoruchko A, Kuyukina M, Peshkur T, Anderson P, Cunningham C. 2016. Removal of polycyclic aromatic hydrocarbons in soil spiked with model mixtures of petroleum hydrocarbons and heterocycles using biosurfactants from Rhodococcus ruber IEGM 231. J Hazard Mater. 312: 8–17. Jiang J Z, Zhu Y, Cui Z G, Binks B P. 2013. Switchable pickering emulsions stabilized by silica nanoparticles hydrophobized in situ with a switchable surfactant. Angew Chem. 52: 12373– 12376. Kabir-ud-Din, Sheikh M S, Dar A A. 2009. Interaction of a cationic gemini surfactant with conventional surfactants in the mixed micelle and monolayer formation in aqueous medium. J Colloid Interface Sci. 333: 605–612. Kaczorek E, Urbanowicz M, Olszanowski A. 2010. The influence of surfactants on cell surface properties of Aeromonas hydrophila during diesel oil biodegradation. Colloid Surf B Biointerf. 81: 363–368. Kang S, Jeong H Y. 2015. Sorption of a nonionic surfactant Tween 80 by minerals and soils. J Hazard Mater. 284: 143– 150. Karakashev S I, Smoukov S K. 2017. CMC prediction for ionic surfactants in pure water and aqueous salt solutions based solely on tabulated molecular parameters. J Colloid Interface Sci. 501: 142–149. Karsa D R, Porter M R. 1995. Biodegradability of Surfactants. Chapman & Hali, London. Khalladi R, Benhabiles O, Bentahar F, Moulai-Mostefa N. 2009. Surfactant remediation of diesel fuel polluted soil. J Hazard Mater. 164: 1179–1184. Khan F I, Husain T, Hejazi R. 2004. An overview and analysis of site remediation technologies. J Environ Manage. 71: 95–122. Kim J S, Lee K. 2000. Influence of surfactant structure on surfactant sorption and diesel removal from kaolin soil. J Environ Sci Health A. 35: 915–928. Knopp G, Prasse C, Ternes T A, Cornel P. 2016. Elimination of micropollutants and transformation products from a wastewater treatment plant effluent through pilot scale ozonation followed by various activated carbon and biological filters. Water Res. 100: 580–592.

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

Ko I, Chang Y Y, Lee C H, Kim K W. 2005. Assessment of pilotscale acid washing of soil contaminated with As, Zn and Ni using the BCR three-step sequential extraction. J Hazard Mater. 127: 1–13. Ko S O, Schlautman M A, Carraway E R. 1998. Partitioning of hydrophobic organic compounds to sorbed surfactants. 1. Experimental studies. Environ Sci Technol. 32: 2769–2775. Kobayashi T, Kaminaga H, Navarro R R, Iimura Y. 2012. Application of aqueous saponin on the remediation of polycyclic aromatic hydrocarbons-contaminated soil. J Environ Sci Health A. 47: 1138–1145. Koner S, Pal A, Adak A. 2011. Utilization of silica gel waste for adsorption of cationic surfactant and adsolubilization of organics from textile wastewater: A case study. Desalination. 276: 142–147. Kuhlman M I, Greenfield T M. 1999. Simplified soil washing processes for a variety of soils. J Hazard Mater. 66: 31–45. Kumar S, Mandal A. 2016. Studies on interfacial behavior and wettability change phenomena by ionic and nonionic surfactants in presence of alkalis and salt for enhanced oil recovery. Appl Surf Sci. 372: 42–51. Kuyukina M S, Ivshina I B, Makarov S O, Litvinenko L V, Cunningham C J, Philp J C. 2005. Effect of biosurfactants on crude oil desorption and mobilization in a soil system. Environ Int. 31: 155–161. Laha S, Tansel B, Ussawarujikulchai A. 2009. Surfactant-soil interactions during surfactant-amended remediation of contaminated soils by hydrophobic organic compounds: A review. J Environ Manage. 90: 95–100. Lai C C, Huang Y C, Wei Y H, Chang J S. 2009. Biosurfactantenhanced removal of total petroleum hydrocarbons from contaminated soil. J Hazard Mater. 167: 609–614. Lee D H, Cody R D, Kim D J, Choi S. 2002. Effect of soil texture on surfactant-based remediation of hydrophobic organiccontaminated soil. Environ Int. 27: 681–688. Lee K S. 2010. Simulation on the surfactant-polymer flushing of heterogeneous aquifers contaminated with nonaqueous phase liquids. Eng Appl Comput Fluid Mech. 4: 558–568. Lee M, Kang H, Do W. 2005. Application of nonionic surfactantenhanced in situ flushing to a diesel contaminated site. Water Res. 39: 139–146. Lee M, Woo S G, Ten L N. 2012. Characterization of novel dieseldegrading strains Acinetobacter haemolyticus MJ01 and Acinetobacter johnsonii MJ4 isolated from oil-contaminated soil. World J Microbiol Biotechnol. 28: 2057–2067. Li G, Guo S H, Hu J X. 2016. The influence of clay minerals and surfactants on hydrocarbon removal during the washing of petroleum-contaminated soil. Chem Eng J. 286: 191–197. Li H L, Qu R H, Li C, Guo W L, Han X M, He F, Ma Y B, Xing B S. 2014. Selective removal of polycyclic aromatic hydrocarbons (PAHs) from soil washing effluents using biochars produced at different pyrolytic temperatures. Bioresour Technol. 163: 193–198. Li J-L, Chen B H. 2002. Solubilization of model polycyclic aromatic hydrocarbons by nonionic surfactants. Chem Eng Sci. 57: 2825–2835. Li Z-Q, Zhang L, Xu Z-C, Liu D-D, Song X-W, Cao X-L, Zhang L, Zhao S. 2013. Effect of zwitterionic surfactants on wetting of quartz surfaces. Colloids Surf A Physicochem Eng Asp. 430: 110–116. Liao C J, Xu W D, Lu G N, Deng F C, Liang X J, Guo C L, Dang Z. 2016. Biosurfactant-enhanced phytoremediation of soils contaminated by crude oil using maize (Zea mays L). Ecol Eng. 92: 10–17.

407

Lim M W, Von Lau E, Poh P E. 2016. A comprehensive guide of remediation technologies for oil contaminated soil — Present works and future directions. Mar Pollut Bull. 109: 14–45. Liu H, Wang C Y, Zou S W, Wei Z J, Tong Z. 2012. Simple, Reversible Emulsion System Switched by pH on the Basis of Chitosan without Any Hydrophobic Modification. Langmuir. 28: 11017–11024. Liu H B, Yin H Y, Feng Y J. 2016. A CO2 -switchable amidine monomer: synthesis and characterization. Des Monomers Polym. 20: 363–367. Liu X P, Feng J, Zhang L, Gong Q T, Zhao S, Yu J Y. 2010. Synthesis and properties of a novel class of anionic gemini surfactants with polyoxyethylene spacers. Colloids Surf A Physicochem Eng Asp. 362: 39–46. Liu Z, Fan Y X, Tian M Z, Wang R J, Han Y C, Wang Y L. 2014. Surfactant selection principle for reducing critical micelle concentration in mixtures of oppositely charged gemini surfactants. Langmuir. 30: 7968–7976. Long J, Tian S, Niu Y, Li G, Ning P. 2014. Reversible solubilization of typical polycyclic aromatic hydrocarbons by a photoresponsive surfactant. Colloids Surf A Physicochem Eng Asp. 454: 172–179. L´ opez-Vizca´ıno R, S´ aez C, Ca˜ nizares P, Rodrigo M A. 2012. The use of a combined process of surfactant-aided soil washing and coagulation for PAH-contaminated soils treatment. Sep Purif Technol. 88: 46–51. Mao X H, Jiang R, Xiao W, Yu J G. 2015. Use of surfactants for the remediation of contaminated soils: A review. J Hazard Mater. 285: 419–435. Mayer P, Vaes W H J, Wijnker F, Legierse K C H M, Kraaij R, Tolls J, Hermens J L M. 2000. Sensing dissolved sediment porewater concentrations of persistent and bioaccumulative pollutants using disposable solid-phase microextraction fibers. Environ Sci Technol. 34: 5177–5183. Menger F M, Keiper J S. 2000. Gemini surfactants. Angew Chem. 39: 1906–1920. Montoneri E, Boffa V, Savarino P, Tambone F, Adani F, Micheletti L, Gianotti C, Chiono R. 2009. Use of biosurfactants from urban wastes compost in textile dyeing and soil remediation. Waste Manag. 29: 383–389. Morales-Guzm´ an G, Ferrera-Cerrato R, Del Carmen RiveraCruz M, Torres-Bustillos L G, Arteaga-Garibay R I, Mendoza-L´ opez M R, Esquivel-Cote R, Alarc´ on A. 2017. Diesel degradation by emulsifying bacteria isolated from soils polluted with weathered petroleum hydrocarbons. Appl Soil Ecol. 121: 127–134. Mousset E, Huguenot D, van Hullebusch E D, Oturan N, Guibaud G, Esposito G, Oturan M A. 2016. Impact of electrochemical treatment of soil washing solution on PAH degradation efficiency and soil respirometry. Environ Pollut. 211: 354–362. Mousset E, Oturan M A, van Hullebusch E D, Guibaud G, Esposito G. 2014a. Soil washing/flushing treatments of organic pollutants enhanced by cyclodextrins and integrated treatments: State of the art. Environ Sci Technol. 44: 705–795. Mousset E, Oturan N, van Hullebusch E D, Guibaud G, Esposito G, Oturan M A. 2014b. Influence of solubilizing agents (cyclodextrin or surfactant) on phenanthrene degradation by electro-Fenton process – Study of soil washing recycling possibilities and environmental impact. Water Res. 48: 306– 316. Muherei M A. 2008. Mixing effect of anionic and nonionic surfactants on micellization, adsorption and partitioning of nonionic surfactant. Mod Appl Sci. 2: 3–12.

408

Mulligan C N. 2005. Environmental applications for biosurfactants. Environ Pollut. 133: 183–198. Mulligan C N, Yong R N, Gibbs B F. 2001. Surfactant-enhanced remediation of contaminated soil: a review. Eng Geol. 60: 371–380. Mu˜ noz I, Rieradevall J, Torrades F, Peral J, Dom´ enech X. 2005. Environmental assessment of different solar driven advanced oxidation processes. Sol Energ. 79: 369–375. Navarro A, Mart´ınez F. 2010. The use of soil-flushing to remediate metal contamination in a smelting slag dumping area: Column and pilot-scale experiments. Eng Geol. 115: 16–27. Nogales B, Lanfranconi M P, Pi˜ na-Villalonga J M, Bosch R. 2011. Anthropogenic perturbations in marine microbial communities. FEMS Microbiol Rev. 35: 275–298. Oller I, Malato S, S´ anchez-P´ erez J A. 2011. Combination of advanced oxidation processes and biological treatments for wastewater decontamination—a review. Sci Total Environ. 409: 4141–4166. Onur G, Yilmaz F, Icgen B. 2015. Diesel oil degradation potential of a bacterium inhabiting petroleum hydrocarbon contaminated surface waters and characterization of its emulsification ability. J Surfact Deterg. 18: 707–717. Oturan M A, Aaron J-J. 2014. Advanced oxidation processes in water/wastewater treatment: Principles and applications. A review. Crit Rev Environ Sci Technol. 44: 2577–2641. Pacwa-Plociniczak M, Plaza G A, Piotrowska-Seget Z, Cameotra S S. 2011. Environmental applications of biosurfactants: Recent advances. Int J Mol Sci. 12: 633–654. Parekh P, Varade D, Parikh J, Bahadur P. 2011. Anioniccationic mixed surfactant systems: Micellar interaction of sodium dodecyl trioxyethylene sulfate with cationic gemini surfactants. Colloid Surf A Physicochem Eng Asp. 385: 111–120. Paria S. 2008. Surfactant-enhanced remediation of organic contaminated soil and water. Adv Colloid Interface Sci. 138: 24–58. Paria S, Khilar K C. 2004. A review on experimental studies of surfactant adsorption at the hydrophilic solid–water interface. Adv Colloid Interface Sci. 110: 75–95. Paria S, Yuet P K. 2007. Adsorption of non-ionic surfactants onto sand and its importance in naphthalene removal. Ind Eng Chem Res. 46: 108–113. Park I B, Son Y, Song I S, Kim J, Khim J. 2008. Remediation of diesel-contaminated soil using supercritical carbon dioxide and ultrasound. Jpn J Appl Phys. 47: 4314–4316. Park I-S, Park J-W. 2011. Determination of a risk management primer at petroleum-contaminated sites: Developing new human health risk assessment strategy. J Hazard Mater. 185: 1374–1380. Pei G P, Sun C F, Zhu Y E, Shi W Y, Li H. 2018. Biosurfactantenhanced removal of o,p-dichlorobenzene from contaminated soil. Environ Sci Pollut Res Int. 25: 18–26. Peng S, Wu W, Chen J. 2011. Removal of PAHs with surfactantenhanced soil washing: Influencing factors and removal effectiveness. Chemosphere. 82: 1173–1177. Perger T M, Beˇster-Rogaˇ c M. 2007. Thermodynamics of micelle formation of alkyltrimethylammonium chlorides from high performance electric conductivity measurements. J Colloid Interface Sci. 313: 288–295. Phillips L A, Greer C W, Germida J J. 2006. Culture-based and culture-independent assessment of the impact of mixed and single plant treatments on rhizosphere microbial communities in hydrocarbon contaminated flare-pit soil. Soil Biol Biochem. 38: 2823–2833. Pienynsku G M, Sims I T, Vance G F. 2000. Soils and Environmental Quality. 2nd Edn. CRC Press, Boca Raton.

A. A. BEFKADU AND Q. Y. CHEN

Rao P H, He M. 2006. Adsorption of anionic and nonionic surfactant mixtures from synthetic detergents on soils. Chemosphere. 63: 1214–1221. R´ıos F, Lechuga M, Fern´ andez-Serrano M, Fern´ andez-Arteaga A. 2017. Aerobic biodegradation of amphoteric amine-oxidebased surfactants: Effect of molecular structure, initial surfactant concentration and pH. Chemosphere. 171: 324–331. Rodr´ıguez-Cruz M S, Sanchez-Martin M J, Sanchez-Camazano M. 2005. A comparative study of adsorption of an anionic and a non-ionic surfactant by soils based on physicochemical and mineralogical properties of soils. Chemosphere. 61: 56–64. Rosas J M, Vicente F, Santos A, Romero A. 2013. Soil remediation using soil washing followed by Fenton oxidation. Chem Eng J. 220: 125–132. Rosen M J. 1989. Selection of surfactant pairs for optimization of interfacial properties. J Am Oil Chem Soc. 66: 1840–1843. Rosen M J, Kunjappu J T. 2012. Surfactants and Interfacial Phenomena. 4th Edn. Wiley, Hoboken. S´ aez C, L´ opez-Vizca´ıno R, Ca˜ nizares P, Rodrigo M A. 2010. Conductive-diamond electrochemical-oxidation of surfactant-aided soil-washing effluents. Ind Eng Chem Res. 49: 9631– 9635. Salehian E, Khodadadi A, Hosseini B. 2012. Remediation of diesel contaminated soils using surfactants: Coulumn study. Am J Environ Sci. 8: 352–359. Samaksaman U, Peng T-H, Kuo J-H, Lu C-H, Wey M-Y. 2016. Thermal treatment of soil co-contaminated with lube oil and heavy metals in a low-temperature two-stage fluidized bed incinerator. Appl Therm Eng. 93: 131–138. S´ anchez-Mart´ın M J, Dorado M C, del Hoyo C, Rodr´ıguez-Cruz M S. 2008. Influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays. J Hazard Mater. 150: 115–123. S´ anchez-Mart´ın M J, Rodr´ıguez-Cruz M S, S´ anchez-Camazano M. 2003. Study of the desorption of linuron from soils to water enhanced by the addition of an anionic surfactant to soil-water system. Water Res. 37: 3110–3117. Santos D K F, Rufino R D, Luna J M, Santos V A, Sarubbo L A. 2016. Biosurfactants: Multifunctional biomolecules of the 21st century. Int J Mol Sci. 17: 401. Saxe J K, Allen H E, Nicol G R. 2000. Fenton oxidation of polycyclic aromatic hydrocarbons after surfactant-enhanced soil washing. Environ Eng Sci. 17: 233–244. Seo S-J, Kim J-H, Shin J-W, Park J-Y. 2015. Treatment of artificial and real co-contaminated soil by an enhanced electrokinetic-Fenton process with a soil flushing method. Water Air Soil Pollut. 226: 86. Shen Y-H. 2000. Sorption of non-ionic surfactants to soil: the role of soil mineral composition. Chemosphere. 41: 711–716. Shi Z T, Chen J J, Liu J F, Wang N, Sun Z, Wang X W. 2015. Anionic-nonionic mixed-surfactant-enhanced remediation of PAH-contaminated soil. Environ Sci Pollut Res. 22: 12769– 12774. Singla R, Grieser F, Ashokkumar M. 2009. Kinetics and mechanism for the sonochemical degradation of a nonionic surfactant. J Phys Chem A. 113: 2865–2872. Smith T J, Wang C, Abbott N L. 2017. Redox-triggered mixing and demixing of surfactants within assemblies formed in solution and at surfaces. J Colloid Interface Sci. 502: 122–133. Sri Ranjan R, Qian Y, Krishnapillai M. 2006. Effects of electrokinetics and cationic surfactant cetyltrimethylammonium bromide [CTAB] on the hydrocarbon removal and retention from contaminated soils. Environ Technol. 27: 767–776.

SOIL WASHING FOR REMOVAL OF HYDROCARBONS

Srinet S S, Basak A, Ghosh P, Chatterjee J. 2017. Separation of anionic surfactant in paste form from its aqueous solutions using foam fractionation. J Environ Chem Eng. 5: 1586– 1598. Stefania G, Lucaciu I, Pascu L. 2012. Biodegradabilityassessment of cationic and amphoteric raw materials. J Environ Prot Ecol. 13: 155–163. ˇ ab M, Zilka ˇ Sv´ M, M¨ ullerov´ a M, Koˇ ci V, M¨ uller V. 2008. Semiempirical approach to modeling of soil flushing: Model development, application to soil polluted by zinc and copper. Sci Total Environ. 392: 187–197. Szymczyk K, Ja´ nczuk B. 2007. The adsorption at solution-air interface and volumetric properties of mixtures of cationic and nonionic surfactants. Colloid Surface A. 293: 39–50. Tadros T. 2013. Chpater 246. Sedimentation of particles in suspensions. In Tadros T (ed.) Encyclopedia of Colloid and Interface Science. Springer, Berlin, Heidelberg. pp. 12–16. Tadros T F. 2005. Introduction. In Tadros T F (ed.) Applied Surfactants: Principles and Applications. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. pp. 1–17. Trellu C, Mousset E, Pechaud Y, Huguenot D, van Hullebusch E D, Esposito G, Oturan M A. 2016. Removal of hydrophobic organic pollutants from soil washing/flushing solutions: A critical review. J Hazard Mater. 306: 149–174. Trellu C, Oturan N, Pechaud Y, van Hullebusch E D, Esposito G, Oturan M A. 2017. Anodic oxidation of surfactants and organic compounds entrapped in micelles – Selective degradation mechanisms and soil washing solution reuse. Water Res. 118: 1–11. Trevors J T, Saier M H. 2010. The legacy of oil spills. Water Air Soil Pollut. 211: 1–3. Tsai T T, Kao C M, Surampalli R Y, Liang S H. 2009. Treatment of fuel-oil contaminated soils by biodegradable surfactant washing followed by fenton-like oxidation. J Environ Eng. 135: 1015–1024. Uhmann A, Aspray T J. 2012. Potential benefit of surfactants in a hydrocarbon contaminated soil washing process: Fluorescence spectroscopy based assessment. J Hazard Mater. 219-220: 141–147. United States Environmental Protection Agency (USEPA). 1996. A Citizen’s Guide to in situ Soil Flushing. Office of Solid Waste and Emergency Response (5102G), USEPA, Washington, D.C. Urum K, Grigson S, Pekdemir T, McMenamy S. 2006. A comparison of the efficiency of different surfactants for removal of crude oil from contaminated soils. Chemosphere. 62: 1403– 1410. Urum K, Pekdemir T, C ¸ opur M. 2004. Surfactants treatment of crude oil contaminated soils. J Colloid Interface Sci. 276: 456–464. Urum K, Pekdemir T, Ross D, Grigson S. 2005. Crude oil contaminated soil washing in air sparging assisted stirred tank reactor using biosurfactants. Chemosphere. 60: 334–343. Ussawarujikulchai A, Laha S, Tansel B. 2008. Synergistic effects of organic contaminants and soil organic matter on the soilwater partitioning and effectiveness of a nonionic surfactant (Triton X-100). Biorem J. 12: 88–97. Van Gestel K, Mergaert J, Swings J, Coosemans J, Ryckeboer J. 2003. Bioremediation of diesel oil-contaminated soil by composting with biowaste. Environ Pollut. 125: 361–368. Varade D, Joshi T, Aswal V K, Goyal P S, Hassan P A, Bahadur P. 2005. Micellar behavior of mixtures of sodium dodecyl sulfate and dodecyldimethylamine oxide in aqueous solutions. Colloild Surface A. 259: 103–109.

409

V´ azquez B, Bandala E R, Reyes R, Torres L G. 2010. Variation of mechanical and hydraulic properties of oil-contaminated soil due to a surfactant-enhanced washing process. Soil Sediment Contam. 19: 531–546. Villa R D, Trov´ o A G, Nogueira R F P. 2010. Soil remediation using a coupled process: soil washing with surfactant followed by photo-Fenton oxidation. J Hazard Mater. 174: 770–775. Vishnyakov A, Lee M T, Neimark A V. 2013. Prediction of the critical micelle concentration of nonionic surfactants by dissipative particle dynamics simulations. J Phys Chem Lett. 4: 797–802. Von Lau E, Gan S, Ng H K, Poh P E. 2014. Extraction agents for the removal of polycyclic aromatic hydrocarbons (PAHs) from soil in soil washing technologies. Environ Pollut. 184: 640–649. Wan J Z, Chai L N, Lu X H, Lin Y S, Zhang S T. 2011. Remediation of hexachlorobenzene contaminated soils by rhamnolipid enhanced soil washing coupled with activated carbon selective adsorption. J Hazard Mater. 189: 458–464. Wan J Z, Yuan S H, Mak K, Chen J, Li T P, Lin L, Lu X. 2009. Enhanced washing of HCB contaminated soils by methyl-β-cyclodextrin combined with ethanol. Chemosphere. 75: 759–764. Wang P, Keller A A. 2008. Partitioning of hydrophobic organic compounds within soil-water-surfactant systems. Water Res. 42: 2093–2101. Wang W, Kwak J C T. 1999. Adsorption at the alumina-water interface from mixed surfactant solutions. Colloids Surf A Physicochem Eng Asp. 156: 95–110. Wei Y F, Liang X J, Tong L, Guo C L, Dang Z. 2015. Enhanced solubilization and desorption of pyrene from soils by saline anionic–nonionic surfactant systems. Colloids Surf A Physicochem Eng Asp. 468: 211–218. Wu M L, Li W, Dick W A, Ye X Q, Chen K L, Kost D, Chen L M. 2017. Bioremediation of hydrocarbon degradation in a petroleum-contaminated soil and microbial population and activity determination. Chemosphere. 169: 124–130. Xu J, Yuan X, Dai S G. 2006. Effect of surfactants on desorption of aldicarb from spiked soil. Chemosphere. 62: 1630–1635. Yan J C, Gao W G, Qian L B, Han L, Chen Y, Chen M F. 2015. Remediation of nitrobenzene contaminated soil by combining surfactant enhanced soil washing and effluent oxidation with persulfate. PLoS ONE. 10: e0132878. Yang G P, Chen Q, Li X X, Cao X Y. 2010. Study on the sorption behaviors of Tween-80 on marine sediments. Chemosphere. 79: 1019–1025. Yang J S, Dong H B. 2016. CO2-responsive aliphatic tertiary amine-modified alginate and its application as a switchable surfactant. Carbohydr Polym. 153: 1–6. Yang K, Zhu L Z, Zhao B W. 2005. Minimizing losses of nonionic and anionic surfactants to a montmorillonite saturated with calcium using their mixtures. J Colloid Interface Sci. 291: 59–66. Yang K, Zhu L, Xing B. 2006. Enhanced soil washing of phenanthrene by mixed solutions of TX100 and SDBS. Environ Sci Technol. 40: 4274–4280. Yang X M, Beckmann D, Fiorenza S, Niedermeier C. 2005. Field study of pulsed air sparging for remediation of petroleum hydrocarbon contaminated soil and groundwater. Environ Sci Technol. 39: 7279–7286. Yu H S, Zhu L Z, Zhou W J. 2007. Enhanced desorption and biodegradation of phenanthrene in soil-water systems with the presence of anionic-nonionic mixed surfactants. J Hazard Mater. 142: 354–361.

410

Yu S, Xu R, Hou L, Song M, Liu J. 2016. Stabilization/solidification of nitrobenzene contaminated soil based on hydrophobilized CaO. Proced Environ Sci. 31: 288–294. Yuan T, Marshall W D. 2007. Optimizing a washing procedure to mobilize polycyclic aromatic hydrocarbons (PAHs) from a field-contaminated soil. Ind Eng Chem Res. 46: 4626–4632. Zamudio-P´ erez E, Bandala E R, Fernandez L C, Torres L G. 2013. Surfactant enhanced washing of soil contaminated with petroleum hydrocarbons and treatment of produced wastewaters using a biofilter. J Environ Treat Technol. 1: 110–116. Zana R. 2002a. Alkanediyl-α, ω-bis(dimethylalkylammonium bromide) surfactants: II. Krafft temperature and melting temperature. J Colloid Interface Sci. 252: 259–261. Zana R. 2002b. Dimeric (gemini) surfactants: Effect of the spacer group on the association behavior in aqueous solution. J Colloid Interface Sci. 248: 203–220. Zhang M, Zhu L Z. 2010. Effect of SDBS-Tween 80 mixed surfactants on the distribution of polycyclic aromatic hydrocarbons in soil-water system. J Soil Sediment. 10: 1123–1130. Zhang R, Somasundaran P. 2006. Advances in adsorption of surfactants and their mixtures at solid/solution interfaces. Adv Colloid Interface Sci. 123-126: 213–229. Zhang X X, Li J B, Huang Y F, Thring R. 2010. Surfactant enhanced biodegradation of petroleum hydrocarbons in oil refinery tank bottom sludge. J Can Petrol Technol. 49: 34– 39. Zhao B W, Zhu L Z, Li W, Chen B L. 2005. Solubilization and biodegradation of phenanthrene in mixed anionic–nonionic surfactant solutions. Chemosphere. 58: 33–40. Zheng Z M, Obbard J P. 2002. Evaluation of an elevated nonionic surfactant critical micelle concentration in a soil/aqueous system. Water Res. 36: 2667–2672. Zhou Q X, Hua T. 2004. Bioremediation: A review of applications and problems to be resolved. Prog Nat Sci. 14: 937– 944. Zhou Q X, Sun F H, Liu R. 2005. Joint chemical flushing of soils contaminated with petroleum hydrocarbons. Environ

A. A. BEFKADU AND Q. Y. CHEN

Int. 31: 835–839. Zhou W J, Wang X H, Chen C P, Zhu L Z. 2013. Enhanced soil washing of phenanthrene by a plant-derived natural biosurfactant, Sapindus saponin. Colloid Surface A. 425: 122–128. Zhou W J, Yang J J, Lou L J, Zhu L Z. 2011. Solubilization properties of polycyclic aromatic hydrocarbons by saponin, a plant-derived biosurfactant. Environ Pollut. 159: 1198– 1204. Zhou W J, Zhu L Z. 2004. Solubilization of pyrene by anionicnonionic mixed surfactants. J Hazard Mater. 109: 213–220. Zhou W J, Zhu L Z. 2005. Solubilization of polycyclic aromatic hydrocarbons by anionic-nonionic mixed surfactant. Colloid Surface A. 255: 145–152. Zhou W J, Zhu L Z. 2007a. Efficiency of surfactant-enhanced desorption for contaminated soils depending on the component characteristics of soil-surfactant-PAHs system. Environ Pollut. 147: 66–73. Zhou W J, Zhu L Z. 2007b. Enhanced desorption of phenanthrene from contaminated soil using anionic/nonionic mixed surfactant. Environ Pollut. 147: 350–357. Zhu K, Hart W, Yang J T. 2005. Remediation of petroleumcontaminated loess soil by surfactant-enhanced flushing technique. J Environ Sci Health A. 40: 1877–1893. Zhu L Z, Chen B L, Tao S, Chiou C T. 2003. Interactions of organic contaminants with mineral-adsorbed surfactants. Environ Sci Technol. 37: 4001–4006. Zhu L Z, Feng S L. 2003. Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed anionic-nonionic surfactants. Chemosphere. 53: 459–467. Zhu L Z, Zhou W J. 2008. Partitioning of polycyclic aromatic hydrocarbons to solid-sorbed nonionic surfactants. Environ Pollut. 152: 130–137. Zou C J, Wang M, Xing Y, Lan G H, Ge T T, Yan X L, Gu T. 2014. Characterization and optimization of biosurfactants produced by Acinetobacter baylyi ZJ2 isolated from crude oil-contaminated soil sample toward microbial enhanced oil recovery applications. Biochem Eng J. 90: 49–58.