Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon

Classification of surfactants and admixtures for producing stable aqueous foam

Surfactants and foam have captured the interest of researchers worldwide due to their unique behavior of surface activity, the dynamic nature of foam formation, and simultaneous destruction. The present review focuses on the surfactants' classification, surfactant-solvent interaction, foam formation, characteristics, and a range of admixtures to enhance the foam performance. Although surfactants have been researched and developed for decades, recently, their sustainability has been given special attention. One such aspect is the development of green foaming agents from natural and renewable sources and assessing their suitability for different applications. Further, widely researched parameters are the type of surfactant, surfactant concentration, surfactant-solvent interaction, and foam production method on the foamability of a surfactant solution and related foam characteristics, including stability and texture. However, still, there is no rule to predict the best foam. Another vital concern is the non-standardization of foam assessment methods across industries and regions. Recently, research has progressed in identifying suitable admixtures for foam performance enhancement and utilizing them to produce stable foams for application in enhanced oil recovery, drug delivery, and manufacturing of aerated food products and foamed concrete. Although foam stabilization using various admixtures has been recognized well in the literature, the underlying mechanism requires further research. The interaction of surfactant and admixtures in solution is complicated and requires more research.

Remediation of soils contaminated with total petroleum hydrocarbons through soil washing with surfactant solutions

Soil fulfils vital functions for life on Earth and so, just like water and air, its protection from all sources of contamination is a major concern. However, the extensive use of petroleum derived products, either as energy sources or as commodities, leads to important environmental liabilities. Ex situ soil washing is a technology to concentrate contaminants, allowing soil cleaning and the reuse of extracted petroleum derived products. This work focuses on the optimization of ex situ soil washing process using surfactants, introducing an evaluation of the washing solution recycling and its after use safe disposal, promoting the reduction of raw materials, energy and water resources costs. Two surfactants, sodium dodecyl sulphate (SDS) and polyoxyethylene sorbitan monooleate (Tween 80), were tested in the decontamination of an artificially contaminated soil with engine lubricant oil waste. The optimization of the washing conditions, such as stirring speed, liquid-solid ratio, number of washing stages, and surfactant concentration, was carried out using a design of experiments (DOE) software, so that the maximum extraction efficiency of total petroleum hydrocarbons (TPHs) was achieved. A TPH removal efficiency of (80.7 ± 3.2)% was obtained with Tween 80 after 5 h of washing and (90.7 ± 2.8)% with SDS after 2 h at 200 rpm on an orbital shaker with a liquid to solid ratio (L/S) of 15. The potential for reuse of the washing solutions was evaluated. Finally, the discharge of the washing solution was considered using activated carbon to remove the surfactants and ensure its safe disposal.

Treatment of PBDEs from Soil-Washing Effluent by Granular-Activated Carbon: Adsorption Behavior, Influencing Factors and Density Functional Theory Calculation

Soil-washing is a potential technology for the disposal of soil contaminated by e-waste; however, the produced soil-washing effluent will contain polybrominated diphenyl ethers (PBDEs) and a large number of surfactants, which are harmful to the environment, so the treatment of PBDEs and the recycling of surfactants are the key to the application of soil-washing technology. In this study, coconut shell granular-activated carbon (GAC) was applied to remove PBDEs from Triton X-100 (TX-100) surfactant which simulates soil-washing effluent. The adsorption results show that, GAC can simultaneously achieve effective removal of 4,4′-dibromodiphenyl ether (BDE-15) and efficient recovery of TX-100. Under optimal conditions, the maximum adsorption capacity of BDE-15 could reach 623.19 μmol/g, and the recovery rate of TX-100 was always higher than 83%. The adsorption process of 4,4′-dibromodiphenyl ether (BDE-15) by GAC could best be described using the pseudo-second-order kinetic model and Freundlich isothermal adsorption model. The coexistence ions had almost no effect on the removal of BDE-15 and the recovery rate of TX-100, and the solution pH had little effect on the recovery rate of TX-100; BDE-15 had the best removal effect under the condition of weak acid to weak base, indicating that GAC has good environmental adaptability. After adsorption, GAC could be regenerated with methanol and the adsorption effect of BDE-15 could still reach more than 81%. Density functional theory (DFT) calculation and characterization results showed that, Van der Waals interaction and π–π interaction are dominant between BDE-15 and GAC, and hydrogen bond interactions also exist. The existence of oxygen-containing functional groups is conducive to the adsorption of BDE-15, and the carboxyl group (-COOH) has the strongest promoting effect. The study proved the feasibility of GAC to effectively remove PBDEs and recover surfactants from the soil-washing effluent, and revealed the interaction mechanism between PBDEs and GAC, which can provide reference for the application of soil-washing technology.

Coupling of desorption of phenanthrene from marine sediments and biodegradation of the sediment washing solution in a novel biochar immobilized-cell reactor

The recurrent dredging of marine sediments needs the use of ex-situ technologies such as sediment washing (SW) to effectively remove polycyclic aromatic hydrocarbons. Notwithstanding, the large volumes of generated spent SW effluents require adequate treatment by employing highly-efficient, inexpensive and environmentally-friendly solutions. This study proposes the phenanthrene (PHE) desorption from sediments using Tween® 80 (TW80) as extracting agent and the treatment of the resulting spent SW solution in a biochar (BC) immobilized-cell bioreactor. The SW process reached the highest PHE removal of about 91% using a surfactant solution containing 10,800 mg L^-1 of TW80. The generated amount of spent PHE-polluted SW solution can be controlled by keeping a solid to liquid ratio of 1:4. A PHE degradation of up to 96% was subsequently achieved after 43 days of continuous reactor operation, aerobically treating the TW80 solution in the BC immobilized-cell bioreactor with a hydraulic retention time of 3.5 days. Brevundimonas, Chryseobacterium, Dysgonomonas, Nubsella, and both uncultured Weeksellaceae and Xanthobacteraceae genera were mainly involved in PHE biodegradation. A rough economic study showed a total cost of 342.60 € ton^-1 of sediment, including the SW operations, TW80 and BC supply and the biological treatment of the SW solution.

Selective sorption of PAHs from TX100 solution by resin SP850: effects of TX100 concentrations and PAHs solubility

Recycling of washing effluent by selective sorption using resins is a feasible method to lower the operation costs of surfactant enhanced remediation (SER). In this study, correlations capable of predicting the selective sorption removal of polycyclic aromatic hydrocarbons (PAHs) by resin SP850 from TX100 solution to recycle washing effluent in SER were developed. A negative relationship of sorption coefficients (log K _f) of PAHs by resin SP850 with TX100 initial concentrations (log C _0,TX100) and water solubilities (log S _w) of PAHs was observed, which indicated that solubility enhancement of PAHs in TX100 micelles was responsible for the decreasing of the selective sorption. Freundlich exponential coefficients (1/n) of PAHs were relatively constant (0.775 ± 0.012), suggesting that the sorption of PAHs by SP850 in the presence of surfactant is a surface adsorption process. The modified selectivity parameter (S*), having a relationship with log C _0,TX100 and PAHs log S _w as well, could be employed to evaluate the efficiency of the selective sorption process and select the optimal TX100 concentration in washing effluents. For example, at the given SP850 dose of 1.0 g L^-1, the optimal TX100 concentrations (C _opTX100) for naphthalene, acenaphthene, phenanthrene, pyrene, anthracene and benzanthracene were about 4200, 7100, 8000, 10 000, 18 000 and 19 500 mg L^-1, respectively, having a negative relationship with their log S _w. Moreover, the C _opTX100 was independent of the solid-to-solution ratio of SP850 and TX100 solution containing PAHs. These correlations would be helpful for the application of SER in contaminated soils by giving a method to quantitatively predict the selective sorption behaviors of PAHs by SP850 from TX100 solution, especially for the C _opTX100, using the S _w of organic compounds and surfactant concentrations.

Comparison of thermal and chemical enhanced recovery of DNAPL in saturated porous media: 2D tank pumping experiments and two-phase flow modelling

Pumping experiments were performed in a 2D tank in order to estimate the recovery yield of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) by varying different parameters: permeability of the saturated zone, pumping flow rates, addition of surfactant and heating. Surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media while temperature was increased to reduce DNAPL viscosity (and hence increase its mobility). Chemical enhancement was performed with the addition of Sodium Dodecyl Benzene Sulfonate (SDBS) (at its Critical Micelle Concentration, to avoid DNAPL dissolution) and thermal enhancement was performed at 50 °C (to avoid DNAPL volatilization). The experiments were monitored with photography allowing, on the basis of image interpretation, to convert optical densities (OD) into water saturations (S_w). Image interpretations were compared with modelling results. The two-phase flow modelling was performed with the pressure-pressure formulation using capillary pressure and relative permeability functions based on the van Genuchten-Mualem equations. Measured volumes of DNAPL recovered as well as the displacement of the DNAPL-water interface (radius and height of the cone of depression) are consistent with the modelling results. Furthermore, chemical enhancement results in a significant increase in the recovery rates of DNAPL. The observed improvement in the recovery of DNAPL with chemical enhancement is due to the fact that: (i) the residual saturation inside the cone of depression is lower and (ii) the cone of depression radius and height increase. Thermal enhancement had no beneficial effect on DNAPL recovery rate or yield. This study shows that it is possible to accurately determine water and DNAPL saturations by image interpretation during pumping tests in a 2D tank in the laboratory. For field-scale applications, the two-phase flow model allows to determine remediation yields as well as the volumes of the cone of depression according to the different operating conditions.

Surfactant-enhanced remediation of oil-contaminated soil and groundwater: A review

Oil leakage, which is inevitable in the process of extraction, processing, transportation and storage, seriously undermines the soil and groundwater environment. Surfactants can facilitate the migration and solution of oil contaminants from nonaqueous phase liquid (NAPL) or solid phase to water by reducing the (air/water) surface tension, (oil/water) interfacial tension and micellar solubilization. They can effectively enhance the hydrodynamic driven remediation technologies by improving the contact efficiency of contaminants and liquid remediation agents or microorganism, and have been widely used to enhance the remediation of oil-contaminated sites. This paper summarizes the characteristics of different types of surfactants such as nonionic, anionic, biological and mixed surfactants, their enhancements to the remediation of oil-contaminated soil and groundwater, and examines the factors influencing surfactant performance. The causes of tailing and rebound effects and the role of surfactants in suppressing them are also discussed. Laboratory researches and actual site remediation practices have shown that various types of surfactants offer diverse options. Biosurfactants and mixed surfactants are superior and worth attention among the surfactants. Using surfactant foams, adding shear-thinning polymers, and combining surfactants with in-situ chemical oxidation are effective ways to resolve tailing and rebound effects. The adsorption of surfactants on soils and aquifer sediments decreases remediation efficiency and may cause secondary pollution, Therefore the adsorption loss should be noticed and minimized.

Remediation of soils contaminated by hydrophobic organic compounds: How to recover extracting agents from soil washing solutions?

A lot of soil (particularly, former industrial and military sites) has been contaminated by various highly toxic contaminants such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs) or chlorinated solvents. Soil remediation is now required for their promotion into new industrial or real estate activities. Therefore, the soil washing (SW) process enhanced by the use of extracting agents (EAs) such as surfactants or cyclodextrins (CDs) has been developed for the removal of hydrophobic organic compounds (HOCs) from contaminated soils. The use of extracting agents allows improving the transfer of HOCs from the soil-sorbed fraction to the washing solution. However, using large amount of extracting agents is also a critical drawback for cost-effectiveness of the SW process. The aim of this review is to examine how extracting agents might be recovered from SW solutions for reuse. Various separation processes are able to recover large amounts of extracting agents according to the physicochemical characteristics of target pollutants and extracting agents. However, an additional treatment step is required for the degradation of recovered pollutants. SW solutions may also undergo degradation processes such as advanced oxidation processes (AOPs) with in situ production of oxidants. Partial recovery of extracting agents can be achieved according to operating conditions and reaction kinetics between organic compounds and oxidant species. The suitability of each process is discussed according to the various physicochemical characteristics of SW solutions. A particular attention is paid to the anodic oxidation process, which allows either a selective degradation of the target pollutants or a complete removal of the organic load depending on the operating conditions.

Pure and mixed aqueous micellar solutions of Sodium Dodecyl sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO): Role of temperature and composition

Aqueous mixtures of anionic and nonionic/cationic surfactants can form non-trivial self-assemblies in solution and exhibit macroscopic responses. Here, we investigate the micellar phase of pure and mixed aqueous solutions of Sodium Dodecyl Sulfate (SDS) and Dimethyldodecyl Amine Oxide (DDAO) using a combination of Small Angle Neutron Scattering (SANS), Fourier-Transform Infrared Spectroscopy (FTIR) and rheological measurements. We examine the effect of temperature (0-60 °C), on the 20 wt% SDS micellar solutions with varying DDAO (⩽5 wt%), and seek to correlate micellar structure with zero-shear solution viscosity. SANS establishes the formation of prolate ellipsoidal micelles in aqueous solutions of pure SDS, DDAO and SDS/DDAO mixtures, whose axial ratio is found to increase upon cooling. Elongation of the ellipsoidal micelles of pure SDS is also induced by the introduction of the non-anionic DDAO, which effectively reduces the repulsive interactions between the anionic SDS head-groups. In FTIR measurements, the formation of elongated mixed ellipsoidal micelles is confirmed by the increase of ordering in the hydrocarbon chain tails and interaction between surfactant head-groups. We find that the zero-shear viscosity of the mixed surfactant solutions increases exponentially with decreasing temperature and increasing DDAO content. Significantly, a master curve for solution viscosity can be obtained in terms of micellar aspect ratio, subsuming the effects of both temperature and DDAO composition in the experimental range investigated. The intrinsic viscosity of mixed micellar solutions is significantly larger than the analytical and numerical predictions for Brownian suspensions of ellipsoidal colloids, highlighting the need to consider interactions of soft micelles under shear, especially at high concentrations.

Enhanced electrokinetic remediation (EKR) for heavy metal-contaminated sediments focusing on treatment of generated effluents from EKR and recovery of EDTA

Electrokinetic remediation (EKR) is one of the most successful remediation techniques to treat the sediments contaminated with heavy metals. EDTA is the most widely used enhancing agent to improve the transport process in EKR. But often the generated effluents from EKR contains a high concentration of heavy metals, which cannot be disposed of without treatment. The major objective of this study includes the estimation of optimal concentration of chelating agent EDTA, followed by treatment of contaminated sediments by EKR technique for heavy metal removal. The effluents generated from EKR were further studied for recovery and reuse of EDTA and for safe discharge of heavy metals. The optimum concentration of EDTA was found as 0.05 M with a solid-to-liquid ratio as 1:10. When fresh EDTA was used as enhancing agent the average removal of heavy metals obtained as 74.8% with EKR, whereas the application of recovered EDTA in treatment process in first, second, and third cycle showed the slight reduction of heavy metals of about 71.1%, 63.5%, and 52.1%, respectively. The heavy metal removal by recovered EDTA was effective in reduction of heavy metals up to three cycles of re-use while reducing the ecological risk in sediments. PRACTITIONER POINTS: Treatment of contaminated sediments with heavy metals achieved by electrokinetic remediation (EKR) technique enhanced with EDTA. The recovery of EDTA and heavy metal reduction from the generated effluents during EKR treatment were performed by the addition of FeCl₃ and Na₂ PO_4, and optimized concentration was evaluated. This study found that the use of recovered EDTA in EKR treatment has effectively reduced the risk associated with heavy metals.

Multifunctional metal-organic frameworks in oil spills and associated organic pollutant remediation

The release of toxic organic compounds into the environment in an event of oil spillage is a global menace due to the potential impacts on the ecosystem. Several approaches have been employed for oil spills clean-up, with adsorption technique proven to be more promising for the total reclamation of a polluted site. Of the several adsorbents so far reported, adsorbent-based porous materials have gained attention for the reduction/total removal of different compounds in environmental remediation applications. The superior potential of mesoporous materials based on metal-organic frameworks (MOFs) against conventional adsorbents is due to their intriguing and enhanced properties. Therefore, this review presents recent development in MOF composites; methods of preparation; and their practical applications towards remediating oil spill, organic pollutants, and toxic gases in different environmental media, as well as potential materials in the possible deployment in reclaiming the polluted Niger Delta due to unabated oil spillage and gas flaring.

Applicability of an anionic-nonionic surfactant in p-cresol contaminated soil washing: Finding the optimal mixing ratio

In this study, the parameters influencing p-cresol removal efficiency in soil washing method were investigated. Primarily, extraction efficiencies of three Tween series surfactants (Tween 20, Tween 60, Tween 80) with 10 mM concentration were compared. Tween 80 showed the best results since its value (55%) was 4% and 13% higher than that of Tween 60 and Tween 20. The impact of mixed surfactant on extraction rate was examined by employing a mixture of Tween 80 and one anionic surfactant (sodium dodecyl sulfate) with different molar ratio as the main washing solution. The results denoted that the molar ratio of 3:2 (SDS:Tween80) could enhance the extraction rate up to 38% compared to using SDS and Tween 80 alone. Regarding the initial p-cresol concentration in the collected sample, the cleanup level (390 mg/kg) could only be achieved using the mixed-surfactant. Thus, the minimum required surfactant concentrations to hit the target level was calculated to be 3.54 g/L of Tween 80 and 2.105 g/L of SDS (molar ratio of 0.27 SDS:Tween80). Studying the role of surfactant concentration indicated that its increment from 10 mM to 20 mM, which is way above all the reagents' critical micelle concentration (CMC), does not affect the removal rate considerably. The same results were obtained comparing the effect of washing time in three different levels (30 min, 60 min and 90 min). However, temperature showed to be a more significant parameter as it could enhance the results up to 20% (for SDS).

Study on the preparation of the hierarchical porous CX-TiO2 composites and their selective degradation of PHE solubilized in soil washing eluent

A series of CX-TiO₂(Carbon Xerogel- TiO₂) composites with a hierarchical porous structure were obtained through the sol-gel method followed by drying and carbonization, and have been applied to treating solubilizing wastewater containing a high concentration of phenanthrene (PHE). The characterizations demonstrated that the CX-TiO₂ exhibits a hierarchical porous structure, with particles of carbon and P25 being uniformly in the matrix. Removal efficiency of CX-TiO₂ on PHE in soil washing eluent (SWE) were evaluated under ultraviolet (UV) irradiation or dark condition, and P25 was employed as the reference. The results revealed that CX-TiO₂(0.2) had the best removal effect on PHE, with the efficiency as high as 97.8% under UV illumination within 15 h. It demonstrated that in the process of PHE removal by CX-TiO₂ whether it was under UV illumination or not, the adsorption plays a dominant role in the early stage. The kinetic behavior of PHE adsorption was fitted using the pseudo-first-order and pseudo-second-order, and Langmuir model and Freundlich models were applied to describe the PHE adsorption isotherms. The results indicating that it was a chemical adsorption process, which was influenced by the interaction between PHE and CX-TiO₂, and PHE is adsorbed on the interface of CX-TiO₂(0.2) in a single layer form, instead of agglomerating in the admicelle. A possible mechanism of removal of solubilized PHE in SWE was speculated, in which both hierarchical porous structure and appropriate micropores size of CX-TiO₂ were indispensable to the selective adsorption and degradation of PHE. Recycling performance certificated that the selective removal efficiency of PHE could still reach 82.09% after five recycles. Thus the excellent performance testified that the CX-TiO₂ have great potential in treating SWE containing solubilized PAHs.

Micellar structure and transformations in sodium alkylbenzenesulfonate (NaLAS) aqueous solutions: effects of concentration, temperature, and salt

We investigate the shape, dimensions, and transformation pathways of micelles of linear sodium alkylbenzenesulfonate (NaLAS), a common anionic surfactant, in aqueous solution. Employing Small Angle Neutron Scattering (SANS) and surface tensiometry, we quantify the effects of surfactant concentration (0.6-15 wt%), temperature (5-40 °C) and added salt (≤0.35 M Na2SO4). Spherical micelles form at low NaLAS (≤2.6 wt%) concentration in water, and become elongated with increasing concentration and decreasing temperature. Addition of salt reduces the critical micelle concentration (CMC) and thus promotes the formation of micelles. At fixed NaLAS concentration, salt addition causes spherical micelles to grow into cylindrical micelles, and then multilamellar vesicles (MLVs), which we examine by SANS and cryo-TEM. Above a threshold salt concentration, the MLVs reach diameters of 100 s of nm to few μm, eventually causing precipitation. While the salt concentrations associated with the micelle-to-cylinder transformation increase only slightly with temperature, those required for the cylinder-to-MLV transformation exhibit a pronounced, linear temperature dependence, which we examine in detail. Our study establishes a solution structure map for this model anionic surfactant in water, quantifying the combined roles of concentration, temperature and salt, at practically relevant conditions.

Thermal and chemical enhanced recovery of heavy chlorinated organic compounds in saturated porous media: 1D cell drainage-imbibition experiments

Chemical and thermal enhanced recovery of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids) was investigated by using lab-scale 1D cells. Temperature was increased to reduce DNAPL viscosity (and hence increase its mobility), while surfactant was added to decrease capillary forces involved in the entrapment of DNAPL in porous media. Laboratory scale experiments, based on mass balance and indirect monitoring methods (i.e., permittivity, electrical resistivity and optical density), were conducted to quantify the effects of these enhancements. Heating the DNAPL up to 50 °C decreased its viscosity by a factor of two. The addition of a surfactant; i.e., Sodium Dodecyl Benzene Sulfonate (SDBS), at its Critical Micelle Concentration (to prevent DNAPL solubilization), decreased interfacial tensions by a factor of 12. Drainage-imbibition experiments performed in 1D cells provided retention curves (capillary pressure as a function of water saturation) of a two-phase (DNAPL-water) system in experimental glass bead porous media. The observed reduction of residual saturation (S_rn) obtained with SDBS was 28% for 0.5 mm-diameter glass beads (GB) and 46% for 0.1 mm GB. No significant decrease in S_m was observed with thermal enhancement. The van Genuchten - Mualem model was found to satisfactorily reproduce the measured retention curves. Indirect measurements of water saturations (S_w) showed that: i. measured permittivities were very close to values modeled with the Complex Refractive Index Model (CRIM); ii. Archie's Law was less successful in reproducing measured electrical resistivities; iii. optical densities provide accurate estimations of S_w. At field scale, the combined monitoring of electrical resistivity (which provides a global picture) and permittivity (which yields locally precise but spatially limited information) is expected to significantly improve the collection of information on residual saturations S_rn.

Effective exploitation of anionic, nonionic, and nanoparticle-stabilized surfactant foams for petroleum hydrocarbon contaminated soil remediation

Contaminated environments posed serious threats to the ecosystems and their living beings. Suitable preventive approaches should be adopted for effective remediation of contaminated environments to remove or lower their health and environmentally-related hazardous aspects. Petroleum or traces of petroleum contamination from oil fields and refineries to exposed soil in the form of gasoline, petrol, diesel, and used motor oil are a rich source of potential damage to the environment. Conventional ways of treatment and management of hydrocarbon are complicated, insufficient, and expensive. Herein, we reviewed a smart approach for the removal of petroleum source contamination from exposed soil using environment-friendly chemical surfactants and nanoscale surfactant system. The host/guest complexes formation of surfactants with the hydrocarbons (hydrophobic contaminants) of soil and water by the encapsulation mechanism of hydrophobes into the (micelles) a self-assembly aggregation of surfactants. Recently, surfactants stabilized by nanoparticles (NPs) acquired more importance and popularity over surfactant alone. The persistence of diverse hydrocarbon-based contaminants and the mechanisms of removal using pristine surfactants or NP-stabilized surfactant foams are discussed with suitable examples. In summary, herein, an effort has been made to present the notable potentialities of pristine surfactants and NP-stabilized surfactant foams to remediate the petroleum hydrocarbon contaminated soil for a greener and sustainable ecosystem.

Investigating the photo-Fenton process for treating soil washing wastewater

PURPOSE

Petroleum hydrocarbons have created numerous problems for water resources. The main objective of this study was focused on the application of advanced oxidation processes (AOPs) in treatment of effluent of petroleum contaminated soil washing operation.

METHODS

The AOP process in the present study was run with Fe²⁺/H₂O₂ (Fenton's reagent), Fe²⁺/H₂O₂/UV (photo-Fenton's reagent) and UV lamp (medium pressure mercury lamp, 400 W) in the batch-mode reactor at laboratory-scale.

RESULTS

Various parameters and optimized values which could maximize the removal efficiency of COD were: Fe²⁺ = 0.1 g/L, H₂O₂ = 1 g/L, pH = 3 and irradiation time of 120 min. Under the optimal conditions, the removal efficiency of COD and TOC were achieved 86.3% and 68% respectively. The results showed that the reaction of the oxidation of diesel fuel by Fenton and photo-Fenton systems followed second-order kinetic model with reaction rate constants (k) of 7 × 10^-6 and 3 × 10^-6 l/mg min^-1 respectively.

CONCLUSIONS

The photo-Fenton process can be used as an effective and environmental friendly method in the degradation of petroleum organic compounds.

Phenanthrene degradation using Fe(III)-EDDS photoactivation under simulated solar light: A model for soil washing effluent treatment

In this work, for the first time, the nonionic surfactant polyoxyethylene-(20)-sorbitan monooleate (Tween 80, C₆₄H₁₂₄O₂₆) aided soil washing effluent was treated by enhanced activation of persulfate (PS) using Fe(III)-EDDS (EDDS: ethylenediamine-N, N-disuccinic acid) complexes under simulated solar light irradiation. The performance of this system was followed via the production and reactivity of radical species (SO₄^-, HO, Cl₂^-) and degradation of phenanthrene (PHE) used as a model pollutant in soils. Different physico-chemical parameters such as the concentration of reactive species and pH were investigated through the PHE degradation efficiency. The second-order rate constants of the reactions for generated radicals with PHE and Tween 80 in solution were identified through competitive reaction experiments under steady-state conditions and application of nanosecond laser flash photolysis (LFP) as well. A kinetic approach was applied to assess the selectivity and reactivity of photo-generated radicals in aqueous medium in order to explain the observed degradation trends. This work proposes an innovative technology of management of soil washing solutions using Fe(III)-EDDS complexes and solar light for the activation of persulfate.

Ozone-encapsulated colloidal gas aphrons for in situ and targeting remediation of phenanthrene-contaminated sediment-aquifer

The hydrophobic polycyclic aromatic hydrocarbons (PAHs) are apt to adhere tightly to the sediments in aquifer and thus pose great threats to the aquatic environment of groundwater and surface water as well as human health. The present study constructed functionalized microbubbles, named colloidal ozone aphrons (COAs), by dissolving ozone-contained air into the nonionic surfactant (Tween-20) solution at the pressure of 300 kPa for the in situ remediation of phenanthrene (PHE)-contaminated sediments. The COA system aimed at improving the PHE elimination in terms of (i) enhancing the migration and transportation ability of the bubble system in the contaminated aquifer matrix, (ii) accurately desorbing the target hydrophobic contaminants from sediments, and (iii) reinforcing the in situ oxidation degradation immediately after or simultaneously when the PAHs are desorbed into the aqueous phase. Experimental results demonstrated that the COAs exhibited similar characteristics as the classical colloidal gas aphrons (CGAs), including the high stability (half-life time > 200 s), typical morphology and average bubble size (114-162 μm); higher air hold-up of COAs was achieved (i. e. > 20%) compared with the air-microbubbles (1-2%) obtained under the same generation conditions. Although the encapsulated ozone could oxidize the surfactant-layers, the properties and behaviors of COAs were not greatly affected. The surfactant multi-layers endowed the COAs with strong hydrophobic attraction with PHE, great migration capacity and enlarged oxidation area in the sediment matrix. Approximately 96.9% of PHE was removed from the sediments and 84.9% of the overall PHE was oxidized at the high ozone concentration of 0.6 mg/L when the initial PHE concentration was 240.0 μg/kg. The COA-involved remediation technology provided the insight of combining the processes of washing and oxidizing through adopting the particularly conceived microbubbles. The in situ and selective removal of hydrophobic organic contaminants from sediments in aquifer was well achieved in this study.

A review on the application of chemical surfactant and surfactant foam for remediation of petroleum oil contaminated soil

Soil, exposed to petroleum oil contaminants (in the form of petrol, diesel, gasoline, crude oil, used motor oil), may cause potential damage to the environment, animal and human health. In this review article, mechanisms of the petroleum oil contaminant removal from soil by chemical surfactant systems such as surfactant solution, surfactant foam and nanoparticle stabilized surfactant foams are explained. Laboratory based research works, reported within the last decade on the application of similar systems towards the removal of petroleum oil contaminant from the soil, have been discussed. It is an important fact that the commercial implementation of the chemical surfactant based technology depends on the environmental properties (biodegradability and toxicity) of the surfactants. In recent times, surfactant foam and nanoparticle stabilized surfactant foam are becoming more popular and considered advantageous over the use of surfactant solution alone. However, more research works have to be conducted on nanoparticle stabilized foam. The impact of physicochemical properties of the nanoparticles on soil remediation has to be explored in depth.

Organo-layered double hydroxides for the removal of polycyclic aromatic hydrocarbons from soil washing effluents containing high concentrations of surfactants

Disposal of soil washing effluent (SWE) resulting from the surfactant-enhanced remediation of soil containing hydrophobic organic contaminants (HOCs)is complicated because of the presence of high levels of surfactants. The synthesized layered double hydroxides (LDHs), modified with sodium dodecyl sulfonate (SDS) in different loading amounts (organo-LDHs),were evaluated in this study as sorbents for the removal of two typical HOCs, phenanthrene (PHE) and pyrene (PYR),from a simulative SWE. The results showed that the organo-LDHs can effectively sorb PHE and PYR from the SWE within an equilibrium time of 2 h. All isotherms were linear and the sorption capabilities of the organo-LDHs increased almost linearly with the increase in the amount of SDS loaded on the LDHs. Besides, the surface areas of the organo-LDHs decreased sharply with the increase in SDS loading owing to the hindrance of the exposed surface of the LDHs by the incorporated SDS. These findings indicated that partitioning dominated the sorption process rather than adsorption, and the strong affinity of HOCs towards the organic phase in LDHs assisted in the effective removal of polycyclic aromatic hydrocarbons (PAHs) from the SWE. Furthermore, the sorption capabilities of organo-LDHs towards PHE and PYR at the higher loading amounts of SDS were much greater than that of commercial activated carbon at the higher concentration ranges of PAHs.

Desorption kinetics and isotherms of phenanthrene from contaminated soil

BACKGROUND

Prediction of polycyclic aromatic hydrocarbons (PAHs) desorption from soil to estimate available fraction regarding to initial concentration of the contaminant is of great important in soil pollution management, which has poorly been understood until now. In the present study estimation of fast desorption fraction which is considered as available fraction was conducted by evaluating desorption kinetics of phenanthrene (a three ring PAH) from artificially contaminated soils through the mathematical models.

METHODS

Desorption rate of phenanthrene (PHE) was investigated by using the nonionic surfactant Tween80 in a series of batch experiments. The effects of reaction time from 5 to 1440 min and initial PHE concentration in the range of 100-1600 mg/kg were studied.

RESULTS

Available fractions of the contaminant were achieved within the first hour of desorption process as the system reached to equilibrium conditions. Experimental data were examined by using kinetic models including pseudo-first-order, pseudo-second-order in four linearized forms, and fractional power. Among the models tested, experimental data were well described by pseudo-second-order model type (III) and (IV) and fractional power equation. Fast desorption rates, as Available fractions were determined 79%, 46%, 40%, 39%, and 35% for initial PHE concentrations of 100, 400, 800, 1200, and 1600 mg/kg respectively. Among the evaluated isotherm models, including Freundlich, Langmuir in four linearized forms, and Temkin, the equilibrium data were well fitted by the first one.

CONCLUSION

Applying the nonionic surfactant Tween80 is a useful method to determine available fraction of the contaminant. This method will provide the management of contaminated sites by choosing a proper technique for remediation and predicting achievable treatment efficiency.

Efficacy of Indigenously Prepared Sugarcane and Pineapple Wine Solvents for Washing Highly Dioxin-Contaminated Field Soils

Poly-chlorinated dibenzo-p-dioxins (PCDDs) and poly-chlorinated dibenzo-furans (PCDFs) negatively affect human health and are often found as unwanted by-products of chemical handling and manufacture procedures. While commercial solvents have been used to remove dioxins from contaminated soil, these solvents themselves may adversely affect soil health. In this study, we examined the effects of washing highly PCDD/F contaminated field-soil with two natural solvents (sugarcane and pineapple wine) under ambient temperature. Performing an initial three-washing-cycle experiment, we found that sugarcane wine more effectively removed the contaminants than pineapple wine (removal, 60% vs. 50%) and chose it to perform a six-washing-cycle experiment facilitated by mechanical stirring and ultrasonication. Sugarcane wine was found to have a high removal efficiency (almost 80%), largely due to its higher alcohol and acid content. We believe that both wines can be used in soil remediation tasks without further damage to soil health. This is the first study employing naturally made wines as soil washing solvents in treating highly PCDD/F contaminated field soil. After soil washing processes, the winery solvents are believed to be beneficial to (if necessary) bioremediation methods and/or monitored natural attenuation.

Removal of Hydrocarbons from Contaminated Soils by Using a Thermally Expanded Graphite Sorbent

Lab-scale experiments on three soil matrices featured by increasing granulometry (sea sand, silica sand and gravel) were carried out in order to evaluate the adsorption capability and the removal efficiency of a new graphene-based material. Soil samples, firstly contaminated with different quantities of used lubricant oil up to final concentrations of 12.5, 25.0, 50.0 g kg^-1, were treated with an opportune amount of thermally expanded graphite (TEG) (i.e. 1/10, 1/20, 1/40 as TEG/pollutant ratio). Results show that the removal efficiency of TEG is directly correlated to the contamination level of the soil. The best removal efficiency (87.04%) was obtained during the treatment of gravel samples at the maximum contamination level by using the highest dosage of TEG. A good removal efficiency (80.83%) was also achieved using lower TEG/pollutant ratio. Moreover, TEG at ratio 1/10 showed worse removal efficiencies in treating sea (81.17%) and silica sand (63.52%) than gravel. In this study, also the thermal regeneration was investigated in order to evaluate a possible reuse of TEG with subsequent technical and economic advantages. TEG-technique proves to be technologically and economically competitive with other currently used technologies, revealing the best choice for the remediation of hydrocarbon-contaminated soils.

Selective adsorption of phenanthrene dissolved in Tween 80 solution using activated carbon derived from walnut shells

In order to remove phenanthrene (PHE) from surfactant solution, activated carbon (AC) was prepared from waste walnut shells and characterized by Brunauer-Emmett-Teller (BET), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). For solutions containing PHE and Tween 80, the former was effectively removed and the latter could be economically recovered after adsorption by the prepared AC. The π-π interactions and oxygen containing functional groups of AC play important roles in the PHE adsorption process. The adsorption kinetics process could best be described using the pseudo-second-order model and adsorption isotherm results indicated that the Langmuir model best fitted the data. Adsorption thermodynamic parameters, including enthalpy change, Gibbs free energy change and entropy change were calculated. Under optimal conditions, PHE removal and Tween 80 recovery reached 95% and 90%, respectively. The results suggest that AC provided an efficient alternative for selective adsorption of PHE and recovery of Tween 80 after the soil washing processes. After adsorption AC could be regenerated with ethanol and even if AC were regenerated twice PHE removal reached 80%.

Preliminary investigations on reducing the high radiation risk level of TENORM scale waste from petroleum industry

The main objective of this study is directed to remove 226Ra, 228Ra radionuclides from TENORM scale waste without seriously degradation the physicochemical characteristics of soils or generating waste. It was found that 82, 87% removal of total radioactivity using successive washing by commercial and TX-100 solutions, respectively, after seven cycles. Some radiation risk before and after treatment with surfactants were determined. It is a promising and efficient as well as economic process. Our results from this task could provide a useful information for defining the establishing and operating on a pilot-scale plant for efficient and economic TENORM treatment.

Assessment of flushing methods for the removal of heavy chlorinated compounds DNAPL in an alluvial aquifer

Immiscible mobilization and foam flushing were assessed as low surfactant consuming technologies, for the enhanced recovery of dense non-aqueous phase liquid (DNAPL) residual at a site contaminated by heavy chlorinated compounds. Preliminary experiments in well-controlled conditions demonstrated the phenomena involved in these remediation technologies and their limitations. Furthermore, we characterized the technologies according to by their surfactant consumption (per kg of DNAPL recovered) and the final DNAPL saturation reached. Surfactant foam flushing (SFF) produced lower DNAPL saturation than immiscible mobilization, thanks to its higher viscosity. However, its efficiency is strongly correlated to the pressure gradient (▽P) used during injection, and that is limited by risks of soil fracturing. The two technologies were tested in field cells (10m×10m×10m) delimited by cement/bentonite walls anchored in the clayey substratum. The deepest soil layer was the most contaminated. It was composed of silt-sandy soil and had an average hydraulic conductivity of 10^-4ms^-1. Field results show that we should now model flushing fluid propagation to design efficient set-ups for recovering the displaced DNAPL.

Biosurfactant-enhanced removal of o,p-dichlorobenzene from contaminated soil

Surfactant-enhanced remediation is less applicable for the treatment of dichlorobenzene (DCB)-contaminated soil. In this study, water solubility enhancements of o-dichlorobenzene (o-DCB) and p-dichlorobenzene (p-DCB) by micellar solutions of biosurfactants (saponin, alkyl polyglycoside) and chemically synthetic surfactant (Tween 80) were measured and compared. Solubilities of o,p-DCB in water were greatly enhanced in a linear fashion by each of Tween 80, saponin, and alkyl polyglycoside. Solubility enhancement efficiencies of surfactants followed the order of Tween 80 > saponin > alkyl polyglycoside. However, the ex situ soil washing experiment demonstrated the opposite result. The removal efficiency of o,p-DCB by biosurfactant saponin and alkyl polyglycoside was higher than that of chemically synthetic surfactant Tween 80 in contaminated soil. This difference may be due to the different adsorption behaviors of the surfactants onto soil. In addition, elution kinetics for o,p-DCB were relatively fast, with apparent elution equilibrium reached within 360 min, and can be described by a pseudo first-order kinetic equation. The elution process of o,p-DCB in soil-aqueous systems obeyed four-parameter biphasic first-order kinetic model including rapid and slow phases. The results confirmed potential application of saponin and alkyl polyglycoside in elution solution for enhanced remediation of DCB-contaminated soil.

Enhanced biodegradation of PAHs in historically contaminated soil by M. gilvum inoculated biochar

The inoculation of rice straw biochar with PAH-degrading Mycobacterium gilvum (1.27 × 10¹¹ ± 1.24 × 10¹⁰ cell g^-1), and the subsequent amendment of this composite material to PAHs contaminated (677 mg kg^-1) coke plant soil, was conducted in order to investigate if would enhance PAHs biodegradation in soils. The microbe-biochar composite showed superior degradation capacity for phenanthrene, fluoranthene and pyrene. Phenanthrene loss in the microbe-biochar composite, free cell alone and biochar alone treatments was, respectively, 62.6 ± 3.2%, 47.3 ± 4.1% and non-significant (P > 0.05); whereas for fluoranthene loss it was 52.1 ± 2.3%; non-significant (P > 0.05) and non-significant (P > 0.05); and for pyrene loss it was 62.1 ± 0.9%; 19.7 ± 6.5% and 13.5 ± 2.8%. It was hypothesized that the improved remediation was underpinned by i) biochar enhanced mass transfer of PAHs from the soil to the carbonaceous biochar "sink", and ii) the subsequent degradation of the PAHs by the immobilized M. gilvum. To test this mechanism, a surfactant (Brij 30; 20 mg g^-1 soil), was added to impede PAHs mass transfer to biochar and sorption. The surfactant increased solution phase PAH concentrations and significantly (P < 0.05) reduced PAH degradation in the biochar immobilized M. gilvum treatments; indicating the enhanced degradation occurred between the immobilized M. gilvum and biochar sorbed PAHs.

The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan's Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.

Anodic oxidation of surfactants and organic compounds entrapped in micelles - Selective degradation mechanisms and soil washing solution reuse

Formation of micelles at high surfactant concentration strongly modifies organic pollutant oxidation mechanisms and kinetics during anodic oxidation (AO) using boron doped diamond (BDD) anode. Results presented and discussed in this study emphasized the following mechanisms: (i) micelles act as a protective environment and reduce the availability of target molecules towards BDD(^•OH); (ii) the use of low current density strongly reduces micelle degradation kinetics due to both steric hindrance phenomenon for oxidation of micelles at the BDD surface and decrease of mediated oxidation in the bulk; (iii) compounds solubilized in surfactant-containing solutions can be either oxidized after degradation of the protective environment formed by micelles or if they are present as free extra-micellar compounds. Therefore, selective degradation of organic compounds entrapped in micelles can be achieved by using low current density and high surfactant concentration. In fact, these operating conditions strongly hinder micelle oxidation, while free (extra-micellar) compounds can still be oxidized. Then, the remaining entrapped compounds can also be continuously released in the aqueous phase, according to the micellar/aqueous phase partitioning coefficient (K_m). These results have been applied for the treatment of a real polycyclic aromatic hydrocarbon-containing soil washing (SW) solution. After 23 h of treatment at 2.1 mA cm^-2, 83% of phenanthrene, 90% of anthracene, 77% of pyrene and 75% of fluoranthene were degraded and the treated SW solution was reused for an additional SW step with only 5% lower extraction capacity than a fresh TW80 solution. A comparative study highlighted the superiority of this treatment strategy, compared to the use of activated carbon for selective adsorption of polycyclic aromatic hydrocarbons and SW solution reuse.

Low effect of phenanthrene bioaccessibility on its biodegradation in diffusely contaminated soil

This study focused on the role of bioaccessibility in the phenanthrene (PHE) biodegradation in diffusely contaminated soil, by combining chemical and microbiological approaches. First, we determined PHE dissipation rates and PHE sorption/desorption isotherms for two soils (PPY and Pv) presenting similar chronic PAH contamination, but different physico-chemical properties. Our results revealed that the PHE dissipation rate was significantly higher in the Pv soil compared to the PPY soil, while PHE sorption/desorption isotherms were similar. Interestingly, increases of PHE desorption and potentially of PHE bioaccessibility were observed for both soils when adding rhamnolipids (biosurfactants produced by Pseudomonas aeruginosa). Second, using ¹³C-PHE incubated in the same soils, we analyzed the PHE degrading bacterial communities. The combination of stable isotope probing (DNA-SIP) and 16S rRNA gene pyrosequencing revealed that Betaproteobacteria were the main PHE degraders in the Pv soil, while a higher bacterial diversity (Alpha-, Beta-, Gammaproteobacteria and Actinobacteria) was involved in PHE degradation in the PPY soil. The amendment of biosurfactants commonly used in biostimulation methods (i.e. rhamnolipids) to the two soils clearly modified the PHE sorption/desorption isotherms, but had no significant impact on PHE degradation rates and PHE-degraders identity. These results demonstrated that increasing the bioaccessibility of PHE has a low impact on its degradation and on the functional populations involved in this degradation.

Tween 80 surfactant-enhanced bioremediation: toward a solution to the soil contamination by hydrophobic organic compounds

The occurrence of hydrophobic organic compounds (HOCs) in the soil has become a highly significant environmental issue. This problem has been exacerbated by the strong sorption of HOCs to the soils, which makes them unavailable for most remediation processes. More and more works show that surfactant-enhanced biological technologies offer a great potential to clear up HOCs-contaminated soils. This article is a critical review of HOCs removal from soils using Tween 80 (one of the mostly used nonionic surfactants) aided biological remediation technologies. The review begins with a discussion of the fundamentals of Tween 80-enhanced desorption of HOCs from contaminated soils, with special emphasis on the biotoxicity of Tween 80. Successful results obtained by Tween 80-enhanced microbial degradation and phytoremediation are documented and discussed in section 3 and section 4, respectively. Results show Tween 80-enhanced biotechnologies are promising for treating HOCs-contaminated soils. However, considering the fact that most of these scientific studies have only been conducted at the laboratory-scale, many improvements are required before these technologies can be scaled up to the full-scale level. Moreover, further research on mechanisms related to the interaction of Tween 80 with degrading microorganisms and the plants is in high demand.

Bioremediation of agricultural solid waste leachates with diverse species of Cu (II) and Cd (II) by periphyton

The aim of this work was to study the bioremediation of agricultural solid waste leachates with high-concentrations of Cu (II) and Cd (II) after washing the wastes with water and Na₂EDTA solution (0.2M). Results indicate that Cu (II) and Cd (II) are mainly comprised of Cu₂(OH)₂²⁺, Cu₃(OH)₄²⁺, CuOH⁺, Cu(H₂O)₄(OH)₂, Cd²⁺ and CdOH⁺ in the water-washed leachates and Cu(EDTA)^2-, Cu(HEDTA)^-, Cd(EDTA)^2- and Cd(HEDTA)^- in the Na₂EDTA-washed leachates. Cu (II) removal efficiency by selected native periphyton from the water- and Na₂EDTA-washed leachates were 80.5% and 68.4% respectively, and for Cd (II) it was 57.1% and 64.6%, because the periphyton was able to maintain a stable pH of the leachates and regulate its microbial composition and carbon metabolic capability to acclimate the chemical conditions of the leachates. This study provides a new biomeasure to treat leachates with high-concentration Cu²⁺ and Cd²⁺, and contribute valuable insights into the relationships between periphyton characteristics and heavy metals.

How Do Modern Pesticide Treatments Influence the Mobility of Old Incurred DDT Contaminations in Agricultural Soils?

Even more than 50 years after the ban of DDT in Germany, farmers are still affected by its persistence in contaminated soils. Depending on the crop cultivated on such soils, this often leads to low-level residues of DDT and its metabolites DDE and DDD ("DDX"), which are perceived as a risk by the food value chain. Pesticide formulations used in modern agriculture commonly contain high levels of surfactants, but so far no open-field studies have evaluated the effects of these treatments on the mobility of lipophilic contaminants, such as DDX. In this field trial, a 1.03 ha section was cultivated with Cucurbita maxima under realistic conditions to monitor the mobility of DDX in low-level contaminated agricultural soils in dependence of common pesticide applications. A typical organic treatment was compared to a conventional protocol. Soil samples were taken before and after each application. Samples from the organic section featured significantly higher extractable DDX contents in soil and water compared to the conventional section. The results show that modern pesticide treatments can have an unforeseen, yet significant influence on the mobilization and, subsequently, on the plant bioavailability of incurred DDX residues depending on the formulation composition.

Scale-up on electrokinetic remediation: Engineering and technological parameters

This study analyses the effect of the scale-up of electrokinetic remediation (EKR) processes in natural soils. A procedure is proposed to prepare soils based on a compacting process to obtaining soils with similar moisture content and density to those found in real soils in the field. The soil used here was from a region with a high agrarian activity (Mora, Spain). The scale-up study was performed in two installations at different scales: a mock-up pilot scale (0.175m(3)) and a prototype with a scale that was very similar to a real application (16m(3)). The electrode configuration selected consisted of rows of graphite electrodes facing each other located in electrolyte wells. The discharge of 20mg of 2,4-dichlorophenoxyacetic acid [2,4-D] per kg of dry soil was treated by applying an electric potential gradient of 1Vcm(-1). An increase in scale was observed to directly influence the amount of energy supplied to the soil being treated. As a result, electroosmotic and electromigration flows and electric heating are more intense than in smaller-scale tests (24%, 1% and 25%, respectively respect to the values in prototype). In addition, possible leaks were evaluated by conducting a watertightness test and quantifying evaporation losses.

Exogenous IAA treatment enhances phytoremediation of soil contaminated with phenanthrene by promoting soil enzyme activity and increasing microbial biomass

In this study, we aimed to confirm that indole-3-acetic acid promotes plant uptake of phenanthrene (PHE), stimulates the activity of soil enzymes or microflora, and thereby accelerates the dissipation of PHE in soil. Four treatments were evaluated: PHE-contaminated soil planted with (1) ryegrass (T0), (2) ryegrass and supplemented with 1 mg kg(-1) indole-3-acetic acid (IAA) (T1), (3) ryegrass and supplemented with 5 mg kg(-1) IAA (T5), and (4) ryegrass and supplemented with 10 mg kg(-1) IAA (T10). After 30 days, PHE concentrations were lower for all treatments and the removal rate was 70.19, 89.17, 91.26, and 97.07 % for T0, T1, T5, and T10, respectively. PHE was only detected in the roots and not in the shoots. IAA facilitated the accumulation of PHE in the roots, and plants subjected to the T10 treatment had the highest levels. Exogenous IAA stimulated soil peroxidase activity in a dose-dependent manner, whereas soil polyphenoloxidase activity was not significantly increased, except in T10. Soil microbial biomass also increased in response to IAA treatment, particularly in T10. Furthermore, phospholipid fatty acid analysis showed that IAA treatment increased microbial biomass and alleviated environmental stress. Gram-positive bacteria are largely responsible for polycyclic aromatic hydrocarbon degradation, and we found that the ratio of gram-positive to gram-negative bacteria in the soil significantly increased as the IAA concentrations increased (P < 0.05). Correlation analysis indicated that the increase in soil microbial biomass, enzyme activity, and plant uptake of PHE promotes removal of PHE from the soil.

Removal of hydrophobic organic pollutants from soil washing/flushing solutions: A critical review

The release of hydrophobic organoxenobiotics such as polycyclic aromatic hydrocarbons, petroleum hydrocarbons or polychlorobiphenyls results in long-term contamination of soils and groundwaters. This constitutes a common concern as these compounds have high potential toxicological impact. Therefore, the development of cost-effective processes with high pollutant removal efficiency is a major challenge for researchers and soil remediation companies. Soil washing (SW) and soil flushing (SF) processes enhanced by the use of extracting agents (surfactants, biosurfactants, cyclodextrins etc.) are conceivable and efficient approaches. However, this generates high strength effluents containing large amount of extracting agent. For the treatment of these SW/SF solutions, the goal is to remove target pollutants and to recover extracting agents for further SW/SF steps. Heterogeneous photocatalysis, technologies based on Fenton reaction chemistry (including homogeneous photocatalysis such as photo-Fenton), ozonation, electrochemical processes and biological treatments have been investigated. Main advantages and drawbacks as well as target pollutant removal mechanisms are reviewed and compared. Promising integrated treatments, particularly the use of a selective adsorption step of target pollutants and the combination of advanced oxidation processes with biological treatments, are also discussed.

Evaluation of surfactant flushing for remediating EDC-tar contamination

Ethylene dichloride tar (EDC-tar) is a dense non-aqueous phase liquid (DNAPL) waste originated from the process of vinyl chloride production, with major constituents including chlorinated aliphatic and aromatic hydrocarbons. This study investigated the feasibility of Surfactant Enhanced Aquifer Remediation (SEAR) for treating EDC-tar contaminated aquifers. Initial experiments explored the potential to enhance the apparent solubility of EDC-tar using single or mixed surfactants. The results showed that an aqueous solution mixed anionic and non-ionic surfactants (i.e., SDS/Tween 80) exhibited higher EDC-tar apparent solubility and lower surface tension than other surfactant systems tested. Additionally, alkaline pH aids in increasing the EDC-tar apparent solubility. In column flushing experiments, it was seen that the alkaline mixed SDS/Tween 80 solution showed better removal of pure EDC-tar from silica sand porous media. Furthermore, separation of EDC-tar in the surfactant solution was conducted employing a salting-out effect. Significant separation of DNAPL was observed when 13 wt.% or more NaCl was added to the solution. Overall, this study evaluates the feasibility of using SEAR for remediating EDC-tar contaminated subsurface soil and groundwater.

Use of surfactants for the remediation of contaminated soils: a review

Due to the great harm caused by soil contamination, there is an increasing interest to apply surfactants to the remediation of a variety of contaminated soils worldwide. This review article summarizes the findings of recent literatures regarding remediation of contaminated soils/sites using surfactants as an enhancing agent. For the surfactant-based remedial technologies, the adsorption behaviors of surfactants onto soil, the solubilizing capability of surfactants, and the toxicity and biocompatibility of surfactants are important considerations. Surfactants can enhance desorption of pollutants from soil, and promote bioremediation of organics by increasing bioavailability of pollutants. The removal of heavy metals and radionuclides from soils involves the mechanisms of dissolution, surfactant-associated complexation, and ionic exchange. In addition to the conventional ionic and nonionic surfactants, gemini surfactants and biosurfactants are also applied to soil remediation due to their benign features like lower critical micelle concentration (CMC) values and better biocompatibility. Mixed surfactant systems and combined use of surfactants with other additives are often adopted to improve the overall performance of soil washing solution for decontamination. Worldwide the field studies and full-scale remediation using surfactant-based technologies are yet limited, however, the already known cases reveal the good prospect of applying surfactant-based technologies to soil remediation.

Remediation of phenanthrene contaminated soils by nonionic-anionic surfactant washing coupled with activated carbon adsorption

Batch experiments were conducted to investigate the performance of nonionic-anionic mixed surfactants and their recovery through activated carbon. The solubilization capabilities of mixed surfactants toward phenanthrene (PHE) were reduced by addition of anionic surfactant to the mixed systems. Results showed that sorption of Triton X-100 (TX100) onto soil decreased with increasing mass fraction of sodium dodecyl sulfate (SDS) in the mixed surfactant solutions. Soil contaminated with PHE at 200 mg/kg was washed with different surfactant concentrations at various mass ratios of nonionic-anionic mixed surfactant. Experiments with low-concentrations of mixed surfactants revealed that removal efficiencies for PHE-contaminated soil close to the individual higher nonionic surfactant concentration can be achieved. Overall performance considering both soil washing and surfactant recovery steps is apposite when an TX100:SDS mass ratio of 8:2 at 3 g/L is used.

Removal of 226Ra and 228Ra from TENORM sludge waste using surfactants solutions

The feasibility of using surfactants as extracting agent for the removal of radium species from TENORM sludge produced from petroleum industry is evaluated. In this investigation cationic and nonionic surfactants were used as extracting agents for the removal of radium radionuclides from the sludge waste. Two surfactants namely cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX100) were investigated as the extracting agents. Different parameters affecting the removal of both (226)Ra and (228)Ra by the two surfactants as well as their admixture were studied by the batch technique. These parameters include effect of shaking time, surfactants concentration and temperature as well as the effect of surfactants admixture. It was found that, higher solution temperature improves the removal efficiency of radium species. Combined extraction of nonionic and cationic surfactants produces synergistic effect in removal both (226)Ra and (228)Ra, where the removals reached 84% and 80% for (226)Ra and (228)Ra, respectively, were obtained using surfactants admixture.