Anionic-nonionic mixed-surfactant-enhanced remediation of PAH-contaminated soil

Surfactant-Based Chemical Washing to Remediate Oil-Contaminated Soil: The State of Knowledge

As the energy demand increases, there is a significant expansion and utilization of oil resources, resulting in the inevitable occurrence of environmental pollution. Oil has been identified as a prevalent soil contaminant, posing substantial risks to the soil ecosystems. The remediation of soil contaminated with oil is a formidable undertaking. Increasing evidence shows that chemical washing, a remediation technique employing chemical reagents like surfactants to augment the solubilization, desorption, and separation of petroleum hydrocarbons in soil, proves to be an efficacious approach, but the latest advances on this topic have not been systematically reviewed. Here, we present the state of knowledge about the surfactant-based chemical washing to remediate oil-contaminated soil. Using the latest data, the present article systematically summarizes the advancements on ex situ chemical washing of oil pollution and provides a concise summary of the underlying principles. The use of various surfactants in chemical washing and the factors influencing remediation efficiency are highlighted. Based on the current research status and knowledge gaps, future perspectives are proposed to facilitate chemical washing of oil-polluted soil. This review can help recognize the application of chemical washing in the remediation of oil-polluted soil.

Recognizing Functional Groups of MES/APG Mixed Surfactants for Enhanced Solubilization toward Benzo[a]pyrene

Benzo[a]pyrene is difficult to remove from soil due to its high octanol/water partition coefficient. The use of mixed surfactants can increase solubility but with the risk of secondary soil contamination, and the compounding mechanism is still unclear. This study introduced a new approach using environmentally friendly fatty acid methyl ester sulfonate (MES) and alkyl polyglucoside (APG) to solubilize benzo[a]pyrene. The best result was obtained when the ratio of MES/APG was 7:1 under 6 g/L total concentration, with an apparent solubility (Sw) of 8.58 mg/L and a molar solubilization ratio (MSR) of 1.31 for benzo[a]pyrene, which is comparable to that of Tween 80 (MSR, 0.95). The mechanism indicates that the hydroxyl groups (-OH) in APG form "O-H···OSO2-" hydrogen bonding with the sulfonic acid group (-SO3-) of MES, which reduces the electrostatic repulsion between MES molecules, thus facilitating the formation of large and stable micelles. Moreover, the strong solubilizing effect on benzo[a]pyrene should be ascribed to the low polarity of ester groups (-COOCH3) in MES. Functional groups capable of forming hydrogen bonds and having low polarity are responsible for the enhanced solubilization of benzo[a]pyrene. This understanding helps choose suitable surfactants for the remediation of PAH-contaminated soils.

AI-assisted systematic review on remediation of contaminated soils with PAHs and heavy metals

This systematic review addresses soil contamination by crude oil, a pressing global environmental issue, by exploring effective treatment strategies for sites co-contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). Our study aims to answer pivotal research questions: (1) What are the interaction mechanisms between heavy metals and PAHs in contaminated soils, and how do these affect the efficacy of different remediation methods? (2) What are the challenges and limitations of combined remediation techniques for co-contaminated soils compared to single-treatment methods in terms of efficiency, stability, and specificity? (3) How do various factors influence the effectiveness of biological, chemical, and physical remediation methods, both individually and combined, in co-contaminated soils, and what role do specific agents play in the degradation, immobilization, or removal of heavy metals and PAHs under diverse environmental conditions? (4) Do AI-powered search tools offer a superior alternative to conventional search methodologies for executing an exhaustive systematic review? Utilizing big-data analytics and AI tools such as Litmaps.co, ResearchRabbit, and MAXQDA, this study conducts a thorough analysis of remediation techniques for soils co-contaminated with heavy metals and PAHs. It emphasizes the significance of cation-π interactions and soil composition in dictating the solubility and behavior of these pollutants. The study pays particular attention to the interplay between heavy metals and PAH solubility, as well as the impact of soil properties like clay type and organic matter on heavy metal adsorption, which results in nonlinear sorption patterns. The research identifies a growing trend towards employing combined remediation techniques, especially biological strategies like biostimulation-bioaugmentation, noting their effectiveness in laboratory settings, albeit with potentially higher costs in field applications. Plants such as Medicago sativa L. and Solanum nigrum L. are highlighted for their effectiveness in phytoremediation, working synergistically with beneficial microbes to decompose contaminants. Furthermore, the study illustrates that the incorporation of biochar and surfactants, along with chelating agents like EDTA, can significantly enhance treatment efficiency. However, the research acknowledges that varying environmental conditions necessitate site-specific adaptations in remediation strategies. Life Cycle Assessment (LCA) findings indicate that while high-energy methods like Steam Enhanced Extraction and Thermal Resistivity - ERH are effective, they also entail substantial environmental and financial costs. Conversely, Natural Attenuation, despite being a low-impact and cost-effective option, may require prolonged monitoring. The study advocates for an integrative approach to soil remediation, one that harmoniously balances environmental sustainability, cost-effectiveness, and the specific requirements of contaminated sites. It underscores the necessity of a holistic strategy that combines various remediation methods, tailored to meet both regulatory compliance and the long-term sustainability of decontamination efforts.

Remediation of heavily PAHs-contaminated soil with high mineral content from a coking plant using surfactant-enhanced soil washing

This study investigated the effectiveness of various surfactants at different concentrations in removing high concentrations of polycyclic aromatic hydrocarbons (PAHs) from soil with high mineral content, focusing on the impact of surfactant treatment on the mobility of the residual PAHs in soil. The results revealed that the cationic surfactant (CTMAB) inhibited removal of PAHs in the whole tested concentration range of 0.1-8 g/L. In contrast, the non-ionic and anionic surfactants (Triton X-100 and SDBS) significantly enhanced removal of PAHs as their amendment concentrations reached 2 g/L and above. Triton X-100 exhibited steadily increased efficacy with increasing amendment concentrations and maintained favorable solubilization capability when continuously amended, making it the preferable choice for remediating PAHs-contaminated soil. Surfactant and water washing processes altered soil physicochemical properties by removing some clay minerals (e.g., faujasite) and organic matter that can bind or sequester PAHs, potentially increasing their extractability and bioavailability in the washed soil, thereby posing higher ecological risks compared to the original one. Although soil washing decreased retention of the remaining PAHs in soil, it did not significantly impact PAHs release from soil by flowing water. These findings provide insights into the long-term effectiveness and ecological impacts of surfactant-enhanced washing as a potential remediation technique for PAHs-contaminated soil.

Bench-Scale and Full-Scale Level Evaluation of the Effect of Parameters on Cleaning Efficacy of the Firefighters' PPE

The National Fire Protection Association (NFPA) 1851 document provides guidelines for firefighters on the care and maintenance of their PPE, including decontamination practices. Firefighters are exposed to various toxic chemicals during fire suppression activities, making effective decontamination crucial for their safety. This study evaluated the efficacy of different washing parameters, including temperature, time, and surfactants, on cleaning outer-shell material contaminated with nine targeted compounds from three different functional groups: phenols, polycyclic aromatic hydrocarbons (PAHs), and phthalates. The study was conducted on both bench-scale and full-scale levels, with contaminated swatches washed in a water shaker bath in the bench-scale evaluation and full-sized washer extractors used in the full-scale evaluation. The results showed that bench-scale washing demonstrated similar trends in contaminant removal to full-scale washing. Importantly, the study highlighted the complexity of removing fireground contaminants from the personal protective ensemble (PPE). The findings of this study have practical implications for the firefighting industry as they provide insight into the effectiveness of different washing parameters for PPE decontamination. Future studies could explore the impact of repeated washing on PPE and investigate the potential for developing more efficient decontamination strategies. Ultimately, the study underscores the importance of ongoing efforts to ensure the safety of firefighters, who face significant occupational hazards.

Effects of Nitrobenzene's mass transfer at water-air interface

As a volatile organic compound, nitrobenzene has high vapor pressure and low boiling point, and it is very volatile when it enters the water body and enters the air. The mass transfer of VOCs at the water-air interface is a complex process of transboundary transport. In this paper, the effects of water temperature, interface turbulence, surfactant concentration, and humic acid concentration on the volatilization of nitrobenzene at the water-air interface were investigated. Under the influence of temperature, the volatilization of nitrobenzene accorded with the first-order kinetic equation. When the temperature increased from 5 ℃ to 25 ℃, the volatilization rate of nitrobenzene increased by 2.03 times. Temperature for volatilization rate constant was in accordance with the Arrhenius equation. The water-gas distribution of volatile organic compounds was in accordance with the Boltzman equation. Under the same temperature conditions, when the agitating intensity increased from 0 r/min to 250 r/min, the volatilization rate constant of nitrobenzene increased by 1.51 times. When the surfactant is greater than the critical micelle concentration, the volatilization rate constant of nitrobenzene decreases with the increase of surfactant. When the concentration of humic acid increased from 100 mg/L to 500 mg/L, the half-life increased by 1.14 h, and the volatilization rate decreased by 1.14 h, reduced by 17%. The results showed that the increase of temperature and the intensification of stirring had a significant promoting effect on the volatilization of nitrobenzene, while the surfactant and humic acid both played an inhibitory effect on the volatilization of nitrobenzene.

Interaction quantitative modeling of mixed surfactants for synergistic solubilization by resonance light scattering

In situ flushing through surfactant-enhanced aquifer remediation (SEAR) technology has long been recognized as a promising technique for NAPL removal from contaminated aquifers. However, there have been few studies on the choice of surfactants. In this work, the interaction quantitative model between resonance light scattering intensity and the concentration of binary surfactant mixtures NP-10+SDBS and NP-10+CTAB was established, and the mechanism of binary surfactant interaction was explored through the model by the resonance light scattering method. The relationship between the model constants and NAPL solubilization was also investigated to better address the application of surfactants in practical NAPL-contaminated site remediation. The critical micelle concentrations (CMCs) of nonylphenol ethoxylate (NP-10), dodecyl benzene sulfonate (SDBS), hexadecyl trimethyl ammonium bromide (CTAB), and the binary surfactant mixtures were measured by resonance light scattering (RLS), which were consistent with those obtained from surface tension measurements. In all cases, the RLS signals exhibited similar variations with surfactant concentration. A quantitative calculation model based on the RLS measurement data was established, and the binding constants K_NP-10+SDBS and K_NP-10+CTAB were calculated to be 0.66 and 1.51 L·mmol^-1, respectively, according to the equilibrium equations. The results showed that the binding constants have a significant positive correlation with NAPL solubilization.

Bio-based dispersants for fuel oil spill remediation based on the Hydrophilic-Lipophilic Deviation (HLD) concept and Box-Behnken design

The high density and viscosity of fuel oil leads to its prolonged persistence in the environment and causes widespread contamination. Dispersants with a low environmental impact are necessary for fuel oil spill remediation. This study aimed to formulate bio-based dispersants by mixing anionic biosurfactant (lipopeptides from Bacillus subtilis GY19) with nonionic oleochemical surfactant (Dehydol LS7TH). The synergistic effect of the anionic-nonionic surfactant mixture produced a Winsor Type III microemulsion, which promoted petroleum mobilization. The hydrophilic-lipophilic deviation (HLD) equations for ionic and nonionic surfactant mixtures were compared, and it was found that the ionic equation was applicable for the calculation of lipopeptides and Dehydol LS7TH concentrations. The best formula contained 6.6% w/v lipopeptides and 11.9% w/v Dehydol LS7TH in seawater, and its dispersion effectiveness for bunker fuels A and C was 92% and 78%, respectively. The application of bio-based dispersants in water sources was optimized by Box-Behnken design. The efficiency of the bio-based dispersant was affected by the dispersant-to-oil ratios (DORs) but not by the water salinity. A suitable range of DORs for different oil contamination levels could be identified from the response surface plot. The dispersed fuel oil was further degraded by adding an oil-degrading bacterial consortium to the chemically enhanced water accommodated fractions (CEWAFs). After 7 days of incubation, the concentration of fuel oil was reduced from 3692 mg/L to 356 mg/L (88% removal efficiency). On the other hand, the abiotic control removed less than 40% fuel oil from the CEWAFs. This bio-based dispersant had an efficiency comparable to that of a commercial dispersant. The process of dispersant formulation and optimization could be applied to other surfactant mixtures.

In-depth investigation of Sodium percarbonate as oxidant of PAHs from soil contaminated with diesel oil

Sodium percarbonate (SPC, 2Na₂CO₃∙3H₂O₂), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H₂O₂/Fe²⁺/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe²⁺), hydrogen peroxide (H₂O₂) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 3³ was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H₂O₂] and [Fe²⁺], between 190.0 and 950.0 mmol L^-1 and 0.0-14.4 mmol L^-1, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe²⁺ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg^-1 to 15,801 mg kg^-1 in TOC and from 85.750 mg kg^-1 to 20.770 mg kg^-1 in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg^-1 and 1.233 mg kg^-1, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

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).

Formulation of Bio-Based Washing Agent and Its Application for Removal of Petroleum Hydrocarbons From Drill Cuttings Before Bioremediation

Drill cuttings from petroleum exploration and production sites can cause diverse environmental problems. Total petroleum hydrocarbons (TPHs) are a major pollutant from the use of polyolefin-based mud. As an alternative to incineration, this study investigated the application of surfactant-enhanced washing technology prior to bioremediation. The washing step was necessary because the initial TPH concentrations were quite high at approximately 15% (w/w). Washing agents were formulated by varying the concentration of lipopeptide biosurfactant (in foamate or cell-free broth), Dehydol LS7TH (fatty alcohol ethoxylate 7EO, oleochemical surfactant) and butanol (as a lipophilic linker) at different salinities. The most efficient formula produced a Winsor Type I microemulsion (oil-in-water microemulsion) with polyolefin and contained only 20% (v/v) foamate and 2% (v/v) Dehydol LS7TH in water. Due to the synergistic behavior between the anionic lipopeptides and non-ionic Dehydol LS7TH, the formula efficiently removed 92% of the TPHs from the drill cuttings when applied in a jar test. To reduce the cost, the concentrations of each surfactant should be reduced; thus, the formula was optimized by the simplex lattice mixture design. In addition, cell-free broth, at a pH of 10, containing 3.0 g/L lipopeptides was applied instead of foamate because it was easy to prepare. The optimized formula removed 81.2% of the TPHs and contained 72.0% cell-free broth and 1.4% Dehydol LS7TH in water. A 20-kg soil washing system was later tested where the petroleum removal efficiency decreased to 70.7% due to polyolefin redeposition during separation of the washing solution. The remaining TPHs (4.5%) in the washed drilled cuttings were further degraded by a mixture of Marinobacter salsuginis RK5, Microbacterium saccharophilum RK15 and Gordonia amicalis JC11. To promote TPH biodegradation, biochar and fertilizer were applied along with bacterial consortia in a microcosm experiment. After 49-day incubation, the TPHs were reduced to 0.9% by both physical and biological mechanisms, while the TPHs in the unamended samples remained unaffected. With the use of the formulated bio-based washing agent and bioremediation approach, the on-site treatment of drill cuttings could be conducted with an acceptable cost and low environmental impacts.

Remediation of Anthracene-Contaminated Soil with Sophorolipids-SDBS-Na2SiO3 and Treatment of Eluting Wastewater

The soil pollution of polycyclic aromatic hydrocarbons (PAHs) is serious in China, which not only affects the living and growing environment of plants and animals but also has a great impact on people’s health. The use of hydrophobic organic compounds to make use of surfactant ectopic elution processing is more convenient and cheaper as a repair scheme and can effectively wash out the polycyclic aromatic hydrocarbons in the soil. Therefore, we mixed sophorolipids:sodium dodecylbenzene sulfonate (SDBS):Na2SiO3 according to the mass ratio of 1:15:150. We explored the influencing factors of high and low concentrations of PAH-contaminated soil using a single factor test and four factors at a two-level factorial design. Then, the elution wastewater was treated by ultrasonic oxidation technology and the alkali-activated sodium persulfate technology. The results showed that: (1) In the single factor test, when the elution time is 8 h, the concentration of the compounded surfactant is 1200 mg/L, the particle size is 60 mesh, the concentration of NaCl is 100 mmol/L, and the concentration of KCl is 50 mmol/L, and the effect of the PAH-contaminated soil eluted by the composite surfactant is the best. Externally added NaCl and KCl salt ions have a more obvious promotion effect on the polycyclic aromatic hydrocarbon-contaminated soil; (2) in the interaction experiment, single factor B (elution time) and D (NaCl concentration) have a significant main effect. There is also a certain interaction between factor A (concentration agent concentration) and factor D, factor B, and factor C (KCl concentration); (3) the treatment of anthracene in the eluate by ultrasonic completely mineralizes the organic pollutants by the thermal and chemical effects produced by the ultrasonic cavitation phenomenon, so that the organic pollutants in the eluate are oxidized and degraded into simple environmentally friendly small molecular substances. When the optimal ultrasonic time is 60 min and the ratio of oxidant to activator is 1:2, the removal rate of contaminants in the eluent can reach 63.7%. At the same time, the turbidity of the eluent is significantly lower than that of the liquid after centrifugal separation, indicating that oxidants can not only remove the pollutants in elution water but also remove the residual soil particulate matter; and (4) by comparing the infrared spectrum of the eluted waste liquid before and after oxidation, it can be seen that during the oxidation process, the inner part of eluent waste liquid underwent a ring-opening reaction, and the ring-opening reaction also occurred in the part of the cyclic ester group of the surfactant, which changed from a ring to non-ring.

Surfactants Enhanced Soil Arsenic Phytoextraction Efficiency by Pteris vittata L

Soil arsenic (As) pollution has become a global problem. It is urgent to improve the phytoextraction efficiency of soil As. This study found chemical activators (Span 80/SDS and GSH/Span 80/SDS) that can significantly improve the availability of As and the phytoextraction efficiency of As by Pteris vittata L. in As-contaminated soil. Compared with the control, in the soil screening experiment, Span 80/SDS and GSH/Span 80/SDS significantly increased available As in soil by 73.4% and 81.4%, respectively. And in the soil pot experiment, the Span 80/SDS and GSH/Span 80/SDS significantly increased the As concentration in the pinnae of Pteris vittata L. by 53.4% and 41.2%, respectively, and the total As amount extraction by Pteris vittata L. increased significantly by 31.7% and 94.2%, respectively. The results suggest that adding Span 80/SDS and GSH/Span 80/SDS to As-contaminated soil can be considered as an effectively method to improve the efficiency of phytoextraction.

Regeneration of Washing Effluents for Remediation of Petroleum-Hydrocarbons-Contaminated Soil by Corncob-Based Biomass Materials

Surfactant-enhanced soil washing is an effective remediation method for petroleum-hydrocarbons-contaminated soil. The residual petroleum hydrocarbons in the washing effluents reduce the elution ability of the washing effluents and cause secondary pollution to the environment. In this work, modified corncobs were prepared and used as selective adsorbents to remove the residual petroleum hydrocarbons in washing effluents. The structure of adsorbent was characterized and the adsorption conditions were optimized. With the adsorption by corncob-based adsorbents, washing effluents can be regenerated and recycled. After five cycles, the recovery efficiency of the washing effluents is still as high as 75.4%. The optimal adsorbent linear alkylbenzene sulfonates (LAS-Cb) also exhibited excellent recyclability, which can be recycled five times. The selective adsorption mechanism of the LAS-Cb for petroleum hydrocarbons in washing effluents, related to its huge hydrophobic core and surface electronegativity, is proposed.

Transport potential of super-hydrophobic organic contaminants in anionic-nonionic surfactant mixture micelles

Surfactant mixtures are commonly used in agricultural and soil remediation applications, necessitating an understanding of their micellization behavior and associated impact on the fate of co-existing chemicals in the subsurface. A polymer-water sorption isotherm approach was shown to present an alternative to traditional methods for quantifying, understanding and predicting surfactant mixture properties. Micelle compositions were measured for anionic-nonionic surfactant mixtures. This is important since micelle composition can alter the apparent aqueous solubility of super-hydrophobic organic contaminants (SHOCs) resulting in surfactant facilitated transport (SFT). A key parameter in predicting SFT for SHOCs is their micelle-water partition constant (K_MI). These were determined for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated biphenyls (PCBs) with representative anionic-nonionic surfactant mixtures using a polymer depletion method. These previously unreported constants were intermediate between those for pure anionic and nonionic surfactant solutions, with magnitude depending on micelle composition. Separate linear relationships were found between log K_MI and log K_OW for PCDDs and PCBs. This work provides new methods and preliminary results relating to binary surfactant mixtures (e.g. critical micelle concentration and micelle composition) and SHOCs (K_MI) that are important in the evaluation of the fate and transport of SHOCs in the subsurface environment and provide insight into the environmental mobility of these important contaminants.

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.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.

Biotoxicity and bioavailability of hydrophobic organic compounds solubilized in nonionic surfactant micelle phase and cloud point system

A recent work has shown that hydrophobic organic compounds solubilized in the micelle phase of some nonionic surfactants present substrate toxicity to microorganisms with increasing bioavailability. However, in cloud point systems, biotoxicity is prevented, because the compounds are solubilized into a coacervate phase, thereby leaving a fraction of compounds with cells in a dilute phase. This study extends the understanding of the relationship between substrate toxicity and bioavailability of hydrophobic organic compounds solubilized in nonionic surfactant micelle phase and cloud point system. Biotoxicity experiments were conducted with naphthalene and phenanthrene in the presence of mixed nonionic surfactants Brij30 and TMN-3, which formed a micelle phase or cloud point system at different concentrations. Saccharomyces cerevisiae, unable to degrade these compounds, was used for the biotoxicity experiments. Glucose in the cloud point system was consumed faster than in the nonionic surfactant micelle phase, indicating that the solubilized compounds had increased toxicity to cells in the nonionic surfactant micelle phase. The results were verified by subsequent biodegradation experiments. The compounds were degraded faster by PAH-degrading bacterium in the cloud point system than in the micelle phase. All these results showed that biotoxicity of the hydrophobic organic compounds increases with bioavailability in the surfactant micelle phase but remains at a low level in the cloud point system. These results provide a guideline for the application of cloud point systems as novel media for microbial transformation or biodegradation.

Treatment of decabromodiphenyl ether (BDE209) contaminated soil by solubilizer-enhanced electrokinetics coupled with ZVI-PRB

Decabromodiphenyl ether (BDE209) is a typical soil contaminant released from e-waste recycling sites (EWRSs). Electrokinetics (EK) has been considered as an excellent treatment technology with a promising potential to effectively remove organic pollutants in soil. In this study, the treatment of BDE209-polluted soil by EK was explored. All the EK experiments were conducted under a constant voltage gradient (2 V cm^-1) for 14 days. Deionized water (DI water), hydroxypropyl-β-cyclodextrin (HPCD), sodium dodecyl sulfate (SDS), and humic acid (HA) were applied as the processing fluid. The experimental results showed that all the solubilizers could effectively promote the mobility and transport of BDE209 in the soil via the electro-osmotic flow (EOF) or electromigration. The removal efficiencies achieved in S1 section were 24, 22, and 26% using HPCD, SDS, and HA as the processing fluid. However, the removal of BDE209 for the entire soil cell was not achieved until zero valence iron (ZVI) was inserted at the center of soil column as a permeable reactive barrier (PRB) or (ZVI-PRB), which enhanced the degradation of BDE209. As ZVI-PRB was installed in EK5 and EK6 experiments, the corresponding average removal efficiencies increased to 16 and 13%, respectively. Additionally, the degradation products of BDE209 analyzed by GC-MS suggested that debromination of BDE209 was the main potential degradation mechanism in the EK treatment in the presence of ZVI-PRB.

Effect of cations on the solubilization/deposition of triclosan in sediment-water-rhamnolipid system

Cations had great influence on the self-assembly of rhamnolipid, which in turn affected the fate of triclosan. The migration of triclosan from sediment to water benefited its biodegradation but it could be transformed into more toxic compounds. To regulate the fate of triclosan and reduce environmental risks extremely, the effect of four common cations in surface water (Na(+)/K(+)/Ca(2+)/Mg(2+)) on the solubilization/deposition of triclosan in sediment-water-rhamnolipid system was investigated. The interaction among cations, triclosan and rhamnolipid was explored based on self-assembly of rhamnolipid and water solubility of triclosan in rhamnolipid solutions. Results showed that cations had little influence on the fate of triclosan in the absence of rhamnolipid. Cations, especially Ca(2+)/Mg(2+), reduced the critical micelle concentration, micellar size and zeta potential of rhamnolipid solutions. The changes in self-assembly of rhamnolipid with different cations led to the difference of residual rhamnolipid concentration in water, which was nearly invariant with 0.01 M Na(+)/K(+) while decreased significantly with 0.01 M Ca(2+)/Mg(2+). Consequently, water solubility of triclosan in rhamnolipid solutions increased with the addition of Na(+)/K(+) whereas decreased with Ca(2+)/Mg(2+). In sediment-water- rhamnolipid system, triclosan was slightly solubilized from sediment to water with Na(+)/K(+) while deposited in sediment with Ca(2+)/Mg(2+). These findings provided an alternative application of rhamnolipid for the remediation of triclosan-polluted sediment.